--- /srv/rebuilderd/tmp/rebuilderdxWd4eS/inputs/erlang-doc_27.3.4.11+dfsg-3_all.deb
+++ /srv/rebuilderd/tmp/rebuilderdxWd4eS/out/erlang-doc_27.3.4.11+dfsg-3_all.deb
├── file list
│ @@ -1,3 +1,3 @@
│  -rw-r--r--   0        0        0        4 2026-05-05 12:33:17.000000 debian-binary
│ --rw-r--r--   0        0        0    40648 2026-05-05 12:33:17.000000 control.tar.xz
│ --rw-r--r--   0        0        0 21043352 2026-05-05 12:33:17.000000 data.tar.xz
│ +-rw-r--r--   0        0        0    40636 2026-05-05 12:33:17.000000 control.tar.xz
│ +-rw-r--r--   0        0        0 21042900 2026-05-05 12:33:17.000000 data.tar.xz
├── control.tar.xz
│ ├── control.tar
│ │ ├── ./md5sums
│ │ │ ├── ./md5sums
│ │ │ │┄ Files differ
│ │ │ ├── line order
│ │ │ │ @@ -247,15 +247,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-ext-300-normal-DG5RYZUK.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-ext-400-normal-ZXDJ7C2U.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-ext-700-normal-3JFX6WED.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/search_data-8B3C849F.js
│ │ │ │ +usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/search_data-FC9EDC58.js
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/sidebar_items-E25F4A7E.js
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/driver.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/driver_entry.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/epmd_cmd.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/erl_cmd.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/erl_dist_protocol.html
│ │ │ │  usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/erl_driver.html
│ │ │ │ @@ -558,15 +558,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/lato-latin-ext-300-normal-DG5RYZUK.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/lato-latin-ext-400-normal-ZXDJ7C2U.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/lato-latin-ext-700-normal-3JFX6WED.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/search_data-67110493.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/search_data-0063A89A.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/dist/sidebar_items-61D5D22A.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/index.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/notes.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/diameter-2.4.1.1/doc/html/search.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/edoc-1.3.2/doc/chunks/edoc.chunk
│ │ │ │  usr/share/doc/erlang-doc/html/lib/edoc-1.3.2/doc/chunks/edoc_cli.chunk
│ │ │ │  usr/share/doc/erlang-doc/html/lib/edoc-1.3.2/doc/chunks/edoc_data.chunk
│ │ │ │ @@ -673,15 +673,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-ext-300-normal-DG5RYZUK.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-ext-400-normal-ZXDJ7C2U.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/lato-latin-ext-700-normal-3JFX6WED.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/search_data-1F14090C.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/search_data-D82831C4.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/dist/sidebar_items-8A5CCEF3.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/ei.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/ei_connect.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/ei_global.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/ei_users_guide.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/erl_call_cmd.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/erl_interface-5.5.2/doc/html/erl_interface.epub
│ │ │ │ @@ -781,15 +781,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/lato-latin-ext-300-normal-DG5RYZUK.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/lato-latin-ext-400-normal-ZXDJ7C2U.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/lato-latin-ext-700-normal-3JFX6WED.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/search_data-D71AAFA6.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/search_data-FF6A1601.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/dist/sidebar_items-B6B07F6E.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/ftp.epub
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/ftp.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/ftp_client.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/index.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/introduction.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/ftp-1.2.3/doc/html/notes.html
│ │ │ │ @@ -1001,15 +1001,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/lato-latin-ext-300-normal-DG5RYZUK.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/lato-latin-ext-400-normal-ZXDJ7C2U.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/lato-latin-ext-700-normal-3JFX6WED.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/search_data-9CA2735F.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/search_data-45DA08B4.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/dist/sidebar_items-FCA6C10D.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/eep48_chapter.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/erl_boot_server.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/erl_ddll.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/erl_epmd.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/erpc.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/kernel-10.2.7.4/doc/html/error_handler.html
│ │ │ │ @@ -1169,15 +1169,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/lato-latin-ext-300-normal-DG5RYZUK.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/lato-latin-ext-400-normal-ZXDJ7C2U.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/lato-latin-ext-700-normal-3JFX6WED.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/search_data-C92E6517.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/search_data-FFC02264.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/dist/sidebar_items-6D9D41B7.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/etop.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/etop_ug.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/index.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/introduction_ug.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/notes.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/observer-2.17/doc/html/observer.epub
│ │ │ │ @@ -1362,15 +1362,15 @@
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/lato-latin-ext-300-normal-DG5RYZUK.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/lato-latin-ext-400-normal-ZXDJ7C2U.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/lato-latin-ext-700-normal-3JFX6WED.woff2
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ │ -usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/search_data-A1188F1F.js
│ │ │ │ +usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/search_data-1DC1D27C.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dist/sidebar_items-E5CACCF4.js
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dtrace.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/dyntrace.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/index.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/instrument.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/lttng.html
│ │ │ │  usr/share/doc/erlang-doc/html/lib/runtime_tools-2.1.1/doc/html/msacc.html
├── data.tar.xz
│ ├── data.tar
│ │ ├── file list
│ │ │ @@ -137,15 +137,15 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)      293 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/ssh.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      294 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/ssl.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      295 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/stdlib.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)      301 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/syntax_tools.html
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     2286 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/.build
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5651 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/404.html
│ │ │ --rw-r--r--   0 root         (0) root         (0)   661070 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/Erlang System Documentation.epub
│ │ │ +-rw-r--r--   0 root         (0) root         (0)   661082 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/Erlang System Documentation.epub
│ │ │  -rw-r--r--   0 root         (0) root         (0)    53766 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/applications.html
│ │ │  -rw-r--r--   0 root         (0) root         (0)   109989 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/appup_cookbook.html
│ │ │  drwxr-xr-x   0 root         (0) root         (0)        0 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/
│ │ │  -rw-r--r--   0 root         (0) root         (0)     7982 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/ballpoint-pen.svg
│ │ │  -rw-r--r--   0 root         (0) root         (0)     2284 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/dist1.gif
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5214 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/dist2.gif
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5007 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/doc/system/assets/dist3.gif
│ │ │ @@ -304,15 +304,15 @@
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23236 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23580 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)    23040 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5820 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-ext-300-normal-DG5RYZUK.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5612 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-ext-400-normal-ZXDJ7C2U.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     5552 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/lato-latin-ext-700-normal-3JFX6WED.woff2
│ │ │  -rw-r--r--   0 root         (0) root         (0)     1956 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/remixicon-NKANDIL5.woff2
│ │ │ --rw-r--r--   0 root         (0) root         (0)  2383296 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/search_data-8B3C849F.js
│ │ │ +-rw-r--r--   0 root         (0) root         (0)  2383296 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/dist/search_data-FC9EDC58.js
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│ │ │ @@ -1790,15 +1790,15 @@
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│ │ │ +-rw-r--r--   0 root         (0) root         (0)   213582 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.7/doc/html/ssl.epub
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│ │ │  -rw-r--r--   0 root         (0) root         (0)    21815 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/lib/ssl-11.2.12.7/doc/html/ssl_crl_cache_api.html
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│ │ │ @@ -1896,15 +1896,15 @@
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│ │ │ @@ -2033,15 +2033,15 @@
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│ │ │  -rw-r--r--   0 root         (0) root         (0)    28575 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/tags.html
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│ │ │ +-rw-r--r--   0 root         (0) root         (0)   239375 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/lib/tools-4.1.1/doc/html/tools.epub
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│ │ │  -rw-r--r--   0 root         (0) root         (0)    63051 2026-05-05 12:33:17.000000 ./usr/share/doc/erlang-doc/html/lib/wx-2.4.3.1/doc/html/wxAuiManager.html
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/Erlang System Documentation.epub
│ │ │ ├── zipinfo {}
│ │ │ │ @@ -1,93 +1,93 @@
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│ │ │ │ +?rw-r--r--  6.1 unx     5214 bx stor 26-May-10 23:47 OEBPS/assets/dist2.gif
│ │ │ │ +?rw-r--r--  6.1 unx     2284 bx stor 26-May-10 23:47 OEBPS/assets/dist1.gif
│ │ │ │ +?rw-r--r--  6.1 unx     7982 bx stor 26-May-10 23:47 OEBPS/assets/ballpoint-pen.svg
│ │ │ │ +?rw-r--r--  6.1 unx   104219 bx defN 26-May-10 23:47 OEBPS/appup_cookbook.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx    47930 bx defN 26-May-10 23:47 OEBPS/applications.xhtml
│ │ │ │ +?rw-r--r--  6.1 unx      252 bx defN 26-May-10 23:47 META-INF/container.xml
│ │ │ │ +?rw-r--r--  6.1 unx      162 bx defN 26-May-10 23:47 META-INF/com.apple.ibooks.display-options.xml
│ │ │ │ +91 files, 3161740 bytes uncompressed, 645150 bytes compressed:  79.6%
│ │ │ ├── zipdetails --redact --walk --utc {}
│ │ │ │ @@ -1,29 +1,29 @@
│ │ │ │  
│ │ │ │  00000 LOCAL HEADER #1       04034B50 (67324752)
│ │ │ │  00004 Extract Zip Spec      0A (10) '1.0'
│ │ │ │  00005 Extract OS            00 (0) 'MS-DOS'
│ │ │ │  00006 General Purpose Flag  0000 (0)
│ │ │ │  00008 Compression Method    0000 (0) 'Stored'
│ │ │ │ -0000A Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ +0000A Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │  0000E CRC                   2CAB616F (749429103)
│ │ │ │  00012 Compressed Size       00000014 (20)
│ │ │ │  00016 Uncompressed Size     00000014 (20)
│ │ │ │  0001A Filename Length       0008 (8)
│ │ │ │  0001C Extra Length          001C (28)
│ │ │ │  0001E Filename              'XXXXXXXX'
│ │ │ │  #
│ │ │ │  # WARNING: Offset 0x1E: Filename 'XXXXXXXX'
│ │ │ │  #          Zero length filename
│ │ │ │  #
│ │ │ │  00026 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │  00028   Length              0009 (9)
│ │ │ │  0002A   Flags               03 (3) 'Modification Access'
│ │ │ │ -0002B   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -0002F   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ +0002B   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +0002F   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │  00033 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │  00035   Length              000B (11)
│ │ │ │  00037   Version             01 (1)
│ │ │ │  00038   UID Size            04 (4)
│ │ │ │  00039   UID                 00000000 (0)
│ │ │ │  0003D   GID Size            04 (4)
│ │ │ │  0003E   GID                 00000000 (0)
│ │ │ │ @@ -31,30 +31,30 @@
│ │ │ │  
│ │ │ │  00056 LOCAL HEADER #2       04034B50 (67324752)
│ │ │ │  0005A Extract Zip Spec      14 (20) '2.0'
│ │ │ │  0005B Extract OS            00 (0) 'MS-DOS'
│ │ │ │  0005C General Purpose Flag  0000 (0)
│ │ │ │        [Bits 1-2]            0 'Normal Compression'
│ │ │ │  0005E Compression Method    0008 (8) 'Deflated'
│ │ │ │ -00060 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ +00060 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │  00064 CRC                   7CFCE72A (2096949034)
│ │ │ │  00068 Compressed Size       000015AD (5549)
│ │ │ │  0006C Uncompressed Size     00004603 (17923)
│ │ │ │  00070 Filename Length       0014 (20)
│ │ │ │  00072 Extra Length          001C (28)
│ │ │ │  00074 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │  #
│ │ │ │  # WARNING: Offset 0x74: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │  #          Zero length filename
│ │ │ │  #
│ │ │ │  00088 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │  0008A   Length              0009 (9)
│ │ │ │  0008C   Flags               03 (3) 'Modification Access'
│ │ │ │ -0008D   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -00091   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ +0008D   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +00091   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │  00095 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │  00097   Length              000B (11)
│ │ │ │  00099   Version             01 (1)
│ │ │ │  0009A   UID Size            04 (4)
│ │ │ │  0009B   UID                 00000000 (0)
│ │ │ │  0009F   GID Size            04 (4)
│ │ │ │  000A0   GID                 00000000 (0)
│ │ │ │ @@ -62,30 +62,30 @@
│ │ │ │  
│ │ │ │  01651 LOCAL HEADER #3       04034B50 (67324752)
│ │ │ │  01655 Extract Zip Spec      14 (20) '2.0'
│ │ │ │  01656 Extract OS            00 (0) 'MS-DOS'
│ │ │ │  01657 General Purpose Flag  0000 (0)
│ │ │ │        [Bits 1-2]            0 'Normal Compression'
│ │ │ │  01659 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -0165B Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ +0165B Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │  0165F CRC                   741FDE60 (1948245600)
│ │ │ │  01663 Compressed Size       000006D6 (1750)
│ │ │ │  01667 Uncompressed Size     00001242 (4674)
│ │ │ │  0166B Filename Length       0013 (19)
│ │ │ │  0166D Extra Length          001C (28)
│ │ │ │  0166F Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │  #
│ │ │ │  # WARNING: Offset 0x166F: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │  #          Zero length filename
│ │ │ │  #
│ │ │ │  01682 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │  01684   Length              0009 (9)
│ │ │ │  01686   Flags               03 (3) 'Modification Access'
│ │ │ │ -01687   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -0168B   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ +01687   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +0168B   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │  0168F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │  01691   Length              000B (11)
│ │ │ │  01693   Version             01 (1)
│ │ │ │  01694   UID Size            04 (4)
│ │ │ │  01695   UID                 00000000 (0)
│ │ │ │  01699   GID Size            04 (4)
│ │ │ │  0169A   GID                 00000000 (0)
│ │ │ │ @@ -93,6187 +93,6187 @@
│ │ │ │  
│ │ │ │  01D74 LOCAL HEADER #4       04034B50 (67324752)
│ │ │ │  01D78 Extract Zip Spec      14 (20) '2.0'
│ │ │ │  01D79 Extract OS            00 (0) 'MS-DOS'
│ │ │ │  01D7A General Purpose Flag  0000 (0)
│ │ │ │        [Bits 1-2]            0 'Normal Compression'
│ │ │ │  01D7C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -01D7E Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -01D82 CRC                   FBBFDC35 (4223654965)
│ │ │ │ -01D86 Compressed Size       00002DA6 (11686)
│ │ │ │ +01D7E Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +01D82 CRC                   19F7DFEB (435675115)
│ │ │ │ +01D86 Compressed Size       00002DA3 (11683)
│ │ │ │  01D8A Uncompressed Size     0000D0C0 (53440)
│ │ │ │  01D8E Filename Length       0014 (20)
│ │ │ │  01D90 Extra Length          001C (28)
│ │ │ │  01D92 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │  #
│ │ │ │  # WARNING: Offset 0x1D92: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │  #          Zero length filename
│ │ │ │  #
│ │ │ │  01DA6 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │  01DA8   Length              0009 (9)
│ │ │ │  01DAA   Flags               03 (3) 'Modification Access'
│ │ │ │ -01DAB   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -01DAF   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ +01DAB   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +01DAF   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │  01DB3 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │  01DB5   Length              000B (11)
│ │ │ │  01DB7   Version             01 (1)
│ │ │ │  01DB8   UID Size            04 (4)
│ │ │ │  01DB9   UID                 00000000 (0)
│ │ │ │  01DBD   GID Size            04 (4)
│ │ │ │  01DBE   GID                 00000000 (0)
│ │ │ │  01DC2 PAYLOAD
│ │ │ │  
│ │ │ │ -04B68 LOCAL HEADER #5       04034B50 (67324752)
│ │ │ │ -04B6C Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -04B6D Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -04B6E General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -04B70 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -04B72 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -04B76 CRC                   AFEB34EA (2951427306)
│ │ │ │ -04B7A Compressed Size       000003F0 (1008)
│ │ │ │ -04B7E Uncompressed Size     00000877 (2167)
│ │ │ │ -04B82 Filename Length       0014 (20)
│ │ │ │ -04B84 Extra Length          001C (28)
│ │ │ │ -04B86 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4B86: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -04B9A Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -04B9C   Length              0009 (9)
│ │ │ │ -04B9E   Flags               03 (3) 'Modification Access'
│ │ │ │ -04B9F   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -04BA3   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -04BA7 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -04BA9   Length              000B (11)
│ │ │ │ -04BAB   Version             01 (1)
│ │ │ │ -04BAC   UID Size            04 (4)
│ │ │ │ -04BAD   UID                 00000000 (0)
│ │ │ │ -04BB1   GID Size            04 (4)
│ │ │ │ -04BB2   GID                 00000000 (0)
│ │ │ │ -04BB6 PAYLOAD
│ │ │ │ -
│ │ │ │ -04FA6 LOCAL HEADER #6       04034B50 (67324752)
│ │ │ │ -04FAA Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -04FAB Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -04FAC General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -04FAE Compression Method    0008 (8) 'Deflated'
│ │ │ │ -04FB0 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -04FB4 CRC                   21AF85A7 (565151143)
│ │ │ │ -04FB8 Compressed Size       000001AE (430)
│ │ │ │ -04FBC Uncompressed Size     000002FE (766)
│ │ │ │ -04FC0 Filename Length       0011 (17)
│ │ │ │ -04FC2 Extra Length          001C (28)
│ │ │ │ -04FC4 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4FC4: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -04FD5 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -04FD7   Length              0009 (9)
│ │ │ │ -04FD9   Flags               03 (3) 'Modification Access'
│ │ │ │ -04FDA   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -04FDE   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -04FE2 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -04FE4   Length              000B (11)
│ │ │ │ -04FE6   Version             01 (1)
│ │ │ │ -04FE7   UID Size            04 (4)
│ │ │ │ -04FE8   UID                 00000000 (0)
│ │ │ │ -04FEC   GID Size            04 (4)
│ │ │ │ -04FED   GID                 00000000 (0)
│ │ │ │ -04FF1 PAYLOAD
│ │ │ │ -
│ │ │ │ -0519F LOCAL HEADER #7       04034B50 (67324752)
│ │ │ │ -051A3 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -051A4 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -051A5 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -051A7 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -051A9 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -051AD CRC                   A0E52D3F (2699373887)
│ │ │ │ -051B1 Compressed Size       000020CA (8394)
│ │ │ │ -051B5 Uncompressed Size     0000B4B1 (46257)
│ │ │ │ -051B9 Filename Length       001B (27)
│ │ │ │ -051BB Extra Length          001C (28)
│ │ │ │ -051BD Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x51BD: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -051D8 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -051DA   Length              0009 (9)
│ │ │ │ -051DC   Flags               03 (3) 'Modification Access'
│ │ │ │ -051DD   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -051E1   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -051E5 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -051E7   Length              000B (11)
│ │ │ │ -051E9   Version             01 (1)
│ │ │ │ -051EA   UID Size            04 (4)
│ │ │ │ -051EB   UID                 00000000 (0)
│ │ │ │ -051EF   GID Size            04 (4)
│ │ │ │ -051F0   GID                 00000000 (0)
│ │ │ │ -051F4 PAYLOAD
│ │ │ │ -
│ │ │ │ -072BE LOCAL HEADER #8       04034B50 (67324752)
│ │ │ │ -072C2 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -072C3 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -072C4 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -072C6 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -072C8 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -072CC CRC                   2D371F1E (758587166)
│ │ │ │ -072D0 Compressed Size       00000E70 (3696)
│ │ │ │ -072D4 Uncompressed Size     000030B3 (12467)
│ │ │ │ -072D8 Filename Length       001D (29)
│ │ │ │ -072DA Extra Length          001C (28)
│ │ │ │ -072DC Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x72DC: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -072F9 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -072FB   Length              0009 (9)
│ │ │ │ -072FD   Flags               03 (3) 'Modification Access'
│ │ │ │ -072FE   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -07302   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -07306 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -07308   Length              000B (11)
│ │ │ │ -0730A   Version             01 (1)
│ │ │ │ -0730B   UID Size            04 (4)
│ │ │ │ -0730C   UID                 00000000 (0)
│ │ │ │ -07310   GID Size            04 (4)
│ │ │ │ -07311   GID                 00000000 (0)
│ │ │ │ -07315 PAYLOAD
│ │ │ │ -
│ │ │ │ -08185 LOCAL HEADER #9       04034B50 (67324752)
│ │ │ │ -08189 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -0818A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -0818B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -0818D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -0818F Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -08193 CRC                   7903D0CB (2030293195)
│ │ │ │ -08197 Compressed Size       00000973 (2419)
│ │ │ │ -0819B Uncompressed Size     00001CB3 (7347)
│ │ │ │ -0819F Filename Length       0019 (25)
│ │ │ │ -081A1 Extra Length          001C (28)
│ │ │ │ -081A3 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x81A3: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -081BC Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -081BE   Length              0009 (9)
│ │ │ │ -081C0   Flags               03 (3) 'Modification Access'
│ │ │ │ -081C1   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -081C5   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -081C9 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -081CB   Length              000B (11)
│ │ │ │ -081CD   Version             01 (1)
│ │ │ │ -081CE   UID Size            04 (4)
│ │ │ │ -081CF   UID                 00000000 (0)
│ │ │ │ -081D3   GID Size            04 (4)
│ │ │ │ -081D4   GID                 00000000 (0)
│ │ │ │ -081D8 PAYLOAD
│ │ │ │ -
│ │ │ │ -08B4B LOCAL HEADER #10      04034B50 (67324752)
│ │ │ │ -08B4F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -08B50 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -08B51 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -08B53 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -08B55 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -08B59 CRC                   9B28EE90 (2603150992)
│ │ │ │ -08B5D Compressed Size       00003880 (14464)
│ │ │ │ -08B61 Uncompressed Size     0000F7F5 (63477)
│ │ │ │ -08B65 Filename Length       0015 (21)
│ │ │ │ -08B67 Extra Length          001C (28)
│ │ │ │ -08B69 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8B69: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -08B7E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -08B80   Length              0009 (9)
│ │ │ │ -08B82   Flags               03 (3) 'Modification Access'
│ │ │ │ -08B83   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -08B87   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -08B8B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -08B8D   Length              000B (11)
│ │ │ │ -08B8F   Version             01 (1)
│ │ │ │ -08B90   UID Size            04 (4)
│ │ │ │ -08B91   UID                 00000000 (0)
│ │ │ │ -08B95   GID Size            04 (4)
│ │ │ │ -08B96   GID                 00000000 (0)
│ │ │ │ -08B9A PAYLOAD
│ │ │ │ -
│ │ │ │ -0C41A LOCAL HEADER #11      04034B50 (67324752)
│ │ │ │ -0C41E Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -0C41F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -0C420 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -0C422 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -0C424 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -0C428 CRC                   A03CCBDB (2688338907)
│ │ │ │ -0C42C Compressed Size       0000AB09 (43785)
│ │ │ │ -0C430 Uncompressed Size     0003E052 (254034)
│ │ │ │ -0C434 Filename Length       0012 (18)
│ │ │ │ -0C436 Extra Length          001C (28)
│ │ │ │ -0C438 Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xC438: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -0C44A Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -0C44C   Length              0009 (9)
│ │ │ │ -0C44E   Flags               03 (3) 'Modification Access'
│ │ │ │ -0C44F   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -0C453   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -0C457 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -0C459   Length              000B (11)
│ │ │ │ -0C45B   Version             01 (1)
│ │ │ │ -0C45C   UID Size            04 (4)
│ │ │ │ -0C45D   UID                 00000000 (0)
│ │ │ │ -0C461   GID Size            04 (4)
│ │ │ │ -0C462   GID                 00000000 (0)
│ │ │ │ -0C466 PAYLOAD
│ │ │ │ -
│ │ │ │ -16F6F LOCAL HEADER #12      04034B50 (67324752)
│ │ │ │ -16F73 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -16F74 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -16F75 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -16F77 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -16F79 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -16F7D CRC                   4650ADC7 (1179692487)
│ │ │ │ -16F81 Compressed Size       00003B0B (15115)
│ │ │ │ -16F85 Uncompressed Size     0001B46D (111725)
│ │ │ │ -16F89 Filename Length       0015 (21)
│ │ │ │ -16F8B Extra Length          001C (28)
│ │ │ │ -16F8D Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x16F8D: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -16FA2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -16FA4   Length              0009 (9)
│ │ │ │ -16FA6   Flags               03 (3) 'Modification Access'
│ │ │ │ -16FA7   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -16FAB   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -16FAF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -16FB1   Length              000B (11)
│ │ │ │ -16FB3   Version             01 (1)
│ │ │ │ -16FB4   UID Size            04 (4)
│ │ │ │ -16FB5   UID                 00000000 (0)
│ │ │ │ -16FB9   GID Size            04 (4)
│ │ │ │ -16FBA   GID                 00000000 (0)
│ │ │ │ -16FBE PAYLOAD
│ │ │ │ -
│ │ │ │ -1AAC9 LOCAL HEADER #13      04034B50 (67324752)
│ │ │ │ -1AACD Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -1AACE Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -1AACF General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -1AAD1 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -1AAD3 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -1AAD7 CRC                   A2B5FF2C (2729836332)
│ │ │ │ -1AADB Compressed Size       000091C4 (37316)
│ │ │ │ -1AADF Uncompressed Size     0003D9DE (252382)
│ │ │ │ -1AAE3 Filename Length       0014 (20)
│ │ │ │ -1AAE5 Extra Length          001C (28)
│ │ │ │ -1AAE7 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x1AAE7: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -1AAFB Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -1AAFD   Length              0009 (9)
│ │ │ │ -1AAFF   Flags               03 (3) 'Modification Access'
│ │ │ │ -1AB00   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -1AB04   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -1AB08 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -1AB0A   Length              000B (11)
│ │ │ │ -1AB0C   Version             01 (1)
│ │ │ │ -1AB0D   UID Size            04 (4)
│ │ │ │ -1AB0E   UID                 00000000 (0)
│ │ │ │ -1AB12   GID Size            04 (4)
│ │ │ │ -1AB13   GID                 00000000 (0)
│ │ │ │ -1AB17 PAYLOAD
│ │ │ │ -
│ │ │ │ -23CDB LOCAL HEADER #14      04034B50 (67324752)
│ │ │ │ -23CDF Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -23CE0 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -23CE1 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -23CE3 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -23CE5 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -23CE9 CRC                   49680290 (1231553168)
│ │ │ │ -23CED Compressed Size       00002A65 (10853)
│ │ │ │ -23CF1 Uncompressed Size     00011520 (70944)
│ │ │ │ -23CF5 Filename Length       0016 (22)
│ │ │ │ -23CF7 Extra Length          001C (28)
│ │ │ │ -23CF9 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x23CF9: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -23D0F Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -23D11   Length              0009 (9)
│ │ │ │ -23D13   Flags               03 (3) 'Modification Access'
│ │ │ │ -23D14   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -23D18   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -23D1C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -23D1E   Length              000B (11)
│ │ │ │ -23D20   Version             01 (1)
│ │ │ │ -23D21   UID Size            04 (4)
│ │ │ │ -23D22   UID                 00000000 (0)
│ │ │ │ -23D26   GID Size            04 (4)
│ │ │ │ -23D27   GID                 00000000 (0)
│ │ │ │ -23D2B PAYLOAD
│ │ │ │ -
│ │ │ │ -26790 LOCAL HEADER #15      04034B50 (67324752)
│ │ │ │ -26794 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -26795 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -26796 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -26798 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -2679A Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2679E CRC                   29BEF9C0 (700381632)
│ │ │ │ -267A2 Compressed Size       000014DB (5339)
│ │ │ │ -267A6 Uncompressed Size     0000518E (20878)
│ │ │ │ -267AA Filename Length       001D (29)
│ │ │ │ -267AC Extra Length          001C (28)
│ │ │ │ -267AE Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x267AE: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -267CB Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -267CD   Length              0009 (9)
│ │ │ │ -267CF   Flags               03 (3) 'Modification Access'
│ │ │ │ -267D0   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -267D4   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -267D8 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -267DA   Length              000B (11)
│ │ │ │ -267DC   Version             01 (1)
│ │ │ │ -267DD   UID Size            04 (4)
│ │ │ │ -267DE   UID                 00000000 (0)
│ │ │ │ -267E2   GID Size            04 (4)
│ │ │ │ -267E3   GID                 00000000 (0)
│ │ │ │ -267E7 PAYLOAD
│ │ │ │ -
│ │ │ │ -27CC2 LOCAL HEADER #16      04034B50 (67324752)
│ │ │ │ -27CC6 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -27CC7 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -27CC8 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -27CCA Compression Method    0008 (8) 'Deflated'
│ │ │ │ -27CCC Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -27CD0 CRC                   B011A27F (2953945727)
│ │ │ │ -27CD4 Compressed Size       000039AF (14767)
│ │ │ │ -27CD8 Uncompressed Size     0000F080 (61568)
│ │ │ │ -27CDC Filename Length       001C (28)
│ │ │ │ -27CDE Extra Length          001C (28)
│ │ │ │ -27CE0 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x27CE0: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -27CFC Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -27CFE   Length              0009 (9)
│ │ │ │ -27D00   Flags               03 (3) 'Modification Access'
│ │ │ │ -27D01   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -27D05   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -27D09 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -27D0B   Length              000B (11)
│ │ │ │ -27D0D   Version             01 (1)
│ │ │ │ -27D0E   UID Size            04 (4)
│ │ │ │ -27D0F   UID                 00000000 (0)
│ │ │ │ -27D13   GID Size            04 (4)
│ │ │ │ -27D14   GID                 00000000 (0)
│ │ │ │ -27D18 PAYLOAD
│ │ │ │ -
│ │ │ │ -2B6C7 LOCAL HEADER #17      04034B50 (67324752)
│ │ │ │ -2B6CB Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -2B6CC Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -2B6CD General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -2B6CF Compression Method    0008 (8) 'Deflated'
│ │ │ │ -2B6D1 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2B6D5 CRC                   7A88ED58 (2055794008)
│ │ │ │ -2B6D9 Compressed Size       000006A3 (1699)
│ │ │ │ -2B6DD Uncompressed Size     000011F5 (4597)
│ │ │ │ -2B6E1 Filename Length       001C (28)
│ │ │ │ -2B6E3 Extra Length          001C (28)
│ │ │ │ -2B6E5 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x2B6E5: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -2B701 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -2B703   Length              0009 (9)
│ │ │ │ -2B705   Flags               03 (3) 'Modification Access'
│ │ │ │ -2B706   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2B70A   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2B70E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -2B710   Length              000B (11)
│ │ │ │ -2B712   Version             01 (1)
│ │ │ │ -2B713   UID Size            04 (4)
│ │ │ │ -2B714   UID                 00000000 (0)
│ │ │ │ -2B718   GID Size            04 (4)
│ │ │ │ -2B719   GID                 00000000 (0)
│ │ │ │ -2B71D PAYLOAD
│ │ │ │ -
│ │ │ │ -2BDC0 LOCAL HEADER #18      04034B50 (67324752)
│ │ │ │ -2BDC4 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -2BDC5 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -2BDC6 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -2BDC8 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -2BDCA Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2BDCE CRC                   0FC65721 (264656673)
│ │ │ │ -2BDD2 Compressed Size       00001081 (4225)
│ │ │ │ -2BDD6 Uncompressed Size     00004C00 (19456)
│ │ │ │ -2BDDA Filename Length       001B (27)
│ │ │ │ -2BDDC Extra Length          001C (28)
│ │ │ │ -2BDDE Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x2BDDE: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -2BDF9 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -2BDFB   Length              0009 (9)
│ │ │ │ -2BDFD   Flags               03 (3) 'Modification Access'
│ │ │ │ -2BDFE   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2BE02   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2BE06 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -2BE08   Length              000B (11)
│ │ │ │ -2BE0A   Version             01 (1)
│ │ │ │ -2BE0B   UID Size            04 (4)
│ │ │ │ -2BE0C   UID                 00000000 (0)
│ │ │ │ -2BE10   GID Size            04 (4)
│ │ │ │ -2BE11   GID                 00000000 (0)
│ │ │ │ -2BE15 PAYLOAD
│ │ │ │ -
│ │ │ │ -2CE96 LOCAL HEADER #19      04034B50 (67324752)
│ │ │ │ -2CE9A Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -2CE9B Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -2CE9C General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -2CE9E Compression Method    0008 (8) 'Deflated'
│ │ │ │ -2CEA0 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2CEA4 CRC                   75FAACB3 (1979362483)
│ │ │ │ -2CEA8 Compressed Size       000033AB (13227)
│ │ │ │ -2CEAC Uncompressed Size     0000BC95 (48277)
│ │ │ │ -2CEB0 Filename Length       001D (29)
│ │ │ │ -2CEB2 Extra Length          001C (28)
│ │ │ │ -2CEB4 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x2CEB4: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -2CED1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -2CED3   Length              0009 (9)
│ │ │ │ -2CED5   Flags               03 (3) 'Modification Access'
│ │ │ │ -2CED6   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2CEDA   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -2CEDE Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -2CEE0   Length              000B (11)
│ │ │ │ -2CEE2   Version             01 (1)
│ │ │ │ -2CEE3   UID Size            04 (4)
│ │ │ │ -2CEE4   UID                 00000000 (0)
│ │ │ │ -2CEE8   GID Size            04 (4)
│ │ │ │ -2CEE9   GID                 00000000 (0)
│ │ │ │ -2CEED PAYLOAD
│ │ │ │ -
│ │ │ │ -30298 LOCAL HEADER #20      04034B50 (67324752)
│ │ │ │ -3029C Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3029D Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3029E General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -302A0 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -302A2 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -302A6 CRC                   D83D1D51 (3627883857)
│ │ │ │ -302AA Compressed Size       00000D6B (3435)
│ │ │ │ -302AE Uncompressed Size     0000388E (14478)
│ │ │ │ -302B2 Filename Length       001D (29)
│ │ │ │ -302B4 Extra Length          001C (28)
│ │ │ │ -302B6 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x302B6: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -302D3 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -302D5   Length              0009 (9)
│ │ │ │ -302D7   Flags               03 (3) 'Modification Access'
│ │ │ │ -302D8   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -302DC   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -302E0 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -302E2   Length              000B (11)
│ │ │ │ -302E4   Version             01 (1)
│ │ │ │ -302E5   UID Size            04 (4)
│ │ │ │ -302E6   UID                 00000000 (0)
│ │ │ │ -302EA   GID Size            04 (4)
│ │ │ │ -302EB   GID                 00000000 (0)
│ │ │ │ -302EF PAYLOAD
│ │ │ │ -
│ │ │ │ -3105A LOCAL HEADER #21      04034B50 (67324752)
│ │ │ │ -3105E Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3105F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -31060 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -31062 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -31064 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -31068 CRC                   C751E37B (3344032635)
│ │ │ │ -3106C Compressed Size       00001C69 (7273)
│ │ │ │ -31070 Uncompressed Size     0000C187 (49543)
│ │ │ │ -31074 Filename Length       001A (26)
│ │ │ │ -31076 Extra Length          001C (28)
│ │ │ │ -31078 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x31078: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -31092 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -31094   Length              0009 (9)
│ │ │ │ -31096   Flags               03 (3) 'Modification Access'
│ │ │ │ -31097   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3109B   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3109F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -310A1   Length              000B (11)
│ │ │ │ -310A3   Version             01 (1)
│ │ │ │ -310A4   UID Size            04 (4)
│ │ │ │ -310A5   UID                 00000000 (0)
│ │ │ │ -310A9   GID Size            04 (4)
│ │ │ │ -310AA   GID                 00000000 (0)
│ │ │ │ -310AE PAYLOAD
│ │ │ │ -
│ │ │ │ -32D17 LOCAL HEADER #22      04034B50 (67324752)
│ │ │ │ -32D1B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -32D1C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -32D1D General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -32D1F Compression Method    0008 (8) 'Deflated'
│ │ │ │ -32D21 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -32D25 CRC                   C41B95CB (3290142155)
│ │ │ │ -32D29 Compressed Size       000003A4 (932)
│ │ │ │ -32D2D Uncompressed Size     0000088F (2191)
│ │ │ │ -32D31 Filename Length       0012 (18)
│ │ │ │ -32D33 Extra Length          001C (28)
│ │ │ │ -32D35 Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x32D35: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -32D47 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -32D49   Length              0009 (9)
│ │ │ │ -32D4B   Flags               03 (3) 'Modification Access'
│ │ │ │ -32D4C   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -32D50   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -32D54 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -32D56   Length              000B (11)
│ │ │ │ -32D58   Version             01 (1)
│ │ │ │ -32D59   UID Size            04 (4)
│ │ │ │ -32D5A   UID                 00000000 (0)
│ │ │ │ -32D5E   GID Size            04 (4)
│ │ │ │ -32D5F   GID                 00000000 (0)
│ │ │ │ -32D63 PAYLOAD
│ │ │ │ -
│ │ │ │ -33107 LOCAL HEADER #23      04034B50 (67324752)
│ │ │ │ -3310B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3310C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3310D General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3310F Compression Method    0008 (8) 'Deflated'
│ │ │ │ -33111 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -33115 CRC                   40B68220 (1085702688)
│ │ │ │ -33119 Compressed Size       000001D4 (468)
│ │ │ │ -3311D Uncompressed Size     00000312 (786)
│ │ │ │ -33121 Filename Length       0020 (32)
│ │ │ │ -33123 Extra Length          001C (28)
│ │ │ │ -33125 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x33125: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -33145 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -33147   Length              0009 (9)
│ │ │ │ -33149   Flags               03 (3) 'Modification Access'
│ │ │ │ -3314A   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3314E   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -33152 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -33154   Length              000B (11)
│ │ │ │ -33156   Version             01 (1)
│ │ │ │ -33157   UID Size            04 (4)
│ │ │ │ -33158   UID                 00000000 (0)
│ │ │ │ -3315C   GID Size            04 (4)
│ │ │ │ -3315D   GID                 00000000 (0)
│ │ │ │ -33161 PAYLOAD
│ │ │ │ -
│ │ │ │ -33335 LOCAL HEADER #24      04034B50 (67324752)
│ │ │ │ -33339 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3333A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3333B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3333D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3333F Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -33343 CRC                   AEDAC289 (2933572233)
│ │ │ │ -33347 Compressed Size       000017AA (6058)
│ │ │ │ -3334B Uncompressed Size     00009D19 (40217)
│ │ │ │ -3334F Filename Length       001B (27)
│ │ │ │ -33351 Extra Length          001C (28)
│ │ │ │ -33353 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x33353: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3336E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -33370   Length              0009 (9)
│ │ │ │ -33372   Flags               03 (3) 'Modification Access'
│ │ │ │ -33373   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -33377   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3337B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3337D   Length              000B (11)
│ │ │ │ -3337F   Version             01 (1)
│ │ │ │ -33380   UID Size            04 (4)
│ │ │ │ -33381   UID                 00000000 (0)
│ │ │ │ -33385   GID Size            04 (4)
│ │ │ │ -33386   GID                 00000000 (0)
│ │ │ │ -3338A PAYLOAD
│ │ │ │ -
│ │ │ │ -34B34 LOCAL HEADER #25      04034B50 (67324752)
│ │ │ │ -34B38 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -34B39 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -34B3A General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -34B3C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -34B3E Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -34B42 CRC                   8B976C32 (2341956658)
│ │ │ │ -34B46 Compressed Size       00001374 (4980)
│ │ │ │ -34B4A Uncompressed Size     00003B67 (15207)
│ │ │ │ -34B4E Filename Length       0015 (21)
│ │ │ │ -34B50 Extra Length          001C (28)
│ │ │ │ -34B52 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x34B52: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -34B67 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -34B69   Length              0009 (9)
│ │ │ │ -34B6B   Flags               03 (3) 'Modification Access'
│ │ │ │ -34B6C   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -34B70   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -34B74 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -34B76   Length              000B (11)
│ │ │ │ -34B78   Version             01 (1)
│ │ │ │ -34B79   UID Size            04 (4)
│ │ │ │ -34B7A   UID                 00000000 (0)
│ │ │ │ -34B7E   GID Size            04 (4)
│ │ │ │ -34B7F   GID                 00000000 (0)
│ │ │ │ -34B83 PAYLOAD
│ │ │ │ -
│ │ │ │ -35EF7 LOCAL HEADER #26      04034B50 (67324752)
│ │ │ │ -35EFB Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -35EFC Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -35EFD General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -35EFF Compression Method    0008 (8) 'Deflated'
│ │ │ │ -35F01 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -35F05 CRC                   2ACCA91C (718055708)
│ │ │ │ -35F09 Compressed Size       00000AD3 (2771)
│ │ │ │ -35F0D Uncompressed Size     00002136 (8502)
│ │ │ │ -35F11 Filename Length       0011 (17)
│ │ │ │ -35F13 Extra Length          001C (28)
│ │ │ │ -35F15 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x35F15: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -35F26 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -35F28   Length              0009 (9)
│ │ │ │ -35F2A   Flags               03 (3) 'Modification Access'
│ │ │ │ -35F2B   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -35F2F   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -35F33 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -35F35   Length              000B (11)
│ │ │ │ -35F37   Version             01 (1)
│ │ │ │ -35F38   UID Size            04 (4)
│ │ │ │ -35F39   UID                 00000000 (0)
│ │ │ │ -35F3D   GID Size            04 (4)
│ │ │ │ -35F3E   GID                 00000000 (0)
│ │ │ │ -35F42 PAYLOAD
│ │ │ │ -
│ │ │ │ -36A15 LOCAL HEADER #27      04034B50 (67324752)
│ │ │ │ -36A19 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -36A1A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -36A1B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -36A1D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -36A1F Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -36A23 CRC                   984552B7 (2554679991)
│ │ │ │ -36A27 Compressed Size       000003FE (1022)
│ │ │ │ -36A2B Uncompressed Size     00000F0D (3853)
│ │ │ │ -36A2F Filename Length       0014 (20)
│ │ │ │ -36A31 Extra Length          001C (28)
│ │ │ │ -36A33 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x36A33: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -36A47 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -36A49   Length              0009 (9)
│ │ │ │ -36A4B   Flags               03 (3) 'Modification Access'
│ │ │ │ -36A4C   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -36A50   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -36A54 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -36A56   Length              000B (11)
│ │ │ │ -36A58   Version             01 (1)
│ │ │ │ -36A59   UID Size            04 (4)
│ │ │ │ -36A5A   UID                 00000000 (0)
│ │ │ │ -36A5E   GID Size            04 (4)
│ │ │ │ -36A5F   GID                 00000000 (0)
│ │ │ │ -36A63 PAYLOAD
│ │ │ │ -
│ │ │ │ -36E61 LOCAL HEADER #28      04034B50 (67324752)
│ │ │ │ -36E65 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -36E66 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -36E67 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -36E69 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -36E6B Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -36E6F CRC                   F2ED2F43 (4075630403)
│ │ │ │ -36E73 Compressed Size       00001263 (4707)
│ │ │ │ -36E77 Uncompressed Size     0000346A (13418)
│ │ │ │ -36E7B Filename Length       0014 (20)
│ │ │ │ -36E7D Extra Length          001C (28)
│ │ │ │ -36E7F Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x36E7F: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -36E93 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -36E95   Length              0009 (9)
│ │ │ │ -36E97   Flags               03 (3) 'Modification Access'
│ │ │ │ -36E98   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -36E9C   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -36EA0 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -36EA2   Length              000B (11)
│ │ │ │ -36EA4   Version             01 (1)
│ │ │ │ -36EA5   UID Size            04 (4)
│ │ │ │ -36EA6   UID                 00000000 (0)
│ │ │ │ -36EAA   GID Size            04 (4)
│ │ │ │ -36EAB   GID                 00000000 (0)
│ │ │ │ -36EAF PAYLOAD
│ │ │ │ -
│ │ │ │ -38112 LOCAL HEADER #29      04034B50 (67324752)
│ │ │ │ -38116 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -38117 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -38118 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3811A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3811C Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -38120 CRC                   3233182B (842209323)
│ │ │ │ -38124 Compressed Size       00000AD1 (2769)
│ │ │ │ -38128 Uncompressed Size     00002300 (8960)
│ │ │ │ -3812C Filename Length       001B (27)
│ │ │ │ -3812E Extra Length          001C (28)
│ │ │ │ -38130 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x38130: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3814B Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3814D   Length              0009 (9)
│ │ │ │ -3814F   Flags               03 (3) 'Modification Access'
│ │ │ │ -38150   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -38154   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -38158 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3815A   Length              000B (11)
│ │ │ │ -3815C   Version             01 (1)
│ │ │ │ -3815D   UID Size            04 (4)
│ │ │ │ -3815E   UID                 00000000 (0)
│ │ │ │ -38162   GID Size            04 (4)
│ │ │ │ -38163   GID                 00000000 (0)
│ │ │ │ -38167 PAYLOAD
│ │ │ │ -
│ │ │ │ -38C38 LOCAL HEADER #30      04034B50 (67324752)
│ │ │ │ -38C3C Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -38C3D Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -38C3E General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -38C40 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -38C42 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -38C46 CRC                   0BD59D77 (198548855)
│ │ │ │ -38C4A Compressed Size       00000A8E (2702)
│ │ │ │ -38C4E Uncompressed Size     0000237B (9083)
│ │ │ │ -38C52 Filename Length       0013 (19)
│ │ │ │ -38C54 Extra Length          001C (28)
│ │ │ │ -38C56 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x38C56: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -38C69 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -38C6B   Length              0009 (9)
│ │ │ │ -38C6D   Flags               03 (3) 'Modification Access'
│ │ │ │ -38C6E   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -38C72   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -38C76 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -38C78   Length              000B (11)
│ │ │ │ -38C7A   Version             01 (1)
│ │ │ │ -38C7B   UID Size            04 (4)
│ │ │ │ -38C7C   UID                 00000000 (0)
│ │ │ │ -38C80   GID Size            04 (4)
│ │ │ │ -38C81   GID                 00000000 (0)
│ │ │ │ -38C85 PAYLOAD
│ │ │ │ -
│ │ │ │ -39713 LOCAL HEADER #31      04034B50 (67324752)
│ │ │ │ -39717 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -39718 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -39719 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3971B Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3971D Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -39721 CRC                   4DABAB86 (1303096198)
│ │ │ │ -39725 Compressed Size       000010E5 (4325)
│ │ │ │ -39729 Uncompressed Size     00005611 (22033)
│ │ │ │ -3972D Filename Length       000F (15)
│ │ │ │ -3972F Extra Length          001C (28)
│ │ │ │ -39731 Filename              'XXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x39731: Filename 'XXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -39740 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -39742   Length              0009 (9)
│ │ │ │ -39744   Flags               03 (3) 'Modification Access'
│ │ │ │ -39745   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -39749   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3974D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3974F   Length              000B (11)
│ │ │ │ -39751   Version             01 (1)
│ │ │ │ -39752   UID Size            04 (4)
│ │ │ │ -39753   UID                 00000000 (0)
│ │ │ │ -39757   GID Size            04 (4)
│ │ │ │ -39758   GID                 00000000 (0)
│ │ │ │ -3975C PAYLOAD
│ │ │ │ -
│ │ │ │ -3A841 LOCAL HEADER #32      04034B50 (67324752)
│ │ │ │ -3A845 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3A846 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3A847 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3A849 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3A84B Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3A84F CRC                   C70CE575 (3339511157)
│ │ │ │ -3A853 Compressed Size       0000066B (1643)
│ │ │ │ -3A857 Uncompressed Size     000018E0 (6368)
│ │ │ │ -3A85B Filename Length       000F (15)
│ │ │ │ -3A85D Extra Length          001C (28)
│ │ │ │ -3A85F Filename              'XXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3A85F: Filename 'XXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3A86E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3A870   Length              0009 (9)
│ │ │ │ -3A872   Flags               03 (3) 'Modification Access'
│ │ │ │ -3A873   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3A877   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3A87B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3A87D   Length              000B (11)
│ │ │ │ -3A87F   Version             01 (1)
│ │ │ │ -3A880   UID Size            04 (4)
│ │ │ │ -3A881   UID                 00000000 (0)
│ │ │ │ -3A885   GID Size            04 (4)
│ │ │ │ -3A886   GID                 00000000 (0)
│ │ │ │ -3A88A PAYLOAD
│ │ │ │ -
│ │ │ │ -3AEF5 LOCAL HEADER #33      04034B50 (67324752)
│ │ │ │ -3AEF9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3AEFA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3AEFB General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3AEFD Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3AEFF Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3AF03 CRC                   B33717CF (3006732239)
│ │ │ │ -3AF07 Compressed Size       00001A4B (6731)
│ │ │ │ -3AF0B Uncompressed Size     000064F3 (25843)
│ │ │ │ -3AF0F Filename Length       0013 (19)
│ │ │ │ -3AF11 Extra Length          001C (28)
│ │ │ │ -3AF13 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3AF13: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3AF26 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3AF28   Length              0009 (9)
│ │ │ │ -3AF2A   Flags               03 (3) 'Modification Access'
│ │ │ │ -3AF2B   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3AF2F   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3AF33 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3AF35   Length              000B (11)
│ │ │ │ -3AF37   Version             01 (1)
│ │ │ │ -3AF38   UID Size            04 (4)
│ │ │ │ -3AF39   UID                 00000000 (0)
│ │ │ │ -3AF3D   GID Size            04 (4)
│ │ │ │ -3AF3E   GID                 00000000 (0)
│ │ │ │ -3AF42 PAYLOAD
│ │ │ │ -
│ │ │ │ -3C98D LOCAL HEADER #34      04034B50 (67324752)
│ │ │ │ -3C991 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3C992 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3C993 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3C995 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3C997 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3C99B CRC                   BA8C2020 (3129745440)
│ │ │ │ -3C99F Compressed Size       000009A7 (2471)
│ │ │ │ -3C9A3 Uncompressed Size     00001B65 (7013)
│ │ │ │ -3C9A7 Filename Length       0010 (16)
│ │ │ │ -3C9A9 Extra Length          001C (28)
│ │ │ │ -3C9AB Filename              'XXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3C9AB: Filename 'XXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3C9BB Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3C9BD   Length              0009 (9)
│ │ │ │ -3C9BF   Flags               03 (3) 'Modification Access'
│ │ │ │ -3C9C0   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3C9C4   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3C9C8 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3C9CA   Length              000B (11)
│ │ │ │ -3C9CC   Version             01 (1)
│ │ │ │ -3C9CD   UID Size            04 (4)
│ │ │ │ -3C9CE   UID                 00000000 (0)
│ │ │ │ -3C9D2   GID Size            04 (4)
│ │ │ │ -3C9D3   GID                 00000000 (0)
│ │ │ │ -3C9D7 PAYLOAD
│ │ │ │ -
│ │ │ │ -3D37E LOCAL HEADER #35      04034B50 (67324752)
│ │ │ │ -3D382 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3D383 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3D384 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3D386 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3D388 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3D38C CRC                   61869F50 (1636212560)
│ │ │ │ -3D390 Compressed Size       000006B9 (1721)
│ │ │ │ -3D394 Uncompressed Size     00001566 (5478)
│ │ │ │ -3D398 Filename Length       0012 (18)
│ │ │ │ -3D39A Extra Length          001C (28)
│ │ │ │ -3D39C Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3D39C: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3D3AE Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3D3B0   Length              0009 (9)
│ │ │ │ -3D3B2   Flags               03 (3) 'Modification Access'
│ │ │ │ -3D3B3   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3D3B7   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3D3BB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3D3BD   Length              000B (11)
│ │ │ │ -3D3BF   Version             01 (1)
│ │ │ │ -3D3C0   UID Size            04 (4)
│ │ │ │ -3D3C1   UID                 00000000 (0)
│ │ │ │ -3D3C5   GID Size            04 (4)
│ │ │ │ -3D3C6   GID                 00000000 (0)
│ │ │ │ -3D3CA PAYLOAD
│ │ │ │ -
│ │ │ │ -3DA83 LOCAL HEADER #36      04034B50 (67324752)
│ │ │ │ -3DA87 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -3DA88 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -3DA89 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -3DA8B Compression Method    0008 (8) 'Deflated'
│ │ │ │ -3DA8D Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3DA91 CRC                   16F2754B (384988491)
│ │ │ │ -3DA95 Compressed Size       00002A14 (10772)
│ │ │ │ -3DA99 Uncompressed Size     0000B1DD (45533)
│ │ │ │ -3DA9D Filename Length       0010 (16)
│ │ │ │ -3DA9F Extra Length          001C (28)
│ │ │ │ -3DAA1 Filename              'XXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x3DAA1: Filename 'XXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -3DAB1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -3DAB3   Length              0009 (9)
│ │ │ │ -3DAB5   Flags               03 (3) 'Modification Access'
│ │ │ │ -3DAB6   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3DABA   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -3DABE Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -3DAC0   Length              000B (11)
│ │ │ │ -3DAC2   Version             01 (1)
│ │ │ │ -3DAC3   UID Size            04 (4)
│ │ │ │ -3DAC4   UID                 00000000 (0)
│ │ │ │ -3DAC8   GID Size            04 (4)
│ │ │ │ -3DAC9   GID                 00000000 (0)
│ │ │ │ -3DACD PAYLOAD
│ │ │ │ -
│ │ │ │ -404E1 LOCAL HEADER #37      04034B50 (67324752)
│ │ │ │ -404E5 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -404E6 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -404E7 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -404E9 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -404EB Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -404EF CRC                   23389B09 (590912265)
│ │ │ │ -404F3 Compressed Size       00001E89 (7817)
│ │ │ │ -404F7 Uncompressed Size     00009AAB (39595)
│ │ │ │ -404FB Filename Length       0012 (18)
│ │ │ │ -404FD Extra Length          001C (28)
│ │ │ │ -404FF Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x404FF: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -40511 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -40513   Length              0009 (9)
│ │ │ │ -40515   Flags               03 (3) 'Modification Access'
│ │ │ │ -40516   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4051A   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4051E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -40520   Length              000B (11)
│ │ │ │ -40522   Version             01 (1)
│ │ │ │ -40523   UID Size            04 (4)
│ │ │ │ -40524   UID                 00000000 (0)
│ │ │ │ -40528   GID Size            04 (4)
│ │ │ │ -40529   GID                 00000000 (0)
│ │ │ │ -4052D PAYLOAD
│ │ │ │ -
│ │ │ │ -423B6 LOCAL HEADER #38      04034B50 (67324752)
│ │ │ │ -423BA Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -423BB Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -423BC General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -423BE Compression Method    0008 (8) 'Deflated'
│ │ │ │ -423C0 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -423C4 CRC                   13847F5A (327450458)
│ │ │ │ -423C8 Compressed Size       0000147C (5244)
│ │ │ │ -423CC Uncompressed Size     00007AD0 (31440)
│ │ │ │ -423D0 Filename Length       0018 (24)
│ │ │ │ -423D2 Extra Length          001C (28)
│ │ │ │ -423D4 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x423D4: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -423EC Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -423EE   Length              0009 (9)
│ │ │ │ -423F0   Flags               03 (3) 'Modification Access'
│ │ │ │ -423F1   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -423F5   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -423F9 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -423FB   Length              000B (11)
│ │ │ │ -423FD   Version             01 (1)
│ │ │ │ -423FE   UID Size            04 (4)
│ │ │ │ -423FF   UID                 00000000 (0)
│ │ │ │ -42403   GID Size            04 (4)
│ │ │ │ -42404   GID                 00000000 (0)
│ │ │ │ -42408 PAYLOAD
│ │ │ │ -
│ │ │ │ -43884 LOCAL HEADER #39      04034B50 (67324752)
│ │ │ │ -43888 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -43889 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4388A General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4388C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4388E Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -43892 CRC                   021B6F33 (35352371)
│ │ │ │ -43896 Compressed Size       000018DA (6362)
│ │ │ │ -4389A Uncompressed Size     0000A83A (43066)
│ │ │ │ -4389E Filename Length       001F (31)
│ │ │ │ -438A0 Extra Length          001C (28)
│ │ │ │ -438A2 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x438A2: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -438C1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -438C3   Length              0009 (9)
│ │ │ │ -438C5   Flags               03 (3) 'Modification Access'
│ │ │ │ -438C6   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -438CA   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -438CE Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -438D0   Length              000B (11)
│ │ │ │ -438D2   Version             01 (1)
│ │ │ │ -438D3   UID Size            04 (4)
│ │ │ │ -438D4   UID                 00000000 (0)
│ │ │ │ -438D8   GID Size            04 (4)
│ │ │ │ -438D9   GID                 00000000 (0)
│ │ │ │ -438DD PAYLOAD
│ │ │ │ -
│ │ │ │ -451B7 LOCAL HEADER #40      04034B50 (67324752)
│ │ │ │ -451BB Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -451BC Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -451BD General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -451BF Compression Method    0008 (8) 'Deflated'
│ │ │ │ -451C1 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -451C5 CRC                   8E4EBF9E (2387525534)
│ │ │ │ -451C9 Compressed Size       000003F8 (1016)
│ │ │ │ -451CD Uncompressed Size     000008A4 (2212)
│ │ │ │ -451D1 Filename Length       001E (30)
│ │ │ │ -451D3 Extra Length          001C (28)
│ │ │ │ -451D5 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x451D5: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -451F3 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -451F5   Length              0009 (9)
│ │ │ │ -451F7   Flags               03 (3) 'Modification Access'
│ │ │ │ -451F8   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -451FC   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -45200 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -45202   Length              000B (11)
│ │ │ │ -45204   Version             01 (1)
│ │ │ │ -45205   UID Size            04 (4)
│ │ │ │ -45206   UID                 00000000 (0)
│ │ │ │ -4520A   GID Size            04 (4)
│ │ │ │ -4520B   GID                 00000000 (0)
│ │ │ │ -4520F PAYLOAD
│ │ │ │ -
│ │ │ │ -45607 LOCAL HEADER #41      04034B50 (67324752)
│ │ │ │ -4560B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4560C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4560D General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4560F Compression Method    0008 (8) 'Deflated'
│ │ │ │ -45611 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -45615 CRC                   D9FD2FF3 (3657248755)
│ │ │ │ -45619 Compressed Size       00004296 (17046)
│ │ │ │ -4561D Uncompressed Size     0000D8E8 (55528)
│ │ │ │ -45621 Filename Length       0013 (19)
│ │ │ │ -45623 Extra Length          001C (28)
│ │ │ │ -45625 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x45625: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -45638 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4563A   Length              0009 (9)
│ │ │ │ -4563C   Flags               03 (3) 'Modification Access'
│ │ │ │ -4563D   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -45641   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -45645 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -45647   Length              000B (11)
│ │ │ │ -45649   Version             01 (1)
│ │ │ │ -4564A   UID Size            04 (4)
│ │ │ │ -4564B   UID                 00000000 (0)
│ │ │ │ -4564F   GID Size            04 (4)
│ │ │ │ -45650   GID                 00000000 (0)
│ │ │ │ -45654 PAYLOAD
│ │ │ │ -
│ │ │ │ -498EA LOCAL HEADER #42      04034B50 (67324752)
│ │ │ │ -498EE Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -498EF Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -498F0 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -498F2 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -498F4 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -498F8 CRC                   A60BB6F3 (2785785587)
│ │ │ │ -498FC Compressed Size       000026C4 (9924)
│ │ │ │ -49900 Uncompressed Size     00006E46 (28230)
│ │ │ │ -49904 Filename Length       0019 (25)
│ │ │ │ -49906 Extra Length          001C (28)
│ │ │ │ -49908 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x49908: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -49921 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -49923   Length              0009 (9)
│ │ │ │ -49925   Flags               03 (3) 'Modification Access'
│ │ │ │ -49926   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4992A   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4992E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -49930   Length              000B (11)
│ │ │ │ -49932   Version             01 (1)
│ │ │ │ -49933   UID Size            04 (4)
│ │ │ │ -49934   UID                 00000000 (0)
│ │ │ │ -49938   GID Size            04 (4)
│ │ │ │ -49939   GID                 00000000 (0)
│ │ │ │ -4993D PAYLOAD
│ │ │ │ -
│ │ │ │ -4C001 LOCAL HEADER #43      04034B50 (67324752)
│ │ │ │ -4C005 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4C006 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4C007 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4C009 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4C00B Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4C00F CRC                   A84F7DF4 (2823781876)
│ │ │ │ -4C013 Compressed Size       0000273B (10043)
│ │ │ │ -4C017 Uncompressed Size     00008B84 (35716)
│ │ │ │ -4C01B Filename Length       0019 (25)
│ │ │ │ -4C01D Extra Length          001C (28)
│ │ │ │ -4C01F Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4C01F: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -4C038 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4C03A   Length              0009 (9)
│ │ │ │ -4C03C   Flags               03 (3) 'Modification Access'
│ │ │ │ -4C03D   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4C041   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4C045 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -4C047   Length              000B (11)
│ │ │ │ -4C049   Version             01 (1)
│ │ │ │ -4C04A   UID Size            04 (4)
│ │ │ │ -4C04B   UID                 00000000 (0)
│ │ │ │ -4C04F   GID Size            04 (4)
│ │ │ │ -4C050   GID                 00000000 (0)
│ │ │ │ -4C054 PAYLOAD
│ │ │ │ -
│ │ │ │ -4E78F LOCAL HEADER #44      04034B50 (67324752)
│ │ │ │ -4E793 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4E794 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4E795 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4E797 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4E799 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4E79D CRC                   20889E86 (545824390)
│ │ │ │ -4E7A1 Compressed Size       00000CF1 (3313)
│ │ │ │ -4E7A5 Uncompressed Size     0000517B (20859)
│ │ │ │ -4E7A9 Filename Length       0021 (33)
│ │ │ │ -4E7AB Extra Length          001C (28)
│ │ │ │ -4E7AD Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4E7AD: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -4E7CE Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4E7D0   Length              0009 (9)
│ │ │ │ -4E7D2   Flags               03 (3) 'Modification Access'
│ │ │ │ -4E7D3   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4E7D7   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4E7DB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -4E7DD   Length              000B (11)
│ │ │ │ -4E7DF   Version             01 (1)
│ │ │ │ -4E7E0   UID Size            04 (4)
│ │ │ │ -4E7E1   UID                 00000000 (0)
│ │ │ │ -4E7E5   GID Size            04 (4)
│ │ │ │ -4E7E6   GID                 00000000 (0)
│ │ │ │ -4E7EA PAYLOAD
│ │ │ │ -
│ │ │ │ -4F4DB LOCAL HEADER #45      04034B50 (67324752)
│ │ │ │ -4F4DF Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4F4E0 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4F4E1 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4F4E3 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4F4E5 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4F4E9 CRC                   4527F9F0 (1160247792)
│ │ │ │ -4F4ED Compressed Size       00000469 (1129)
│ │ │ │ -4F4F1 Uncompressed Size     00000932 (2354)
│ │ │ │ -4F4F5 Filename Length       001B (27)
│ │ │ │ -4F4F7 Extra Length          001C (28)
│ │ │ │ -4F4F9 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4F4F9: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -4F514 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4F516   Length              0009 (9)
│ │ │ │ -4F518   Flags               03 (3) 'Modification Access'
│ │ │ │ -4F519   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4F51D   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4F521 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -4F523   Length              000B (11)
│ │ │ │ -4F525   Version             01 (1)
│ │ │ │ -4F526   UID Size            04 (4)
│ │ │ │ -4F527   UID                 00000000 (0)
│ │ │ │ -4F52B   GID Size            04 (4)
│ │ │ │ -4F52C   GID                 00000000 (0)
│ │ │ │ -4F530 PAYLOAD
│ │ │ │ -
│ │ │ │ -4F999 LOCAL HEADER #46      04034B50 (67324752)
│ │ │ │ -4F99D Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -4F99E Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -4F99F General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -4F9A1 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -4F9A3 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4F9A7 CRC                   51FBB037 (1375449143)
│ │ │ │ -4F9AB Compressed Size       000016F1 (5873)
│ │ │ │ -4F9AF Uncompressed Size     00007A6E (31342)
│ │ │ │ -4F9B3 Filename Length       001F (31)
│ │ │ │ -4F9B5 Extra Length          001C (28)
│ │ │ │ -4F9B7 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x4F9B7: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -4F9D6 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -4F9D8   Length              0009 (9)
│ │ │ │ -4F9DA   Flags               03 (3) 'Modification Access'
│ │ │ │ -4F9DB   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4F9DF   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -4F9E3 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -4F9E5   Length              000B (11)
│ │ │ │ -4F9E7   Version             01 (1)
│ │ │ │ -4F9E8   UID Size            04 (4)
│ │ │ │ -4F9E9   UID                 00000000 (0)
│ │ │ │ -4F9ED   GID Size            04 (4)
│ │ │ │ -4F9EE   GID                 00000000 (0)
│ │ │ │ -4F9F2 PAYLOAD
│ │ │ │ -
│ │ │ │ -510E3 LOCAL HEADER #47      04034B50 (67324752)
│ │ │ │ -510E7 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -510E8 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -510E9 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -510EB Compression Method    0008 (8) 'Deflated'
│ │ │ │ -510ED Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -510F1 CRC                   2414B628 (605337128)
│ │ │ │ -510F5 Compressed Size       00004161 (16737)
│ │ │ │ -510F9 Uncompressed Size     0001D160 (119136)
│ │ │ │ -510FD Filename Length       0010 (16)
│ │ │ │ -510FF Extra Length          001C (28)
│ │ │ │ -51101 Filename              'XXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x51101: Filename 'XXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -51111 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -51113   Length              0009 (9)
│ │ │ │ -51115   Flags               03 (3) 'Modification Access'
│ │ │ │ -51116   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -5111A   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -5111E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -51120   Length              000B (11)
│ │ │ │ -51122   Version             01 (1)
│ │ │ │ -51123   UID Size            04 (4)
│ │ │ │ -51124   UID                 00000000 (0)
│ │ │ │ -51128   GID Size            04 (4)
│ │ │ │ -51129   GID                 00000000 (0)
│ │ │ │ -5112D PAYLOAD
│ │ │ │ -
│ │ │ │ -5528E LOCAL HEADER #48      04034B50 (67324752)
│ │ │ │ -55292 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -55293 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -55294 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -55296 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -55298 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -5529C CRC                   1C486A07 (474507783)
│ │ │ │ -552A0 Compressed Size       00000A98 (2712)
│ │ │ │ -552A4 Uncompressed Size     00002106 (8454)
│ │ │ │ -552A8 Filename Length       0014 (20)
│ │ │ │ -552AA Extra Length          001C (28)
│ │ │ │ -552AC Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x552AC: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -552C0 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -552C2   Length              0009 (9)
│ │ │ │ -552C4   Flags               03 (3) 'Modification Access'
│ │ │ │ -552C5   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -552C9   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -552CD Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -552CF   Length              000B (11)
│ │ │ │ -552D1   Version             01 (1)
│ │ │ │ -552D2   UID Size            04 (4)
│ │ │ │ -552D3   UID                 00000000 (0)
│ │ │ │ -552D7   GID Size            04 (4)
│ │ │ │ -552D8   GID                 00000000 (0)
│ │ │ │ -552DC PAYLOAD
│ │ │ │ -
│ │ │ │ -55D74 LOCAL HEADER #49      04034B50 (67324752)
│ │ │ │ -55D78 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -55D79 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -55D7A General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -55D7C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -55D7E Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -55D82 CRC                   7F22DF82 (2132991874)
│ │ │ │ -55D86 Compressed Size       0000AD78 (44408)
│ │ │ │ -55D8A Uncompressed Size     0003EB1B (256795)
│ │ │ │ -55D8E Filename Length       0017 (23)
│ │ │ │ -55D90 Extra Length          001C (28)
│ │ │ │ -55D92 Filename              'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x55D92: Filename 'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -55DA9 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -55DAB   Length              0009 (9)
│ │ │ │ -55DAD   Flags               03 (3) 'Modification Access'
│ │ │ │ -55DAE   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -55DB2   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -55DB6 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -55DB8   Length              000B (11)
│ │ │ │ -55DBA   Version             01 (1)
│ │ │ │ -55DBB   UID Size            04 (4)
│ │ │ │ -55DBC   UID                 00000000 (0)
│ │ │ │ -55DC0   GID Size            04 (4)
│ │ │ │ -55DC1   GID                 00000000 (0)
│ │ │ │ -55DC5 PAYLOAD
│ │ │ │ -
│ │ │ │ -60B3D LOCAL HEADER #50      04034B50 (67324752)
│ │ │ │ -60B41 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -60B42 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -60B43 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -60B45 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -60B47 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -60B4B CRC                   A0A15D62 (2694929762)
│ │ │ │ -60B4F Compressed Size       00000464 (1124)
│ │ │ │ -60B53 Uncompressed Size     00000DF4 (3572)
│ │ │ │ -60B57 Filename Length       0013 (19)
│ │ │ │ -60B59 Extra Length          001C (28)
│ │ │ │ -60B5B Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x60B5B: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -60B6E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -60B70   Length              0009 (9)
│ │ │ │ -60B72   Flags               03 (3) 'Modification Access'
│ │ │ │ -60B73   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -60B77   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -60B7B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -60B7D   Length              000B (11)
│ │ │ │ -60B7F   Version             01 (1)
│ │ │ │ -60B80   UID Size            04 (4)
│ │ │ │ -60B81   UID                 00000000 (0)
│ │ │ │ -60B85   GID Size            04 (4)
│ │ │ │ -60B86   GID                 00000000 (0)
│ │ │ │ -60B8A PAYLOAD
│ │ │ │ -
│ │ │ │ -60FEE LOCAL HEADER #51      04034B50 (67324752)
│ │ │ │ -60FF2 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -60FF3 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -60FF4 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -60FF6 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -60FF8 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -60FFC CRC                   D825044E (3626304590)
│ │ │ │ -61000 Compressed Size       000014D6 (5334)
│ │ │ │ -61004 Uncompressed Size     00006893 (26771)
│ │ │ │ -61008 Filename Length       0012 (18)
│ │ │ │ -6100A Extra Length          001C (28)
│ │ │ │ -6100C Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6100C: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6101E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -61020   Length              0009 (9)
│ │ │ │ -61022   Flags               03 (3) 'Modification Access'
│ │ │ │ -61023   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -61027   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6102B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6102D   Length              000B (11)
│ │ │ │ -6102F   Version             01 (1)
│ │ │ │ -61030   UID Size            04 (4)
│ │ │ │ -61031   UID                 00000000 (0)
│ │ │ │ -61035   GID Size            04 (4)
│ │ │ │ -61036   GID                 00000000 (0)
│ │ │ │ -6103A PAYLOAD
│ │ │ │ -
│ │ │ │ -62510 LOCAL HEADER #52      04034B50 (67324752)
│ │ │ │ -62514 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -62515 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -62516 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -62518 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6251A Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6251E CRC                   C193E548 (3247695176)
│ │ │ │ -62522 Compressed Size       000011F0 (4592)
│ │ │ │ -62526 Uncompressed Size     0000410D (16653)
│ │ │ │ -6252A Filename Length       0012 (18)
│ │ │ │ -6252C Extra Length          001C (28)
│ │ │ │ -6252E Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6252E: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -62540 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -62542   Length              0009 (9)
│ │ │ │ -62544   Flags               03 (3) 'Modification Access'
│ │ │ │ -62545   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -62549   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6254D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6254F   Length              000B (11)
│ │ │ │ -62551   Version             01 (1)
│ │ │ │ -62552   UID Size            04 (4)
│ │ │ │ -62553   UID                 00000000 (0)
│ │ │ │ -62557   GID Size            04 (4)
│ │ │ │ -62558   GID                 00000000 (0)
│ │ │ │ -6255C PAYLOAD
│ │ │ │ -
│ │ │ │ -6374C LOCAL HEADER #53      04034B50 (67324752)
│ │ │ │ -63750 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -63751 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -63752 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -63754 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -63756 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6375A CRC                   10C49B8F (281320335)
│ │ │ │ -6375E Compressed Size       000009D9 (2521)
│ │ │ │ -63762 Uncompressed Size     0000352A (13610)
│ │ │ │ -63766 Filename Length       0019 (25)
│ │ │ │ -63768 Extra Length          001C (28)
│ │ │ │ -6376A Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6376A: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -63783 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -63785   Length              0009 (9)
│ │ │ │ -63787   Flags               03 (3) 'Modification Access'
│ │ │ │ -63788   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6378C   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -63790 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -63792   Length              000B (11)
│ │ │ │ -63794   Version             01 (1)
│ │ │ │ -63795   UID Size            04 (4)
│ │ │ │ -63796   UID                 00000000 (0)
│ │ │ │ -6379A   GID Size            04 (4)
│ │ │ │ -6379B   GID                 00000000 (0)
│ │ │ │ -6379F PAYLOAD
│ │ │ │ -
│ │ │ │ -64178 LOCAL HEADER #54      04034B50 (67324752)
│ │ │ │ -6417C Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6417D Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6417E General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -64180 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -64182 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -64186 CRC                   F2CB28F8 (4073400568)
│ │ │ │ -6418A Compressed Size       00002023 (8227)
│ │ │ │ -6418E Uncompressed Size     00010945 (67909)
│ │ │ │ -64192 Filename Length       0019 (25)
│ │ │ │ -64194 Extra Length          001C (28)
│ │ │ │ -64196 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x64196: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -641AF Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -641B1   Length              0009 (9)
│ │ │ │ -641B3   Flags               03 (3) 'Modification Access'
│ │ │ │ -641B4   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -641B8   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -641BC Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -641BE   Length              000B (11)
│ │ │ │ -641C0   Version             01 (1)
│ │ │ │ -641C1   UID Size            04 (4)
│ │ │ │ -641C2   UID                 00000000 (0)
│ │ │ │ -641C6   GID Size            04 (4)
│ │ │ │ -641C7   GID                 00000000 (0)
│ │ │ │ -641CB PAYLOAD
│ │ │ │ -
│ │ │ │ -661EE LOCAL HEADER #55      04034B50 (67324752)
│ │ │ │ -661F2 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -661F3 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -661F4 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -661F6 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -661F8 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -661FC CRC                   D0372DB1 (3493277105)
│ │ │ │ -66200 Compressed Size       0000177F (6015)
│ │ │ │ -66204 Uncompressed Size     0000472D (18221)
│ │ │ │ -66208 Filename Length       0014 (20)
│ │ │ │ -6620A Extra Length          001C (28)
│ │ │ │ -6620C Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6620C: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -66220 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -66222   Length              0009 (9)
│ │ │ │ -66224   Flags               03 (3) 'Modification Access'
│ │ │ │ -66225   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -66229   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6622D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6622F   Length              000B (11)
│ │ │ │ -66231   Version             01 (1)
│ │ │ │ -66232   UID Size            04 (4)
│ │ │ │ -66233   UID                 00000000 (0)
│ │ │ │ -66237   GID Size            04 (4)
│ │ │ │ -66238   GID                 00000000 (0)
│ │ │ │ -6623C PAYLOAD
│ │ │ │ -
│ │ │ │ -679BB LOCAL HEADER #56      04034B50 (67324752)
│ │ │ │ -679BF Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -679C0 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -679C1 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -679C3 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -679C5 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -679C9 CRC                   FAE30038 (4209180728)
│ │ │ │ -679CD Compressed Size       0000040B (1035)
│ │ │ │ -679D1 Uncompressed Size     00000826 (2086)
│ │ │ │ -679D5 Filename Length       001C (28)
│ │ │ │ -679D7 Extra Length          001C (28)
│ │ │ │ -679D9 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x679D9: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -679F5 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -679F7   Length              0009 (9)
│ │ │ │ -679F9   Flags               03 (3) 'Modification Access'
│ │ │ │ -679FA   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -679FE   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -67A02 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -67A04   Length              000B (11)
│ │ │ │ -67A06   Version             01 (1)
│ │ │ │ -67A07   UID Size            04 (4)
│ │ │ │ -67A08   UID                 00000000 (0)
│ │ │ │ -67A0C   GID Size            04 (4)
│ │ │ │ -67A0D   GID                 00000000 (0)
│ │ │ │ -67A11 PAYLOAD
│ │ │ │ -
│ │ │ │ -67E1C LOCAL HEADER #57      04034B50 (67324752)
│ │ │ │ -67E20 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -67E21 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -67E22 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -67E24 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -67E26 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -67E2A CRC                   60701273 (1617957491)
│ │ │ │ -67E2E Compressed Size       00002499 (9369)
│ │ │ │ -67E32 Uncompressed Size     0000B5FA (46586)
│ │ │ │ -67E36 Filename Length       001F (31)
│ │ │ │ -67E38 Extra Length          001C (28)
│ │ │ │ -67E3A Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x67E3A: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -67E59 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -67E5B   Length              0009 (9)
│ │ │ │ -67E5D   Flags               03 (3) 'Modification Access'
│ │ │ │ -67E5E   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -67E62   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -67E66 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -67E68   Length              000B (11)
│ │ │ │ -67E6A   Version             01 (1)
│ │ │ │ -67E6B   UID Size            04 (4)
│ │ │ │ -67E6C   UID                 00000000 (0)
│ │ │ │ -67E70   GID Size            04 (4)
│ │ │ │ -67E71   GID                 00000000 (0)
│ │ │ │ -67E75 PAYLOAD
│ │ │ │ -
│ │ │ │ -6A30E LOCAL HEADER #58      04034B50 (67324752)
│ │ │ │ -6A312 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6A313 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6A314 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6A316 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6A318 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6A31C CRC                   92A69325 (2460390181)
│ │ │ │ -6A320 Compressed Size       00000E81 (3713)
│ │ │ │ -6A324 Uncompressed Size     000052DA (21210)
│ │ │ │ -6A328 Filename Length       001F (31)
│ │ │ │ -6A32A Extra Length          001C (28)
│ │ │ │ -6A32C Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6A32C: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6A34B Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6A34D   Length              0009 (9)
│ │ │ │ -6A34F   Flags               03 (3) 'Modification Access'
│ │ │ │ -6A350   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6A354   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6A358 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6A35A   Length              000B (11)
│ │ │ │ -6A35C   Version             01 (1)
│ │ │ │ -6A35D   UID Size            04 (4)
│ │ │ │ -6A35E   UID                 00000000 (0)
│ │ │ │ -6A362   GID Size            04 (4)
│ │ │ │ -6A363   GID                 00000000 (0)
│ │ │ │ -6A367 PAYLOAD
│ │ │ │ -
│ │ │ │ -6B1E8 LOCAL HEADER #59      04034B50 (67324752)
│ │ │ │ -6B1EC Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6B1ED Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6B1EE General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6B1F0 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6B1F2 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6B1F6 CRC                   A77B8D6E (2809892206)
│ │ │ │ -6B1FA Compressed Size       00000A46 (2630)
│ │ │ │ -6B1FE Uncompressed Size     0000247B (9339)
│ │ │ │ -6B202 Filename Length       0013 (19)
│ │ │ │ -6B204 Extra Length          001C (28)
│ │ │ │ -6B206 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6B206: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6B219 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6B21B   Length              0009 (9)
│ │ │ │ -6B21D   Flags               03 (3) 'Modification Access'
│ │ │ │ -6B21E   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6B222   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6B226 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6B228   Length              000B (11)
│ │ │ │ -6B22A   Version             01 (1)
│ │ │ │ -6B22B   UID Size            04 (4)
│ │ │ │ -6B22C   UID                 00000000 (0)
│ │ │ │ -6B230   GID Size            04 (4)
│ │ │ │ -6B231   GID                 00000000 (0)
│ │ │ │ -6B235 PAYLOAD
│ │ │ │ -
│ │ │ │ -6BC7B LOCAL HEADER #60      04034B50 (67324752)
│ │ │ │ -6BC7F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6BC80 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6BC81 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6BC83 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6BC85 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6BC89 CRC                   30B97F5F (817463135)
│ │ │ │ -6BC8D Compressed Size       00002486 (9350)
│ │ │ │ -6BC91 Uncompressed Size     0000B84D (47181)
│ │ │ │ -6BC95 Filename Length       0019 (25)
│ │ │ │ -6BC97 Extra Length          001C (28)
│ │ │ │ -6BC99 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6BC99: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6BCB2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6BCB4   Length              0009 (9)
│ │ │ │ -6BCB6   Flags               03 (3) 'Modification Access'
│ │ │ │ -6BCB7   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6BCBB   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6BCBF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6BCC1   Length              000B (11)
│ │ │ │ -6BCC3   Version             01 (1)
│ │ │ │ -6BCC4   UID Size            04 (4)
│ │ │ │ -6BCC5   UID                 00000000 (0)
│ │ │ │ -6BCC9   GID Size            04 (4)
│ │ │ │ -6BCCA   GID                 00000000 (0)
│ │ │ │ -6BCCE PAYLOAD
│ │ │ │ -
│ │ │ │ -6E154 LOCAL HEADER #61      04034B50 (67324752)
│ │ │ │ -6E158 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6E159 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6E15A General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6E15C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6E15E Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6E162 CRC                   DC97F08B (3700945035)
│ │ │ │ -6E166 Compressed Size       00000EFB (3835)
│ │ │ │ -6E16A Uncompressed Size     00003A2D (14893)
│ │ │ │ -6E16E Filename Length       0024 (36)
│ │ │ │ -6E170 Extra Length          001C (28)
│ │ │ │ -6E172 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6E172: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6E196 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6E198   Length              0009 (9)
│ │ │ │ -6E19A   Flags               03 (3) 'Modification Access'
│ │ │ │ -6E19B   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6E19F   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6E1A3 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6E1A5   Length              000B (11)
│ │ │ │ -6E1A7   Version             01 (1)
│ │ │ │ -6E1A8   UID Size            04 (4)
│ │ │ │ -6E1A9   UID                 00000000 (0)
│ │ │ │ -6E1AD   GID Size            04 (4)
│ │ │ │ -6E1AE   GID                 00000000 (0)
│ │ │ │ -6E1B2 PAYLOAD
│ │ │ │ -
│ │ │ │ -6F0AD LOCAL HEADER #62      04034B50 (67324752)
│ │ │ │ -6F0B1 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -6F0B2 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -6F0B3 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -6F0B5 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -6F0B7 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6F0BB CRC                   396B41A9 (963330473)
│ │ │ │ -6F0BF Compressed Size       00001ABA (6842)
│ │ │ │ -6F0C3 Uncompressed Size     00005F39 (24377)
│ │ │ │ -6F0C7 Filename Length       0017 (23)
│ │ │ │ -6F0C9 Extra Length          001C (28)
│ │ │ │ -6F0CB Filename              'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x6F0CB: Filename 'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -6F0E2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -6F0E4   Length              0009 (9)
│ │ │ │ -6F0E6   Flags               03 (3) 'Modification Access'
│ │ │ │ -6F0E7   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6F0EB   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -6F0EF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -6F0F1   Length              000B (11)
│ │ │ │ -6F0F3   Version             01 (1)
│ │ │ │ -6F0F4   UID Size            04 (4)
│ │ │ │ -6F0F5   UID                 00000000 (0)
│ │ │ │ -6F0F9   GID Size            04 (4)
│ │ │ │ -6F0FA   GID                 00000000 (0)
│ │ │ │ -6F0FE PAYLOAD
│ │ │ │ -
│ │ │ │ -70BB8 LOCAL HEADER #63      04034B50 (67324752)
│ │ │ │ -70BBC Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -70BBD Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -70BBE General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -70BC0 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -70BC2 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -70BC6 CRC                   3DD8544C (1037587532)
│ │ │ │ -70BCA Compressed Size       00000ED1 (3793)
│ │ │ │ -70BCE Uncompressed Size     000038DE (14558)
│ │ │ │ -70BD2 Filename Length       0023 (35)
│ │ │ │ -70BD4 Extra Length          001C (28)
│ │ │ │ -70BD6 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x70BD6: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -70BF9 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -70BFB   Length              0009 (9)
│ │ │ │ -70BFD   Flags               03 (3) 'Modification Access'
│ │ │ │ -70BFE   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -70C02   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -70C06 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -70C08   Length              000B (11)
│ │ │ │ -70C0A   Version             01 (1)
│ │ │ │ -70C0B   UID Size            04 (4)
│ │ │ │ -70C0C   UID                 00000000 (0)
│ │ │ │ -70C10   GID Size            04 (4)
│ │ │ │ -70C11   GID                 00000000 (0)
│ │ │ │ -70C15 PAYLOAD
│ │ │ │ -
│ │ │ │ -71AE6 LOCAL HEADER #64      04034B50 (67324752)
│ │ │ │ -71AEA Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -71AEB Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -71AEC General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -71AEE Compression Method    0008 (8) 'Deflated'
│ │ │ │ -71AF0 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -71AF4 CRC                   2DB7929F (767005343)
│ │ │ │ -71AF8 Compressed Size       00000113 (275)
│ │ │ │ -71AFC Uncompressed Size     000001F3 (499)
│ │ │ │ -71B00 Filename Length       001B (27)
│ │ │ │ -71B02 Extra Length          001C (28)
│ │ │ │ -71B04 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x71B04: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -71B1F Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -71B21   Length              0009 (9)
│ │ │ │ -71B23   Flags               03 (3) 'Modification Access'
│ │ │ │ -71B24   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -71B28   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -71B2C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -71B2E   Length              000B (11)
│ │ │ │ -71B30   Version             01 (1)
│ │ │ │ -71B31   UID Size            04 (4)
│ │ │ │ -71B32   UID                 00000000 (0)
│ │ │ │ -71B36   GID Size            04 (4)
│ │ │ │ -71B37   GID                 00000000 (0)
│ │ │ │ -71B3B PAYLOAD
│ │ │ │ -
│ │ │ │ -71C4E LOCAL HEADER #65      04034B50 (67324752)
│ │ │ │ -71C52 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -71C53 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -71C54 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -71C56 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -71C58 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -71C5C CRC                   B802BFBB (3087187899)
│ │ │ │ -71C60 Compressed Size       0000188E (6286)
│ │ │ │ -71C64 Uncompressed Size     00008FAD (36781)
│ │ │ │ -71C68 Filename Length       001D (29)
│ │ │ │ -71C6A Extra Length          001C (28)
│ │ │ │ -71C6C Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x71C6C: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -71C89 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -71C8B   Length              0009 (9)
│ │ │ │ -71C8D   Flags               03 (3) 'Modification Access'
│ │ │ │ -71C8E   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -71C92   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -71C96 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -71C98   Length              000B (11)
│ │ │ │ -71C9A   Version             01 (1)
│ │ │ │ -71C9B   UID Size            04 (4)
│ │ │ │ -71C9C   UID                 00000000 (0)
│ │ │ │ -71CA0   GID Size            04 (4)
│ │ │ │ -71CA1   GID                 00000000 (0)
│ │ │ │ -71CA5 PAYLOAD
│ │ │ │ -
│ │ │ │ -73533 LOCAL HEADER #66      04034B50 (67324752)
│ │ │ │ -73537 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -73538 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -73539 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -7353B Compression Method    0008 (8) 'Deflated'
│ │ │ │ -7353D Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -73541 CRC                   516C0F5D (1366036317)
│ │ │ │ -73545 Compressed Size       0000164A (5706)
│ │ │ │ -73549 Uncompressed Size     00003A9C (15004)
│ │ │ │ -7354D Filename Length       0015 (21)
│ │ │ │ -7354F Extra Length          001C (28)
│ │ │ │ -73551 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x73551: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -73566 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -73568   Length              0009 (9)
│ │ │ │ -7356A   Flags               03 (3) 'Modification Access'
│ │ │ │ -7356B   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -7356F   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -73573 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -73575   Length              000B (11)
│ │ │ │ -73577   Version             01 (1)
│ │ │ │ -73578   UID Size            04 (4)
│ │ │ │ -73579   UID                 00000000 (0)
│ │ │ │ -7357D   GID Size            04 (4)
│ │ │ │ -7357E   GID                 00000000 (0)
│ │ │ │ -73582 PAYLOAD
│ │ │ │ -
│ │ │ │ -74BCC LOCAL HEADER #67      04034B50 (67324752)
│ │ │ │ -74BD0 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -74BD1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -74BD2 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -74BD4 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -74BD6 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -74BDA CRC                   3708308C (923283596)
│ │ │ │ -74BDE Compressed Size       00003B4E (15182)
│ │ │ │ -74BE2 Uncompressed Size     00011CC3 (72899)
│ │ │ │ -74BE6 Filename Length       0016 (22)
│ │ │ │ -74BE8 Extra Length          001C (28)
│ │ │ │ -74BEA Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x74BEA: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -74C00 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -74C02   Length              0009 (9)
│ │ │ │ -74C04   Flags               03 (3) 'Modification Access'
│ │ │ │ -74C05   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -74C09   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -74C0D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -74C0F   Length              000B (11)
│ │ │ │ -74C11   Version             01 (1)
│ │ │ │ -74C12   UID Size            04 (4)
│ │ │ │ -74C13   UID                 00000000 (0)
│ │ │ │ -74C17   GID Size            04 (4)
│ │ │ │ -74C18   GID                 00000000 (0)
│ │ │ │ -74C1C PAYLOAD
│ │ │ │ -
│ │ │ │ -7876A LOCAL HEADER #68      04034B50 (67324752)
│ │ │ │ -7876E Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -7876F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -78770 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -78772 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -78774 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -78778 CRC                   7096BE5F (1888927327)
│ │ │ │ -7877C Compressed Size       00003EC5 (16069)
│ │ │ │ -78780 Uncompressed Size     0001C79C (116636)
│ │ │ │ -78784 Filename Length       0019 (25)
│ │ │ │ -78786 Extra Length          001C (28)
│ │ │ │ -78788 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x78788: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -787A1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -787A3   Length              0009 (9)
│ │ │ │ -787A5   Flags               03 (3) 'Modification Access'
│ │ │ │ -787A6   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -787AA   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -787AE Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -787B0   Length              000B (11)
│ │ │ │ -787B2   Version             01 (1)
│ │ │ │ -787B3   UID Size            04 (4)
│ │ │ │ -787B4   UID                 00000000 (0)
│ │ │ │ -787B8   GID Size            04 (4)
│ │ │ │ -787B9   GID                 00000000 (0)
│ │ │ │ -787BD PAYLOAD
│ │ │ │ -
│ │ │ │ -7C682 LOCAL HEADER #69      04034B50 (67324752)
│ │ │ │ -7C686 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -7C687 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -7C688 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -7C68A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -7C68C Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -7C690 CRC                   9FB04586 (2679129478)
│ │ │ │ -7C694 Compressed Size       00000835 (2101)
│ │ │ │ -7C698 Uncompressed Size     00003384 (13188)
│ │ │ │ -7C69C Filename Length       0011 (17)
│ │ │ │ -7C69E Extra Length          001C (28)
│ │ │ │ -7C6A0 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x7C6A0: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -7C6B1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -7C6B3   Length              0009 (9)
│ │ │ │ -7C6B5   Flags               03 (3) 'Modification Access'
│ │ │ │ -7C6B6   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -7C6BA   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -7C6BE Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -7C6C0   Length              000B (11)
│ │ │ │ -7C6C2   Version             01 (1)
│ │ │ │ -7C6C3   UID Size            04 (4)
│ │ │ │ -7C6C4   UID                 00000000 (0)
│ │ │ │ -7C6C8   GID Size            04 (4)
│ │ │ │ -7C6C9   GID                 00000000 (0)
│ │ │ │ -7C6CD PAYLOAD
│ │ │ │ -
│ │ │ │ -7CF02 LOCAL HEADER #70      04034B50 (67324752)
│ │ │ │ -7CF06 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -7CF07 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -7CF08 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -7CF0A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -7CF0C Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -7CF10 CRC                   48157666 (1209366118)
│ │ │ │ -7CF14 Compressed Size       000051AB (20907)
│ │ │ │ -7CF18 Uncompressed Size     0001FBE0 (130016)
│ │ │ │ -7CF1C Filename Length       0015 (21)
│ │ │ │ -7CF1E Extra Length          001C (28)
│ │ │ │ -7CF20 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x7CF20: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -7CF35 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -7CF37   Length              0009 (9)
│ │ │ │ -7CF39   Flags               03 (3) 'Modification Access'
│ │ │ │ -7CF3A   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -7CF3E   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -7CF42 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -7CF44   Length              000B (11)
│ │ │ │ -7CF46   Version             01 (1)
│ │ │ │ -7CF47   UID Size            04 (4)
│ │ │ │ -7CF48   UID                 00000000 (0)
│ │ │ │ -7CF4C   GID Size            04 (4)
│ │ │ │ -7CF4D   GID                 00000000 (0)
│ │ │ │ -7CF51 PAYLOAD
│ │ │ │ -
│ │ │ │ -820FC LOCAL HEADER #71      04034B50 (67324752)
│ │ │ │ -82100 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -82101 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -82102 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -82104 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -82106 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8210A CRC                   11C15F57 (297885527)
│ │ │ │ -8210E Compressed Size       00001B09 (6921)
│ │ │ │ -82112 Uncompressed Size     000081D0 (33232)
│ │ │ │ -82116 Filename Length       0019 (25)
│ │ │ │ -82118 Extra Length          001C (28)
│ │ │ │ -8211A Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8211A: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -82133 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -82135   Length              0009 (9)
│ │ │ │ -82137   Flags               03 (3) 'Modification Access'
│ │ │ │ -82138   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8213C   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -82140 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -82142   Length              000B (11)
│ │ │ │ -82144   Version             01 (1)
│ │ │ │ -82145   UID Size            04 (4)
│ │ │ │ -82146   UID                 00000000 (0)
│ │ │ │ -8214A   GID Size            04 (4)
│ │ │ │ -8214B   GID                 00000000 (0)
│ │ │ │ -8214F PAYLOAD
│ │ │ │ -
│ │ │ │ -83C58 LOCAL HEADER #72      04034B50 (67324752)
│ │ │ │ -83C5C Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -83C5D Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -83C5E General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -83C60 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -83C62 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -83C66 CRC                   ECB3AEBD (3971198653)
│ │ │ │ -83C6A Compressed Size       00000D99 (3481)
│ │ │ │ -83C6E Uncompressed Size     00002EA0 (11936)
│ │ │ │ -83C72 Filename Length       0018 (24)
│ │ │ │ -83C74 Extra Length          001C (28)
│ │ │ │ -83C76 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x83C76: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -83C8E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -83C90   Length              0009 (9)
│ │ │ │ -83C92   Flags               03 (3) 'Modification Access'
│ │ │ │ -83C93   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -83C97   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -83C9B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -83C9D   Length              000B (11)
│ │ │ │ -83C9F   Version             01 (1)
│ │ │ │ -83CA0   UID Size            04 (4)
│ │ │ │ -83CA1   UID                 00000000 (0)
│ │ │ │ -83CA5   GID Size            04 (4)
│ │ │ │ -83CA6   GID                 00000000 (0)
│ │ │ │ -83CAA PAYLOAD
│ │ │ │ -
│ │ │ │ -84A43 LOCAL HEADER #73      04034B50 (67324752)
│ │ │ │ -84A47 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -84A48 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -84A49 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -84A4B Compression Method    0008 (8) 'Deflated'
│ │ │ │ -84A4D Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -84A51 CRC                   037E3A9E (58604190)
│ │ │ │ -84A55 Compressed Size       000001E1 (481)
│ │ │ │ -84A59 Uncompressed Size     00000324 (804)
│ │ │ │ -84A5D Filename Length       0011 (17)
│ │ │ │ -84A5F Extra Length          001C (28)
│ │ │ │ -84A61 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x84A61: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -84A72 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -84A74   Length              0009 (9)
│ │ │ │ -84A76   Flags               03 (3) 'Modification Access'
│ │ │ │ -84A77   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -84A7B   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -84A7F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -84A81   Length              000B (11)
│ │ │ │ -84A83   Version             01 (1)
│ │ │ │ -84A84   UID Size            04 (4)
│ │ │ │ -84A85   UID                 00000000 (0)
│ │ │ │ -84A89   GID Size            04 (4)
│ │ │ │ -84A8A   GID                 00000000 (0)
│ │ │ │ -84A8E PAYLOAD
│ │ │ │ -
│ │ │ │ -84C6F LOCAL HEADER #74      04034B50 (67324752)
│ │ │ │ -84C73 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -84C74 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -84C75 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -84C77 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -84C79 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -84C7D CRC                   55187787 (1427666823)
│ │ │ │ -84C81 Compressed Size       000006C3 (1731)
│ │ │ │ -84C85 Uncompressed Size     0000143A (5178)
│ │ │ │ -84C89 Filename Length       0019 (25)
│ │ │ │ -84C8B Extra Length          001C (28)
│ │ │ │ -84C8D Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x84C8D: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -84CA6 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -84CA8   Length              0009 (9)
│ │ │ │ -84CAA   Flags               03 (3) 'Modification Access'
│ │ │ │ -84CAB   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -84CAF   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -84CB3 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -84CB5   Length              000B (11)
│ │ │ │ -84CB7   Version             01 (1)
│ │ │ │ -84CB8   UID Size            04 (4)
│ │ │ │ -84CB9   UID                 00000000 (0)
│ │ │ │ -84CBD   GID Size            04 (4)
│ │ │ │ -84CBE   GID                 00000000 (0)
│ │ │ │ -84CC2 PAYLOAD
│ │ │ │ -
│ │ │ │ -85385 LOCAL HEADER #75      04034B50 (67324752)
│ │ │ │ -85389 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8538A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8538B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8538D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8538F Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -85393 CRC                   B80689A0 (3087436192)
│ │ │ │ -85397 Compressed Size       00001EAE (7854)
│ │ │ │ -8539B Uncompressed Size     0000CA81 (51841)
│ │ │ │ -8539F Filename Length       0018 (24)
│ │ │ │ -853A1 Extra Length          001C (28)
│ │ │ │ -853A3 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x853A3: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -853BB Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -853BD   Length              0009 (9)
│ │ │ │ -853BF   Flags               03 (3) 'Modification Access'
│ │ │ │ -853C0   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -853C4   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -853C8 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -853CA   Length              000B (11)
│ │ │ │ -853CC   Version             01 (1)
│ │ │ │ -853CD   UID Size            04 (4)
│ │ │ │ -853CE   UID                 00000000 (0)
│ │ │ │ -853D2   GID Size            04 (4)
│ │ │ │ -853D3   GID                 00000000 (0)
│ │ │ │ -853D7 PAYLOAD
│ │ │ │ -
│ │ │ │ -87285 LOCAL HEADER #76      04034B50 (67324752)
│ │ │ │ -87289 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8728A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8728B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8728D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8728F Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -87293 CRC                   70CE7879 (1892579449)
│ │ │ │ -87297 Compressed Size       00001BEA (7146)
│ │ │ │ -8729B Uncompressed Size     0000C5EA (50666)
│ │ │ │ -8729F Filename Length       0012 (18)
│ │ │ │ -872A1 Extra Length          001C (28)
│ │ │ │ -872A3 Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x872A3: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -872B5 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -872B7   Length              0009 (9)
│ │ │ │ -872B9   Flags               03 (3) 'Modification Access'
│ │ │ │ -872BA   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -872BE   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -872C2 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -872C4   Length              000B (11)
│ │ │ │ -872C6   Version             01 (1)
│ │ │ │ -872C7   UID Size            04 (4)
│ │ │ │ -872C8   UID                 00000000 (0)
│ │ │ │ -872CC   GID Size            04 (4)
│ │ │ │ -872CD   GID                 00000000 (0)
│ │ │ │ -872D1 PAYLOAD
│ │ │ │ -
│ │ │ │ -88EBB LOCAL HEADER #77      04034B50 (67324752)
│ │ │ │ -88EBF Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -88EC0 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -88EC1 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -88EC3 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -88EC5 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -88EC9 CRC                   A289EFE2 (2726948834)
│ │ │ │ -88ECD Compressed Size       00001E0F (7695)
│ │ │ │ -88ED1 Uncompressed Size     00008804 (34820)
│ │ │ │ -88ED5 Filename Length       0016 (22)
│ │ │ │ -88ED7 Extra Length          001C (28)
│ │ │ │ -88ED9 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x88ED9: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -88EEF Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -88EF1   Length              0009 (9)
│ │ │ │ -88EF3   Flags               03 (3) 'Modification Access'
│ │ │ │ -88EF4   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -88EF8   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -88EFC Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -88EFE   Length              000B (11)
│ │ │ │ -88F00   Version             01 (1)
│ │ │ │ -88F01   UID Size            04 (4)
│ │ │ │ -88F02   UID                 00000000 (0)
│ │ │ │ -88F06   GID Size            04 (4)
│ │ │ │ -88F07   GID                 00000000 (0)
│ │ │ │ -88F0B PAYLOAD
│ │ │ │ -
│ │ │ │ -8AD1A LOCAL HEADER #78      04034B50 (67324752)
│ │ │ │ -8AD1E Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8AD1F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8AD20 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8AD22 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8AD24 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8AD28 CRC                   A54D678B (2773313419)
│ │ │ │ -8AD2C Compressed Size       000029A3 (10659)
│ │ │ │ -8AD30 Uncompressed Size     0000D050 (53328)
│ │ │ │ -8AD34 Filename Length       001A (26)
│ │ │ │ -8AD36 Extra Length          001C (28)
│ │ │ │ -8AD38 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8AD38: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8AD52 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -8AD54   Length              0009 (9)
│ │ │ │ -8AD56   Flags               03 (3) 'Modification Access'
│ │ │ │ -8AD57   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8AD5B   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8AD5F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8AD61   Length              000B (11)
│ │ │ │ -8AD63   Version             01 (1)
│ │ │ │ -8AD64   UID Size            04 (4)
│ │ │ │ -8AD65   UID                 00000000 (0)
│ │ │ │ -8AD69   GID Size            04 (4)
│ │ │ │ -8AD6A   GID                 00000000 (0)
│ │ │ │ -8AD6E PAYLOAD
│ │ │ │ -
│ │ │ │ -8D711 LOCAL HEADER #79      04034B50 (67324752)
│ │ │ │ -8D715 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8D716 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8D717 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8D719 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8D71B Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8D71F CRC                   80E743AF (2162639791)
│ │ │ │ -8D723 Compressed Size       000009AE (2478)
│ │ │ │ -8D727 Uncompressed Size     00001DB7 (7607)
│ │ │ │ -8D72B Filename Length       0018 (24)
│ │ │ │ -8D72D Extra Length          001C (28)
│ │ │ │ -8D72F Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8D72F: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8D747 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -8D749   Length              0009 (9)
│ │ │ │ -8D74B   Flags               03 (3) 'Modification Access'
│ │ │ │ -8D74C   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8D750   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8D754 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8D756   Length              000B (11)
│ │ │ │ -8D758   Version             01 (1)
│ │ │ │ -8D759   UID Size            04 (4)
│ │ │ │ -8D75A   UID                 00000000 (0)
│ │ │ │ -8D75E   GID Size            04 (4)
│ │ │ │ -8D75F   GID                 00000000 (0)
│ │ │ │ -8D763 PAYLOAD
│ │ │ │ -
│ │ │ │ -8E111 LOCAL HEADER #80      04034B50 (67324752)
│ │ │ │ -8E115 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8E116 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8E117 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8E119 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8E11B Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8E11F CRC                   F5E2129F (4125233823)
│ │ │ │ -8E123 Compressed Size       000016BC (5820)
│ │ │ │ -8E127 Uncompressed Size     000016CD (5837)
│ │ │ │ -8E12B Filename Length       0015 (21)
│ │ │ │ -8E12D Extra Length          001C (28)
│ │ │ │ -8E12F Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8E12F: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8E144 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -8E146   Length              0009 (9)
│ │ │ │ -8E148   Flags               03 (3) 'Modification Access'
│ │ │ │ -8E149   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8E14D   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8E151 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8E153   Length              000B (11)
│ │ │ │ -8E155   Version             01 (1)
│ │ │ │ -8E156   UID Size            04 (4)
│ │ │ │ -8E157   UID                 00000000 (0)
│ │ │ │ -8E15B   GID Size            04 (4)
│ │ │ │ -8E15C   GID                 00000000 (0)
│ │ │ │ -8E160 PAYLOAD
│ │ │ │ -
│ │ │ │ -8F81C LOCAL HEADER #81      04034B50 (67324752)
│ │ │ │ -8F820 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -8F821 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -8F822 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -8F824 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -8F826 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8F82A CRC                   F5E2129F (4125233823)
│ │ │ │ -8F82E Compressed Size       000016BC (5820)
│ │ │ │ -8F832 Uncompressed Size     000016CD (5837)
│ │ │ │ -8F836 Filename Length       001C (28)
│ │ │ │ -8F838 Extra Length          001C (28)
│ │ │ │ -8F83A Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x8F83A: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -8F856 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -8F858   Length              0009 (9)
│ │ │ │ -8F85A   Flags               03 (3) 'Modification Access'
│ │ │ │ -8F85B   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8F85F   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -8F863 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -8F865   Length              000B (11)
│ │ │ │ -8F867   Version             01 (1)
│ │ │ │ -8F868   UID Size            04 (4)
│ │ │ │ -8F869   UID                 00000000 (0)
│ │ │ │ -8F86D   GID Size            04 (4)
│ │ │ │ -8F86E   GID                 00000000 (0)
│ │ │ │ -8F872 PAYLOAD
│ │ │ │ -
│ │ │ │ -90F2E LOCAL HEADER #82      04034B50 (67324752)
│ │ │ │ -90F32 Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -90F33 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -90F34 General Purpose Flag  0000 (0)
│ │ │ │ -90F36 Compression Method    0000 (0) 'Stored'
│ │ │ │ -90F38 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -90F3C CRC                   FC95F24B (4237685323)
│ │ │ │ -90F40 Compressed Size       00001B84 (7044)
│ │ │ │ -90F44 Uncompressed Size     00001B84 (7044)
│ │ │ │ -90F48 Filename Length       0016 (22)
│ │ │ │ -90F4A Extra Length          001C (28)
│ │ │ │ -90F4C Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x90F4C: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -90F62 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -90F64   Length              0009 (9)
│ │ │ │ -90F66   Flags               03 (3) 'Modification Access'
│ │ │ │ -90F67   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -90F6B   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -90F6F Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -90F71   Length              000B (11)
│ │ │ │ -90F73   Version             01 (1)
│ │ │ │ -90F74   UID Size            04 (4)
│ │ │ │ -90F75   UID                 00000000 (0)
│ │ │ │ -90F79   GID Size            04 (4)
│ │ │ │ -90F7A   GID                 00000000 (0)
│ │ │ │ -90F7E PAYLOAD
│ │ │ │ -
│ │ │ │ -92B02 LOCAL HEADER #83      04034B50 (67324752)
│ │ │ │ -92B06 Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -92B07 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -92B08 General Purpose Flag  0000 (0)
│ │ │ │ -92B0A Compression Method    0000 (0) 'Stored'
│ │ │ │ -92B0C Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -92B10 CRC                   D0D71F86 (3503759238)
│ │ │ │ -92B14 Compressed Size       00000B7B (2939)
│ │ │ │ -92B18 Uncompressed Size     00000B7B (2939)
│ │ │ │ -92B1C Filename Length       0016 (22)
│ │ │ │ -92B1E Extra Length          001C (28)
│ │ │ │ -92B20 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x92B20: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -92B36 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -92B38   Length              0009 (9)
│ │ │ │ -92B3A   Flags               03 (3) 'Modification Access'
│ │ │ │ -92B3B   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -92B3F   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -92B43 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -92B45   Length              000B (11)
│ │ │ │ -92B47   Version             01 (1)
│ │ │ │ -92B48   UID Size            04 (4)
│ │ │ │ -92B49   UID                 00000000 (0)
│ │ │ │ -92B4D   GID Size            04 (4)
│ │ │ │ -92B4E   GID                 00000000 (0)
│ │ │ │ -92B52 PAYLOAD
│ │ │ │ -
│ │ │ │ -936CD LOCAL HEADER #84      04034B50 (67324752)
│ │ │ │ -936D1 Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -936D2 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -936D3 General Purpose Flag  0000 (0)
│ │ │ │ -936D5 Compression Method    0000 (0) 'Stored'
│ │ │ │ -936D7 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -936DB CRC                   FFF9C4D2 (4294558930)
│ │ │ │ -936DF Compressed Size       0000138F (5007)
│ │ │ │ -936E3 Uncompressed Size     0000138F (5007)
│ │ │ │ -936E7 Filename Length       0016 (22)
│ │ │ │ -936E9 Extra Length          001C (28)
│ │ │ │ -936EB Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x936EB: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -93701 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -93703   Length              0009 (9)
│ │ │ │ -93705   Flags               03 (3) 'Modification Access'
│ │ │ │ -93706   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9370A   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9370E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -93710   Length              000B (11)
│ │ │ │ -93712   Version             01 (1)
│ │ │ │ -93713   UID Size            04 (4)
│ │ │ │ -93714   UID                 00000000 (0)
│ │ │ │ -93718   GID Size            04 (4)
│ │ │ │ -93719   GID                 00000000 (0)
│ │ │ │ -9371D PAYLOAD
│ │ │ │ -
│ │ │ │ -94AAC LOCAL HEADER #85      04034B50 (67324752)
│ │ │ │ -94AB0 Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -94AB1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -94AB2 General Purpose Flag  0000 (0)
│ │ │ │ -94AB4 Compression Method    0000 (0) 'Stored'
│ │ │ │ -94AB6 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -94ABA CRC                   A1037E8E (2701360782)
│ │ │ │ -94ABE Compressed Size       0000145E (5214)
│ │ │ │ -94AC2 Uncompressed Size     0000145E (5214)
│ │ │ │ -94AC6 Filename Length       0016 (22)
│ │ │ │ -94AC8 Extra Length          001C (28)
│ │ │ │ -94ACA Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x94ACA: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -94AE0 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -94AE2   Length              0009 (9)
│ │ │ │ -94AE4   Flags               03 (3) 'Modification Access'
│ │ │ │ -94AE5   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -94AE9   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -94AED Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -94AEF   Length              000B (11)
│ │ │ │ -94AF1   Version             01 (1)
│ │ │ │ -94AF2   UID Size            04 (4)
│ │ │ │ -94AF3   UID                 00000000 (0)
│ │ │ │ -94AF7   GID Size            04 (4)
│ │ │ │ -94AF8   GID                 00000000 (0)
│ │ │ │ -94AFC PAYLOAD
│ │ │ │ -
│ │ │ │ -95F5A LOCAL HEADER #86      04034B50 (67324752)
│ │ │ │ -95F5E Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -95F5F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -95F60 General Purpose Flag  0000 (0)
│ │ │ │ -95F62 Compression Method    0000 (0) 'Stored'
│ │ │ │ -95F64 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -95F68 CRC                   5E9E64F1 (1587438833)
│ │ │ │ -95F6C Compressed Size       000008EC (2284)
│ │ │ │ -95F70 Uncompressed Size     000008EC (2284)
│ │ │ │ -95F74 Filename Length       0016 (22)
│ │ │ │ -95F76 Extra Length          001C (28)
│ │ │ │ -95F78 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x95F78: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -95F8E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -95F90   Length              0009 (9)
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│ │ │ │ -95F93   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -95F97   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -95F9B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -95F9D   Length              000B (11)
│ │ │ │ -95F9F   Version             01 (1)
│ │ │ │ -95FA0   UID Size            04 (4)
│ │ │ │ -95FA1   UID                 00000000 (0)
│ │ │ │ -95FA5   GID Size            04 (4)
│ │ │ │ -95FA6   GID                 00000000 (0)
│ │ │ │ -95FAA PAYLOAD
│ │ │ │ -
│ │ │ │ -96896 LOCAL HEADER #87      04034B50 (67324752)
│ │ │ │ -9689A Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -9689B Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -9689C General Purpose Flag  0000 (0)
│ │ │ │ -9689E Compression Method    0000 (0) 'Stored'
│ │ │ │ -968A0 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -968A4 CRC                   42E340AB (1122189483)
│ │ │ │ -968A8 Compressed Size       00001F2E (7982)
│ │ │ │ -968AC Uncompressed Size     00001F2E (7982)
│ │ │ │ -968B0 Filename Length       001E (30)
│ │ │ │ -968B2 Extra Length          001C (28)
│ │ │ │ -968B4 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x968B4: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -968D2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -968D4   Length              0009 (9)
│ │ │ │ -968D6   Flags               03 (3) 'Modification Access'
│ │ │ │ -968D7   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -968DB   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -968DF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -968E1   Length              000B (11)
│ │ │ │ -968E3   Version             01 (1)
│ │ │ │ -968E4   UID Size            04 (4)
│ │ │ │ -968E5   UID                 00000000 (0)
│ │ │ │ -968E9   GID Size            04 (4)
│ │ │ │ -968EA   GID                 00000000 (0)
│ │ │ │ -968EE PAYLOAD
│ │ │ │ -
│ │ │ │ -9881C LOCAL HEADER #88      04034B50 (67324752)
│ │ │ │ -98820 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -98821 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -98822 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -98824 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -98826 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9882A CRC                   A2C99D83 (2731122051)
│ │ │ │ -9882E Compressed Size       00004096 (16534)
│ │ │ │ -98832 Uncompressed Size     0001971B (104219)
│ │ │ │ -98836 Filename Length       001A (26)
│ │ │ │ -98838 Extra Length          001C (28)
│ │ │ │ -9883A Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9883A: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -98854 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -98856   Length              0009 (9)
│ │ │ │ -98858   Flags               03 (3) 'Modification Access'
│ │ │ │ -98859   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9885D   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -98861 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -98863   Length              000B (11)
│ │ │ │ -98865   Version             01 (1)
│ │ │ │ -98866   UID Size            04 (4)
│ │ │ │ -98867   UID                 00000000 (0)
│ │ │ │ -9886B   GID Size            04 (4)
│ │ │ │ -9886C   GID                 00000000 (0)
│ │ │ │ -98870 PAYLOAD
│ │ │ │ -
│ │ │ │ -9C906 LOCAL HEADER #89      04034B50 (67324752)
│ │ │ │ -9C90A Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -9C90B Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -9C90C General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -9C90E Compression Method    0008 (8) 'Deflated'
│ │ │ │ -9C910 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9C914 CRC                   57F9A5F4 (1475978740)
│ │ │ │ -9C918 Compressed Size       000029CF (10703)
│ │ │ │ -9C91C Uncompressed Size     0000BB3A (47930)
│ │ │ │ -9C920 Filename Length       0018 (24)
│ │ │ │ -9C922 Extra Length          001C (28)
│ │ │ │ -9C924 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9C924: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9C93C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -9C93E   Length              0009 (9)
│ │ │ │ -9C940   Flags               03 (3) 'Modification Access'
│ │ │ │ -9C941   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9C945   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9C949 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -9C94B   Length              000B (11)
│ │ │ │ -9C94D   Version             01 (1)
│ │ │ │ -9C94E   UID Size            04 (4)
│ │ │ │ -9C94F   UID                 00000000 (0)
│ │ │ │ -9C953   GID Size            04 (4)
│ │ │ │ -9C954   GID                 00000000 (0)
│ │ │ │ -9C958 PAYLOAD
│ │ │ │ -
│ │ │ │ -9F327 LOCAL HEADER #90      04034B50 (67324752)
│ │ │ │ -9F32B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -9F32C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -9F32D General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -9F32F Compression Method    0008 (8) 'Deflated'
│ │ │ │ -9F331 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9F335 CRC                   DCB3B516 (3702764822)
│ │ │ │ -9F339 Compressed Size       000000AE (174)
│ │ │ │ -9F33D Uncompressed Size     000000FC (252)
│ │ │ │ -9F341 Filename Length       0016 (22)
│ │ │ │ -9F343 Extra Length          001C (28)
│ │ │ │ -9F345 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9F345: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9F35B Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -9F35D   Length              0009 (9)
│ │ │ │ -9F35F   Flags               03 (3) 'Modification Access'
│ │ │ │ -9F360   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9F364   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9F368 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -9F36A   Length              000B (11)
│ │ │ │ -9F36C   Version             01 (1)
│ │ │ │ -9F36D   UID Size            04 (4)
│ │ │ │ -9F36E   UID                 00000000 (0)
│ │ │ │ -9F372   GID Size            04 (4)
│ │ │ │ -9F373   GID                 00000000 (0)
│ │ │ │ -9F377 PAYLOAD               XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
│ │ │ │ +04B65 LOCAL HEADER #5       04034B50 (67324752)
│ │ │ │ +04B69 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +04B6A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +04B6B General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +04B6D Compression Method    0008 (8) 'Deflated'
│ │ │ │ +04B6F Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +04B73 CRC                   AFEB34EA (2951427306)
│ │ │ │ +04B77 Compressed Size       000003F0 (1008)
│ │ │ │ +04B7B Uncompressed Size     00000877 (2167)
│ │ │ │ +04B7F Filename Length       0014 (20)
│ │ │ │ +04B81 Extra Length          001C (28)
│ │ │ │ +04B83 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x4B83: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +04B97 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +04B99   Length              0009 (9)
│ │ │ │ +04B9B   Flags               03 (3) 'Modification Access'
│ │ │ │ +04B9C   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +04BA0   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +04BA4 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +04BA6   Length              000B (11)
│ │ │ │ +04BA8   Version             01 (1)
│ │ │ │ +04BA9   UID Size            04 (4)
│ │ │ │ +04BAA   UID                 00000000 (0)
│ │ │ │ +04BAE   GID Size            04 (4)
│ │ │ │ +04BAF   GID                 00000000 (0)
│ │ │ │ +04BB3 PAYLOAD
│ │ │ │ +
│ │ │ │ +04FA3 LOCAL HEADER #6       04034B50 (67324752)
│ │ │ │ +04FA7 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +04FA8 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +04FA9 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +04FAB Compression Method    0008 (8) 'Deflated'
│ │ │ │ +04FAD Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +04FB1 CRC                   21AF85A7 (565151143)
│ │ │ │ +04FB5 Compressed Size       000001AE (430)
│ │ │ │ +04FB9 Uncompressed Size     000002FE (766)
│ │ │ │ +04FBD Filename Length       0011 (17)
│ │ │ │ +04FBF Extra Length          001C (28)
│ │ │ │ +04FC1 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x4FC1: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +04FD2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +04FD4   Length              0009 (9)
│ │ │ │ +04FD6   Flags               03 (3) 'Modification Access'
│ │ │ │ +04FD7   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +04FDB   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +04FDF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +04FE1   Length              000B (11)
│ │ │ │ +04FE3   Version             01 (1)
│ │ │ │ +04FE4   UID Size            04 (4)
│ │ │ │ +04FE5   UID                 00000000 (0)
│ │ │ │ +04FE9   GID Size            04 (4)
│ │ │ │ +04FEA   GID                 00000000 (0)
│ │ │ │ +04FEE PAYLOAD
│ │ │ │ +
│ │ │ │ +0519C LOCAL HEADER #7       04034B50 (67324752)
│ │ │ │ +051A0 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +051A1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +051A2 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +051A4 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +051A6 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +051AA CRC                   9BD5D9C7 (2614483399)
│ │ │ │ +051AE Compressed Size       000020C5 (8389)
│ │ │ │ +051B2 Uncompressed Size     0000B4B1 (46257)
│ │ │ │ +051B6 Filename Length       001B (27)
│ │ │ │ +051B8 Extra Length          001C (28)
│ │ │ │ +051BA Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x51BA: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +051D5 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +051D7   Length              0009 (9)
│ │ │ │ +051D9   Flags               03 (3) 'Modification Access'
│ │ │ │ +051DA   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +051DE   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +051E2 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +051E4   Length              000B (11)
│ │ │ │ +051E6   Version             01 (1)
│ │ │ │ +051E7   UID Size            04 (4)
│ │ │ │ +051E8   UID                 00000000 (0)
│ │ │ │ +051EC   GID Size            04 (4)
│ │ │ │ +051ED   GID                 00000000 (0)
│ │ │ │ +051F1 PAYLOAD
│ │ │ │ +
│ │ │ │ +072B6 LOCAL HEADER #8       04034B50 (67324752)
│ │ │ │ +072BA Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +072BB Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +072BC General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +072BE Compression Method    0008 (8) 'Deflated'
│ │ │ │ +072C0 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +072C4 CRC                   2D371F1E (758587166)
│ │ │ │ +072C8 Compressed Size       00000E70 (3696)
│ │ │ │ +072CC Uncompressed Size     000030B3 (12467)
│ │ │ │ +072D0 Filename Length       001D (29)
│ │ │ │ +072D2 Extra Length          001C (28)
│ │ │ │ +072D4 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x72D4: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +072F1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +072F3   Length              0009 (9)
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│ │ │ │ +072FA   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +0730D PAYLOAD
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│ │ │ │ +08182 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +08183 General Purpose Flag  0000 (0)
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│ │ │ │ +08187 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +0818B CRC                   7903D0CB (2030293195)
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│ │ │ │ +08197 Filename Length       0019 (25)
│ │ │ │ +08199 Extra Length          001C (28)
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│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x819B: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
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│ │ │ │ +0C41C Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +0C420 CRC                   430C8466 (1124893798)
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│ │ │ │ +#
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│ │ │ │ +#          Zero length filename
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│ │ │ │ +16F6C Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +16F71 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +16F75 CRC                   1EC6C3B8 (516342712)
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│ │ │ │ +16FB6 PAYLOAD
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│ │ │ │ +1AACA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +1AACB General Purpose Flag  0000 (0)
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│ │ │ │ +23CDD Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +26796 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +2679B Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +2679F CRC                   A70066B2 (2801821362)
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│ │ │ │ +27CC4 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +27CC5 General Purpose Flag  0000 (0)
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│ │ │ │ +27CC9 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +27CCD CRC                   82F97239 (2197385785)
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│ │ │ │ +2B6C5 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +2B6C6 General Purpose Flag  0000 (0)
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│ │ │ │ +2B6CA Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +2B6CE CRC                   7A88ED58 (2055794008)
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│ │ │ │ +2BDBE Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +2BDBF General Purpose Flag  0000 (0)
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│ │ │ │ +2BDC3 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +2BDC7 CRC                   F5E61E1F (4125498911)
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│ │ │ │ +2BDD7 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +#          Zero length filename
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│ │ │ │ +2CE95 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +2CE96 General Purpose Flag  0000 (0)
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│ │ │ │ +2CE9A Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +2CE9E CRC                   4CF55DF8 (1291148792)
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│ │ │ │ +2CEAE Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x2CEAE: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +30297 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +30298 General Purpose Flag  0000 (0)
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│ │ │ │ +3029C Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +302A0 CRC                   797D5C21 (2038258721)
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│ │ │ │ +3105D Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +3A847 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +3A857 Filename Length       000F (15)
│ │ │ │ +3A859 Extra Length          001C (28)
│ │ │ │ +3A85B Filename              'XXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x3A85B: Filename 'XXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +3A873   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +3A886 PAYLOAD
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│ │ │ │ +3AEF6 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +3AEF7 General Purpose Flag  0000 (0)
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│ │ │ │ +3AEFB Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +3AEFF CRC                   1194DF58 (294969176)
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│ │ │ │ +#          Zero length filename
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│ │ │ │ +3C989 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +3C98A General Purpose Flag  0000 (0)
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│ │ │ │ +3C98E Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +3D37F Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +3DA84 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +423B8 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +423C8 Filename Length       0018 (24)
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│ │ │ │ +423ED   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +43882 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +43887 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +451B2 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +451B7 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +451F2   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +45602 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +45607 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +498EA Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +# WARNING: Offset 0x498FE: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +49920   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +4BFFC Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +4BFFD General Purpose Flag  0000 (0)
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│ │ │ │ +4C001 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +4C005 CRC                   A84F7DF4 (2823781876)
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│ │ │ │ +# WARNING: Offset 0x4C015: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +4E789 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +4E78A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +4E78B General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
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│ │ │ │ +4E78F Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +4E793 CRC                   3C47A4AF (1011328175)
│ │ │ │ +4E797 Compressed Size       00000CF2 (3314)
│ │ │ │ +4E79B Uncompressed Size     0000517B (20859)
│ │ │ │ +4E79F Filename Length       0021 (33)
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│ │ │ │ +4E7A3 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x4E7A3: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +4E7CD   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +4E7D1 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +4E7E0 PAYLOAD
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│ │ │ │ +4F4D2 LOCAL HEADER #45      04034B50 (67324752)
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│ │ │ │ +4F4D7 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +4F4D8 General Purpose Flag  0000 (0)
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│ │ │ │ +4F4DC Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +4F4E0 CRC                   4527F9F0 (1160247792)
│ │ │ │ +4F4E4 Compressed Size       00000469 (1129)
│ │ │ │ +4F4E8 Uncompressed Size     00000932 (2354)
│ │ │ │ +4F4EC Filename Length       001B (27)
│ │ │ │ +4F4EE Extra Length          001C (28)
│ │ │ │ +4F4F0 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x4F4F0: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +4F514   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +4F995 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +4F996 General Purpose Flag  0000 (0)
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│ │ │ │ +4F99A Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +4F99E CRC                   A2B6650C (2729862412)
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│ │ │ │ +4F9A6 Uncompressed Size     00007A6E (31342)
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│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x4F9AE: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +510D6 LOCAL HEADER #47      04034B50 (67324752)
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│ │ │ │ +510DB Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +510DC General Purpose Flag  0000 (0)
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│ │ │ │ +510E0 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +510E4 CRC                   06C4AFCE (113553358)
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│ │ │ │ +510F0 Filename Length       0010 (16)
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│ │ │ │ +#
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│ │ │ │ +5110D   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +5528B Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +5528C General Purpose Flag  0000 (0)
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│ │ │ │ +55290 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +55294 CRC                   1C486A07 (474507783)
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│ │ │ │ +552C1   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +55D72 General Purpose Flag  0000 (0)
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│ │ │ │ +55D76 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +55D7A CRC                   A5D82A4E (2782407246)
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│ │ │ │ +60B32 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +60B33 General Purpose Flag  0000 (0)
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│ │ │ │ +60B37 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +60B3B CRC                   4F9531C5 (1335177669)
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│ │ │ │ +60FE1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +60FE2 General Purpose Flag  0000 (0)
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│ │ │ │ +60FE6 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +60FEA CRC                   EEF96960 (4009322848)
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│ │ │ │ +61015   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +62504 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +62509 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +63741 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +63746 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +6374A CRC                   1410FCEA (336657642)
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│ │ │ │ +6377C   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +6416F Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +64174 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +64178 CRC                   64462F48 (1682321224)
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│ │ │ │ +64188 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x64188: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +641AA   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +661DE LOCAL HEADER #55      04034B50 (67324752)
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│ │ │ │ +661E3 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +661E4 General Purpose Flag  0000 (0)
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│ │ │ │ +661E8 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +661EC CRC                   D0372DB1 (3493277105)
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│ │ │ │ +661FC Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x661FC: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +66210 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +66219   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +679B5 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +67E16 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +6A30A Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +6B1DE Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +6BC75 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +6E155 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +73534 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +74BFC   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +74C00   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +74C04 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +74C08   Version             01 (1)
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│ │ │ │ +74C0A   UID                 00000000 (0)
│ │ │ │ +74C0E   GID Size            04 (4)
│ │ │ │ +74C0F   GID                 00000000 (0)
│ │ │ │ +74C13 PAYLOAD
│ │ │ │ +
│ │ │ │ +78765 LOCAL HEADER #68      04034B50 (67324752)
│ │ │ │ +78769 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +7876A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +7876B General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +7876D Compression Method    0008 (8) 'Deflated'
│ │ │ │ +7876F Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +78773 CRC                   26977330 (647459632)
│ │ │ │ +78777 Compressed Size       00003EC8 (16072)
│ │ │ │ +7877B Uncompressed Size     0001C79C (116636)
│ │ │ │ +7877F Filename Length       0019 (25)
│ │ │ │ +78781 Extra Length          001C (28)
│ │ │ │ +78783 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x78783: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +7879C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +7879E   Length              0009 (9)
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│ │ │ │ +787A1   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +787A5   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +787A9 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +787AD   Version             01 (1)
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│ │ │ │ +787AF   UID                 00000000 (0)
│ │ │ │ +787B3   GID Size            04 (4)
│ │ │ │ +787B4   GID                 00000000 (0)
│ │ │ │ +787B8 PAYLOAD
│ │ │ │ +
│ │ │ │ +7C680 LOCAL HEADER #69      04034B50 (67324752)
│ │ │ │ +7C684 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +7C685 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +7C686 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +7C688 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +7C68A Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +7C68E CRC                   510D6570 (1359832432)
│ │ │ │ +7C692 Compressed Size       00000838 (2104)
│ │ │ │ +7C696 Uncompressed Size     00003384 (13188)
│ │ │ │ +7C69A Filename Length       0011 (17)
│ │ │ │ +7C69C Extra Length          001C (28)
│ │ │ │ +7C69E Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x7C69E: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +7C6AF Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +7C6B4   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +7C6B8   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +7C6BC Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +7C6C0   Version             01 (1)
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│ │ │ │ +7C6C2   UID                 00000000 (0)
│ │ │ │ +7C6C6   GID Size            04 (4)
│ │ │ │ +7C6C7   GID                 00000000 (0)
│ │ │ │ +7C6CB PAYLOAD
│ │ │ │ +
│ │ │ │ +7CF03 LOCAL HEADER #70      04034B50 (67324752)
│ │ │ │ +7CF07 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +7CF08 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +7CF09 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +7CF0B Compression Method    0008 (8) 'Deflated'
│ │ │ │ +7CF0D Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +7CF11 CRC                   B744432E (3074704174)
│ │ │ │ +7CF15 Compressed Size       000051A7 (20903)
│ │ │ │ +7CF19 Uncompressed Size     0001FBE0 (130016)
│ │ │ │ +7CF1D Filename Length       0015 (21)
│ │ │ │ +7CF1F Extra Length          001C (28)
│ │ │ │ +7CF21 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x7CF21: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +7CF36 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +7CF3B   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +7CF3F   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +7CF43 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +7CF47   Version             01 (1)
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│ │ │ │ +7CF49   UID                 00000000 (0)
│ │ │ │ +7CF4D   GID Size            04 (4)
│ │ │ │ +7CF4E   GID                 00000000 (0)
│ │ │ │ +7CF52 PAYLOAD
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│ │ │ │ +820F9 LOCAL HEADER #71      04034B50 (67324752)
│ │ │ │ +820FD Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +820FE Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +820FF General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +82101 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +82103 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +82107 CRC                   5D0D793D (1561164093)
│ │ │ │ +8210B Compressed Size       00001B0A (6922)
│ │ │ │ +8210F Uncompressed Size     000081D0 (33232)
│ │ │ │ +82113 Filename Length       0019 (25)
│ │ │ │ +82115 Extra Length          001C (28)
│ │ │ │ +82117 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x82117: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +82130 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +82135   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +82139   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +8213D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +82141   Version             01 (1)
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│ │ │ │ +82143   UID                 00000000 (0)
│ │ │ │ +82147   GID Size            04 (4)
│ │ │ │ +82148   GID                 00000000 (0)
│ │ │ │ +8214C PAYLOAD
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│ │ │ │ +83C5A Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +83C5B Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +83C5C General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +83C5E Compression Method    0008 (8) 'Deflated'
│ │ │ │ +83C60 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +83C64 CRC                   392C251C (959194396)
│ │ │ │ +83C68 Compressed Size       00000D9A (3482)
│ │ │ │ +83C6C Uncompressed Size     00002EA0 (11936)
│ │ │ │ +83C70 Filename Length       0018 (24)
│ │ │ │ +83C72 Extra Length          001C (28)
│ │ │ │ +83C74 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x83C74: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +83C8C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +83C95   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +83C99 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +83C9F   UID                 00000000 (0)
│ │ │ │ +83CA3   GID Size            04 (4)
│ │ │ │ +83CA4   GID                 00000000 (0)
│ │ │ │ +83CA8 PAYLOAD
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│ │ │ │ +84A46 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +84A47 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +84A48 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +84A4A Compression Method    0008 (8) 'Deflated'
│ │ │ │ +84A4C Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +84A50 CRC                   037E3A9E (58604190)
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│ │ │ │ +84A58 Uncompressed Size     00000324 (804)
│ │ │ │ +84A5C Filename Length       0011 (17)
│ │ │ │ +84A5E Extra Length          001C (28)
│ │ │ │ +84A60 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x84A60: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +84A71 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +84A76   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +84A7A   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +84A7E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +84A82   Version             01 (1)
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│ │ │ │ +84A88   GID Size            04 (4)
│ │ │ │ +84A89   GID                 00000000 (0)
│ │ │ │ +84A8D PAYLOAD
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│ │ │ │ +84C72 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +84C73 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +84C74 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +84C76 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +84C78 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +84C7C CRC                   55187787 (1427666823)
│ │ │ │ +84C80 Compressed Size       000006C3 (1731)
│ │ │ │ +84C84 Uncompressed Size     0000143A (5178)
│ │ │ │ +84C88 Filename Length       0019 (25)
│ │ │ │ +84C8A Extra Length          001C (28)
│ │ │ │ +84C8C Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x84C8C: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +84CA5 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +84CAA   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +84CAE   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +84CB2 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +84CB6   Version             01 (1)
│ │ │ │ +84CB7   UID Size            04 (4)
│ │ │ │ +84CB8   UID                 00000000 (0)
│ │ │ │ +84CBC   GID Size            04 (4)
│ │ │ │ +84CBD   GID                 00000000 (0)
│ │ │ │ +84CC1 PAYLOAD
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│ │ │ │ +85384 LOCAL HEADER #75      04034B50 (67324752)
│ │ │ │ +85388 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +85389 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +8538A General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +8538C Compression Method    0008 (8) 'Deflated'
│ │ │ │ +8538E Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +85392 CRC                   107EE648 (276751944)
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│ │ │ │ +8539A Uncompressed Size     0000CA81 (51841)
│ │ │ │ +8539E Filename Length       0018 (24)
│ │ │ │ +853A0 Extra Length          001C (28)
│ │ │ │ +853A2 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x853A2: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +853BA Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +853C3   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +853C7 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +853D1   GID Size            04 (4)
│ │ │ │ +853D2   GID                 00000000 (0)
│ │ │ │ +853D6 PAYLOAD
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│ │ │ │ +87286 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +87287 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +87288 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +8728A Compression Method    0008 (8) 'Deflated'
│ │ │ │ +8728C Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +87290 CRC                   45F6BF5A (1173798746)
│ │ │ │ +87294 Compressed Size       00001BEB (7147)
│ │ │ │ +87298 Uncompressed Size     0000C5EA (50666)
│ │ │ │ +8729C Filename Length       0012 (18)
│ │ │ │ +8729E Extra Length          001C (28)
│ │ │ │ +872A0 Filename              'XXXXXXXXXXXXXXXXXX'
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│ │ │ │ +# WARNING: Offset 0x872A0: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +872B2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +872BB   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +872BF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +872C9   GID Size            04 (4)
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│ │ │ │ +872CE PAYLOAD
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│ │ │ │ +88EB9 LOCAL HEADER #77      04034B50 (67324752)
│ │ │ │ +88EBD Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +88EBE Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +88EBF General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +88EC1 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +88EC3 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +88EC7 CRC                   317BA035 (830185525)
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│ │ │ │ +88ECF Uncompressed Size     00008804 (34820)
│ │ │ │ +88ED3 Filename Length       0016 (22)
│ │ │ │ +88ED5 Extra Length          001C (28)
│ │ │ │ +88ED7 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x88ED7: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +88EED Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +88EF2   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +88EF6   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +88EFA Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +88EFC   Length              000B (11)
│ │ │ │ +88EFE   Version             01 (1)
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│ │ │ │ +88F04   GID Size            04 (4)
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│ │ │ │ +88F09 PAYLOAD
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│ │ │ │ +8AD20 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +8AD21 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +8AD22 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +8AD24 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +8AD26 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +8AD2A CRC                   B0584996 (2958576022)
│ │ │ │ +8AD2E Compressed Size       000029AA (10666)
│ │ │ │ +8AD32 Uncompressed Size     0000D050 (53328)
│ │ │ │ +8AD36 Filename Length       001A (26)
│ │ │ │ +8AD38 Extra Length          001C (28)
│ │ │ │ +8AD3A Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x8AD3A: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +8AD54 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +8AD59   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +8AD5D   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +8AD61 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +8AD65   Version             01 (1)
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│ │ │ │ +8D71E Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +8D71F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +8D720 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +8D722 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +8D724 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +8D728 CRC                   7FA7262B (2141660715)
│ │ │ │ +8D72C Compressed Size       000009AD (2477)
│ │ │ │ +8D730 Uncompressed Size     00001DB7 (7607)
│ │ │ │ +8D734 Filename Length       0018 (24)
│ │ │ │ +8D736 Extra Length          001C (28)
│ │ │ │ +8D738 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0x8D738: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +8D759   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +8E123 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +8E127 CRC                   F5E2129F (4125233823)
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│ │ │ │ +8F82E Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +90F3C General Purpose Flag  0000 (0)
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│ │ │ │ +90F44 CRC                   FC95F24B (4237685323)
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│ │ │ │ +92B18 CRC                   D0D71F86 (3503759238)
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│ │ │ │ +936DA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +936DB General Purpose Flag  0000 (0)
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│ │ │ │ +936E3 CRC                   FFF9C4D2 (4294558930)
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│ │ │ │ +93712   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +94AB9 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +98829 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +9882E Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +98865   Access Time         6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
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│ │ │ │ +9C91B Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +9F33D Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │                              XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
│ │ │ │  
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│ │ │ │ -9F42F Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9F433 CRC                   58439733 (1480824627)
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│ │ │ │ -9F479   Access Time         69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9F68C: Filename 'XXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9F79E: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9F801: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9F860: Filename 'XXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ -# WARNING: Offset 0x9FA24: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9FB4B: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9FBAC: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -#
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -#
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -9FC95 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -9FD0C CRC                   40B68220 (1085702688)
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9FD90: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -# WARNING: Offset 0x9FDF1: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9FE4C: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -9FE85 CRC                   984552B7 (2554679991)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9FEA3: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9FEB7 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -9FEC0 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -9FEDF CRC                   F2ED2F43 (4075630403)
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│ │ │ │ -9FEED Extra Length          0018 (24)
│ │ │ │ -9FEEF Comment Length        0000 (0)
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│ │ │ │ -9FEF9 Local Header Offset   00036E61 (224865)
│ │ │ │ -9FEFD Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9FEFD: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9FF11 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -9FF1A Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -9FF2E Created OS            03 (3) 'Unix'
│ │ │ │ -9FF2F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -9FF30 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -9FF31 General Purpose Flag  0000 (0)
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│ │ │ │ -9FF35 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9FF39 CRC                   3233182B (842209323)
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│ │ │ │ -9FF47 Extra Length          0018 (24)
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│ │ │ │ -9FF4D Int File Attributes   0000 (0)
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│ │ │ │ -9FF57 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9FF57: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9FF72 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -9FF77   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9FF7B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -9FF8E Created Zip Spec      3D (61) '6.1'
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│ │ │ │ -9FF91 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -9FF94 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -9FF96 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9FF9A CRC                   0BD59D77 (198548855)
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│ │ │ │ -9FFA2 Uncompressed Size     0000237B (9083)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0x9FFB8: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -9FFCB Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -9FFCD   Length              0005 (5)
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│ │ │ │ -9FFD4 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -9FFDF   GID                 00000000 (0)
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│ │ │ │ -9FFE7 Created Zip Spec      3D (61) '6.1'
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│ │ │ │ -9FFE9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -9FFEA Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -9FFEF Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -9FFF3 CRC                   4DABAB86 (1303096198)
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│ │ │ │ -A000D Local Header Offset   00039713 (235283)
│ │ │ │ -A0011 Filename              'XXXXXXXXXXXXXXX'
│ │ │ │ -#
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│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0020 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A0029 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A003F Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A0042 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0044 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0048 CRC                   C70CE575 (3339511157)
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│ │ │ │ -A0050 Uncompressed Size     000018E0 (6368)
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│ │ │ │ -A0056 Extra Length          0018 (24)
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│ │ │ │ -A0062 Local Header Offset   0003A841 (239681)
│ │ │ │ -A0066 Filename              'XXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0066: Filename 'XXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0075 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0077   Length              0005 (5)
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│ │ │ │ -A007E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A0089   GID                 00000000 (0)
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│ │ │ │ -A0094 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A0099 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A009D CRC                   B33717CF (3006732239)
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│ │ │ │ -A00B7 Local Header Offset   0003AEF5 (241397)
│ │ │ │ -A00BB Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA00BB: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A00CE Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A00D0   Length              0005 (5)
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│ │ │ │ -A00D7 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A00F2 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A00F6 CRC                   BA8C2020 (3129745440)
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│ │ │ │ -A010A Int File Attributes   0000 (0)
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│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0110 Local Header Offset   0003C98D (248205)
│ │ │ │ -A0114 Filename              'XXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0114: Filename 'XXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0124 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0126   Length              0005 (5)
│ │ │ │ -A0128   Flags               01 (1) 'Modification'
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│ │ │ │ -A012D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A0143 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A0146 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0148 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A014C CRC                   61869F50 (1636212560)
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│ │ │ │ -A0154 Uncompressed Size     00001566 (5478)
│ │ │ │ -A0158 Filename Length       0012 (18)
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│ │ │ │ -A015E Disk Start            0000 (0)
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│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0166 Local Header Offset   0003D37E (250750)
│ │ │ │ -A016A Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA016A: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A017C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A017E   Length              0005 (5)
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│ │ │ │ -A0181   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0185 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0187   Length              000B (11)
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│ │ │ │ -A0198 Created Zip Spec      3D (61) '6.1'
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│ │ │ │ -A019B Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A019E Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A01A0 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A01A4 CRC                   16F2754B (384988491)
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│ │ │ │ -A01B2 Extra Length          0018 (24)
│ │ │ │ -A01B4 Comment Length        0000 (0)
│ │ │ │ -A01B6 Disk Start            0000 (0)
│ │ │ │ -A01B8 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A01BA Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A01BE Local Header Offset   0003DA83 (252547)
│ │ │ │ -A01C2 Filename              'XXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA01C2: Filename 'XXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A01D2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A01D4   Length              0005 (5)
│ │ │ │ -A01D6   Flags               01 (1) 'Modification'
│ │ │ │ -A01D7   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A01DB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A01DD   Length              000B (11)
│ │ │ │ -A01DF   Version             01 (1)
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│ │ │ │ -A01E1   UID                 00000000 (0)
│ │ │ │ -A01E5   GID Size            04 (4)
│ │ │ │ -A01E6   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A01EA CENTRAL HEADER #37    02014B50 (33639248)
│ │ │ │ -A01EE Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A01EF Created OS            03 (3) 'Unix'
│ │ │ │ -A01F0 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A01F1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A01F2 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A01F4 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A01F6 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A01FA CRC                   23389B09 (590912265)
│ │ │ │ -A01FE Compressed Size       00001E89 (7817)
│ │ │ │ -A0202 Uncompressed Size     00009AAB (39595)
│ │ │ │ -A0206 Filename Length       0012 (18)
│ │ │ │ -A0208 Extra Length          0018 (24)
│ │ │ │ -A020A Comment Length        0000 (0)
│ │ │ │ -A020C Disk Start            0000 (0)
│ │ │ │ -A020E Int File Attributes   0000 (0)
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│ │ │ │ -A0210 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0214 Local Header Offset   000404E1 (263393)
│ │ │ │ -A0218 Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0218: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A022A Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A022C   Length              0005 (5)
│ │ │ │ -A022E   Flags               01 (1) 'Modification'
│ │ │ │ -A022F   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0233 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0235   Length              000B (11)
│ │ │ │ -A0237   Version             01 (1)
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│ │ │ │ -A023E   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0242 CENTRAL HEADER #38    02014B50 (33639248)
│ │ │ │ -A0246 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0247 Created OS            03 (3) 'Unix'
│ │ │ │ -A0248 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0249 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A024A General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A024C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A024E Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0252 CRC                   13847F5A (327450458)
│ │ │ │ -A0256 Compressed Size       0000147C (5244)
│ │ │ │ -A025A Uncompressed Size     00007AD0 (31440)
│ │ │ │ -A025E Filename Length       0018 (24)
│ │ │ │ -A0260 Extra Length          0018 (24)
│ │ │ │ -A0262 Comment Length        0000 (0)
│ │ │ │ -A0264 Disk Start            0000 (0)
│ │ │ │ -A0266 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0268 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A026C Local Header Offset   000423B6 (271286)
│ │ │ │ -A0270 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0270: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -A0288 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A0291 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A02A6 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A02A7 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A02AA Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A02AC Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A02B0 CRC                   021B6F33 (35352371)
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│ │ │ │ -A02C2 Disk Start            0000 (0)
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│ │ │ │ -A02CA Local Header Offset   00043884 (276612)
│ │ │ │ -A02CE Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA02CE: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A02ED Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A02F6 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A030B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A030C Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A0311 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0315 CRC                   8E4EBF9E (2387525534)
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│ │ │ │ -A032F Local Header Offset   000451B7 (283063)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0333: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0351 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A035A Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A0364   GID Size            04 (4)
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│ │ │ │ -A036F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0370 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0371 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0373 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0375 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0379 CRC                   D9FD2FF3 (3657248755)
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│ │ │ │ -A0381 Uncompressed Size     0000D8E8 (55528)
│ │ │ │ -A0385 Filename Length       0013 (19)
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│ │ │ │ -A0393 Local Header Offset   00045607 (284167)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0397: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A03AA Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A03AC   Length              0005 (5)
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│ │ │ │ -A03C9 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A03CC Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A03CE Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A03D2 CRC                   A60BB6F3 (2785785587)
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│ │ │ │ -A03DE Filename Length       0019 (25)
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│ │ │ │ -A03E2 Comment Length        0000 (0)
│ │ │ │ -A03E4 Disk Start            0000 (0)
│ │ │ │ -A03E6 Int File Attributes   0000 (0)
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│ │ │ │ -A03EC Local Header Offset   000498EA (301290)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA03F0: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0409 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A0412 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A0427 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0428 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0429 General Purpose Flag  0000 (0)
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│ │ │ │ -A042D Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0431 CRC                   A84F7DF4 (2823781876)
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│ │ │ │ -A0439 Uncompressed Size     00008B84 (35716)
│ │ │ │ -A043D Filename Length       0019 (25)
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│ │ │ │ -A044B Local Header Offset   0004C001 (311297)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA044F: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0468 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A046A   Length              0005 (5)
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│ │ │ │ -A046D   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0471 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A0485 Created OS            03 (3) 'Unix'
│ │ │ │ -A0486 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0487 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A048A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A048C Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0490 CRC                   20889E86 (545824390)
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│ │ │ │ -A0498 Uncompressed Size     0000517B (20859)
│ │ │ │ -A049C Filename Length       0021 (33)
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│ │ │ │ -A04A0 Comment Length        0000 (0)
│ │ │ │ -A04A2 Disk Start            0000 (0)
│ │ │ │ -A04A4 Int File Attributes   0000 (0)
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│ │ │ │ -A04A6 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A04AA Local Header Offset   0004E78F (321423)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA04AE: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A04CF Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A04D4   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A04D8 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A04EE Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A04EF General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A04F1 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A04F3 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A04F7 CRC                   4527F9F0 (1160247792)
│ │ │ │ -A04FB Compressed Size       00000469 (1129)
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│ │ │ │ -A0507 Comment Length        0000 (0)
│ │ │ │ -A0509 Disk Start            0000 (0)
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│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0511 Local Header Offset   0004F4DB (324827)
│ │ │ │ -A0515 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0515: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0530 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0532   Length              0005 (5)
│ │ │ │ -A0534   Flags               01 (1) 'Modification'
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│ │ │ │ -A0539 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A053B   Length              000B (11)
│ │ │ │ -A053D   Version             01 (1)
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│ │ │ │ -A053F   UID                 00000000 (0)
│ │ │ │ -A0543   GID Size            04 (4)
│ │ │ │ -A0544   GID                 00000000 (0)
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│ │ │ │ -A0548 CENTRAL HEADER #46    02014B50 (33639248)
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│ │ │ │ -A054D Created OS            03 (3) 'Unix'
│ │ │ │ -A054E Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A054F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0550 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0552 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0554 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0558 CRC                   51FBB037 (1375449143)
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│ │ │ │ -A0560 Uncompressed Size     00007A6E (31342)
│ │ │ │ -A0564 Filename Length       001F (31)
│ │ │ │ -A0566 Extra Length          0018 (24)
│ │ │ │ -A0568 Comment Length        0000 (0)
│ │ │ │ -A056A Disk Start            0000 (0)
│ │ │ │ -A056C Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A056E Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0572 Local Header Offset   0004F999 (326041)
│ │ │ │ -A0576 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0576: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0595 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0597   Length              0005 (5)
│ │ │ │ -A0599   Flags               01 (1) 'Modification'
│ │ │ │ -A059A   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A059E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A05A0   Length              000B (11)
│ │ │ │ -A05A2   Version             01 (1)
│ │ │ │ -A05A3   UID Size            04 (4)
│ │ │ │ -A05A4   UID                 00000000 (0)
│ │ │ │ -A05A8   GID Size            04 (4)
│ │ │ │ -A05A9   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A05AD CENTRAL HEADER #47    02014B50 (33639248)
│ │ │ │ -A05B1 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A05B2 Created OS            03 (3) 'Unix'
│ │ │ │ -A05B3 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A05B4 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A05B5 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A05B7 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A05B9 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A05BD CRC                   2414B628 (605337128)
│ │ │ │ -A05C1 Compressed Size       00004161 (16737)
│ │ │ │ -A05C5 Uncompressed Size     0001D160 (119136)
│ │ │ │ -A05C9 Filename Length       0010 (16)
│ │ │ │ -A05CB Extra Length          0018 (24)
│ │ │ │ -A05CD Comment Length        0000 (0)
│ │ │ │ -A05CF Disk Start            0000 (0)
│ │ │ │ -A05D1 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A05D3 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A05D7 Local Header Offset   000510E3 (332003)
│ │ │ │ -A05DB Filename              'XXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA05DB: Filename 'XXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A05EB Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A05ED   Length              0005 (5)
│ │ │ │ -A05EF   Flags               01 (1) 'Modification'
│ │ │ │ -A05F0   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A05F4 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A05F6   Length              000B (11)
│ │ │ │ -A05F8   Version             01 (1)
│ │ │ │ -A05F9   UID Size            04 (4)
│ │ │ │ -A05FA   UID                 00000000 (0)
│ │ │ │ -A05FE   GID Size            04 (4)
│ │ │ │ -A05FF   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0603 CENTRAL HEADER #48    02014B50 (33639248)
│ │ │ │ -A0607 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0608 Created OS            03 (3) 'Unix'
│ │ │ │ -A0609 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A060A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A060B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A060D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A060F Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0613 CRC                   1C486A07 (474507783)
│ │ │ │ -A0617 Compressed Size       00000A98 (2712)
│ │ │ │ -A061B Uncompressed Size     00002106 (8454)
│ │ │ │ -A061F Filename Length       0014 (20)
│ │ │ │ -A0621 Extra Length          0018 (24)
│ │ │ │ -A0623 Comment Length        0000 (0)
│ │ │ │ -A0625 Disk Start            0000 (0)
│ │ │ │ -A0627 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0629 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A062D Local Header Offset   0005528E (348814)
│ │ │ │ -A0631 Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0631: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0645 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0647   Length              0005 (5)
│ │ │ │ -A0649   Flags               01 (1) 'Modification'
│ │ │ │ -A064A   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A064E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0650   Length              000B (11)
│ │ │ │ -A0652   Version             01 (1)
│ │ │ │ -A0653   UID Size            04 (4)
│ │ │ │ -A0654   UID                 00000000 (0)
│ │ │ │ -A0658   GID Size            04 (4)
│ │ │ │ -A0659   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A065D CENTRAL HEADER #49    02014B50 (33639248)
│ │ │ │ -A0661 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0662 Created OS            03 (3) 'Unix'
│ │ │ │ -A0663 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0664 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0665 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0667 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0669 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A066D CRC                   7F22DF82 (2132991874)
│ │ │ │ -A0671 Compressed Size       0000AD78 (44408)
│ │ │ │ -A0675 Uncompressed Size     0003EB1B (256795)
│ │ │ │ -A0679 Filename Length       0017 (23)
│ │ │ │ -A067B Extra Length          0018 (24)
│ │ │ │ -A067D Comment Length        0000 (0)
│ │ │ │ -A067F Disk Start            0000 (0)
│ │ │ │ -A0681 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0683 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0687 Local Header Offset   00055D74 (351604)
│ │ │ │ -A068B Filename              'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA068B: Filename 'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A06A2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A06A4   Length              0005 (5)
│ │ │ │ -A06A6   Flags               01 (1) 'Modification'
│ │ │ │ -A06A7   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A06AB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A06AD   Length              000B (11)
│ │ │ │ -A06AF   Version             01 (1)
│ │ │ │ -A06B0   UID Size            04 (4)
│ │ │ │ -A06B1   UID                 00000000 (0)
│ │ │ │ -A06B5   GID Size            04 (4)
│ │ │ │ -A06B6   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A06BA CENTRAL HEADER #50    02014B50 (33639248)
│ │ │ │ -A06BE Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A06BF Created OS            03 (3) 'Unix'
│ │ │ │ -A06C0 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A06C1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A06C2 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A06C4 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A06C6 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A06CA CRC                   A0A15D62 (2694929762)
│ │ │ │ -A06CE Compressed Size       00000464 (1124)
│ │ │ │ -A06D2 Uncompressed Size     00000DF4 (3572)
│ │ │ │ -A06D6 Filename Length       0013 (19)
│ │ │ │ -A06D8 Extra Length          0018 (24)
│ │ │ │ -A06DA Comment Length        0000 (0)
│ │ │ │ -A06DC Disk Start            0000 (0)
│ │ │ │ -A06DE Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A06E0 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A06E4 Local Header Offset   00060B3D (396093)
│ │ │ │ -A06E8 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA06E8: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A06FB Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A06FD   Length              0005 (5)
│ │ │ │ -A06FF   Flags               01 (1) 'Modification'
│ │ │ │ -A0700   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0704 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0706   Length              000B (11)
│ │ │ │ -A0708   Version             01 (1)
│ │ │ │ -A0709   UID Size            04 (4)
│ │ │ │ -A070A   UID                 00000000 (0)
│ │ │ │ -A070E   GID Size            04 (4)
│ │ │ │ -A070F   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0713 CENTRAL HEADER #51    02014B50 (33639248)
│ │ │ │ -A0717 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0718 Created OS            03 (3) 'Unix'
│ │ │ │ -A0719 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A071A Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A071B General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A071D Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A071F Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0723 CRC                   D825044E (3626304590)
│ │ │ │ -A0727 Compressed Size       000014D6 (5334)
│ │ │ │ -A072B Uncompressed Size     00006893 (26771)
│ │ │ │ -A072F Filename Length       0012 (18)
│ │ │ │ -A0731 Extra Length          0018 (24)
│ │ │ │ -A0733 Comment Length        0000 (0)
│ │ │ │ -A0735 Disk Start            0000 (0)
│ │ │ │ -A0737 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0739 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A073D Local Header Offset   00060FEE (397294)
│ │ │ │ -A0741 Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0741: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0753 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0755   Length              0005 (5)
│ │ │ │ -A0757   Flags               01 (1) 'Modification'
│ │ │ │ -A0758   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A075C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A075E   Length              000B (11)
│ │ │ │ -A0760   Version             01 (1)
│ │ │ │ -A0761   UID Size            04 (4)
│ │ │ │ -A0762   UID                 00000000 (0)
│ │ │ │ -A0766   GID Size            04 (4)
│ │ │ │ -A0767   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A076B CENTRAL HEADER #52    02014B50 (33639248)
│ │ │ │ -A076F Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0770 Created OS            03 (3) 'Unix'
│ │ │ │ -A0771 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0772 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0773 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0775 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0777 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A077B CRC                   C193E548 (3247695176)
│ │ │ │ -A077F Compressed Size       000011F0 (4592)
│ │ │ │ -A0783 Uncompressed Size     0000410D (16653)
│ │ │ │ -A0787 Filename Length       0012 (18)
│ │ │ │ -A0789 Extra Length          0018 (24)
│ │ │ │ -A078B Comment Length        0000 (0)
│ │ │ │ -A078D Disk Start            0000 (0)
│ │ │ │ -A078F Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0791 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0795 Local Header Offset   00062510 (402704)
│ │ │ │ -A0799 Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0799: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A07AB Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A07AD   Length              0005 (5)
│ │ │ │ -A07AF   Flags               01 (1) 'Modification'
│ │ │ │ -A07B0   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A07B4 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A07B6   Length              000B (11)
│ │ │ │ -A07B8   Version             01 (1)
│ │ │ │ -A07B9   UID Size            04 (4)
│ │ │ │ -A07BA   UID                 00000000 (0)
│ │ │ │ -A07BE   GID Size            04 (4)
│ │ │ │ -A07BF   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A07C3 CENTRAL HEADER #53    02014B50 (33639248)
│ │ │ │ -A07C7 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A07C8 Created OS            03 (3) 'Unix'
│ │ │ │ -A07C9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A07CA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A07CB General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A07CD Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A07CF Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A07D3 CRC                   10C49B8F (281320335)
│ │ │ │ -A07D7 Compressed Size       000009D9 (2521)
│ │ │ │ -A07DB Uncompressed Size     0000352A (13610)
│ │ │ │ -A07DF Filename Length       0019 (25)
│ │ │ │ -A07E1 Extra Length          0018 (24)
│ │ │ │ -A07E3 Comment Length        0000 (0)
│ │ │ │ -A07E5 Disk Start            0000 (0)
│ │ │ │ -A07E7 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A07E9 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A07ED Local Header Offset   0006374C (407372)
│ │ │ │ -A07F1 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA07F1: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A080A Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A080C   Length              0005 (5)
│ │ │ │ -A080E   Flags               01 (1) 'Modification'
│ │ │ │ -A080F   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0813 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0815   Length              000B (11)
│ │ │ │ -A0817   Version             01 (1)
│ │ │ │ -A0818   UID Size            04 (4)
│ │ │ │ -A0819   UID                 00000000 (0)
│ │ │ │ -A081D   GID Size            04 (4)
│ │ │ │ -A081E   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0822 CENTRAL HEADER #54    02014B50 (33639248)
│ │ │ │ -A0826 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0827 Created OS            03 (3) 'Unix'
│ │ │ │ -A0828 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0829 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A082A General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A082C Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A082E Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0832 CRC                   F2CB28F8 (4073400568)
│ │ │ │ -A0836 Compressed Size       00002023 (8227)
│ │ │ │ -A083A Uncompressed Size     00010945 (67909)
│ │ │ │ -A083E Filename Length       0019 (25)
│ │ │ │ -A0840 Extra Length          0018 (24)
│ │ │ │ -A0842 Comment Length        0000 (0)
│ │ │ │ -A0844 Disk Start            0000 (0)
│ │ │ │ -A0846 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0848 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A084C Local Header Offset   00064178 (409976)
│ │ │ │ -A0850 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0850: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0869 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A086B   Length              0005 (5)
│ │ │ │ -A086D   Flags               01 (1) 'Modification'
│ │ │ │ -A086E   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0872 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0874   Length              000B (11)
│ │ │ │ -A0876   Version             01 (1)
│ │ │ │ -A0877   UID Size            04 (4)
│ │ │ │ -A0878   UID                 00000000 (0)
│ │ │ │ -A087C   GID Size            04 (4)
│ │ │ │ -A087D   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0881 CENTRAL HEADER #55    02014B50 (33639248)
│ │ │ │ -A0885 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0886 Created OS            03 (3) 'Unix'
│ │ │ │ -A0887 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0888 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0889 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A088B Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A088D Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0891 CRC                   D0372DB1 (3493277105)
│ │ │ │ -A0895 Compressed Size       0000177F (6015)
│ │ │ │ -A0899 Uncompressed Size     0000472D (18221)
│ │ │ │ -A089D Filename Length       0014 (20)
│ │ │ │ -A089F Extra Length          0018 (24)
│ │ │ │ -A08A1 Comment Length        0000 (0)
│ │ │ │ -A08A3 Disk Start            0000 (0)
│ │ │ │ -A08A5 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A08A7 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A08AB Local Header Offset   000661EE (418286)
│ │ │ │ -A08AF Filename              'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA08AF: Filename 'XXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A08C3 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A08C5   Length              0005 (5)
│ │ │ │ -A08C7   Flags               01 (1) 'Modification'
│ │ │ │ -A08C8   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A08CC Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A08CE   Length              000B (11)
│ │ │ │ -A08D0   Version             01 (1)
│ │ │ │ -A08D1   UID Size            04 (4)
│ │ │ │ -A08D2   UID                 00000000 (0)
│ │ │ │ -A08D6   GID Size            04 (4)
│ │ │ │ -A08D7   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A08DB CENTRAL HEADER #56    02014B50 (33639248)
│ │ │ │ -A08DF Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A08E0 Created OS            03 (3) 'Unix'
│ │ │ │ -A08E1 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A08E2 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A08E3 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A08E5 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A08E7 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A08EB CRC                   FAE30038 (4209180728)
│ │ │ │ -A08EF Compressed Size       0000040B (1035)
│ │ │ │ -A08F3 Uncompressed Size     00000826 (2086)
│ │ │ │ -A08F7 Filename Length       001C (28)
│ │ │ │ -A08F9 Extra Length          0018 (24)
│ │ │ │ -A08FB Comment Length        0000 (0)
│ │ │ │ -A08FD Disk Start            0000 (0)
│ │ │ │ -A08FF Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0901 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0905 Local Header Offset   000679BB (424379)
│ │ │ │ -A0909 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0909: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0925 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0927   Length              0005 (5)
│ │ │ │ -A0929   Flags               01 (1) 'Modification'
│ │ │ │ -A092A   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A092E Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0930   Length              000B (11)
│ │ │ │ -A0932   Version             01 (1)
│ │ │ │ -A0933   UID Size            04 (4)
│ │ │ │ -A0934   UID                 00000000 (0)
│ │ │ │ -A0938   GID Size            04 (4)
│ │ │ │ -A0939   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A093D CENTRAL HEADER #57    02014B50 (33639248)
│ │ │ │ -A0941 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0942 Created OS            03 (3) 'Unix'
│ │ │ │ -A0943 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0944 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0945 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0947 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0949 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A094D CRC                   60701273 (1617957491)
│ │ │ │ -A0951 Compressed Size       00002499 (9369)
│ │ │ │ -A0955 Uncompressed Size     0000B5FA (46586)
│ │ │ │ -A0959 Filename Length       001F (31)
│ │ │ │ -A095B Extra Length          0018 (24)
│ │ │ │ -A095D Comment Length        0000 (0)
│ │ │ │ -A095F Disk Start            0000 (0)
│ │ │ │ -A0961 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0963 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0967 Local Header Offset   00067E1C (425500)
│ │ │ │ -A096B Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA096B: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A098A Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A098C   Length              0005 (5)
│ │ │ │ -A098E   Flags               01 (1) 'Modification'
│ │ │ │ -A098F   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0993 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0995   Length              000B (11)
│ │ │ │ -A0997   Version             01 (1)
│ │ │ │ -A0998   UID Size            04 (4)
│ │ │ │ -A0999   UID                 00000000 (0)
│ │ │ │ -A099D   GID Size            04 (4)
│ │ │ │ -A099E   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A09A2 CENTRAL HEADER #58    02014B50 (33639248)
│ │ │ │ -A09A6 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A09A7 Created OS            03 (3) 'Unix'
│ │ │ │ -A09A8 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A09A9 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A09AA General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A09AC Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A09AE Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A09B2 CRC                   92A69325 (2460390181)
│ │ │ │ -A09B6 Compressed Size       00000E81 (3713)
│ │ │ │ -A09BA Uncompressed Size     000052DA (21210)
│ │ │ │ -A09BE Filename Length       001F (31)
│ │ │ │ -A09C0 Extra Length          0018 (24)
│ │ │ │ -A09C2 Comment Length        0000 (0)
│ │ │ │ -A09C4 Disk Start            0000 (0)
│ │ │ │ -A09C6 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A09C8 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A09CC Local Header Offset   0006A30E (434958)
│ │ │ │ -A09D0 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA09D0: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A09EF Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A09F1   Length              0005 (5)
│ │ │ │ -A09F3   Flags               01 (1) 'Modification'
│ │ │ │ -A09F4   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A09F8 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A09FA   Length              000B (11)
│ │ │ │ -A09FC   Version             01 (1)
│ │ │ │ -A09FD   UID Size            04 (4)
│ │ │ │ -A09FE   UID                 00000000 (0)
│ │ │ │ -A0A02   GID Size            04 (4)
│ │ │ │ -A0A03   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0A07 CENTRAL HEADER #59    02014B50 (33639248)
│ │ │ │ -A0A0B Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0A0C Created OS            03 (3) 'Unix'
│ │ │ │ -A0A0D Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0A0E Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0A0F General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0A11 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0A13 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0A17 CRC                   A77B8D6E (2809892206)
│ │ │ │ -A0A1B Compressed Size       00000A46 (2630)
│ │ │ │ -A0A1F Uncompressed Size     0000247B (9339)
│ │ │ │ -A0A23 Filename Length       0013 (19)
│ │ │ │ -A0A25 Extra Length          0018 (24)
│ │ │ │ -A0A27 Comment Length        0000 (0)
│ │ │ │ -A0A29 Disk Start            0000 (0)
│ │ │ │ -A0A2B Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0A2D Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0A31 Local Header Offset   0006B1E8 (438760)
│ │ │ │ -A0A35 Filename              'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0A35: Filename 'XXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0A48 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0A4A   Length              0005 (5)
│ │ │ │ -A0A4C   Flags               01 (1) 'Modification'
│ │ │ │ -A0A4D   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0A51 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0A53   Length              000B (11)
│ │ │ │ -A0A55   Version             01 (1)
│ │ │ │ -A0A56   UID Size            04 (4)
│ │ │ │ -A0A57   UID                 00000000 (0)
│ │ │ │ -A0A5B   GID Size            04 (4)
│ │ │ │ -A0A5C   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0A60 CENTRAL HEADER #60    02014B50 (33639248)
│ │ │ │ -A0A64 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0A65 Created OS            03 (3) 'Unix'
│ │ │ │ -A0A66 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0A67 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0A68 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0A6A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0A6C Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0A70 CRC                   30B97F5F (817463135)
│ │ │ │ -A0A74 Compressed Size       00002486 (9350)
│ │ │ │ -A0A78 Uncompressed Size     0000B84D (47181)
│ │ │ │ -A0A7C Filename Length       0019 (25)
│ │ │ │ -A0A7E Extra Length          0018 (24)
│ │ │ │ -A0A80 Comment Length        0000 (0)
│ │ │ │ -A0A82 Disk Start            0000 (0)
│ │ │ │ -A0A84 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0A86 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0A8A Local Header Offset   0006BC7B (441467)
│ │ │ │ -A0A8E Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0A8E: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0AA7 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0AA9   Length              0005 (5)
│ │ │ │ -A0AAB   Flags               01 (1) 'Modification'
│ │ │ │ -A0AAC   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0AB0 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0AB2   Length              000B (11)
│ │ │ │ -A0AB4   Version             01 (1)
│ │ │ │ -A0AB5   UID Size            04 (4)
│ │ │ │ -A0AB6   UID                 00000000 (0)
│ │ │ │ -A0ABA   GID Size            04 (4)
│ │ │ │ -A0ABB   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0ABF CENTRAL HEADER #61    02014B50 (33639248)
│ │ │ │ -A0AC3 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0AC4 Created OS            03 (3) 'Unix'
│ │ │ │ -A0AC5 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0AC6 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0AC7 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0AC9 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0ACB Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0ACF CRC                   DC97F08B (3700945035)
│ │ │ │ -A0AD3 Compressed Size       00000EFB (3835)
│ │ │ │ -A0AD7 Uncompressed Size     00003A2D (14893)
│ │ │ │ -A0ADB Filename Length       0024 (36)
│ │ │ │ -A0ADD Extra Length          0018 (24)
│ │ │ │ -A0ADF Comment Length        0000 (0)
│ │ │ │ -A0AE1 Disk Start            0000 (0)
│ │ │ │ -A0AE3 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0AE5 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0AE9 Local Header Offset   0006E154 (450900)
│ │ │ │ -A0AED Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0AED: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0B11 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0B13   Length              0005 (5)
│ │ │ │ -A0B15   Flags               01 (1) 'Modification'
│ │ │ │ -A0B16   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0B1A Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0B1C   Length              000B (11)
│ │ │ │ -A0B1E   Version             01 (1)
│ │ │ │ -A0B1F   UID Size            04 (4)
│ │ │ │ -A0B20   UID                 00000000 (0)
│ │ │ │ -A0B24   GID Size            04 (4)
│ │ │ │ -A0B25   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0B29 CENTRAL HEADER #62    02014B50 (33639248)
│ │ │ │ -A0B2D Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0B2E Created OS            03 (3) 'Unix'
│ │ │ │ -A0B2F Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0B30 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0B31 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0B33 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0B35 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0B39 CRC                   396B41A9 (963330473)
│ │ │ │ -A0B3D Compressed Size       00001ABA (6842)
│ │ │ │ -A0B41 Uncompressed Size     00005F39 (24377)
│ │ │ │ -A0B45 Filename Length       0017 (23)
│ │ │ │ -A0B47 Extra Length          0018 (24)
│ │ │ │ -A0B49 Comment Length        0000 (0)
│ │ │ │ -A0B4B Disk Start            0000 (0)
│ │ │ │ -A0B4D Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0B4F Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0B53 Local Header Offset   0006F0AD (454829)
│ │ │ │ -A0B57 Filename              'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0B57: Filename 'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0B6E Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0B70   Length              0005 (5)
│ │ │ │ -A0B72   Flags               01 (1) 'Modification'
│ │ │ │ -A0B73   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0B77 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0B79   Length              000B (11)
│ │ │ │ -A0B7B   Version             01 (1)
│ │ │ │ -A0B7C   UID Size            04 (4)
│ │ │ │ -A0B7D   UID                 00000000 (0)
│ │ │ │ -A0B81   GID Size            04 (4)
│ │ │ │ -A0B82   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0B86 CENTRAL HEADER #63    02014B50 (33639248)
│ │ │ │ -A0B8A Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0B8B Created OS            03 (3) 'Unix'
│ │ │ │ -A0B8C Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0B8D Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0B8E General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0B90 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0B92 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0B96 CRC                   3DD8544C (1037587532)
│ │ │ │ -A0B9A Compressed Size       00000ED1 (3793)
│ │ │ │ -A0B9E Uncompressed Size     000038DE (14558)
│ │ │ │ -A0BA2 Filename Length       0023 (35)
│ │ │ │ -A0BA4 Extra Length          0018 (24)
│ │ │ │ -A0BA6 Comment Length        0000 (0)
│ │ │ │ -A0BA8 Disk Start            0000 (0)
│ │ │ │ -A0BAA Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0BAC Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0BB0 Local Header Offset   00070BB8 (461752)
│ │ │ │ -A0BB4 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0BB4: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0BD7 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0BD9   Length              0005 (5)
│ │ │ │ -A0BDB   Flags               01 (1) 'Modification'
│ │ │ │ -A0BDC   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0BE0 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0BE2   Length              000B (11)
│ │ │ │ -A0BE4   Version             01 (1)
│ │ │ │ -A0BE5   UID Size            04 (4)
│ │ │ │ -A0BE6   UID                 00000000 (0)
│ │ │ │ -A0BEA   GID Size            04 (4)
│ │ │ │ -A0BEB   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0BEF CENTRAL HEADER #64    02014B50 (33639248)
│ │ │ │ -A0BF3 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0BF4 Created OS            03 (3) 'Unix'
│ │ │ │ -A0BF5 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0BF6 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0BF7 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0BF9 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0BFB Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0BFF CRC                   2DB7929F (767005343)
│ │ │ │ -A0C03 Compressed Size       00000113 (275)
│ │ │ │ -A0C07 Uncompressed Size     000001F3 (499)
│ │ │ │ -A0C0B Filename Length       001B (27)
│ │ │ │ -A0C0D Extra Length          0018 (24)
│ │ │ │ -A0C0F Comment Length        0000 (0)
│ │ │ │ -A0C11 Disk Start            0000 (0)
│ │ │ │ -A0C13 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0C15 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0C19 Local Header Offset   00071AE6 (465638)
│ │ │ │ -A0C1D Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0C1D: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0C38 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0C3A   Length              0005 (5)
│ │ │ │ -A0C3C   Flags               01 (1) 'Modification'
│ │ │ │ -A0C3D   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0C41 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0C43   Length              000B (11)
│ │ │ │ -A0C45   Version             01 (1)
│ │ │ │ -A0C46   UID Size            04 (4)
│ │ │ │ -A0C47   UID                 00000000 (0)
│ │ │ │ -A0C4B   GID Size            04 (4)
│ │ │ │ -A0C4C   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0C50 CENTRAL HEADER #65    02014B50 (33639248)
│ │ │ │ -A0C54 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0C55 Created OS            03 (3) 'Unix'
│ │ │ │ -A0C56 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0C57 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0C58 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0C5A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0C5C Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0C60 CRC                   B802BFBB (3087187899)
│ │ │ │ -A0C64 Compressed Size       0000188E (6286)
│ │ │ │ -A0C68 Uncompressed Size     00008FAD (36781)
│ │ │ │ -A0C6C Filename Length       001D (29)
│ │ │ │ -A0C6E Extra Length          0018 (24)
│ │ │ │ -A0C70 Comment Length        0000 (0)
│ │ │ │ -A0C72 Disk Start            0000 (0)
│ │ │ │ -A0C74 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0C76 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0C7A Local Header Offset   00071C4E (465998)
│ │ │ │ -A0C7E Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0C7E: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0C9B Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0C9D   Length              0005 (5)
│ │ │ │ -A0C9F   Flags               01 (1) 'Modification'
│ │ │ │ -A0CA0   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0CA4 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0CA6   Length              000B (11)
│ │ │ │ -A0CA8   Version             01 (1)
│ │ │ │ -A0CA9   UID Size            04 (4)
│ │ │ │ -A0CAA   UID                 00000000 (0)
│ │ │ │ -A0CAE   GID Size            04 (4)
│ │ │ │ -A0CAF   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0CB3 CENTRAL HEADER #66    02014B50 (33639248)
│ │ │ │ -A0CB7 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0CB8 Created OS            03 (3) 'Unix'
│ │ │ │ -A0CB9 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0CBA Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0CBB General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0CBD Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0CBF Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0CC3 CRC                   516C0F5D (1366036317)
│ │ │ │ -A0CC7 Compressed Size       0000164A (5706)
│ │ │ │ -A0CCB Uncompressed Size     00003A9C (15004)
│ │ │ │ -A0CCF Filename Length       0015 (21)
│ │ │ │ -A0CD1 Extra Length          0018 (24)
│ │ │ │ -A0CD3 Comment Length        0000 (0)
│ │ │ │ -A0CD5 Disk Start            0000 (0)
│ │ │ │ -A0CD7 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0CD9 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0CDD Local Header Offset   00073533 (472371)
│ │ │ │ -A0CE1 Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0CE1: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0CF6 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0CF8   Length              0005 (5)
│ │ │ │ -A0CFA   Flags               01 (1) 'Modification'
│ │ │ │ -A0CFB   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0CFF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0D01   Length              000B (11)
│ │ │ │ -A0D03   Version             01 (1)
│ │ │ │ -A0D04   UID Size            04 (4)
│ │ │ │ -A0D05   UID                 00000000 (0)
│ │ │ │ -A0D09   GID Size            04 (4)
│ │ │ │ -A0D0A   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0D0E CENTRAL HEADER #67    02014B50 (33639248)
│ │ │ │ -A0D12 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0D13 Created OS            03 (3) 'Unix'
│ │ │ │ -A0D14 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0D15 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0D16 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0D18 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0D1A Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0D1E CRC                   3708308C (923283596)
│ │ │ │ -A0D22 Compressed Size       00003B4E (15182)
│ │ │ │ -A0D26 Uncompressed Size     00011CC3 (72899)
│ │ │ │ -A0D2A Filename Length       0016 (22)
│ │ │ │ -A0D2C Extra Length          0018 (24)
│ │ │ │ -A0D2E Comment Length        0000 (0)
│ │ │ │ -A0D30 Disk Start            0000 (0)
│ │ │ │ -A0D32 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0D34 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0D38 Local Header Offset   00074BCC (478156)
│ │ │ │ -A0D3C Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0D3C: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0D52 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0D54   Length              0005 (5)
│ │ │ │ -A0D56   Flags               01 (1) 'Modification'
│ │ │ │ -A0D57   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0D5B Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0D5D   Length              000B (11)
│ │ │ │ -A0D5F   Version             01 (1)
│ │ │ │ -A0D60   UID Size            04 (4)
│ │ │ │ -A0D61   UID                 00000000 (0)
│ │ │ │ -A0D65   GID Size            04 (4)
│ │ │ │ -A0D66   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0D6A CENTRAL HEADER #68    02014B50 (33639248)
│ │ │ │ -A0D6E Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0D6F Created OS            03 (3) 'Unix'
│ │ │ │ -A0D70 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0D71 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0D72 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0D74 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0D76 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0D7A CRC                   7096BE5F (1888927327)
│ │ │ │ -A0D7E Compressed Size       00003EC5 (16069)
│ │ │ │ -A0D82 Uncompressed Size     0001C79C (116636)
│ │ │ │ -A0D86 Filename Length       0019 (25)
│ │ │ │ -A0D88 Extra Length          0018 (24)
│ │ │ │ -A0D8A Comment Length        0000 (0)
│ │ │ │ -A0D8C Disk Start            0000 (0)
│ │ │ │ -A0D8E Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0D90 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0D94 Local Header Offset   0007876A (493418)
│ │ │ │ -A0D98 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0D98: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0DB1 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0DB3   Length              0005 (5)
│ │ │ │ -A0DB5   Flags               01 (1) 'Modification'
│ │ │ │ -A0DB6   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0DBA Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0DBC   Length              000B (11)
│ │ │ │ -A0DBE   Version             01 (1)
│ │ │ │ -A0DBF   UID Size            04 (4)
│ │ │ │ -A0DC0   UID                 00000000 (0)
│ │ │ │ -A0DC4   GID Size            04 (4)
│ │ │ │ -A0DC5   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0DC9 CENTRAL HEADER #69    02014B50 (33639248)
│ │ │ │ -A0DCD Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0DCE Created OS            03 (3) 'Unix'
│ │ │ │ -A0DCF Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0DD0 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0DD1 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0DD3 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0DD5 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0DD9 CRC                   9FB04586 (2679129478)
│ │ │ │ -A0DDD Compressed Size       00000835 (2101)
│ │ │ │ -A0DE1 Uncompressed Size     00003384 (13188)
│ │ │ │ -A0DE5 Filename Length       0011 (17)
│ │ │ │ -A0DE7 Extra Length          0018 (24)
│ │ │ │ -A0DE9 Comment Length        0000 (0)
│ │ │ │ -A0DEB Disk Start            0000 (0)
│ │ │ │ -A0DED Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0DEF Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0DF3 Local Header Offset   0007C682 (509570)
│ │ │ │ -A0DF7 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0DF7: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0E08 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0E0A   Length              0005 (5)
│ │ │ │ -A0E0C   Flags               01 (1) 'Modification'
│ │ │ │ -A0E0D   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0E11 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0E13   Length              000B (11)
│ │ │ │ -A0E15   Version             01 (1)
│ │ │ │ -A0E16   UID Size            04 (4)
│ │ │ │ -A0E17   UID                 00000000 (0)
│ │ │ │ -A0E1B   GID Size            04 (4)
│ │ │ │ -A0E1C   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0E20 CENTRAL HEADER #70    02014B50 (33639248)
│ │ │ │ -A0E24 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0E25 Created OS            03 (3) 'Unix'
│ │ │ │ -A0E26 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0E27 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0E28 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0E2A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0E2C Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0E30 CRC                   48157666 (1209366118)
│ │ │ │ -A0E34 Compressed Size       000051AB (20907)
│ │ │ │ -A0E38 Uncompressed Size     0001FBE0 (130016)
│ │ │ │ -A0E3C Filename Length       0015 (21)
│ │ │ │ -A0E3E Extra Length          0018 (24)
│ │ │ │ -A0E40 Comment Length        0000 (0)
│ │ │ │ -A0E42 Disk Start            0000 (0)
│ │ │ │ -A0E44 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0E46 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0E4A Local Header Offset   0007CF02 (511746)
│ │ │ │ -A0E4E Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0E4E: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0E63 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0E65   Length              0005 (5)
│ │ │ │ -A0E67   Flags               01 (1) 'Modification'
│ │ │ │ -A0E68   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0E6C Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0E6E   Length              000B (11)
│ │ │ │ -A0E70   Version             01 (1)
│ │ │ │ -A0E71   UID Size            04 (4)
│ │ │ │ -A0E72   UID                 00000000 (0)
│ │ │ │ -A0E76   GID Size            04 (4)
│ │ │ │ -A0E77   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0E7B CENTRAL HEADER #71    02014B50 (33639248)
│ │ │ │ -A0E7F Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0E80 Created OS            03 (3) 'Unix'
│ │ │ │ -A0E81 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0E82 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0E83 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0E85 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0E87 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0E8B CRC                   11C15F57 (297885527)
│ │ │ │ -A0E8F Compressed Size       00001B09 (6921)
│ │ │ │ -A0E93 Uncompressed Size     000081D0 (33232)
│ │ │ │ -A0E97 Filename Length       0019 (25)
│ │ │ │ -A0E99 Extra Length          0018 (24)
│ │ │ │ -A0E9B Comment Length        0000 (0)
│ │ │ │ -A0E9D Disk Start            0000 (0)
│ │ │ │ -A0E9F Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0EA1 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0EA5 Local Header Offset   000820FC (532732)
│ │ │ │ -A0EA9 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0EA9: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0EC2 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0EC4   Length              0005 (5)
│ │ │ │ -A0EC6   Flags               01 (1) 'Modification'
│ │ │ │ -A0EC7   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0ECB Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0ECD   Length              000B (11)
│ │ │ │ -A0ECF   Version             01 (1)
│ │ │ │ -A0ED0   UID Size            04 (4)
│ │ │ │ -A0ED1   UID                 00000000 (0)
│ │ │ │ -A0ED5   GID Size            04 (4)
│ │ │ │ -A0ED6   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0EDA CENTRAL HEADER #72    02014B50 (33639248)
│ │ │ │ -A0EDE Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0EDF Created OS            03 (3) 'Unix'
│ │ │ │ -A0EE0 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0EE1 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0EE2 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0EE4 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0EE6 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0EEA CRC                   ECB3AEBD (3971198653)
│ │ │ │ -A0EEE Compressed Size       00000D99 (3481)
│ │ │ │ -A0EF2 Uncompressed Size     00002EA0 (11936)
│ │ │ │ -A0EF6 Filename Length       0018 (24)
│ │ │ │ -A0EF8 Extra Length          0018 (24)
│ │ │ │ -A0EFA Comment Length        0000 (0)
│ │ │ │ -A0EFC Disk Start            0000 (0)
│ │ │ │ -A0EFE Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0F00 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0F04 Local Header Offset   00083C58 (539736)
│ │ │ │ -A0F08 Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0F08: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0F20 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0F22   Length              0005 (5)
│ │ │ │ -A0F24   Flags               01 (1) 'Modification'
│ │ │ │ -A0F25   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0F29 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0F2B   Length              000B (11)
│ │ │ │ -A0F2D   Version             01 (1)
│ │ │ │ -A0F2E   UID Size            04 (4)
│ │ │ │ -A0F2F   UID                 00000000 (0)
│ │ │ │ -A0F33   GID Size            04 (4)
│ │ │ │ -A0F34   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0F38 CENTRAL HEADER #73    02014B50 (33639248)
│ │ │ │ -A0F3C Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0F3D Created OS            03 (3) 'Unix'
│ │ │ │ -A0F3E Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0F3F Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0F40 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0F42 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0F44 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0F48 CRC                   037E3A9E (58604190)
│ │ │ │ -A0F4C Compressed Size       000001E1 (481)
│ │ │ │ -A0F50 Uncompressed Size     00000324 (804)
│ │ │ │ -A0F54 Filename Length       0011 (17)
│ │ │ │ -A0F56 Extra Length          0018 (24)
│ │ │ │ -A0F58 Comment Length        0000 (0)
│ │ │ │ -A0F5A Disk Start            0000 (0)
│ │ │ │ -A0F5C Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0F5E Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0F62 Local Header Offset   00084A43 (543299)
│ │ │ │ -A0F66 Filename              'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0F66: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0F77 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0F79   Length              0005 (5)
│ │ │ │ -A0F7B   Flags               01 (1) 'Modification'
│ │ │ │ -A0F7C   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0F80 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0F82   Length              000B (11)
│ │ │ │ -A0F84   Version             01 (1)
│ │ │ │ -A0F85   UID Size            04 (4)
│ │ │ │ -A0F86   UID                 00000000 (0)
│ │ │ │ -A0F8A   GID Size            04 (4)
│ │ │ │ -A0F8B   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0F8F CENTRAL HEADER #74    02014B50 (33639248)
│ │ │ │ -A0F93 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0F94 Created OS            03 (3) 'Unix'
│ │ │ │ -A0F95 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0F96 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0F97 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0F99 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0F9B Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0F9F CRC                   55187787 (1427666823)
│ │ │ │ -A0FA3 Compressed Size       000006C3 (1731)
│ │ │ │ -A0FA7 Uncompressed Size     0000143A (5178)
│ │ │ │ -A0FAB Filename Length       0019 (25)
│ │ │ │ -A0FAD Extra Length          0018 (24)
│ │ │ │ -A0FAF Comment Length        0000 (0)
│ │ │ │ -A0FB1 Disk Start            0000 (0)
│ │ │ │ -A0FB3 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A0FB5 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A0FB9 Local Header Offset   00084C6F (543855)
│ │ │ │ -A0FBD Filename              'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA0FBD: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A0FD6 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A0FD8   Length              0005 (5)
│ │ │ │ -A0FDA   Flags               01 (1) 'Modification'
│ │ │ │ -A0FDB   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0FDF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A0FE1   Length              000B (11)
│ │ │ │ -A0FE3   Version             01 (1)
│ │ │ │ -A0FE4   UID Size            04 (4)
│ │ │ │ -A0FE5   UID                 00000000 (0)
│ │ │ │ -A0FE9   GID Size            04 (4)
│ │ │ │ -A0FEA   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A0FEE CENTRAL HEADER #75    02014B50 (33639248)
│ │ │ │ -A0FF2 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A0FF3 Created OS            03 (3) 'Unix'
│ │ │ │ -A0FF4 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A0FF5 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A0FF6 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A0FF8 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A0FFA Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A0FFE CRC                   B80689A0 (3087436192)
│ │ │ │ -A1002 Compressed Size       00001EAE (7854)
│ │ │ │ -A1006 Uncompressed Size     0000CA81 (51841)
│ │ │ │ -A100A Filename Length       0018 (24)
│ │ │ │ -A100C Extra Length          0018 (24)
│ │ │ │ -A100E Comment Length        0000 (0)
│ │ │ │ -A1010 Disk Start            0000 (0)
│ │ │ │ -A1012 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A1014 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A1018 Local Header Offset   00085385 (545669)
│ │ │ │ -A101C Filename              'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA101C: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A1034 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A1036   Length              0005 (5)
│ │ │ │ -A1038   Flags               01 (1) 'Modification'
│ │ │ │ -A1039   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A103D Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ -A103F   Length              000B (11)
│ │ │ │ -A1041   Version             01 (1)
│ │ │ │ -A1042   UID Size            04 (4)
│ │ │ │ -A1043   UID                 00000000 (0)
│ │ │ │ -A1047   GID Size            04 (4)
│ │ │ │ -A1048   GID                 00000000 (0)
│ │ │ │ -
│ │ │ │ -A104C CENTRAL HEADER #76    02014B50 (33639248)
│ │ │ │ -A1050 Created Zip Spec      3D (61) '6.1'
│ │ │ │ -A1051 Created OS            03 (3) 'Unix'
│ │ │ │ -A1052 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A1053 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A1054 General Purpose Flag  0000 (0)
│ │ │ │ -      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ -A1056 Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A1058 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A105C CRC                   70CE7879 (1892579449)
│ │ │ │ -A1060 Compressed Size       00001BEA (7146)
│ │ │ │ -A1064 Uncompressed Size     0000C5EA (50666)
│ │ │ │ -A1068 Filename Length       0012 (18)
│ │ │ │ -A106A Extra Length          0018 (24)
│ │ │ │ -A106C Comment Length        0000 (0)
│ │ │ │ -A106E Disk Start            0000 (0)
│ │ │ │ -A1070 Int File Attributes   0000 (0)
│ │ │ │ -      [Bit 0]               0 'Binary Data'
│ │ │ │ -A1072 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A1076 Local Header Offset   00087285 (553605)
│ │ │ │ -A107A Filename              'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA107A: Filename 'XXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A108C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A1091   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A1095 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A10A0   GID                 00000000 (0)
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│ │ │ │ -A10AA Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A10AB Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A10AE Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A10B0 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A10B4 CRC                   A289EFE2 (2726948834)
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│ │ │ │ -A10C0 Filename Length       0016 (22)
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│ │ │ │ -A10C4 Comment Length        0000 (0)
│ │ │ │ -A10C6 Disk Start            0000 (0)
│ │ │ │ -A10C8 Int File Attributes   0000 (0)
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│ │ │ │ -A10CE Local Header Offset   00088EBB (560827)
│ │ │ │ -A10D2 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA10D2: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A10E8 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A10EA   Length              0005 (5)
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│ │ │ │ -A10F1 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A1106 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ -A1107 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A110A Compression Method    0008 (8) 'Deflated'
│ │ │ │ -A110C Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A1110 CRC                   A54D678B (2773313419)
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│ │ │ │ -A1118 Uncompressed Size     0000D050 (53328)
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│ │ │ │ -A1120 Comment Length        0000 (0)
│ │ │ │ -A1122 Disk Start            0000 (0)
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│ │ │ │ -A112E Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA112E: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A1148 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A1151 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A1167 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A116A Compression Method    0008 (8) 'Deflated'
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│ │ │ │ -A1170 CRC                   80E743AF (2162639791)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA118E: Filename 'XXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
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│ │ │ │ -A11AF Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A11C5 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A11CA Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A11CE CRC                   F5E2129F (4125233823)
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│ │ │ │ -A11DA Filename Length       0015 (21)
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│ │ │ │ -A11DE Comment Length        0000 (0)
│ │ │ │ -A11E0 Disk Start            0000 (0)
│ │ │ │ -A11E2 Int File Attributes   0000 (0)
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│ │ │ │ -A11E8 Local Header Offset   0008E111 (581905)
│ │ │ │ -A11EC Filename              'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA11EC: Filename 'XXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A1201 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A120A Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A1229 CRC                   F5E2129F (4125233823)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA1247: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A1263 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A1265   Length              0005 (5)
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│ │ │ │ -A1282 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A1287 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A128B CRC                   FC95F24B (4237685323)
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│ │ │ │ -A1297 Filename Length       0016 (22)
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│ │ │ │ -A129F Int File Attributes   0000 (0)
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA12A9: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
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│ │ │ │ -A12DE Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA1305: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A131B Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A1324 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A1343 CRC                   FFF9C4D2 (4294558930)
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│ │ │ │ -A134F Filename Length       0016 (22)
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│ │ │ │ -A1353 Comment Length        0000 (0)
│ │ │ │ -A1355 Disk Start            0000 (0)
│ │ │ │ -A1357 Int File Attributes   0000 (0)
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│ │ │ │ -A1359 Ext File Attributes   01A40000 (27525120)
│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A135D Local Header Offset   000936CD (603853)
│ │ │ │ -A1361 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA1361: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A1377 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ -A1379   Length              0005 (5)
│ │ │ │ -A137B   Flags               01 (1) 'Modification'
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│ │ │ │ -A1380 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A1384   Version             01 (1)
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│ │ │ │ -A1393 Created Zip Spec      3D (61) '6.1'
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│ │ │ │ -A1395 Extract Zip Spec      0A (10) '1.0'
│ │ │ │ -A1396 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ -A1397 General Purpose Flag  0000 (0)
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│ │ │ │ -A139F CRC                   A1037E8E (2701360782)
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│ │ │ │ -A13AB Filename Length       0016 (22)
│ │ │ │ -A13AD Extra Length          0018 (24)
│ │ │ │ -A13AF Comment Length        0000 (0)
│ │ │ │ -A13B1 Disk Start            0000 (0)
│ │ │ │ -A13B3 Int File Attributes   0000 (0)
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│ │ │ │ -      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ -A13B9 Local Header Offset   00094AAC (608940)
│ │ │ │ -A13BD Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#
│ │ │ │ -# WARNING: Offset 0xA13BD: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ -#          Zero length filename
│ │ │ │ -#
│ │ │ │ -A13D3 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ -A13D8   Modification Time   69F9F608 (1777989128) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A13DC Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ -A13F2 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -A13F7 Modification Time     5CA56E84 (1554345604) 'Tue May  5 13:52:08 2026'
│ │ │ │ -A13FB CRC                   5E9E64F1 (1587438833)
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -A144E Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ -#          Zero length filename
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│ │ │ │ -#
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│ │ │ │ -#          Zero length filename
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│ │ │ │ +A0AD3 General Purpose Flag  0000 (0)
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│ │ │ │ +A0AD5 Compression Method    0008 (8) 'Deflated'
│ │ │ │ +A0AD7 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +A0ADB CRC                   687822FC (1752703740)
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│ │ │ │ +A0AE3 Uncompressed Size     00003A2D (14893)
│ │ │ │ +A0AE7 Filename Length       0024 (36)
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│ │ │ │ +A0AEF Int File Attributes   0000 (0)
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│ │ │ │ +A0AF5 Local Header Offset   0006E14B (450891)
│ │ │ │ +A0AF9 Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0xA0AF9: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +A0B1D Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +A0B26 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +A0B35 CENTRAL HEADER #62    02014B50 (33639248)
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│ │ │ │ +A0B3C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +A0B3D General Purpose Flag  0000 (0)
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│ │ │ │ +A0B41 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +A0B45 CRC                   726CE69D (1919739549)
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│ │ │ │ +# WARNING: Offset 0xA0B63: Filename 'XXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +A0B7A Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +A0B99 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +A0B9E Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +A0BA2 CRC                   3DD8544C (1037587532)
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│ │ │ │ +A0BAE Filename Length       0023 (35)
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│ │ │ │ +A0BB6 Int File Attributes   0000 (0)
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│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0xA0BC0: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +A0BE3 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +A0BEC Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
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│ │ │ │ +A0C02 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +A0C07 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +A0C0B CRC                   2DB7929F (767005343)
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│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0xA0C29: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +A0C44 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +A0C63 Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +A0C68 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +A0C6C CRC                   8C77D705 (2356664069)
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│ │ │ │ +# WARNING: Offset 0xA0C8A: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
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│ │ │ │ +A0D2A CRC                   A1AA00A3 (2712273059)
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│ │ │ │ +# WARNING: Offset 0xA0DA4: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +A0DBD Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +A0DDC Extract OS            00 (0) 'MS-DOS'
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│ │ │ │ +# WARNING: Offset 0xA0E03: Filename 'XXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
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│ │ │ │ +A0E14 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
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│ │ │ │ +A0E38 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
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│ │ │ │ +A1562   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +A1566 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +A1568   Length              000B (11)
│ │ │ │ +A156A   Version             01 (1)
│ │ │ │ +A156B   UID Size            04 (4)
│ │ │ │ +A156C   UID                 00000000 (0)
│ │ │ │ +A1570   GID Size            04 (4)
│ │ │ │ +A1571   GID                 00000000 (0)
│ │ │ │ +
│ │ │ │ +A1575 CENTRAL HEADER #90    02014B50 (33639248)
│ │ │ │ +A1579 Created Zip Spec      3D (61) '6.1'
│ │ │ │ +A157A Created OS            03 (3) 'Unix'
│ │ │ │ +A157B Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +A157C Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +A157D General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +A157F Compression Method    0008 (8) 'Deflated'
│ │ │ │ +A1581 Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +A1585 CRC                   DCB3B516 (3702764822)
│ │ │ │ +A1589 Compressed Size       000000AE (174)
│ │ │ │ +A158D Uncompressed Size     000000FC (252)
│ │ │ │ +A1591 Filename Length       0016 (22)
│ │ │ │ +A1593 Extra Length          0018 (24)
│ │ │ │ +A1595 Comment Length        0000 (0)
│ │ │ │ +A1597 Disk Start            0000 (0)
│ │ │ │ +A1599 Int File Attributes   0000 (0)
│ │ │ │ +      [Bit 0]               0 'Binary Data'
│ │ │ │ +A159B Ext File Attributes   01A40000 (27525120)
│ │ │ │ +      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ +A159F Local Header Offset   0009F333 (652083)
│ │ │ │ +A15A3 Filename              'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0xA15A3: Filename 'XXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +A15B9 Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +A15BB   Length              0005 (5)
│ │ │ │ +A15BD   Flags               01 (1) 'Modification'
│ │ │ │ +A15BE   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +A15C2 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +A15C4   Length              000B (11)
│ │ │ │ +A15C6   Version             01 (1)
│ │ │ │ +A15C7   UID Size            04 (4)
│ │ │ │ +A15C8   UID                 00000000 (0)
│ │ │ │ +A15CC   GID Size            04 (4)
│ │ │ │ +A15CD   GID                 00000000 (0)
│ │ │ │ +
│ │ │ │ +A15D1 CENTRAL HEADER #91    02014B50 (33639248)
│ │ │ │ +A15D5 Created Zip Spec      3D (61) '6.1'
│ │ │ │ +A15D6 Created OS            03 (3) 'Unix'
│ │ │ │ +A15D7 Extract Zip Spec      14 (20) '2.0'
│ │ │ │ +A15D8 Extract OS            00 (0) 'MS-DOS'
│ │ │ │ +A15D9 General Purpose Flag  0000 (0)
│ │ │ │ +      [Bits 1-2]            0 'Normal Compression'
│ │ │ │ +A15DB Compression Method    0008 (8) 'Deflated'
│ │ │ │ +A15DD Modification Time     5CAABDEA (1554693610) 'Sun May 10 23:47:20 2026'
│ │ │ │ +A15E1 CRC                   58439733 (1480824627)
│ │ │ │ +A15E5 Compressed Size       00000077 (119)
│ │ │ │ +A15E9 Uncompressed Size     000000A2 (162)
│ │ │ │ +A15ED Filename Length       002D (45)
│ │ │ │ +A15EF Extra Length          0018 (24)
│ │ │ │ +A15F1 Comment Length        0000 (0)
│ │ │ │ +A15F3 Disk Start            0000 (0)
│ │ │ │ +A15F5 Int File Attributes   0000 (0)
│ │ │ │ +      [Bit 0]               0 'Binary Data'
│ │ │ │ +A15F7 Ext File Attributes   01A40000 (27525120)
│ │ │ │ +      [Bits 16-24]          01A4 (420) 'Unix attrib: rw-r--r--'
│ │ │ │ +A15FB Local Header Offset   0009F431 (652337)
│ │ │ │ +A15FF Filename              'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#
│ │ │ │ +# WARNING: Offset 0xA15FF: Filename 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
│ │ │ │ +#          Zero length filename
│ │ │ │ +#
│ │ │ │ +A162C Extra ID #1           5455 (21589) 'Extended Timestamp [UT]'
│ │ │ │ +A162E   Length              0005 (5)
│ │ │ │ +A1630   Flags               01 (1) 'Modification'
│ │ │ │ +A1631   Modification Time   6A011909 (1778456841) 'Sun May 10 23:47:21 2026'
│ │ │ │ +A1635 Extra ID #2           7875 (30837) 'Unix Extra type 3 [ux]'
│ │ │ │ +A1637   Length              000B (11)
│ │ │ │ +A1639   Version             01 (1)
│ │ │ │ +A163A   UID Size            04 (4)
│ │ │ │ +A163B   UID                 00000000 (0)
│ │ │ │ +A163F   GID Size            04 (4)
│ │ │ │ +A1640   GID                 00000000 (0)
│ │ │ │ +
│ │ │ │ +A1644 END CENTRAL HEADER    06054B50 (101010256)
│ │ │ │ +A1648 Number of this disk   0000 (0)
│ │ │ │ +A164A Central Dir Disk no   0000 (0)
│ │ │ │ +A164C Entries in this disk  005B (91)
│ │ │ │ +A164E Total Entries         005B (91)
│ │ │ │ +A1650 Size of Central Dir   00002135 (8501)
│ │ │ │ +A1654 Offset to Central Dir 0009F50F (652559)
│ │ │ │ +A1658 Comment Length        0000 (0)
│ │ │ │  #
│ │ │ │  # Warning Count: 182
│ │ │ │  #
│ │ │ │  # Done
│ │ │ ├── filetype from file(1)
│ │ │ │ @@ -1 +1 @@
│ │ │ │ -Zip archive data, made by v6.1 UNIX, extract using at least v1.0, last modified May 05 2026 13:52:08, uncompressed size 20, method=store
│ │ │ │ +Zip archive data, made by v6.1 UNIX, extract using at least v1.0, last modified May 10 2026 23:47:20, uncompressed size 20, method=store
│ │ │ ├── OEBPS/typespec.xhtml
│ │ │ │ @@ -143,122 +143,122 @@
│ │ │ │  and optional <code class="inline">(=&gt;)</code> association types. If an association type is mandatory, an
│ │ │ │  association with that type needs to be present. In the case of an optional
│ │ │ │  association type it is not required for the key type to be present.</p><p>The notation <code class="inline">#{}</code> specifies the singleton type for the empty map. Note that
│ │ │ │  this notation is not a shorthand for the <a href="../../../lib/../erts/doc/html/erlang.html#t:map/0"><code class="inline">map/0</code></a> type.</p><p>For convenience, the following types are also built-in. They can be thought as
│ │ │ │  predefined aliases for the type unions also shown in the table.</p><p><a href="" id="builtin_types"></a></p><table><thead><tr><th style="text-align: left;"><em>Built-in type</em></th><th style="text-align: left;"><em>Defined as</em></th></tr></thead><tbody><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:term/0"><code class="inline">term/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:any/0"><code class="inline">any/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:binary/0"><code class="inline">binary/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:_*8&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_binary/0"><code class="inline">nonempty_binary/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:8, _:_*8&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:bitstring/0"><code class="inline">bitstring/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:_*1&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_bitstring/0"><code class="inline">nonempty_bitstring/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:1, _:_*1&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a></td><td style="text-align: left;"><code class="inline">'false'</code> | <code class="inline">'true'</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:byte/0"><code class="inline">byte/0</code></a></td><td style="text-align: left;"><code class="inline">0..255</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:char/0"><code class="inline">char/0</code></a></td><td style="text-align: left;"><code class="inline">0..16#10ffff</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nil/0"><code class="inline">nil/0</code></a></td><td style="text-align: left;"><code class="inline">[]</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:number/0"><code class="inline">number/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:integer/0"><code class="inline">integer/0</code></a> | <a href="../../../lib/../erts/doc/html/erlang.html#t:float/0"><code class="inline">float/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:list/0"><code class="inline">list/0</code></a></td><td style="text-align: left;"><code class="inline">[any()]</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:maybe_improper_list/0"><code class="inline">maybe_improper_list/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:maybe_improper_list/2"><code class="inline">maybe_improper_list(any(), any())</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_list/0"><code class="inline">nonempty_list/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_list/1"><code class="inline">nonempty_list(any())</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:string/0"><code class="inline">string/0</code></a></td><td style="text-align: left;"><code class="inline">[char()]</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:nonempty_string/0"><code class="inline">nonempty_string/0</code></a></td><td style="text-align: left;"><code class="inline">[char(),...]</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:iodata/0"><code class="inline">iodata/0</code></a></td><td style="text-align: left;"><code class="inline">iolist()</code> | <code class="inline">binary()</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:iolist/0"><code class="inline">iolist/0</code></a></td><td style="text-align: left;"><code class="inline">maybe_improper_list(byte()</code> | <code class="inline">binary()</code> | <code class="inline">iolist(), binary()</code> | <code class="inline">[])</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:map/0"><code class="inline">map/0</code></a></td><td style="text-align: left;"><code class="inline">#{any() =&gt; any()}</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:function/0"><code class="inline">function/0</code></a></td><td style="text-align: left;"><code class="inline">fun()</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:module/0"><code class="inline">module/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:atom/0"><code class="inline">atom/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:mfa/0"><code class="inline">mfa/0</code></a></td><td style="text-align: left;"><code class="inline">{module(),atom(),arity()}</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:arity/0"><code class="inline">arity/0</code></a></td><td style="text-align: left;"><code class="inline">0..255</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:identifier/0"><code class="inline">identifier/0</code></a></td><td style="text-align: left;"><code class="inline">pid()</code> | <code class="inline">port()</code> | <code class="inline">reference()</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#node/0"><code class="inline">node/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:atom/0"><code class="inline">atom/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:timeout/0"><code class="inline">timeout/0</code></a></td><td style="text-align: left;"><code class="inline">'infinity'</code> | <code class="inline">non_neg_integer()</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a></td><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:none/0"><code class="inline">none/0</code></a></td></tr></tbody></table><p><em>Table: Built-in types, predefined aliases</em></p><p>In addition, the following three built-in types exist and can be thought as
│ │ │ │  defined below, though strictly their &quot;type definition&quot; is not valid syntax
│ │ │ │  according to the type language defined above.</p><table><thead><tr><th style="text-align: left;"><em>Built-in type</em></th><th style="text-align: left;"><em>Can be thought defined by the syntax</em></th></tr></thead><tbody><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:non_neg_integer/0"><code class="inline">non_neg_integer/0</code></a></td><td style="text-align: left;"><code class="inline">0..</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:pos_integer/0"><code class="inline">pos_integer/0</code></a></td><td style="text-align: left;"><code class="inline">1..</code></td></tr><tr><td style="text-align: left;"><a href="../../../lib/../erts/doc/html/erlang.html#t:neg_integer/0"><code class="inline">neg_integer/0</code></a></td><td style="text-align: left;"><code class="inline">..-1</code></td></tr></tbody></table><p><em>Table: Additional built-in types</em></p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The following built-in list types also exist, but they are expected to be
│ │ │ │ -rarely used. Hence, they have long names:</p></section><pre><code class="makeup erlang" translate="no"><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="3738166367-1">(</span><span class="p" data-group-id="3738166367-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="3738166367-2">(</span><span class="nf">any</span><span class="p" data-group-id="3738166367-3">(</span><span class="p" data-group-id="3738166367-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="3738166367-4">(</span><span class="p" data-group-id="3738166367-4">)</span><span class="p" data-group-id="3738166367-2">)</span><span class="w">
│ │ │ │ -</span><span class="nf">nonempty_improper_list</span><span class="p" data-group-id="3738166367-5">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="3738166367-5">)</span><span class="w">
│ │ │ │ -</span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="3738166367-6">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="3738166367-6">)</span></code></pre><p>where the last two types define the set of Erlang terms one would expect.</p><p>Also for convenience, record notation is allowed to be used. Records are
│ │ │ │ -shorthands for the corresponding tuples:</p><pre><code class="makeup erlang" translate="no"><span class="n">Record</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="4967736209-1">{</span><span class="p" data-group-id="4967736209-1">}</span><span class="w">
│ │ │ │ -        </span><span class="p">|</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="4967736209-2">{</span><span class="n">Fields</span><span class="p" data-group-id="4967736209-2">}</span></code></pre><p>Records are extended to possibly contain type information. This is described in
│ │ │ │ +rarely used. Hence, they have long names:</p></section><pre><code class="makeup erlang" translate="no"><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="9687760220-1">(</span><span class="p" data-group-id="9687760220-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="9687760220-2">(</span><span class="nf">any</span><span class="p" data-group-id="9687760220-3">(</span><span class="p" data-group-id="9687760220-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="9687760220-4">(</span><span class="p" data-group-id="9687760220-4">)</span><span class="p" data-group-id="9687760220-2">)</span><span class="w">
│ │ │ │ +</span><span class="nf">nonempty_improper_list</span><span class="p" data-group-id="9687760220-5">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="9687760220-5">)</span><span class="w">
│ │ │ │ +</span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="9687760220-6">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="9687760220-6">)</span></code></pre><p>where the last two types define the set of Erlang terms one would expect.</p><p>Also for convenience, record notation is allowed to be used. Records are
│ │ │ │ +shorthands for the corresponding tuples:</p><pre><code class="makeup erlang" translate="no"><span class="n">Record</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="2300426264-1">{</span><span class="p" data-group-id="2300426264-1">}</span><span class="w">
│ │ │ │ +        </span><span class="p">|</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="2300426264-2">{</span><span class="n">Fields</span><span class="p" data-group-id="2300426264-2">}</span></code></pre><p>Records are extended to possibly contain type information. This is described in
│ │ │ │  <a href="typespec.xhtml#typeinrecords">Type Information in Record Declarations</a>.</p><h3 id="redefining-built-in-types" class="section-heading">
│ │ │ │    <a href="#redefining-built-in-types" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Redefining built-in types</span>
│ │ │ │  </h3>
│ │ │ │  <section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Starting from Erlang/OTP 26, it is permitted to define a type having the same
│ │ │ │  name as a built-in type.</p></section><p>It is recommended to avoid deliberately reusing built-in names because it can be
│ │ │ │  confusing. However, when an Erlang/OTP release introduces a new type, code that
│ │ │ │  happened to define its own type having the same name will continue to work.</p><p>As an example, imagine that the Erlang/OTP 42 release introduces a new type
│ │ │ │ -<code class="inline">gadget()</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="4670681491-1">(</span><span class="p" data-group-id="4670681491-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4670681491-2">{</span><span class="ss">&#39;gadget&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">reference</span><span class="p" data-group-id="4670681491-3">(</span><span class="p" data-group-id="4670681491-3">)</span><span class="p" data-group-id="4670681491-2">}</span><span class="p">.</span></code></pre><p>Further imagine that some code has its own (different) definition of <code class="inline">gadget()</code>,
│ │ │ │ -for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="1281659418-1">(</span><span class="p" data-group-id="1281659418-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1281659418-2">#{</span><span class="p" data-group-id="1281659418-2">}</span><span class="p">.</span></code></pre><p>Since redefinitions are allowed, the code will still compile (but with a
│ │ │ │ +<code class="inline">gadget()</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="4454790584-1">(</span><span class="p" data-group-id="4454790584-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4454790584-2">{</span><span class="ss">&#39;gadget&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">reference</span><span class="p" data-group-id="4454790584-3">(</span><span class="p" data-group-id="4454790584-3">)</span><span class="p" data-group-id="4454790584-2">}</span><span class="p">.</span></code></pre><p>Further imagine that some code has its own (different) definition of <code class="inline">gadget()</code>,
│ │ │ │ +for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="6212842922-1">(</span><span class="p" data-group-id="6212842922-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6212842922-2">#{</span><span class="p" data-group-id="6212842922-2">}</span><span class="p">.</span></code></pre><p>Since redefinitions are allowed, the code will still compile (but with a
│ │ │ │  warning), and Dialyzer will not emit any additional warnings.</p><h2 id="type-declarations-of-user-defined-types" class="section-heading">
│ │ │ │    <a href="#type-declarations-of-user-defined-types" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Type Declarations of User-Defined Types</span>
│ │ │ │  </h2>
│ │ │ │  <p>As seen, the basic syntax of a type is an atom followed by closed parentheses.
│ │ │ │  New types are declared using <code class="inline">-type</code> and <code class="inline">-opaque</code> attributes as in the
│ │ │ │ -following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_struct_type</span><span class="p" data-group-id="1458346185-1">(</span><span class="p" data-group-id="1458346185-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">my_opaq_type</span><span class="p" data-group-id="1458346185-2">(</span><span class="p" data-group-id="1458346185-2">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span></code></pre><p>The type name is the atom <code class="inline">my_struct_type</code>, followed by parentheses. <code class="inline">Type</code> is a
│ │ │ │ +following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_struct_type</span><span class="p" data-group-id="7002966166-1">(</span><span class="p" data-group-id="7002966166-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">my_opaq_type</span><span class="p" data-group-id="7002966166-2">(</span><span class="p" data-group-id="7002966166-2">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span></code></pre><p>The type name is the atom <code class="inline">my_struct_type</code>, followed by parentheses. <code class="inline">Type</code> is a
│ │ │ │  type as defined in the previous section. A current restriction is that <code class="inline">Type</code>
│ │ │ │  can contain only predefined types, or user-defined types which are either of the
│ │ │ │  following:</p><ul><li>Module-local type, that is, with a definition that is present in the code of
│ │ │ │  the module</li><li>Remote type, that is, type defined in, and exported by, other modules; more
│ │ │ │  about this soon.</li></ul><p>For module-local types, the restriction that their definition exists in the
│ │ │ │  module is enforced by the compiler and results in a compilation error. (A
│ │ │ │  similar restriction currently exists for records.)</p><p>Type declarations can also be parameterized by including type variables between
│ │ │ │  the parentheses. The syntax of type variables is the same as Erlang variables,
│ │ │ │  that is, starts with an upper-case letter. These variables is to
│ │ │ │ -appear on the RHS of the definition. A concrete example follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">orddict</span><span class="p" data-group-id="8411261604-1">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="8411261604-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="8411261604-2">[</span><span class="p" data-group-id="8411261604-3">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="8411261604-3">}</span><span class="p" data-group-id="8411261604-2">]</span><span class="p">.</span></code></pre><p>A module can export some types to declare that other modules are allowed to
│ │ │ │ -refer to them as <em>remote types</em>. This declaration has the following form:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="9018218883-1">(</span><span class="p" data-group-id="9018218883-2">[</span><span class="n">T1</span><span class="o">/</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Tk</span><span class="o">/</span><span class="n">Ak</span><span class="p" data-group-id="9018218883-2">]</span><span class="p" data-group-id="9018218883-1">)</span><span class="p">.</span></code></pre><p>Here the <code class="inline">Ti</code>s are atoms (the name of the type) and the <code class="inline">Ai</code>s are their arguments.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="1630552729-1">(</span><span class="p" data-group-id="1630552729-2">[</span><span class="ss">my_struct_type</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">orddict</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1630552729-2">]</span><span class="p" data-group-id="1630552729-1">)</span><span class="p">.</span></code></pre><p>Assuming that these types are exported from module <code class="inline">'mod'</code>, you can refer to
│ │ │ │ -them from other modules using remote type expressions like the following:</p><pre><code class="makeup erlang" translate="no"><span class="nc">mod</span><span class="p">:</span><span class="nf">my_struct_type</span><span class="p" data-group-id="1191842538-1">(</span><span class="p" data-group-id="1191842538-1">)</span><span class="w">
│ │ │ │ -</span><span class="nc">mod</span><span class="p">:</span><span class="nf">orddict</span><span class="p" data-group-id="1191842538-2">(</span><span class="nf">atom</span><span class="p" data-group-id="1191842538-3">(</span><span class="p" data-group-id="1191842538-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1191842538-4">(</span><span class="p" data-group-id="1191842538-4">)</span><span class="p" data-group-id="1191842538-2">)</span></code></pre><p>It is not allowed to refer to types that are not declared as exported.</p><p>Types declared as <code class="inline">opaque</code> represent sets of terms whose structure is not
│ │ │ │ +appear on the RHS of the definition. A concrete example follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">orddict</span><span class="p" data-group-id="2057074612-1">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="2057074612-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="2057074612-2">[</span><span class="p" data-group-id="2057074612-3">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="2057074612-3">}</span><span class="p" data-group-id="2057074612-2">]</span><span class="p">.</span></code></pre><p>A module can export some types to declare that other modules are allowed to
│ │ │ │ +refer to them as <em>remote types</em>. This declaration has the following form:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="7194891391-1">(</span><span class="p" data-group-id="7194891391-2">[</span><span class="n">T1</span><span class="o">/</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Tk</span><span class="o">/</span><span class="n">Ak</span><span class="p" data-group-id="7194891391-2">]</span><span class="p" data-group-id="7194891391-1">)</span><span class="p">.</span></code></pre><p>Here the <code class="inline">Ti</code>s are atoms (the name of the type) and the <code class="inline">Ai</code>s are their arguments.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="2184954461-1">(</span><span class="p" data-group-id="2184954461-2">[</span><span class="ss">my_struct_type</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">orddict</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2184954461-2">]</span><span class="p" data-group-id="2184954461-1">)</span><span class="p">.</span></code></pre><p>Assuming that these types are exported from module <code class="inline">'mod'</code>, you can refer to
│ │ │ │ +them from other modules using remote type expressions like the following:</p><pre><code class="makeup erlang" translate="no"><span class="nc">mod</span><span class="p">:</span><span class="nf">my_struct_type</span><span class="p" data-group-id="4420763550-1">(</span><span class="p" data-group-id="4420763550-1">)</span><span class="w">
│ │ │ │ +</span><span class="nc">mod</span><span class="p">:</span><span class="nf">orddict</span><span class="p" data-group-id="4420763550-2">(</span><span class="nf">atom</span><span class="p" data-group-id="4420763550-3">(</span><span class="p" data-group-id="4420763550-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="4420763550-4">(</span><span class="p" data-group-id="4420763550-4">)</span><span class="p" data-group-id="4420763550-2">)</span></code></pre><p>It is not allowed to refer to types that are not declared as exported.</p><p>Types declared as <code class="inline">opaque</code> represent sets of terms whose structure is not
│ │ │ │  supposed to be visible from outside of their defining module. That is, only the
│ │ │ │  module defining them is allowed to depend on their term structure. Consequently,
│ │ │ │  such types do not make much sense as module local - module local types are not
│ │ │ │  accessible by other modules anyway - and is always to be exported.</p><p>Read more on <a href="opaques.xhtml">Opaques</a></p><p><a href="" id="typeinrecords"></a></p><h2 id="type-information-in-record-declarations" class="section-heading">
│ │ │ │    <a href="#type-information-in-record-declarations" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Type Information in Record Declarations</span>
│ │ │ │  </h2>
│ │ │ │  <p>The types of record fields can be specified in the declaration of the record.
│ │ │ │ -The syntax for this is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4997910520-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4997910520-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="4997910520-2">}</span><span class="p" data-group-id="4997910520-1">)</span><span class="p">.</span></code></pre><p>For fields without type annotations, their type defaults to <code class="inline">any()</code>. That is, the
│ │ │ │ -previous example is a shorthand for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5025236693-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5025236693-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="5025236693-3">(</span><span class="p" data-group-id="5025236693-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="5025236693-2">}</span><span class="p" data-group-id="5025236693-1">)</span><span class="p">.</span></code></pre><p>In the presence of initial values for fields, the type must be declared after
│ │ │ │ -the initialization, as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4737049426-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4737049426-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4737049426-3">[</span><span class="p" data-group-id="4737049426-3">]</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="4737049426-2">}</span><span class="p" data-group-id="4737049426-1">)</span><span class="p">.</span></code></pre><p>The initial values for fields are to be compatible with (that is, a member of)
│ │ │ │ +The syntax for this is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0250080495-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0250080495-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="0250080495-2">}</span><span class="p" data-group-id="0250080495-1">)</span><span class="p">.</span></code></pre><p>For fields without type annotations, their type defaults to <code class="inline">any()</code>. That is, the
│ │ │ │ +previous example is a shorthand for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0646506537-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0646506537-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="0646506537-3">(</span><span class="p" data-group-id="0646506537-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="0646506537-2">}</span><span class="p" data-group-id="0646506537-1">)</span><span class="p">.</span></code></pre><p>In the presence of initial values for fields, the type must be declared after
│ │ │ │ +the initialization, as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9374410077-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9374410077-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9374410077-3">[</span><span class="p" data-group-id="9374410077-3">]</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="9374410077-2">}</span><span class="p" data-group-id="9374410077-1">)</span><span class="p">.</span></code></pre><p>The initial values for fields are to be compatible with (that is, a member of)
│ │ │ │  the corresponding types. This is checked by the compiler and results in a
│ │ │ │  compilation error if a violation is detected.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 19, for fields without initial values, the singleton type
│ │ │ │  <code class="inline">'undefined'</code> was added to all declared types. In other words, the following
│ │ │ │ -two record declarations had identical effects:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0652234326-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0652234326-2">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0652234326-3">(</span><span class="p" data-group-id="0652234326-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="0652234326-4">(</span><span class="p" data-group-id="0652234326-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="0652234326-2">}</span><span class="p" data-group-id="0652234326-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +two record declarations had identical effects:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2108818082-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2108818082-2">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="2108818082-3">(</span><span class="p" data-group-id="2108818082-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="2108818082-4">(</span><span class="p" data-group-id="2108818082-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="2108818082-2">}</span><span class="p" data-group-id="2108818082-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0652234326-5">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0652234326-6">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0652234326-7">(</span><span class="p" data-group-id="0652234326-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="0652234326-8">(</span><span class="p" data-group-id="0652234326-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="0652234326-6">}</span><span class="p" data-group-id="0652234326-5">)</span><span class="p">.</span></code></pre><p>This is no longer the case. If you require <code class="inline">'undefined'</code> in your record field
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2108818082-5">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2108818082-6">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="2108818082-7">(</span><span class="p" data-group-id="2108818082-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="2108818082-8">(</span><span class="p" data-group-id="2108818082-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="2108818082-6">}</span><span class="p" data-group-id="2108818082-5">)</span><span class="p">.</span></code></pre><p>This is no longer the case. If you require <code class="inline">'undefined'</code> in your record field
│ │ │ │  type, you must explicitly add it to the typespec, as in the 2nd example.</p></section><p>Any record, containing type information or not, once defined, can be used as a
│ │ │ │  type using the following syntax:</p><pre><code class="text">#rec{}</code></pre><p>In addition, the record fields can be further specified when using a record type
│ │ │ │  by adding type information about the field as follows:</p><pre><code class="text">#rec{some_field :: Type}</code></pre><p>Any unspecified fields are assumed to have the type in the original record
│ │ │ │  declaration.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>When records are used to create patterns for ETS and Mnesia match functions,
│ │ │ │ -Dialyzer may need some help not to emit bad warnings. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7481563534-1">(</span><span class="p" data-group-id="7481563534-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="7481563534-2">(</span><span class="p" data-group-id="7481563534-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7481563534-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7481563534-4">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="7481563534-5">(</span><span class="p" data-group-id="7481563534-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7481563534-6">(</span><span class="p" data-group-id="7481563534-6">)</span><span class="p" data-group-id="7481563534-4">}</span><span class="p" data-group-id="7481563534-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +Dialyzer may need some help not to emit bad warnings. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="9914303385-1">(</span><span class="p" data-group-id="9914303385-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="9914303385-2">(</span><span class="p" data-group-id="9914303385-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9914303385-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9914303385-4">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="9914303385-5">(</span><span class="p" data-group-id="9914303385-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="9914303385-6">(</span><span class="p" data-group-id="9914303385-6">)</span><span class="p" data-group-id="9914303385-4">}</span><span class="p" data-group-id="9914303385-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="7481563534-7">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="7481563534-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="7481563534-8">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7481563534-9">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="7481563534-9">}</span><span class="p" data-group-id="7481563534-8">)</span><span class="p">.</span></code></pre><p>Dialyzer will emit a warning since <code class="inline">'_'</code> is not in the type of record field
│ │ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="9914303385-7">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="9914303385-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="9914303385-8">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9914303385-9">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="9914303385-9">}</span><span class="p" data-group-id="9914303385-8">)</span><span class="p">.</span></code></pre><p>Dialyzer will emit a warning since <code class="inline">'_'</code> is not in the type of record field
│ │ │ │  <code class="inline">height</code>.</p><p>The recommended way of dealing with this is to declare the smallest record
│ │ │ │  field types to accommodate all your needs, and then create refinements as
│ │ │ │ -needed. The modified example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2051832881-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2051832881-2">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="2051832881-3">(</span><span class="p" data-group-id="2051832881-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="2051832881-4">(</span><span class="p" data-group-id="2051832881-4">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="2051832881-2">}</span><span class="p" data-group-id="2051832881-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +needed. The modified example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6395841344-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6395841344-2">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="6395841344-3">(</span><span class="p" data-group-id="6395841344-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="6395841344-4">(</span><span class="p" data-group-id="6395841344-4">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6395841344-2">}</span><span class="p" data-group-id="6395841344-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">person</span><span class="p" data-group-id="2051832881-5">(</span><span class="p" data-group-id="2051832881-5">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2051832881-6">{</span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="2051832881-7">(</span><span class="p" data-group-id="2051832881-7">)</span><span class="p" data-group-id="2051832881-6">}</span><span class="p">.</span></code></pre><p>In specifications and type declarations the type <code class="inline">person()</code> is to be preferred
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">person</span><span class="p" data-group-id="6395841344-5">(</span><span class="p" data-group-id="6395841344-5">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6395841344-6">{</span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="6395841344-7">(</span><span class="p" data-group-id="6395841344-7">)</span><span class="p" data-group-id="6395841344-6">}</span><span class="p">.</span></code></pre><p>In specifications and type declarations the type <code class="inline">person()</code> is to be preferred
│ │ │ │  before <code class="inline">#person{}</code>.</p></section><h2 id="specifications-for-functions" class="section-heading">
│ │ │ │    <a href="#specifications-for-functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Specifications for Functions</span>
│ │ │ │  </h2>
│ │ │ │  <p>A specification (or contract) for a function is given using the <code class="inline">-spec</code>
│ │ │ │  attribute. The general format is as follows:</p><pre><code class="text">-spec Function(ArgType1, ..., ArgTypeN) -&gt; ReturnType.</code></pre><p>An implementation of the function with the same name <code class="inline">Function</code> must exist in
│ │ │ │  the current module, and the arity of the function must match the number of
│ │ │ │  arguments, otherwise the compilation fails.</p><p>The following longer format with module name is also valid as long as <code class="inline">Module</code>
│ │ │ │  is the name of the current module. This can be useful for documentation
│ │ │ │  purposes.</p><pre><code class="text">-spec Module:Function(ArgType1, ..., ArgTypeN) -&gt; ReturnType.</code></pre><p>Also, for documentation purposes, argument names can be given:</p><pre><code class="text">-spec Function(ArgName1 :: Type1, ..., ArgNameN :: TypeN) -&gt; RT.</code></pre><p>A function specification can be overloaded. That is, it can have several types,
│ │ │ │ -separated by a semicolon (<code class="inline">;</code>). For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0850467675-1">(</span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="0850467675-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T3</span><span class="p">;</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="0850467675-2">(</span><span class="n">T4</span><span class="p">,</span><span class="w"> </span><span class="n">T5</span><span class="p" data-group-id="0850467675-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T6</span><span class="p">.</span></code></pre><p>A current restriction, which currently results in a warning by Dialyzer, is that
│ │ │ │ +separated by a semicolon (<code class="inline">;</code>). For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="7037800014-1">(</span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="7037800014-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T3</span><span class="p">;</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="7037800014-2">(</span><span class="n">T4</span><span class="p">,</span><span class="w"> </span><span class="n">T5</span><span class="p" data-group-id="7037800014-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T6</span><span class="p">.</span></code></pre><p>A current restriction, which currently results in a warning by Dialyzer, is that
│ │ │ │  the domains of the argument types cannot overlap. For example, the following
│ │ │ │ -specification results in a warning:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="1410192746-1">(</span><span class="nf">pos_integer</span><span class="p" data-group-id="1410192746-2">(</span><span class="p" data-group-id="1410192746-2">)</span><span class="p" data-group-id="1410192746-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="1410192746-3">(</span><span class="p" data-group-id="1410192746-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="1410192746-4">(</span><span class="nf">integer</span><span class="p" data-group-id="1410192746-5">(</span><span class="p" data-group-id="1410192746-5">)</span><span class="p" data-group-id="1410192746-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1410192746-6">(</span><span class="p" data-group-id="1410192746-6">)</span><span class="p">.</span></code></pre><p>Type variables can be used in specifications to specify relations for the input
│ │ │ │ +specification results in a warning:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="1288364307-1">(</span><span class="nf">pos_integer</span><span class="p" data-group-id="1288364307-2">(</span><span class="p" data-group-id="1288364307-2">)</span><span class="p" data-group-id="1288364307-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="1288364307-3">(</span><span class="p" data-group-id="1288364307-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="1288364307-4">(</span><span class="nf">integer</span><span class="p" data-group-id="1288364307-5">(</span><span class="p" data-group-id="1288364307-5">)</span><span class="p" data-group-id="1288364307-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1288364307-6">(</span><span class="p" data-group-id="1288364307-6">)</span><span class="p">.</span></code></pre><p>Type variables can be used in specifications to specify relations for the input
│ │ │ │  and output arguments of a function. For example, the following specification
│ │ │ │  defines the type of a polymorphic identity function:</p><pre><code class="text">-spec id(X) -&gt; X.</code></pre><p>Notice that the above specification does not restrict the input and output type
│ │ │ │  in any way. These types can be constrained by guard-like subtype constraints and
│ │ │ │ -provide bounded quantification:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="1288286182-1">(</span><span class="n">X</span><span class="p" data-group-id="1288286182-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="1288286182-2">(</span><span class="p" data-group-id="1288286182-2">)</span><span class="p">.</span></code></pre><p>Currently, the <code class="inline">::</code> constraint (read as &quot;is a subtype of&quot;) is the only guard
│ │ │ │ +provide bounded quantification:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="0901878963-1">(</span><span class="n">X</span><span class="p" data-group-id="0901878963-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="0901878963-2">(</span><span class="p" data-group-id="0901878963-2">)</span><span class="p">.</span></code></pre><p>Currently, the <code class="inline">::</code> constraint (read as &quot;is a subtype of&quot;) is the only guard
│ │ │ │  constraint that can be used in the <code class="inline">when</code> part of a <code class="inline">-spec</code> attribute.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The above function specification uses multiple occurrences of the same type
│ │ │ │  variable. That provides more type information than the following function
│ │ │ │ -specification, where the type variables are missing:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="4470521841-1">(</span><span class="nf">tuple</span><span class="p" data-group-id="4470521841-2">(</span><span class="p" data-group-id="4470521841-2">)</span><span class="p" data-group-id="4470521841-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="4470521841-3">(</span><span class="p" data-group-id="4470521841-3">)</span><span class="p">.</span></code></pre><p>The latter specification says that the function takes some tuple and returns
│ │ │ │ +specification, where the type variables are missing:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="2311822404-1">(</span><span class="nf">tuple</span><span class="p" data-group-id="2311822404-2">(</span><span class="p" data-group-id="2311822404-2">)</span><span class="p" data-group-id="2311822404-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="2311822404-3">(</span><span class="p" data-group-id="2311822404-3">)</span><span class="p">.</span></code></pre><p>The latter specification says that the function takes some tuple and returns
│ │ │ │  some tuple. The specification with the <code class="inline">X</code> type variable specifies that the
│ │ │ │  function takes a tuple and returns <em>the same</em> tuple.</p><p>However, it is up to the tools that process the specifications to choose
│ │ │ │  whether to take this extra information into account or not.</p></section><p>The scope of a <code class="inline">::</code> constraint is the <code class="inline">(...) -&gt; RetType</code> specification after
│ │ │ │  which it appears. To avoid confusion, it is suggested that different variables
│ │ │ │  are used in different constituents of an overloaded contract, as shown in the
│ │ │ │ -following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0078556227-1">(</span><span class="p" data-group-id="0078556227-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0078556227-3">(</span><span class="p" data-group-id="0078556227-3">)</span><span class="p" data-group-id="0078556227-2">}</span><span class="p" data-group-id="0078556227-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="0078556227-4">(</span><span class="p" data-group-id="0078556227-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="0078556227-5">(</span><span class="p" data-group-id="0078556227-6">[</span><span class="n">Y</span><span class="p" data-group-id="0078556227-6">]</span><span class="p" data-group-id="0078556227-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0078556227-7">(</span><span class="p" data-group-id="0078556227-7">)</span><span class="p">.</span></code></pre><p>Some functions in Erlang are not meant to return; either because they define
│ │ │ │ +following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="5780029072-1">(</span><span class="p" data-group-id="5780029072-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="5780029072-3">(</span><span class="p" data-group-id="5780029072-3">)</span><span class="p" data-group-id="5780029072-2">}</span><span class="p" data-group-id="5780029072-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="5780029072-4">(</span><span class="p" data-group-id="5780029072-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="5780029072-5">(</span><span class="p" data-group-id="5780029072-6">[</span><span class="n">Y</span><span class="p" data-group-id="5780029072-6">]</span><span class="p" data-group-id="5780029072-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5780029072-7">(</span><span class="p" data-group-id="5780029072-7">)</span><span class="p">.</span></code></pre><p>Some functions in Erlang are not meant to return; either because they define
│ │ │ │  servers or because they are used to throw exceptions, as in the following
│ │ │ │ -function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_error</span><span class="p" data-group-id="2311662484-1">(</span><span class="n">Err</span><span class="p" data-group-id="2311662484-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="2311662484-2">(</span><span class="p" data-group-id="2311662484-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Err</span><span class="p" data-group-id="2311662484-3">}</span><span class="p" data-group-id="2311662484-2">)</span><span class="p">.</span></code></pre><p>For such functions, it is recommended to use the special <a href="../../../lib/../erts/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a> type
│ │ │ │ +function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_error</span><span class="p" data-group-id="9207363675-1">(</span><span class="n">Err</span><span class="p" data-group-id="9207363675-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="9207363675-2">(</span><span class="p" data-group-id="9207363675-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Err</span><span class="p" data-group-id="9207363675-3">}</span><span class="p" data-group-id="9207363675-2">)</span><span class="p">.</span></code></pre><p>For such functions, it is recommended to use the special <a href="../../../lib/../erts/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a> type
│ │ │ │  for their &quot;return&quot;, through a contract of the following form:</p><pre><code class="text">-spec my_error(term()) -&gt; no_return().</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Erlang uses the shorthand version <code class="inline">_</code> as an anonymous type variable equivalent
│ │ │ │  to <a href="../../../lib/../erts/doc/html/erlang.html#t:term/0"><code class="inline">term/0</code></a> or <a href="../../../lib/../erts/doc/html/erlang.html#t:any/0"><code class="inline">any/0</code></a>. For example, the following function</p><pre><code class="text">-spec Function(string(), _) -&gt; string().</code></pre><p>is equivalent to:</p><pre><code class="text">-spec Function(string(), any()) -&gt; string().</code></pre></section>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/tablesdatabases.xhtml
│ │ │ │ @@ -51,73 +51,73 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Deleting an Element</span>
│ │ │ │  </h3>
│ │ │ │  <p>The <code class="inline">delete</code> operation is considered successful if the element was not present
│ │ │ │  in the table. Hence all attempts to check that the element is present in the
│ │ │ │  Ets/Mnesia table before deletion are unnecessary. Here follows an example for
│ │ │ │ -Ets tables:</p><p><strong>DO</strong></p><pre><code class="text">ets:delete(Tab, Key),</code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="6742216049-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="6742216049-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6742216049-2">[</span><span class="p" data-group-id="6742216049-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +Ets tables:</p><p><strong>DO</strong></p><pre><code class="text">ets:delete(Tab, Key),</code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="6497059197-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="6497059197-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6497059197-2">[</span><span class="p" data-group-id="6497059197-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6742216049-3">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="6742216049-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">ets</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="6742216049-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="6742216049-4">)</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6497059197-3">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="6497059197-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">ets</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="6497059197-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="6497059197-4">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre><h3 id="fetching-data" class="section-heading">
│ │ │ │    <a href="#fetching-data" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Fetching Data</span>
│ │ │ │  </h3>
│ │ │ │  <p>Do not fetch data that you already have.</p><p>Consider that you have a module that handles the abstract data type <code class="inline">Person</code>.
│ │ │ │  You export the interface function <code class="inline">print_person/1</code>, which uses the internal
│ │ │ │  functions <code class="inline">print_name/1</code>, <code class="inline">print_age/1</code>, and <code class="inline">print_occupation/1</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>If the function <code class="inline">print_name/1</code>, and so on, had been interface functions, the
│ │ │ │  situation would have been different, as you do not want the user of the
│ │ │ │  interface to know about the internal data representation.</p></section><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ │ -</span><span class="nf">print_person</span><span class="p" data-group-id="8904705458-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="8904705458-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_person</span><span class="p" data-group-id="8359652242-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="8359652242-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Look up the person in the named table person,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="8904705458-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="8904705458-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8904705458-3">[</span><span class="n">Person</span><span class="p" data-group-id="8904705458-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_name</span><span class="p" data-group-id="8904705458-4">(</span><span class="n">Person</span><span class="p" data-group-id="8904705458-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_age</span><span class="p" data-group-id="8904705458-5">(</span><span class="n">Person</span><span class="p" data-group-id="8904705458-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_occupation</span><span class="p" data-group-id="8904705458-6">(</span><span class="n">Person</span><span class="p" data-group-id="8904705458-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8904705458-7">[</span><span class="p" data-group-id="8904705458-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8904705458-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8904705458-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="8904705458-9">]</span><span class="p" data-group-id="8904705458-8">)</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="8359652242-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="8359652242-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8359652242-3">[</span><span class="n">Person</span><span class="p" data-group-id="8359652242-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_name</span><span class="p" data-group-id="8359652242-4">(</span><span class="n">Person</span><span class="p" data-group-id="8359652242-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_age</span><span class="p" data-group-id="8359652242-5">(</span><span class="n">Person</span><span class="p" data-group-id="8359652242-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_occupation</span><span class="p" data-group-id="8359652242-6">(</span><span class="n">Person</span><span class="p" data-group-id="8359652242-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8359652242-7">[</span><span class="p" data-group-id="8359652242-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8359652242-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8359652242-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="8359652242-9">]</span><span class="p" data-group-id="8359652242-8">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Internal functions</span><span class="w">
│ │ │ │ -</span><span class="nf">print_name</span><span class="p" data-group-id="8904705458-10">(</span><span class="n">Person</span><span class="p" data-group-id="8904705458-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8904705458-11">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8904705458-12">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="8904705458-12">]</span><span class="p" data-group-id="8904705458-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">print_name</span><span class="p" data-group-id="8359652242-10">(</span><span class="n">Person</span><span class="p" data-group-id="8359652242-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8359652242-11">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8359652242-12">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="8359652242-12">]</span><span class="p" data-group-id="8359652242-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">print_age</span><span class="p" data-group-id="8904705458-13">(</span><span class="n">Person</span><span class="p" data-group-id="8904705458-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8904705458-14">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8904705458-15">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="8904705458-15">]</span><span class="p" data-group-id="8904705458-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">print_age</span><span class="p" data-group-id="8359652242-13">(</span><span class="n">Person</span><span class="p" data-group-id="8359652242-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8359652242-14">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8359652242-15">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="8359652242-15">]</span><span class="p" data-group-id="8359652242-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">print_occupation</span><span class="p" data-group-id="8904705458-16">(</span><span class="n">Person</span><span class="p" data-group-id="8904705458-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8904705458-17">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8904705458-18">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="8904705458-18">]</span><span class="p" data-group-id="8904705458-17">)</span><span class="p">.</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ │ -</span><span class="nf">print_person</span><span class="p" data-group-id="4210059132-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="4210059132-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_occupation</span><span class="p" data-group-id="8359652242-16">(</span><span class="n">Person</span><span class="p" data-group-id="8359652242-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8359652242-17">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8359652242-18">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="8359652242-18">]</span><span class="p" data-group-id="8359652242-17">)</span><span class="p">.</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ │ +</span><span class="nf">print_person</span><span class="p" data-group-id="7120225067-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="7120225067-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Look up the person in the named table person,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="4210059132-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="4210059132-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4210059132-3">[</span><span class="n">Person</span><span class="p" data-group-id="4210059132-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_name</span><span class="p" data-group-id="4210059132-4">(</span><span class="n">PersonID</span><span class="p" data-group-id="4210059132-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_age</span><span class="p" data-group-id="4210059132-5">(</span><span class="n">PersonID</span><span class="p" data-group-id="4210059132-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">print_occupation</span><span class="p" data-group-id="4210059132-6">(</span><span class="n">PersonID</span><span class="p" data-group-id="4210059132-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4210059132-7">[</span><span class="p" data-group-id="4210059132-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4210059132-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4210059132-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="4210059132-9">]</span><span class="p" data-group-id="4210059132-8">)</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7120225067-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="7120225067-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7120225067-3">[</span><span class="n">Person</span><span class="p" data-group-id="7120225067-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_name</span><span class="p" data-group-id="7120225067-4">(</span><span class="n">PersonID</span><span class="p" data-group-id="7120225067-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_age</span><span class="p" data-group-id="7120225067-5">(</span><span class="n">PersonID</span><span class="p" data-group-id="7120225067-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">print_occupation</span><span class="p" data-group-id="7120225067-6">(</span><span class="n">PersonID</span><span class="p" data-group-id="7120225067-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7120225067-7">[</span><span class="p" data-group-id="7120225067-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7120225067-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7120225067-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="7120225067-9">]</span><span class="p" data-group-id="7120225067-8">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Internal functions</span><span class="w">
│ │ │ │ -</span><span class="nf">print_name</span><span class="p" data-group-id="4210059132-10">(</span><span class="n">PersonID</span><span class="p" data-group-id="4210059132-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4210059132-11">[</span><span class="n">Person</span><span class="p" data-group-id="4210059132-11">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="4210059132-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="4210059132-12">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4210059132-13">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4210059132-14">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="4210059132-14">]</span><span class="p" data-group-id="4210059132-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_age</span><span class="p" data-group-id="4210059132-15">(</span><span class="n">PersonID</span><span class="p" data-group-id="4210059132-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4210059132-16">[</span><span class="n">Person</span><span class="p" data-group-id="4210059132-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="4210059132-17">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="4210059132-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4210059132-18">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4210059132-19">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="4210059132-19">]</span><span class="p" data-group-id="4210059132-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_occupation</span><span class="p" data-group-id="4210059132-20">(</span><span class="n">PersonID</span><span class="p" data-group-id="4210059132-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4210059132-21">[</span><span class="n">Person</span><span class="p" data-group-id="4210059132-21">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="4210059132-22">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="4210059132-22">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4210059132-23">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4210059132-24">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="4210059132-24">]</span><span class="p" data-group-id="4210059132-23">)</span><span class="p">.</span></code></pre><h3 id="non-persistent-database-storage" class="section-heading">
│ │ │ │ +</span><span class="nf">print_name</span><span class="p" data-group-id="7120225067-10">(</span><span class="n">PersonID</span><span class="p" data-group-id="7120225067-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7120225067-11">[</span><span class="n">Person</span><span class="p" data-group-id="7120225067-11">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7120225067-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="7120225067-12">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7120225067-13">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7120225067-14">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="7120225067-14">]</span><span class="p" data-group-id="7120225067-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_age</span><span class="p" data-group-id="7120225067-15">(</span><span class="n">PersonID</span><span class="p" data-group-id="7120225067-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7120225067-16">[</span><span class="n">Person</span><span class="p" data-group-id="7120225067-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7120225067-17">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="7120225067-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7120225067-18">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7120225067-19">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="7120225067-19">]</span><span class="p" data-group-id="7120225067-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_occupation</span><span class="p" data-group-id="7120225067-20">(</span><span class="n">PersonID</span><span class="p" data-group-id="7120225067-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7120225067-21">[</span><span class="n">Person</span><span class="p" data-group-id="7120225067-21">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7120225067-22">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="7120225067-22">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7120225067-23">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7120225067-24">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="7120225067-24">]</span><span class="p" data-group-id="7120225067-23">)</span><span class="p">.</span></code></pre><h3 id="non-persistent-database-storage" class="section-heading">
│ │ │ │    <a href="#non-persistent-database-storage" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Non-Persistent Database Storage</span>
│ │ │ │  </h3>
│ │ │ │  <p>For non-persistent database storage, prefer Ets tables over Mnesia
│ │ │ │  <code class="inline">local_content</code> tables. Even the Mnesia <code class="inline">dirty_write</code> operations carry a fixed
│ │ │ │ @@ -131,38 +131,38 @@
│ │ │ │  </h3>
│ │ │ │  <p>Assuming an Ets table that uses <code class="inline">idno</code> as key and contains the following:</p><pre><code class="text">[#person{idno = 1, name = &quot;Adam&quot;,  age = 31, occupation = &quot;mailman&quot;},
│ │ │ │   #person{idno = 2, name = &quot;Bryan&quot;, age = 31, occupation = &quot;cashier&quot;},
│ │ │ │   #person{idno = 3, name = &quot;Bryan&quot;, age = 35, occupation = &quot;banker&quot;},
│ │ │ │   #person{idno = 4, name = &quot;Carl&quot;,  age = 25, occupation = &quot;mailman&quot;}]</code></pre><p>If you <em>must</em> return all data stored in the Ets table, you can use
│ │ │ │  <a href="../../../lib/stdlib/doc/html/ets.html#tab2list/1"><code class="inline">ets:tab2list/1</code></a>. However, usually you are only interested in a subset of the
│ │ │ │  information in which case <a href="../../../lib/stdlib/doc/html/ets.html#tab2list/1"><code class="inline">ets:tab2list/1</code></a> is expensive. If you only want to
│ │ │ │ -extract one field from each record, for example, the age of every person, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="3407730015-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3407730015-2">[</span><span class="p" data-group-id="3407730015-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3407730015-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ +extract one field from each record, for example, the age of every person, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="5448637516-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5448637516-2">[</span><span class="p" data-group-id="5448637516-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5448637516-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;$1&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="3407730015-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="3407730015-5">[</span><span class="p" data-group-id="3407730015-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="3407730015-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="3407730015-6">]</span><span class="p" data-group-id="3407730015-3">}</span><span class="p" data-group-id="3407730015-2">]</span><span class="p" data-group-id="3407730015-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="8576139059-1">(</span><span class="n">Tab</span><span class="p" data-group-id="8576139059-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="8576139059-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8576139059-3">(</span><span class="n">X</span><span class="p" data-group-id="8576139059-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="8576139059-2">)</span><span class="p">,</span></code></pre><p>If you are only interested in the age of all persons named &quot;Bryan&quot;, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="2871993059-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2871993059-2">[</span><span class="p" data-group-id="2871993059-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2871993059-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="5448637516-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="5448637516-5">[</span><span class="p" data-group-id="5448637516-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="5448637516-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="5448637516-6">]</span><span class="p" data-group-id="5448637516-3">}</span><span class="p" data-group-id="5448637516-2">]</span><span class="p" data-group-id="5448637516-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="7921336624-1">(</span><span class="n">Tab</span><span class="p" data-group-id="7921336624-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7921336624-2">(</span><span class="nf">fun</span><span class="p" data-group-id="7921336624-3">(</span><span class="n">X</span><span class="p" data-group-id="7921336624-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="7921336624-2">)</span><span class="p">,</span></code></pre><p>If you are only interested in the age of all persons named &quot;Bryan&quot;, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="0984564304-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0984564304-2">[</span><span class="p" data-group-id="0984564304-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0984564304-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Bryan&quot;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;$1&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="2871993059-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="2871993059-5">[</span><span class="p" data-group-id="2871993059-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="2871993059-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="2871993059-6">]</span><span class="p" data-group-id="2871993059-3">}</span><span class="p" data-group-id="2871993059-2">]</span><span class="p" data-group-id="2871993059-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="0830032663-1">(</span><span class="n">Tab</span><span class="p" data-group-id="0830032663-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="0830032663-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0830032663-3">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0830032663-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="0984564304-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="0984564304-5">[</span><span class="p" data-group-id="0984564304-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="0984564304-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="0984564304-6">]</span><span class="p" data-group-id="0984564304-3">}</span><span class="p" data-group-id="0984564304-2">]</span><span class="p" data-group-id="0984564304-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="5978217903-1">(</span><span class="n">Tab</span><span class="p" data-group-id="5978217903-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="5978217903-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5978217903-3">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5978217903-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │                                  </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                                    </span><span class="p" data-group-id="0830032663-4">[</span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="0830032663-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +                                    </span><span class="p" data-group-id="5978217903-4">[</span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="5978217903-4">]</span><span class="p">;</span><span class="w">
│ │ │ │                                   </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                                       </span><span class="n">Acc</span><span class="w">
│ │ │ │                             </span><span class="k">end</span><span class="w">
│ │ │ │ -             </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0830032663-5">[</span><span class="p" data-group-id="0830032663-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="0830032663-2">)</span></code></pre><p>If you need all information stored in the Ets table about persons named &quot;Bryan&quot;,
│ │ │ │ -then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="9050464388-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9050464388-2">[</span><span class="p" data-group-id="9050464388-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9050464388-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5978217903-5">[</span><span class="p" data-group-id="5978217903-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="5978217903-2">)</span></code></pre><p>If you need all information stored in the Ets table about persons named &quot;Bryan&quot;,
│ │ │ │ +then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="6750408140-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6750408140-2">[</span><span class="p" data-group-id="6750408140-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6750408140-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Bryan&quot;</span><span class="p">,</span><span class="w">
│ │ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="9050464388-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9050464388-5">[</span><span class="p" data-group-id="9050464388-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9050464388-6">[</span><span class="ss">&#39;$_&#39;</span><span class="p" data-group-id="9050464388-6">]</span><span class="p" data-group-id="9050464388-3">}</span><span class="p" data-group-id="9050464388-2">]</span><span class="p" data-group-id="9050464388-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="9575383204-1">(</span><span class="n">Tab</span><span class="p" data-group-id="9575383204-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="9575383204-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9575383204-3">(</span><span class="n">X</span><span class="p" data-group-id="9575383204-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="9575383204-2">)</span><span class="p">,</span></code></pre><h3 id="ordered_set-tables" class="section-heading">
│ │ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6750408140-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6750408140-5">[</span><span class="p" data-group-id="6750408140-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6750408140-6">[</span><span class="ss">&#39;$_&#39;</span><span class="p" data-group-id="6750408140-6">]</span><span class="p" data-group-id="6750408140-3">}</span><span class="p" data-group-id="6750408140-2">]</span><span class="p" data-group-id="6750408140-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="5106231468-1">(</span><span class="n">Tab</span><span class="p" data-group-id="5106231468-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="5106231468-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5106231468-3">(</span><span class="n">X</span><span class="p" data-group-id="5106231468-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="5106231468-2">)</span><span class="p">,</span></code></pre><h3 id="ordered_set-tables" class="section-heading">
│ │ │ │    <a href="#ordered_set-tables" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text"><code class="inline">ordered_set</code> Tables</span>
│ │ │ │  </h3>
│ │ │ │  <p>If the data in the table is to be accessed so that the order of the keys in the
│ │ │ │  table is significant, the table type <code class="inline">ordered_set</code> can be used instead of the
│ │ │ │ @@ -198,20 +198,20 @@
│ │ │ │  Clearly, the second table would have to be kept consistent with the master
│ │ │ │  table. Mnesia can do this for you, but a home-brew index table can be very
│ │ │ │  efficient compared to the overhead involved in using Mnesia.</p><p>An index table for the table in the previous examples would have to be a bag (as
│ │ │ │  keys would appear more than once) and can have the following contents:</p><pre><code class="text">[#index_entry{name=&quot;Adam&quot;, idno=1},
│ │ │ │   #index_entry{name=&quot;Bryan&quot;, idno=2},
│ │ │ │   #index_entry{name=&quot;Bryan&quot;, idno=3},
│ │ │ │   #index_entry{name=&quot;Carl&quot;, idno=4}]</code></pre><p>Given this index table, a lookup of the <code class="inline">age</code> fields for all persons named
│ │ │ │ -&quot;Bryan&quot; can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">MatchingIDs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="0195341502-1">(</span><span class="n">IndexTable</span><span class="p">,</span><span class="s">&quot;Bryan&quot;</span><span class="p" data-group-id="0195341502-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0195341502-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0195341502-3">(</span><span class="o">#</span><span class="ss">index_entry</span><span class="p" data-group-id="0195341502-4">{</span><span class="ss">idno</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="0195341502-4">}</span><span class="p" data-group-id="0195341502-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="0195341502-5">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0195341502-6">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="0195341502-6">}</span><span class="p" data-group-id="0195341502-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="0195341502-7">(</span><span class="n">PersonTable</span><span class="p">,</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="0195341502-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +&quot;Bryan&quot; can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">MatchingIDs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="6449106631-1">(</span><span class="n">IndexTable</span><span class="p">,</span><span class="s">&quot;Bryan&quot;</span><span class="p" data-group-id="6449106631-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="6449106631-2">(</span><span class="nf">fun</span><span class="p" data-group-id="6449106631-3">(</span><span class="o">#</span><span class="ss">index_entry</span><span class="p" data-group-id="6449106631-4">{</span><span class="ss">idno</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="6449106631-4">}</span><span class="p" data-group-id="6449106631-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="6449106631-5">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6449106631-6">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="6449106631-6">}</span><span class="p" data-group-id="6449106631-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="6449106631-7">(</span><span class="n">PersonTable</span><span class="p">,</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="6449106631-7">)</span><span class="p">,</span><span class="w">
│ │ │ │                   </span><span class="n">Age</span><span class="w">
│ │ │ │            </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="n">MatchingIDs</span><span class="p" data-group-id="0195341502-2">)</span><span class="p">,</span></code></pre><p>Notice that this code does not use <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>, but instead uses the
│ │ │ │ +          </span><span class="n">MatchingIDs</span><span class="p" data-group-id="6449106631-2">)</span><span class="p">,</span></code></pre><p>Notice that this code does not use <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>, but instead uses the
│ │ │ │  <a href="../../../lib/stdlib/doc/html/ets.html#lookup/2"><code class="inline">ets:lookup/2</code></a> call. The <a href="../../../lib/stdlib/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> call is only used to traverse the <code class="inline">idno</code>s
│ │ │ │  matching the name &quot;Bryan&quot; in the table; thus the number of lookups in the master
│ │ │ │  table is minimized.</p><p>Keeping an index table introduces some overhead when inserting records in the
│ │ │ │  table. The number of operations gained from the table must therefore be compared
│ │ │ │  against the number of operations inserting objects in the table. However, notice
│ │ │ │  that the gain is significant when the key can be used to lookup elements.</p><h2 id="mnesia" class="section-heading">
│ │ │ │    <a href="#mnesia" class="hover-link">
│ │ │ │ @@ -226,47 +226,47 @@
│ │ │ │    <span class="text">Secondary Index</span>
│ │ │ │  </h3>
│ │ │ │  <p>If you frequently do lookups on a field that is not the key of the table, you
│ │ │ │  lose performance using <a href="../../../lib/mnesia/doc/html/mnesia.html#select/3">mnesia:select()</a> or
│ │ │ │  <a href="../../../lib/mnesia/doc/html/mnesia.html#match_object/1"><code class="inline">mnesia:match_object()</code></a> as these function traverse
│ │ │ │  the whole table. Instead, you can create a secondary index and use
│ │ │ │  <a href="../../../lib/mnesia/doc/html/mnesia.html#index_read/3"><code class="inline">mnesia:index_read/3</code></a> to get faster access at the expense of using more
│ │ │ │ -memory.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2882046445-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2882046445-2">{</span><span class="ss">idno</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">occupation</span><span class="p" data-group-id="2882046445-2">}</span><span class="p" data-group-id="2882046445-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +memory.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9051935093-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9051935093-2">{</span><span class="ss">idno</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">occupation</span><span class="p" data-group-id="9051935093-2">}</span><span class="p" data-group-id="9051935093-1">)</span><span class="p">.</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2882046445-3">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="2882046445-3">}</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">create_table</span><span class="p" data-group-id="2882046445-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2882046445-5">[</span><span class="p" data-group-id="2882046445-6">{</span><span class="ss">index</span><span class="p">,</span><span class="p" data-group-id="2882046445-7">[</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="2882046445-7">]</span><span class="p" data-group-id="2882046445-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                              </span><span class="p" data-group-id="2882046445-8">{</span><span class="ss">attributes</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="nf">record_info</span><span class="p" data-group-id="2882046445-9">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="2882046445-9">)</span><span class="p" data-group-id="2882046445-8">}</span><span class="p" data-group-id="2882046445-5">]</span><span class="p" data-group-id="2882046445-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2882046445-10">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="2882046445-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">add_table_index</span><span class="p" data-group-id="2882046445-11">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="2882046445-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9051935093-3">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="9051935093-3">}</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ +</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">create_table</span><span class="p" data-group-id="9051935093-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9051935093-5">[</span><span class="p" data-group-id="9051935093-6">{</span><span class="ss">index</span><span class="p">,</span><span class="p" data-group-id="9051935093-7">[</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="9051935093-7">]</span><span class="p" data-group-id="9051935093-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                              </span><span class="p" data-group-id="9051935093-8">{</span><span class="ss">attributes</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="nf">record_info</span><span class="p" data-group-id="9051935093-9">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="9051935093-9">)</span><span class="p" data-group-id="9051935093-8">}</span><span class="p" data-group-id="9051935093-5">]</span><span class="p" data-group-id="9051935093-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9051935093-10">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="9051935093-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">add_table_index</span><span class="p" data-group-id="9051935093-11">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="9051935093-11">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="n">PersonsAge42</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -     </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_index_read</span><span class="p" data-group-id="2882046445-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="2882046445-12">)</span><span class="p">,</span></code></pre><h3 id="transactions" class="section-heading">
│ │ │ │ +     </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_index_read</span><span class="p" data-group-id="9051935093-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="9051935093-12">)</span><span class="p">,</span></code></pre><h3 id="transactions" class="section-heading">
│ │ │ │    <a href="#transactions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Transactions</span>
│ │ │ │  </h3>
│ │ │ │  <p>Using transactions is a way to guarantee that the distributed Mnesia database
│ │ │ │  remains consistent, even when many different processes update it in parallel.
│ │ │ │  However, if you have real-time requirements it is recommended to use dirtry
│ │ │ │  operations instead of transactions. When using dirty operations, you lose the
│ │ │ │  consistency guarantee; this is usually solved by only letting one process update
│ │ │ │  the table. Other processes must send update requests to that process.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Using transaction</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5135408982-1">(</span><span class="p" data-group-id="5135408982-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="5135408982-2">[</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="5135408982-3">(</span><span class="p" data-group-id="5135408982-4">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5135408982-4">}</span><span class="p" data-group-id="5135408982-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -           </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="5135408982-5">(</span><span class="p" data-group-id="5135408982-6">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="5135408982-6">}</span><span class="p" data-group-id="5135408982-5">)</span><span class="p" data-group-id="5135408982-2">]</span><span class="w">
│ │ │ │ +</span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9251745029-1">(</span><span class="p" data-group-id="9251745029-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="9251745029-2">[</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="9251745029-3">(</span><span class="p" data-group-id="9251745029-4">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9251745029-4">}</span><span class="p" data-group-id="9251745029-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +           </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="9251745029-5">(</span><span class="p" data-group-id="9251745029-6">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="9251745029-6">}</span><span class="p" data-group-id="9251745029-5">)</span><span class="p" data-group-id="9251745029-2">]</span><span class="w">
│ │ │ │        </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="5135408982-7">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5135408982-8">[</span><span class="n">Result1</span><span class="p">,</span><span class="w"> </span><span class="n">Result2</span><span class="p" data-group-id="5135408982-8">]</span><span class="p" data-group-id="5135408982-7">}</span><span class="w">  </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">transaction</span><span class="p" data-group-id="5135408982-9">(</span><span class="n">Fun</span><span class="p" data-group-id="5135408982-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9251745029-7">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9251745029-8">[</span><span class="n">Result1</span><span class="p">,</span><span class="w"> </span><span class="n">Result2</span><span class="p" data-group-id="9251745029-8">]</span><span class="p" data-group-id="9251745029-7">}</span><span class="w">  </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">transaction</span><span class="p" data-group-id="9251745029-9">(</span><span class="n">Fun</span><span class="p" data-group-id="9251745029-9">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Same thing using dirty operations</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Result1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="5135408982-10">(</span><span class="p" data-group-id="5135408982-11">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5135408982-11">}</span><span class="p" data-group-id="5135408982-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Result2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="5135408982-12">(</span><span class="p" data-group-id="5135408982-13">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="5135408982-13">}</span><span class="p" data-group-id="5135408982-12">)</span><span class="p">,</span></code></pre>
│ │ │ │ +</span><span class="n">Result1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="9251745029-10">(</span><span class="p" data-group-id="9251745029-11">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9251745029-11">}</span><span class="p" data-group-id="9251745029-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Result2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="9251745029-12">(</span><span class="p" data-group-id="9251745029-13">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="9251745029-13">}</span><span class="p" data-group-id="9251745029-12">)</span><span class="p">,</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/sup_princ.xhtml
│ │ │ │ @@ -33,48 +33,48 @@
│ │ │ │  the order specified by this list, and are terminated in the reverse order.</p><h2 id="example" class="section-heading">
│ │ │ │    <a href="#example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>The callback module for a supervisor starting the server from
│ │ │ │ -<a href="gen_server_concepts.xhtml#ex">gen_server Behaviour</a> can look as follows:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6506593766-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="6506593766-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6506593766-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="6506593766-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<a href="gen_server_concepts.xhtml#ex">gen_server Behaviour</a> can look as follows:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8103795731-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="8103795731-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8103795731-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="8103795731-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6506593766-3">(</span><span class="p" data-group-id="6506593766-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6506593766-4">]</span><span class="p" data-group-id="6506593766-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6506593766-5">(</span><span class="p" data-group-id="6506593766-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6506593766-6">]</span><span class="p" data-group-id="6506593766-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8103795731-3">(</span><span class="p" data-group-id="8103795731-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8103795731-4">]</span><span class="p" data-group-id="8103795731-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8103795731-5">(</span><span class="p" data-group-id="8103795731-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8103795731-6">]</span><span class="p" data-group-id="8103795731-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="6506593766-7">(</span><span class="p" data-group-id="6506593766-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6506593766-8">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6506593766-9">[</span><span class="p" data-group-id="6506593766-9">]</span><span class="p" data-group-id="6506593766-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="8103795731-7">(</span><span class="p" data-group-id="8103795731-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8103795731-8">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8103795731-9">[</span><span class="p" data-group-id="8103795731-9">]</span><span class="p" data-group-id="8103795731-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6506593766-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6506593766-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6506593766-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_one</span><span class="p">,</span><span class="w"> </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="6506593766-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6506593766-12">[</span><span class="p" data-group-id="6506593766-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6506593766-14">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6506593766-15">[</span><span class="p" data-group-id="6506593766-15">]</span><span class="p" data-group-id="6506593766-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8103795731-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="8103795731-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8103795731-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_one</span><span class="p">,</span><span class="w"> </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="8103795731-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8103795731-12">[</span><span class="p" data-group-id="8103795731-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8103795731-14">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8103795731-15">[</span><span class="p" data-group-id="8103795731-15">]</span><span class="p" data-group-id="8103795731-14">}</span><span class="p">,</span><span class="w">
│ │ │ │                      </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">permanent</span><span class="p">,</span><span class="w">
│ │ │ │                      </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w">
│ │ │ │                      </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6506593766-16">[</span><span class="ss">ch3</span><span class="p" data-group-id="6506593766-16">]</span><span class="p" data-group-id="6506593766-13">}</span><span class="p" data-group-id="6506593766-12">]</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6506593766-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6506593766-18">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="6506593766-18">}</span><span class="p" data-group-id="6506593766-17">}</span><span class="p">.</span></code></pre><p>The <code class="inline">SupFlags</code> variable in the return value from <code class="inline">init/1</code> represents the
│ │ │ │ +                    </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8103795731-16">[</span><span class="ss">ch3</span><span class="p" data-group-id="8103795731-16">]</span><span class="p" data-group-id="8103795731-13">}</span><span class="p" data-group-id="8103795731-12">]</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8103795731-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8103795731-18">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="8103795731-18">}</span><span class="p" data-group-id="8103795731-17">}</span><span class="p">.</span></code></pre><p>The <code class="inline">SupFlags</code> variable in the return value from <code class="inline">init/1</code> represents the
│ │ │ │  <a href="sup_princ.xhtml#flags">supervisor flags</a>.</p><p>The <code class="inline">ChildSpecs</code> variable in the return value from <code class="inline">init/1</code> is a list of
│ │ │ │  <a href="sup_princ.xhtml#spec">child specifications</a>.</p><p><a href="" id="flags"></a></p><h2 id="supervisor-flags" class="section-heading">
│ │ │ │    <a href="#supervisor-flags" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Supervisor Flags</span>
│ │ │ │  </h2>
│ │ │ │ -<p>This is the type definition for the supervisor flags:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sup_flags</span><span class="p" data-group-id="0216881247-1">(</span><span class="p" data-group-id="0216881247-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0216881247-2">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">strategy</span><span class="p" data-group-id="0216881247-3">(</span><span class="p" data-group-id="0216881247-3">)</span><span class="p">,</span><span class="w">           </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="0216881247-4">(</span><span class="p" data-group-id="0216881247-4">)</span><span class="p">,</span><span class="w">   </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="0216881247-5">(</span><span class="p" data-group-id="0216881247-5">)</span><span class="p">,</span><span class="w">          </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                </span><span class="ss">auto_shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="0216881247-6">(</span><span class="p" data-group-id="0216881247-6">)</span><span class="p" data-group-id="0216881247-2">}</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -    </span><span class="nf">strategy</span><span class="p" data-group-id="0216881247-7">(</span><span class="p" data-group-id="0216881247-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">one_for_all</span><span class="w">
│ │ │ │ +<p>This is the type definition for the supervisor flags:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sup_flags</span><span class="p" data-group-id="5371369288-1">(</span><span class="p" data-group-id="5371369288-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5371369288-2">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">strategy</span><span class="p" data-group-id="5371369288-3">(</span><span class="p" data-group-id="5371369288-3">)</span><span class="p">,</span><span class="w">           </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="5371369288-4">(</span><span class="p" data-group-id="5371369288-4">)</span><span class="p">,</span><span class="w">   </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="5371369288-5">(</span><span class="p" data-group-id="5371369288-5">)</span><span class="p">,</span><span class="w">          </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                </span><span class="ss">auto_shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="5371369288-6">(</span><span class="p" data-group-id="5371369288-6">)</span><span class="p" data-group-id="5371369288-2">}</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +    </span><span class="nf">strategy</span><span class="p" data-group-id="5371369288-7">(</span><span class="p" data-group-id="5371369288-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">one_for_all</span><span class="w">
│ │ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">one_for_one</span><span class="w">
│ │ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">rest_for_one</span><span class="w">
│ │ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="w">
│ │ │ │ -    </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="0216881247-8">(</span><span class="p" data-group-id="0216881247-8">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">never</span><span class="w">
│ │ │ │ +    </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="5371369288-8">(</span><span class="p" data-group-id="5371369288-8">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">never</span><span class="w">
│ │ │ │                      </span><span class="p">|</span><span class="w"> </span><span class="ss">any_significant</span><span class="w">
│ │ │ │                      </span><span class="p">|</span><span class="w"> </span><span class="ss">all_significant</span></code></pre><ul><li><code class="inline">strategy</code> specifies the <a href="sup_princ.xhtml#strategy">restart strategy</a>.</li><li><code class="inline">intensity</code> and <code class="inline">period</code> specify the
│ │ │ │  <a href="sup_princ.xhtml#max_intensity">maximum restart intensity</a>.</li><li><code class="inline">auto_shutdown</code> specifies whether and when a supervisor should
│ │ │ │  <a href="sup_princ.xhtml#automatic-shutdown">automatically shut itself down</a>.</li></ul><p><a href="" id="strategy"></a></p><h2 id="restart-strategy" class="section-heading">
│ │ │ │    <a href="#restart-strategy" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -313,28 +313,28 @@
│ │ │ │  exhaust the <a href="sup_princ.xhtml#max_intensity">Maximum Restart Intensity</a> of the
│ │ │ │  parent supervisor.</p></section><p><a href="" id="spec"></a></p><h2 id="child-specification" class="section-heading">
│ │ │ │    <a href="#child-specification" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Child Specification</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The type definition for a child specification is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">child_spec</span><span class="p" data-group-id="1404143156-1">(</span><span class="p" data-group-id="1404143156-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1404143156-2">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">child_id</span><span class="p" data-group-id="1404143156-3">(</span><span class="p" data-group-id="1404143156-3">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% mandatory</span><span class="w">
│ │ │ │ -                 </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">mfargs</span><span class="p" data-group-id="1404143156-4">(</span><span class="p" data-group-id="1404143156-4">)</span><span class="p">,</span><span class="w">            </span><span class="c1">% mandatory</span><span class="w">
│ │ │ │ -                 </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">restart</span><span class="p" data-group-id="1404143156-5">(</span><span class="p" data-group-id="1404143156-5">)</span><span class="p">,</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                 </span><span class="ss">significant</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">significant</span><span class="p" data-group-id="1404143156-6">(</span><span class="p" data-group-id="1404143156-6">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                 </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">shutdown</span><span class="p" data-group-id="1404143156-7">(</span><span class="p" data-group-id="1404143156-7">)</span><span class="p">,</span><span class="w">       </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                 </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">worker</span><span class="p" data-group-id="1404143156-8">(</span><span class="p" data-group-id="1404143156-8">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -                 </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">modules</span><span class="p" data-group-id="1404143156-9">(</span><span class="p" data-group-id="1404143156-9">)</span><span class="p" data-group-id="1404143156-2">}</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ │ -    </span><span class="nf">child_id</span><span class="p" data-group-id="1404143156-10">(</span><span class="p" data-group-id="1404143156-10">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1404143156-11">(</span><span class="p" data-group-id="1404143156-11">)</span><span class="w">
│ │ │ │ -    </span><span class="nf">mfargs</span><span class="p" data-group-id="1404143156-12">(</span><span class="p" data-group-id="1404143156-12">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1404143156-13">{</span><span class="n">M</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="1404143156-14">(</span><span class="p" data-group-id="1404143156-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="1404143156-15">(</span><span class="p" data-group-id="1404143156-15">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1404143156-16">[</span><span class="nf">term</span><span class="p" data-group-id="1404143156-17">(</span><span class="p" data-group-id="1404143156-17">)</span><span class="p" data-group-id="1404143156-16">]</span><span class="p" data-group-id="1404143156-13">}</span><span class="w">
│ │ │ │ -    </span><span class="nf">modules</span><span class="p" data-group-id="1404143156-18">(</span><span class="p" data-group-id="1404143156-18">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1404143156-19">[</span><span class="nf">module</span><span class="p" data-group-id="1404143156-20">(</span><span class="p" data-group-id="1404143156-20">)</span><span class="p" data-group-id="1404143156-19">]</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">dynamic</span><span class="w">
│ │ │ │ -    </span><span class="nf">restart</span><span class="p" data-group-id="1404143156-21">(</span><span class="p" data-group-id="1404143156-21">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">permanent</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">transient</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">temporary</span><span class="w">
│ │ │ │ -    </span><span class="nf">significant</span><span class="p" data-group-id="1404143156-22">(</span><span class="p" data-group-id="1404143156-22">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="1404143156-23">(</span><span class="p" data-group-id="1404143156-23">)</span><span class="w">
│ │ │ │ -    </span><span class="nf">shutdown</span><span class="p" data-group-id="1404143156-24">(</span><span class="p" data-group-id="1404143156-24">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">timeout</span><span class="p" data-group-id="1404143156-25">(</span><span class="p" data-group-id="1404143156-25">)</span><span class="w">
│ │ │ │ -    </span><span class="nf">worker</span><span class="p" data-group-id="1404143156-26">(</span><span class="p" data-group-id="1404143156-26">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">worker</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">supervisor</span></code></pre><ul><li><p><code class="inline">id</code> is used to identify the child specification internally by the supervisor.</p><p>The <code class="inline">id</code> key is mandatory.</p><p>Note that this identifier occasionally has been called &quot;name&quot;. As far as
│ │ │ │ +<p>The type definition for a child specification is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">child_spec</span><span class="p" data-group-id="2673523654-1">(</span><span class="p" data-group-id="2673523654-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2673523654-2">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">child_id</span><span class="p" data-group-id="2673523654-3">(</span><span class="p" data-group-id="2673523654-3">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% mandatory</span><span class="w">
│ │ │ │ +                 </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">mfargs</span><span class="p" data-group-id="2673523654-4">(</span><span class="p" data-group-id="2673523654-4">)</span><span class="p">,</span><span class="w">            </span><span class="c1">% mandatory</span><span class="w">
│ │ │ │ +                 </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">restart</span><span class="p" data-group-id="2673523654-5">(</span><span class="p" data-group-id="2673523654-5">)</span><span class="p">,</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                 </span><span class="ss">significant</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">significant</span><span class="p" data-group-id="2673523654-6">(</span><span class="p" data-group-id="2673523654-6">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                 </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">shutdown</span><span class="p" data-group-id="2673523654-7">(</span><span class="p" data-group-id="2673523654-7">)</span><span class="p">,</span><span class="w">       </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                 </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">worker</span><span class="p" data-group-id="2673523654-8">(</span><span class="p" data-group-id="2673523654-8">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +                 </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">modules</span><span class="p" data-group-id="2673523654-9">(</span><span class="p" data-group-id="2673523654-9">)</span><span class="p" data-group-id="2673523654-2">}</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ │ +    </span><span class="nf">child_id</span><span class="p" data-group-id="2673523654-10">(</span><span class="p" data-group-id="2673523654-10">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2673523654-11">(</span><span class="p" data-group-id="2673523654-11">)</span><span class="w">
│ │ │ │ +    </span><span class="nf">mfargs</span><span class="p" data-group-id="2673523654-12">(</span><span class="p" data-group-id="2673523654-12">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2673523654-13">{</span><span class="n">M</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="2673523654-14">(</span><span class="p" data-group-id="2673523654-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="2673523654-15">(</span><span class="p" data-group-id="2673523654-15">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="2673523654-16">[</span><span class="nf">term</span><span class="p" data-group-id="2673523654-17">(</span><span class="p" data-group-id="2673523654-17">)</span><span class="p" data-group-id="2673523654-16">]</span><span class="p" data-group-id="2673523654-13">}</span><span class="w">
│ │ │ │ +    </span><span class="nf">modules</span><span class="p" data-group-id="2673523654-18">(</span><span class="p" data-group-id="2673523654-18">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2673523654-19">[</span><span class="nf">module</span><span class="p" data-group-id="2673523654-20">(</span><span class="p" data-group-id="2673523654-20">)</span><span class="p" data-group-id="2673523654-19">]</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">dynamic</span><span class="w">
│ │ │ │ +    </span><span class="nf">restart</span><span class="p" data-group-id="2673523654-21">(</span><span class="p" data-group-id="2673523654-21">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">permanent</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">transient</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">temporary</span><span class="w">
│ │ │ │ +    </span><span class="nf">significant</span><span class="p" data-group-id="2673523654-22">(</span><span class="p" data-group-id="2673523654-22">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="2673523654-23">(</span><span class="p" data-group-id="2673523654-23">)</span><span class="w">
│ │ │ │ +    </span><span class="nf">shutdown</span><span class="p" data-group-id="2673523654-24">(</span><span class="p" data-group-id="2673523654-24">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">timeout</span><span class="p" data-group-id="2673523654-25">(</span><span class="p" data-group-id="2673523654-25">)</span><span class="w">
│ │ │ │ +    </span><span class="nf">worker</span><span class="p" data-group-id="2673523654-26">(</span><span class="p" data-group-id="2673523654-26">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">worker</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">supervisor</span></code></pre><ul><li><p><code class="inline">id</code> is used to identify the child specification internally by the supervisor.</p><p>The <code class="inline">id</code> key is mandatory.</p><p>Note that this identifier occasionally has been called &quot;name&quot;. As far as
│ │ │ │  possible, the terms &quot;identifier&quot; or &quot;id&quot; are now used but in order to keep
│ │ │ │  backwards compatibility, some occurrences of &quot;name&quot; can still be found, for
│ │ │ │  example in error messages.</p></li><li><p><code class="inline">start</code> defines the function call used to start the child process. It is a
│ │ │ │  module-function-arguments tuple used as <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply(M, F, A)</code></a>.</p><p>It is to be (or result in) a call to any of the following:</p><ul><li><a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link/2,3</code></a></li><li><a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/3,4</code></a></li><li><a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/3,4</code></a></li><li><a href="../../../lib/stdlib/doc/html/gen_event.html#start_link/2"><code class="inline">gen_event:start_link/0,1,2</code></a></li><li>A function compliant with these functions. For details, see
│ │ │ │  <a href="../../../lib/stdlib/doc/html/supervisor.html"><code class="inline">supervisor</code></a>.</li></ul><p>The <code class="inline">start</code> key is mandatory.</p></li><li><p><a href="" id="restart"></a> <code class="inline">restart</code> defines when a terminated child process is to be
│ │ │ │  restarted.</p><ul><li>A <code class="inline">permanent</code> child process is always restarted.</li><li>A <code class="inline">temporary</code> child process is never restarted (not even when the supervisor
│ │ │ │  restart strategy is <code class="inline">rest_for_one</code> or <code class="inline">one_for_all</code> and a sibling death
│ │ │ │ @@ -362,53 +362,53 @@
│ │ │ │  <code class="inline">supervisor</code>, the default value <code class="inline">infinity</code> will be used.</p></li><li><p><code class="inline">type</code> specifies whether the child process is a supervisor or a worker.</p><p>The <code class="inline">type</code> key is optional. If it is not given, the default value <code class="inline">worker</code>
│ │ │ │  will be used.</p></li><li><p><code class="inline">modules</code> has to be a list consisting of a single element. The value
│ │ │ │  of that element depends on the behaviour of the process:</p><ul><li>If the child process is a <code class="inline">gen_event</code>, the element has to be the atom
│ │ │ │  <code class="inline">dynamic</code>.</li><li>Otherwise, the element should be <code class="inline">Module</code>, where <code class="inline">Module</code> is the
│ │ │ │  name of the callback module.</li></ul><p>This information is used by the release handler during upgrades and
│ │ │ │  downgrades; see <a href="release_handling.xhtml">Release Handling</a>.</p><p>The <code class="inline">modules</code> key is optional. If it is not given, it defaults to <code class="inline">[M]</code>, where
│ │ │ │  <code class="inline">M</code> comes from the child's start <code class="inline">{M,F,A}</code>.</p></li></ul><p><em>Example:</em> The child specification to start the server <code class="inline">ch3</code> in the previous
│ │ │ │ -example look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2542036451-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2542036451-2">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2542036451-3">[</span><span class="p" data-group-id="2542036451-3">]</span><span class="p" data-group-id="2542036451-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +example look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1908795414-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1908795414-2">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1908795414-3">[</span><span class="p" data-group-id="1908795414-3">]</span><span class="p" data-group-id="1908795414-2">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">permanent</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2542036451-4">[</span><span class="ss">ch3</span><span class="p" data-group-id="2542036451-4">]</span><span class="p" data-group-id="2542036451-1">}</span></code></pre><p>or simplified, relying on the default values:</p><pre><code class="text">#{id =&gt; ch3,
│ │ │ │ +  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1908795414-4">[</span><span class="ss">ch3</span><span class="p" data-group-id="1908795414-4">]</span><span class="p" data-group-id="1908795414-1">}</span></code></pre><p>or simplified, relying on the default values:</p><pre><code class="text">#{id =&gt; ch3,
│ │ │ │    start =&gt; {ch3, start_link, []},
│ │ │ │    shutdown =&gt; brutal_kill}</code></pre><p>Example: A child specification to start the event manager from the chapter about
│ │ │ │ -<a href="events.xhtml#mgr">gen_event</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7323680853-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">error_man</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7323680853-2">{</span><span class="ss">gen_event</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7323680853-3">[</span><span class="p" data-group-id="7323680853-4">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="7323680853-4">}</span><span class="p" data-group-id="7323680853-3">]</span><span class="p" data-group-id="7323680853-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">dynamic</span><span class="p" data-group-id="7323680853-1">}</span></code></pre><p>Both server and event manager are registered processes which can be expected to
│ │ │ │ +<a href="events.xhtml#mgr">gen_event</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4181087775-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">error_man</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4181087775-2">{</span><span class="ss">gen_event</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4181087775-3">[</span><span class="p" data-group-id="4181087775-4">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="4181087775-4">}</span><span class="p" data-group-id="4181087775-3">]</span><span class="p" data-group-id="4181087775-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">dynamic</span><span class="p" data-group-id="4181087775-1">}</span></code></pre><p>Both server and event manager are registered processes which can be expected to
│ │ │ │  be always accessible. Thus they are specified to be <code class="inline">permanent</code>.</p><p><code class="inline">ch3</code> does not need to do any cleaning up before termination. Thus, no shutdown
│ │ │ │  time is needed, but <code class="inline">brutal_kill</code> is sufficient. <code class="inline">error_man</code> can need some time
│ │ │ │  for the event handlers to clean up, thus the shutdown time is set to 5000 ms
│ │ │ │ -(which is the default value).</p><p>Example: A child specification to start another supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8065037802-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">sup</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8065037802-2">{</span><span class="ss">sup</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8065037802-3">[</span><span class="p" data-group-id="8065037802-3">]</span><span class="p" data-group-id="8065037802-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +(which is the default value).</p><p>Example: A child specification to start another supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9238131831-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">sup</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9238131831-2">{</span><span class="ss">sup</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9238131831-3">[</span><span class="p" data-group-id="9238131831-3">]</span><span class="p" data-group-id="9238131831-2">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">transient</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="8065037802-1">}</span><span class="w"> </span><span class="c1">% will cause default shutdown=&gt;infinity</span></code></pre><p><a href="" id="super_tree"></a></p><h2 id="starting-a-supervisor" class="section-heading">
│ │ │ │ +  </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="9238131831-1">}</span><span class="w"> </span><span class="c1">% will cause default shutdown=&gt;infinity</span></code></pre><p><a href="" id="super_tree"></a></p><h2 id="starting-a-supervisor" class="section-heading">
│ │ │ │    <a href="#starting-a-supervisor" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting a Supervisor</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the previous example, the supervisor is started by calling
│ │ │ │ -<code class="inline">ch_sup:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="3786998757-1">(</span><span class="p" data-group-id="3786998757-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3786998757-2">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3786998757-3">[</span><span class="p" data-group-id="3786998757-3">]</span><span class="p" data-group-id="3786998757-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch_sup:start_link</code> calls function <a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/2"><code class="inline">supervisor:start_link/2</code></a>, which spawns and
│ │ │ │ +<code class="inline">ch_sup:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="1030596478-1">(</span><span class="p" data-group-id="1030596478-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1030596478-2">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1030596478-3">[</span><span class="p" data-group-id="1030596478-3">]</span><span class="p" data-group-id="1030596478-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch_sup:start_link</code> calls function <a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/2"><code class="inline">supervisor:start_link/2</code></a>, which spawns and
│ │ │ │  links to a new process, a supervisor.</p><ul><li>The first argument, <code class="inline">ch_sup</code>, is the name of the callback module, that is, the
│ │ │ │  module where the <code class="inline">init</code> callback function is located.</li><li>The second argument, <code class="inline">[]</code>, is a term that is passed as is to the callback
│ │ │ │  function <code class="inline">init</code>. Here, <code class="inline">init</code> does not need any data and ignores the argument.</li></ul><p>In this case, the supervisor is not registered. Instead its pid must be used. A
│ │ │ │  name can be specified by calling
│ │ │ │  <a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link({local, Name}, Module, Args)</code></a>
│ │ │ │  or
│ │ │ │  <a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link({global, Name}, Module, Args)</code></a>.</p><p>The new supervisor process calls the callback function <code class="inline">ch_sup:init([])</code>. <code class="inline">init</code>
│ │ │ │ -has to return <code class="inline">{ok, {SupFlags, ChildSpecs}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5194492708-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5194492708-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5194492708-2">#{</span><span class="p" data-group-id="5194492708-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5194492708-3">[</span><span class="p" data-group-id="5194492708-4">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5194492708-5">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5194492708-6">[</span><span class="p" data-group-id="5194492708-6">]</span><span class="p" data-group-id="5194492708-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="5194492708-4">}</span><span class="p" data-group-id="5194492708-3">]</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5194492708-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5194492708-8">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="5194492708-8">}</span><span class="p" data-group-id="5194492708-7">}</span><span class="p">.</span></code></pre><p>Subsequently, the supervisor starts its child processes according to the child
│ │ │ │ +has to return <code class="inline">{ok, {SupFlags, ChildSpecs}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8907836581-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="8907836581-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8907836581-2">#{</span><span class="p" data-group-id="8907836581-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8907836581-3">[</span><span class="p" data-group-id="8907836581-4">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8907836581-5">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8907836581-6">[</span><span class="p" data-group-id="8907836581-6">]</span><span class="p" data-group-id="8907836581-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="8907836581-4">}</span><span class="p" data-group-id="8907836581-3">]</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8907836581-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8907836581-8">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="8907836581-8">}</span><span class="p" data-group-id="8907836581-7">}</span><span class="p">.</span></code></pre><p>Subsequently, the supervisor starts its child processes according to the child
│ │ │ │  specifications in the start specification. In this case there is a single child
│ │ │ │  process, called <code class="inline">ch3</code>.</p><p><a href="../../../lib/stdlib/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link/3</code></a> is synchronous. It does not return until all child
│ │ │ │  processes have been started.</p><h2 id="adding-a-child-process" class="section-heading">
│ │ │ │    <a href="#adding-a-child-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Adding a Child Process</span>
│ │ │ │ @@ -437,31 +437,31 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simplified one_for_one Supervisors</span>
│ │ │ │  </h2>
│ │ │ │  <p>A supervisor with restart strategy <code class="inline">simple_one_for_one</code> is a simplified
│ │ │ │  <code class="inline">one_for_one</code> supervisor, where all child processes are dynamically added
│ │ │ │  instances of the same process.</p><p>The following is an example of a callback module for a <code class="inline">simple_one_for_one</code>
│ │ │ │ -supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6150394743-1">(</span><span class="ss">simple_sup</span><span class="p" data-group-id="6150394743-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6150394743-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="6150394743-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8981597491-1">(</span><span class="ss">simple_sup</span><span class="p" data-group-id="8981597491-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8981597491-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="8981597491-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6150394743-3">(</span><span class="p" data-group-id="6150394743-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6150394743-4">]</span><span class="p" data-group-id="6150394743-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6150394743-5">(</span><span class="p" data-group-id="6150394743-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6150394743-6">]</span><span class="p" data-group-id="6150394743-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8981597491-3">(</span><span class="p" data-group-id="8981597491-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8981597491-4">]</span><span class="p" data-group-id="8981597491-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8981597491-5">(</span><span class="p" data-group-id="8981597491-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8981597491-6">]</span><span class="p" data-group-id="8981597491-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="6150394743-7">(</span><span class="p" data-group-id="6150394743-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6150394743-8">(</span><span class="ss">simple_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6150394743-9">[</span><span class="p" data-group-id="6150394743-9">]</span><span class="p" data-group-id="6150394743-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="8981597491-7">(</span><span class="p" data-group-id="8981597491-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8981597491-8">(</span><span class="ss">simple_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8981597491-9">[</span><span class="p" data-group-id="8981597491-9">]</span><span class="p" data-group-id="8981597491-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6150394743-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6150394743-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6150394743-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8981597491-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="8981597491-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8981597491-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="p">,</span><span class="w">
│ │ │ │                   </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6150394743-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6150394743-12">[</span><span class="p" data-group-id="6150394743-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">call</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6150394743-14">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6150394743-15">[</span><span class="p" data-group-id="6150394743-15">]</span><span class="p" data-group-id="6150394743-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="6150394743-13">}</span><span class="p" data-group-id="6150394743-12">]</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6150394743-16">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6150394743-17">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="6150394743-17">}</span><span class="p" data-group-id="6150394743-16">}</span><span class="p">.</span></code></pre><p>When started, the supervisor does not start any child
│ │ │ │ +                 </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8981597491-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8981597491-12">[</span><span class="p" data-group-id="8981597491-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">call</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8981597491-14">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8981597491-15">[</span><span class="p" data-group-id="8981597491-15">]</span><span class="p" data-group-id="8981597491-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="8981597491-13">}</span><span class="p" data-group-id="8981597491-12">]</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8981597491-16">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8981597491-17">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="8981597491-17">}</span><span class="p" data-group-id="8981597491-16">}</span><span class="p">.</span></code></pre><p>When started, the supervisor does not start any child
│ │ │ │  processes. Instead, all child processes need to be added dynamically by
│ │ │ │  calling <a href="../../../lib/stdlib/doc/html/supervisor.html#start_child/2"><code class="inline">supervisor:start_child(Sup, List)</code></a>.</p><p><code class="inline">Sup</code> is the pid, or name, of the supervisor. <code class="inline">List</code> is an arbitrary list of
│ │ │ │  terms, which are added to the list of arguments specified in the child
│ │ │ │  specification. If the start function is specified as <code class="inline">{M, F, A}</code>, the child
│ │ │ │  process is started by calling <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply(M, F, A++List)</code></a>.</p><p>For example, adding a child to <code class="inline">simple_sup</code> above:</p><pre><code class="text">supervisor:start_child(Pid, [id1])</code></pre><p>The result is that the child process is started by calling
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply(call, start_link, []++[id1])</code></a>, or actually:</p><pre><code class="text">call:start_link(id1)</code></pre><p>A child under a <code class="inline">simple_one_for_one</code> supervisor can be terminated with the
│ │ │ │  following:</p><pre><code class="text">supervisor:terminate_child(Sup, Pid)</code></pre><p><code class="inline">Sup</code> is the pid, or name, of the supervisor and <code class="inline">Pid</code> is the pid of the child.</p><p>Because a <code class="inline">simple_one_for_one</code> supervisor can have many children, it shuts them
│ │ │ ├── OEBPS/statem.xhtml
│ │ │ │ @@ -29,15 +29,15 @@
│ │ │ │  </h2>
│ │ │ │  <p>Established Automata Theory does not deal much with how a <em>state transition</em>
│ │ │ │  is triggered, but assumes that the output is a function of the input
│ │ │ │  (and the state) and that they are some kind of values.</p><p>For an Event-Driven State Machine, the input is an <em>event</em> that triggers
│ │ │ │  a <em>state transition</em> and the output is actions executed during
│ │ │ │  the <em>state transition</em>.  Analogously to the mathematical model
│ │ │ │  of a Finite State Machine, it can be described as a set of relations
│ │ │ │ -of the following form:</p><pre><code class="makeup erlang" translate="no"><span class="n">State</span><span class="p" data-group-id="4139611785-1">(</span><span class="n">S</span><span class="p" data-group-id="4139611785-1">)</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="4139611785-2">(</span><span class="n">E</span><span class="p" data-group-id="4139611785-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Actions</span><span class="p" data-group-id="4139611785-3">(</span><span class="n">A</span><span class="p" data-group-id="4139611785-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4139611785-4">(</span><span class="n">S</span><span class="err">&#39;</span><span class="p" data-group-id="4139611785-4">)</span></code></pre><p>These relations are interpreted as follows: if we are in state <code class="inline">S</code>,
│ │ │ │ +of the following form:</p><pre><code class="makeup erlang" translate="no"><span class="n">State</span><span class="p" data-group-id="3931694503-1">(</span><span class="n">S</span><span class="p" data-group-id="3931694503-1">)</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="3931694503-2">(</span><span class="n">E</span><span class="p" data-group-id="3931694503-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Actions</span><span class="p" data-group-id="3931694503-3">(</span><span class="n">A</span><span class="p" data-group-id="3931694503-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3931694503-4">(</span><span class="n">S</span><span class="err">&#39;</span><span class="p" data-group-id="3931694503-4">)</span></code></pre><p>These relations are interpreted as follows: if we are in state <code class="inline">S</code>,
│ │ │ │  and event <code class="inline">E</code> occurs, we are to perform actions <code class="inline">A</code>, and make a transition
│ │ │ │  to state <code class="inline">S'</code>.  Notice that <code class="inline">S'</code> can be equal to <code class="inline">S</code>,
│ │ │ │  and that <code class="inline">A</code> can be empty.</p><p>In <code class="inline">gen_statem</code> we define a <em>state change</em> as a <em>state transition</em> in which the
│ │ │ │  new state <code class="inline">S'</code> is different from the current state <code class="inline">S</code>, where &quot;different&quot; means
│ │ │ │  Erlang's strict inequality: <code class="inline">=/=</code> also known as &quot;does not match&quot;. <code class="inline">gen_statem</code>
│ │ │ │  does more things during <em>state changes</em> than during other <em>state transitions</em>.</p><p>As <code class="inline">A</code> and <code class="inline">S'</code> depend only on <code class="inline">S</code> and <code class="inline">E</code>, the kind of state machine described
│ │ │ │  here is a Mealy machine (see, for example, the Wikipedia article
│ │ │ │ @@ -310,20 +310,20 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">State Enter Calls</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <code class="inline">gen_statem</code> behaviour can, if this is enabled, regardless of <em>callback
│ │ │ │  mode</em>, automatically call the <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:state_enter/0"><em>state callback</em></a>
│ │ │ │  with special arguments whenever the state changes, so you can write
│ │ │ │  state enter actions near the rest of the <em>state transition</em> rules.
│ │ │ │ -It typically looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">StateName</span><span class="p" data-group-id="6643479601-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6643479601-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +It typically looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">StateName</span><span class="p" data-group-id="2057868623-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2057868623-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">enter</span><span class="w"> </span><span class="ss">actions</span><span class="w"> </span><span class="ss">here</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6643479601-2">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="6643479601-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="n">StateName</span><span class="p" data-group-id="6643479601-3">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6643479601-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2057868623-2">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="2057868623-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="n">StateName</span><span class="p" data-group-id="2057868623-3">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2057868623-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">actions</span><span class="w"> </span><span class="ss">here</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6643479601-4">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewStateName</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="6643479601-4">}</span><span class="p">.</span></code></pre><p>Since the <em>state enter call</em> is not an event there are restrictions on the
│ │ │ │ +    </span><span class="p" data-group-id="2057868623-4">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewStateName</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="2057868623-4">}</span><span class="p">.</span></code></pre><p>Since the <em>state enter call</em> is not an event there are restrictions on the
│ │ │ │  allowed return value and state <a href="#transition-actions"><em>transition actions</em></a>.
│ │ │ │  You must not change the state, <a href="#postponing-events">postpone</a> this non-event,
│ │ │ │  <a href="#inserted-events">insert any events</a>, or change the
│ │ │ │  <a href="#callback-module"><em>callback module</em></a>.</p><p>The first state that is entered after <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:init/1"><code class="inline">gen_statem:init/1</code></a> will get
│ │ │ │  a <em>state enter call</em> with <code class="inline">OldState</code> equal to the current state.</p><p>You may repeat the <em>state enter call</em> using the <code class="inline">{repeat_state,...}</code> return
│ │ │ │  value from the <a href="#state-callback"><em>state callback</em></a>. In this case
│ │ │ │  <code class="inline">OldState</code> will also be equal to the current state.</p><p>Depending on how your state machine is specified, this can be a very useful
│ │ │ │ @@ -404,72 +404,72 @@
│ │ │ │  
│ │ │ │      locked      --&gt; check_code : {button, Button}\n* Collect Buttons
│ │ │ │      check_code  --&gt; locked     : Incorrect code
│ │ │ │      check_code  --&gt; open       : Correct code\n* do_unlock()\n* Clear Buttons\n* Set state_timeout 10 s
│ │ │ │  
│ │ │ │      open        --&gt; open   : {button, Digit}
│ │ │ │      open        --&gt; locked : state_timeout\n* do_lock()</code></pre><p>This code lock state machine can be implemented using <a href="../../../lib/stdlib/doc/html/gen_statem.html"><code class="inline">gen_statem</code></a> with
│ │ │ │ -the following <em>callback module</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5859264420-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="5859264420-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5859264420-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="5859264420-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5859264420-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock</span><span class="p" data-group-id="5859264420-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the following <em>callback module</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3680633203-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="3680633203-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3680633203-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="3680633203-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3680633203-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock</span><span class="p" data-group-id="3680633203-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5859264420-4">(</span><span class="p" data-group-id="5859264420-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5859264420-5">]</span><span class="p" data-group-id="5859264420-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5859264420-6">(</span><span class="p" data-group-id="5859264420-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5859264420-7">]</span><span class="p" data-group-id="5859264420-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5859264420-8">(</span><span class="p" data-group-id="5859264420-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="5859264420-9">]</span><span class="p" data-group-id="5859264420-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5859264420-10">(</span><span class="p" data-group-id="5859264420-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="5859264420-11">]</span><span class="p" data-group-id="5859264420-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="5859264420-12">(</span><span class="n">Code</span><span class="p" data-group-id="5859264420-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5859264420-13">(</span><span class="p" data-group-id="5859264420-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="5859264420-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5859264420-15">[</span><span class="p" data-group-id="5859264420-15">]</span><span class="p" data-group-id="5859264420-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="5859264420-16">(</span><span class="n">Button</span><span class="p" data-group-id="5859264420-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="5859264420-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5859264420-18">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5859264420-18">}</span><span class="p" data-group-id="5859264420-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="5859264420-19">(</span><span class="n">Code</span><span class="p" data-group-id="5859264420-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="5859264420-20">(</span><span class="p" data-group-id="5859264420-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5859264420-21">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="5859264420-22">(</span><span class="n">Code</span><span class="p" data-group-id="5859264420-22">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5859264420-23">[</span><span class="p" data-group-id="5859264420-23">]</span><span class="p" data-group-id="5859264420-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5859264420-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5859264420-24">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="5859264420-25">(</span><span class="p" data-group-id="5859264420-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="0946848748-1">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0946848748-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0946848748-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0946848748-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="0946848748-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0946848748-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3680633203-4">(</span><span class="p" data-group-id="3680633203-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3680633203-5">]</span><span class="p" data-group-id="3680633203-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3680633203-6">(</span><span class="p" data-group-id="3680633203-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3680633203-7">]</span><span class="p" data-group-id="3680633203-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3680633203-8">(</span><span class="p" data-group-id="3680633203-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="3680633203-9">]</span><span class="p" data-group-id="3680633203-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3680633203-10">(</span><span class="p" data-group-id="3680633203-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="3680633203-11">]</span><span class="p" data-group-id="3680633203-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="3680633203-12">(</span><span class="n">Code</span><span class="p" data-group-id="3680633203-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3680633203-13">(</span><span class="p" data-group-id="3680633203-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="3680633203-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3680633203-15">[</span><span class="p" data-group-id="3680633203-15">]</span><span class="p" data-group-id="3680633203-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="3680633203-16">(</span><span class="n">Button</span><span class="p" data-group-id="3680633203-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="3680633203-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3680633203-18">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3680633203-18">}</span><span class="p" data-group-id="3680633203-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3680633203-19">(</span><span class="n">Code</span><span class="p" data-group-id="3680633203-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="3680633203-20">(</span><span class="p" data-group-id="3680633203-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3680633203-21">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="3680633203-22">(</span><span class="n">Code</span><span class="p" data-group-id="3680633203-22">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3680633203-23">[</span><span class="p" data-group-id="3680633203-23">]</span><span class="p" data-group-id="3680633203-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3680633203-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3680633203-24">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="3680633203-25">(</span><span class="p" data-group-id="3680633203-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="8658877169-1">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8658877169-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8658877169-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="8658877169-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8658877169-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8658877169-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="0946848748-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="0946848748-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="8658877169-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="8658877169-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="0946848748-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="0946848748-5">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0946848748-6">[</span><span class="n">Button</span><span class="p" data-group-id="0946848748-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="8658877169-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="8658877169-5">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="8658877169-6">[</span><span class="n">Button</span><span class="p" data-group-id="8658877169-6">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0946848748-7">(</span><span class="p" data-group-id="0946848748-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="0946848748-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0946848748-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="0946848748-10">[</span><span class="p" data-group-id="0946848748-10">]</span><span class="p" data-group-id="0946848748-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="0946848748-11">[</span><span class="p" data-group-id="0946848748-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="0946848748-12">}</span><span class="p" data-group-id="0946848748-11">]</span><span class="p" data-group-id="0946848748-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8658877169-7">(</span><span class="p" data-group-id="8658877169-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="8658877169-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8658877169-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8658877169-10">[</span><span class="p" data-group-id="8658877169-10">]</span><span class="p" data-group-id="8658877169-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="8658877169-11">[</span><span class="p" data-group-id="8658877169-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8658877169-12">}</span><span class="p" data-group-id="8658877169-11">]</span><span class="p" data-group-id="8658877169-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="0946848748-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0946848748-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="0946848748-14">}</span><span class="p" data-group-id="0946848748-13">}</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="8959648431-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="8959648431-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="8959648431-2">(</span><span class="p" data-group-id="8959648431-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8959648431-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8959648431-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8959648431-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8959648431-5">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8959648431-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8959648431-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8959648431-6">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8959648431-6">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="4779388907-1">(</span><span class="p" data-group-id="4779388907-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4779388907-2">(</span><span class="s">&quot;Lock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4779388907-3">[</span><span class="p" data-group-id="4779388907-3">]</span><span class="p" data-group-id="4779388907-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="4779388907-4">(</span><span class="p" data-group-id="4779388907-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4779388907-5">(</span><span class="s">&quot;Unlock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4779388907-6">[</span><span class="p" data-group-id="4779388907-6">]</span><span class="p" data-group-id="4779388907-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="8658877169-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8658877169-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="8658877169-14">}</span><span class="p" data-group-id="8658877169-13">}</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="9265138137-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="9265138137-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="9265138137-2">(</span><span class="p" data-group-id="9265138137-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9265138137-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9265138137-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="9265138137-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9265138137-5">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9265138137-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9265138137-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9265138137-6">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9265138137-6">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="8773910324-1">(</span><span class="p" data-group-id="8773910324-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8773910324-2">(</span><span class="s">&quot;Lock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8773910324-3">[</span><span class="p" data-group-id="8773910324-3">]</span><span class="p" data-group-id="8773910324-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="8773910324-4">(</span><span class="p" data-group-id="8773910324-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8773910324-5">(</span><span class="s">&quot;Unlock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8773910324-6">[</span><span class="p" data-group-id="8773910324-6">]</span><span class="p" data-group-id="8773910324-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="4779388907-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="4779388907-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="4779388907-8">(</span><span class="p" data-group-id="4779388907-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="8773910324-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8773910324-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="8773910324-8">(</span><span class="p" data-group-id="8773910324-8">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-gen_statem" class="section-heading">
│ │ │ │    <a href="#starting-gen_statem" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting gen_statem</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the example in the previous section, <code class="inline">gen_statem</code> is started by calling
│ │ │ │ -<code class="inline">code_lock:start_link(Code)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="8239839121-1">(</span><span class="n">Code</span><span class="p" data-group-id="8239839121-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8239839121-2">(</span><span class="p" data-group-id="8239839121-3">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="8239839121-3">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8239839121-4">[</span><span class="p" data-group-id="8239839121-4">]</span><span class="p" data-group-id="8239839121-2">)</span><span class="p">.</span></code></pre><p><code class="inline">start_link/1</code> calls function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/4</code></a>,
│ │ │ │ +<code class="inline">code_lock:start_link(Code)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="6404692029-1">(</span><span class="n">Code</span><span class="p" data-group-id="6404692029-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6404692029-2">(</span><span class="p" data-group-id="6404692029-3">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="6404692029-3">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6404692029-4">[</span><span class="p" data-group-id="6404692029-4">]</span><span class="p" data-group-id="6404692029-2">)</span><span class="p">.</span></code></pre><p><code class="inline">start_link/1</code> calls function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/4</code></a>,
│ │ │ │  which spawns and links to a new process, a <code class="inline">gen_statem</code>.</p><ul><li><p>The first argument, <code class="inline">{local,?NAME}</code>, specifies the name. In this case, the
│ │ │ │  <code class="inline">gen_statem</code> is locally registered as <code class="inline">code_lock</code> through the macro <code class="inline">?NAME</code>.</p><p>If the name is omitted, the <code class="inline">gen_statem</code> is not registered. Instead its pid
│ │ │ │  must be used. The name can also be specified as <code class="inline">{global, Name}</code>, then the
│ │ │ │  <code class="inline">gen_statem</code> is registered using <a href="../../../lib/kernel/doc/html/global.html#register_name/2"><code class="inline">global:register_name/2</code></a> in Kernel.</p></li><li><p>The second argument, <code class="inline">?MODULE</code>, is the name of the <em>callback module</em>,
│ │ │ │  that is, the module where the callback functions are located,
│ │ │ │  which is this module.</p><p>The interface functions (<code class="inline">start_link/1</code> and <code class="inline">button/1</code>) are located in the
│ │ │ │  same module as the callback functions (<code class="inline">init/1</code>, <code class="inline">locked/3</code>, and <code class="inline">open/3</code>).
│ │ │ │ @@ -479,184 +479,184 @@
│ │ │ │  see <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3</code></a>.</p></li></ul><p>If name registration succeeds, the new <code class="inline">gen_statem</code> process calls callback
│ │ │ │  function <code class="inline">code_lock:init(Code)</code>. This function is expected to return
│ │ │ │  <code class="inline">{ok, State, Data}</code>, where <code class="inline">State</code> is the initial state of the <code class="inline">gen_statem</code>,
│ │ │ │  in this case <code class="inline">locked</code>; assuming that the door is locked to begin with.
│ │ │ │  <code class="inline">Data</code> is the internal server data of the <code class="inline">gen_statem</code>. Here the server data
│ │ │ │  is a <a href="../../../lib/stdlib/doc/html/maps.html"><code class="inline">map()</code></a> with key <code class="inline">code</code> that stores the correct
│ │ │ │  button sequence, key <code class="inline">length</code> store its length, and key <code class="inline">buttons</code>
│ │ │ │ -that stores the collected buttons up to the same length.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9956561790-1">(</span><span class="n">Code</span><span class="p" data-group-id="9956561790-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="9956561790-2">(</span><span class="p" data-group-id="9956561790-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9956561790-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9956561790-4">(</span><span class="n">Code</span><span class="p" data-group-id="9956561790-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9956561790-5">[</span><span class="p" data-group-id="9956561790-5">]</span><span class="p" data-group-id="9956561790-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9956561790-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9956561790-6">}</span><span class="p">.</span></code></pre><p>Function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │ │ +that stores the collected buttons up to the same length.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6940007520-1">(</span><span class="n">Code</span><span class="p" data-group-id="6940007520-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="6940007520-2">(</span><span class="p" data-group-id="6940007520-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6940007520-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="6940007520-4">(</span><span class="n">Code</span><span class="p" data-group-id="6940007520-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6940007520-5">[</span><span class="p" data-group-id="6940007520-5">]</span><span class="p" data-group-id="6940007520-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6940007520-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6940007520-6">}</span><span class="p">.</span></code></pre><p>Function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │ │  is synchronous. It does not return until the <code class="inline">gen_statem</code> is initialized
│ │ │ │  and is ready to receive events.</p><p>Function <a href="../../../lib/stdlib/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │ │  must be used if the <code class="inline">gen_statem</code> is part of a supervision tree, that is,
│ │ │ │  started by a supervisor.  Function,
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#start/3"><code class="inline">gen_statem:start/3,4</code></a> can be used to start
│ │ │ │  a standalone <code class="inline">gen_statem</code>, meaning it is not part of a supervision tree.</p><p>Function <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:callback_mode/0"><code class="inline">Module:callback_mode/0</code></a> selects
│ │ │ │  the <a href="#callback-modes"><code class="inline">CallbackMode</code></a> for the <em>callback module</em>,
│ │ │ │  in this case <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:callback_mode/0"><code class="inline">state_functions</code></a>.
│ │ │ │ -That is, each state has its own handler function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="7152872050-1">(</span><span class="p" data-group-id="7152872050-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +That is, each state has its own handler function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="5655684600-1">(</span><span class="p" data-group-id="5655684600-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><h2 id="handling-events" class="section-heading">
│ │ │ │    <a href="#handling-events" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Handling Events</span>
│ │ │ │  </h2>
│ │ │ │  <p>The function notifying the code lock about a button event is implemented using
│ │ │ │ -<a href="../../../lib/stdlib/doc/html/gen_statem.html#cast/2"><code class="inline">gen_statem:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">button</span><span class="p" data-group-id="6052743745-1">(</span><span class="n">Button</span><span class="p" data-group-id="6052743745-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6052743745-2">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6052743745-3">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6052743745-3">}</span><span class="p" data-group-id="6052743745-2">)</span><span class="p">.</span></code></pre><p>The first argument is the name of the <code class="inline">gen_statem</code> and must agree with
│ │ │ │ +<a href="../../../lib/stdlib/doc/html/gen_statem.html#cast/2"><code class="inline">gen_statem:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">button</span><span class="p" data-group-id="5141534008-1">(</span><span class="n">Button</span><span class="p" data-group-id="5141534008-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="5141534008-2">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5141534008-3">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5141534008-3">}</span><span class="p" data-group-id="5141534008-2">)</span><span class="p">.</span></code></pre><p>The first argument is the name of the <code class="inline">gen_statem</code> and must agree with
│ │ │ │  the name used to start it. So, we use the same macro <code class="inline">?NAME</code> as when starting.
│ │ │ │  <code class="inline">{button, Button}</code> is the event content.</p><p>The event is sent to the <code class="inline">gen_statem</code>. When the event is received, the
│ │ │ │  <code class="inline">gen_statem</code> calls <code class="inline">StateName(cast, Event, Data)</code>, which is expected
│ │ │ │  to return a tuple <code class="inline">{next_state, NewStateName, NewData}</code>, or
│ │ │ │  <code class="inline">{next_state, NewStateName, NewData, Actions}</code>. <code class="inline">StateName</code> is the name
│ │ │ │  of the current state and <code class="inline">NewStateName</code> is the name of the next state.
│ │ │ │  <code class="inline">NewData</code> is a new value for the server data of the <code class="inline">gen_statem</code>,
│ │ │ │ -and <code class="inline">Actions</code> is a list of actions to be performed by the <code class="inline">gen_statem</code> engine.</p><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="9622714649-1">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9622714649-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9622714649-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9622714649-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9622714649-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9622714649-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +and <code class="inline">Actions</code> is a list of actions to be performed by the <code class="inline">gen_statem</code> engine.</p><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="4469207318-1">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4469207318-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4469207318-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4469207318-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4469207318-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4469207318-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="9622714649-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="9622714649-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="4469207318-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="4469207318-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="9622714649-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="9622714649-5">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9622714649-6">[</span><span class="n">Button</span><span class="p" data-group-id="9622714649-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="4469207318-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="4469207318-5">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4469207318-6">[</span><span class="n">Button</span><span class="p" data-group-id="4469207318-6">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="9622714649-7">(</span><span class="p" data-group-id="9622714649-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9622714649-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9622714649-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9622714649-10">[</span><span class="p" data-group-id="9622714649-10">]</span><span class="p" data-group-id="9622714649-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="9622714649-11">[</span><span class="p" data-group-id="9622714649-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="9622714649-12">}</span><span class="p" data-group-id="9622714649-11">]</span><span class="p" data-group-id="9622714649-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="4469207318-7">(</span><span class="p" data-group-id="4469207318-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="4469207318-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4469207318-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4469207318-10">[</span><span class="p" data-group-id="4469207318-10">]</span><span class="p" data-group-id="4469207318-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="4469207318-11">[</span><span class="p" data-group-id="4469207318-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="4469207318-12">}</span><span class="p" data-group-id="4469207318-11">]</span><span class="p" data-group-id="4469207318-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9622714649-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9622714649-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="9622714649-14">}</span><span class="p" data-group-id="9622714649-13">}</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="4469207318-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4469207318-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="4469207318-14">}</span><span class="p" data-group-id="4469207318-13">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>In state <code class="inline">locked</code>, when a button is pressed, it is collected with the
│ │ │ │  previously pressed buttons up to the length of the correct code, then
│ │ │ │  compared with the correct code. Depending on the result, the door is
│ │ │ │  either unlocked and the <code class="inline">gen_statem</code> goes to state <code class="inline">open</code>, or the door
│ │ │ │  remains in state <code class="inline">locked</code>.</p><p>When changing to state <code class="inline">open</code>, the collected buttons are reset, the lock
│ │ │ │ -unlocked, and a <em>state time-out</em> for 10 seconds is started.</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="9631263527-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9631263527-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9631263527-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9631263527-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9631263527-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9631263527-3">}</span><span class="p">.</span></code></pre><p>In state <code class="inline">open</code>, a button event is ignored by staying in the same state.
│ │ │ │ +unlocked, and a <em>state time-out</em> for 10 seconds is started.</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="3033090703-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3033090703-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3033090703-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3033090703-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3033090703-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3033090703-3">}</span><span class="p">.</span></code></pre><p>In state <code class="inline">open</code>, a button event is ignored by staying in the same state.
│ │ │ │  This can also be done by returning <code class="inline">{keep_state, Data}</code>, or in this case
│ │ │ │  since <code class="inline">Data</code> is unchanged, by returning <code class="inline">keep_state_and_data</code>.</p><h2 id="state-time-outs" class="section-heading">
│ │ │ │    <a href="#state-time-outs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">State Time-Outs</span>
│ │ │ │  </h2>
│ │ │ │  <p>When a correct code has been given, the door is unlocked and the following
│ │ │ │ -tuple is returned from <code class="inline">locked/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5737658584-1">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5737658584-2">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5737658584-3">[</span><span class="p" data-group-id="5737658584-3">]</span><span class="p" data-group-id="5737658584-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5737658584-4">[</span><span class="p" data-group-id="5737658584-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="5737658584-5">}</span><span class="p" data-group-id="5737658584-4">]</span><span class="p" data-group-id="5737658584-1">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span></code></pre><p>10,000 is a time-out value in milliseconds. After this time (10 seconds),
│ │ │ │ +tuple is returned from <code class="inline">locked/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2313165346-1">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2313165346-2">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2313165346-3">[</span><span class="p" data-group-id="2313165346-3">]</span><span class="p" data-group-id="2313165346-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2313165346-4">[</span><span class="p" data-group-id="2313165346-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="2313165346-5">}</span><span class="p" data-group-id="2313165346-4">]</span><span class="p" data-group-id="2313165346-1">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span></code></pre><p>10,000 is a time-out value in milliseconds. After this time (10 seconds),
│ │ │ │  a time-out occurs. Then, <code class="inline">StateName(state_timeout, lock, Data)</code> is called.
│ │ │ │  The time-out occurs when the door has been in state <code class="inline">open</code> for 10 seconds.
│ │ │ │ -After that the door is locked again:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="1606316395-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="1606316395-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="1606316395-2">(</span><span class="p" data-group-id="1606316395-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1606316395-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1606316395-3">}</span><span class="p">;</span></code></pre><p>The timer for a <em>state time-out</em> is automatically canceled when
│ │ │ │ +After that the door is locked again:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="0181592732-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="0181592732-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="0181592732-2">(</span><span class="p" data-group-id="0181592732-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0181592732-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0181592732-3">}</span><span class="p">;</span></code></pre><p>The timer for a <em>state time-out</em> is automatically canceled when
│ │ │ │  the state machine does a <em>state change</em>.</p><p>You can restart, cancel, or update a <em>state time-out</em>. See section
│ │ │ │  <a href="#time-outs"><em>Time-Outs</em></a> for details.</p><h2 id="all-state-events" class="section-heading">
│ │ │ │    <a href="#all-state-events" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">All State Events</span>
│ │ │ │  </h2>
│ │ │ │  <p>Sometimes events can arrive in any state of the <code class="inline">gen_statem</code>. It is convenient
│ │ │ │  to handle these in a common state handler function that all state functions
│ │ │ │  call for events not specific to the state.</p><p>Consider a <code class="inline">code_length/0</code> function that returns the length
│ │ │ │  of the correct code.  We dispatch all events that are not state-specific
│ │ │ │  to the common function <code class="inline">handle_common/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7963479200-1">(</span><span class="p" data-group-id="7963479200-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7963479200-2">]</span><span class="p" data-group-id="7963479200-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3775684285-1">(</span><span class="p" data-group-id="3775684285-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3775684285-2">]</span><span class="p" data-group-id="3775684285-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="7963479200-3">(</span><span class="p" data-group-id="7963479200-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="7963479200-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="7963479200-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="3775684285-3">(</span><span class="p" data-group-id="3775684285-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3775684285-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="3775684285-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="7963479200-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7963479200-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="7963479200-6">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7963479200-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">handle_common</span><span class="p" data-group-id="7963479200-7">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7963479200-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="3775684285-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3775684285-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="3775684285-6">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3775684285-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">handle_common</span><span class="p" data-group-id="3775684285-7">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3775684285-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="7963479200-8">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7963479200-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="7963479200-9">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7963479200-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">handle_common</span><span class="p" data-group-id="7963479200-10">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7963479200-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="7963479200-11">(</span><span class="p" data-group-id="7963479200-12">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="7963479200-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7963479200-13">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="7963479200-13">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7963479200-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7963479200-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="7963479200-15">[</span><span class="p" data-group-id="7963479200-16">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="7963479200-17">(</span><span class="n">Code</span><span class="p" data-group-id="7963479200-17">)</span><span class="p" data-group-id="7963479200-16">}</span><span class="p" data-group-id="7963479200-15">]</span><span class="p" data-group-id="7963479200-14">}</span><span class="p">.</span></code></pre><p>Another way to do it is through a convenience macro <code class="inline">?HANDLE_COMMON/0</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0802038215-1">(</span><span class="p" data-group-id="0802038215-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0802038215-2">]</span><span class="p" data-group-id="0802038215-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="3775684285-8">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3775684285-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="3775684285-9">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3775684285-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">handle_common</span><span class="p" data-group-id="3775684285-10">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3775684285-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="3775684285-11">(</span><span class="p" data-group-id="3775684285-12">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="3775684285-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3775684285-13">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="3775684285-13">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3775684285-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3775684285-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="3775684285-15">[</span><span class="p" data-group-id="3775684285-16">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="3775684285-17">(</span><span class="n">Code</span><span class="p" data-group-id="3775684285-17">)</span><span class="p" data-group-id="3775684285-16">}</span><span class="p" data-group-id="3775684285-15">]</span><span class="p" data-group-id="3775684285-14">}</span><span class="p">.</span></code></pre><p>Another way to do it is through a convenience macro <code class="inline">?HANDLE_COMMON/0</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9012084811-1">(</span><span class="p" data-group-id="9012084811-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9012084811-2">]</span><span class="p" data-group-id="9012084811-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="0802038215-3">(</span><span class="p" data-group-id="0802038215-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="0802038215-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="0802038215-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="9012084811-3">(</span><span class="p" data-group-id="9012084811-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="9012084811-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="9012084811-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0802038215-5">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="0802038215-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="0802038215-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="0802038215-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="0802038215-7">)</span><span class="p" data-group-id="0802038215-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9012084811-5">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="9012084811-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9012084811-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="9012084811-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9012084811-7">)</span><span class="p" data-group-id="9012084811-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="0802038215-8">(</span><span class="p" data-group-id="0802038215-9">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="0802038215-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0802038215-10">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="0802038215-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0802038215-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0802038215-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0802038215-12">[</span><span class="p" data-group-id="0802038215-13">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="0802038215-14">(</span><span class="n">Code</span><span class="p" data-group-id="0802038215-14">)</span><span class="p" data-group-id="0802038215-13">}</span><span class="p" data-group-id="0802038215-12">]</span><span class="p" data-group-id="0802038215-11">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="9012084811-8">(</span><span class="p" data-group-id="9012084811-9">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="9012084811-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9012084811-10">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="9012084811-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9012084811-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9012084811-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="9012084811-12">[</span><span class="p" data-group-id="9012084811-13">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="9012084811-14">(</span><span class="n">Code</span><span class="p" data-group-id="9012084811-14">)</span><span class="p" data-group-id="9012084811-13">}</span><span class="p" data-group-id="9012084811-12">]</span><span class="p" data-group-id="9012084811-11">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="0802038215-15">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0802038215-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="9012084811-15">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9012084811-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="0802038215-16">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0802038215-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="9012084811-16">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9012084811-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><p>This example uses <a href="../../../lib/stdlib/doc/html/gen_statem.html#call/2"><code class="inline">gen_statem:call/2</code></a>, which waits for a reply from the server.
│ │ │ │  The reply is sent with a <code class="inline">{reply, From, Reply}</code> tuple in an action list in the
│ │ │ │  <code class="inline">{keep_state, ...}</code> tuple that retains the current state. This return form is
│ │ │ │  convenient when you want to stay in the current state but do not know or care
│ │ │ │  about what it is.</p><p>If the common <em>state callback</em> needs to know the current state a function
│ │ │ │ -<code class="inline">handle_common/4</code> can be used instead:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9748196149-1">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="9748196149-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9748196149-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="9748196149-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9748196149-3">)</span><span class="p" data-group-id="9748196149-1">)</span><span class="p">.</span></code></pre><h2 id="one-state-callback" class="section-heading">
│ │ │ │ +<code class="inline">handle_common/4</code> can be used instead:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3877800717-1">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="3877800717-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="3877800717-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="3877800717-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="3877800717-3">)</span><span class="p" data-group-id="3877800717-1">)</span><span class="p">.</span></code></pre><h2 id="one-state-callback" class="section-heading">
│ │ │ │    <a href="#one-state-callback" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">One State Callback</span>
│ │ │ │  </h2>
│ │ │ │  <p>If <a href="#callback-modes"><em>callback mode</em></a> <code class="inline">handle_event_function</code> is used,
│ │ │ │  all events are handled in
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:handle_event/4"><code class="inline">Module:handle_event/4</code></a> and we can
│ │ │ │  (but do not have to) use an event-centered approach where we first branch
│ │ │ │  depending on event and then depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2472336689-1">(</span><span class="p" data-group-id="2472336689-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="2472336689-2">]</span><span class="p" data-group-id="2472336689-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7342587600-1">(</span><span class="p" data-group-id="7342587600-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="7342587600-2">]</span><span class="p" data-group-id="7342587600-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="2472336689-3">(</span><span class="p" data-group-id="2472336689-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="7342587600-3">(</span><span class="p" data-group-id="7342587600-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">handle_event_function</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="2472336689-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2472336689-5">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2472336689-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2472336689-6">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="2472336689-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2472336689-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7342587600-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7342587600-5">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7342587600-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7342587600-6">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="7342587600-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7342587600-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │  	</span><span class="ss">locked</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="2472336689-7">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="2472336689-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="7342587600-7">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7342587600-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │                  </span><span class="k">if</span><span class="w">
│ │ │ │ -                    </span><span class="nf">length</span><span class="p" data-group-id="2472336689-8">(</span><span class="n">Buttons</span><span class="p" data-group-id="2472336689-8">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                    </span><span class="nf">length</span><span class="p" data-group-id="7342587600-8">(</span><span class="n">Buttons</span><span class="p" data-group-id="7342587600-8">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                          </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │                      </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                        </span><span class="nf">tl</span><span class="p" data-group-id="2472336689-9">(</span><span class="n">Buttons</span><span class="p" data-group-id="2472336689-9">)</span><span class="w">
│ │ │ │ -                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2472336689-10">[</span><span class="n">Button</span><span class="p" data-group-id="2472336689-10">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                        </span><span class="nf">tl</span><span class="p" data-group-id="7342587600-9">(</span><span class="n">Buttons</span><span class="p" data-group-id="7342587600-9">)</span><span class="w">
│ │ │ │ +                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="7342587600-10">[</span><span class="n">Button</span><span class="p" data-group-id="7342587600-10">]</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="k">if</span><span class="w">
│ │ │ │                  </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2472336689-11">(</span><span class="p" data-group-id="2472336689-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="2472336689-12">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2472336689-13">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2472336689-14">[</span><span class="p" data-group-id="2472336689-14">]</span><span class="p" data-group-id="2472336689-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                     </span><span class="p" data-group-id="2472336689-15">[</span><span class="p" data-group-id="2472336689-16">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="2472336689-16">}</span><span class="p" data-group-id="2472336689-15">]</span><span class="p" data-group-id="2472336689-12">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="7342587600-11">(</span><span class="p" data-group-id="7342587600-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="7342587600-12">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7342587600-13">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7342587600-14">[</span><span class="p" data-group-id="7342587600-14">]</span><span class="p" data-group-id="7342587600-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                     </span><span class="p" data-group-id="7342587600-15">[</span><span class="p" data-group-id="7342587600-16">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="7342587600-16">}</span><span class="p" data-group-id="7342587600-15">]</span><span class="p" data-group-id="7342587600-12">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │                  </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="2472336689-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2472336689-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="2472336689-18">}</span><span class="p" data-group-id="2472336689-17">}</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="7342587600-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7342587600-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="7342587600-18">}</span><span class="p" data-group-id="7342587600-17">}</span><span class="w">
│ │ │ │              </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">open</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="2472336689-19">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2472336689-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="2472336689-20">(</span><span class="p" data-group-id="2472336689-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2472336689-21">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2472336689-21">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="2472336689-22">(</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2472336689-23">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="2472336689-23">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2472336689-24">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="2472336689-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2472336689-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2472336689-25">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="2472336689-26">[</span><span class="p" data-group-id="2472336689-27">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="2472336689-28">(</span><span class="n">Code</span><span class="p" data-group-id="2472336689-28">)</span><span class="p" data-group-id="2472336689-27">}</span><span class="p" data-group-id="2472336689-26">]</span><span class="p" data-group-id="2472336689-25">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7342587600-19">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7342587600-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="7342587600-20">(</span><span class="p" data-group-id="7342587600-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7342587600-21">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7342587600-21">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7342587600-22">(</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7342587600-23">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="7342587600-23">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7342587600-24">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="7342587600-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7342587600-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7342587600-25">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7342587600-26">[</span><span class="p" data-group-id="7342587600-27">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="7342587600-28">(</span><span class="n">Code</span><span class="p" data-group-id="7342587600-28">)</span><span class="p" data-group-id="7342587600-27">}</span><span class="p" data-group-id="7342587600-26">]</span><span class="p" data-group-id="7342587600-25">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │ │    <a href="#stopping" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Stopping</span>
│ │ │ │  </h2>
│ │ │ │ @@ -668,59 +668,59 @@
│ │ │ │  </h3>
│ │ │ │  <p>If the <code class="inline">gen_statem</code> is part of a supervision tree, no stop function is needed.
│ │ │ │  The <code class="inline">gen_statem</code> is automatically terminated by its supervisor. Exactly how
│ │ │ │  this is done is defined by a <a href="sup_princ.xhtml#shutdown">shutdown strategy</a>
│ │ │ │  set in the supervisor.</p><p>If it is necessary to clean up before termination, the shutdown strategy
│ │ │ │  must be a time-out value and the <code class="inline">gen_statem</code> must in function <code class="inline">init/1</code>
│ │ │ │  set itself to trap exit signals by calling
│ │ │ │ -<a href="../../../lib/../erts/doc/html/erlang.html#process_flag/2"><code class="inline">process_flag(trap_exit, true)</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4275981155-1">(</span><span class="n">Args</span><span class="p" data-group-id="4275981155-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="4275981155-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4275981155-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="4275981155-3">(</span><span class="p" data-group-id="4275981155-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +<a href="../../../lib/../erts/doc/html/erlang.html#process_flag/2"><code class="inline">process_flag(trap_exit, true)</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5544392033-1">(</span><span class="n">Args</span><span class="p" data-group-id="5544392033-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="5544392033-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5544392033-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="5544392033-3">(</span><span class="p" data-group-id="5544392033-3">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>When ordered to shut down, the <code class="inline">gen_statem</code> then calls callback function
│ │ │ │  <code class="inline">terminate(shutdown, State, Data)</code>.</p><p>In this example, function <code class="inline">terminate/3</code> locks the door if it is open,
│ │ │ │  so we do not accidentally leave the door open
│ │ │ │ -when the supervision tree terminates:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="6769997216-1">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="6769997216-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="6769997216-2">(</span><span class="p" data-group-id="6769997216-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +when the supervision tree terminates:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="2711101976-1">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2711101976-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="2711101976-2">(</span><span class="p" data-group-id="2711101976-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="standalone-gen_statem" class="section-heading">
│ │ │ │    <a href="#standalone-gen_statem" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Standalone gen_statem</span>
│ │ │ │  </h3>
│ │ │ │  <p>If the <code class="inline">gen_statem</code> is not part of a supervision tree, it can be stopped
│ │ │ │  using <a href="../../../lib/stdlib/doc/html/gen_statem.html#stop/1"><code class="inline">gen_statem:stop/1</code></a>, preferably through
│ │ │ │  an API function:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7459409480-1">(</span><span class="p" data-group-id="7459409480-2">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7459409480-2">]</span><span class="p" data-group-id="7459409480-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6081881857-1">(</span><span class="p" data-group-id="6081881857-2">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6081881857-2">]</span><span class="p" data-group-id="6081881857-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="7459409480-3">(</span><span class="p" data-group-id="7459409480-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7459409480-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="7459409480-4">)</span><span class="p">.</span></code></pre><p>This makes the <code class="inline">gen_statem</code> call callback function <code class="inline">terminate/3</code> just like
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="6081881857-3">(</span><span class="p" data-group-id="6081881857-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="6081881857-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="6081881857-4">)</span><span class="p">.</span></code></pre><p>This makes the <code class="inline">gen_statem</code> call callback function <code class="inline">terminate/3</code> just like
│ │ │ │  for a supervised server and waits for the process to terminate.</p><h2 id="event-time-outs" class="section-heading">
│ │ │ │    <a href="#event-time-outs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Event Time-Outs</span>
│ │ │ │  </h2>
│ │ │ │  <p>A time-out feature inherited from <code class="inline">gen_statem</code>'s predecessor <a href="../../../lib/stdlib/doc/html/gen_fsm.html"><code class="inline">gen_fsm</code></a>,
│ │ │ │  is an <em>event time-out</em>, that is, if an event arrives the timer is canceled.
│ │ │ │  You get either an event or a time-out, but not both.</p><p>It is ordered by the
│ │ │ │  <a href="#transition-actions"><em>transition action</em></a> <code class="inline">{timeout, Time, EventContent}</code>,
│ │ │ │  or just an integer <code class="inline">Time</code>, even without the enclosing actions list (the latter
│ │ │ │  is a form inherited from <code class="inline">gen_fsm</code>).</p><p>This type of time-out is useful, for example, to act on inactivity.
│ │ │ │  Let's restart the code sequence if no button is pressed for say 30 seconds:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="9580142222-1">(</span><span class="ss">timeout</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9580142222-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9580142222-2">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9580142222-3">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9580142222-4">[</span><span class="p" data-group-id="9580142222-4">]</span><span class="p" data-group-id="9580142222-3">}</span><span class="p" data-group-id="9580142222-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="9580142222-5">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9580142222-6">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9580142222-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9580142222-7">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9580142222-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9580142222-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="7311500121-1">(</span><span class="ss">timeout</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7311500121-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7311500121-2">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7311500121-3">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7311500121-4">[</span><span class="p" data-group-id="7311500121-4">]</span><span class="p" data-group-id="7311500121-3">}</span><span class="p" data-group-id="7311500121-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="7311500121-5">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7311500121-6">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7311500121-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7311500121-7">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7311500121-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7311500121-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9580142222-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9580142222-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="9580142222-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p" data-group-id="9580142222-8">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="7311500121-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7311500121-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="7311500121-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p" data-group-id="7311500121-8">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Whenever we receive a button event we start an <em>event time-out</em> of 30 seconds,
│ │ │ │  and if we get an <em>event type</em> of <code class="inline">timeout</code> we reset the remaining
│ │ │ │  code sequence.</p><p>An <em>event time-out</em> is canceled by any other event so you either get
│ │ │ │  some other event or the time-out event. Therefore, canceling,
│ │ │ │  restarting, or updating an <em>event time-out</em> is neither possible nor
│ │ │ │  necessary. Whatever event you act on has already canceled
│ │ │ │  the <em>event time-out</em>, so there is never a running <em>event time-out</em>
│ │ │ │ @@ -739,30 +739,30 @@
│ │ │ │  another, maybe cancel the time-out without changing states, or perhaps run
│ │ │ │  multiple time-outs in parallel. All this can be accomplished with
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:generic_timeout/0"><em>generic time-outs</em></a>. They may look a little
│ │ │ │  bit like <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:event_timeout/0"><em>event time-outs</em></a> but contain
│ │ │ │  a name to allow for any number of them simultaneously and they are
│ │ │ │  not automatically canceled.</p><p>Here is how to accomplish the <em>state time-out</em> in the previous example
│ │ │ │  by instead using a <em>generic time-out</em> named for example <code class="inline">open</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="9494326524-1">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9494326524-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9494326524-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9494326524-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9494326524-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9494326524-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="9993852207-1">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9993852207-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9993852207-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9993852207-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9993852207-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9993852207-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="9494326524-4">(</span><span class="p" data-group-id="9494326524-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9494326524-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9494326524-6">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9494326524-7">[</span><span class="p" data-group-id="9494326524-7">]</span><span class="p" data-group-id="9494326524-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="9494326524-8">[</span><span class="p" data-group-id="9494326524-9">{</span><span class="p" data-group-id="9494326524-10">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="9494326524-10">}</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="9494326524-9">}</span><span class="p" data-group-id="9494326524-8">]</span><span class="p" data-group-id="9494326524-5">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="9993852207-4">(</span><span class="p" data-group-id="9993852207-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9993852207-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9993852207-6">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9993852207-7">[</span><span class="p" data-group-id="9993852207-7">]</span><span class="p" data-group-id="9993852207-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="9993852207-8">[</span><span class="p" data-group-id="9993852207-9">{</span><span class="p" data-group-id="9993852207-10">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="9993852207-10">}</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="9993852207-9">}</span><span class="p" data-group-id="9993852207-8">]</span><span class="p" data-group-id="9993852207-5">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="9494326524-11">(</span><span class="p" data-group-id="9494326524-12">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="9494326524-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9494326524-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="9494326524-13">(</span><span class="p" data-group-id="9494326524-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9494326524-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="9494326524-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="9494326524-15">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9494326524-16">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9494326524-16">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9494326524-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9494326524-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="9494326524-17">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="9993852207-11">(</span><span class="p" data-group-id="9993852207-12">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="9993852207-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9993852207-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="9993852207-13">(</span><span class="p" data-group-id="9993852207-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9993852207-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="9993852207-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="9993852207-15">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9993852207-16">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9993852207-16">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9993852207-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9993852207-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="9993852207-17">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Specific <em>generic time-outs</em> can just as <a href="#state-time-outs"><em>state time-outs</em></a>
│ │ │ │  be restarted or canceled by setting it to a new time or <code class="inline">infinity</code>.</p><p>In this particular case we do not need to cancel the time-out since
│ │ │ │  the time-out event is the only possible reason to do a <em>state change</em>
│ │ │ │  from <code class="inline">open</code> to <code class="inline">locked</code>.</p><p>Instead of bothering with when to cancel a time-out, a late time-out event
│ │ │ │  can be handled by ignoring it if it arrives in a state
│ │ │ │  where it is known to be late.</p><p>You can restart, cancel, or update a <em>generic time-out</em>.
│ │ │ │  See section <a href="#time-outs"><em>Time-Outs</em></a> for details.</p><h2 id="erlang-timers" class="section-heading">
│ │ │ │ @@ -774,32 +774,32 @@
│ │ │ │  <p>The most versatile way to handle time-outs is to use Erlang Timers; see
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#start_timer/4"><code class="inline">erlang:start_timer/3,4</code></a>. Most time-out tasks
│ │ │ │  can be performed with the time-out features in <a href="../../../lib/stdlib/doc/html/gen_statem.html"><code class="inline">gen_statem</code></a>,
│ │ │ │  but an example of one that cannot is if you should need the return value
│ │ │ │  from <a href="../../../lib/../erts/doc/html/erlang.html#cancel_timer/2"><code class="inline">erlang:cancel_timer(Tref)</code></a>, that is,
│ │ │ │  the remaining time of the timer.</p><p>Here is how to accomplish the <em>state time-out</em> in the previous example
│ │ │ │  by instead using an Erlang Timer:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="5878963680-1">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5878963680-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5878963680-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5878963680-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="5878963680-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5878963680-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="8527417628-1">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8527417628-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8527417628-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="8527417628-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8527417628-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8527417628-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="5878963680-4">(</span><span class="p" data-group-id="5878963680-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="8527417628-4">(</span><span class="p" data-group-id="8527417628-4">)</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="n">Tref</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -                 </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">start_timer</span><span class="p" data-group-id="5878963680-5">(</span><span class="w">
│ │ │ │ -                     </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5878963680-6">(</span><span class="p" data-group-id="5878963680-6">)</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p" data-group-id="5878963680-5">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="5878963680-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5878963680-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5878963680-9">[</span><span class="p" data-group-id="5878963680-9">]</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="5878963680-8">}</span><span class="p" data-group-id="5878963680-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +                 </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">start_timer</span><span class="p" data-group-id="8527417628-5">(</span><span class="w">
│ │ │ │ +                     </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8527417628-6">(</span><span class="p" data-group-id="8527417628-6">)</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p" data-group-id="8527417628-5">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="8527417628-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8527417628-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8527417628-9">[</span><span class="p" data-group-id="8527417628-9">]</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="8527417628-8">}</span><span class="p" data-group-id="8527417628-7">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5878963680-10">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5878963680-11">{</span><span class="ss">timeout</span><span class="p">,</span><span class="n">Tref</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="5878963680-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5878963680-12">#{</span><span class="ss">timer</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="5878963680-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5878963680-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="5878963680-13">(</span><span class="p" data-group-id="5878963680-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5878963680-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="5878963680-15">(</span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5878963680-15">)</span><span class="p" data-group-id="5878963680-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5878963680-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5878963680-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5878963680-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5878963680-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5878963680-18">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="5878963680-18">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="8527417628-10">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8527417628-11">{</span><span class="ss">timeout</span><span class="p">,</span><span class="n">Tref</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="8527417628-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8527417628-12">#{</span><span class="ss">timer</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="8527417628-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8527417628-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="8527417628-13">(</span><span class="p" data-group-id="8527417628-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8527417628-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="8527417628-15">(</span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8527417628-15">)</span><span class="p" data-group-id="8527417628-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="8527417628-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8527417628-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8527417628-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8527417628-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8527417628-18">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="8527417628-18">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Removing the <code class="inline">timer</code> key from the map when we do a <em>state change</em> to <code class="inline">locked</code>
│ │ │ │  is not strictly necessary since we can only get into state <code class="inline">open</code>
│ │ │ │  with an updated <code class="inline">timer</code> map value. But it can be nice to not have
│ │ │ │  outdated values in the state <code class="inline">Data</code>.</p><p>If you need to cancel a timer because of some other event, you can use
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#cancel_timer/2"><code class="inline">erlang:cancel_timer(Tref)</code></a>. Note that no time-out
│ │ │ │  message will arrive after this (because the timer has been
│ │ │ │  explicitly canceled), unless you have already postponed one earlier
│ │ │ │ @@ -815,16 +815,16 @@
│ │ │ │    <span class="text">Postponing Events</span>
│ │ │ │  </h2>
│ │ │ │  <p>If you want to ignore a particular event in the current state and handle it
│ │ │ │  in a future state, you can postpone the event. A postponed event
│ │ │ │  is retried after a <em>state change</em>, that is, <code class="inline">OldState =/= NewState</code>.</p><p>Postponing is ordered by the
│ │ │ │  <a href="#transition-actions"><em>transition action</em></a> <code class="inline">postpone</code>.</p><p>In this example, instead of ignoring button events while in the <code class="inline">open</code> state,
│ │ │ │  we can postpone them handle them later in the <code class="inline">locked</code> state:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="9783696608-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9783696608-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9783696608-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9783696608-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9783696608-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="9783696608-4">[</span><span class="ss">postpone</span><span class="p" data-group-id="9783696608-4">]</span><span class="p" data-group-id="9783696608-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="9161550812-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9161550812-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9161550812-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9161550812-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9161550812-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="9161550812-4">[</span><span class="ss">postpone</span><span class="p" data-group-id="9161550812-4">]</span><span class="p" data-group-id="9161550812-3">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Since a postponed event is only retried after a <em>state change</em>, you have to
│ │ │ │  think about where to keep a state data item. You can keep it in the server
│ │ │ │  <code class="inline">Data</code> or in the <code class="inline">State</code> itself, for example by having two more or less
│ │ │ │  identical states to keep a boolean value, or by using a complex state (see
│ │ │ │  section <a href="#complex-state"><em>Complex State</em></a>) with
│ │ │ │  <a href="#callback-modes"><em>callback mode</em></a>
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:callback_mode/0"><code class="inline">handle_event_function</code></a>. If a change
│ │ │ │ @@ -845,55 +845,55 @@
│ │ │ │    <a href="#selective-receive" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Selective Receive</span>
│ │ │ │  </h3>
│ │ │ │  <p>Erlang's selective <code class="inline">receive</code> statement is often used to describe simple state
│ │ │ │  machine examples in straightforward Erlang code. The following is a possible
│ │ │ │ -implementation of the first example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1742626447-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="1742626447-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1742626447-2">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_1</span><span class="p" data-group-id="1742626447-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1742626447-3">(</span><span class="p" data-group-id="1742626447-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1742626447-4">]</span><span class="p" data-group-id="1742626447-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="1742626447-5">(</span><span class="n">Code</span><span class="p" data-group-id="1742626447-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1742626447-6">(</span><span class="w">
│ │ │ │ -      </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1742626447-7">(</span><span class="p" data-group-id="1742626447-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">register</span><span class="p" data-group-id="1742626447-8">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1742626447-9">(</span><span class="p" data-group-id="1742626447-9">)</span><span class="p" data-group-id="1742626447-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	      </span><span class="nf">do_lock</span><span class="p" data-group-id="1742626447-10">(</span><span class="p" data-group-id="1742626447-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	      </span><span class="nf">locked</span><span class="p" data-group-id="1742626447-11">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1742626447-12">(</span><span class="n">Code</span><span class="p" data-group-id="1742626447-12">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1742626447-13">[</span><span class="p" data-group-id="1742626447-13">]</span><span class="p" data-group-id="1742626447-11">)</span><span class="w">
│ │ │ │ -      </span><span class="k">end</span><span class="p" data-group-id="1742626447-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +implementation of the first example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0269257123-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="0269257123-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0269257123-2">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_1</span><span class="p" data-group-id="0269257123-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0269257123-3">(</span><span class="p" data-group-id="0269257123-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0269257123-4">]</span><span class="p" data-group-id="0269257123-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="0269257123-5">(</span><span class="n">Code</span><span class="p" data-group-id="0269257123-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="0269257123-6">(</span><span class="w">
│ │ │ │ +      </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0269257123-7">(</span><span class="p" data-group-id="0269257123-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">register</span><span class="p" data-group-id="0269257123-8">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0269257123-9">(</span><span class="p" data-group-id="0269257123-9">)</span><span class="p" data-group-id="0269257123-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	      </span><span class="nf">do_lock</span><span class="p" data-group-id="0269257123-10">(</span><span class="p" data-group-id="0269257123-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	      </span><span class="nf">locked</span><span class="p" data-group-id="0269257123-11">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0269257123-12">(</span><span class="n">Code</span><span class="p" data-group-id="0269257123-12">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0269257123-13">[</span><span class="p" data-group-id="0269257123-13">]</span><span class="p" data-group-id="0269257123-11">)</span><span class="w">
│ │ │ │ +      </span><span class="k">end</span><span class="p" data-group-id="0269257123-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="1742626447-14">(</span><span class="n">Button</span><span class="p" data-group-id="1742626447-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">NAME</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1742626447-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1742626447-15">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="0233662601-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="0233662601-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="0269257123-14">(</span><span class="n">Button</span><span class="p" data-group-id="0269257123-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">NAME</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0269257123-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0269257123-15">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="3331661253-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="3331661253-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0233662601-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0233662601-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3331661253-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3331661253-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │                  </span><span class="k">if</span><span class="w">
│ │ │ │ -                    </span><span class="nf">length</span><span class="p" data-group-id="0233662601-3">(</span><span class="n">Buttons</span><span class="p" data-group-id="0233662601-3">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                    </span><span class="nf">length</span><span class="p" data-group-id="3331661253-3">(</span><span class="n">Buttons</span><span class="p" data-group-id="3331661253-3">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                          </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │                      </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                        </span><span class="nf">tl</span><span class="p" data-group-id="0233662601-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="0233662601-4">)</span><span class="w">
│ │ │ │ -                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0233662601-5">[</span><span class="n">Button</span><span class="p" data-group-id="0233662601-5">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                        </span><span class="nf">tl</span><span class="p" data-group-id="3331661253-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="3331661253-4">)</span><span class="w">
│ │ │ │ +                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3331661253-5">[</span><span class="n">Button</span><span class="p" data-group-id="3331661253-5">]</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="k">if</span><span class="w">
│ │ │ │                  </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0233662601-6">(</span><span class="p" data-group-id="0233662601-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -		    </span><span class="nf">open</span><span class="p" data-group-id="0233662601-7">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="0233662601-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3331661253-6">(</span><span class="p" data-group-id="3331661253-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +		    </span><span class="nf">open</span><span class="p" data-group-id="3331661253-7">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="3331661253-7">)</span><span class="p">;</span><span class="w">
│ │ │ │                  </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -                    </span><span class="nf">locked</span><span class="p" data-group-id="0233662601-8">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="0233662601-8">)</span><span class="w">
│ │ │ │ +                    </span><span class="nf">locked</span><span class="p" data-group-id="3331661253-8">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="3331661253-8">)</span><span class="w">
│ │ │ │              </span><span class="k">end</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="9427711858-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="9427711858-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="3802798318-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="3802798318-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -	    </span><span class="nf">do_lock</span><span class="p" data-group-id="9427711858-2">(</span><span class="p" data-group-id="9427711858-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">locked</span><span class="p" data-group-id="9427711858-3">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9427711858-4">[</span><span class="p" data-group-id="9427711858-4">]</span><span class="p" data-group-id="9427711858-3">)</span><span class="w">
│ │ │ │ +	    </span><span class="nf">do_lock</span><span class="p" data-group-id="3802798318-2">(</span><span class="p" data-group-id="3802798318-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="nf">locked</span><span class="p" data-group-id="3802798318-3">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3802798318-4">[</span><span class="p" data-group-id="3802798318-4">]</span><span class="p" data-group-id="3802798318-3">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">do_lock</span><span class="p" data-group-id="9427711858-5">(</span><span class="p" data-group-id="9427711858-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9427711858-6">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9427711858-7">[</span><span class="p" data-group-id="9427711858-7">]</span><span class="p" data-group-id="9427711858-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="9427711858-8">(</span><span class="p" data-group-id="9427711858-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9427711858-9">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9427711858-10">[</span><span class="p" data-group-id="9427711858-10">]</span><span class="p" data-group-id="9427711858-9">)</span><span class="p">.</span></code></pre><p>The selective receive in this case causes <code class="inline">open</code> to implicitly postpone any
│ │ │ │ +</span><span class="nf">do_lock</span><span class="p" data-group-id="3802798318-5">(</span><span class="p" data-group-id="3802798318-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3802798318-6">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3802798318-7">[</span><span class="p" data-group-id="3802798318-7">]</span><span class="p" data-group-id="3802798318-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="3802798318-8">(</span><span class="p" data-group-id="3802798318-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3802798318-9">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3802798318-10">[</span><span class="p" data-group-id="3802798318-10">]</span><span class="p" data-group-id="3802798318-9">)</span><span class="p">.</span></code></pre><p>The selective receive in this case causes <code class="inline">open</code> to implicitly postpone any
│ │ │ │  events to the <code class="inline">locked</code> state.</p><p>A catch-all receive should never be used from a <code class="inline">gen_statem</code> behaviour
│ │ │ │  (or from any <code class="inline">gen_*</code> behaviour), as the receive statement is within
│ │ │ │  the <code class="inline">gen_*</code> engine itself. <a href="../../../lib/stdlib/doc/html/sys.html"><code class="inline">sys</code></a>-compatible behaviours must respond to
│ │ │ │  system messages and therefore do that in their engine receive loop,
│ │ │ │  passing non-system messages to the <em>callback module</em>. Using a catch-all
│ │ │ │  receive can result in system messages being discarded, which in turn
│ │ │ │  can lead to unexpected behaviour. If a selective receive must be used,
│ │ │ │ @@ -916,40 +916,40 @@
│ │ │ │  section), especially if only one or a few states have state enter actions,
│ │ │ │  this is a perfect use case for the built in
│ │ │ │  <a href="#state-enter-calls"><em>state enter calls</em></a>.</p><p>You return a list containing <code class="inline">state_enter</code> from your
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:callback_mode/0"><code class="inline">callback_mode/0</code></a> function and the
│ │ │ │  <code class="inline">gen_statem</code> engine will call your <em>state callback</em> once with an event
│ │ │ │  <code class="inline">(enter, OldState, ...)</code> whenever it does a <em>state change</em>. Then you
│ │ │ │  just need to handle these event-like calls in all states.</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="0710960073-1">(</span><span class="n">Code</span><span class="p" data-group-id="0710960073-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="0710960073-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0710960073-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0710960073-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0710960073-4">(</span><span class="n">Code</span><span class="p" data-group-id="0710960073-4">)</span><span class="p" data-group-id="0710960073-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0710960073-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0710960073-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="0710960073-6">(</span><span class="p" data-group-id="0710960073-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0710960073-7">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="0710960073-7">]</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="0710960073-8">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0710960073-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="0710960073-9">(</span><span class="p" data-group-id="0710960073-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0710960073-10">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="0710960073-11">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0710960073-12">[</span><span class="p" data-group-id="0710960073-12">]</span><span class="p" data-group-id="0710960073-11">}</span><span class="p" data-group-id="0710960073-10">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="0710960073-13">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0710960073-14">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0710960073-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0710960073-15">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="0710960073-15">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0710960073-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="7646387988-1">(</span><span class="n">Code</span><span class="p" data-group-id="7646387988-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="7646387988-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7646387988-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7646387988-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7646387988-4">(</span><span class="n">Code</span><span class="p" data-group-id="7646387988-4">)</span><span class="p" data-group-id="7646387988-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7646387988-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7646387988-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="7646387988-6">(</span><span class="p" data-group-id="7646387988-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7646387988-7">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="7646387988-7">]</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="7646387988-8">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7646387988-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="7646387988-9">(</span><span class="p" data-group-id="7646387988-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7646387988-10">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="7646387988-11">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7646387988-12">[</span><span class="p" data-group-id="7646387988-12">]</span><span class="p" data-group-id="7646387988-11">}</span><span class="p" data-group-id="7646387988-10">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="7646387988-13">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7646387988-14">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7646387988-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7646387988-15">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7646387988-15">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7646387988-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="0710960073-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0710960073-16">}</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="7646387988-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7646387988-16">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="0710960073-17">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0710960073-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0710960073-18">(</span><span class="p" data-group-id="0710960073-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0710960073-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0710960073-20">[</span><span class="p" data-group-id="0710960073-21">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="0710960073-21">}</span><span class="p" data-group-id="0710960073-20">]</span><span class="p" data-group-id="0710960073-19">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="0710960073-22">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0710960073-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0710960073-23">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0710960073-23">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="7646387988-17">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="7646387988-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="7646387988-18">(</span><span class="p" data-group-id="7646387988-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7646387988-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7646387988-20">[</span><span class="p" data-group-id="7646387988-21">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="7646387988-21">}</span><span class="p" data-group-id="7646387988-20">]</span><span class="p" data-group-id="7646387988-19">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="7646387988-22">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7646387988-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7646387988-23">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7646387988-23">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>You can repeat the state enter code by returning one of
│ │ │ │  <code class="inline">{repeat_state, ...}</code>,<code class="inline">{repeat_state_and_data, _}</code>,
│ │ │ │  or <code class="inline">repeat_state_and_data</code> that otherwise behaves exactly like their
│ │ │ │  <code class="inline">keep_state</code> siblings.  See the type
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:state_callback_result/2"><code class="inline">state_callback_result()</code></a>
│ │ │ │  in the Reference Manual.</p><h2 id="inserted-events" class="section-heading">
│ │ │ │    <a href="#inserted-events" class="hover-link">
│ │ │ │ @@ -971,44 +971,44 @@
│ │ │ │  to dispatch pre-processed events as internal events to the main state
│ │ │ │  machine.</p><p>Using internal events also can make it easier to synchronize the state
│ │ │ │  machines.</p><p>A variant of this is to use a <a href="#complex-state">complex state</a> with
│ │ │ │  <a href="#one-state-callback">one state callback</a>, modeling the state
│ │ │ │  with, for example, a tuple <code class="inline">{MainFSMState, SubFSMState}</code>.</p><p>To illustrate this we make up an example where the buttons instead generate
│ │ │ │  down and up (press and release) events, and the lock responds
│ │ │ │  to an up event only after the corresponding down event.</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7841917076-1">(</span><span class="p" data-group-id="7841917076-2">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7841917076-2">]</span><span class="p" data-group-id="7841917076-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9800227718-1">(</span><span class="p" data-group-id="9800227718-2">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9800227718-2">]</span><span class="p" data-group-id="9800227718-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">down</span><span class="p" data-group-id="7841917076-3">(</span><span class="n">Button</span><span class="p" data-group-id="7841917076-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="7841917076-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7841917076-5">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7841917076-5">}</span><span class="p" data-group-id="7841917076-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">down</span><span class="p" data-group-id="9800227718-3">(</span><span class="n">Button</span><span class="p" data-group-id="9800227718-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="9800227718-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9800227718-5">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9800227718-5">}</span><span class="p" data-group-id="9800227718-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">up</span><span class="p" data-group-id="7841917076-6">(</span><span class="n">Button</span><span class="p" data-group-id="7841917076-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="7841917076-7">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7841917076-8">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7841917076-8">}</span><span class="p" data-group-id="7841917076-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">up</span><span class="p" data-group-id="9800227718-6">(</span><span class="n">Button</span><span class="p" data-group-id="9800227718-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="9800227718-7">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9800227718-8">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9800227718-8">}</span><span class="p" data-group-id="9800227718-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="7841917076-9">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7841917076-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="7841917076-10">(</span><span class="p" data-group-id="7841917076-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7841917076-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="7841917076-12">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7841917076-13">[</span><span class="p" data-group-id="7841917076-13">]</span><span class="p" data-group-id="7841917076-12">}</span><span class="p" data-group-id="7841917076-11">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="7841917076-14">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7841917076-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7841917076-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="7841917076-16">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7841917076-16">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7841917076-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">handle_common</span><span class="p" data-group-id="7879827479-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7879827479-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7879827479-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7879827479-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7879827479-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7879827479-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="7879827479-4">}</span><span class="p" data-group-id="7879827479-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="7879827479-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7879827479-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7879827479-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7879827479-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="9800227718-9">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9800227718-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="9800227718-10">(</span><span class="p" data-group-id="9800227718-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9800227718-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="9800227718-12">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9800227718-13">[</span><span class="p" data-group-id="9800227718-13">]</span><span class="p" data-group-id="9800227718-12">}</span><span class="p" data-group-id="9800227718-11">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="9800227718-14">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9800227718-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9800227718-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9800227718-16">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9800227718-16">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9800227718-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">handle_common</span><span class="p" data-group-id="7392293867-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7392293867-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7392293867-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7392293867-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7392293867-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7392293867-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="7392293867-4">}</span><span class="p" data-group-id="7392293867-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="7392293867-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7392293867-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7392293867-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7392293867-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7879827479-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="7879827479-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="7879827479-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="7879827479-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7879827479-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="7879827479-10">[</span><span class="p" data-group-id="7879827479-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="7879827479-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7879827479-12">}</span><span class="p" data-group-id="7879827479-11">}</span><span class="p" data-group-id="7879827479-10">]</span><span class="p" data-group-id="7879827479-8">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7879827479-13">#{</span><span class="p" data-group-id="7879827479-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7392293867-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="7392293867-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="7392293867-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="7392293867-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7392293867-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="7392293867-10">[</span><span class="p" data-group-id="7392293867-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="7392293867-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7392293867-12">}</span><span class="p" data-group-id="7392293867-11">}</span><span class="p" data-group-id="7392293867-10">]</span><span class="p" data-group-id="7392293867-8">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7392293867-13">#{</span><span class="p" data-group-id="7392293867-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="7879827479-14">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7879827479-15">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7879827479-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7879827479-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7879827479-16">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="7879827479-17">[</span><span class="ss">postpone</span><span class="p" data-group-id="7879827479-17">]</span><span class="p" data-group-id="7879827479-16">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="7392293867-14">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7392293867-15">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7392293867-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7392293867-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7392293867-16">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="7392293867-17">[</span><span class="ss">postpone</span><span class="p" data-group-id="7392293867-17">]</span><span class="p" data-group-id="7392293867-16">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>If you start this program with <code class="inline">code_lock:start([17])</code> you can unlock with
│ │ │ │  <code class="inline">code_lock:down(17), code_lock:up(17).</code></p><h2 id="example-revisited" class="section-heading">
│ │ │ │    <a href="#example-revisited" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example Revisited</span>
│ │ │ │  </h2>
│ │ │ │ @@ -1036,152 +1036,152 @@
│ │ │ │  Also, the state diagram does not show that the <code class="inline">code_length/0</code> call
│ │ │ │  must be handled in every state.</p><h3 id="callback-mode-state_functions" class="section-heading">
│ │ │ │    <a href="#callback-mode-state_functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Callback Mode: state_functions</span>
│ │ │ │  </h3>
│ │ │ │ -<p>Using state functions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4822676969-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="4822676969-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4822676969-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="4822676969-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4822676969-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_2</span><span class="p" data-group-id="4822676969-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>Using state functions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0934369912-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="0934369912-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0934369912-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="0934369912-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0934369912-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_2</span><span class="p" data-group-id="0934369912-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4822676969-4">(</span><span class="p" data-group-id="4822676969-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4822676969-5">]</span><span class="p" data-group-id="4822676969-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4822676969-6">(</span><span class="p" data-group-id="4822676969-7">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4822676969-7">]</span><span class="p" data-group-id="4822676969-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4822676969-8">(</span><span class="p" data-group-id="4822676969-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4822676969-9">]</span><span class="p" data-group-id="4822676969-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4822676969-10">(</span><span class="p" data-group-id="4822676969-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4822676969-11">]</span><span class="p" data-group-id="4822676969-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="4822676969-12">(</span><span class="n">Code</span><span class="p" data-group-id="4822676969-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4822676969-13">(</span><span class="p" data-group-id="4822676969-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4822676969-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4822676969-15">[</span><span class="p" data-group-id="4822676969-15">]</span><span class="p" data-group-id="4822676969-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="4822676969-16">(</span><span class="p" data-group-id="4822676969-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="4822676969-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4822676969-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">down</span><span class="p" data-group-id="4822676969-18">(</span><span class="n">Button</span><span class="p" data-group-id="4822676969-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4822676969-19">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4822676969-20">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4822676969-20">}</span><span class="p" data-group-id="4822676969-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">up</span><span class="p" data-group-id="4822676969-21">(</span><span class="n">Button</span><span class="p" data-group-id="4822676969-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4822676969-22">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4822676969-23">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4822676969-23">}</span><span class="p" data-group-id="4822676969-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="4822676969-24">(</span><span class="p" data-group-id="4822676969-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4822676969-25">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="4822676969-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="0296965463-1">(</span><span class="n">Code</span><span class="p" data-group-id="0296965463-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="0296965463-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0296965463-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0296965463-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0296965463-4">(</span><span class="n">Code</span><span class="p" data-group-id="0296965463-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0296965463-5">[</span><span class="p" data-group-id="0296965463-5">]</span><span class="p" data-group-id="0296965463-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0296965463-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0296965463-6">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0934369912-4">(</span><span class="p" data-group-id="0934369912-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0934369912-5">]</span><span class="p" data-group-id="0934369912-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0934369912-6">(</span><span class="p" data-group-id="0934369912-7">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0934369912-7">]</span><span class="p" data-group-id="0934369912-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0934369912-8">(</span><span class="p" data-group-id="0934369912-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="0934369912-9">]</span><span class="p" data-group-id="0934369912-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0934369912-10">(</span><span class="p" data-group-id="0934369912-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="0934369912-11">]</span><span class="p" data-group-id="0934369912-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="0934369912-12">(</span><span class="n">Code</span><span class="p" data-group-id="0934369912-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0934369912-13">(</span><span class="p" data-group-id="0934369912-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="0934369912-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0934369912-15">[</span><span class="p" data-group-id="0934369912-15">]</span><span class="p" data-group-id="0934369912-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="0934369912-16">(</span><span class="p" data-group-id="0934369912-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="0934369912-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="0934369912-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">down</span><span class="p" data-group-id="0934369912-18">(</span><span class="n">Button</span><span class="p" data-group-id="0934369912-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="0934369912-19">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0934369912-20">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0934369912-20">}</span><span class="p" data-group-id="0934369912-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">up</span><span class="p" data-group-id="0934369912-21">(</span><span class="n">Button</span><span class="p" data-group-id="0934369912-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="0934369912-22">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0934369912-23">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0934369912-23">}</span><span class="p" data-group-id="0934369912-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="0934369912-24">(</span><span class="p" data-group-id="0934369912-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="0934369912-25">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="0934369912-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4916375423-1">(</span><span class="n">Code</span><span class="p" data-group-id="4916375423-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="4916375423-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4916375423-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4916375423-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="4916375423-4">(</span><span class="n">Code</span><span class="p" data-group-id="4916375423-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4916375423-5">[</span><span class="p" data-group-id="4916375423-5">]</span><span class="p" data-group-id="4916375423-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4916375423-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4916375423-6">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="0296965463-7">(</span><span class="p" data-group-id="0296965463-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0296965463-8">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="0296965463-8">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="4916375423-7">(</span><span class="p" data-group-id="4916375423-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4916375423-8">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="4916375423-8">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0296965463-9">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="0296965463-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="0296965463-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="0296965463-11">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="0296965463-11">)</span><span class="p" data-group-id="0296965463-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4916375423-9">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="4916375423-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="4916375423-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="4916375423-11">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="4916375423-11">)</span><span class="p" data-group-id="4916375423-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="0296965463-12">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0296965463-13">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0296965463-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0296965463-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0296965463-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0296965463-15">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="0296965463-15">}</span><span class="p" data-group-id="0296965463-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="0296965463-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0296965463-17">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0296965463-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0296965463-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="4916375423-12">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4916375423-13">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4916375423-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4916375423-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4916375423-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4916375423-15">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="4916375423-15">}</span><span class="p" data-group-id="4916375423-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="4916375423-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4916375423-17">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4916375423-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4916375423-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0296965463-18">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="0296965463-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="0296965463-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="0296965463-20">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0296965463-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="0296965463-21">[</span><span class="p" data-group-id="0296965463-22">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="0296965463-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0296965463-23">}</span><span class="p" data-group-id="0296965463-22">}</span><span class="p" data-group-id="0296965463-21">]</span><span class="p" data-group-id="0296965463-19">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0296965463-24">#{</span><span class="p" data-group-id="0296965463-24">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4916375423-18">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="4916375423-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="4916375423-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="4916375423-20">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4916375423-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="4916375423-21">[</span><span class="p" data-group-id="4916375423-22">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="4916375423-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4916375423-23">}</span><span class="p" data-group-id="4916375423-22">}</span><span class="p" data-group-id="4916375423-21">]</span><span class="p" data-group-id="4916375423-19">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4916375423-24">#{</span><span class="p" data-group-id="4916375423-24">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="0296965463-25">(</span><span class="p" data-group-id="0296965463-26">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="0296965463-26">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0296965463-27">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="0296965463-27">}</span><span class="p" data-group-id="0296965463-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0296965463-28">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0296965463-29">[</span><span class="p" data-group-id="0296965463-30">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="0296965463-31">(</span><span class="n">Code</span><span class="p" data-group-id="0296965463-31">)</span><span class="p" data-group-id="0296965463-30">}</span><span class="p" data-group-id="0296965463-29">]</span><span class="p" data-group-id="0296965463-28">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="4693517341-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693517341-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="4693517341-2">(</span><span class="p" data-group-id="4693517341-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4693517341-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693517341-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4693517341-5">[</span><span class="p" data-group-id="4693517341-5">]</span><span class="p" data-group-id="4693517341-4">}</span><span class="p" data-group-id="4693517341-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="4693517341-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693517341-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4693517341-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693517341-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4693517341-9">[</span><span class="p" data-group-id="4693517341-9">]</span><span class="p" data-group-id="4693517341-8">}</span><span class="p" data-group-id="4693517341-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="4693517341-10">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4693517341-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4693517341-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4693517341-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4693517341-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693517341-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="4916375423-25">(</span><span class="p" data-group-id="4916375423-26">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="4916375423-26">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4916375423-27">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="4916375423-27">}</span><span class="p" data-group-id="4916375423-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4916375423-28">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="4916375423-29">[</span><span class="p" data-group-id="4916375423-30">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="4916375423-31">(</span><span class="n">Code</span><span class="p" data-group-id="4916375423-31">)</span><span class="p" data-group-id="4916375423-30">}</span><span class="p" data-group-id="4916375423-29">]</span><span class="p" data-group-id="4916375423-28">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="6205192043-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6205192043-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="6205192043-2">(</span><span class="p" data-group-id="6205192043-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6205192043-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6205192043-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="6205192043-5">[</span><span class="p" data-group-id="6205192043-5">]</span><span class="p" data-group-id="6205192043-4">}</span><span class="p" data-group-id="6205192043-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="6205192043-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6205192043-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6205192043-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6205192043-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="6205192043-9">[</span><span class="p" data-group-id="6205192043-9">]</span><span class="p" data-group-id="6205192043-8">}</span><span class="p" data-group-id="6205192043-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="6205192043-10">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6205192043-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6205192043-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6205192043-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6205192043-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6205192043-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="4693517341-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="4693517341-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="6205192043-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="6205192043-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="4693517341-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="4693517341-14">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4693517341-15">[</span><span class="n">Button</span><span class="p" data-group-id="4693517341-15">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="6205192043-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="6205192043-14">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6205192043-15">[</span><span class="n">Button</span><span class="p" data-group-id="6205192043-15">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="4693517341-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693517341-16">}</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6205192043-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6205192043-16">}</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="4693517341-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693517341-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="4693517341-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="4693517341-19">[</span><span class="p" data-group-id="4693517341-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="4693517341-20">}</span><span class="p" data-group-id="4693517341-19">]</span><span class="p" data-group-id="4693517341-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6205192043-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6205192043-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="6205192043-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="6205192043-19">[</span><span class="p" data-group-id="6205192043-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="6205192043-20">}</span><span class="p" data-group-id="6205192043-19">]</span><span class="p" data-group-id="6205192043-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="6311172079-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="6311172079-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="6311172079-2">(</span><span class="p" data-group-id="6311172079-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6311172079-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="6311172079-4">[</span><span class="p" data-group-id="6311172079-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="6311172079-5">}</span><span class="p" data-group-id="6311172079-4">]</span><span class="p" data-group-id="6311172079-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="6311172079-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6311172079-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6311172079-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6311172079-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="6311172079-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6311172079-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6311172079-9">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6311172079-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6311172079-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6311172079-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="6311172079-11">]</span><span class="p" data-group-id="6311172079-10">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="7118706811-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="7118706811-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="7118706811-2">(</span><span class="p" data-group-id="7118706811-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7118706811-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7118706811-4">[</span><span class="p" data-group-id="7118706811-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="7118706811-5">}</span><span class="p" data-group-id="7118706811-4">]</span><span class="p" data-group-id="7118706811-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="7118706811-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7118706811-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7118706811-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7118706811-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="7118706811-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7118706811-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7118706811-9">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7118706811-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7118706811-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7118706811-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="7118706811-11">]</span><span class="p" data-group-id="7118706811-10">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">do_lock</span><span class="p" data-group-id="6311172079-12">(</span><span class="p" data-group-id="6311172079-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6311172079-13">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6311172079-14">[</span><span class="p" data-group-id="6311172079-14">]</span><span class="p" data-group-id="6311172079-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="6311172079-15">(</span><span class="p" data-group-id="6311172079-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6311172079-16">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6311172079-17">[</span><span class="p" data-group-id="6311172079-17">]</span><span class="p" data-group-id="6311172079-16">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_lock</span><span class="p" data-group-id="7118706811-12">(</span><span class="p" data-group-id="7118706811-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7118706811-13">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7118706811-14">[</span><span class="p" data-group-id="7118706811-14">]</span><span class="p" data-group-id="7118706811-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="7118706811-15">(</span><span class="p" data-group-id="7118706811-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7118706811-16">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7118706811-17">[</span><span class="p" data-group-id="7118706811-17">]</span><span class="p" data-group-id="7118706811-16">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="6311172079-18">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="6311172079-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="6311172079-19">(</span><span class="p" data-group-id="6311172079-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="7118706811-18">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="7118706811-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="7118706811-19">(</span><span class="p" data-group-id="7118706811-19">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="callback-mode-handle_event_function" class="section-heading">
│ │ │ │    <a href="#callback-mode-handle_event_function" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Callback Mode: handle_event_function</span>
│ │ │ │  </h3>
│ │ │ │  <p>This section describes what to change in the example to use one
│ │ │ │  <code class="inline">handle_event/4</code> function.  The previously used approach to first branch
│ │ │ │  depending on event does not work that well here because of
│ │ │ │ -the <em>state enter calls</em>, so this example first branches depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5199121067-1">(</span><span class="p" data-group-id="5199121067-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="5199121067-2">]</span><span class="p" data-group-id="5199121067-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="3268476700-1">(</span><span class="p" data-group-id="3268476700-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3268476700-2">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="3268476700-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │ +the <em>state enter calls</em>, so this example first branches depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0196502559-1">(</span><span class="p" data-group-id="0196502559-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="0196502559-2">]</span><span class="p" data-group-id="0196502559-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="7808763362-1">(</span><span class="p" data-group-id="7808763362-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7808763362-2">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="7808763362-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% State: locked</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5230881682-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5230881682-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="5230881682-2">(</span><span class="p" data-group-id="5230881682-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5230881682-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5230881682-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5230881682-5">[</span><span class="p" data-group-id="5230881682-5">]</span><span class="p" data-group-id="5230881682-4">}</span><span class="p" data-group-id="5230881682-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5230881682-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5230881682-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5230881682-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5230881682-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5230881682-9">[</span><span class="p" data-group-id="5230881682-9">]</span><span class="p" data-group-id="5230881682-8">}</span><span class="p" data-group-id="5230881682-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5230881682-10">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5230881682-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5230881682-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5230881682-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="5230881682-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5230881682-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="9058778232-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9058778232-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="9058778232-2">(</span><span class="p" data-group-id="9058778232-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9058778232-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9058778232-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9058778232-5">[</span><span class="p" data-group-id="9058778232-5">]</span><span class="p" data-group-id="9058778232-4">}</span><span class="p" data-group-id="9058778232-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="9058778232-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9058778232-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9058778232-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9058778232-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9058778232-9">[</span><span class="p" data-group-id="9058778232-9">]</span><span class="p" data-group-id="9058778232-8">}</span><span class="p" data-group-id="9058778232-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="9058778232-10">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9058778232-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9058778232-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9058778232-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9058778232-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9058778232-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="5230881682-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="5230881682-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="9058778232-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="9058778232-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="5230881682-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="5230881682-14">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="5230881682-15">[</span><span class="n">Button</span><span class="p" data-group-id="5230881682-15">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="9058778232-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="9058778232-14">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9058778232-15">[</span><span class="n">Button</span><span class="p" data-group-id="9058778232-15">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="5230881682-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5230881682-16">}</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9058778232-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9058778232-16">}</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="5230881682-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5230881682-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="5230881682-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="5230881682-19">[</span><span class="p" data-group-id="5230881682-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="5230881682-20">}</span><span class="p" data-group-id="5230881682-19">]</span><span class="p" data-group-id="5230881682-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9058778232-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9058778232-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="9058778232-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="9058778232-19">[</span><span class="p" data-group-id="9058778232-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="9058778232-20">}</span><span class="p" data-group-id="9058778232-19">]</span><span class="p" data-group-id="9058778232-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4730498840-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="4730498840-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="4730498840-2">(</span><span class="p" data-group-id="4730498840-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4730498840-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="4730498840-4">[</span><span class="p" data-group-id="4730498840-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="4730498840-5">}</span><span class="p" data-group-id="4730498840-4">]</span><span class="p" data-group-id="4730498840-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4730498840-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4730498840-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4730498840-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4730498840-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4730498840-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4730498840-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4730498840-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="4730498840-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4730498840-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="4730498840-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="4730498840-11">]</span><span class="p" data-group-id="4730498840-10">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%% Common events</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="2693310055-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2693310055-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2693310055-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2693310055-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2693310055-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2693310055-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2693310055-4">}</span><span class="p" data-group-id="2693310055-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="2693310055-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2693310055-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2693310055-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2693310055-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3554068475-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3554068475-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3554068475-2">(</span><span class="p" data-group-id="3554068475-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3554068475-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="3554068475-4">[</span><span class="p" data-group-id="3554068475-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3554068475-5">}</span><span class="p" data-group-id="3554068475-4">]</span><span class="p" data-group-id="3554068475-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3554068475-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3554068475-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3554068475-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3554068475-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3554068475-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3554068475-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3554068475-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3554068475-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3554068475-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="3554068475-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="3554068475-11">]</span><span class="p" data-group-id="3554068475-10">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%% Common events</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3091302758-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3091302758-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3091302758-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3091302758-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3091302758-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3091302758-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="3091302758-4">}</span><span class="p" data-group-id="3091302758-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3091302758-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3091302758-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3091302758-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3091302758-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2693310055-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2693310055-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="2693310055-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="2693310055-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2693310055-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="2693310055-10">[</span><span class="p" data-group-id="2693310055-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="2693310055-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2693310055-12">}</span><span class="p" data-group-id="2693310055-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="2693310055-13">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="2693310055-13">}</span><span class="p" data-group-id="2693310055-10">]</span><span class="p" data-group-id="2693310055-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2693310055-14">#{</span><span class="p" data-group-id="2693310055-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3091302758-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="3091302758-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="3091302758-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="3091302758-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3091302758-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="3091302758-10">[</span><span class="p" data-group-id="3091302758-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="3091302758-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3091302758-12">}</span><span class="p" data-group-id="3091302758-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="3091302758-13">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="3091302758-13">}</span><span class="p" data-group-id="3091302758-10">]</span><span class="p" data-group-id="3091302758-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="3091302758-14">#{</span><span class="p" data-group-id="3091302758-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="2693310055-15">(</span><span class="p" data-group-id="2693310055-16">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="2693310055-16">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2693310055-17">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="2693310055-17">}</span><span class="p" data-group-id="2693310055-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2693310055-18">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="2693310055-19">[</span><span class="p" data-group-id="2693310055-20">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">Length</span><span class="p" data-group-id="2693310055-20">}</span><span class="p" data-group-id="2693310055-19">]</span><span class="p" data-group-id="2693310055-18">}</span><span class="p">.</span></code></pre><p>Notice that postponing buttons from the <code class="inline">open</code> state to the <code class="inline">locked</code> state
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3091302758-15">(</span><span class="p" data-group-id="3091302758-16">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="3091302758-16">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3091302758-17">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="3091302758-17">}</span><span class="p" data-group-id="3091302758-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3091302758-18">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="3091302758-19">[</span><span class="p" data-group-id="3091302758-20">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">Length</span><span class="p" data-group-id="3091302758-20">}</span><span class="p" data-group-id="3091302758-19">]</span><span class="p" data-group-id="3091302758-18">}</span><span class="p">.</span></code></pre><p>Notice that postponing buttons from the <code class="inline">open</code> state to the <code class="inline">locked</code> state
│ │ │ │  seems like a strange thing to do for a code lock, but it at least
│ │ │ │  illustrates event postponing.</p><h2 id="filter-the-state" class="section-heading">
│ │ │ │    <a href="#filter-the-state" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Filter the State</span>
│ │ │ │  </h2>
│ │ │ │ @@ -1191,30 +1191,30 @@
│ │ │ │  and which digits that remain to unlock.</p><p>This state data can be regarded as sensitive, and maybe not what you want
│ │ │ │  in the error log because of some unpredictable event.</p><p>Another reason to filter the state can be that the state is too large to print,
│ │ │ │  as it fills the error log with uninteresting details.</p><p>To avoid this, you can format the internal state that gets in the error log
│ │ │ │  and gets returned from <a href="../../../lib/stdlib/doc/html/sys.html#get_status/1"><code class="inline">sys:get_status/1,2</code></a>
│ │ │ │  by implementing function
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:format_status/2"><code class="inline">Module:format_status/2</code></a>,
│ │ │ │  for example like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1819613949-1">(</span><span class="p" data-group-id="1819613949-2">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">format_status</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1819613949-2">]</span><span class="p" data-group-id="1819613949-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6303877691-1">(</span><span class="p" data-group-id="6303877691-2">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">format_status</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6303877691-2">]</span><span class="p" data-group-id="6303877691-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">format_status</span><span class="p" data-group-id="1819613949-3">(</span><span class="n">Opt</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1819613949-4">[</span><span class="p">_</span><span class="n">PDict</span><span class="p">,</span><span class="n">State</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="1819613949-4">]</span><span class="p" data-group-id="1819613949-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">format_status</span><span class="p" data-group-id="6303877691-3">(</span><span class="n">Opt</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6303877691-4">[</span><span class="p">_</span><span class="n">PDict</span><span class="p">,</span><span class="n">State</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="6303877691-4">]</span><span class="p" data-group-id="6303877691-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">StateData</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1819613949-5">{</span><span class="n">State</span><span class="p">,</span><span class="w">
│ │ │ │ -	 </span><span class="nc">maps</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="1819613949-6">(</span><span class="w">
│ │ │ │ -	   </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1819613949-7">(</span><span class="ss">code</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1819613949-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="p">;</span><span class="w">
│ │ │ │ -	       </span><span class="p" data-group-id="1819613949-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1819613949-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="6303877691-5">{</span><span class="n">State</span><span class="p">,</span><span class="w">
│ │ │ │ +	 </span><span class="nc">maps</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="6303877691-6">(</span><span class="w">
│ │ │ │ +	   </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="6303877691-7">(</span><span class="ss">code</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6303877691-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="p">;</span><span class="w">
│ │ │ │ +	       </span><span class="p" data-group-id="6303877691-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6303877691-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="w">
│ │ │ │  	   </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	   </span><span class="n">Data</span><span class="p" data-group-id="1819613949-6">)</span><span class="p" data-group-id="1819613949-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	   </span><span class="n">Data</span><span class="p" data-group-id="6303877691-6">)</span><span class="p" data-group-id="6303877691-5">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Opt</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │  	</span><span class="ss">terminate</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">StateData</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">normal</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="p" data-group-id="1819613949-9">[</span><span class="p" data-group-id="1819613949-10">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="1819613949-11">[</span><span class="p" data-group-id="1819613949-12">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="n">StateData</span><span class="p" data-group-id="1819613949-12">}</span><span class="p" data-group-id="1819613949-11">]</span><span class="p" data-group-id="1819613949-10">}</span><span class="p" data-group-id="1819613949-9">]</span><span class="w">
│ │ │ │ +	    </span><span class="p" data-group-id="6303877691-9">[</span><span class="p" data-group-id="6303877691-10">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="6303877691-11">[</span><span class="p" data-group-id="6303877691-12">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="n">StateData</span><span class="p" data-group-id="6303877691-12">}</span><span class="p" data-group-id="6303877691-11">]</span><span class="p" data-group-id="6303877691-10">}</span><span class="p" data-group-id="6303877691-9">]</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>It is not mandatory to implement a
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_statem.html#c:format_status/2"><code class="inline">Module:format_status/2</code></a> function.
│ │ │ │  If you do not, a default implementation is used that does the same
│ │ │ │  as this example function without filtering the <code class="inline">Data</code> term, that is,
│ │ │ │  <code class="inline">StateData = {State, Data}</code>, in this example containing sensitive information.</p><h2 id="complex-state" class="section-heading">
│ │ │ │    <a href="#complex-state" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -1227,104 +1227,104 @@
│ │ │ │  like a tuple.</p><p>One reason to use this is when you have a state item that when changed
│ │ │ │  should cancel the <a href="#state-time-outs"><em>state time-out</em></a>, or one that affects
│ │ │ │  the event handling in combination with postponing events. We will go for
│ │ │ │  the latter and complicate the previous example by introducing
│ │ │ │  a configurable lock button (this is the state item in question),
│ │ │ │  which in the <code class="inline">open</code> state immediately locks the door, and an API function
│ │ │ │  <code class="inline">set_lock_button/1</code> to set the lock button.</p><p>Suppose now that we call <code class="inline">set_lock_button</code> while the door is open,
│ │ │ │ -and we have already postponed a button event that was the new lock button:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1237888685-1">(</span><span class="p" data-group-id="1237888685-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1237888685-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">x</span><span class="p" data-group-id="1237888685-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1237888685-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.666</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="1237888685-3">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1237888685-4">(</span><span class="ss">a</span><span class="p" data-group-id="1237888685-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +and we have already postponed a button event that was the new lock button:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1870312775-1">(</span><span class="p" data-group-id="1870312775-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1870312775-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">x</span><span class="p" data-group-id="1870312775-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1870312775-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.666</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="1870312775-3">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1870312775-4">(</span><span class="ss">a</span><span class="p" data-group-id="1870312775-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1237888685-5">(</span><span class="ss">b</span><span class="p" data-group-id="1237888685-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1870312775-5">(</span><span class="ss">b</span><span class="p" data-group-id="1870312775-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1237888685-6">(</span><span class="ss">c</span><span class="p" data-group-id="1237888685-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1870312775-6">(</span><span class="ss">c</span><span class="p" data-group-id="1870312775-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="n">Open</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1237888685-7">(</span><span class="ss">y</span><span class="p" data-group-id="1237888685-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="1870312775-7">(</span><span class="ss">y</span><span class="p" data-group-id="1870312775-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">set_lock_button</span><span class="p" data-group-id="1237888685-8">(</span><span class="ss">y</span><span class="p" data-group-id="1237888685-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">set_lock_button</span><span class="p" data-group-id="1870312775-8">(</span><span class="ss">y</span><span class="p" data-group-id="1870312775-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">x</span><span class="w">
│ │ │ │  </span><span class="c1">% What should happen here?  Immediate lock or nothing?</span></code></pre><p>We could say that the button was pressed too early so it should not be
│ │ │ │  recognized as the lock button. Or we can make the lock button part of
│ │ │ │  the state so when we then change the lock button in the locked state,
│ │ │ │  the change becomes a <em>state change</em> and all postponed events are retried,
│ │ │ │  therefore the lock is immediately locked!</p><p>We define the state as <code class="inline">{StateName, LockButton}</code>, where <code class="inline">StateName</code>
│ │ │ │ -is as before and <code class="inline">LockButton</code> is the current lock button:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4681954865-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="4681954865-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4681954865-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="4681954865-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4681954865-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_3</span><span class="p" data-group-id="4681954865-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +is as before and <code class="inline">LockButton</code> is the current lock button:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2161815189-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="2161815189-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2161815189-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="2161815189-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2161815189-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_3</span><span class="p" data-group-id="2161815189-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4681954865-4">(</span><span class="p" data-group-id="4681954865-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4681954865-5">]</span><span class="p" data-group-id="4681954865-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4681954865-6">(</span><span class="p" data-group-id="4681954865-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">set_lock_button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4681954865-7">]</span><span class="p" data-group-id="4681954865-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4681954865-8">(</span><span class="p" data-group-id="4681954865-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4681954865-9">]</span><span class="p" data-group-id="4681954865-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4681954865-10">(</span><span class="p" data-group-id="4681954865-11">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="4681954865-11">]</span><span class="p" data-group-id="4681954865-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="4681954865-12">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">LockButton</span><span class="p" data-group-id="4681954865-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4681954865-13">(</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4681954865-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4681954865-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4681954865-15">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="4681954865-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4681954865-16">[</span><span class="p" data-group-id="4681954865-16">]</span><span class="p" data-group-id="4681954865-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="4681954865-17">(</span><span class="p" data-group-id="4681954865-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="4681954865-18">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4681954865-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="4681954865-19">(</span><span class="n">Button</span><span class="p" data-group-id="4681954865-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4681954865-20">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4681954865-21">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4681954865-21">}</span><span class="p" data-group-id="4681954865-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">set_lock_button</span><span class="p" data-group-id="4681954865-22">(</span><span class="n">LockButton</span><span class="p" data-group-id="4681954865-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4681954865-23">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4681954865-24">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="4681954865-24">}</span><span class="p" data-group-id="4681954865-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8113306516-1">(</span><span class="p" data-group-id="8113306516-2">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="8113306516-2">}</span><span class="p" data-group-id="8113306516-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="8113306516-3">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8113306516-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8113306516-4">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8113306516-5">(</span><span class="n">Code</span><span class="p" data-group-id="8113306516-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8113306516-6">[</span><span class="p" data-group-id="8113306516-6">]</span><span class="p" data-group-id="8113306516-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8113306516-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8113306516-8">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="8113306516-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8113306516-7">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2161815189-4">(</span><span class="p" data-group-id="2161815189-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2161815189-5">]</span><span class="p" data-group-id="2161815189-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2161815189-6">(</span><span class="p" data-group-id="2161815189-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">set_lock_button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2161815189-7">]</span><span class="p" data-group-id="2161815189-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2161815189-8">(</span><span class="p" data-group-id="2161815189-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="2161815189-9">]</span><span class="p" data-group-id="2161815189-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2161815189-10">(</span><span class="p" data-group-id="2161815189-11">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="2161815189-11">]</span><span class="p" data-group-id="2161815189-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="2161815189-12">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">LockButton</span><span class="p" data-group-id="2161815189-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2161815189-13">(</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2161815189-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="2161815189-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2161815189-15">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2161815189-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2161815189-16">[</span><span class="p" data-group-id="2161815189-16">]</span><span class="p" data-group-id="2161815189-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="2161815189-17">(</span><span class="p" data-group-id="2161815189-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="2161815189-18">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="2161815189-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="2161815189-19">(</span><span class="n">Button</span><span class="p" data-group-id="2161815189-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="2161815189-20">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2161815189-21">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2161815189-21">}</span><span class="p" data-group-id="2161815189-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">set_lock_button</span><span class="p" data-group-id="2161815189-22">(</span><span class="n">LockButton</span><span class="p" data-group-id="2161815189-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="2161815189-23">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2161815189-24">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2161815189-24">}</span><span class="p" data-group-id="2161815189-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7143358764-1">(</span><span class="p" data-group-id="7143358764-2">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="7143358764-2">}</span><span class="p" data-group-id="7143358764-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="7143358764-3">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7143358764-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7143358764-4">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7143358764-5">(</span><span class="n">Code</span><span class="p" data-group-id="7143358764-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7143358764-6">[</span><span class="p" data-group-id="7143358764-6">]</span><span class="p" data-group-id="7143358764-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7143358764-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7143358764-8">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="7143358764-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7143358764-7">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="8113306516-9">(</span><span class="p" data-group-id="8113306516-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8113306516-10">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="8113306516-10">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="7143358764-9">(</span><span class="p" data-group-id="7143358764-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7143358764-10">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="7143358764-10">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% State: locked</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="8113306516-11">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8113306516-12">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8113306516-12">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8113306516-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="8113306516-13">(</span><span class="p" data-group-id="8113306516-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8113306516-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8113306516-15">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8113306516-16">[</span><span class="p" data-group-id="8113306516-16">]</span><span class="p" data-group-id="8113306516-15">}</span><span class="p" data-group-id="8113306516-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="8113306516-17">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8113306516-18">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8113306516-18">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8113306516-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8113306516-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8113306516-20">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8113306516-21">[</span><span class="p" data-group-id="8113306516-21">]</span><span class="p" data-group-id="8113306516-20">}</span><span class="p" data-group-id="8113306516-19">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="8113306516-22">(</span><span class="w">
│ │ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8113306516-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8113306516-23">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8113306516-24">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="8113306516-24">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8113306516-25">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8113306516-25">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8113306516-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7143358764-11">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7143358764-12">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7143358764-12">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7143358764-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="7143358764-13">(</span><span class="p" data-group-id="7143358764-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7143358764-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7143358764-15">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7143358764-16">[</span><span class="p" data-group-id="7143358764-16">]</span><span class="p" data-group-id="7143358764-15">}</span><span class="p" data-group-id="7143358764-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7143358764-17">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7143358764-18">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7143358764-18">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7143358764-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7143358764-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7143358764-20">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7143358764-21">[</span><span class="p" data-group-id="7143358764-21">]</span><span class="p" data-group-id="7143358764-20">}</span><span class="p" data-group-id="7143358764-19">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7143358764-22">(</span><span class="w">
│ │ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7143358764-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7143358764-23">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7143358764-24">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="7143358764-24">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7143358764-25">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7143358764-25">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7143358764-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │          </span><span class="k">if</span><span class="w">
│ │ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="8113306516-26">(</span><span class="n">Buttons</span><span class="p" data-group-id="8113306516-26">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="7143358764-26">(</span><span class="n">Buttons</span><span class="p" data-group-id="7143358764-26">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="8113306516-27">(</span><span class="n">Buttons</span><span class="p" data-group-id="8113306516-27">)</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="8113306516-28">[</span><span class="n">Button</span><span class="p" data-group-id="8113306516-28">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="7143358764-27">(</span><span class="n">Buttons</span><span class="p" data-group-id="7143358764-27">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="7143358764-28">[</span><span class="n">Button</span><span class="p" data-group-id="7143358764-28">]</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="8113306516-29">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8113306516-30">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="8113306516-30">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8113306516-29">}</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="7143358764-29">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7143358764-30">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="7143358764-30">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7143358764-29">}</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="8113306516-31">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8113306516-32">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="8113306516-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="8113306516-33">[</span><span class="p" data-group-id="8113306516-34">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="8113306516-34">}</span><span class="p" data-group-id="8113306516-33">]</span><span class="p" data-group-id="8113306516-31">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="7143358764-31">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7143358764-32">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="7143358764-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="7143358764-33">[</span><span class="p" data-group-id="7143358764-34">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="7143358764-34">}</span><span class="p" data-group-id="7143358764-33">]</span><span class="p" data-group-id="7143358764-31">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1143123906-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1143123906-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1143123906-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1143123906-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="1143123906-3">(</span><span class="p" data-group-id="1143123906-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1143123906-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="1143123906-5">[</span><span class="p" data-group-id="1143123906-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1143123906-6">}</span><span class="p" data-group-id="1143123906-5">]</span><span class="p" data-group-id="1143123906-4">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1143123906-7">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1143123906-8">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1143123906-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1143123906-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1143123906-9">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1143123906-10">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1143123906-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1143123906-9">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1143123906-11">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1143123906-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1143123906-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1143123906-13">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1143123906-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1143123906-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1143123906-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1143123906-15">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="1143123906-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1143123906-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1143123906-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1143123906-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1143123906-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1143123906-18">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1143123906-18">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1143123906-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1143123906-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="1143123906-20">[</span><span class="ss">postpone</span><span class="p" data-group-id="1143123906-20">]</span><span class="p" data-group-id="1143123906-19">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2134128641-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2134128641-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2134128641-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2134128641-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2134128641-3">(</span><span class="p" data-group-id="2134128641-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2134128641-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="2134128641-5">[</span><span class="p" data-group-id="2134128641-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="2134128641-6">}</span><span class="p" data-group-id="2134128641-5">]</span><span class="p" data-group-id="2134128641-4">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2134128641-7">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2134128641-8">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2134128641-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2134128641-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2134128641-9">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2134128641-10">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2134128641-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2134128641-9">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2134128641-11">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2134128641-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2134128641-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2134128641-13">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2134128641-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2134128641-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2134128641-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2134128641-15">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2134128641-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2134128641-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2134128641-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2134128641-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2134128641-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2134128641-18">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2134128641-18">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2134128641-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2134128641-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="2134128641-20">[</span><span class="ss">postpone</span><span class="p" data-group-id="2134128641-20">]</span><span class="p" data-group-id="2134128641-19">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% Common events</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="8473100422-1">(</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8473100422-2">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="8473100422-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8473100422-3">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="8473100422-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8473100422-4">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="8473100422-4">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8473100422-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8473100422-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8473100422-6">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="8473100422-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="8473100422-7">[</span><span class="p" data-group-id="8473100422-8">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="8473100422-8">}</span><span class="p" data-group-id="8473100422-7">]</span><span class="p" data-group-id="8473100422-5">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="0072562855-1">(</span><span class="p" data-group-id="0072562855-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0072562855-2">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0072562855-3">[</span><span class="p" data-group-id="0072562855-3">]</span><span class="p" data-group-id="0072562855-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="0072562855-4">(</span><span class="p" data-group-id="0072562855-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0072562855-5">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0072562855-6">[</span><span class="p" data-group-id="0072562855-6">]</span><span class="p" data-group-id="0072562855-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7094532097-1">(</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7094532097-2">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="7094532097-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7094532097-3">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="7094532097-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7094532097-4">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="7094532097-4">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7094532097-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7094532097-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7094532097-6">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="7094532097-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7094532097-7">[</span><span class="p" data-group-id="7094532097-8">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="7094532097-8">}</span><span class="p" data-group-id="7094532097-7">]</span><span class="p" data-group-id="7094532097-5">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="9622604120-1">(</span><span class="p" data-group-id="9622604120-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9622604120-2">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9622604120-3">[</span><span class="p" data-group-id="9622604120-3">]</span><span class="p" data-group-id="9622604120-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="9622604120-4">(</span><span class="p" data-group-id="9622604120-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9622604120-5">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9622604120-6">[</span><span class="p" data-group-id="9622604120-6">]</span><span class="p" data-group-id="9622604120-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="0072562855-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0072562855-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="0072562855-8">(</span><span class="p" data-group-id="0072562855-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="9622604120-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="9622604120-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="9622604120-8">(</span><span class="p" data-group-id="9622604120-8">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h2 id="hibernation" class="section-heading">
│ │ │ │    <a href="#hibernation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Hibernation</span>
│ │ │ │  </h2>
│ │ │ │  <p>If you have many servers in one node and they have some state(s) in their
│ │ │ │ @@ -1333,19 +1333,19 @@
│ │ │ │  footprint of a server can be minimized by hibernating it through
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#hibernate/3"><code class="inline">proc_lib:hibernate/3</code></a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>It is rather costly to hibernate a process; see <a href="../../../lib/../erts/doc/html/erlang.html#hibernate/3"><code class="inline">erlang:hibernate/3</code></a>. It is
│ │ │ │  not something you want to do after every event.</p></section><p>We can in this example hibernate in the <code class="inline">{open, _}</code> state,
│ │ │ │  because what normally occurs in that state is that the <em>state time-out</em>
│ │ │ │  after a while triggers a transition to <code class="inline">{locked, _}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="3889767769-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3889767769-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3889767769-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3889767769-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3889767769-3">(</span><span class="p" data-group-id="3889767769-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3889767769-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="3889767769-5">[</span><span class="p" data-group-id="3889767769-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3889767769-6">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ -      </span><span class="ss">hibernate</span><span class="p" data-group-id="3889767769-5">]</span><span class="p" data-group-id="3889767769-4">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="5262166317-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5262166317-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5262166317-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="5262166317-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="5262166317-3">(</span><span class="p" data-group-id="5262166317-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5262166317-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="5262166317-5">[</span><span class="p" data-group-id="5262166317-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="5262166317-6">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ │ +      </span><span class="ss">hibernate</span><span class="p" data-group-id="5262166317-5">]</span><span class="p" data-group-id="5262166317-4">}</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The atom <a href="../../../lib/stdlib/doc/html/gen_statem.html#t:hibernate/0"><code class="inline">hibernate</code></a> in the action list on the
│ │ │ │  last line when entering the <code class="inline">{open, _}</code> state is the only change. If any event
│ │ │ │  arrives in the <code class="inline">{open, _},</code> state, we do not bother to rehibernate,
│ │ │ │  so the server stays awake after any event.</p><p>To change that we would need to insert action <code class="inline">hibernate</code> in more places.
│ │ │ │  For example, the state-independent <code class="inline">set_lock_button</code> operation
│ │ │ │  would have to use <code class="inline">hibernate</code> but only in the <code class="inline">{open, _}</code> state,
│ │ │ │  which would clutter the code.</p><p>Another not uncommon scenario is to use the
│ │ │ ├── OEBPS/spec_proc.xhtml
│ │ │ │ @@ -28,72 +28,72 @@
│ │ │ │    <a href="#simple-debugging" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simple Debugging</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <a href="../../../lib/stdlib/doc/html/sys.html"><code class="inline">sys</code></a> module has functions for simple debugging of processes implemented
│ │ │ │  using behaviours. The <code class="inline">code_lock</code> example from
│ │ │ │ -<a href="statem.xhtml#example">gen_statem Behaviour</a> is used to illustrate this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="0308977782-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="0308977782-1">]</span><span class="w"> </span><span class="p" data-group-id="0308977782-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0308977782-2">]</span><span class="w"> </span><span class="p" data-group-id="0308977782-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0308977782-3">]</span><span class="w"> </span><span class="p" data-group-id="0308977782-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="0308977782-4">]</span><span class="w"> </span><span class="p" data-group-id="0308977782-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0308977782-5">]</span><span class="w"> </span><span class="p" data-group-id="0308977782-6">[</span><span class="ss">jit</span><span class="p" data-group-id="0308977782-6">]</span><span class="w">
│ │ │ │ +<a href="statem.xhtml#example">gen_statem Behaviour</a> is used to illustrate this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="0966649428-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="0966649428-1">]</span><span class="w"> </span><span class="p" data-group-id="0966649428-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0966649428-2">]</span><span class="w"> </span><span class="p" data-group-id="0966649428-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0966649428-3">]</span><span class="w"> </span><span class="p" data-group-id="0966649428-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="0966649428-4">]</span><span class="w"> </span><span class="p" data-group-id="0966649428-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0966649428-5">]</span><span class="w"> </span><span class="p" data-group-id="0966649428-6">[</span><span class="ss">jit</span><span class="p" data-group-id="0966649428-6">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="0308977782-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="0308977782-8">(</span><span class="p" data-group-id="0308977782-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="0308977782-7">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0308977782-9">(</span><span class="p" data-group-id="0308977782-10">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0308977782-10">]</span><span class="p" data-group-id="0308977782-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="0966649428-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="0966649428-8">(</span><span class="p" data-group-id="0966649428-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="0966649428-7">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0966649428-9">(</span><span class="p" data-group-id="0966649428-10">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0966649428-10">]</span><span class="p" data-group-id="0966649428-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">Lock</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0308977782-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0308977782-11">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0308977782-12">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0308977782-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0966649428-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0966649428-11">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0966649428-12">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0966649428-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="0308977782-13">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0308977782-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="0966649428-13">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0966649428-13">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="0308977782-14">(</span><span class="mi">1</span><span class="p" data-group-id="0308977782-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0308977782-15">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0308977782-15">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="0966649428-14">(</span><span class="mi">1</span><span class="p" data-group-id="0966649428-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0966649428-15">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0966649428-15">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0308977782-16">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0308977782-16">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="0308977782-17">(</span><span class="mi">2</span><span class="p" data-group-id="0308977782-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0308977782-18">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0308977782-18">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0966649428-16">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0966649428-16">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="0966649428-17">(</span><span class="mi">2</span><span class="p" data-group-id="0966649428-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0966649428-18">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0966649428-18">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0308977782-19">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0308977782-19">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="0308977782-20">(</span><span class="mi">3</span><span class="p" data-group-id="0308977782-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0308977782-21">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0308977782-21">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0966649428-19">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0966649428-19">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="0966649428-20">(</span><span class="mi">3</span><span class="p" data-group-id="0966649428-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0966649428-21">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0966649428-21">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0308977782-22">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0308977782-22">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="0308977782-23">(</span><span class="mi">4</span><span class="p" data-group-id="0308977782-23">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0308977782-24">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0308977782-24">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0966649428-22">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0966649428-22">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="0966649428-23">(</span><span class="mi">4</span><span class="p" data-group-id="0966649428-23">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0966649428-24">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0966649428-24">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="n">Unlock</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0308977782-25">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0308977782-25">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="nb">start_timer</span><span class="w"> </span><span class="p" data-group-id="0308977782-26">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10000</span><span class="p">,</span><span class="ss">lock</span><span class="p">,</span><span class="p" data-group-id="0308977782-27">[</span><span class="p" data-group-id="0308977782-27">]</span><span class="p" data-group-id="0308977782-26">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="0966649428-25">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0966649428-25">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="nb">start_timer</span><span class="w"> </span><span class="p" data-group-id="0966649428-26">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10000</span><span class="p">,</span><span class="ss">lock</span><span class="p">,</span><span class="p" data-group-id="0966649428-27">[</span><span class="p" data-group-id="0966649428-27">]</span><span class="p" data-group-id="0966649428-26">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │  </span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">state_timeout</span><span class="w"> </span><span class="ss">lock</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ │  </span><span class="n">Lock</span><span class="w">
│ │ │ │  </span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">state_timeout</span><span class="w"> </span><span class="ss">lock</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0308977782-28">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="0308977782-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0308977782-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="0308977782-30">[</span><span class="p" data-group-id="0308977782-31">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="0308977782-32">{</span><span class="p" data-group-id="0308977782-33">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0308977782-33">}</span><span class="p">,</span><span class="p" data-group-id="0308977782-34">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0308977782-34">}</span><span class="p" data-group-id="0308977782-32">}</span><span class="p" data-group-id="0308977782-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0308977782-35">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="0308977782-36">{</span><span class="p" data-group-id="0308977782-37">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0308977782-37">}</span><span class="p">,</span><span class="p" data-group-id="0308977782-38">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">48</span><span class="p" data-group-id="0308977782-38">}</span><span class="p" data-group-id="0308977782-36">}</span><span class="p" data-group-id="0308977782-35">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0308977782-39">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">4098</span><span class="p" data-group-id="0308977782-39">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0308977782-40">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0308977782-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0308977782-41">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="0308977782-41">}</span><span class="p" data-group-id="0308977782-30">]</span><span class="p" data-group-id="0308977782-29">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0308977782-42">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0308977782-42">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="0308977782-43">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0308977782-43">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">11&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="0308977782-44">(</span><span class="ss">code_lock</span><span class="p" data-group-id="0308977782-44">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0308977782-45">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0308977782-46">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">gen_statem</span><span class="p" data-group-id="0308977782-46">}</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0308977782-47">[</span><span class="p" data-group-id="0308977782-48">[</span><span class="p" data-group-id="0308977782-49">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="0308977782-50">{</span><span class="ss">code_lock</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0308977782-50">}</span><span class="p" data-group-id="0308977782-49">}</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="0308977782-51">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="0308977782-52">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0308977782-52">]</span><span class="p" data-group-id="0308977782-51">}</span><span class="p" data-group-id="0308977782-48">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="0308977782-53">[</span><span class="p" data-group-id="0308977782-53">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="0308977782-54">[</span><span class="p" data-group-id="0308977782-55">{</span><span class="ss">header</span><span class="p">,</span><span class="s">&quot;Status for state machine code_lock&quot;</span><span class="p" data-group-id="0308977782-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="0308977782-56">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="0308977782-57">[</span><span class="p" data-group-id="0308977782-58">{</span><span class="s">&quot;Status&quot;</span><span class="p">,</span><span class="ss">running</span><span class="p" data-group-id="0308977782-58">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="0308977782-59">{</span><span class="s">&quot;Parent&quot;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0308977782-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="0308977782-60">{</span><span class="s">&quot;Modules&quot;</span><span class="p">,</span><span class="p" data-group-id="0308977782-61">[</span><span class="ss">code_lock</span><span class="p" data-group-id="0308977782-61">]</span><span class="p" data-group-id="0308977782-60">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="0308977782-62">{</span><span class="s">&quot;Time-outs&quot;</span><span class="p">,</span><span class="p" data-group-id="0308977782-63">{</span><span class="mi">0</span><span class="p">,</span><span class="p" data-group-id="0308977782-64">[</span><span class="p" data-group-id="0308977782-64">]</span><span class="p" data-group-id="0308977782-63">}</span><span class="p" data-group-id="0308977782-62">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="0308977782-65">{</span><span class="s">&quot;Logged Events&quot;</span><span class="p">,</span><span class="p" data-group-id="0308977782-66">[</span><span class="p" data-group-id="0308977782-66">]</span><span class="p" data-group-id="0308977782-65">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                 </span><span class="p" data-group-id="0308977782-67">{</span><span class="s">&quot;Postponed&quot;</span><span class="p">,</span><span class="p" data-group-id="0308977782-68">[</span><span class="p" data-group-id="0308977782-68">]</span><span class="p" data-group-id="0308977782-67">}</span><span class="p" data-group-id="0308977782-57">]</span><span class="p" data-group-id="0308977782-56">}</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="0308977782-69">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="0308977782-70">[</span><span class="p" data-group-id="0308977782-71">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -                  </span><span class="p" data-group-id="0308977782-72">{</span><span class="ss">locked</span><span class="p">,</span><span class="p" data-group-id="0308977782-73">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0308977782-74">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0308977782-74">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                            </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0308977782-75">[</span><span class="p" data-group-id="0308977782-75">]</span><span class="p" data-group-id="0308977782-73">}</span><span class="p" data-group-id="0308977782-72">}</span><span class="p" data-group-id="0308977782-71">}</span><span class="p" data-group-id="0308977782-70">]</span><span class="p" data-group-id="0308977782-69">}</span><span class="p" data-group-id="0308977782-54">]</span><span class="p" data-group-id="0308977782-47">]</span><span class="p" data-group-id="0308977782-45">}</span></code></pre><h2 id="special-processes" class="section-heading">
│ │ │ │ +</span><span class="gp unselectable">8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0966649428-28">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="0966649428-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0966649428-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="0966649428-30">[</span><span class="p" data-group-id="0966649428-31">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="0966649428-32">{</span><span class="p" data-group-id="0966649428-33">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0966649428-33">}</span><span class="p">,</span><span class="p" data-group-id="0966649428-34">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0966649428-34">}</span><span class="p" data-group-id="0966649428-32">}</span><span class="p" data-group-id="0966649428-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="0966649428-35">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="0966649428-36">{</span><span class="p" data-group-id="0966649428-37">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0966649428-37">}</span><span class="p">,</span><span class="p" data-group-id="0966649428-38">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">48</span><span class="p" data-group-id="0966649428-38">}</span><span class="p" data-group-id="0966649428-36">}</span><span class="p" data-group-id="0966649428-35">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="0966649428-39">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">4098</span><span class="p" data-group-id="0966649428-39">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="0966649428-40">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0966649428-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="0966649428-41">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="0966649428-41">}</span><span class="p" data-group-id="0966649428-30">]</span><span class="p" data-group-id="0966649428-29">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0966649428-42">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0966649428-42">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="0966649428-43">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0966649428-43">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">11&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="0966649428-44">(</span><span class="ss">code_lock</span><span class="p" data-group-id="0966649428-44">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0966649428-45">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0966649428-46">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">gen_statem</span><span class="p" data-group-id="0966649428-46">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0966649428-47">[</span><span class="p" data-group-id="0966649428-48">[</span><span class="p" data-group-id="0966649428-49">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="0966649428-50">{</span><span class="ss">code_lock</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0966649428-50">}</span><span class="p" data-group-id="0966649428-49">}</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="0966649428-51">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="0966649428-52">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0966649428-52">]</span><span class="p" data-group-id="0966649428-51">}</span><span class="p" data-group-id="0966649428-48">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="0966649428-53">[</span><span class="p" data-group-id="0966649428-53">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="0966649428-54">[</span><span class="p" data-group-id="0966649428-55">{</span><span class="ss">header</span><span class="p">,</span><span class="s">&quot;Status for state machine code_lock&quot;</span><span class="p" data-group-id="0966649428-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="0966649428-56">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="0966649428-57">[</span><span class="p" data-group-id="0966649428-58">{</span><span class="s">&quot;Status&quot;</span><span class="p">,</span><span class="ss">running</span><span class="p" data-group-id="0966649428-58">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="0966649428-59">{</span><span class="s">&quot;Parent&quot;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0966649428-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="0966649428-60">{</span><span class="s">&quot;Modules&quot;</span><span class="p">,</span><span class="p" data-group-id="0966649428-61">[</span><span class="ss">code_lock</span><span class="p" data-group-id="0966649428-61">]</span><span class="p" data-group-id="0966649428-60">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="0966649428-62">{</span><span class="s">&quot;Time-outs&quot;</span><span class="p">,</span><span class="p" data-group-id="0966649428-63">{</span><span class="mi">0</span><span class="p">,</span><span class="p" data-group-id="0966649428-64">[</span><span class="p" data-group-id="0966649428-64">]</span><span class="p" data-group-id="0966649428-63">}</span><span class="p" data-group-id="0966649428-62">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="0966649428-65">{</span><span class="s">&quot;Logged Events&quot;</span><span class="p">,</span><span class="p" data-group-id="0966649428-66">[</span><span class="p" data-group-id="0966649428-66">]</span><span class="p" data-group-id="0966649428-65">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                 </span><span class="p" data-group-id="0966649428-67">{</span><span class="s">&quot;Postponed&quot;</span><span class="p">,</span><span class="p" data-group-id="0966649428-68">[</span><span class="p" data-group-id="0966649428-68">]</span><span class="p" data-group-id="0966649428-67">}</span><span class="p" data-group-id="0966649428-57">]</span><span class="p" data-group-id="0966649428-56">}</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="0966649428-69">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="0966649428-70">[</span><span class="p" data-group-id="0966649428-71">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +                  </span><span class="p" data-group-id="0966649428-72">{</span><span class="ss">locked</span><span class="p">,</span><span class="p" data-group-id="0966649428-73">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0966649428-74">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0966649428-74">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                            </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0966649428-75">[</span><span class="p" data-group-id="0966649428-75">]</span><span class="p" data-group-id="0966649428-73">}</span><span class="p" data-group-id="0966649428-72">}</span><span class="p" data-group-id="0966649428-71">}</span><span class="p" data-group-id="0966649428-70">]</span><span class="p" data-group-id="0966649428-69">}</span><span class="p" data-group-id="0966649428-54">]</span><span class="p" data-group-id="0966649428-47">]</span><span class="p" data-group-id="0966649428-45">}</span></code></pre><h2 id="special-processes" class="section-heading">
│ │ │ │    <a href="#special-processes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Special Processes</span>
│ │ │ │  </h2>
│ │ │ │  <p>This section describes how to write a process that complies to the OTP design
│ │ │ │  principles, without using a standard behaviour. Such a process is to:</p><ul><li>Be started in a way that makes the process fit into a supervision tree</li><li>Support the <code class="inline">sys</code> <a href="spec_proc.xhtml#debug">debug facilities</a></li><li>Take care of <a href="spec_proc.xhtml#msg">system messages</a>.</li></ul><p>System messages are messages with a special meaning, used in the supervision
│ │ │ │ @@ -103,238 +103,238 @@
│ │ │ │    <a href="#example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example</span>
│ │ │ │  </h3>
│ │ │ │  <p>Here follows the simple server from
│ │ │ │  <a href="design_principles.xhtml#ch1">Overview</a>,
│ │ │ │ -implemented using <code class="inline">sys</code> and <code class="inline">proc_lib</code> to fit into a supervision tree:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0582555563-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="0582555563-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0582555563-2">(</span><span class="p" data-group-id="0582555563-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0582555563-3">]</span><span class="p" data-group-id="0582555563-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0582555563-4">(</span><span class="p" data-group-id="0582555563-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0582555563-5">]</span><span class="p" data-group-id="0582555563-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0582555563-6">(</span><span class="p" data-group-id="0582555563-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0582555563-7">]</span><span class="p" data-group-id="0582555563-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0582555563-8">(</span><span class="p" data-group-id="0582555563-9">[</span><span class="ss">system_continue</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">system_terminate</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w">
│ │ │ │ +implemented using <code class="inline">sys</code> and <code class="inline">proc_lib</code> to fit into a supervision tree:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0508524746-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="0508524746-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0508524746-2">(</span><span class="p" data-group-id="0508524746-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0508524746-3">]</span><span class="p" data-group-id="0508524746-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0508524746-4">(</span><span class="p" data-group-id="0508524746-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0508524746-5">]</span><span class="p" data-group-id="0508524746-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0508524746-6">(</span><span class="p" data-group-id="0508524746-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0508524746-7">]</span><span class="p" data-group-id="0508524746-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0508524746-8">(</span><span class="p" data-group-id="0508524746-9">[</span><span class="ss">system_continue</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">system_terminate</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w">
│ │ │ │           </span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="ss">system_get_state</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">system_replace_state</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0582555563-9">]</span><span class="p" data-group-id="0582555563-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +         </span><span class="ss">system_get_state</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">system_replace_state</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0508524746-9">]</span><span class="p" data-group-id="0508524746-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="0582555563-10">(</span><span class="p" data-group-id="0582555563-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0582555563-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582555563-12">[</span><span class="nf">self</span><span class="p" data-group-id="0582555563-13">(</span><span class="p" data-group-id="0582555563-13">)</span><span class="p" data-group-id="0582555563-12">]</span><span class="p" data-group-id="0582555563-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="0508524746-10">(</span><span class="p" data-group-id="0508524746-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0508524746-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0508524746-12">[</span><span class="nf">self</span><span class="p" data-group-id="0508524746-13">(</span><span class="p" data-group-id="0508524746-13">)</span><span class="p" data-group-id="0508524746-12">]</span><span class="p" data-group-id="0508524746-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="0582555563-14">(</span><span class="p" data-group-id="0582555563-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0582555563-15">{</span><span class="nf">self</span><span class="p" data-group-id="0582555563-16">(</span><span class="p" data-group-id="0582555563-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0582555563-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="0508524746-14">(</span><span class="p" data-group-id="0508524746-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0508524746-15">{</span><span class="nf">self</span><span class="p" data-group-id="0508524746-16">(</span><span class="p" data-group-id="0508524746-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0508524746-15">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0582555563-17">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="0582555563-17">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0508524746-17">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="0508524746-17">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Res</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="0582555563-18">(</span><span class="n">Ch</span><span class="p" data-group-id="0582555563-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0582555563-19">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0582555563-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="0508524746-18">(</span><span class="n">Ch</span><span class="p" data-group-id="0508524746-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0508524746-19">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0508524746-19">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="0582555563-20">(</span><span class="n">Parent</span><span class="p" data-group-id="0582555563-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="0582555563-21">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0582555563-22">(</span><span class="p" data-group-id="0582555563-22">)</span><span class="p" data-group-id="0582555563-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="0582555563-23">(</span><span class="p" data-group-id="0582555563-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="0582555563-24">(</span><span class="p" data-group-id="0582555563-25">[</span><span class="p" data-group-id="0582555563-25">]</span><span class="p" data-group-id="0582555563-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="0582555563-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582555563-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0582555563-28">(</span><span class="p" data-group-id="0582555563-28">)</span><span class="p" data-group-id="0582555563-27">}</span><span class="p" data-group-id="0582555563-26">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="0582555563-29">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0582555563-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="0508524746-20">(</span><span class="n">Parent</span><span class="p" data-group-id="0508524746-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="0508524746-21">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0508524746-22">(</span><span class="p" data-group-id="0508524746-22">)</span><span class="p" data-group-id="0508524746-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="0508524746-23">(</span><span class="p" data-group-id="0508524746-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="0508524746-24">(</span><span class="p" data-group-id="0508524746-25">[</span><span class="p" data-group-id="0508524746-25">]</span><span class="p" data-group-id="0508524746-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="0508524746-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0508524746-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0508524746-28">(</span><span class="p" data-group-id="0508524746-28">)</span><span class="p" data-group-id="0508524746-27">}</span><span class="p" data-group-id="0508524746-26">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="0508524746-29">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0508524746-29">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="0582555563-30">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0582555563-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="0508524746-30">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0508524746-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0582555563-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0582555563-31">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0582555563-32">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582555563-33">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0582555563-33">}</span><span class="p" data-group-id="0582555563-32">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="0582555563-34">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="0582555563-34">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="0582555563-35">(</span><span class="n">Chs</span><span class="p" data-group-id="0582555563-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0582555563-36">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0582555563-36">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0582555563-37">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582555563-38">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582555563-39">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0582555563-39">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0582555563-38">}</span><span class="p" data-group-id="0582555563-37">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="0582555563-40">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="0582555563-40">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0582555563-41">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0582555563-41">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0582555563-42">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582555563-43">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582555563-44">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0582555563-44">}</span><span class="p" data-group-id="0582555563-43">}</span><span class="p" data-group-id="0582555563-42">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="0582555563-45">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0582555563-45">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="0582555563-46">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="0582555563-46">)</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -        </span><span class="p" data-group-id="0582555563-47">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0582555563-47">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="0582555563-48">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ │ -                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0582555563-48">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0508524746-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0508524746-31">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0508524746-32">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0508524746-33">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0508524746-33">}</span><span class="p" data-group-id="0508524746-32">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="0508524746-34">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="0508524746-34">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="0508524746-35">(</span><span class="n">Chs</span><span class="p" data-group-id="0508524746-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0508524746-36">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0508524746-36">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0508524746-37">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0508524746-38">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0508524746-39">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0508524746-39">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0508524746-38">}</span><span class="p" data-group-id="0508524746-37">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0508524746-40">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="0508524746-40">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0508524746-41">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0508524746-41">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0508524746-42">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0508524746-43">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0508524746-44">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0508524746-44">}</span><span class="p" data-group-id="0508524746-43">}</span><span class="p" data-group-id="0508524746-42">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="0508524746-45">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0508524746-45">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0508524746-46">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="0508524746-46">)</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +        </span><span class="p" data-group-id="0508524746-47">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0508524746-47">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="0508524746-48">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ │ +                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0508524746-48">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_continue</span><span class="p" data-group-id="0582555563-49">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0582555563-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="0582555563-50">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0582555563-50">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_continue</span><span class="p" data-group-id="0508524746-49">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0508524746-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="0508524746-50">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0508524746-50">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_terminate</span><span class="p" data-group-id="0582555563-51">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Chs</span><span class="p" data-group-id="0582555563-51">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="0582555563-52">(</span><span class="n">Reason</span><span class="p" data-group-id="0582555563-52">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_terminate</span><span class="p" data-group-id="0508524746-51">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Chs</span><span class="p" data-group-id="0508524746-51">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="0508524746-52">(</span><span class="n">Reason</span><span class="p" data-group-id="0508524746-52">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_get_state</span><span class="p" data-group-id="0582555563-53">(</span><span class="n">Chs</span><span class="p" data-group-id="0582555563-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0582555563-54">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0582555563-54">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_get_state</span><span class="p" data-group-id="0508524746-53">(</span><span class="n">Chs</span><span class="p" data-group-id="0508524746-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0508524746-54">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0508524746-54">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_replace_state</span><span class="p" data-group-id="0582555563-55">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0582555563-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="0582555563-56">(</span><span class="n">Chs</span><span class="p" data-group-id="0582555563-56">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0582555563-57">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="0582555563-57">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_replace_state</span><span class="p" data-group-id="0508524746-55">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0508524746-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="0508524746-56">(</span><span class="n">Chs</span><span class="p" data-group-id="0508524746-56">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0508524746-57">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="0508524746-57">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">write_debug</span><span class="p" data-group-id="0582555563-58">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0582555563-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0582555563-59">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582555563-60">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="0582555563-60">]</span><span class="p" data-group-id="0582555563-59">)</span><span class="p">.</span></code></pre><p id="ex">As it is not relevant to the example, the channel handling functions have been
│ │ │ │ +</span><span class="nf">write_debug</span><span class="p" data-group-id="0508524746-58">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0508524746-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0508524746-59">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0508524746-60">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="0508524746-60">]</span><span class="p" data-group-id="0508524746-59">)</span><span class="p">.</span></code></pre><p id="ex">As it is not relevant to the example, the channel handling functions have been
│ │ │ │  omitted. To compile this example, the
│ │ │ │  <a href="design_principles.xhtml#channels-implementation">implementation of channel handling</a>
│ │ │ │  needs to be added to the module.</p><p>Here is an example showing how the debugging functions in the <code class="inline">sys</code>
│ │ │ │  module can be used for <code class="inline">ch4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="6089057964-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="6089057964-1">]</span><span class="w"> </span><span class="p" data-group-id="6089057964-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="6089057964-2">]</span><span class="w"> </span><span class="p" data-group-id="6089057964-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="6089057964-3">]</span><span class="w"> </span><span class="p" data-group-id="6089057964-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="6089057964-4">]</span><span class="w"> </span><span class="p" data-group-id="6089057964-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6089057964-5">]</span><span class="w"> </span><span class="p" data-group-id="6089057964-6">[</span><span class="ss">jit</span><span class="p" data-group-id="6089057964-6">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="4413145063-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="4413145063-1">]</span><span class="w"> </span><span class="p" data-group-id="4413145063-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4413145063-2">]</span><span class="w"> </span><span class="p" data-group-id="4413145063-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4413145063-3">]</span><span class="w"> </span><span class="p" data-group-id="4413145063-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4413145063-4">]</span><span class="w"> </span><span class="p" data-group-id="4413145063-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4413145063-5">]</span><span class="w"> </span><span class="p" data-group-id="4413145063-6">[</span><span class="ss">jit</span><span class="p" data-group-id="4413145063-6">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="6089057964-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="6089057964-8">(</span><span class="p" data-group-id="6089057964-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="6089057964-7">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6089057964-9">(</span><span class="p" data-group-id="6089057964-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6089057964-10">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6089057964-10">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="6089057964-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6089057964-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="6089057964-12">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6089057964-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">alloc</span><span class="p" data-group-id="6089057964-13">(</span><span class="p" data-group-id="6089057964-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6089057964-14">{</span><span class="ss">in</span><span class="p">,</span><span class="ss">alloc</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6089057964-14">}</span><span class="w">
│ │ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6089057964-15">{</span><span class="ss">out</span><span class="p">,</span><span class="p" data-group-id="6089057964-16">{</span><span class="ss">ch4</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6089057964-16">}</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6089057964-15">}</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="4413145063-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4413145063-8">(</span><span class="p" data-group-id="4413145063-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4413145063-7">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4413145063-9">(</span><span class="p" data-group-id="4413145063-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4413145063-10">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4413145063-10">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="4413145063-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4413145063-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="4413145063-12">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4413145063-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">alloc</span><span class="p" data-group-id="4413145063-13">(</span><span class="p" data-group-id="4413145063-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4413145063-14">{</span><span class="ss">in</span><span class="p">,</span><span class="ss">alloc</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4413145063-14">}</span><span class="w">
│ │ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4413145063-15">{</span><span class="ss">out</span><span class="p">,</span><span class="p" data-group-id="4413145063-16">{</span><span class="ss">ch4</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4413145063-16">}</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4413145063-15">}</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">free</span><span class="p" data-group-id="6089057964-17">(</span><span class="ss">ch1</span><span class="p" data-group-id="6089057964-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6089057964-18">{</span><span class="ss">in</span><span class="p">,</span><span class="p" data-group-id="6089057964-19">{</span><span class="ss">free</span><span class="p">,</span><span class="ss">ch1</span><span class="p" data-group-id="6089057964-19">}</span><span class="p" data-group-id="6089057964-18">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">free</span><span class="p" data-group-id="4413145063-17">(</span><span class="ss">ch1</span><span class="p" data-group-id="4413145063-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4413145063-18">{</span><span class="ss">in</span><span class="p">,</span><span class="p" data-group-id="4413145063-19">{</span><span class="ss">free</span><span class="p">,</span><span class="ss">ch1</span><span class="p" data-group-id="4413145063-19">}</span><span class="p" data-group-id="4413145063-18">}</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="6089057964-20">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="6089057964-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6089057964-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="6089057964-22">[</span><span class="p" data-group-id="6089057964-23">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="6089057964-24">{</span><span class="p" data-group-id="6089057964-25">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6089057964-25">}</span><span class="p">,</span><span class="p" data-group-id="6089057964-26">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="6089057964-26">}</span><span class="p" data-group-id="6089057964-24">}</span><span class="p" data-group-id="6089057964-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="6089057964-27">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="6089057964-28">{</span><span class="p" data-group-id="6089057964-29">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6089057964-29">}</span><span class="p">,</span><span class="p" data-group-id="6089057964-30">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">49</span><span class="p" data-group-id="6089057964-30">}</span><span class="p" data-group-id="6089057964-28">}</span><span class="p" data-group-id="6089057964-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="6089057964-31">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">202</span><span class="p" data-group-id="6089057964-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="6089057964-32">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6089057964-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="6089057964-33">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6089057964-33">}</span><span class="p" data-group-id="6089057964-22">]</span><span class="p" data-group-id="6089057964-21">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="6089057964-34">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="6089057964-34">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="6089057964-35">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="6089057964-35">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="6089057964-36">(</span><span class="ss">ch4</span><span class="p" data-group-id="6089057964-36">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6089057964-37">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6089057964-38">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">ch4</span><span class="p" data-group-id="6089057964-38">}</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6089057964-39">[</span><span class="p" data-group-id="6089057964-40">[</span><span class="p" data-group-id="6089057964-41">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="6089057964-42">{</span><span class="ss">ch4</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6089057964-42">}</span><span class="p" data-group-id="6089057964-41">}</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="6089057964-43">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="6089057964-44">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6089057964-44">]</span><span class="p" data-group-id="6089057964-43">}</span><span class="p" data-group-id="6089057964-40">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="6089057964-45">[</span><span class="p" data-group-id="6089057964-45">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="6089057964-46">{</span><span class="p" data-group-id="6089057964-47">[</span><span class="mi">1</span><span class="p" data-group-id="6089057964-47">]</span><span class="p">,</span><span class="p" data-group-id="6089057964-48">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">18</span><span class="p">,</span><span class="mi">19</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6089057964-48">]</span><span class="p" data-group-id="6089057964-46">}</span><span class="p" data-group-id="6089057964-39">]</span><span class="p" data-group-id="6089057964-37">}</span></code></pre><h3 id="starting-the-process" class="section-heading">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="4413145063-20">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="4413145063-20">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4413145063-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="4413145063-22">[</span><span class="p" data-group-id="4413145063-23">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="4413145063-24">{</span><span class="p" data-group-id="4413145063-25">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4413145063-25">}</span><span class="p">,</span><span class="p" data-group-id="4413145063-26">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="4413145063-26">}</span><span class="p" data-group-id="4413145063-24">}</span><span class="p" data-group-id="4413145063-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="4413145063-27">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="4413145063-28">{</span><span class="p" data-group-id="4413145063-29">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4413145063-29">}</span><span class="p">,</span><span class="p" data-group-id="4413145063-30">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">49</span><span class="p" data-group-id="4413145063-30">}</span><span class="p" data-group-id="4413145063-28">}</span><span class="p" data-group-id="4413145063-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="4413145063-31">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">202</span><span class="p" data-group-id="4413145063-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="4413145063-32">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4413145063-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="4413145063-33">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4413145063-33">}</span><span class="p" data-group-id="4413145063-22">]</span><span class="p" data-group-id="4413145063-21">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="4413145063-34">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="4413145063-34">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="4413145063-35">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="4413145063-35">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="4413145063-36">(</span><span class="ss">ch4</span><span class="p" data-group-id="4413145063-36">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4413145063-37">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4413145063-38">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">ch4</span><span class="p" data-group-id="4413145063-38">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4413145063-39">[</span><span class="p" data-group-id="4413145063-40">[</span><span class="p" data-group-id="4413145063-41">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="4413145063-42">{</span><span class="ss">ch4</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4413145063-42">}</span><span class="p" data-group-id="4413145063-41">}</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="4413145063-43">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="4413145063-44">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4413145063-44">]</span><span class="p" data-group-id="4413145063-43">}</span><span class="p" data-group-id="4413145063-40">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="4413145063-45">[</span><span class="p" data-group-id="4413145063-45">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="4413145063-46">{</span><span class="p" data-group-id="4413145063-47">[</span><span class="mi">1</span><span class="p" data-group-id="4413145063-47">]</span><span class="p">,</span><span class="p" data-group-id="4413145063-48">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">18</span><span class="p">,</span><span class="mi">19</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4413145063-48">]</span><span class="p" data-group-id="4413145063-46">}</span><span class="p" data-group-id="4413145063-39">]</span><span class="p" data-group-id="4413145063-37">}</span></code></pre><h3 id="starting-the-process" class="section-heading">
│ │ │ │    <a href="#starting-the-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting the Process</span>
│ │ │ │  </h3>
│ │ │ │  <p>A function in the <a href="../../../lib/stdlib/doc/html/proc_lib.html"><code class="inline">proc_lib</code></a> module is to be used to start the process. Several
│ │ │ │  functions are available, for example,
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#spawn_link/4"><code class="inline">proc_lib:spawn_link/3,4</code></a>
│ │ │ │  for asynchronous start and
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/5"><code class="inline">proc_lib:start_link/3,4,5</code></a> for synchronous start.</p><p>Information necessary for a process within a supervision tree, such as
│ │ │ │  details on ancestors and the initial call, is stored when a process
│ │ │ │  is started through one of these functions.</p><p>If the process terminates with a reason other than <code class="inline">normal</code> or <code class="inline">shutdown</code>, a
│ │ │ │  crash report is generated. For more information about the crash report, see
│ │ │ │  <a href="../../../lib/kernel/doc/html/logger_chapter.xhtml">Logging</a> in Kernel User's Guide.</p><p>In the example, synchronous start is used. The process starts by calling
│ │ │ │ -<code class="inline">ch4:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="6169565616-1">(</span><span class="p" data-group-id="6169565616-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6169565616-2">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6169565616-3">[</span><span class="nf">self</span><span class="p" data-group-id="6169565616-4">(</span><span class="p" data-group-id="6169565616-4">)</span><span class="p" data-group-id="6169565616-3">]</span><span class="p" data-group-id="6169565616-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch4:start_link/0</code> calls <a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>, which takes a module
│ │ │ │ +<code class="inline">ch4:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="3937484510-1">(</span><span class="p" data-group-id="3937484510-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3937484510-2">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3937484510-3">[</span><span class="nf">self</span><span class="p" data-group-id="3937484510-4">(</span><span class="p" data-group-id="3937484510-4">)</span><span class="p" data-group-id="3937484510-3">]</span><span class="p" data-group-id="3937484510-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch4:start_link/0</code> calls <a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>, which takes a module
│ │ │ │  name, a function name, and an argument list as arguments. It then
│ │ │ │  spawns a new process and establishes a link. The new process starts
│ │ │ │  by executing the given function, here <code class="inline">ch4:init(Pid)</code>, where <code class="inline">Pid</code> is
│ │ │ │  the pid of the parent process (obtained by the call to
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self()</code></a> in the call to <a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>).</p><p>All initialization, including name registration, is done in <code class="inline">init/1</code>. The new
│ │ │ │ -process has to acknowledge that it has been started to the parent:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="3604738413-1">(</span><span class="n">Parent</span><span class="p" data-group-id="3604738413-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +process has to acknowledge that it has been started to the parent:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5923702120-1">(</span><span class="n">Parent</span><span class="p" data-group-id="5923702120-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="3604738413-2">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3604738413-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3604738413-4">(</span><span class="p" data-group-id="3604738413-4">)</span><span class="p" data-group-id="3604738413-3">}</span><span class="p" data-group-id="3604738413-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="3604738413-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3604738413-5">)</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a> is synchronous and does not return until
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="5923702120-2">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5923702120-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5923702120-4">(</span><span class="p" data-group-id="5923702120-4">)</span><span class="p" data-group-id="5923702120-3">}</span><span class="p" data-group-id="5923702120-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="5923702120-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5923702120-5">)</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a> is synchronous and does not return until
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#init_ack/2"><code class="inline">proc_lib:init_ack/1,2</code></a> or
│ │ │ │  <a href="../../../lib/stdlib/doc/html/proc_lib.html#init_fail/3"><code class="inline">proc_lib:init_fail/2,3</code></a> has been called,
│ │ │ │  or the process has exited.</p><p><a href="" id="debug"></a></p><h3 id="debugging" class="section-heading">
│ │ │ │    <a href="#debugging" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Debugging</span>
│ │ │ │  </h3>
│ │ │ │  <p>To support the debug facilities in <code class="inline">sys</code>, a <em>debug structure</em> is needed. The
│ │ │ │ -<code class="inline">Deb</code> term is initialized using <a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5583514197-1">(</span><span class="n">Parent</span><span class="p" data-group-id="5583514197-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<code class="inline">Deb</code> term is initialized using <a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8574605987-1">(</span><span class="n">Parent</span><span class="p" data-group-id="8574605987-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="5583514197-2">(</span><span class="p" data-group-id="5583514197-3">[</span><span class="p" data-group-id="5583514197-3">]</span><span class="p" data-group-id="5583514197-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="8574605987-2">(</span><span class="p" data-group-id="8574605987-3">[</span><span class="p" data-group-id="8574605987-3">]</span><span class="p" data-group-id="8574605987-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="5583514197-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="5583514197-4">)</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a> takes a list of options. Given an empty list as in this
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="8574605987-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="8574605987-4">)</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a> takes a list of options. Given an empty list as in this
│ │ │ │  example means that debugging is initially disabled. For information about the
│ │ │ │  possible options, see <a href="../../../lib/stdlib/doc/html/sys.html"><code class="inline">sys</code></a> in STDLIB.</p><p>For each <em>system event</em> to be logged or traced, the following function
│ │ │ │ -is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="9538432383-1">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Func</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="9538432383-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Deb1</span></code></pre><p>The arguments have the follow meaning:</p><ul><li><code class="inline">Deb</code> is the debug structure as returned from <a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>.</li><li><code class="inline">Func</code> is a fun specifying a (user-defined) function used to format trace
│ │ │ │ +is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0966461634-1">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Func</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="0966461634-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Deb1</span></code></pre><p>The arguments have the follow meaning:</p><ul><li><code class="inline">Deb</code> is the debug structure as returned from <a href="../../../lib/stdlib/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>.</li><li><code class="inline">Func</code> is a fun specifying a (user-defined) function used to format trace
│ │ │ │  output. For each system event, the format function is called as
│ │ │ │  <code class="inline">Func(Dev, Event, Info)</code>, where:<ul><li><code class="inline">Dev</code> is the I/O device to which the output is to be printed. See <a href="../../../lib/stdlib/doc/html/io.html"><code class="inline">io</code></a>
│ │ │ │  in STDLIB.</li><li><code class="inline">Event</code> and <code class="inline">Info</code> are passed as-is from the call to <a href="../../../lib/stdlib/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a>.</li></ul></li><li><code class="inline">Info</code> is used to pass more information to <code class="inline">Func</code>. It can be any term, and it
│ │ │ │  is passed as-is.</li><li><code class="inline">Event</code> is the system event. It is up to the user to define what a system
│ │ │ │  event is and how it is to be represented. Typically, at least incoming and
│ │ │ │  outgoing messages are considered system events and represented by the tuples
│ │ │ │  <code class="inline">{in,Msg[,From]}</code> and <code class="inline">{out,Msg,To[,State]}</code>, respectively.</li></ul><p><a href="../../../lib/stdlib/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a> returns an updated debug structure <code class="inline">Deb1</code>.</p><p>In the example, <a href="../../../lib/stdlib/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a> is called for each incoming and
│ │ │ │  outgoing message. The format function <code class="inline">Func</code> is the function
│ │ │ │ -<code class="inline">ch4:write_debug/3</code>, which prints the message using <a href="../../../lib/stdlib/doc/html/io.html#format/3"><code class="inline">io:format/3</code></a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="9809389743-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="9809389743-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<code class="inline">ch4:write_debug/3</code>, which prints the message using <a href="../../../lib/stdlib/doc/html/io.html#format/3"><code class="inline">io:format/3</code></a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="9582769654-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="9582769654-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9809389743-2">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="9809389743-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="9809389743-3">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9809389743-4">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="9809389743-4">}</span><span class="p" data-group-id="9809389743-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9809389743-5">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="9809389743-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="9809389743-6">(</span><span class="n">Chs</span><span class="p" data-group-id="9809389743-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9809389743-7">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9809389743-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="9809389743-8">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9809389743-9">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9809389743-10">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9809389743-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="9809389743-9">}</span><span class="p" data-group-id="9809389743-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="9809389743-11">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="9809389743-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9809389743-12">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9809389743-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="9809389743-13">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9809389743-14">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9809389743-15">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9809389743-15">}</span><span class="p" data-group-id="9809389743-14">}</span><span class="p" data-group-id="9809389743-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="9809389743-16">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9809389743-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="9809389743-17">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="9809389743-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9582769654-2">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="9582769654-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="9582769654-3">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9582769654-4">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="9582769654-4">}</span><span class="p" data-group-id="9582769654-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9582769654-5">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="9582769654-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="9582769654-6">(</span><span class="n">Chs</span><span class="p" data-group-id="9582769654-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9582769654-7">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9582769654-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="9582769654-8">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9582769654-9">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9582769654-10">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9582769654-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="9582769654-9">}</span><span class="p" data-group-id="9582769654-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="9582769654-11">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="9582769654-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9582769654-12">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9582769654-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="9582769654-13">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9582769654-14">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9582769654-15">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9582769654-15">}</span><span class="p" data-group-id="9582769654-14">}</span><span class="p" data-group-id="9582769654-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="9582769654-16">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9582769654-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="9582769654-17">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="9582769654-17">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">write_debug</span><span class="p" data-group-id="9809389743-18">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9809389743-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9809389743-19">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9809389743-20">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="9809389743-20">]</span><span class="p" data-group-id="9809389743-19">)</span><span class="p">.</span></code></pre><p><a href="" id="msg"></a></p><h3 id="handling-system-messages" class="section-heading">
│ │ │ │ +</span><span class="nf">write_debug</span><span class="p" data-group-id="9582769654-18">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9582769654-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9582769654-19">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9582769654-20">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="9582769654-20">]</span><span class="p" data-group-id="9582769654-19">)</span><span class="p">.</span></code></pre><p><a href="" id="msg"></a></p><h3 id="handling-system-messages" class="section-heading">
│ │ │ │    <a href="#handling-system-messages" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Handling System Messages</span>
│ │ │ │  </h3>
│ │ │ │  <p><em>System messages</em> are received as:</p><pre><code class="text">{system, From, Request}</code></pre><p>The content and meaning of these messages are not to be interpreted by the
│ │ │ │ -process. Instead the following function is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="9861642631-1">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9861642631-1">)</span></code></pre><p>The arguments have the following meaning:</p><ul><li><code class="inline">Request</code> and <code class="inline">From</code> from the received system message are to be
│ │ │ │ +process. Instead the following function is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="6657969596-1">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6657969596-1">)</span></code></pre><p>The arguments have the following meaning:</p><ul><li><code class="inline">Request</code> and <code class="inline">From</code> from the received system message are to be
│ │ │ │  passed as-is to the call to <a href="../../../lib/stdlib/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a>.</li><li><code class="inline">Parent</code> is the pid of the parent process.</li><li><code class="inline">Module</code> is the name of the module implementing the speciall process.</li><li><code class="inline">Deb</code> is the debug structure.</li><li><code class="inline">State</code> is a term describing the internal state and is passed on to
│ │ │ │  <code class="inline">Module:system_continue/3</code>, <code class="inline">Module:system_terminate/4</code>/
│ │ │ │  <code class="inline">Module:system_get_state/1</code>, and <code class="inline">Module:system_replace_state/2</code>.</li></ul><p><a href="../../../lib/stdlib/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a> does not return. It handles the system
│ │ │ │  message and <em>eventually</em> calls either of the following functions:</p><ul><li><p><code class="inline">Module:system_continue(Parent, Deb, State)</code> - if process execution is to
│ │ │ │  continue.</p></li><li><p><code class="inline">Module:system_terminate(Reason, Parent, Deb, State)</code> - if the
│ │ │ │  process is to terminate.</p></li></ul><p>While handling the system message, <a href="../../../lib/stdlib/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a> can call
│ │ │ │  one of the following functions:</p><ul><li><p><code class="inline">Module:system_get_state(State)</code> - if the process is to return its state.</p></li><li><p><code class="inline">Module:system_replace_state(StateFun, State)</code> - if the process is
│ │ │ │  to replace its state using the fun <code class="inline">StateFun</code> fun. See <a href="../../../lib/stdlib/doc/html/sys.html#replace_state/3"><code class="inline">sys:replace_state/3</code></a>
│ │ │ │  for more information.</p></li><li><p><code class="inline">system_code_change(Misc, Module, OldVsn, Extra)</code> - if the process is to
│ │ │ │  perform a code change.</p></li></ul><p>A process in a supervision tree is expected to terminate with the same reason as
│ │ │ │ -its parent.</p><p>In the example, system messages are handed by the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="2410015209-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="2410015209-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +its parent.</p><p>In the example, system messages are handed by the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="7793945553-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="7793945553-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -        </span><span class="p" data-group-id="2410015209-2">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="2410015209-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="2410015209-3">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ │ -                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2410015209-3">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7793945553-2">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="7793945553-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="7793945553-3">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ │ +                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7793945553-3">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_continue</span><span class="p" data-group-id="2410015209-4">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2410015209-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="2410015209-5">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="2410015209-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_continue</span><span class="p" data-group-id="7793945553-4">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7793945553-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="7793945553-5">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="7793945553-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_terminate</span><span class="p" data-group-id="2410015209-6">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2410015209-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="2410015209-7">(</span><span class="n">Reason</span><span class="p" data-group-id="2410015209-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_terminate</span><span class="p" data-group-id="7793945553-6">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7793945553-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="7793945553-7">(</span><span class="n">Reason</span><span class="p" data-group-id="7793945553-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_get_state</span><span class="p" data-group-id="2410015209-8">(</span><span class="n">Chs</span><span class="p" data-group-id="2410015209-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2410015209-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2410015209-9">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">system_get_state</span><span class="p" data-group-id="7793945553-8">(</span><span class="n">Chs</span><span class="p" data-group-id="7793945553-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7793945553-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7793945553-9">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_replace_state</span><span class="p" data-group-id="2410015209-10">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2410015209-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="2410015209-11">(</span><span class="n">Chs</span><span class="p" data-group-id="2410015209-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2410015209-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="2410015209-12">}</span><span class="p">.</span></code></pre><p>If a special process is configured to trap exits, it must take notice
│ │ │ │ +</span><span class="nf">system_replace_state</span><span class="p" data-group-id="7793945553-10">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7793945553-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="7793945553-11">(</span><span class="n">Chs</span><span class="p" data-group-id="7793945553-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7793945553-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="7793945553-12">}</span><span class="p">.</span></code></pre><p>If a special process is configured to trap exits, it must take notice
│ │ │ │  of 'EXIT' messages from its parent process and terminate using the
│ │ │ │ -same exit reason once the parent process has terminated.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5604370953-1">(</span><span class="n">Parent</span><span class="p" data-group-id="5604370953-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +same exit reason once the parent process has terminated.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9307580919-1">(</span><span class="n">Parent</span><span class="p" data-group-id="9307580919-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="5604370953-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5604370953-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="9307580919-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9307580919-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="5604370953-3">(</span><span class="n">Parent</span><span class="p" data-group-id="5604370953-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="9307580919-3">(</span><span class="n">Parent</span><span class="p" data-group-id="9307580919-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="5604370953-4">(</span><span class="n">Parent</span><span class="p" data-group-id="5604370953-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="9307580919-4">(</span><span class="n">Parent</span><span class="p" data-group-id="9307580919-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="5604370953-5">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5604370953-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9307580919-5">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9307580919-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="c1">%% Clean up here, if needed.</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="5604370953-6">(</span><span class="n">Reason</span><span class="p" data-group-id="5604370953-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="9307580919-6">(</span><span class="n">Reason</span><span class="p" data-group-id="9307580919-6">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="user-defined-behaviours" class="section-heading">
│ │ │ │    <a href="#user-defined-behaviours" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">User-Defined Behaviours</span>
│ │ │ │  </h2>
│ │ │ │ @@ -353,69 +353,69 @@
│ │ │ │  function. Note that the <code class="inline">-optional_callbacks</code> attribute is to be used together
│ │ │ │  with the <code class="inline">-callback</code> attribute; it cannot be combined with the
│ │ │ │  <code class="inline">behaviour_info()</code> function described below.</p><p>Tools that need to know about optional callback functions can call
│ │ │ │  <code class="inline">Behaviour:behaviour_info(optional_callbacks)</code> to get a list of all optional
│ │ │ │  callback functions.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>We recommend using the <code class="inline">-callback</code> attribute rather than the
│ │ │ │  <code class="inline">behaviour_info()</code> function. The reason is that the extra type information can
│ │ │ │  be used by tools to produce documentation or find discrepancies.</p></section><p>As an alternative to the <code class="inline">-callback</code> and <code class="inline">-optional_callbacks</code> attributes you
│ │ │ │ -may directly implement and export <code class="inline">behaviour_info()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="6035399591-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="6035399591-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6035399591-2">[</span><span class="p" data-group-id="6035399591-3">{</span><span class="n">Name1</span><span class="p">,</span><span class="w"> </span><span class="n">Arity1</span><span class="p" data-group-id="6035399591-3">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="p" data-group-id="6035399591-4">{</span><span class="n">NameN</span><span class="p">,</span><span class="w"> </span><span class="n">ArityN</span><span class="p" data-group-id="6035399591-4">}</span><span class="p" data-group-id="6035399591-2">]</span><span class="p">.</span></code></pre><p>where each <code class="inline">{Name, Arity}</code> specifies the name and arity of a callback function.
│ │ │ │ +may directly implement and export <code class="inline">behaviour_info()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="7206166191-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="7206166191-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7206166191-2">[</span><span class="p" data-group-id="7206166191-3">{</span><span class="n">Name1</span><span class="p">,</span><span class="w"> </span><span class="n">Arity1</span><span class="p" data-group-id="7206166191-3">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="p" data-group-id="7206166191-4">{</span><span class="n">NameN</span><span class="p">,</span><span class="w"> </span><span class="n">ArityN</span><span class="p" data-group-id="7206166191-4">}</span><span class="p" data-group-id="7206166191-2">]</span><span class="p">.</span></code></pre><p>where each <code class="inline">{Name, Arity}</code> specifies the name and arity of a callback function.
│ │ │ │  This function is otherwise automatically generated by the compiler using the
│ │ │ │  <code class="inline">-callback</code> attributes.</p><p>When the compiler encounters the module attribute <code class="inline">-behaviour(Behaviour).</code> in a
│ │ │ │  module <code class="inline">Mod</code>, it calls <code class="inline">Behaviour:behaviour_info(callbacks)</code> and compares the
│ │ │ │  result with the set of functions actually exported from <code class="inline">Mod</code>, and issues a
│ │ │ │  warning if any callback function is missing.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">%% User-defined behaviour module</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2996928563-1">(</span><span class="ss">simple_server</span><span class="p" data-group-id="2996928563-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2996928563-2">(</span><span class="p" data-group-id="2996928563-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2996928563-3">]</span><span class="p" data-group-id="2996928563-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2266010801-1">(</span><span class="ss">simple_server</span><span class="p" data-group-id="2266010801-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2266010801-2">(</span><span class="p" data-group-id="2266010801-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2266010801-3">]</span><span class="p" data-group-id="2266010801-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">init</span><span class="p" data-group-id="2996928563-4">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2996928563-5">(</span><span class="p" data-group-id="2996928563-5">)</span><span class="p" data-group-id="2996928563-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="2996928563-6">(</span><span class="n">Req</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2996928563-7">(</span><span class="p" data-group-id="2996928563-7">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2996928563-8">(</span><span class="p" data-group-id="2996928563-8">)</span><span class="p" data-group-id="2996928563-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2996928563-9">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2996928563-10">(</span><span class="p" data-group-id="2996928563-10">)</span><span class="p" data-group-id="2996928563-9">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">terminate</span><span class="p" data-group-id="2996928563-11">(</span><span class="p" data-group-id="2996928563-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">format_state</span><span class="p" data-group-id="2996928563-12">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2996928563-13">(</span><span class="p" data-group-id="2996928563-13">)</span><span class="p" data-group-id="2996928563-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2996928563-14">(</span><span class="p" data-group-id="2996928563-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">init</span><span class="p" data-group-id="2266010801-4">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2266010801-5">(</span><span class="p" data-group-id="2266010801-5">)</span><span class="p" data-group-id="2266010801-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="2266010801-6">(</span><span class="n">Req</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2266010801-7">(</span><span class="p" data-group-id="2266010801-7">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2266010801-8">(</span><span class="p" data-group-id="2266010801-8">)</span><span class="p" data-group-id="2266010801-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2266010801-9">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2266010801-10">(</span><span class="p" data-group-id="2266010801-10">)</span><span class="p" data-group-id="2266010801-9">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">terminate</span><span class="p" data-group-id="2266010801-11">(</span><span class="p" data-group-id="2266010801-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">format_state</span><span class="p" data-group-id="2266010801-12">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2266010801-13">(</span><span class="p" data-group-id="2266010801-13">)</span><span class="p" data-group-id="2266010801-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2266010801-14">(</span><span class="p" data-group-id="2266010801-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">optional_callbacks</span><span class="p" data-group-id="2996928563-15">(</span><span class="p" data-group-id="2996928563-16">[</span><span class="ss">format_state</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2996928563-16">]</span><span class="p" data-group-id="2996928563-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">optional_callbacks</span><span class="p" data-group-id="2266010801-15">(</span><span class="p" data-group-id="2266010801-16">[</span><span class="ss">format_state</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2266010801-16">]</span><span class="p" data-group-id="2266010801-15">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Alternatively you may define:</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │  </span><span class="c1">%% -export([behaviour_info/1]).</span><span class="w">
│ │ │ │  </span><span class="c1">%% behaviour_info(callbacks) -&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%%     [{init,1},</span><span class="w">
│ │ │ │  </span><span class="c1">%%      {handle_req,2},</span><span class="w">
│ │ │ │  </span><span class="c1">%%      {terminate,0}].</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="2996928563-17">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2996928563-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2996928563-18">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2996928563-19">[</span><span class="nf">self</span><span class="p" data-group-id="2996928563-20">(</span><span class="p" data-group-id="2996928563-20">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2996928563-19">]</span><span class="p" data-group-id="2996928563-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="2266010801-17">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2266010801-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2266010801-18">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2266010801-19">[</span><span class="nf">self</span><span class="p" data-group-id="2266010801-20">(</span><span class="p" data-group-id="2266010801-20">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2266010801-19">]</span><span class="p" data-group-id="2266010801-18">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="2996928563-21">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2996928563-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="2996928563-22">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2996928563-23">(</span><span class="p" data-group-id="2996928563-23">)</span><span class="p" data-group-id="2996928563-22">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2266010801-21">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="2266010801-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="2266010801-22">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2266010801-23">(</span><span class="p" data-group-id="2266010801-23">)</span><span class="p" data-group-id="2266010801-22">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Dbg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="2996928563-24">(</span><span class="p" data-group-id="2996928563-25">[</span><span class="p" data-group-id="2996928563-25">]</span><span class="p" data-group-id="2996928563-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="2996928563-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2996928563-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2996928563-28">(</span><span class="p" data-group-id="2996928563-28">)</span><span class="p" data-group-id="2996928563-27">}</span><span class="p" data-group-id="2996928563-26">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="2996928563-29">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2996928563-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="n">Dbg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="2266010801-24">(</span><span class="p" data-group-id="2266010801-25">[</span><span class="p" data-group-id="2266010801-25">]</span><span class="p" data-group-id="2266010801-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="2266010801-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2266010801-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2266010801-28">(</span><span class="p" data-group-id="2266010801-28">)</span><span class="p" data-group-id="2266010801-27">}</span><span class="p" data-group-id="2266010801-26">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="2266010801-29">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2266010801-29">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>In a callback module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9995370355-1">(</span><span class="ss">db</span><span class="p" data-group-id="9995370355-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="9995370355-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="9995370355-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>In a callback module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2391682516-1">(</span><span class="ss">db</span><span class="p" data-group-id="2391682516-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2391682516-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="2391682516-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9995370355-3">(</span><span class="p" data-group-id="9995370355-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9995370355-4">]</span><span class="p" data-group-id="9995370355-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2391682516-3">(</span><span class="p" data-group-id="2391682516-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2391682516-4">]</span><span class="p" data-group-id="2391682516-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The contracts specified with <code class="inline">-callback</code> attributes in behaviour modules can be
│ │ │ │  further refined by adding <code class="inline">-spec</code> attributes in callback modules. This can be
│ │ │ │  useful as <code class="inline">-callback</code> contracts are usually generic. The same callback module
│ │ │ │ -with contracts for the callbacks:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4953964619-1">(</span><span class="ss">db</span><span class="p" data-group-id="4953964619-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4953964619-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="4953964619-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +with contracts for the callbacks:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1841878719-1">(</span><span class="ss">db</span><span class="p" data-group-id="1841878719-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1841878719-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="1841878719-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4953964619-3">(</span><span class="p" data-group-id="4953964619-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4953964619-4">]</span><span class="p" data-group-id="4953964619-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1841878719-3">(</span><span class="p" data-group-id="1841878719-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1841878719-4">]</span><span class="p" data-group-id="1841878719-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4953964619-5">(</span><span class="ss">state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4953964619-6">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4953964619-7">[</span><span class="nf">atom</span><span class="p" data-group-id="4953964619-8">(</span><span class="p" data-group-id="4953964619-8">)</span><span class="p" data-group-id="4953964619-7">]</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4953964619-9">(</span><span class="p" data-group-id="4953964619-9">)</span><span class="p" data-group-id="4953964619-6">}</span><span class="p" data-group-id="4953964619-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1841878719-5">(</span><span class="ss">state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1841878719-6">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1841878719-7">[</span><span class="nf">atom</span><span class="p" data-group-id="1841878719-8">(</span><span class="p" data-group-id="1841878719-8">)</span><span class="p" data-group-id="1841878719-7">]</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1841878719-9">(</span><span class="p" data-group-id="1841878719-9">)</span><span class="p" data-group-id="1841878719-6">}</span><span class="p" data-group-id="1841878719-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="4953964619-10">(</span><span class="p" data-group-id="4953964619-10">)</span><span class="w">   </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="4953964619-11">{</span><span class="p" data-group-id="4953964619-11">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">request</span><span class="p" data-group-id="4953964619-12">(</span><span class="p" data-group-id="4953964619-12">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4953964619-13">{</span><span class="ss">&#39;store&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="4953964619-14">(</span><span class="p" data-group-id="4953964619-14">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="4953964619-15">(</span><span class="p" data-group-id="4953964619-15">)</span><span class="p" data-group-id="4953964619-13">}</span><span class="p">;</span><span class="w">
│ │ │ │ -                   </span><span class="p" data-group-id="4953964619-16">{</span><span class="ss">&#39;lookup&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="4953964619-17">(</span><span class="p" data-group-id="4953964619-17">)</span><span class="p" data-group-id="4953964619-16">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="1841878719-10">(</span><span class="p" data-group-id="1841878719-10">)</span><span class="w">   </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="1841878719-11">{</span><span class="p" data-group-id="1841878719-11">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">request</span><span class="p" data-group-id="1841878719-12">(</span><span class="p" data-group-id="1841878719-12">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1841878719-13">{</span><span class="ss">&#39;store&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1841878719-14">(</span><span class="p" data-group-id="1841878719-14">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1841878719-15">(</span><span class="p" data-group-id="1841878719-15">)</span><span class="p" data-group-id="1841878719-13">}</span><span class="p">;</span><span class="w">
│ │ │ │ +                   </span><span class="p" data-group-id="1841878719-16">{</span><span class="ss">&#39;lookup&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1841878719-17">(</span><span class="p" data-group-id="1841878719-17">)</span><span class="p" data-group-id="1841878719-16">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="4953964619-18">(</span><span class="nf">request</span><span class="p" data-group-id="4953964619-19">(</span><span class="p" data-group-id="4953964619-19">)</span><span class="p">,</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="4953964619-20">(</span><span class="p" data-group-id="4953964619-20">)</span><span class="p" data-group-id="4953964619-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4953964619-21">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="4953964619-22">(</span><span class="p" data-group-id="4953964619-22">)</span><span class="p" data-group-id="4953964619-21">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="1841878719-18">(</span><span class="nf">request</span><span class="p" data-group-id="1841878719-19">(</span><span class="p" data-group-id="1841878719-19">)</span><span class="p">,</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="1841878719-20">(</span><span class="p" data-group-id="1841878719-20">)</span><span class="p" data-group-id="1841878719-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1841878719-21">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1841878719-22">(</span><span class="p" data-group-id="1841878719-22">)</span><span class="p" data-group-id="1841878719-21">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Each <code class="inline">-spec</code> contract is to be a subtype of the respective <code class="inline">-callback</code> contract.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/seq_prog.xhtml
│ │ │ │ @@ -41,293 +41,293 @@
│ │ │ │  </span><span class="mi">7</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">2&gt; </span></code></pre><p>As shown, the Erlang shell numbers the lines that can be entered, (as 1&gt; 2&gt;) and
│ │ │ │  that it correctly says that 2 + 5 is 7. If you make writing mistakes in the
│ │ │ │  shell, you can delete with the backspace key, as in most shells. There are many
│ │ │ │  more editing commands in the shell (see
│ │ │ │  <a href="../../../lib/../erts/doc/html/tty.xhtml">tty - A command line interface</a> in ERTS User's Guide).</p><p>(Notice that many line numbers given by the shell in the following examples are
│ │ │ │  out of sequence. This is because this tutorial was written and code-tested in
│ │ │ │ -separate sessions).</p><p>Here is a bit more complex calculation:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="5132161967-1">(</span><span class="mi">42</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">77</span><span class="p" data-group-id="5132161967-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">66</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │ +separate sessions).</p><p>Here is a bit more complex calculation:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="6352724346-1">(</span><span class="mi">42</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">77</span><span class="p" data-group-id="6352724346-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">66</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">2618.0</span></code></pre><p>Notice the use of brackets, the multiplication operator <code class="inline">*</code>, and the division
│ │ │ │  operator <code class="inline">/</code>, as in normal arithmetic (see
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml">Expressions</a>).</p><p>Press Control-C to shut down the Erlang system and the Erlang shell.</p><p>The following output is shown:</p><pre><code class="text">BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
│ │ │ │         (v)ersion (k)ill (D)b-tables (d)istribution
│ │ │ │  a
│ │ │ │ -$</code></pre><p>Type <code class="inline">a</code> to leave the Erlang system.</p><p>Another way to shut down the Erlang system is by entering <a href="../../../lib/../erts/doc/html/erlang.html#halt/0"><code class="inline">halt/0</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">halt</span><span class="p" data-group-id="1883708419-1">(</span><span class="p" data-group-id="1883708419-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +$</code></pre><p>Type <code class="inline">a</code> to leave the Erlang system.</p><p>Another way to shut down the Erlang system is by entering <a href="../../../lib/../erts/doc/html/erlang.html#halt/0"><code class="inline">halt/0</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">halt</span><span class="p" data-group-id="7078773023-1">(</span><span class="p" data-group-id="7078773023-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="err">$</span></code></pre><h2 id="modules-and-functions" class="section-heading">
│ │ │ │    <a href="#modules-and-functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Modules and Functions</span>
│ │ │ │  </h2>
│ │ │ │  <p>A programming language is not much use if you only can run code from the shell.
│ │ │ │  So here is a small Erlang program. Enter it into a file named <code class="inline">tut.erl</code> using a
│ │ │ │  suitable text editor. The file name <code class="inline">tut.erl</code> is important, and also that it is
│ │ │ │  in the same directory as the one where you started <code class="inline">erl</code>). If you are lucky your
│ │ │ │  editor has an Erlang mode that makes it easier for you to enter and format your
│ │ │ │  code nicely (see <a href="../../../lib/tools/doc/html/erlang_mode_chapter.xhtml">The Erlang mode for Emacs</a>
│ │ │ │  in Tools User's Guide), but you can manage perfectly well without. Here is the
│ │ │ │ -code to enter:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4256973172-1">(</span><span class="ss">tut</span><span class="p" data-group-id="4256973172-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4256973172-2">(</span><span class="p" data-group-id="4256973172-3">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4256973172-3">]</span><span class="p" data-group-id="4256973172-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +code to enter:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6289221017-1">(</span><span class="ss">tut</span><span class="p" data-group-id="6289221017-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6289221017-2">(</span><span class="p" data-group-id="6289221017-3">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6289221017-3">]</span><span class="p" data-group-id="6289221017-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="4256973172-4">(</span><span class="n">X</span><span class="p" data-group-id="4256973172-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="6289221017-4">(</span><span class="n">X</span><span class="p" data-group-id="6289221017-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="p">.</span></code></pre><p>It is not hard to guess that this program doubles the value of numbers. The
│ │ │ │  first two lines of the code are described later. Let us compile the program.
│ │ │ │ -This can be done in an Erlang shell as follows, where <code class="inline">c</code> means compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">c</span><span class="p" data-group-id="2542381992-1">(</span><span class="ss">tut</span><span class="p" data-group-id="2542381992-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2542381992-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut</span><span class="p" data-group-id="2542381992-2">}</span></code></pre><p>The <code class="inline">{ok,tut}</code> means that the compilation is OK. If it says <code class="inline">error</code> it means
│ │ │ │ +This can be done in an Erlang shell as follows, where <code class="inline">c</code> means compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">c</span><span class="p" data-group-id="6965720580-1">(</span><span class="ss">tut</span><span class="p" data-group-id="6965720580-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6965720580-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut</span><span class="p" data-group-id="6965720580-2">}</span></code></pre><p>The <code class="inline">{ok,tut}</code> means that the compilation is OK. If it says <code class="inline">error</code> it means
│ │ │ │  that there is some mistake in the text that you entered. Additional error
│ │ │ │  messages gives an idea to what is wrong so you can modify the text and then try
│ │ │ │ -to compile the program again.</p><p>Now run the program:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="3890546144-1">(</span><span class="mi">10</span><span class="p" data-group-id="3890546144-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +to compile the program again.</p><p>Now run the program:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="0807425906-1">(</span><span class="mi">10</span><span class="p" data-group-id="0807425906-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">20</span></code></pre><p>As expected, double of 10 is 20.</p><p>Now let us get back to the first two lines of the code. Erlang programs are
│ │ │ │  written in files. Each file contains an Erlang <em>module</em>. The first line of code
│ │ │ │ -in the module is the module name (see <a href="../../../lib/../system/doc/html/modules.xhtml">Modules</a>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2639985211-1">(</span><span class="ss">tut</span><span class="p" data-group-id="2639985211-1">)</span><span class="p">.</span></code></pre><p>Thus, the module is called <em>tut</em>. Notice the full stop <code class="inline">.</code> at the end of the
│ │ │ │ +in the module is the module name (see <a href="../../../lib/../system/doc/html/modules.xhtml">Modules</a>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7092579645-1">(</span><span class="ss">tut</span><span class="p" data-group-id="7092579645-1">)</span><span class="p">.</span></code></pre><p>Thus, the module is called <em>tut</em>. Notice the full stop <code class="inline">.</code> at the end of the
│ │ │ │  line. The files which are used to store the module must have the same name as
│ │ │ │  the module but with the extension <code class="inline">.erl</code>. In this case the file name is
│ │ │ │  <code class="inline">tut.erl</code>. When using a function in another module, the syntax
│ │ │ │  <code class="inline">module_name:function_name(arguments)</code> is used. So the following means call
│ │ │ │ -function <code class="inline">double</code> in module <code class="inline">tut</code> with argument <code class="inline">10</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="8005949219-1">(</span><span class="mi">10</span><span class="p" data-group-id="8005949219-1">)</span><span class="p">.</span></code></pre><p>The second line says that the module <code class="inline">tut</code> contains a function called <code class="inline">double</code>,
│ │ │ │ -which takes one argument (<code class="inline">X</code> in our example):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8326356878-1">(</span><span class="p" data-group-id="8326356878-2">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8326356878-2">]</span><span class="p" data-group-id="8326356878-1">)</span><span class="p">.</span></code></pre><p>The second line also says that this function can be called from outside the
│ │ │ │ +function <code class="inline">double</code> in module <code class="inline">tut</code> with argument <code class="inline">10</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="4746730913-1">(</span><span class="mi">10</span><span class="p" data-group-id="4746730913-1">)</span><span class="p">.</span></code></pre><p>The second line says that the module <code class="inline">tut</code> contains a function called <code class="inline">double</code>,
│ │ │ │ +which takes one argument (<code class="inline">X</code> in our example):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4253541680-1">(</span><span class="p" data-group-id="4253541680-2">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4253541680-2">]</span><span class="p" data-group-id="4253541680-1">)</span><span class="p">.</span></code></pre><p>The second line also says that this function can be called from outside the
│ │ │ │  module <code class="inline">tut</code>. More about this later. Again, notice the <code class="inline">.</code> at the end of the
│ │ │ │  line.</p><p>Now for a more complicated example, the factorial of a number. For example, the
│ │ │ │ -factorial of 4 is 4 <em> 3 </em> 2 * 1, which equals 24.</p><p>Enter the following code in a file named <code class="inline">tut1.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5839601572-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="5839601572-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5839601572-2">(</span><span class="p" data-group-id="5839601572-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5839601572-3">]</span><span class="p" data-group-id="5839601572-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +factorial of 4 is 4 <em> 3 </em> 2 * 1, which equals 24.</p><p>Enter the following code in a file named <code class="inline">tut1.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7355282388-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="7355282388-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7355282388-2">(</span><span class="p" data-group-id="7355282388-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7355282388-3">]</span><span class="p" data-group-id="7355282388-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="5839601572-4">(</span><span class="mi">1</span><span class="p" data-group-id="5839601572-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="7355282388-4">(</span><span class="mi">1</span><span class="p" data-group-id="7355282388-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="5839601572-5">(</span><span class="n">N</span><span class="p" data-group-id="5839601572-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="5839601572-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5839601572-6">)</span><span class="p">.</span></code></pre><p>So this is a module, called <code class="inline">tut1</code> that contains a function called <code class="inline">fac&gt;</code>, which
│ │ │ │ -takes one argument, <code class="inline">N</code>.</p><p>The first part says that the factorial of 1 is 1.:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="2872909816-1">(</span><span class="mi">1</span><span class="p" data-group-id="2872909816-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="7355282388-5">(</span><span class="n">N</span><span class="p" data-group-id="7355282388-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="7355282388-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7355282388-6">)</span><span class="p">.</span></code></pre><p>So this is a module, called <code class="inline">tut1</code> that contains a function called <code class="inline">fac&gt;</code>, which
│ │ │ │ +takes one argument, <code class="inline">N</code>.</p><p>The first part says that the factorial of 1 is 1.:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="5490399764-1">(</span><span class="mi">1</span><span class="p" data-group-id="5490399764-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">;</span></code></pre><p>Notice that this part ends with a semicolon <code class="inline">;</code> that indicates that there is
│ │ │ │  more of the function <code class="inline">fac&gt;</code> to come.</p><p>The second part says that the factorial of N is N multiplied by the factorial of
│ │ │ │ -N - 1:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="0414412589-1">(</span><span class="n">N</span><span class="p" data-group-id="0414412589-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="0414412589-2">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0414412589-2">)</span><span class="p">.</span></code></pre><p>Notice that this part ends with a <code class="inline">.</code> saying that there are no more parts of
│ │ │ │ -this function.</p><p>Compile the file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="3718738089-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="3718738089-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3718738089-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="3718738089-2">}</span></code></pre><p>And now calculate the factorial of 4.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">fac</span><span class="p" data-group-id="3911663675-1">(</span><span class="mi">4</span><span class="p" data-group-id="3911663675-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +N - 1:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="5007147924-1">(</span><span class="n">N</span><span class="p" data-group-id="5007147924-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="5007147924-2">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5007147924-2">)</span><span class="p">.</span></code></pre><p>Notice that this part ends with a <code class="inline">.</code> saying that there are no more parts of
│ │ │ │ +this function.</p><p>Compile the file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="6168158476-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="6168158476-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6168158476-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="6168158476-2">}</span></code></pre><p>And now calculate the factorial of 4.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">fac</span><span class="p" data-group-id="2192316359-1">(</span><span class="mi">4</span><span class="p" data-group-id="2192316359-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">24</span></code></pre><p>Here the function <code class="inline">fac&gt;</code> in module <code class="inline">tut1</code> is called with argument <code class="inline">4</code>.</p><p>A function can have many arguments. Let us expand the module <code class="inline">tut1</code> with the
│ │ │ │ -function to multiply two numbers:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6070605121-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="6070605121-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6070605121-2">(</span><span class="p" data-group-id="6070605121-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">mult</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6070605121-3">]</span><span class="p" data-group-id="6070605121-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +function to multiply two numbers:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4856628856-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="4856628856-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4856628856-2">(</span><span class="p" data-group-id="4856628856-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">mult</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4856628856-3">]</span><span class="p" data-group-id="4856628856-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="6070605121-4">(</span><span class="mi">1</span><span class="p" data-group-id="6070605121-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="4856628856-4">(</span><span class="mi">1</span><span class="p" data-group-id="4856628856-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="6070605121-5">(</span><span class="n">N</span><span class="p" data-group-id="6070605121-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="6070605121-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6070605121-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="4856628856-5">(</span><span class="n">N</span><span class="p" data-group-id="4856628856-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="4856628856-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4856628856-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">mult</span><span class="p" data-group-id="6070605121-7">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6070605121-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">mult</span><span class="p" data-group-id="4856628856-7">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4856628856-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>Notice that it is also required to expand the <code class="inline">-export</code> line with the
│ │ │ │ -information that there is another function <code class="inline">mult</code> with two arguments.</p><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nf">c</span><span class="p" data-group-id="2202216133-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="2202216133-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2202216133-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="2202216133-2">}</span></code></pre><p>Try out the new function <code class="inline">mult</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">8&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">mult</span><span class="p" data-group-id="4043683689-1">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4043683689-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +information that there is another function <code class="inline">mult</code> with two arguments.</p><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nf">c</span><span class="p" data-group-id="0319371345-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="0319371345-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0319371345-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="0319371345-2">}</span></code></pre><p>Try out the new function <code class="inline">mult</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">8&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">mult</span><span class="p" data-group-id="0436701795-1">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0436701795-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">12</span></code></pre><p>In this example the numbers are integers and the arguments in the functions in
│ │ │ │  the code <code class="inline">N</code>, <code class="inline">X</code>, and <code class="inline">Y</code> are called variables. Variables must start with a
│ │ │ │  capital letter (see <a href="../../../lib/../system/doc/html/expressions.xhtml">Variables</a>). Examples of
│ │ │ │  variables are <code class="inline">Number</code>, <code class="inline">ShoeSize</code>, and <code class="inline">Age</code>.</p><h2 id="atoms" class="section-heading">
│ │ │ │    <a href="#atoms" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Atoms</span>
│ │ │ │  </h2>
│ │ │ │  <p>Atom is another data type in Erlang. Atoms start with a small letter (see
│ │ │ │  <a href="../../../lib/../system/doc/html/data_types.xhtml">Atom</a>), for example, <code class="inline">charles</code>, <code class="inline">centimeter</code>, and
│ │ │ │  <code class="inline">inch</code>. Atoms are simply names, nothing else. They are not like variables, which
│ │ │ │  can have a value.</p><p>Enter the next program in a file named <code class="inline">tut2.erl</code>). It can be useful for
│ │ │ │ -converting from inches to centimeters and conversely:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3137320768-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="3137320768-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3137320768-2">(</span><span class="p" data-group-id="3137320768-3">[</span><span class="ss">convert</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3137320768-3">]</span><span class="p" data-group-id="3137320768-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +converting from inches to centimeters and conversely:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8789447149-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="8789447149-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8789447149-2">(</span><span class="p" data-group-id="8789447149-3">[</span><span class="ss">convert</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8789447149-3">]</span><span class="p" data-group-id="8789447149-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert</span><span class="p" data-group-id="3137320768-4">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="3137320768-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert</span><span class="p" data-group-id="8789447149-4">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="8789447149-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">M</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert</span><span class="p" data-group-id="3137320768-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="3137320768-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p">.</span></code></pre><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nf">c</span><span class="p" data-group-id="1495197787-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="1495197787-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1495197787-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut2</span><span class="p" data-group-id="1495197787-2">}</span></code></pre><p>Test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">10&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="1664888750-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="1664888750-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">convert</span><span class="p" data-group-id="8789447149-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="8789447149-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p">.</span></code></pre><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nf">c</span><span class="p" data-group-id="5049869058-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="5049869058-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5049869058-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut2</span><span class="p" data-group-id="5049869058-2">}</span></code></pre><p>Test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">10&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="3585027060-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="3585027060-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">1.1811023622047243</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">11&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="1664888750-2">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="1664888750-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">11&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="3585027060-2">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="3585027060-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">17.78</span></code></pre><p>Notice the introduction of decimals (floating point numbers) without any
│ │ │ │  explanation. Hopefully you can cope with that.</p><p>Let us see what happens if something other than <code class="inline">centimeter</code> or <code class="inline">inch</code> is
│ │ │ │ -entered in the <code class="inline">convert</code> function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">12&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="1981496783-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">miles</span><span class="p" data-group-id="1981496783-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +entered in the <code class="inline">convert</code> function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">12&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="7344476971-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">miles</span><span class="p" data-group-id="7344476971-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no function clause matching tut2:convert(3,miles) (tut2.erl, line 4)</span></code></pre><p>The two parts of the <code class="inline">convert</code> function are called its clauses. As shown,
│ │ │ │  <code class="inline">miles</code> is not part of either of the clauses. The Erlang system cannot <em>match</em>
│ │ │ │  either of the clauses so an error message <code class="inline">function_clause</code> is returned. The
│ │ │ │  shell formats the error message nicely, but the error tuple is saved in the
│ │ │ │ -shell's history list and can be output by the shell command <code class="inline">v/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">13&gt; </span><span class="nf">v</span><span class="p" data-group-id="2014325912-1">(</span><span class="mi">12</span><span class="p" data-group-id="2014325912-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2014325912-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="2014325912-3">{</span><span class="ss">function_clause</span><span class="p">,</span><span class="p" data-group-id="2014325912-4">[</span><span class="p" data-group-id="2014325912-5">{</span><span class="ss">tut2</span><span class="p">,</span><span class="ss">convert</span><span class="p">,</span><span class="w">
│ │ │ │ -                                </span><span class="p" data-group-id="2014325912-6">[</span><span class="mi">3</span><span class="p">,</span><span class="ss">miles</span><span class="p" data-group-id="2014325912-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                                </span><span class="p" data-group-id="2014325912-7">[</span><span class="p" data-group-id="2014325912-8">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;tut2.erl&quot;</span><span class="p" data-group-id="2014325912-8">}</span><span class="p">,</span><span class="p" data-group-id="2014325912-9">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="2014325912-9">}</span><span class="p" data-group-id="2014325912-7">]</span><span class="p" data-group-id="2014325912-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="p" data-group-id="2014325912-10">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="w">
│ │ │ │ -                                    </span><span class="p" data-group-id="2014325912-11">[</span><span class="p" data-group-id="2014325912-12">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="2014325912-12">}</span><span class="p">,</span><span class="p" data-group-id="2014325912-13">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="2014325912-13">}</span><span class="p" data-group-id="2014325912-11">]</span><span class="p" data-group-id="2014325912-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="p" data-group-id="2014325912-14">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="2014325912-15">[</span><span class="p" data-group-id="2014325912-16">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="2014325912-16">}</span><span class="p">,</span><span class="p" data-group-id="2014325912-17">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="2014325912-17">}</span><span class="p" data-group-id="2014325912-15">]</span><span class="p" data-group-id="2014325912-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="p" data-group-id="2014325912-18">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="2014325912-19">[</span><span class="p" data-group-id="2014325912-20">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="2014325912-20">}</span><span class="p">,</span><span class="p" data-group-id="2014325912-21">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="2014325912-21">}</span><span class="p" data-group-id="2014325912-19">]</span><span class="p" data-group-id="2014325912-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="p" data-group-id="2014325912-22">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ -                                 </span><span class="p" data-group-id="2014325912-23">[</span><span class="p" data-group-id="2014325912-24">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="2014325912-24">}</span><span class="p">,</span><span class="p" data-group-id="2014325912-25">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="2014325912-25">}</span><span class="p" data-group-id="2014325912-23">]</span><span class="p" data-group-id="2014325912-22">}</span><span class="p" data-group-id="2014325912-4">]</span><span class="p" data-group-id="2014325912-3">}</span><span class="p" data-group-id="2014325912-2">}</span></code></pre><h2 id="tuples" class="section-heading">
│ │ │ │ +shell's history list and can be output by the shell command <code class="inline">v/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">13&gt; </span><span class="nf">v</span><span class="p" data-group-id="0761949138-1">(</span><span class="mi">12</span><span class="p" data-group-id="0761949138-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0761949138-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="0761949138-3">{</span><span class="ss">function_clause</span><span class="p">,</span><span class="p" data-group-id="0761949138-4">[</span><span class="p" data-group-id="0761949138-5">{</span><span class="ss">tut2</span><span class="p">,</span><span class="ss">convert</span><span class="p">,</span><span class="w">
│ │ │ │ +                                </span><span class="p" data-group-id="0761949138-6">[</span><span class="mi">3</span><span class="p">,</span><span class="ss">miles</span><span class="p" data-group-id="0761949138-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                                </span><span class="p" data-group-id="0761949138-7">[</span><span class="p" data-group-id="0761949138-8">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;tut2.erl&quot;</span><span class="p" data-group-id="0761949138-8">}</span><span class="p">,</span><span class="p" data-group-id="0761949138-9">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0761949138-9">}</span><span class="p" data-group-id="0761949138-7">]</span><span class="p" data-group-id="0761949138-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="p" data-group-id="0761949138-10">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="w">
│ │ │ │ +                                    </span><span class="p" data-group-id="0761949138-11">[</span><span class="p" data-group-id="0761949138-12">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="0761949138-12">}</span><span class="p">,</span><span class="p" data-group-id="0761949138-13">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="0761949138-13">}</span><span class="p" data-group-id="0761949138-11">]</span><span class="p" data-group-id="0761949138-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="p" data-group-id="0761949138-14">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="0761949138-15">[</span><span class="p" data-group-id="0761949138-16">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="0761949138-16">}</span><span class="p">,</span><span class="p" data-group-id="0761949138-17">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="0761949138-17">}</span><span class="p" data-group-id="0761949138-15">]</span><span class="p" data-group-id="0761949138-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="p" data-group-id="0761949138-18">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="0761949138-19">[</span><span class="p" data-group-id="0761949138-20">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="0761949138-20">}</span><span class="p">,</span><span class="p" data-group-id="0761949138-21">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="0761949138-21">}</span><span class="p" data-group-id="0761949138-19">]</span><span class="p" data-group-id="0761949138-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="p" data-group-id="0761949138-22">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ │ +                                 </span><span class="p" data-group-id="0761949138-23">[</span><span class="p" data-group-id="0761949138-24">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="0761949138-24">}</span><span class="p">,</span><span class="p" data-group-id="0761949138-25">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="0761949138-25">}</span><span class="p" data-group-id="0761949138-23">]</span><span class="p" data-group-id="0761949138-22">}</span><span class="p" data-group-id="0761949138-4">]</span><span class="p" data-group-id="0761949138-3">}</span><span class="p" data-group-id="0761949138-2">}</span></code></pre><h2 id="tuples" class="section-heading">
│ │ │ │    <a href="#tuples" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Tuples</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Now the <code class="inline">tut2</code> program is hardly good programming style. Consider:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="2560093207-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="2560093207-1">)</span><span class="p">.</span></code></pre><p>Does this mean that 3 is in inches? Or does it mean that 3 is in centimeters and
│ │ │ │ +<p>Now the <code class="inline">tut2</code> program is hardly good programming style. Consider:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="9423637541-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="9423637541-1">)</span><span class="p">.</span></code></pre><p>Does this mean that 3 is in inches? Or does it mean that 3 is in centimeters and
│ │ │ │  is to be converted to inches? Erlang has a way to group things together to make
│ │ │ │  things more understandable. These are called <em>tuples</em> and are surrounded by
│ │ │ │  curly brackets, <code class="inline">{</code> and <code class="inline">}</code>.</p><p>So, <code class="inline">{inch,3}</code> denotes 3 inches and <code class="inline">{centimeter,5}</code> denotes 5 centimeters. Now
│ │ │ │  let us write a new program that converts centimeters to inches and conversely.
│ │ │ │ -Enter the following code in a file called <code class="inline">tut3.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8514440927-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="8514440927-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8514440927-2">(</span><span class="p" data-group-id="8514440927-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8514440927-3">]</span><span class="p" data-group-id="8514440927-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +Enter the following code in a file called <code class="inline">tut3.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5661496599-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="5661496599-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5661496599-2">(</span><span class="p" data-group-id="5661496599-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5661496599-3">]</span><span class="p" data-group-id="5661496599-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="8514440927-4">(</span><span class="p" data-group-id="8514440927-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8514440927-5">}</span><span class="p" data-group-id="8514440927-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8514440927-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="8514440927-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="8514440927-7">(</span><span class="p" data-group-id="8514440927-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8514440927-8">}</span><span class="p" data-group-id="8514440927-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8514440927-9">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="8514440927-9">}</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">14&gt; </span><span class="nf">c</span><span class="p" data-group-id="9347407832-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="9347407832-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9347407832-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut3</span><span class="p" data-group-id="9347407832-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">15&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9347407832-3">(</span><span class="p" data-group-id="9347407832-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="9347407832-4">}</span><span class="p" data-group-id="9347407832-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9347407832-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">12.7</span><span class="p" data-group-id="9347407832-5">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">16&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9347407832-6">(</span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="9347407832-7">(</span><span class="p" data-group-id="9347407832-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="9347407832-8">}</span><span class="p" data-group-id="9347407832-7">)</span><span class="p" data-group-id="9347407832-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9347407832-9">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">5.0</span><span class="p" data-group-id="9347407832-9">}</span></code></pre><p>Notice on line 16 that 5 inches is converted to centimeters and back again and
│ │ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="5661496599-4">(</span><span class="p" data-group-id="5661496599-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5661496599-5">}</span><span class="p" data-group-id="5661496599-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5661496599-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="5661496599-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="5661496599-7">(</span><span class="p" data-group-id="5661496599-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5661496599-8">}</span><span class="p" data-group-id="5661496599-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5661496599-9">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="5661496599-9">}</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">14&gt; </span><span class="nf">c</span><span class="p" data-group-id="8081674341-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="8081674341-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8081674341-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut3</span><span class="p" data-group-id="8081674341-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">15&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="8081674341-3">(</span><span class="p" data-group-id="8081674341-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="8081674341-4">}</span><span class="p" data-group-id="8081674341-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8081674341-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">12.7</span><span class="p" data-group-id="8081674341-5">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">16&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="8081674341-6">(</span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="8081674341-7">(</span><span class="p" data-group-id="8081674341-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="8081674341-8">}</span><span class="p" data-group-id="8081674341-7">)</span><span class="p" data-group-id="8081674341-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8081674341-9">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">5.0</span><span class="p" data-group-id="8081674341-9">}</span></code></pre><p>Notice on line 16 that 5 inches is converted to centimeters and back again and
│ │ │ │  reassuringly get back to the original value. That is, the argument to a function
│ │ │ │  can be the result of another function. Consider how line 16 (above) works. The
│ │ │ │  argument given to the function <code class="inline">{inch,5}</code> is first matched against the first
│ │ │ │  head clause of <code class="inline">convert_length</code>, that is, <code class="inline">convert_length({centimeter,X})</code>. It
│ │ │ │  can be seen that <code class="inline">{centimeter,X}</code> does not match <code class="inline">{inch,5}</code> (the head is the bit
│ │ │ │  before the <code class="inline">-&gt;</code>). This having failed, let us try the head of the next clause
│ │ │ │  that is, <code class="inline">convert_length({inch,Y})</code>. This matches, and <code class="inline">Y</code> gets the value 5.</p><p>Tuples can have more than two parts, in fact as many parts as you want, and
│ │ │ │  contain any valid Erlang <em>term</em>. For example, to represent the temperature of
│ │ │ │ -various cities of the world:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8363549046-1">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8363549046-2">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8363549046-2">}</span><span class="p" data-group-id="8363549046-1">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8363549046-3">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8363549046-4">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8363549046-4">}</span><span class="p" data-group-id="8363549046-3">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8363549046-5">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8363549046-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8363549046-6">}</span><span class="p" data-group-id="8363549046-5">}</span></code></pre><p>Tuples have a fixed number of items in them. Each item in a tuple is called an
│ │ │ │ +various cities of the world:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3502422372-1">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3502422372-2">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="3502422372-2">}</span><span class="p" data-group-id="3502422372-1">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3502422372-3">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3502422372-4">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="3502422372-4">}</span><span class="p" data-group-id="3502422372-3">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3502422372-5">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3502422372-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="3502422372-6">}</span><span class="p" data-group-id="3502422372-5">}</span></code></pre><p>Tuples have a fixed number of items in them. Each item in a tuple is called an
│ │ │ │  <em>element</em>. In the tuple <code class="inline">{moscow,{c,-10}}</code>, element 1 is <code class="inline">moscow</code> and element 2
│ │ │ │  is <code class="inline">{c,-10}</code>. Here <code class="inline">c</code> represents Celsius and <code class="inline">f</code> Fahrenheit.</p><h2 id="lists" class="section-heading">
│ │ │ │    <a href="#lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Lists</span>
│ │ │ │  </h2>
│ │ │ │  <p>Whereas tuples group things together, it is also needed to represent lists of
│ │ │ │  things. Lists in Erlang are surrounded by square brackets, <code class="inline">[</code> and <code class="inline">]</code>. For
│ │ │ │ -example, a list of the temperatures of various cities in the world can be:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4738853490-1">[</span><span class="p" data-group-id="4738853490-2">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4738853490-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4738853490-3">}</span><span class="p" data-group-id="4738853490-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4738853490-4">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4738853490-5">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4738853490-5">}</span><span class="p" data-group-id="4738853490-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4738853490-6">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4738853490-7">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4738853490-7">}</span><span class="p" data-group-id="4738853490-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4738853490-8">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4738853490-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4738853490-9">}</span><span class="p" data-group-id="4738853490-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4738853490-10">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4738853490-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4738853490-11">}</span><span class="p" data-group-id="4738853490-10">}</span><span class="p" data-group-id="4738853490-1">]</span></code></pre><p>Notice that this list was so long that it did not fit on one line. This does not
│ │ │ │ +example, a list of the temperatures of various cities in the world can be:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2866876319-1">[</span><span class="p" data-group-id="2866876319-2">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2866876319-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2866876319-3">}</span><span class="p" data-group-id="2866876319-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2866876319-4">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2866876319-5">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="2866876319-5">}</span><span class="p" data-group-id="2866876319-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2866876319-6">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2866876319-7">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2866876319-7">}</span><span class="p" data-group-id="2866876319-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2866876319-8">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2866876319-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="2866876319-9">}</span><span class="p" data-group-id="2866876319-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2866876319-10">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2866876319-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="2866876319-11">}</span><span class="p" data-group-id="2866876319-10">}</span><span class="p" data-group-id="2866876319-1">]</span></code></pre><p>Notice that this list was so long that it did not fit on one line. This does not
│ │ │ │  matter, Erlang allows line breaks at all &quot;sensible places&quot; but not, for example,
│ │ │ │  in the middle of atoms, integers, and others.</p><p>A useful way of looking at parts of lists, is by using <code class="inline">|</code>. This is best
│ │ │ │ -explained by an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">17&gt; </span><span class="p" data-group-id="0598022060-1">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="n">TheRest</span><span class="p" data-group-id="0598022060-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0598022060-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0598022060-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0598022060-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0598022060-3">]</span><span class="w">
│ │ │ │ +explained by an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">17&gt; </span><span class="p" data-group-id="9719992140-1">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="n">TheRest</span><span class="p" data-group-id="9719992140-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9719992140-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9719992140-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9719992140-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9719992140-3">]</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">18&gt; </span><span class="n">First</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">19&gt; </span><span class="n">TheRest</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0598022060-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0598022060-4">]</span></code></pre><p>To separate the first elements of the list from the rest of the list, <code class="inline">|</code> is
│ │ │ │ -used. <code class="inline">First</code> has got value <code class="inline">1</code> and <code class="inline">TheRest</code> has got the value <code class="inline">[2,3,4,5]</code>.</p><p>Another example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">20&gt; </span><span class="p" data-group-id="5458167043-1">[</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">R</span><span class="p" data-group-id="5458167043-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5458167043-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="5458167043-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5458167043-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="5458167043-3">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9719992140-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9719992140-4">]</span></code></pre><p>To separate the first elements of the list from the rest of the list, <code class="inline">|</code> is
│ │ │ │ +used. <code class="inline">First</code> has got value <code class="inline">1</code> and <code class="inline">TheRest</code> has got the value <code class="inline">[2,3,4,5]</code>.</p><p>Another example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">20&gt; </span><span class="p" data-group-id="7244068102-1">[</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">R</span><span class="p" data-group-id="7244068102-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7244068102-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7244068102-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7244068102-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7244068102-3">]</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">21&gt; </span><span class="n">E1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">22&gt; </span><span class="n">E2</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">2</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">23&gt; </span><span class="n">R</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5458167043-4">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="5458167043-4">]</span></code></pre><p>Here you see the use of <code class="inline">|</code> to get the first two elements from the list. If you
│ │ │ │ +</span><span class="p" data-group-id="7244068102-4">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7244068102-4">]</span></code></pre><p>Here you see the use of <code class="inline">|</code> to get the first two elements from the list. If you
│ │ │ │  try to get more elements from the list than there are elements in the list, an
│ │ │ │  error is returned. Notice also the special case of the list with no elements,
│ │ │ │ -<code class="inline">[]</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">24&gt; </span><span class="p" data-group-id="9593036984-1">[</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="9593036984-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9593036984-2">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9593036984-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9593036984-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9593036984-3">]</span><span class="w">
│ │ │ │ +<code class="inline">[]</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">24&gt; </span><span class="p" data-group-id="4668808664-1">[</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="4668808664-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4668808664-2">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4668808664-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4668808664-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4668808664-3">]</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">25&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">26&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">2</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">27&gt; </span><span class="n">C</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9593036984-4">[</span><span class="p" data-group-id="9593036984-4">]</span></code></pre><p>In the previous examples, new variable names are used, instead of reusing the
│ │ │ │ +</span><span class="p" data-group-id="4668808664-4">[</span><span class="p" data-group-id="4668808664-4">]</span></code></pre><p>In the previous examples, new variable names are used, instead of reusing the
│ │ │ │  old ones: <code class="inline">First</code>, <code class="inline">TheRest</code>, <code class="inline">E1</code>, <code class="inline">E2</code>, <code class="inline">R</code>, <code class="inline">A</code>, <code class="inline">B</code>, and <code class="inline">C</code>. The reason for
│ │ │ │  this is that a variable can only be given a value once in its context (scope).
│ │ │ │  More about this later.</p><p>The following example shows how to find the length of a list. Enter the
│ │ │ │ -following code in a file named <code class="inline">tut4.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5763659382-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="5763659382-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +following code in a file named <code class="inline">tut4.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3099541599-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="3099541599-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5763659382-2">(</span><span class="p" data-group-id="5763659382-3">[</span><span class="ss">list_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5763659382-3">]</span><span class="p" data-group-id="5763659382-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3099541599-2">(</span><span class="p" data-group-id="3099541599-3">[</span><span class="ss">list_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3099541599-3">]</span><span class="p" data-group-id="3099541599-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">list_length</span><span class="p" data-group-id="5763659382-4">(</span><span class="p" data-group-id="5763659382-5">[</span><span class="p" data-group-id="5763659382-5">]</span><span class="p" data-group-id="5763659382-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">list_length</span><span class="p" data-group-id="3099541599-4">(</span><span class="p" data-group-id="3099541599-5">[</span><span class="p" data-group-id="3099541599-5">]</span><span class="p" data-group-id="3099541599-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">list_length</span><span class="p" data-group-id="5763659382-6">(</span><span class="p" data-group-id="5763659382-7">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="5763659382-7">]</span><span class="p" data-group-id="5763659382-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="5763659382-8">(</span><span class="n">Rest</span><span class="p" data-group-id="5763659382-8">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">28&gt; </span><span class="nf">c</span><span class="p" data-group-id="7802360688-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="7802360688-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7802360688-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut4</span><span class="p" data-group-id="7802360688-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">29&gt; </span><span class="nc">tut4</span><span class="p">:</span><span class="nf">list_length</span><span class="p" data-group-id="7802360688-3">(</span><span class="p" data-group-id="7802360688-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7802360688-4">]</span><span class="p" data-group-id="7802360688-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mi">7</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="7159495187-1">(</span><span class="p" data-group-id="7159495187-2">[</span><span class="p" data-group-id="7159495187-2">]</span><span class="p" data-group-id="7159495187-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="mi">0</span><span class="p">;</span></code></pre><p>The length of an empty list is obviously 0.</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="2844521708-1">(</span><span class="p" data-group-id="2844521708-2">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2844521708-2">]</span><span class="p" data-group-id="2844521708-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="2844521708-3">(</span><span class="n">Rest</span><span class="p" data-group-id="2844521708-3">)</span><span class="p">.</span></code></pre><p>The length of a list with the first element <code class="inline">First</code> and the remaining elements
│ │ │ │ +</span><span class="nf">list_length</span><span class="p" data-group-id="3099541599-6">(</span><span class="p" data-group-id="3099541599-7">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3099541599-7">]</span><span class="p" data-group-id="3099541599-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="3099541599-8">(</span><span class="n">Rest</span><span class="p" data-group-id="3099541599-8">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">28&gt; </span><span class="nf">c</span><span class="p" data-group-id="1113457565-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="1113457565-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1113457565-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut4</span><span class="p" data-group-id="1113457565-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">29&gt; </span><span class="nc">tut4</span><span class="p">:</span><span class="nf">list_length</span><span class="p" data-group-id="1113457565-3">(</span><span class="p" data-group-id="1113457565-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="1113457565-4">]</span><span class="p" data-group-id="1113457565-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="mi">7</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="3756676244-1">(</span><span class="p" data-group-id="3756676244-2">[</span><span class="p" data-group-id="3756676244-2">]</span><span class="p" data-group-id="3756676244-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="mi">0</span><span class="p">;</span></code></pre><p>The length of an empty list is obviously 0.</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="3934613382-1">(</span><span class="p" data-group-id="3934613382-2">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3934613382-2">]</span><span class="p" data-group-id="3934613382-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="3934613382-3">(</span><span class="n">Rest</span><span class="p" data-group-id="3934613382-3">)</span><span class="p">.</span></code></pre><p>The length of a list with the first element <code class="inline">First</code> and the remaining elements
│ │ │ │  <code class="inline">Rest</code> is 1 + the length of <code class="inline">Rest</code>.</p><p>(Advanced readers only: This is not tail recursive, there is a better way to
│ │ │ │  write this function.)</p><p>In general, tuples are used where &quot;records&quot; or &quot;structs&quot; are used in other
│ │ │ │  languages. Also, lists are used when representing things with varying sizes,
│ │ │ │  that is, where linked lists are used in other languages.</p><p>Erlang does not have a string data type. Instead, strings can be represented by
│ │ │ │  lists of Unicode characters. This implies for example that the list <code class="inline">[97,98,99]</code>
│ │ │ │  is equivalent to <code class="inline">&quot;abc&quot;</code>. The Erlang shell is &quot;clever&quot; and guesses what list you
│ │ │ │ -mean and outputs it in what it thinks is the most appropriate form, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">30&gt; </span><span class="p" data-group-id="7669721238-1">[</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="7669721238-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +mean and outputs it in what it thinks is the most appropriate form, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">30&gt; </span><span class="p" data-group-id="7881097834-1">[</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="7881097834-1">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;abc&quot;</span></code></pre><h2 id="maps" class="section-heading">
│ │ │ │    <a href="#maps" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Maps</span>
│ │ │ │  </h2>
│ │ │ │  <p>Maps are a set of key to value associations. These associations are encapsulated
│ │ │ │ -with <code class="inline">#{</code> and <code class="inline">}</code>. To create an association from <code class="inline">&quot;key&quot;</code> to value <code class="inline">42</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="9641873365-1">#{</span><span class="w"> </span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p" data-group-id="9641873365-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9641873365-2">#{</span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="9641873365-2">}</span></code></pre><p>Let us jump straight into the deep end with an example using some interesting
│ │ │ │ +with <code class="inline">#{</code> and <code class="inline">}</code>. To create an association from <code class="inline">&quot;key&quot;</code> to value <code class="inline">42</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="5351857885-1">#{</span><span class="w"> </span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p" data-group-id="5351857885-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5351857885-2">#{</span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="5351857885-2">}</span></code></pre><p>Let us jump straight into the deep end with an example using some interesting
│ │ │ │  features.</p><p>The following example shows how to calculate alpha blending using maps to
│ │ │ │ -reference color and alpha channels. Enter the code in a file named <code class="inline">color.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3285202324-1">(</span><span class="ss">color</span><span class="p" data-group-id="3285202324-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +reference color and alpha channels. Enter the code in a file named <code class="inline">color.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7013028465-1">(</span><span class="ss">color</span><span class="p" data-group-id="7013028465-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3285202324-2">(</span><span class="p" data-group-id="3285202324-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="ss">blend</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3285202324-3">]</span><span class="p" data-group-id="3285202324-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7013028465-2">(</span><span class="p" data-group-id="7013028465-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="ss">blend</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7013028465-3">]</span><span class="p" data-group-id="7013028465-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3285202324-4">(</span><span class="nf">is_channel</span><span class="p" data-group-id="3285202324-5">(</span><span class="n">V</span><span class="p" data-group-id="3285202324-5">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3285202324-6">(</span><span class="nf">is_float</span><span class="p" data-group-id="3285202324-7">(</span><span class="n">V</span><span class="p" data-group-id="3285202324-7">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="3285202324-6">)</span><span class="p" data-group-id="3285202324-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="7013028465-4">(</span><span class="nf">is_channel</span><span class="p" data-group-id="7013028465-5">(</span><span class="n">V</span><span class="p" data-group-id="7013028465-5">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7013028465-6">(</span><span class="nf">is_float</span><span class="p" data-group-id="7013028465-7">(</span><span class="n">V</span><span class="p" data-group-id="7013028465-7">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="7013028465-6">)</span><span class="p" data-group-id="7013028465-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">new</span><span class="p" data-group-id="3285202324-8">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="3285202324-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="3285202324-9">(</span><span class="n">R</span><span class="p" data-group-id="3285202324-9">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="3285202324-10">(</span><span class="n">G</span><span class="p" data-group-id="3285202324-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="3285202324-11">(</span><span class="n">B</span><span class="p" data-group-id="3285202324-11">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="3285202324-12">(</span><span class="n">A</span><span class="p" data-group-id="3285202324-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3285202324-13">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="3285202324-13">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="3285202324-14">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="3285202324-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">blend</span><span class="p" data-group-id="3285202324-15">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="nf">alpha</span><span class="p" data-group-id="3285202324-16">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="3285202324-16">)</span><span class="p" data-group-id="3285202324-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="3285202324-17">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="3285202324-17">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="3285202324-18">#{</span><span class="w">
│ │ │ │ -        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="3285202324-19">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="3285202324-19">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="3285202324-20">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="3285202324-20">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="3285202324-21">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="3285202324-21">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">new</span><span class="p" data-group-id="7013028465-8">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="7013028465-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="7013028465-9">(</span><span class="n">R</span><span class="p" data-group-id="7013028465-9">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="7013028465-10">(</span><span class="n">G</span><span class="p" data-group-id="7013028465-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="7013028465-11">(</span><span class="n">B</span><span class="p" data-group-id="7013028465-11">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="7013028465-12">(</span><span class="n">A</span><span class="p" data-group-id="7013028465-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7013028465-13">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="7013028465-13">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="7013028465-14">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="7013028465-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">blend</span><span class="p" data-group-id="7013028465-15">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="nf">alpha</span><span class="p" data-group-id="7013028465-16">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="7013028465-16">)</span><span class="p" data-group-id="7013028465-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="7013028465-17">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="7013028465-17">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="7013028465-18">#{</span><span class="w">
│ │ │ │ +        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="7013028465-19">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="7013028465-19">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="7013028465-20">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="7013028465-20">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="7013028465-21">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="7013028465-21">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Alpha</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3285202324-18">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="3285202324-22">(</span><span class="p">_</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3285202324-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="3285202324-23">#{</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7013028465-18">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="7013028465-22">(</span><span class="p">_</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7013028465-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="7013028465-23">#{</span><span class="w">
│ │ │ │          </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3285202324-23">}</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7013028465-23">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alpha</span><span class="p" data-group-id="3285202324-24">(</span><span class="p" data-group-id="3285202324-25">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3285202324-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3285202324-26">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="3285202324-26">}</span><span class="p" data-group-id="3285202324-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="3285202324-27">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3285202324-27">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">alpha</span><span class="p" data-group-id="7013028465-24">(</span><span class="p" data-group-id="7013028465-25">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7013028465-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7013028465-26">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="7013028465-26">}</span><span class="p" data-group-id="7013028465-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="7013028465-27">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7013028465-27">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">red</span><span class="p" data-group-id="3285202324-28">(</span><span class="p" data-group-id="3285202324-29">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3285202324-29">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3285202324-30">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="3285202324-30">}</span><span class="p" data-group-id="3285202324-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="3285202324-31">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3285202324-31">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">green</span><span class="p" data-group-id="3285202324-32">(</span><span class="p" data-group-id="3285202324-33">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3285202324-33">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3285202324-34">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="3285202324-34">}</span><span class="p" data-group-id="3285202324-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="3285202324-35">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3285202324-35">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">blue</span><span class="p" data-group-id="3285202324-36">(</span><span class="p" data-group-id="3285202324-37">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3285202324-37">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3285202324-38">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="3285202324-38">}</span><span class="p" data-group-id="3285202324-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="3285202324-39">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3285202324-39">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">c</span><span class="p" data-group-id="4655198833-1">(</span><span class="ss">color</span><span class="p" data-group-id="4655198833-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4655198833-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">color</span><span class="p" data-group-id="4655198833-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">C1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="4655198833-3">(</span><span class="mf">0.3</span><span class="p">,</span><span class="mf">0.4</span><span class="p">,</span><span class="mf">0.5</span><span class="p">,</span><span class="mf">1.0</span><span class="p" data-group-id="4655198833-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4655198833-4">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="4655198833-4">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">C2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="4655198833-5">(</span><span class="mf">1.0</span><span class="p">,</span><span class="mf">0.8</span><span class="p">,</span><span class="mf">0.1</span><span class="p">,</span><span class="mf">0.3</span><span class="p" data-group-id="4655198833-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4655198833-6">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.1</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.8</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="4655198833-6">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="4655198833-7">(</span><span class="n">C1</span><span class="p">,</span><span class="n">C2</span><span class="p" data-group-id="4655198833-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4655198833-8">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="4655198833-8">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="4655198833-9">(</span><span class="n">C2</span><span class="p">,</span><span class="n">C1</span><span class="p" data-group-id="4655198833-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4655198833-10">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.38</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.52</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.51</span><span class="p" data-group-id="4655198833-10">}</span></code></pre><p>This example warrants some explanation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="7056109953-1">(</span><span class="nf">is_channel</span><span class="p" data-group-id="7056109953-2">(</span><span class="n">V</span><span class="p" data-group-id="7056109953-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7056109953-3">(</span><span class="nf">is_float</span><span class="p" data-group-id="7056109953-4">(</span><span class="n">V</span><span class="p" data-group-id="7056109953-4">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="7056109953-3">)</span><span class="p" data-group-id="7056109953-1">)</span><span class="p">.</span></code></pre><p>First a macro <code class="inline">is_channel</code> is defined to help with the guard tests. This is only
│ │ │ │ +</span><span class="nf">red</span><span class="p" data-group-id="7013028465-28">(</span><span class="p" data-group-id="7013028465-29">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7013028465-29">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7013028465-30">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="7013028465-30">}</span><span class="p" data-group-id="7013028465-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="7013028465-31">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7013028465-31">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">green</span><span class="p" data-group-id="7013028465-32">(</span><span class="p" data-group-id="7013028465-33">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7013028465-33">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7013028465-34">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="7013028465-34">}</span><span class="p" data-group-id="7013028465-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="7013028465-35">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7013028465-35">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">blue</span><span class="p" data-group-id="7013028465-36">(</span><span class="p" data-group-id="7013028465-37">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7013028465-37">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7013028465-38">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="7013028465-38">}</span><span class="p" data-group-id="7013028465-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="7013028465-39">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7013028465-39">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">c</span><span class="p" data-group-id="2393168525-1">(</span><span class="ss">color</span><span class="p" data-group-id="2393168525-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2393168525-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">color</span><span class="p" data-group-id="2393168525-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">C1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2393168525-3">(</span><span class="mf">0.3</span><span class="p">,</span><span class="mf">0.4</span><span class="p">,</span><span class="mf">0.5</span><span class="p">,</span><span class="mf">1.0</span><span class="p" data-group-id="2393168525-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2393168525-4">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="2393168525-4">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">C2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2393168525-5">(</span><span class="mf">1.0</span><span class="p">,</span><span class="mf">0.8</span><span class="p">,</span><span class="mf">0.1</span><span class="p">,</span><span class="mf">0.3</span><span class="p" data-group-id="2393168525-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2393168525-6">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.1</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.8</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="2393168525-6">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="2393168525-7">(</span><span class="n">C1</span><span class="p">,</span><span class="n">C2</span><span class="p" data-group-id="2393168525-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2393168525-8">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="2393168525-8">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="2393168525-9">(</span><span class="n">C2</span><span class="p">,</span><span class="n">C1</span><span class="p" data-group-id="2393168525-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2393168525-10">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.38</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.52</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.51</span><span class="p" data-group-id="2393168525-10">}</span></code></pre><p>This example warrants some explanation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8261972578-1">(</span><span class="nf">is_channel</span><span class="p" data-group-id="8261972578-2">(</span><span class="n">V</span><span class="p" data-group-id="8261972578-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8261972578-3">(</span><span class="nf">is_float</span><span class="p" data-group-id="8261972578-4">(</span><span class="n">V</span><span class="p" data-group-id="8261972578-4">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="8261972578-3">)</span><span class="p" data-group-id="8261972578-1">)</span><span class="p">.</span></code></pre><p>First a macro <code class="inline">is_channel</code> is defined to help with the guard tests. This is only
│ │ │ │  here for convenience and to reduce syntax cluttering. For more information about
│ │ │ │ -macros, see <a href="../../../lib/../system/doc/html/macros.xhtml">The Preprocessor</a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="7860419284-1">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="7860419284-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="7860419284-2">(</span><span class="n">R</span><span class="p" data-group-id="7860419284-2">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="7860419284-3">(</span><span class="n">G</span><span class="p" data-group-id="7860419284-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="7860419284-4">(</span><span class="n">B</span><span class="p" data-group-id="7860419284-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="7860419284-5">(</span><span class="n">A</span><span class="p" data-group-id="7860419284-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7860419284-6">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="7860419284-6">}</span><span class="p">.</span></code></pre><p>The function <code class="inline">new/4</code> creates a new map term and lets the keys <code class="inline">red</code>, <code class="inline">green</code>,
│ │ │ │ +macros, see <a href="../../../lib/../system/doc/html/macros.xhtml">The Preprocessor</a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="3140278171-1">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="3140278171-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="3140278171-2">(</span><span class="n">R</span><span class="p" data-group-id="3140278171-2">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="3140278171-3">(</span><span class="n">G</span><span class="p" data-group-id="3140278171-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="3140278171-4">(</span><span class="n">B</span><span class="p" data-group-id="3140278171-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="3140278171-5">(</span><span class="n">A</span><span class="p" data-group-id="3140278171-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3140278171-6">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="3140278171-6">}</span><span class="p">.</span></code></pre><p>The function <code class="inline">new/4</code> creates a new map term and lets the keys <code class="inline">red</code>, <code class="inline">green</code>,
│ │ │ │  <code class="inline">blue</code>, and <code class="inline">alpha</code> be associated with an initial value. In this case, only
│ │ │ │  float values between and including 0.0 and 1.0 are allowed, as ensured by the
│ │ │ │  <code class="inline">?is_channel/1</code> macro for each argument. Only the <code class="inline">=&gt;</code> operator is allowed when
│ │ │ │  creating a new map.</p><p>By calling <code class="inline">blend/2</code> on any color term created by <code class="inline">new/4</code>, the resulting color
│ │ │ │ -can be calculated as determined by the two map terms.</p><p>The first thing <code class="inline">blend/2</code> does is to calculate the resulting alpha channel:</p><pre><code class="makeup erlang" translate="no"><span class="nf">alpha</span><span class="p" data-group-id="3233245159-1">(</span><span class="p" data-group-id="3233245159-2">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3233245159-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3233245159-3">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="3233245159-3">}</span><span class="p" data-group-id="3233245159-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="3233245159-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3233245159-4">)</span><span class="p">.</span></code></pre><p>The value associated with key <code class="inline">alpha</code> is fetched for both arguments using the
│ │ │ │ +can be calculated as determined by the two map terms.</p><p>The first thing <code class="inline">blend/2</code> does is to calculate the resulting alpha channel:</p><pre><code class="makeup erlang" translate="no"><span class="nf">alpha</span><span class="p" data-group-id="7798032706-1">(</span><span class="p" data-group-id="7798032706-2">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7798032706-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7798032706-3">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="7798032706-3">}</span><span class="p" data-group-id="7798032706-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="7798032706-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7798032706-4">)</span><span class="p">.</span></code></pre><p>The value associated with key <code class="inline">alpha</code> is fetched for both arguments using the
│ │ │ │  <code class="inline">:=</code> operator. The other keys in the map are ignored, only the key <code class="inline">alpha</code> is
│ │ │ │ -required and checked for.</p><p>This is also the case for functions <code class="inline">red/2</code>, <code class="inline">blue/2</code>, and <code class="inline">green/2</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">red</span><span class="p" data-group-id="0994073014-1">(</span><span class="p" data-group-id="0994073014-2">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0994073014-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0994073014-3">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="0994073014-3">}</span><span class="p" data-group-id="0994073014-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="0994073014-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="0994073014-4">)</span><span class="p">.</span></code></pre><p>The difference here is that a check is made for two keys in each map argument.
│ │ │ │ -The other keys are ignored.</p><p>Finally, let us return the resulting color in <code class="inline">blend/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">blend</span><span class="p" data-group-id="1508671911-1">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="1508671911-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="1508671911-2">#{</span><span class="w">
│ │ │ │ -        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="1508671911-3">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="1508671911-3">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="1508671911-4">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="1508671911-4">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="1508671911-5">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="1508671911-5">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +required and checked for.</p><p>This is also the case for functions <code class="inline">red/2</code>, <code class="inline">blue/2</code>, and <code class="inline">green/2</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">red</span><span class="p" data-group-id="7915046178-1">(</span><span class="p" data-group-id="7915046178-2">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7915046178-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7915046178-3">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="7915046178-3">}</span><span class="p" data-group-id="7915046178-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="7915046178-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="7915046178-4">)</span><span class="p">.</span></code></pre><p>The difference here is that a check is made for two keys in each map argument.
│ │ │ │ +The other keys are ignored.</p><p>Finally, let us return the resulting color in <code class="inline">blend/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">blend</span><span class="p" data-group-id="5707659327-1">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="5707659327-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="5707659327-2">#{</span><span class="w">
│ │ │ │ +        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="5707659327-3">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="5707659327-3">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="5707659327-4">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="5707659327-4">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="5707659327-5">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="5707659327-5">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Alpha</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1508671911-2">}</span><span class="p">;</span></code></pre><p>The <code class="inline">Dst</code> map is updated with new channel values. The syntax for updating an
│ │ │ │ +    </span><span class="p" data-group-id="5707659327-2">}</span><span class="p">;</span></code></pre><p>The <code class="inline">Dst</code> map is updated with new channel values. The syntax for updating an
│ │ │ │  existing key with a new value is with the <code class="inline">:=</code> operator.</p><h2 id="standard-modules-and-manual-pages" class="section-heading">
│ │ │ │    <a href="#standard-modules-and-manual-pages" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Standard Modules and Manual Pages</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang has many standard modules to help you do things. For example, the module
│ │ │ │ @@ -347,24 +347,24 @@
│ │ │ │    <a href="#writing-output-to-a-terminal" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Writing Output to a Terminal</span>
│ │ │ │  </h2>
│ │ │ │  <p>It is nice to be able to do formatted output in examples, so the next example
│ │ │ │  shows a simple way to use the <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function. Like all other exported
│ │ │ │ -functions, you can test the <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">31&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5384509329-1">(</span><span class="s">&quot;hello world</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5384509329-2">[</span><span class="p" data-group-id="5384509329-2">]</span><span class="p" data-group-id="5384509329-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +functions, you can test the <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">31&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6291009333-1">(</span><span class="s">&quot;hello world</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6291009333-2">[</span><span class="p" data-group-id="6291009333-2">]</span><span class="p" data-group-id="6291009333-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w"> </span><span class="ss">world</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">32&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5384509329-3">(</span><span class="s">&quot;this outputs one Erlang term: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5384509329-4">[</span><span class="ss">hello</span><span class="p" data-group-id="5384509329-4">]</span><span class="p" data-group-id="5384509329-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">32&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6291009333-3">(</span><span class="s">&quot;this outputs one Erlang term: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6291009333-4">[</span><span class="ss">hello</span><span class="p" data-group-id="6291009333-4">]</span><span class="p" data-group-id="6291009333-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">one</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">term</span><span class="p">:</span><span class="w"> </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">33&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5384509329-5">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5384509329-6">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="5384509329-6">]</span><span class="p" data-group-id="5384509329-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">33&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6291009333-5">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6291009333-6">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="6291009333-6">]</span><span class="p" data-group-id="6291009333-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">terms</span><span class="p">:</span><span class="w"> </span><span class="ss">helloworld</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">34&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5384509329-7">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5384509329-8">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="5384509329-8">]</span><span class="p" data-group-id="5384509329-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">34&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6291009333-7">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6291009333-8">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="6291009333-8">]</span><span class="p" data-group-id="6291009333-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">terms</span><span class="p">:</span><span class="w"> </span><span class="ss">hello</span><span class="w"> </span><span class="ss">world</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>The function <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> (that is, <code class="inline">format</code> with two arguments) takes two lists.
│ │ │ │  The first one is nearly always a list written between <code class="inline">&quot; &quot;</code>. This list is printed
│ │ │ │  out as it is, except that each <code class="inline">~w</code> is replaced by a term taken in order from the
│ │ │ │  second list. Each ~n is replaced by a new line. The <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function
│ │ │ │  itself returns the atom <code class="inline">ok</code> if everything goes as planned. Like other functions
│ │ │ │  in Erlang, it crashes if an error occurs. This is not a fault in Erlang, it is a
│ │ │ │ @@ -378,34 +378,34 @@
│ │ │ │    <span class="text">A Larger Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>Now for a larger example to consolidate what you have learnt so far. Assume that
│ │ │ │  you have a list of temperature readings from a number of cities in the world.
│ │ │ │  Some of them are in Celsius and some in Fahrenheit (as in the previous list).
│ │ │ │  First let us convert them all to Celsius, then let us print the data neatly.</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% This module is in file tut5.erl</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3918627712-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="3918627712-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3918627712-2">(</span><span class="p" data-group-id="3918627712-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3918627712-3">]</span><span class="p" data-group-id="3918627712-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6366485289-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="6366485289-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6366485289-2">(</span><span class="p" data-group-id="6366485289-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6366485289-3">]</span><span class="p" data-group-id="6366485289-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Only this function is exported</span><span class="w">
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="3918627712-4">(</span><span class="p" data-group-id="3918627712-5">[</span><span class="p" data-group-id="3918627712-5">]</span><span class="p" data-group-id="3918627712-4">)</span><span class="p">-&gt;</span><span class="w">                        </span><span class="c1">% No output for an empty list</span><span class="w">
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="6366485289-4">(</span><span class="p" data-group-id="6366485289-5">[</span><span class="p" data-group-id="6366485289-5">]</span><span class="p" data-group-id="6366485289-4">)</span><span class="p">-&gt;</span><span class="w">                        </span><span class="c1">% No output for an empty list</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="3918627712-6">(</span><span class="p" data-group-id="3918627712-7">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3918627712-7">]</span><span class="p" data-group-id="3918627712-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="3918627712-8">(</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="3918627712-9">(</span><span class="n">City</span><span class="p" data-group-id="3918627712-9">)</span><span class="p" data-group-id="3918627712-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">format_temps</span><span class="p" data-group-id="3918627712-10">(</span><span class="n">Rest</span><span class="p" data-group-id="3918627712-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="3918627712-11">(</span><span class="p" data-group-id="3918627712-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3918627712-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3918627712-13">}</span><span class="p" data-group-id="3918627712-12">}</span><span class="p" data-group-id="3918627712-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% No conversion needed</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3918627712-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3918627712-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3918627712-15">}</span><span class="p" data-group-id="3918627712-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="3918627712-16">(</span><span class="p" data-group-id="3918627712-17">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3918627712-18">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3918627712-18">}</span><span class="p" data-group-id="3918627712-17">}</span><span class="p" data-group-id="3918627712-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Do the conversion</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3918627712-19">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3918627712-20">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3918627712-21">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="3918627712-21">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="3918627712-20">}</span><span class="p" data-group-id="3918627712-19">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="3918627712-22">(</span><span class="p" data-group-id="3918627712-23">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3918627712-24">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3918627712-24">}</span><span class="p" data-group-id="3918627712-23">}</span><span class="p" data-group-id="3918627712-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3918627712-25">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3918627712-26">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3918627712-26">]</span><span class="p" data-group-id="3918627712-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">35&gt; </span><span class="nf">c</span><span class="p" data-group-id="1856842925-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="1856842925-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1856842925-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut5</span><span class="p" data-group-id="1856842925-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">36&gt; </span><span class="nc">tut5</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="1856842925-3">(</span><span class="p" data-group-id="1856842925-4">[</span><span class="p" data-group-id="1856842925-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1856842925-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="1856842925-6">}</span><span class="p" data-group-id="1856842925-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1856842925-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1856842925-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="1856842925-8">}</span><span class="p" data-group-id="1856842925-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1856842925-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1856842925-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="1856842925-10">}</span><span class="p" data-group-id="1856842925-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1856842925-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1856842925-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="1856842925-12">}</span><span class="p" data-group-id="1856842925-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1856842925-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1856842925-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="1856842925-14">}</span><span class="p" data-group-id="1856842925-13">}</span><span class="p" data-group-id="1856842925-4">]</span><span class="p" data-group-id="1856842925-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="6366485289-6">(</span><span class="p" data-group-id="6366485289-7">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6366485289-7">]</span><span class="p" data-group-id="6366485289-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="6366485289-8">(</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="6366485289-9">(</span><span class="n">City</span><span class="p" data-group-id="6366485289-9">)</span><span class="p" data-group-id="6366485289-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">format_temps</span><span class="p" data-group-id="6366485289-10">(</span><span class="n">Rest</span><span class="p" data-group-id="6366485289-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="6366485289-11">(</span><span class="p" data-group-id="6366485289-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6366485289-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6366485289-13">}</span><span class="p" data-group-id="6366485289-12">}</span><span class="p" data-group-id="6366485289-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% No conversion needed</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6366485289-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6366485289-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6366485289-15">}</span><span class="p" data-group-id="6366485289-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="6366485289-16">(</span><span class="p" data-group-id="6366485289-17">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6366485289-18">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6366485289-18">}</span><span class="p" data-group-id="6366485289-17">}</span><span class="p" data-group-id="6366485289-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Do the conversion</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6366485289-19">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6366485289-20">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6366485289-21">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="6366485289-21">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="6366485289-20">}</span><span class="p" data-group-id="6366485289-19">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="6366485289-22">(</span><span class="p" data-group-id="6366485289-23">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6366485289-24">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6366485289-24">}</span><span class="p" data-group-id="6366485289-23">}</span><span class="p" data-group-id="6366485289-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6366485289-25">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6366485289-26">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6366485289-26">]</span><span class="p" data-group-id="6366485289-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">35&gt; </span><span class="nf">c</span><span class="p" data-group-id="6728860517-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="6728860517-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6728860517-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut5</span><span class="p" data-group-id="6728860517-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">36&gt; </span><span class="nc">tut5</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="6728860517-3">(</span><span class="p" data-group-id="6728860517-4">[</span><span class="p" data-group-id="6728860517-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6728860517-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6728860517-6">}</span><span class="p" data-group-id="6728860517-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6728860517-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6728860517-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6728860517-8">}</span><span class="p" data-group-id="6728860517-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6728860517-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6728860517-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6728860517-10">}</span><span class="p" data-group-id="6728860517-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6728860517-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6728860517-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6728860517-12">}</span><span class="p" data-group-id="6728860517-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6728860517-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6728860517-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6728860517-14">}</span><span class="p" data-group-id="6728860517-13">}</span><span class="p" data-group-id="6728860517-4">]</span><span class="p" data-group-id="6728860517-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>Before looking at how this program works, notice that a few comments are added
│ │ │ │  to the code. A comment starts with a %-character and goes on to the end of the
│ │ │ │ @@ -433,28 +433,28 @@
│ │ │ │    <a href="#matching-guards-and-scope-of-variables" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Matching, Guards, and Scope of Variables</span>
│ │ │ │  </h2>
│ │ │ │  <p>It can be useful to find the maximum and minimum temperature in lists like this.
│ │ │ │  Before extending the program to do this, let us look at functions for finding
│ │ │ │ -the maximum value of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5929324492-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="5929324492-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5929324492-2">(</span><span class="p" data-group-id="5929324492-3">[</span><span class="ss">list_max</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5929324492-3">]</span><span class="p" data-group-id="5929324492-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the maximum value of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4258555343-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="4258555343-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4258555343-2">(</span><span class="p" data-group-id="4258555343-3">[</span><span class="ss">list_max</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4258555343-3">]</span><span class="p" data-group-id="4258555343-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="5929324492-4">(</span><span class="p" data-group-id="5929324492-5">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="5929324492-5">]</span><span class="p" data-group-id="5929324492-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="nf">list_max</span><span class="p" data-group-id="5929324492-6">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="5929324492-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="4258555343-4">(</span><span class="p" data-group-id="4258555343-5">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="4258555343-5">]</span><span class="p" data-group-id="4258555343-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="nf">list_max</span><span class="p" data-group-id="4258555343-6">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="4258555343-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="5929324492-7">(</span><span class="p" data-group-id="5929324492-8">[</span><span class="p" data-group-id="5929324492-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="5929324492-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="4258555343-7">(</span><span class="p" data-group-id="4258555343-8">[</span><span class="p" data-group-id="4258555343-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="4258555343-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Res</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="5929324492-9">(</span><span class="p" data-group-id="5929324492-10">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="5929324492-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="5929324492-9">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="5929324492-11">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="5929324492-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="5929324492-12">(</span><span class="p" data-group-id="5929324492-13">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="5929324492-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="5929324492-12">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="5929324492-14">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="5929324492-14">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">37&gt; </span><span class="nf">c</span><span class="p" data-group-id="7639582480-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="7639582480-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7639582480-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut6</span><span class="p" data-group-id="7639582480-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">38&gt; </span><span class="nc">tut6</span><span class="p">:</span><span class="nf">list_max</span><span class="p" data-group-id="7639582480-3">(</span><span class="p" data-group-id="7639582480-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7639582480-4">]</span><span class="p" data-group-id="7639582480-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="4258555343-9">(</span><span class="p" data-group-id="4258555343-10">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="4258555343-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="4258555343-9">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="4258555343-11">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="4258555343-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="4258555343-12">(</span><span class="p" data-group-id="4258555343-13">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="4258555343-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="4258555343-12">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="4258555343-14">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="4258555343-14">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">37&gt; </span><span class="nf">c</span><span class="p" data-group-id="7769122288-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="7769122288-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7769122288-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut6</span><span class="p" data-group-id="7769122288-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">38&gt; </span><span class="nc">tut6</span><span class="p">:</span><span class="nf">list_max</span><span class="p" data-group-id="7769122288-3">(</span><span class="p" data-group-id="7769122288-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7769122288-4">]</span><span class="p" data-group-id="7769122288-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">7</span></code></pre><p>First notice that two functions have the same name, <code class="inline">list_max</code>. However, each of
│ │ │ │  these takes a different number of arguments (parameters). In Erlang these are
│ │ │ │  regarded as completely different functions. Where you need to distinguish
│ │ │ │  between these functions, you write Name/Arity, where Name is the function name
│ │ │ │  and Arity is the number of arguments, in this case <code class="inline">list_max/1</code> and
│ │ │ │  <code class="inline">list_max/2</code>.</p><p>In this example you walk through a list &quot;carrying&quot; a value, in this case
│ │ │ │  <code class="inline">Result_so_far</code>. <code class="inline">list_max/1</code> simply assumes that the max value of the list is
│ │ │ │ @@ -483,180 +483,180 @@
│ │ │ │  </span><span class="mi">5</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">40&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value 6</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">41&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value 6</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">42&gt; </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">6</span></code></pre><p>The use of the match operator is particularly useful for pulling apart Erlang
│ │ │ │ -terms and creating new ones.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">43&gt; </span><span class="p" data-group-id="8772985751-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8772985751-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8772985751-2">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8772985751-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8772985751-3">}</span><span class="p" data-group-id="8772985751-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8772985751-4">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="8772985751-5">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="8772985751-5">}</span><span class="p" data-group-id="8772985751-4">}</span><span class="w">
│ │ │ │ +terms and creating new ones.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">43&gt; </span><span class="p" data-group-id="7160912908-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7160912908-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7160912908-2">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7160912908-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="7160912908-3">}</span><span class="p" data-group-id="7160912908-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7160912908-4">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="7160912908-5">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="7160912908-5">}</span><span class="p" data-group-id="7160912908-4">}</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">44&gt; </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">45&gt; </span><span class="n">Y</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8772985751-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="8772985751-6">}</span></code></pre><p>Here <code class="inline">X</code> gets the value <code class="inline">paris</code> and <code class="inline">Y</code> the value <code class="inline">{f,28}</code>.</p><p>If you try to do the same again with another city, an error is returned:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">46&gt; </span><span class="p" data-group-id="7129760709-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7129760709-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7129760709-2">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7129760709-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="7129760709-3">}</span><span class="p" data-group-id="7129760709-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7160912908-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="7160912908-6">}</span></code></pre><p>Here <code class="inline">X</code> gets the value <code class="inline">paris</code> and <code class="inline">Y</code> the value <code class="inline">{f,28}</code>.</p><p>If you try to do the same again with another city, an error is returned:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">46&gt; </span><span class="p" data-group-id="0838105446-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0838105446-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0838105446-2">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0838105446-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="0838105446-3">}</span><span class="p" data-group-id="0838105446-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value {london,{f,36}}</span></code></pre><p>Variables can also be used to improve the readability of programs. For example,
│ │ │ │ -in function <code class="inline">list_max/2</code> above, you can write:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_max</span><span class="p" data-group-id="6621797257-1">(</span><span class="p" data-group-id="6621797257-2">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="6621797257-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="6621797257-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +in function <code class="inline">list_max/2</code> above, you can write:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_max</span><span class="p" data-group-id="6625158730-1">(</span><span class="p" data-group-id="6625158730-2">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="6625158730-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="6625158730-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">New_result_far</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Head</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="6621797257-3">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">New_result_far</span><span class="p" data-group-id="6621797257-3">)</span><span class="p">;</span></code></pre><p>This is possibly a little clearer.</p><h2 id="more-about-lists" class="section-heading">
│ │ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="6625158730-3">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">New_result_far</span><span class="p" data-group-id="6625158730-3">)</span><span class="p">;</span></code></pre><p>This is possibly a little clearer.</p><h2 id="more-about-lists" class="section-heading">
│ │ │ │    <a href="#more-about-lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">More About Lists</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Remember that the <code class="inline">|</code> operator can be used to get the head of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">47&gt; </span><span class="p" data-group-id="8169432818-1">[</span><span class="n">M1</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="8169432818-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8169432818-2">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="ss">rome</span><span class="p" data-group-id="8169432818-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8169432818-3">[</span><span class="ss">paris</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="8169432818-3">]</span><span class="w">
│ │ │ │ +<p>Remember that the <code class="inline">|</code> operator can be used to get the head of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">47&gt; </span><span class="p" data-group-id="3009649226-1">[</span><span class="n">M1</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="3009649226-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3009649226-2">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="ss">rome</span><span class="p" data-group-id="3009649226-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3009649226-3">[</span><span class="ss">paris</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="3009649226-3">]</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">48&gt; </span><span class="n">M1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">49&gt; </span><span class="n">T1</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8169432818-4">[</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="8169432818-4">]</span></code></pre><p>The <code class="inline">|</code> operator can also be used to add a head to a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">50&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0449033316-1">[</span><span class="ss">madrid</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="0449033316-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0449033316-2">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="0449033316-2">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3009649226-4">[</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="3009649226-4">]</span></code></pre><p>The <code class="inline">|</code> operator can also be used to add a head to a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">50&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9751030175-1">[</span><span class="ss">madrid</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="9751030175-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9751030175-2">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="9751030175-2">]</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">51&gt; </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0449033316-3">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="0449033316-3">]</span></code></pre><p>Now an example of this when working with lists - reversing the order of a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7217928730-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="7217928730-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9751030175-3">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="9751030175-3">]</span></code></pre><p>Now an example of this when working with lists - reversing the order of a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3998110711-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="3998110711-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7217928730-2">(</span><span class="p" data-group-id="7217928730-3">[</span><span class="ss">reverse</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7217928730-3">]</span><span class="p" data-group-id="7217928730-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3998110711-2">(</span><span class="p" data-group-id="3998110711-3">[</span><span class="ss">reverse</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3998110711-3">]</span><span class="p" data-group-id="3998110711-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="7217928730-4">(</span><span class="n">List</span><span class="p" data-group-id="7217928730-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="7217928730-5">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7217928730-6">[</span><span class="p" data-group-id="7217928730-6">]</span><span class="p" data-group-id="7217928730-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="3998110711-4">(</span><span class="n">List</span><span class="p" data-group-id="3998110711-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="3998110711-5">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3998110711-6">[</span><span class="p" data-group-id="3998110711-6">]</span><span class="p" data-group-id="3998110711-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="7217928730-7">(</span><span class="p" data-group-id="7217928730-8">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7217928730-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="7217928730-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="7217928730-9">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7217928730-10">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="7217928730-10">]</span><span class="p" data-group-id="7217928730-9">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="7217928730-11">(</span><span class="p" data-group-id="7217928730-12">[</span><span class="p" data-group-id="7217928730-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="7217928730-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Reversed_List</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">52&gt; </span><span class="nf">c</span><span class="p" data-group-id="1506427684-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="1506427684-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1506427684-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut8</span><span class="p" data-group-id="1506427684-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">53&gt; </span><span class="nc">tut8</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="1506427684-3">(</span><span class="p" data-group-id="1506427684-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1506427684-4">]</span><span class="p" data-group-id="1506427684-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1506427684-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1506427684-5">]</span></code></pre><p>Consider how <code class="inline">Reversed_List</code> is built. It starts as [], then successively the
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="3998110711-7">(</span><span class="p" data-group-id="3998110711-8">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3998110711-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="3998110711-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="3998110711-9">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3998110711-10">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="3998110711-10">]</span><span class="p" data-group-id="3998110711-9">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="3998110711-11">(</span><span class="p" data-group-id="3998110711-12">[</span><span class="p" data-group-id="3998110711-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="3998110711-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Reversed_List</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">52&gt; </span><span class="nf">c</span><span class="p" data-group-id="2336778745-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="2336778745-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2336778745-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut8</span><span class="p" data-group-id="2336778745-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">53&gt; </span><span class="nc">tut8</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2336778745-3">(</span><span class="p" data-group-id="2336778745-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2336778745-4">]</span><span class="p" data-group-id="2336778745-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2336778745-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2336778745-5">]</span></code></pre><p>Consider how <code class="inline">Reversed_List</code> is built. It starts as [], then successively the
│ │ │ │  heads are taken off of the list to be reversed and added to the the
│ │ │ │ -<code class="inline">Reversed_List</code>, as shown in the following:</p><pre><code class="makeup erlang" translate="no"><span class="nf">reverse</span><span class="p" data-group-id="0593628490-1">(</span><span class="p" data-group-id="0593628490-2">[</span><span class="mi">1</span><span class="p">|</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0593628490-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0593628490-3">[</span><span class="p" data-group-id="0593628490-3">]</span><span class="p" data-group-id="0593628490-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="0593628490-4">(</span><span class="p" data-group-id="0593628490-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0593628490-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0593628490-6">[</span><span class="mi">1</span><span class="p">|</span><span class="p" data-group-id="0593628490-7">[</span><span class="p" data-group-id="0593628490-7">]</span><span class="p" data-group-id="0593628490-6">]</span><span class="p" data-group-id="0593628490-4">)</span><span class="w">
│ │ │ │ +<code class="inline">Reversed_List</code>, as shown in the following:</p><pre><code class="makeup erlang" translate="no"><span class="nf">reverse</span><span class="p" data-group-id="8901796230-1">(</span><span class="p" data-group-id="8901796230-2">[</span><span class="mi">1</span><span class="p">|</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8901796230-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901796230-3">[</span><span class="p" data-group-id="8901796230-3">]</span><span class="p" data-group-id="8901796230-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="8901796230-4">(</span><span class="p" data-group-id="8901796230-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8901796230-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901796230-6">[</span><span class="mi">1</span><span class="p">|</span><span class="p" data-group-id="8901796230-7">[</span><span class="p" data-group-id="8901796230-7">]</span><span class="p" data-group-id="8901796230-6">]</span><span class="p" data-group-id="8901796230-4">)</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="0593628490-8">(</span><span class="p" data-group-id="0593628490-9">[</span><span class="mi">2</span><span class="p">|</span><span class="mi">3</span><span class="p" data-group-id="0593628490-9">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0593628490-10">[</span><span class="mi">1</span><span class="p" data-group-id="0593628490-10">]</span><span class="p" data-group-id="0593628490-8">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="0593628490-11">(</span><span class="p" data-group-id="0593628490-12">[</span><span class="mi">3</span><span class="p" data-group-id="0593628490-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0593628490-13">[</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="0593628490-14">[</span><span class="mi">1</span><span class="p" data-group-id="0593628490-14">]</span><span class="p">)</span><span class="w">
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="8901796230-8">(</span><span class="p" data-group-id="8901796230-9">[</span><span class="mi">2</span><span class="p">|</span><span class="mi">3</span><span class="p" data-group-id="8901796230-9">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901796230-10">[</span><span class="mi">1</span><span class="p" data-group-id="8901796230-10">]</span><span class="p" data-group-id="8901796230-8">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="8901796230-11">(</span><span class="p" data-group-id="8901796230-12">[</span><span class="mi">3</span><span class="p" data-group-id="8901796230-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901796230-13">[</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="8901796230-14">[</span><span class="mi">1</span><span class="p" data-group-id="8901796230-14">]</span><span class="p">)</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="0593628490-15">(</span><span class="p" data-group-id="0593628490-16">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="0593628490-17">[</span><span class="p" data-group-id="0593628490-17">]</span><span class="p" data-group-id="0593628490-16">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0593628490-18">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0593628490-18">]</span><span class="p" data-group-id="0593628490-15">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="0593628490-19">(</span><span class="p" data-group-id="0593628490-20">[</span><span class="p" data-group-id="0593628490-20">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0593628490-21">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="0593628490-22">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0593628490-22">]</span><span class="p" data-group-id="0593628490-21">]</span><span class="p" data-group-id="0593628490-19">)</span><span class="w">
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="8901796230-15">(</span><span class="p" data-group-id="8901796230-16">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="8901796230-17">[</span><span class="p" data-group-id="8901796230-17">]</span><span class="p" data-group-id="8901796230-16">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901796230-18">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8901796230-18">]</span><span class="p" data-group-id="8901796230-15">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="8901796230-19">(</span><span class="p" data-group-id="8901796230-20">[</span><span class="p" data-group-id="8901796230-20">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901796230-21">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="8901796230-22">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8901796230-22">]</span><span class="p" data-group-id="8901796230-21">]</span><span class="p" data-group-id="8901796230-19">)</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="0593628490-23">(</span><span class="p" data-group-id="0593628490-24">[</span><span class="p" data-group-id="0593628490-24">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0593628490-25">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0593628490-25">]</span><span class="p" data-group-id="0593628490-23">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0593628490-26">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0593628490-26">]</span></code></pre><p>The module <code class="inline">lists</code> contains many functions for manipulating lists, for example,
│ │ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="8901796230-23">(</span><span class="p" data-group-id="8901796230-24">[</span><span class="p" data-group-id="8901796230-24">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8901796230-25">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8901796230-25">]</span><span class="p" data-group-id="8901796230-23">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8901796230-26">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8901796230-26">]</span></code></pre><p>The module <code class="inline">lists</code> contains many functions for manipulating lists, for example,
│ │ │ │  for reversing them. So before writing a list-manipulating function it is a good
│ │ │ │  idea to check if one not already is written for you (see the <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a> manual
│ │ │ │  page in STDLIB).</p><p>Now let us get back to the cities and temperatures, but take a more structured
│ │ │ │ -approach this time. First let us convert the whole list to Celsius as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9660417899-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="9660417899-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9660417899-2">(</span><span class="p" data-group-id="9660417899-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9660417899-3">]</span><span class="p" data-group-id="9660417899-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +approach this time. First let us convert the whole list to Celsius as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6888452829-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="6888452829-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6888452829-2">(</span><span class="p" data-group-id="6888452829-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6888452829-3">]</span><span class="p" data-group-id="6888452829-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="9660417899-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="9660417899-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9660417899-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="9660417899-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="6888452829-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="6888452829-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6888452829-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="6888452829-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9660417899-6">(</span><span class="p" data-group-id="9660417899-7">[</span><span class="p" data-group-id="9660417899-8">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9660417899-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="9660417899-9">}</span><span class="p" data-group-id="9660417899-8">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9660417899-7">]</span><span class="p" data-group-id="9660417899-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9660417899-10">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9660417899-11">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9660417899-12">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="9660417899-12">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9660417899-11">}</span><span class="p" data-group-id="9660417899-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9660417899-13">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9660417899-14">(</span><span class="n">Rest</span><span class="p" data-group-id="9660417899-14">)</span><span class="p" data-group-id="9660417899-13">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9660417899-15">(</span><span class="p" data-group-id="9660417899-16">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9660417899-16">]</span><span class="p" data-group-id="9660417899-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9660417899-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9660417899-18">(</span><span class="n">Rest</span><span class="p" data-group-id="9660417899-18">)</span><span class="p" data-group-id="9660417899-17">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9660417899-19">(</span><span class="p" data-group-id="9660417899-20">[</span><span class="p" data-group-id="9660417899-20">]</span><span class="p" data-group-id="9660417899-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9660417899-21">[</span><span class="p" data-group-id="9660417899-21">]</span><span class="p">.</span></code></pre><p>Test the function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">54&gt; </span><span class="nf">c</span><span class="p" data-group-id="5575555850-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="5575555850-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5575555850-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="5575555850-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">55&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="5575555850-3">(</span><span class="p" data-group-id="5575555850-4">[</span><span class="p" data-group-id="5575555850-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5575555850-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="5575555850-6">}</span><span class="p" data-group-id="5575555850-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5575555850-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5575555850-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="5575555850-8">}</span><span class="p" data-group-id="5575555850-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5575555850-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5575555850-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="5575555850-10">}</span><span class="p" data-group-id="5575555850-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5575555850-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5575555850-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="5575555850-12">}</span><span class="p" data-group-id="5575555850-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5575555850-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5575555850-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="5575555850-14">}</span><span class="p" data-group-id="5575555850-13">}</span><span class="p" data-group-id="5575555850-4">]</span><span class="p" data-group-id="5575555850-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5575555850-15">[</span><span class="p" data-group-id="5575555850-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="5575555850-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="5575555850-17">}</span><span class="p" data-group-id="5575555850-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5575555850-18">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="5575555850-19">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">21.11111111111111</span><span class="p" data-group-id="5575555850-19">}</span><span class="p" data-group-id="5575555850-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5575555850-20">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="5575555850-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="5575555850-21">}</span><span class="p" data-group-id="5575555850-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5575555850-22">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="5575555850-23">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="5575555850-23">}</span><span class="p" data-group-id="5575555850-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5575555850-24">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="5575555850-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="5575555850-25">}</span><span class="p" data-group-id="5575555850-24">}</span><span class="p" data-group-id="5575555850-15">]</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">format_temps</span><span class="p" data-group-id="8818644738-1">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8818644738-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8818644738-2">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8818644738-2">)</span><span class="p">.</span></code></pre><p>Here <code class="inline">format_temps/1</code> calls <code class="inline">convert_list_to_c/1</code>. <code class="inline">convert_list_to_c/1</code> takes
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6888452829-6">(</span><span class="p" data-group-id="6888452829-7">[</span><span class="p" data-group-id="6888452829-8">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6888452829-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="6888452829-9">}</span><span class="p" data-group-id="6888452829-8">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6888452829-7">]</span><span class="p" data-group-id="6888452829-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6888452829-10">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6888452829-11">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6888452829-12">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="6888452829-12">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="6888452829-11">}</span><span class="p" data-group-id="6888452829-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6888452829-13">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6888452829-14">(</span><span class="n">Rest</span><span class="p" data-group-id="6888452829-14">)</span><span class="p" data-group-id="6888452829-13">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6888452829-15">(</span><span class="p" data-group-id="6888452829-16">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6888452829-16">]</span><span class="p" data-group-id="6888452829-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6888452829-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6888452829-18">(</span><span class="n">Rest</span><span class="p" data-group-id="6888452829-18">)</span><span class="p" data-group-id="6888452829-17">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6888452829-19">(</span><span class="p" data-group-id="6888452829-20">[</span><span class="p" data-group-id="6888452829-20">]</span><span class="p" data-group-id="6888452829-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6888452829-21">[</span><span class="p" data-group-id="6888452829-21">]</span><span class="p">.</span></code></pre><p>Test the function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">54&gt; </span><span class="nf">c</span><span class="p" data-group-id="6854866033-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="6854866033-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6854866033-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="6854866033-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">55&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="6854866033-3">(</span><span class="p" data-group-id="6854866033-4">[</span><span class="p" data-group-id="6854866033-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6854866033-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6854866033-6">}</span><span class="p" data-group-id="6854866033-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6854866033-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6854866033-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6854866033-8">}</span><span class="p" data-group-id="6854866033-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6854866033-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6854866033-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6854866033-10">}</span><span class="p" data-group-id="6854866033-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6854866033-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6854866033-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6854866033-12">}</span><span class="p" data-group-id="6854866033-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6854866033-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6854866033-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6854866033-14">}</span><span class="p" data-group-id="6854866033-13">}</span><span class="p" data-group-id="6854866033-4">]</span><span class="p" data-group-id="6854866033-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6854866033-15">[</span><span class="p" data-group-id="6854866033-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="6854866033-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6854866033-17">}</span><span class="p" data-group-id="6854866033-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6854866033-18">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="6854866033-19">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">21.11111111111111</span><span class="p" data-group-id="6854866033-19">}</span><span class="p" data-group-id="6854866033-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6854866033-20">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="6854866033-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6854866033-21">}</span><span class="p" data-group-id="6854866033-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6854866033-22">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="6854866033-23">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="6854866033-23">}</span><span class="p" data-group-id="6854866033-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6854866033-24">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="6854866033-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="6854866033-25">}</span><span class="p" data-group-id="6854866033-24">}</span><span class="p" data-group-id="6854866033-15">]</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">format_temps</span><span class="p" data-group-id="3023817736-1">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="3023817736-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3023817736-2">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="3023817736-2">)</span><span class="p">.</span></code></pre><p>Here <code class="inline">format_temps/1</code> calls <code class="inline">convert_list_to_c/1</code>. <code class="inline">convert_list_to_c/1</code> takes
│ │ │ │  off the head of the <code class="inline">List_of_cities</code>, converts it to Celsius if needed. The <code class="inline">|</code>
│ │ │ │ -operator is used to add the (maybe) converted to the converted rest of the list:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2349651151-1">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2349651151-2">(</span><span class="n">Rest</span><span class="p" data-group-id="2349651151-2">)</span><span class="p" data-group-id="2349651151-1">]</span><span class="p">;</span></code></pre><p>or:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6325528010-1">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6325528010-2">(</span><span class="n">Rest</span><span class="p" data-group-id="6325528010-2">)</span><span class="p" data-group-id="6325528010-1">]</span><span class="p">;</span></code></pre><p>This is done until the end of the list is reached, that is, the list is empty:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1314164336-1">(</span><span class="p" data-group-id="1314164336-2">[</span><span class="p" data-group-id="1314164336-2">]</span><span class="p" data-group-id="1314164336-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1314164336-3">[</span><span class="p" data-group-id="1314164336-3">]</span><span class="p">.</span></code></pre><p>Now when the list is converted, a function to print it is added:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0038030319-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="0038030319-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0038030319-2">(</span><span class="p" data-group-id="0038030319-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0038030319-3">]</span><span class="p" data-group-id="0038030319-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="0038030319-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="0038030319-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0038030319-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="0038030319-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="0038030319-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="0038030319-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0038030319-7">(</span><span class="p" data-group-id="0038030319-8">[</span><span class="p" data-group-id="0038030319-9">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0038030319-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="0038030319-10">}</span><span class="p" data-group-id="0038030319-9">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0038030319-8">]</span><span class="p" data-group-id="0038030319-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0038030319-11">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0038030319-12">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0038030319-13">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="0038030319-13">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="0038030319-12">}</span><span class="p" data-group-id="0038030319-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0038030319-14">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0038030319-15">(</span><span class="n">Rest</span><span class="p" data-group-id="0038030319-15">)</span><span class="p" data-group-id="0038030319-14">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0038030319-16">(</span><span class="p" data-group-id="0038030319-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0038030319-17">]</span><span class="p" data-group-id="0038030319-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0038030319-18">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0038030319-19">(</span><span class="n">Rest</span><span class="p" data-group-id="0038030319-19">)</span><span class="p" data-group-id="0038030319-18">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0038030319-20">(</span><span class="p" data-group-id="0038030319-21">[</span><span class="p" data-group-id="0038030319-21">]</span><span class="p" data-group-id="0038030319-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0038030319-22">[</span><span class="p" data-group-id="0038030319-22">]</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="0038030319-23">(</span><span class="p" data-group-id="0038030319-24">[</span><span class="p" data-group-id="0038030319-25">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0038030319-26">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="0038030319-26">}</span><span class="p" data-group-id="0038030319-25">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0038030319-24">]</span><span class="p" data-group-id="0038030319-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0038030319-27">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0038030319-28">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="0038030319-28">]</span><span class="p" data-group-id="0038030319-27">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="0038030319-29">(</span><span class="n">Rest</span><span class="p" data-group-id="0038030319-29">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="0038030319-30">(</span><span class="p" data-group-id="0038030319-31">[</span><span class="p" data-group-id="0038030319-31">]</span><span class="p" data-group-id="0038030319-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">56&gt; </span><span class="nf">c</span><span class="p" data-group-id="2532202798-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="2532202798-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2532202798-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut7</span><span class="p" data-group-id="2532202798-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">57&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="2532202798-3">(</span><span class="p" data-group-id="2532202798-4">[</span><span class="p" data-group-id="2532202798-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2532202798-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2532202798-6">}</span><span class="p" data-group-id="2532202798-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2532202798-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2532202798-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="2532202798-8">}</span><span class="p" data-group-id="2532202798-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2532202798-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2532202798-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2532202798-10">}</span><span class="p" data-group-id="2532202798-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2532202798-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2532202798-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="2532202798-12">}</span><span class="p" data-group-id="2532202798-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2532202798-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2532202798-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="2532202798-14">}</span><span class="p" data-group-id="2532202798-13">}</span><span class="p" data-group-id="2532202798-4">]</span><span class="p" data-group-id="2532202798-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +operator is used to add the (maybe) converted to the converted rest of the list:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4812303075-1">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4812303075-2">(</span><span class="n">Rest</span><span class="p" data-group-id="4812303075-2">)</span><span class="p" data-group-id="4812303075-1">]</span><span class="p">;</span></code></pre><p>or:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1375634481-1">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1375634481-2">(</span><span class="n">Rest</span><span class="p" data-group-id="1375634481-2">)</span><span class="p" data-group-id="1375634481-1">]</span><span class="p">;</span></code></pre><p>This is done until the end of the list is reached, that is, the list is empty:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0358381330-1">(</span><span class="p" data-group-id="0358381330-2">[</span><span class="p" data-group-id="0358381330-2">]</span><span class="p" data-group-id="0358381330-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0358381330-3">[</span><span class="p" data-group-id="0358381330-3">]</span><span class="p">.</span></code></pre><p>Now when the list is converted, a function to print it is added:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7335762233-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="7335762233-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7335762233-2">(</span><span class="p" data-group-id="7335762233-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7335762233-3">]</span><span class="p" data-group-id="7335762233-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="7335762233-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="7335762233-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7335762233-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="7335762233-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="7335762233-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="7335762233-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7335762233-7">(</span><span class="p" data-group-id="7335762233-8">[</span><span class="p" data-group-id="7335762233-9">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7335762233-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="7335762233-10">}</span><span class="p" data-group-id="7335762233-9">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7335762233-8">]</span><span class="p" data-group-id="7335762233-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7335762233-11">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7335762233-12">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7335762233-13">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="7335762233-13">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="7335762233-12">}</span><span class="p" data-group-id="7335762233-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7335762233-14">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7335762233-15">(</span><span class="n">Rest</span><span class="p" data-group-id="7335762233-15">)</span><span class="p" data-group-id="7335762233-14">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7335762233-16">(</span><span class="p" data-group-id="7335762233-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7335762233-17">]</span><span class="p" data-group-id="7335762233-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7335762233-18">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7335762233-19">(</span><span class="n">Rest</span><span class="p" data-group-id="7335762233-19">)</span><span class="p" data-group-id="7335762233-18">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7335762233-20">(</span><span class="p" data-group-id="7335762233-21">[</span><span class="p" data-group-id="7335762233-21">]</span><span class="p" data-group-id="7335762233-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7335762233-22">[</span><span class="p" data-group-id="7335762233-22">]</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="7335762233-23">(</span><span class="p" data-group-id="7335762233-24">[</span><span class="p" data-group-id="7335762233-25">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7335762233-26">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7335762233-26">}</span><span class="p" data-group-id="7335762233-25">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7335762233-24">]</span><span class="p" data-group-id="7335762233-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7335762233-27">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7335762233-28">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7335762233-28">]</span><span class="p" data-group-id="7335762233-27">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="7335762233-29">(</span><span class="n">Rest</span><span class="p" data-group-id="7335762233-29">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="7335762233-30">(</span><span class="p" data-group-id="7335762233-31">[</span><span class="p" data-group-id="7335762233-31">]</span><span class="p" data-group-id="7335762233-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">56&gt; </span><span class="nf">c</span><span class="p" data-group-id="7582498184-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="7582498184-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7582498184-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut7</span><span class="p" data-group-id="7582498184-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">57&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="7582498184-3">(</span><span class="p" data-group-id="7582498184-4">[</span><span class="p" data-group-id="7582498184-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7582498184-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="7582498184-6">}</span><span class="p" data-group-id="7582498184-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7582498184-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7582498184-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="7582498184-8">}</span><span class="p" data-group-id="7582498184-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7582498184-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7582498184-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="7582498184-10">}</span><span class="p" data-group-id="7582498184-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7582498184-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7582498184-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="7582498184-12">}</span><span class="p" data-group-id="7582498184-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7582498184-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7582498184-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="7582498184-14">}</span><span class="p" data-group-id="7582498184-13">}</span><span class="p" data-group-id="7582498184-4">]</span><span class="p" data-group-id="7582498184-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>Now a function has to be added to find the cities with the maximum and minimum
│ │ │ │  temperatures. The following program is not the most efficient way of doing this
│ │ │ │  as you walk through the list of cities four times. But it is better to first
│ │ │ │  strive for clarity and correctness and to make programs efficient only if
│ │ │ │ -needed.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3306180544-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="3306180544-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3306180544-2">(</span><span class="p" data-group-id="3306180544-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3306180544-3">]</span><span class="p" data-group-id="3306180544-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +needed.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8576367101-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="8576367101-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8576367101-2">(</span><span class="p" data-group-id="8576367101-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8576367101-3">]</span><span class="p" data-group-id="8576367101-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="3306180544-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="3306180544-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3306180544-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="3306180544-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="3306180544-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="3306180544-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3306180544-7">{</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="3306180544-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3306180544-8">(</span><span class="n">Converted_List</span><span class="p" data-group-id="3306180544-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_max_and_min</span><span class="p" data-group-id="3306180544-9">(</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="3306180544-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3306180544-10">(</span><span class="p" data-group-id="3306180544-11">[</span><span class="p" data-group-id="3306180544-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-13">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3306180544-13">}</span><span class="p" data-group-id="3306180544-12">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3306180544-11">]</span><span class="p" data-group-id="3306180544-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3306180544-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-16">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="3306180544-16">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="3306180544-15">}</span><span class="p" data-group-id="3306180544-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3306180544-17">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3306180544-18">(</span><span class="n">Rest</span><span class="p" data-group-id="3306180544-18">)</span><span class="p" data-group-id="3306180544-17">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3306180544-19">(</span><span class="p" data-group-id="3306180544-20">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3306180544-20">]</span><span class="p" data-group-id="3306180544-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3306180544-21">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3306180544-22">(</span><span class="n">Rest</span><span class="p" data-group-id="3306180544-22">)</span><span class="p" data-group-id="3306180544-21">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3306180544-23">(</span><span class="p" data-group-id="3306180544-24">[</span><span class="p" data-group-id="3306180544-24">]</span><span class="p" data-group-id="3306180544-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3306180544-25">[</span><span class="p" data-group-id="3306180544-25">]</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="3306180544-26">(</span><span class="p" data-group-id="3306180544-27">[</span><span class="p" data-group-id="3306180544-28">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-29">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3306180544-29">}</span><span class="p" data-group-id="3306180544-28">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3306180544-27">]</span><span class="p" data-group-id="3306180544-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3306180544-30">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-31">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3306180544-31">]</span><span class="p" data-group-id="3306180544-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="3306180544-32">(</span><span class="n">Rest</span><span class="p" data-group-id="3306180544-32">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="3306180544-33">(</span><span class="p" data-group-id="3306180544-34">[</span><span class="p" data-group-id="3306180544-34">]</span><span class="p" data-group-id="3306180544-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="8576367101-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8576367101-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8576367101-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="8576367101-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="8576367101-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="8576367101-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8576367101-7">{</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="8576367101-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8576367101-8">(</span><span class="n">Converted_List</span><span class="p" data-group-id="8576367101-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_max_and_min</span><span class="p" data-group-id="8576367101-9">(</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="8576367101-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8576367101-10">(</span><span class="p" data-group-id="8576367101-11">[</span><span class="p" data-group-id="8576367101-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-13">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8576367101-13">}</span><span class="p" data-group-id="8576367101-12">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8576367101-11">]</span><span class="p" data-group-id="8576367101-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8576367101-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-16">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="8576367101-16">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="8576367101-15">}</span><span class="p" data-group-id="8576367101-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8576367101-17">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8576367101-18">(</span><span class="n">Rest</span><span class="p" data-group-id="8576367101-18">)</span><span class="p" data-group-id="8576367101-17">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8576367101-19">(</span><span class="p" data-group-id="8576367101-20">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8576367101-20">]</span><span class="p" data-group-id="8576367101-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8576367101-21">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8576367101-22">(</span><span class="n">Rest</span><span class="p" data-group-id="8576367101-22">)</span><span class="p" data-group-id="8576367101-21">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8576367101-23">(</span><span class="p" data-group-id="8576367101-24">[</span><span class="p" data-group-id="8576367101-24">]</span><span class="p" data-group-id="8576367101-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8576367101-25">[</span><span class="p" data-group-id="8576367101-25">]</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="8576367101-26">(</span><span class="p" data-group-id="8576367101-27">[</span><span class="p" data-group-id="8576367101-28">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-29">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8576367101-29">}</span><span class="p" data-group-id="8576367101-28">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8576367101-27">]</span><span class="p" data-group-id="8576367101-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8576367101-30">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-31">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8576367101-31">]</span><span class="p" data-group-id="8576367101-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="8576367101-32">(</span><span class="n">Rest</span><span class="p" data-group-id="8576367101-32">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="8576367101-33">(</span><span class="p" data-group-id="8576367101-34">[</span><span class="p" data-group-id="8576367101-34">]</span><span class="p" data-group-id="8576367101-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3306180544-35">(</span><span class="p" data-group-id="3306180544-36">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3306180544-36">]</span><span class="p" data-group-id="3306180544-35">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3306180544-37">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p" data-group-id="3306180544-37">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8576367101-35">(</span><span class="p" data-group-id="8576367101-36">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8576367101-36">]</span><span class="p" data-group-id="8576367101-35">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8576367101-37">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p" data-group-id="8576367101-37">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3306180544-38">(</span><span class="p" data-group-id="3306180544-39">[</span><span class="p" data-group-id="3306180544-40">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-41">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3306180544-41">}</span><span class="p" data-group-id="3306180544-40">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3306180544-39">]</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="3306180544-42">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-43">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="3306180544-43">}</span><span class="p" data-group-id="3306180544-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="3306180544-44">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-45">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="3306180544-45">}</span><span class="p" data-group-id="3306180544-44">}</span><span class="p" data-group-id="3306180544-38">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8576367101-38">(</span><span class="p" data-group-id="8576367101-39">[</span><span class="p" data-group-id="8576367101-40">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-41">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8576367101-41">}</span><span class="p" data-group-id="8576367101-40">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8576367101-39">]</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="8576367101-42">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-43">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="8576367101-43">}</span><span class="p" data-group-id="8576367101-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="8576367101-44">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-45">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="8576367101-45">}</span><span class="p" data-group-id="8576367101-44">}</span><span class="p" data-group-id="8576367101-38">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">Temp</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Max_Temp</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3306180544-46">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-47">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3306180544-47">}</span><span class="p" data-group-id="3306180544-46">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ │ +            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8576367101-46">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-47">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8576367101-47">}</span><span class="p" data-group-id="8576367101-46">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3306180544-48">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-49">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="3306180544-49">}</span><span class="p" data-group-id="3306180544-48">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ │ +            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8576367101-48">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-49">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="8576367101-49">}</span><span class="p" data-group-id="8576367101-48">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │           </span><span class="n">Temp</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Min_Temp</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3306180544-50">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-51">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3306180544-51">}</span><span class="p" data-group-id="3306180544-50">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ │ +            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8576367101-50">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-51">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8576367101-51">}</span><span class="p" data-group-id="8576367101-50">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3306180544-52">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-53">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="3306180544-53">}</span><span class="p" data-group-id="3306180544-52">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ │ +            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8576367101-52">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-53">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="8576367101-53">}</span><span class="p" data-group-id="8576367101-52">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3306180544-54">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="3306180544-54">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8576367101-54">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="8576367101-54">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="3306180544-55">(</span><span class="p" data-group-id="3306180544-56">[</span><span class="p" data-group-id="3306180544-56">]</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="3306180544-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3306180544-57">{</span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="3306180544-57">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="8576367101-55">(</span><span class="p" data-group-id="8576367101-56">[</span><span class="p" data-group-id="8576367101-56">]</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="8576367101-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8576367101-57">{</span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="8576367101-57">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">print_max_and_min</span><span class="p" data-group-id="3306180544-58">(</span><span class="p" data-group-id="3306180544-59">{</span><span class="n">Max_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-60">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_temp</span><span class="p" data-group-id="3306180544-60">}</span><span class="p" data-group-id="3306180544-59">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-61">{</span><span class="n">Min_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-62">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_temp</span><span class="p" data-group-id="3306180544-62">}</span><span class="p" data-group-id="3306180544-61">}</span><span class="p" data-group-id="3306180544-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3306180544-63">(</span><span class="s">&quot;Max temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-64">[</span><span class="n">Max_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Max_name</span><span class="p" data-group-id="3306180544-64">]</span><span class="p" data-group-id="3306180544-63">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3306180544-65">(</span><span class="s">&quot;Min temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3306180544-66">[</span><span class="n">Min_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Min_name</span><span class="p" data-group-id="3306180544-66">]</span><span class="p" data-group-id="3306180544-65">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">58&gt; </span><span class="nf">c</span><span class="p" data-group-id="2481270142-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="2481270142-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2481270142-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="2481270142-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">59&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="2481270142-3">(</span><span class="p" data-group-id="2481270142-4">[</span><span class="p" data-group-id="2481270142-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2481270142-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2481270142-6">}</span><span class="p" data-group-id="2481270142-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2481270142-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2481270142-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="2481270142-8">}</span><span class="p" data-group-id="2481270142-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2481270142-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2481270142-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2481270142-10">}</span><span class="p" data-group-id="2481270142-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2481270142-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2481270142-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="2481270142-12">}</span><span class="p" data-group-id="2481270142-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2481270142-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2481270142-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="2481270142-14">}</span><span class="p" data-group-id="2481270142-13">}</span><span class="p" data-group-id="2481270142-4">]</span><span class="p" data-group-id="2481270142-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">print_max_and_min</span><span class="p" data-group-id="8576367101-58">(</span><span class="p" data-group-id="8576367101-59">{</span><span class="n">Max_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-60">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_temp</span><span class="p" data-group-id="8576367101-60">}</span><span class="p" data-group-id="8576367101-59">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-61">{</span><span class="n">Min_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-62">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_temp</span><span class="p" data-group-id="8576367101-62">}</span><span class="p" data-group-id="8576367101-61">}</span><span class="p" data-group-id="8576367101-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8576367101-63">(</span><span class="s">&quot;Max temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-64">[</span><span class="n">Max_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Max_name</span><span class="p" data-group-id="8576367101-64">]</span><span class="p" data-group-id="8576367101-63">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8576367101-65">(</span><span class="s">&quot;Min temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8576367101-66">[</span><span class="n">Min_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Min_name</span><span class="p" data-group-id="8576367101-66">]</span><span class="p" data-group-id="8576367101-65">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">58&gt; </span><span class="nf">c</span><span class="p" data-group-id="4274806780-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="4274806780-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4274806780-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="4274806780-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">59&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="4274806780-3">(</span><span class="p" data-group-id="4274806780-4">[</span><span class="p" data-group-id="4274806780-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4274806780-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4274806780-6">}</span><span class="p" data-group-id="4274806780-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4274806780-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4274806780-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4274806780-8">}</span><span class="p" data-group-id="4274806780-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4274806780-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4274806780-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4274806780-10">}</span><span class="p" data-group-id="4274806780-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4274806780-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4274806780-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4274806780-12">}</span><span class="p" data-group-id="4274806780-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4274806780-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4274806780-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4274806780-14">}</span><span class="p" data-group-id="4274806780-13">}</span><span class="p" data-group-id="4274806780-4">]</span><span class="p" data-group-id="4274806780-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │ │  </span><span class="n">Max</span><span class="w"> </span><span class="ss">temperature</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">cape_town</span><span class="w">
│ │ │ │  </span><span class="n">Min</span><span class="w"> </span><span class="ss">temperature</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">moscow</span><span class="w">
│ │ │ │ @@ -678,88 +678,88 @@
│ │ │ │          </span><span class="no">Action</span><span class="w"> </span><span class="mi">4</span><span class="w">
│ │ │ │  </span><span class="n">end</span></code></pre><p>Notice that there is no <code class="inline">;</code> before <code class="inline">end</code>. Conditions do the same as guards, that
│ │ │ │  is, tests that succeed or fail. Erlang starts at the top and tests until it
│ │ │ │  finds a condition that succeeds. Then it evaluates (performs) the action
│ │ │ │  following the condition and ignores all other conditions and actions before the
│ │ │ │  <code class="inline">end</code>. If no condition matches, a run-time failure occurs. A condition that
│ │ │ │  always succeeds is the atom <code class="inline">true</code>. This is often used last in an <code class="inline">if</code>, meaning,
│ │ │ │ -do the action following the <code class="inline">true</code> if all other conditions have failed.</p><p>The following is a short program to show the workings of <code class="inline">if</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9010010242-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="9010010242-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9010010242-2">(</span><span class="p" data-group-id="9010010242-3">[</span><span class="ss">test_if</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9010010242-3">]</span><span class="p" data-group-id="9010010242-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +do the action following the <code class="inline">true</code> if all other conditions have failed.</p><p>The following is a short program to show the workings of <code class="inline">if</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1301403893-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="1301403893-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1301403893-2">(</span><span class="p" data-group-id="1301403893-3">[</span><span class="ss">test_if</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1301403893-3">]</span><span class="p" data-group-id="1301403893-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">test_if</span><span class="p" data-group-id="9010010242-4">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9010010242-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">test_if</span><span class="p" data-group-id="1301403893-4">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="1301403893-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9010010242-5">(</span><span class="s">&quot;A == 5</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9010010242-6">[</span><span class="p" data-group-id="9010010242-6">]</span><span class="p" data-group-id="9010010242-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1301403893-5">(</span><span class="s">&quot;A == 5</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1301403893-6">[</span><span class="p" data-group-id="1301403893-6">]</span><span class="p" data-group-id="1301403893-5">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="ss">a_equals_5</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9010010242-7">(</span><span class="s">&quot;B == 6</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9010010242-8">[</span><span class="p" data-group-id="9010010242-8">]</span><span class="p" data-group-id="9010010242-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1301403893-7">(</span><span class="s">&quot;B == 6</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1301403893-8">[</span><span class="p" data-group-id="1301403893-8">]</span><span class="p" data-group-id="1301403893-7">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="ss">b_equals_6</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">                      </span><span class="c1">%That is A equals 2 and B equals 3</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9010010242-9">(</span><span class="s">&quot;A == 2, B == 3</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9010010242-10">[</span><span class="p" data-group-id="9010010242-10">]</span><span class="p" data-group-id="9010010242-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1301403893-9">(</span><span class="s">&quot;A == 2, B == 3</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1301403893-10">[</span><span class="p" data-group-id="1301403893-10">]</span><span class="p" data-group-id="1301403893-9">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="ss">a_equals_2_b_equals_3</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">                     </span><span class="c1">%That is A equals 1 or B equals 7</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9010010242-11">(</span><span class="s">&quot;A == 1 ; B == 7</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9010010242-12">[</span><span class="p" data-group-id="9010010242-12">]</span><span class="p" data-group-id="9010010242-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1301403893-11">(</span><span class="s">&quot;A == 1 ; B == 7</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1301403893-12">[</span><span class="p" data-group-id="1301403893-12">]</span><span class="p" data-group-id="1301403893-11">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Testing this program gives:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">60&gt; </span><span class="nf">c</span><span class="p" data-group-id="9095106907-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="9095106907-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9095106907-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut9</span><span class="p" data-group-id="9095106907-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">61&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9095106907-3">(</span><span class="mi">5</span><span class="p">,</span><span class="mi">33</span><span class="p" data-group-id="9095106907-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Testing this program gives:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">60&gt; </span><span class="nf">c</span><span class="p" data-group-id="4214256181-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="4214256181-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4214256181-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut9</span><span class="p" data-group-id="4214256181-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">61&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4214256181-3">(</span><span class="mi">5</span><span class="p">,</span><span class="mi">33</span><span class="p" data-group-id="4214256181-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │  </span><span class="ss">a_equals_5</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">62&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9095106907-4">(</span><span class="mi">33</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9095106907-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">62&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4214256181-4">(</span><span class="mi">33</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4214256181-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">6</span><span class="w">
│ │ │ │  </span><span class="ss">b_equals_6</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">63&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9095106907-5">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9095106907-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">63&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4214256181-5">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4214256181-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="w">
│ │ │ │  </span><span class="ss">a_equals_2_b_equals_3</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">64&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9095106907-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="9095106907-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">64&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4214256181-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="4214256181-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w">
│ │ │ │  </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">65&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9095106907-7">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="9095106907-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">65&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4214256181-7">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="4214256181-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w">
│ │ │ │  </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">66&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="9095106907-8">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="9095106907-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">66&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4214256181-8">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="4214256181-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no true branch found when evaluating an if expression
│ │ │ │       in function  tut9:test_if/2 (tut9.erl, line 5)</span></code></pre><p>Notice that <code class="inline">tut9:test_if(33,33)</code> does not cause any condition to succeed. This
│ │ │ │  leads to the run time error <code class="inline">if_clause</code>, here nicely formatted by the shell. See
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml">Guard Sequences</a> for details of the many guard tests
│ │ │ │  available.</p><p><code class="inline">case</code> is another construct in Erlang. Recall that the <code class="inline">convert_length</code> function
│ │ │ │ -was written as:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_length</span><span class="p" data-group-id="8479610651-1">(</span><span class="p" data-group-id="8479610651-2">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8479610651-2">}</span><span class="p" data-group-id="8479610651-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8479610651-3">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="8479610651-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="8479610651-4">(</span><span class="p" data-group-id="8479610651-5">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8479610651-5">}</span><span class="p" data-group-id="8479610651-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8479610651-6">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="8479610651-6">}</span><span class="p">.</span></code></pre><p>The same program can also be written as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2265156287-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="2265156287-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2265156287-2">(</span><span class="p" data-group-id="2265156287-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2265156287-3">]</span><span class="p" data-group-id="2265156287-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +was written as:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_length</span><span class="p" data-group-id="7837382262-1">(</span><span class="p" data-group-id="7837382262-2">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7837382262-2">}</span><span class="p" data-group-id="7837382262-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7837382262-3">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="7837382262-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="7837382262-4">(</span><span class="p" data-group-id="7837382262-5">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7837382262-5">}</span><span class="p" data-group-id="7837382262-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7837382262-6">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="7837382262-6">}</span><span class="p">.</span></code></pre><p>The same program can also be written as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5145449378-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="5145449378-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5145449378-2">(</span><span class="p" data-group-id="5145449378-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5145449378-3">]</span><span class="p" data-group-id="5145449378-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="2265156287-4">(</span><span class="n">Length</span><span class="p" data-group-id="2265156287-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="5145449378-4">(</span><span class="n">Length</span><span class="p" data-group-id="5145449378-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2265156287-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2265156287-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="2265156287-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="2265156287-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2265156287-7">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2265156287-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="2265156287-8">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="2265156287-8">}</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">67&gt; </span><span class="nf">c</span><span class="p" data-group-id="2464829495-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="2464829495-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2464829495-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut10</span><span class="p" data-group-id="2464829495-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">68&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2464829495-3">(</span><span class="p" data-group-id="2464829495-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="2464829495-4">}</span><span class="p" data-group-id="2464829495-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2464829495-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">15.24</span><span class="p" data-group-id="2464829495-5">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">69&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2464829495-6">(</span><span class="p" data-group-id="2464829495-7">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="mf">2.5</span><span class="p" data-group-id="2464829495-7">}</span><span class="p" data-group-id="2464829495-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2464829495-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">0.984251968503937</span><span class="p" data-group-id="2464829495-8">}</span></code></pre><p>Both <code class="inline">case</code> and <code class="inline">if</code> have <em>return values</em>, that is, in the above example <code class="inline">case</code>
│ │ │ │ +        </span><span class="p" data-group-id="5145449378-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5145449378-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="5145449378-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="5145449378-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="5145449378-7">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5145449378-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="5145449378-8">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="5145449378-8">}</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">67&gt; </span><span class="nf">c</span><span class="p" data-group-id="3358056446-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="3358056446-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3358056446-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut10</span><span class="p" data-group-id="3358056446-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">68&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="3358056446-3">(</span><span class="p" data-group-id="3358056446-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="3358056446-4">}</span><span class="p" data-group-id="3358056446-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3358056446-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">15.24</span><span class="p" data-group-id="3358056446-5">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">69&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="3358056446-6">(</span><span class="p" data-group-id="3358056446-7">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="mf">2.5</span><span class="p" data-group-id="3358056446-7">}</span><span class="p" data-group-id="3358056446-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3358056446-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">0.984251968503937</span><span class="p" data-group-id="3358056446-8">}</span></code></pre><p>Both <code class="inline">case</code> and <code class="inline">if</code> have <em>return values</em>, that is, in the above example <code class="inline">case</code>
│ │ │ │  returned either <code class="inline">{inch,X/2.54}</code> or <code class="inline">{centimeter,Y*2.54}</code>. The behaviour of
│ │ │ │  <code class="inline">case</code> can also be modified by using guards. The following example clarifies
│ │ │ │  this. It tells us the length of a month, given the year. The year must be known,
│ │ │ │ -since February has 29 days in a leap year.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8229299322-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="8229299322-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8229299322-2">(</span><span class="p" data-group-id="8229299322-3">[</span><span class="ss">month_length</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8229299322-3">]</span><span class="p" data-group-id="8229299322-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +since February has 29 days in a leap year.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7694880822-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="7694880822-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7694880822-2">(</span><span class="p" data-group-id="7694880822-3">[</span><span class="ss">month_length</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7694880822-3">]</span><span class="p" data-group-id="7694880822-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">month_length</span><span class="p" data-group-id="8229299322-4">(</span><span class="n">Year</span><span class="p">,</span><span class="w"> </span><span class="n">Month</span><span class="p" data-group-id="8229299322-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">month_length</span><span class="p" data-group-id="7694880822-4">(</span><span class="n">Year</span><span class="p">,</span><span class="w"> </span><span class="n">Month</span><span class="p" data-group-id="7694880822-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% All years divisible by 400 are leap</span><span class="w">
│ │ │ │      </span><span class="c1">%% Years divisible by 100 are not leap (except the 400 rule above)</span><span class="w">
│ │ │ │      </span><span class="c1">%% Years divisible by 4 are leap (except the 100 rule above)</span><span class="w">
│ │ │ │      </span><span class="n">Leap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">if</span><span class="w">
│ │ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="8229299322-5">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="8229299322-5">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="7694880822-5">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="7694880822-5">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">leap</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="8229299322-6">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="8229299322-6">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">100</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="7694880822-6">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="7694880822-6">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">100</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_leap</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="8229299322-7">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="8229299322-7">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="7694880822-7">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="7694880822-7">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">leap</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_leap</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Month</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">sep</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">30</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">apr</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">30</span><span class="p">;</span><span class="w">
│ │ │ │ @@ -770,151 +770,151 @@
│ │ │ │          </span><span class="ss">jan</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">mar</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">may</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">jul</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">aug</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">oct</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">dec</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">70&gt; </span><span class="nf">c</span><span class="p" data-group-id="5918900240-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="5918900240-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5918900240-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut11</span><span class="p" data-group-id="5918900240-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">71&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="5918900240-3">(</span><span class="mi">2004</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="5918900240-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">70&gt; </span><span class="nf">c</span><span class="p" data-group-id="7777639386-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="7777639386-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7777639386-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut11</span><span class="p" data-group-id="7777639386-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">71&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="7777639386-3">(</span><span class="mi">2004</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="7777639386-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">29</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">72&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="5918900240-4">(</span><span class="mi">2003</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="5918900240-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">72&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="7777639386-4">(</span><span class="mi">2003</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="7777639386-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">28</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">73&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="5918900240-5">(</span><span class="mi">1947</span><span class="p">,</span><span class="w"> </span><span class="ss">aug</span><span class="p" data-group-id="5918900240-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">73&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="7777639386-5">(</span><span class="mi">1947</span><span class="p">,</span><span class="w"> </span><span class="ss">aug</span><span class="p" data-group-id="7777639386-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">31</span></code></pre><h2 id="built-in-functions-bifs" class="section-heading">
│ │ │ │    <a href="#built-in-functions-bifs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Built-In Functions (BIFs)</span>
│ │ │ │  </h2>
│ │ │ │  <p>BIFs are functions that for some reason are built-in to the Erlang virtual
│ │ │ │  machine. BIFs often implement functionality that is impossible or is too
│ │ │ │  inefficient to implement in Erlang. Some BIFs can be called using the function
│ │ │ │  name only but they are by default belonging to the <code class="inline">erlang</code> module. For example,
│ │ │ │  the call to the BIF <code class="inline">trunc</code> below is equivalent to a call to <code class="inline">erlang:trunc</code>.</p><p>As shown, first it is checked if a year is leap. If a year is divisible by 400,
│ │ │ │  it is a leap year. To determine this, first divide the year by 400 and use the
│ │ │ │  BIF <code class="inline">trunc</code> (more about this later) to cut off any decimals. Then multiply by
│ │ │ │  400 again and see if the same value is returned again. For example, year 2004:</p><pre><code class="makeup erlang" translate="no"><span class="mi">2004</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">5.01</span><span class="w">
│ │ │ │ -</span><span class="nf">trunc</span><span class="p" data-group-id="9485703817-1">(</span><span class="mf">5.01</span><span class="p" data-group-id="9485703817-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │ +</span><span class="nf">trunc</span><span class="p" data-group-id="4184336036-1">(</span><span class="mf">5.01</span><span class="p" data-group-id="4184336036-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │  </span><span class="mi">5</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2000</span></code></pre><p>2000 is not the same as 2004, so 2004 is not divisible by 400. Year 2000:</p><pre><code class="makeup erlang" translate="no"><span class="mi">2000</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">5.0</span><span class="w">
│ │ │ │ -</span><span class="nf">trunc</span><span class="p" data-group-id="8120735101-1">(</span><span class="mf">5.0</span><span class="p" data-group-id="8120735101-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │ +</span><span class="nf">trunc</span><span class="p" data-group-id="9937870882-1">(</span><span class="mf">5.0</span><span class="p" data-group-id="9937870882-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ │  </span><span class="mi">5</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2000</span></code></pre><p>That is, a leap year. The next two <code class="inline">trunc</code>-tests evaluate if the year is
│ │ │ │  divisible by 100 or 4 in the same way. The first <code class="inline">if</code> returns <code class="inline">leap</code> or
│ │ │ │  <code class="inline">not_leap</code>, which lands up in the variable <code class="inline">Leap</code>. This variable is used in the
│ │ │ │  guard for <code class="inline">feb</code> in the following <code class="inline">case</code> that tells us how long the month is.</p><p>This example showed the use of <code class="inline">trunc</code>. It is easier to use the Erlang operator
│ │ │ │  <code class="inline">rem</code> that gives the remainder after division, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">74&gt; </span><span class="mi">2004</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">400</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mi">4</span></code></pre><p>So instead of writing:</p><pre><code class="makeup erlang" translate="no"><span class="nf">trunc</span><span class="p" data-group-id="9562029075-1">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="9562029075-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="mi">4</span></code></pre><p>So instead of writing:</p><pre><code class="makeup erlang" translate="no"><span class="nf">trunc</span><span class="p" data-group-id="3463789207-1">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="3463789207-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">leap</span><span class="p">;</span></code></pre><p>it can be written:</p><pre><code class="makeup erlang" translate="no"><span class="n">Year</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">leap</span><span class="p">;</span></code></pre><p>There are many other BIFs such as <code class="inline">trunc</code>. Only a few BIFs can be used in
│ │ │ │  guards, and you cannot use functions you have defined yourself in guards. (see
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml">Guard Sequences</a>) (For advanced readers: This is to
│ │ │ │  ensure that guards do not have side effects.) Let us play with a few of these
│ │ │ │ -functions in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">75&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="4770500775-1">(</span><span class="mf">5.6</span><span class="p" data-group-id="4770500775-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +functions in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">75&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="0143260511-1">(</span><span class="mf">5.6</span><span class="p" data-group-id="0143260511-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">5</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">76&gt; </span><span class="nf">round</span><span class="p" data-group-id="4770500775-2">(</span><span class="mf">5.6</span><span class="p" data-group-id="4770500775-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">76&gt; </span><span class="nf">round</span><span class="p" data-group-id="0143260511-2">(</span><span class="mf">5.6</span><span class="p" data-group-id="0143260511-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">6</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">77&gt; </span><span class="nf">length</span><span class="p" data-group-id="4770500775-3">(</span><span class="p" data-group-id="4770500775-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="4770500775-4">]</span><span class="p" data-group-id="4770500775-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">77&gt; </span><span class="nf">length</span><span class="p" data-group-id="0143260511-3">(</span><span class="p" data-group-id="0143260511-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="0143260511-4">]</span><span class="p" data-group-id="0143260511-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">78&gt; </span><span class="nf">float</span><span class="p" data-group-id="4770500775-5">(</span><span class="mi">5</span><span class="p" data-group-id="4770500775-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">78&gt; </span><span class="nf">float</span><span class="p" data-group-id="0143260511-5">(</span><span class="mi">5</span><span class="p" data-group-id="0143260511-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">5.0</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">79&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="4770500775-6">(</span><span class="ss">hello</span><span class="p" data-group-id="4770500775-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">79&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="0143260511-6">(</span><span class="ss">hello</span><span class="p" data-group-id="0143260511-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">80&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="4770500775-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4770500775-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">80&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="0143260511-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0143260511-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">81&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="4770500775-8">(</span><span class="p" data-group-id="4770500775-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4770500775-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="4770500775-10">}</span><span class="p" data-group-id="4770500775-9">}</span><span class="p" data-group-id="4770500775-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">81&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="0143260511-8">(</span><span class="p" data-group-id="0143260511-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0143260511-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="0143260511-10">}</span><span class="p" data-group-id="0143260511-9">}</span><span class="p" data-group-id="0143260511-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">82&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="4770500775-11">(</span><span class="p" data-group-id="4770500775-12">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4770500775-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="4770500775-13">}</span><span class="p" data-group-id="4770500775-12">]</span><span class="p" data-group-id="4770500775-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">82&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="0143260511-11">(</span><span class="p" data-group-id="0143260511-12">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0143260511-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="0143260511-13">}</span><span class="p" data-group-id="0143260511-12">]</span><span class="p" data-group-id="0143260511-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><p>All of these can be used in guards. Now for some BIFs that cannot be used in
│ │ │ │ -guards:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">83&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="2484447568-1">(</span><span class="ss">hello</span><span class="p" data-group-id="2484447568-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +guards:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">83&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="2034029178-1">(</span><span class="ss">hello</span><span class="p" data-group-id="2034029178-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">84&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="2484447568-2">(</span><span class="s">&quot;goodbye&quot;</span><span class="p" data-group-id="2484447568-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">84&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="2034029178-2">(</span><span class="s">&quot;goodbye&quot;</span><span class="p" data-group-id="2034029178-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">85&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="2484447568-3">(</span><span class="mi">22</span><span class="p" data-group-id="2484447568-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">85&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="2034029178-3">(</span><span class="mi">22</span><span class="p" data-group-id="2034029178-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;22&quot;</span></code></pre><p>These three BIFs do conversions that would be difficult (or impossible) to do in
│ │ │ │  Erlang.</p><h2 id="higher-order-functions-funs" class="section-heading">
│ │ │ │    <a href="#higher-order-functions-funs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Higher-Order Functions (Funs)</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang, like most modern functional programming languages, has higher-order
│ │ │ │ -functions. Here is an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">86&gt; </span><span class="n">Xf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4785518070-1">(</span><span class="n">X</span><span class="p" data-group-id="4785518070-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +functions. Here is an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">86&gt; </span><span class="n">Xf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5072553228-1">(</span><span class="n">X</span><span class="p" data-group-id="5072553228-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">87&gt; </span><span class="n">Xf</span><span class="p" data-group-id="4785518070-2">(</span><span class="mi">5</span><span class="p" data-group-id="4785518070-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">87&gt; </span><span class="n">Xf</span><span class="p" data-group-id="5072553228-2">(</span><span class="mi">5</span><span class="p" data-group-id="5072553228-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span></code></pre><p>Here is defined a function that doubles the value of a number and assigned this
│ │ │ │  function to a variable. Thus <code class="inline">Xf(5)</code> returns value 10. Two useful functions when
│ │ │ │ -working with lists are <code class="inline">foreach</code> and <code class="inline">map</code>, which are defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="0369712807-1">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369712807-2">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0369712807-2">]</span><span class="p" data-group-id="0369712807-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Fun</span><span class="p" data-group-id="0369712807-3">(</span><span class="n">First</span><span class="p" data-group-id="0369712807-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="0369712807-4">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0369712807-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="0369712807-5">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369712807-6">[</span><span class="p" data-group-id="0369712807-6">]</span><span class="p" data-group-id="0369712807-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +working with lists are <code class="inline">foreach</code> and <code class="inline">map</code>, which are defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="9855968662-1">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9855968662-2">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="9855968662-2">]</span><span class="p" data-group-id="9855968662-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Fun</span><span class="p" data-group-id="9855968662-3">(</span><span class="n">First</span><span class="p" data-group-id="9855968662-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="9855968662-4">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9855968662-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="9855968662-5">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9855968662-6">[</span><span class="p" data-group-id="9855968662-6">]</span><span class="p" data-group-id="9855968662-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="0369712807-7">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369712807-8">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0369712807-8">]</span><span class="p" data-group-id="0369712807-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0369712807-9">[</span><span class="n">Fun</span><span class="p" data-group-id="0369712807-10">(</span><span class="n">First</span><span class="p" data-group-id="0369712807-10">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="0369712807-11">(</span><span class="n">Fun</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="0369712807-11">)</span><span class="p" data-group-id="0369712807-9">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="0369712807-12">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0369712807-13">[</span><span class="p" data-group-id="0369712807-13">]</span><span class="p" data-group-id="0369712807-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0369712807-14">[</span><span class="p" data-group-id="0369712807-14">]</span><span class="p">.</span></code></pre><p>These two functions are provided in the standard module <code class="inline">lists</code>. <code class="inline">foreach</code> takes
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="9855968662-7">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9855968662-8">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="9855968662-8">]</span><span class="p" data-group-id="9855968662-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9855968662-9">[</span><span class="n">Fun</span><span class="p" data-group-id="9855968662-10">(</span><span class="n">First</span><span class="p" data-group-id="9855968662-10">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="9855968662-11">(</span><span class="n">Fun</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="9855968662-11">)</span><span class="p" data-group-id="9855968662-9">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="9855968662-12">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9855968662-13">[</span><span class="p" data-group-id="9855968662-13">]</span><span class="p" data-group-id="9855968662-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9855968662-14">[</span><span class="p" data-group-id="9855968662-14">]</span><span class="p">.</span></code></pre><p>These two functions are provided in the standard module <code class="inline">lists</code>. <code class="inline">foreach</code> takes
│ │ │ │  a list and applies a fun to every element in the list. <code class="inline">map</code> creates a new list
│ │ │ │  by applying a fun to every element in a list. Going back to the shell, <code class="inline">map</code> is
│ │ │ │ -used and a fun to add 3 to every element of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">88&gt; </span><span class="n">Add_3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6299771173-1">(</span><span class="n">X</span><span class="p" data-group-id="6299771173-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +used and a fun to add 3 to every element of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">88&gt; </span><span class="n">Add_3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8917013692-1">(</span><span class="n">X</span><span class="p" data-group-id="8917013692-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">89&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="6299771173-2">(</span><span class="n">Add_3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6299771173-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6299771173-3">]</span><span class="p" data-group-id="6299771173-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6299771173-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6299771173-4">]</span></code></pre><p>Let us (again) print the temperatures in a list of cities:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">90&gt; </span><span class="n">Print_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4901947474-1">(</span><span class="p" data-group-id="4901947474-2">{</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4901947474-3">}</span><span class="p" data-group-id="4901947474-2">}</span><span class="p" data-group-id="4901947474-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4901947474-4">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4901947474-5">[</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4901947474-5">]</span><span class="p" data-group-id="4901947474-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">89&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="8917013692-2">(</span><span class="n">Add_3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8917013692-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8917013692-3">]</span><span class="p" data-group-id="8917013692-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8917013692-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8917013692-4">]</span></code></pre><p>Let us (again) print the temperatures in a list of cities:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">90&gt; </span><span class="n">Print_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6194542463-1">(</span><span class="p" data-group-id="6194542463-2">{</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6194542463-3">}</span><span class="p" data-group-id="6194542463-2">}</span><span class="p" data-group-id="6194542463-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6194542463-4">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6194542463-5">[</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6194542463-5">]</span><span class="p" data-group-id="6194542463-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">91&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="4901947474-6">(</span><span class="n">Print_City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-7">[</span><span class="p" data-group-id="4901947474-8">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-9">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4901947474-9">}</span><span class="p" data-group-id="4901947474-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-10">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4901947474-11">}</span><span class="p" data-group-id="4901947474-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4901947474-12">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4901947474-13">}</span><span class="p" data-group-id="4901947474-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-14">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-15">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4901947474-15">}</span><span class="p" data-group-id="4901947474-14">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-16">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4901947474-17">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4901947474-17">}</span><span class="p" data-group-id="4901947474-16">}</span><span class="p" data-group-id="4901947474-7">]</span><span class="p" data-group-id="4901947474-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">91&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="6194542463-6">(</span><span class="n">Print_City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-7">[</span><span class="p" data-group-id="6194542463-8">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-9">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6194542463-9">}</span><span class="p" data-group-id="6194542463-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-10">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6194542463-11">}</span><span class="p" data-group-id="6194542463-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6194542463-12">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6194542463-13">}</span><span class="p" data-group-id="6194542463-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-14">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-15">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6194542463-15">}</span><span class="p" data-group-id="6194542463-14">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-16">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6194542463-17">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6194542463-17">}</span><span class="p" data-group-id="6194542463-16">}</span><span class="p" data-group-id="6194542463-7">]</span><span class="p" data-group-id="6194542463-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="w">
│ │ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="ss">f</span><span class="w"> </span><span class="mi">70</span><span class="w">
│ │ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="w">
│ │ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="ss">f</span><span class="w"> </span><span class="mi">28</span><span class="w">
│ │ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="ss">f</span><span class="w"> </span><span class="mi">36</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>Let us now define a fun that can be used to go through a list of cities and
│ │ │ │ -temperatures and transform them all to Celsius.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9773075655-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="9773075655-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +temperatures and transform them all to Celsius.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4048494165-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="4048494165-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9773075655-2">(</span><span class="p" data-group-id="9773075655-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9773075655-3">]</span><span class="p" data-group-id="9773075655-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4048494165-2">(</span><span class="p" data-group-id="4048494165-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4048494165-3">]</span><span class="p" data-group-id="4048494165-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="9773075655-4">(</span><span class="p" data-group-id="9773075655-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9773075655-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9773075655-6">}</span><span class="p" data-group-id="9773075655-5">}</span><span class="p" data-group-id="9773075655-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9773075655-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9773075655-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="9773075655-9">(</span><span class="p" data-group-id="9773075655-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="9773075655-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9773075655-9">)</span><span class="p" data-group-id="9773075655-8">}</span><span class="p" data-group-id="9773075655-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="9773075655-11">(</span><span class="p" data-group-id="9773075655-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9773075655-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9773075655-13">}</span><span class="p" data-group-id="9773075655-12">}</span><span class="p" data-group-id="9773075655-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9773075655-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9773075655-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9773075655-15">}</span><span class="p" data-group-id="9773075655-14">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9773075655-16">(</span><span class="n">List</span><span class="p" data-group-id="9773075655-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="9773075655-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9773075655-17">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">92&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3635864119-1">(</span><span class="p" data-group-id="3635864119-2">[</span><span class="p" data-group-id="3635864119-3">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3635864119-4">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="3635864119-4">}</span><span class="p" data-group-id="3635864119-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3635864119-5">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3635864119-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="3635864119-6">}</span><span class="p" data-group-id="3635864119-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3635864119-7">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3635864119-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="3635864119-8">}</span><span class="p" data-group-id="3635864119-7">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3635864119-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3635864119-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="3635864119-10">}</span><span class="p" data-group-id="3635864119-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3635864119-11">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3635864119-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="3635864119-12">}</span><span class="p" data-group-id="3635864119-11">}</span><span class="p" data-group-id="3635864119-2">]</span><span class="p" data-group-id="3635864119-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3635864119-13">[</span><span class="p" data-group-id="3635864119-14">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="3635864119-15">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="3635864119-15">}</span><span class="p" data-group-id="3635864119-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3635864119-16">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="3635864119-17">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="3635864119-17">}</span><span class="p" data-group-id="3635864119-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3635864119-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="3635864119-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="3635864119-19">}</span><span class="p" data-group-id="3635864119-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3635864119-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="3635864119-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="3635864119-21">}</span><span class="p" data-group-id="3635864119-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3635864119-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="3635864119-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3635864119-23">}</span><span class="p" data-group-id="3635864119-22">}</span><span class="p" data-group-id="3635864119-13">]</span></code></pre><p>The <code class="inline">convert_to_c</code> function is the same as before, but here it is used as a fun:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="3882720093-1">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3882720093-1">)</span></code></pre><p>When a function defined elsewhere is used as a fun, it can be referred to as
│ │ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="4048494165-4">(</span><span class="p" data-group-id="4048494165-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4048494165-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4048494165-6">}</span><span class="p" data-group-id="4048494165-5">}</span><span class="p" data-group-id="4048494165-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4048494165-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4048494165-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="4048494165-9">(</span><span class="p" data-group-id="4048494165-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="4048494165-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="4048494165-9">)</span><span class="p" data-group-id="4048494165-8">}</span><span class="p" data-group-id="4048494165-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="4048494165-11">(</span><span class="p" data-group-id="4048494165-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4048494165-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4048494165-13">}</span><span class="p" data-group-id="4048494165-12">}</span><span class="p" data-group-id="4048494165-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4048494165-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4048494165-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4048494165-15">}</span><span class="p" data-group-id="4048494165-14">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4048494165-16">(</span><span class="n">List</span><span class="p" data-group-id="4048494165-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="4048494165-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4048494165-17">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">92&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="5280442770-1">(</span><span class="p" data-group-id="5280442770-2">[</span><span class="p" data-group-id="5280442770-3">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5280442770-4">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="5280442770-4">}</span><span class="p" data-group-id="5280442770-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5280442770-5">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5280442770-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="5280442770-6">}</span><span class="p" data-group-id="5280442770-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5280442770-7">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5280442770-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="5280442770-8">}</span><span class="p" data-group-id="5280442770-7">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5280442770-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5280442770-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="5280442770-10">}</span><span class="p" data-group-id="5280442770-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5280442770-11">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5280442770-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="5280442770-12">}</span><span class="p" data-group-id="5280442770-11">}</span><span class="p" data-group-id="5280442770-2">]</span><span class="p" data-group-id="5280442770-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5280442770-13">[</span><span class="p" data-group-id="5280442770-14">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="5280442770-15">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="5280442770-15">}</span><span class="p" data-group-id="5280442770-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5280442770-16">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="5280442770-17">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="5280442770-17">}</span><span class="p" data-group-id="5280442770-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5280442770-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="5280442770-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="5280442770-19">}</span><span class="p" data-group-id="5280442770-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5280442770-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="5280442770-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="5280442770-21">}</span><span class="p" data-group-id="5280442770-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5280442770-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="5280442770-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5280442770-23">}</span><span class="p" data-group-id="5280442770-22">}</span><span class="p" data-group-id="5280442770-13">]</span></code></pre><p>The <code class="inline">convert_to_c</code> function is the same as before, but here it is used as a fun:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0707980998-1">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="0707980998-1">)</span></code></pre><p>When a function defined elsewhere is used as a fun, it can be referred to as
│ │ │ │  <code class="inline">Function/Arity</code> (remember that <code class="inline">Arity</code> = number of arguments). So in the
│ │ │ │  <code class="inline">map</code>-call <code class="inline">lists:map(fun convert_to_c/1, List)</code> is written. As shown,
│ │ │ │  <code class="inline">convert_list_to_c</code> becomes much shorter and easier to understand.</p><p>The standard module <code class="inline">lists</code> also contains a function <code class="inline">sort(Fun, List)</code> where
│ │ │ │  <code class="inline">Fun</code> is a fun with two arguments. This fun returns <code class="inline">true</code> if the first argument
│ │ │ │  is less than the second argument, or else <code class="inline">false</code>. Sorting is added to the
│ │ │ │ -<code class="inline">convert_list_to_c</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8598549713-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="8598549713-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">convert_list_to_c</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0671980006-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="0671980006-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8598549713-2">(</span><span class="p" data-group-id="8598549713-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8598549713-3">]</span><span class="p" data-group-id="8598549713-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0671980006-2">(</span><span class="p" data-group-id="0671980006-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0671980006-3">]</span><span class="p" data-group-id="0671980006-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="8598549713-4">(</span><span class="p" data-group-id="8598549713-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598549713-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8598549713-6">}</span><span class="p" data-group-id="8598549713-5">}</span><span class="p" data-group-id="8598549713-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8598549713-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598549713-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="8598549713-9">(</span><span class="p" data-group-id="8598549713-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="8598549713-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="8598549713-9">)</span><span class="p" data-group-id="8598549713-8">}</span><span class="p" data-group-id="8598549713-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="8598549713-11">(</span><span class="p" data-group-id="8598549713-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598549713-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8598549713-13">}</span><span class="p" data-group-id="8598549713-12">}</span><span class="p" data-group-id="8598549713-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8598549713-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598549713-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="8598549713-15">}</span><span class="p" data-group-id="8598549713-14">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8598549713-16">(</span><span class="n">List</span><span class="p" data-group-id="8598549713-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">New_list</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="8598549713-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="8598549713-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="8598549713-18">(</span><span class="nf">fun</span><span class="p" data-group-id="8598549713-19">(</span><span class="p" data-group-id="8598549713-20">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598549713-21">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="8598549713-21">}</span><span class="p" data-group-id="8598549713-20">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598549713-22">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8598549713-23">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="8598549713-23">}</span><span class="p" data-group-id="8598549713-22">}</span><span class="p" data-group-id="8598549713-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                       </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">New_list</span><span class="p" data-group-id="8598549713-18">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">93&gt; </span><span class="nf">c</span><span class="p" data-group-id="2415633255-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="2415633255-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2415633255-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut13</span><span class="p" data-group-id="2415633255-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">94&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2415633255-3">(</span><span class="p" data-group-id="2415633255-4">[</span><span class="p" data-group-id="2415633255-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2415633255-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2415633255-6">}</span><span class="p" data-group-id="2415633255-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2415633255-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2415633255-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="2415633255-8">}</span><span class="p" data-group-id="2415633255-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2415633255-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2415633255-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2415633255-10">}</span><span class="p" data-group-id="2415633255-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2415633255-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2415633255-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="2415633255-12">}</span><span class="p" data-group-id="2415633255-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2415633255-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2415633255-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="2415633255-14">}</span><span class="p" data-group-id="2415633255-13">}</span><span class="p" data-group-id="2415633255-4">]</span><span class="p" data-group-id="2415633255-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2415633255-15">[</span><span class="p" data-group-id="2415633255-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="2415633255-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2415633255-17">}</span><span class="p" data-group-id="2415633255-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2415633255-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="2415633255-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2415633255-19">}</span><span class="p" data-group-id="2415633255-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2415633255-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="2415633255-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="2415633255-21">}</span><span class="p" data-group-id="2415633255-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2415633255-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="2415633255-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2415633255-23">}</span><span class="p" data-group-id="2415633255-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2415633255-24">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="2415633255-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="2415633255-25">}</span><span class="p" data-group-id="2415633255-24">}</span><span class="p" data-group-id="2415633255-15">]</span></code></pre><p>In <code class="inline">sort</code> the fun is used:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="p" data-group-id="9000866774-1">(</span><span class="p" data-group-id="9000866774-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9000866774-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="9000866774-3">}</span><span class="p" data-group-id="9000866774-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9000866774-4">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9000866774-5">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="9000866774-5">}</span><span class="p" data-group-id="9000866774-4">}</span><span class="p" data-group-id="9000866774-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span></code></pre><p>Here the concept of an <em>anonymous variable</em> <code class="inline">_</code> is introduced. This is simply
│ │ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="0671980006-4">(</span><span class="p" data-group-id="0671980006-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0671980006-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="0671980006-6">}</span><span class="p" data-group-id="0671980006-5">}</span><span class="p" data-group-id="0671980006-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0671980006-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0671980006-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="0671980006-9">(</span><span class="p" data-group-id="0671980006-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="0671980006-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="0671980006-9">)</span><span class="p" data-group-id="0671980006-8">}</span><span class="p" data-group-id="0671980006-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="0671980006-11">(</span><span class="p" data-group-id="0671980006-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0671980006-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="0671980006-13">}</span><span class="p" data-group-id="0671980006-12">}</span><span class="p" data-group-id="0671980006-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0671980006-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0671980006-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="0671980006-15">}</span><span class="p" data-group-id="0671980006-14">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="0671980006-16">(</span><span class="n">List</span><span class="p" data-group-id="0671980006-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">New_list</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0671980006-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="0671980006-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="0671980006-18">(</span><span class="nf">fun</span><span class="p" data-group-id="0671980006-19">(</span><span class="p" data-group-id="0671980006-20">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0671980006-21">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="0671980006-21">}</span><span class="p" data-group-id="0671980006-20">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0671980006-22">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0671980006-23">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="0671980006-23">}</span><span class="p" data-group-id="0671980006-22">}</span><span class="p" data-group-id="0671980006-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                       </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">New_list</span><span class="p" data-group-id="0671980006-18">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">93&gt; </span><span class="nf">c</span><span class="p" data-group-id="8782549507-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="8782549507-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8782549507-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut13</span><span class="p" data-group-id="8782549507-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">94&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="8782549507-3">(</span><span class="p" data-group-id="8782549507-4">[</span><span class="p" data-group-id="8782549507-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8782549507-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8782549507-6">}</span><span class="p" data-group-id="8782549507-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8782549507-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8782549507-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="8782549507-8">}</span><span class="p" data-group-id="8782549507-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8782549507-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8782549507-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8782549507-10">}</span><span class="p" data-group-id="8782549507-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8782549507-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8782549507-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="8782549507-12">}</span><span class="p" data-group-id="8782549507-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8782549507-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8782549507-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="8782549507-14">}</span><span class="p" data-group-id="8782549507-13">}</span><span class="p" data-group-id="8782549507-4">]</span><span class="p" data-group-id="8782549507-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8782549507-15">[</span><span class="p" data-group-id="8782549507-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="8782549507-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="8782549507-17">}</span><span class="p" data-group-id="8782549507-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8782549507-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="8782549507-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="8782549507-19">}</span><span class="p" data-group-id="8782549507-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8782549507-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="8782549507-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="8782549507-21">}</span><span class="p" data-group-id="8782549507-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8782549507-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="8782549507-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8782549507-23">}</span><span class="p" data-group-id="8782549507-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8782549507-24">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="8782549507-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="8782549507-25">}</span><span class="p" data-group-id="8782549507-24">}</span><span class="p" data-group-id="8782549507-15">]</span></code></pre><p>In <code class="inline">sort</code> the fun is used:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="p" data-group-id="5231868856-1">(</span><span class="p" data-group-id="5231868856-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5231868856-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="5231868856-3">}</span><span class="p" data-group-id="5231868856-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5231868856-4">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5231868856-5">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="5231868856-5">}</span><span class="p" data-group-id="5231868856-4">}</span><span class="p" data-group-id="5231868856-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span></code></pre><p>Here the concept of an <em>anonymous variable</em> <code class="inline">_</code> is introduced. This is simply
│ │ │ │  shorthand for a variable that gets a value, but the value is ignored. This can
│ │ │ │  be used anywhere suitable, not just in funs. <code class="inline">Temp1 &lt; Temp2</code> returns <code class="inline">true</code> if
│ │ │ │  <code class="inline">Temp1</code> is less than <code class="inline">Temp2</code>.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/robustness.xhtml
│ │ │ │ @@ -33,68 +33,68 @@
│ │ │ │  </h2>
│ │ │ │  <p>Before improving the messenger program, let us look at some general principles,
│ │ │ │  using the ping pong program as an example. Recall that when &quot;ping&quot; finishes, it
│ │ │ │  tells &quot;pong&quot; that it has done so by sending the atom <code class="inline">finished</code> as a message to
│ │ │ │  &quot;pong&quot; so that &quot;pong&quot; can also finish. Another way to let &quot;pong&quot; finish is to
│ │ │ │  make &quot;pong&quot; exit if it does not receive a message from ping within a certain
│ │ │ │  time. This can be done by adding a <em>time-out</em> to <code class="inline">pong</code> as shown in the
│ │ │ │ -following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2427420476-1">(</span><span class="ss">tut19</span><span class="p" data-group-id="2427420476-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7987391277-1">(</span><span class="ss">tut19</span><span class="p" data-group-id="7987391277-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2427420476-2">(</span><span class="p" data-group-id="2427420476-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2427420476-3">]</span><span class="p" data-group-id="2427420476-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7987391277-2">(</span><span class="p" data-group-id="7987391277-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7987391277-3">]</span><span class="p" data-group-id="7987391277-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2427420476-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2427420476-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2427420476-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2427420476-6">[</span><span class="p" data-group-id="2427420476-6">]</span><span class="p" data-group-id="2427420476-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="7987391277-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7987391277-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7987391277-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7987391277-6">[</span><span class="p" data-group-id="7987391277-6">]</span><span class="p" data-group-id="7987391277-5">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2427420476-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2427420476-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2427420476-8">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2427420476-8">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2427420476-9">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2427420476-10">(</span><span class="p" data-group-id="2427420476-10">)</span><span class="p" data-group-id="2427420476-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="7987391277-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7987391277-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7987391277-8">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7987391277-8">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7987391277-9">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7987391277-10">(</span><span class="p" data-group-id="7987391277-10">)</span><span class="p" data-group-id="7987391277-9">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2427420476-11">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2427420476-12">[</span><span class="p" data-group-id="2427420476-12">]</span><span class="p" data-group-id="2427420476-11">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7987391277-11">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7987391277-12">[</span><span class="p" data-group-id="7987391277-12">]</span><span class="p" data-group-id="7987391277-11">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="2427420476-13">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2427420476-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="7987391277-13">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7987391277-13">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="2427420476-14">(</span><span class="p" data-group-id="2427420476-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="7987391277-14">(</span><span class="p" data-group-id="7987391277-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2427420476-15">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2427420476-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2427420476-16">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2427420476-17">[</span><span class="p" data-group-id="2427420476-17">]</span><span class="p" data-group-id="2427420476-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="7987391277-15">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="7987391277-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7987391277-16">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7987391277-17">[</span><span class="p" data-group-id="7987391277-17">]</span><span class="p" data-group-id="7987391277-16">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="2427420476-18">(</span><span class="p" data-group-id="2427420476-18">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="7987391277-18">(</span><span class="p" data-group-id="7987391277-18">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2427420476-19">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2427420476-20">[</span><span class="p" data-group-id="2427420476-20">]</span><span class="p" data-group-id="2427420476-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7987391277-19">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7987391277-20">[</span><span class="p" data-group-id="7987391277-20">]</span><span class="p" data-group-id="7987391277-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_pong</span><span class="p" data-group-id="2427420476-21">(</span><span class="p" data-group-id="2427420476-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="2427420476-22">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2427420476-23">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2427420476-24">[</span><span class="p" data-group-id="2427420476-24">]</span><span class="p" data-group-id="2427420476-23">)</span><span class="p" data-group-id="2427420476-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_pong</span><span class="p" data-group-id="7987391277-21">(</span><span class="p" data-group-id="7987391277-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="7987391277-22">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7987391277-23">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7987391277-24">[</span><span class="p" data-group-id="7987391277-24">]</span><span class="p" data-group-id="7987391277-23">)</span><span class="p" data-group-id="7987391277-22">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_ping</span><span class="p" data-group-id="2427420476-25">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="2427420476-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2427420476-26">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2427420476-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2427420476-27">]</span><span class="p" data-group-id="2427420476-26">)</span><span class="p">.</span></code></pre><p>After this is compiled and the file <code class="inline">tut19.beam</code> is copied to the necessary
│ │ │ │ +</span><span class="nf">start_ping</span><span class="p" data-group-id="7987391277-25">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="7987391277-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="7987391277-26">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7987391277-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7987391277-27">]</span><span class="p" data-group-id="7987391277-26">)</span><span class="p">.</span></code></pre><p>After this is compiled and the file <code class="inline">tut19.beam</code> is copied to the necessary
│ │ │ │  directories, the following is seen on (pong@kosken):</p><pre><code class="text">(pong@kosken)1&gt; tut19:start_pong().
│ │ │ │  true
│ │ │ │  Pong received ping
│ │ │ │  Pong received ping
│ │ │ │  Pong received ping
│ │ │ │  Pong timed out</code></pre><p>And the following is seen on (ping@gollum):</p><pre><code class="text">(ping@gollum)1&gt; tut19:start_ping(pong@kosken).
│ │ │ │  &lt;0.36.0&gt;
│ │ │ │  Ping received pong
│ │ │ │  Ping received pong
│ │ │ │  Ping received pong
│ │ │ │ -ping finished</code></pre><p>The time-out is set in:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pong</span><span class="p" data-group-id="7964625926-1">(</span><span class="p" data-group-id="7964625926-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +ping finished</code></pre><p>The time-out is set in:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pong</span><span class="p" data-group-id="0570773823-1">(</span><span class="p" data-group-id="0570773823-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7964625926-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="7964625926-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7964625926-3">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7964625926-4">[</span><span class="p" data-group-id="7964625926-4">]</span><span class="p" data-group-id="7964625926-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0570773823-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="0570773823-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0570773823-3">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0570773823-4">[</span><span class="p" data-group-id="0570773823-4">]</span><span class="p" data-group-id="0570773823-3">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="7964625926-5">(</span><span class="p" data-group-id="7964625926-5">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="0570773823-5">(</span><span class="p" data-group-id="0570773823-5">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7964625926-6">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7964625926-7">[</span><span class="p" data-group-id="7964625926-7">]</span><span class="p" data-group-id="7964625926-6">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0570773823-6">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0570773823-7">[</span><span class="p" data-group-id="0570773823-7">]</span><span class="p" data-group-id="0570773823-6">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The time-out (<code class="inline">after 5000</code>) is started when <code class="inline">receive</code> is entered. The time-out
│ │ │ │  is canceled if <code class="inline">{ping,Ping_PID}</code> is received. If <code class="inline">{ping,Ping_PID}</code> is not
│ │ │ │  received, the actions following the time-out are done after 5000 milliseconds.
│ │ │ │  <code class="inline">after</code> must be last in the <code class="inline">receive</code>, that is, preceded by all other message
│ │ │ │  reception specifications in the <code class="inline">receive</code>. It is also possible to call a
│ │ │ │ -function that returned an integer for the time-out:</p><pre><code class="makeup erlang" translate="no"><span class="k">after</span><span class="w"> </span><span class="nf">pong_timeout</span><span class="p" data-group-id="8845035128-1">(</span><span class="p" data-group-id="8845035128-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>In general, there are better ways than using time-outs to supervise parts of a
│ │ │ │ +function that returned an integer for the time-out:</p><pre><code class="makeup erlang" translate="no"><span class="k">after</span><span class="w"> </span><span class="nf">pong_timeout</span><span class="p" data-group-id="8420314592-1">(</span><span class="p" data-group-id="8420314592-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>In general, there are better ways than using time-outs to supervise parts of a
│ │ │ │  distributed Erlang system. Time-outs are usually appropriate to supervise
│ │ │ │  external events, for example, if you have expected a message from some external
│ │ │ │  system within a specified time. For example, a time-out can be used to log a
│ │ │ │  user out of the messenger system if they have not accessed it for, say, ten
│ │ │ │  minutes.</p><h2 id="error-handling" class="section-heading">
│ │ │ │    <a href="#error-handling" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -114,96 +114,96 @@
│ │ │ │  something called a <em>signal</em> to all the processes it has links to.</p><p>The signal carries information about the pid it was sent from and the exit
│ │ │ │  reason.</p><p>The default behaviour of a process that receives a normal exit is to ignore the
│ │ │ │  signal.</p><p>The default behaviour in the two other cases (that is, abnormal exit) above is
│ │ │ │  to:</p><ul><li>Bypass all messages to the receiving process.</li><li>Kill the receiving process.</li><li>Propagate the same error signal to the links of the killed process.</li></ul><p>In this way you can connect all processes in a transaction together using links.
│ │ │ │  If one of the processes exits abnormally, all the processes in the transaction
│ │ │ │  are killed. As it is often wanted to create a process and link to it at the same
│ │ │ │  time, there is a special BIF, <a href="../../../lib/../erts/doc/html/erlang.html#spawn_link/1">spawn_link</a> that does the
│ │ │ │ -same as <code class="inline">spawn</code>, but also creates a link to the spawned process.</p><p>Now an example of the ping pong example using links to terminate &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6842609409-1">(</span><span class="ss">tut20</span><span class="p" data-group-id="6842609409-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +same as <code class="inline">spawn</code>, but also creates a link to the spawned process.</p><p>Now an example of the ping pong example using links to terminate &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9157579486-1">(</span><span class="ss">tut20</span><span class="p" data-group-id="9157579486-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6842609409-2">(</span><span class="p" data-group-id="6842609409-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6842609409-3">]</span><span class="p" data-group-id="6842609409-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9157579486-2">(</span><span class="p" data-group-id="9157579486-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9157579486-3">]</span><span class="p" data-group-id="9157579486-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="6842609409-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="6842609409-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">link</span><span class="p" data-group-id="6842609409-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="6842609409-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="6842609409-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="6842609409-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="9157579486-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="9157579486-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">link</span><span class="p" data-group-id="9157579486-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="9157579486-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="9157579486-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="9157579486-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="6842609409-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6842609409-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="6842609409-8">(</span><span class="ss">ping</span><span class="p" data-group-id="6842609409-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="9157579486-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9157579486-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="9157579486-8">(</span><span class="ss">ping</span><span class="p" data-group-id="9157579486-8">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="6842609409-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="6842609409-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6842609409-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6842609409-11">(</span><span class="p" data-group-id="6842609409-11">)</span><span class="p" data-group-id="6842609409-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="9157579486-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="9157579486-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9157579486-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9157579486-11">(</span><span class="p" data-group-id="9157579486-11">)</span><span class="p" data-group-id="9157579486-10">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6842609409-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6842609409-13">[</span><span class="p" data-group-id="6842609409-13">]</span><span class="p" data-group-id="6842609409-12">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9157579486-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9157579486-13">[</span><span class="p" data-group-id="9157579486-13">]</span><span class="p" data-group-id="9157579486-12">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="6842609409-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="6842609409-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="9157579486-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="9157579486-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="6842609409-15">(</span><span class="p" data-group-id="6842609409-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="9157579486-15">(</span><span class="p" data-group-id="9157579486-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6842609409-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="6842609409-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6842609409-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6842609409-18">[</span><span class="p" data-group-id="6842609409-18">]</span><span class="p" data-group-id="6842609409-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9157579486-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9157579486-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9157579486-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9157579486-18">[</span><span class="p" data-group-id="9157579486-18">]</span><span class="p" data-group-id="9157579486-17">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="6842609409-19">(</span><span class="p" data-group-id="6842609409-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="9157579486-19">(</span><span class="p" data-group-id="9157579486-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="6842609409-20">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="6842609409-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="6842609409-21">(</span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6842609409-22">[</span><span class="p" data-group-id="6842609409-22">]</span><span class="p" data-group-id="6842609409-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="6842609409-23">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6842609409-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="6842609409-24">]</span><span class="p" data-group-id="6842609409-23">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)3&gt; tut20:start(s2@kosken).
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="9157579486-20">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="9157579486-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9157579486-21">(</span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9157579486-22">[</span><span class="p" data-group-id="9157579486-22">]</span><span class="p" data-group-id="9157579486-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9157579486-23">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9157579486-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="9157579486-24">]</span><span class="p" data-group-id="9157579486-23">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)3&gt; tut20:start(s2@kosken).
│ │ │ │  Pong received ping
│ │ │ │  &lt;3820.41.0&gt;
│ │ │ │  Ping received pong
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong</code></pre><p>This is a slight modification of the ping pong program where both processes are
│ │ │ │  spawned from the same <code class="inline">start/1</code> function, and the &quot;ping&quot; process can be spawned
│ │ │ │  on a separate node. Notice the use of the <code class="inline">link</code> BIF. &quot;Ping&quot; calls
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(ping)</code></a> when it finishes and this causes an exit signal to be
│ │ │ │  sent to &quot;pong&quot;, which also terminates.</p><p>It is possible to modify the default behaviour of a process so that it does not
│ │ │ │  get killed when it receives abnormal exit signals. Instead, all signals are
│ │ │ │  turned into normal messages on the format <code class="inline">{'EXIT',FromPID,Reason}</code> and added to
│ │ │ │ -the end of the receiving process' message queue. This behaviour is set by:</p><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="5725494476-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5725494476-1">)</span></code></pre><p>There are several other process flags, see <a href="../../../lib/../erts/doc/html/erlang.html#process_flag/2">erlang(3)</a>.
│ │ │ │ +the end of the receiving process' message queue. This behaviour is set by:</p><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="2277250181-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2277250181-1">)</span></code></pre><p>There are several other process flags, see <a href="../../../lib/../erts/doc/html/erlang.html#process_flag/2">erlang(3)</a>.
│ │ │ │  Changing the default behaviour of a process in this way is usually not done in
│ │ │ │  standard user programs, but is left to the supervisory programs in OTP. However,
│ │ │ │ -the ping pong program is modified to illustrate exit trapping.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5728653908-1">(</span><span class="ss">tut21</span><span class="p" data-group-id="5728653908-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the ping pong program is modified to illustrate exit trapping.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1544873966-1">(</span><span class="ss">tut21</span><span class="p" data-group-id="1544873966-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5728653908-2">(</span><span class="p" data-group-id="5728653908-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5728653908-3">]</span><span class="p" data-group-id="5728653908-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1544873966-2">(</span><span class="p" data-group-id="1544873966-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1544873966-3">]</span><span class="p" data-group-id="1544873966-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="5728653908-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="5728653908-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">link</span><span class="p" data-group-id="5728653908-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="5728653908-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="5728653908-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="5728653908-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="1544873966-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="1544873966-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">link</span><span class="p" data-group-id="1544873966-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="1544873966-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="1544873966-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="1544873966-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="5728653908-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="5728653908-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="5728653908-8">(</span><span class="ss">ping</span><span class="p" data-group-id="5728653908-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="1544873966-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1544873966-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="1544873966-8">(</span><span class="ss">ping</span><span class="p" data-group-id="1544873966-8">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="5728653908-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="5728653908-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5728653908-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5728653908-11">(</span><span class="p" data-group-id="5728653908-11">)</span><span class="p" data-group-id="5728653908-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="1544873966-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="1544873966-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1544873966-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1544873966-11">(</span><span class="p" data-group-id="1544873966-11">)</span><span class="p" data-group-id="1544873966-10">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5728653908-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5728653908-13">[</span><span class="p" data-group-id="5728653908-13">]</span><span class="p" data-group-id="5728653908-12">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1544873966-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1544873966-13">[</span><span class="p" data-group-id="1544873966-13">]</span><span class="p" data-group-id="1544873966-12">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="5728653908-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="5728653908-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="1544873966-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="1544873966-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="5728653908-15">(</span><span class="p" data-group-id="5728653908-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="5728653908-16">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5728653908-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">pong1</span><span class="p" data-group-id="5728653908-17">(</span><span class="p" data-group-id="5728653908-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="1544873966-15">(</span><span class="p" data-group-id="1544873966-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="1544873966-16">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1544873966-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">pong1</span><span class="p" data-group-id="1544873966-17">(</span><span class="p" data-group-id="1544873966-17">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong1</span><span class="p" data-group-id="5728653908-18">(</span><span class="p" data-group-id="5728653908-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong1</span><span class="p" data-group-id="1544873966-18">(</span><span class="p" data-group-id="1544873966-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="5728653908-19">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="5728653908-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5728653908-20">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5728653908-21">[</span><span class="p" data-group-id="5728653908-21">]</span><span class="p" data-group-id="5728653908-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="1544873966-19">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="1544873966-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1544873966-20">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1544873966-21">[</span><span class="p" data-group-id="1544873966-21">]</span><span class="p" data-group-id="1544873966-20">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong1</span><span class="p" data-group-id="5728653908-22">(</span><span class="p" data-group-id="5728653908-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="5728653908-23">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5728653908-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5728653908-24">(</span><span class="s">&quot;pong exiting, got </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5728653908-25">[</span><span class="p" data-group-id="5728653908-26">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5728653908-26">}</span><span class="p" data-group-id="5728653908-25">]</span><span class="p" data-group-id="5728653908-24">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong1</span><span class="p" data-group-id="1544873966-22">(</span><span class="p" data-group-id="1544873966-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="1544873966-23">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1544873966-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1544873966-24">(</span><span class="s">&quot;pong exiting, got </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1544873966-25">[</span><span class="p" data-group-id="1544873966-26">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1544873966-26">}</span><span class="p" data-group-id="1544873966-25">]</span><span class="p" data-group-id="1544873966-24">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="5728653908-27">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="5728653908-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5728653908-28">(</span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5728653908-29">[</span><span class="p" data-group-id="5728653908-29">]</span><span class="p" data-group-id="5728653908-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5728653908-30">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5728653908-31">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="5728653908-31">]</span><span class="p" data-group-id="5728653908-30">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)1&gt; tut21:start(s2@gollum).
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="1544873966-27">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="1544873966-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1544873966-28">(</span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1544873966-29">[</span><span class="p" data-group-id="1544873966-29">]</span><span class="p" data-group-id="1544873966-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="1544873966-30">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1544873966-31">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="1544873966-31">]</span><span class="p" data-group-id="1544873966-30">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)1&gt; tut21:start(s2@gollum).
│ │ │ │  &lt;3820.39.0&gt;
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong
│ │ │ │  Pong received ping
│ │ │ │  Ping received pong
│ │ │ │ @@ -256,135 +256,135 @@
│ │ │ │  </span><span class="c1">%%% Started: messenger:client(Server_Node, Name)</span><span class="w">
│ │ │ │  </span><span class="c1">%%% To client: logoff</span><span class="w">
│ │ │ │  </span><span class="c1">%%% To client: {message_to, ToName, Message}</span><span class="w">
│ │ │ │  </span><span class="c1">%%%</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Configuration: change the server_node() function to return the</span><span class="w">
│ │ │ │  </span><span class="c1">%%% name of the node where the messenger server runs</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4252003348-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="4252003348-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4252003348-2">(</span><span class="p" data-group-id="4252003348-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4252003348-3">]</span><span class="p" data-group-id="4252003348-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6219141961-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="6219141961-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6219141961-2">(</span><span class="p" data-group-id="6219141961-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6219141961-3">]</span><span class="p" data-group-id="6219141961-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Change the function below to return the name of the node where the</span><span class="w">
│ │ │ │  </span><span class="c1">%%% messenger server runs</span><span class="w">
│ │ │ │ -</span><span class="nf">server_node</span><span class="p" data-group-id="4252003348-4">(</span><span class="p" data-group-id="4252003348-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_node</span><span class="p" data-group-id="6219141961-4">(</span><span class="p" data-group-id="6219141961-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">messenger@super</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% This is the server process for the &quot;messenger&quot;</span><span class="w">
│ │ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="4252003348-5">(</span><span class="p" data-group-id="4252003348-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="4252003348-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4252003348-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="4252003348-7">(</span><span class="p" data-group-id="4252003348-8">[</span><span class="p" data-group-id="4252003348-8">]</span><span class="p" data-group-id="4252003348-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="6219141961-5">(</span><span class="p" data-group-id="6219141961-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="6219141961-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6219141961-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="6219141961-7">(</span><span class="p" data-group-id="6219141961-8">[</span><span class="p" data-group-id="6219141961-8">]</span><span class="p" data-group-id="6219141961-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="4252003348-9">(</span><span class="n">User_List</span><span class="p" data-group-id="4252003348-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="6219141961-9">(</span><span class="n">User_List</span><span class="p" data-group-id="6219141961-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4252003348-10">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4252003348-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="4252003348-11">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="4252003348-12">(</span><span class="n">New_User_List</span><span class="p" data-group-id="4252003348-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4252003348-13">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="4252003348-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="4252003348-14">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="4252003348-15">(</span><span class="n">New_User_List</span><span class="p" data-group-id="4252003348-15">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4252003348-16">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4252003348-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="4252003348-17">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4252003348-18">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4252003348-19">[</span><span class="n">User_List</span><span class="p" data-group-id="4252003348-19">]</span><span class="p" data-group-id="4252003348-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="4252003348-20">(</span><span class="n">User_List</span><span class="p" data-group-id="4252003348-20">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6219141961-10">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6219141961-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="6219141961-11">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="6219141961-12">(</span><span class="n">New_User_List</span><span class="p" data-group-id="6219141961-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6219141961-13">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6219141961-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="6219141961-14">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="6219141961-15">(</span><span class="n">New_User_List</span><span class="p" data-group-id="6219141961-15">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6219141961-16">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6219141961-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="6219141961-17">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6219141961-18">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6219141961-19">[</span><span class="n">User_List</span><span class="p" data-group-id="6219141961-19">]</span><span class="p" data-group-id="6219141961-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="6219141961-20">(</span><span class="n">User_List</span><span class="p" data-group-id="6219141961-20">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="4252003348-21">(</span><span class="p" data-group-id="4252003348-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="4252003348-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="4252003348-23">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4252003348-24">[</span><span class="p" data-group-id="4252003348-24">]</span><span class="p" data-group-id="4252003348-23">)</span><span class="p" data-group-id="4252003348-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="6219141961-21">(</span><span class="p" data-group-id="6219141961-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="6219141961-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="6219141961-23">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6219141961-24">[</span><span class="p" data-group-id="6219141961-24">]</span><span class="p" data-group-id="6219141961-23">)</span><span class="p" data-group-id="6219141961-22">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="4252003348-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="6219141961-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="4252003348-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="6219141961-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4252003348-27">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="4252003348-27">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6219141961-27">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="6219141961-27">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4252003348-28">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="4252003348-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">link</span><span class="p" data-group-id="4252003348-29">(</span><span class="n">From</span><span class="p" data-group-id="4252003348-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="4252003348-30">[</span><span class="p" data-group-id="4252003348-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4252003348-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6219141961-28">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="6219141961-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">link</span><span class="p" data-group-id="6219141961-29">(</span><span class="n">From</span><span class="p" data-group-id="6219141961-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6219141961-30">[</span><span class="p" data-group-id="6219141961-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6219141961-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="4252003348-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="4252003348-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-33">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="6219141961-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="6219141961-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-33">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="4252003348-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="6219141961-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="4252003348-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6219141961-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4252003348-36">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="4252003348-36">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4252003348-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4252003348-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4252003348-38">}</span><span class="p" data-group-id="4252003348-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="4252003348-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-39">)</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6219141961-36">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="6219141961-36">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6219141961-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6219141961-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6219141961-38">}</span><span class="p" data-group-id="6219141961-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="6219141961-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-39">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="4252003348-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="6219141961-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="4252003348-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="4252003348-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6219141961-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6219141961-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4252003348-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="4252003348-42">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4252003348-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4252003348-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="4252003348-44">}</span><span class="p" data-group-id="4252003348-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4252003348-45">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4252003348-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4252003348-46">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="4252003348-46">}</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6219141961-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="6219141961-42">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6219141961-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6219141961-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6219141961-44">}</span><span class="p" data-group-id="6219141961-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6219141961-45">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6219141961-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6219141961-46">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="6219141961-46">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% User Commands</span><span class="w">
│ │ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="4252003348-47">(</span><span class="n">Name</span><span class="p" data-group-id="4252003348-47">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="4252003348-48">(</span><span class="ss">mess_client</span><span class="p" data-group-id="4252003348-48">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="6219141961-47">(</span><span class="n">Name</span><span class="p" data-group-id="6219141961-47">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="6219141961-48">(</span><span class="ss">mess_client</span><span class="p" data-group-id="6219141961-48">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="4252003348-49">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="4252003348-50">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4252003348-51">[</span><span class="nf">server_node</span><span class="p" data-group-id="4252003348-52">(</span><span class="p" data-group-id="4252003348-52">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4252003348-51">]</span><span class="p" data-group-id="4252003348-50">)</span><span class="p" data-group-id="4252003348-49">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="6219141961-49">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="6219141961-50">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6219141961-51">[</span><span class="nf">server_node</span><span class="p" data-group-id="6219141961-52">(</span><span class="p" data-group-id="6219141961-52">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6219141961-51">]</span><span class="p" data-group-id="6219141961-50">)</span><span class="p" data-group-id="6219141961-49">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="4252003348-53">(</span><span class="p" data-group-id="4252003348-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="6219141961-53">(</span><span class="p" data-group-id="6219141961-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="4252003348-54">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4252003348-54">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="4252003348-55">(</span><span class="ss">mess_client</span><span class="p" data-group-id="4252003348-55">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="6219141961-54">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6219141961-54">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="6219141961-55">(</span><span class="ss">mess_client</span><span class="p" data-group-id="6219141961-55">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4252003348-56">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4252003348-56">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6219141961-56">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6219141961-56">}</span><span class="p">,</span><span class="w">
│ │ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% The client process which runs on each user node</span><span class="w">
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="4252003348-57">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4252003348-57">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4252003348-58">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="4252003348-58">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4252003348-59">{</span><span class="nf">self</span><span class="p" data-group-id="4252003348-60">(</span><span class="p" data-group-id="4252003348-60">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4252003348-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="4252003348-61">(</span><span class="p" data-group-id="4252003348-61">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="4252003348-62">(</span><span class="n">Server_Node</span><span class="p" data-group-id="4252003348-62">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="6219141961-57">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6219141961-57">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6219141961-58">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6219141961-58">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6219141961-59">{</span><span class="nf">self</span><span class="p" data-group-id="6219141961-60">(</span><span class="p" data-group-id="6219141961-60">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6219141961-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="6219141961-61">(</span><span class="p" data-group-id="6219141961-61">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="6219141961-62">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6219141961-62">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="4252003348-63">(</span><span class="n">Server_Node</span><span class="p" data-group-id="4252003348-63">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="6219141961-63">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6219141961-63">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="4252003348-64">(</span><span class="ss">normal</span><span class="p" data-group-id="4252003348-64">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4252003348-65">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4252003348-65">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="4252003348-66">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="4252003348-66">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4252003348-67">{</span><span class="nf">self</span><span class="p" data-group-id="4252003348-68">(</span><span class="p" data-group-id="4252003348-68">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4252003348-67">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="4252003348-69">(</span><span class="p" data-group-id="4252003348-69">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4252003348-70">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4252003348-70">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4252003348-71">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4252003348-72">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4252003348-72">]</span><span class="p" data-group-id="4252003348-71">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="6219141961-64">(</span><span class="ss">normal</span><span class="p" data-group-id="6219141961-64">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6219141961-65">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6219141961-65">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6219141961-66">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6219141961-66">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6219141961-67">{</span><span class="nf">self</span><span class="p" data-group-id="6219141961-68">(</span><span class="p" data-group-id="6219141961-68">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6219141961-67">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="6219141961-69">(</span><span class="p" data-group-id="6219141961-69">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6219141961-70">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6219141961-70">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6219141961-71">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6219141961-72">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6219141961-72">]</span><span class="p" data-group-id="6219141961-71">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="4252003348-73">(</span><span class="n">Server_Node</span><span class="p" data-group-id="4252003348-73">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="6219141961-73">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6219141961-73">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="4252003348-74">(</span><span class="p" data-group-id="4252003348-74">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="6219141961-74">(</span><span class="p" data-group-id="6219141961-74">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4252003348-75">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="4252003348-75">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4252003348-76">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4252003348-77">[</span><span class="n">Why</span><span class="p" data-group-id="4252003348-77">]</span><span class="p" data-group-id="4252003348-76">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="4252003348-78">(</span><span class="ss">normal</span><span class="p" data-group-id="4252003348-78">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="4252003348-79">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="4252003348-79">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4252003348-80">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4252003348-81">[</span><span class="n">What</span><span class="p" data-group-id="4252003348-81">]</span><span class="p" data-group-id="4252003348-80">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6219141961-75">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="6219141961-75">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6219141961-76">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6219141961-77">[</span><span class="n">Why</span><span class="p" data-group-id="6219141961-77">]</span><span class="p" data-group-id="6219141961-76">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="6219141961-78">(</span><span class="ss">normal</span><span class="p" data-group-id="6219141961-78">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6219141961-79">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="6219141961-79">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6219141961-80">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6219141961-81">[</span><span class="n">What</span><span class="p" data-group-id="6219141961-81">]</span><span class="p" data-group-id="6219141961-80">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4252003348-82">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4252003348-83">[</span><span class="p" data-group-id="4252003348-83">]</span><span class="p" data-group-id="4252003348-82">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="4252003348-84">(</span><span class="ss">timeout</span><span class="p" data-group-id="4252003348-84">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6219141961-82">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6219141961-83">[</span><span class="p" data-group-id="6219141961-83">]</span><span class="p" data-group-id="6219141961-82">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="6219141961-84">(</span><span class="ss">timeout</span><span class="p" data-group-id="6219141961-84">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The following changes are added:</p><p>The messenger server traps exits. If it receives an exit signal,
│ │ │ │  <code class="inline">{'EXIT',From,Reason}</code>, this means that a client process has terminated or is
│ │ │ │  unreachable for one of the following reasons:</p><ul><li>The user has logged off (the &quot;logoff&quot; message is removed).</li><li>The network connection to the client is broken.</li><li>The node on which the client process resides has gone down.</li><li>The client processes has done some illegal operation.</li></ul><p>If an exit signal is received as above, the tuple <code class="inline">{From,Name}</code> is deleted from
│ │ │ │  the servers <code class="inline">User_List</code> using the <code class="inline">server_logoff</code> function. If the node on which
│ │ │ │  the server runs goes down, an exit signal (automatically generated by the
│ │ │ │  system) is sent to all of the client processes:
│ │ │ │  <code class="inline">{'EXIT',MessengerPID,noconnection}</code> causing all the client processes to
│ │ │ ├── OEBPS/release_structure.xhtml
│ │ │ │ @@ -41,37 +41,37 @@
│ │ │ │    <a href="#release-resource-file" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Release Resource File</span>
│ │ │ │  </h2>
│ │ │ │  <p>To define a release, create a <em>release resource file</em>, or in short a <code class="inline">.rel</code>
│ │ │ │  file. In the file, specify the name and version of the release, which ERTS
│ │ │ │ -version it is based on, and which applications it consists of:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2301907638-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2301907638-2">{</span><span class="n">Name</span><span class="p">,</span><span class="n">Vsn</span><span class="p" data-group-id="2301907638-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2301907638-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">EVsn</span><span class="p" data-group-id="2301907638-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2301907638-4">[</span><span class="p" data-group-id="2301907638-5">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsn1</span><span class="p" data-group-id="2301907638-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +version it is based on, and which applications it consists of:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8071180608-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8071180608-2">{</span><span class="n">Name</span><span class="p">,</span><span class="n">Vsn</span><span class="p" data-group-id="8071180608-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8071180608-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">EVsn</span><span class="p" data-group-id="8071180608-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8071180608-4">[</span><span class="p" data-group-id="8071180608-5">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsn1</span><span class="p" data-group-id="8071180608-5">}</span><span class="p">,</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2301907638-6">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsnN</span><span class="p" data-group-id="2301907638-6">}</span><span class="p" data-group-id="2301907638-4">]</span><span class="p" data-group-id="2301907638-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Name</code>, <code class="inline">Vsn</code>, <code class="inline">EVsn</code>, and <code class="inline">AppVsn</code> are strings.</p><p>The file must be named <code class="inline">Rel.rel</code>, where <code class="inline">Rel</code> is a unique name.</p><p>Each <code class="inline">Application</code> (atom) and <code class="inline">AppVsn</code> is the name and version of an application
│ │ │ │ +  </span><span class="p" data-group-id="8071180608-6">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsnN</span><span class="p" data-group-id="8071180608-6">}</span><span class="p" data-group-id="8071180608-4">]</span><span class="p" data-group-id="8071180608-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Name</code>, <code class="inline">Vsn</code>, <code class="inline">EVsn</code>, and <code class="inline">AppVsn</code> are strings.</p><p>The file must be named <code class="inline">Rel.rel</code>, where <code class="inline">Rel</code> is a unique name.</p><p>Each <code class="inline">Application</code> (atom) and <code class="inline">AppVsn</code> is the name and version of an application
│ │ │ │  included in the release. The minimal release based on Erlang/OTP consists of the
│ │ │ │  Kernel and STDLIB applications, so these applications must be included in the
│ │ │ │  list.</p><p>If the release is to be upgraded, it must also include the SASL application.</p><p><a href="" id="ch_rel"></a></p><p>Here is an example showing the <code class="inline">.app</code> file for a release of <code class="inline">ch_app</code> from
│ │ │ │ -the <a href="applications.xhtml#ch_app">Applications</a> section:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6116779774-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6116779774-2">[</span><span class="p" data-group-id="6116779774-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="6116779774-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6116779774-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6116779774-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6116779774-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6116779774-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6116779774-6">]</span><span class="p" data-group-id="6116779774-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6116779774-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6116779774-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="6116779774-8">]</span><span class="p" data-group-id="6116779774-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6116779774-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6116779774-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="6116779774-10">]</span><span class="p" data-group-id="6116779774-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6116779774-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6116779774-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="6116779774-13">[</span><span class="p" data-group-id="6116779774-13">]</span><span class="p" data-group-id="6116779774-12">}</span><span class="p" data-group-id="6116779774-11">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6116779774-2">]</span><span class="p" data-group-id="6116779774-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">.rel</code> file must also contain <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code>, as these
│ │ │ │ -applications are required by <code class="inline">ch_app</code>. The file is called <code class="inline">ch_rel-1.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6282220953-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6282220953-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;A&quot;</span><span class="p" data-group-id="6282220953-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6282220953-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="6282220953-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6282220953-4">[</span><span class="p" data-group-id="6282220953-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="6282220953-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6282220953-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="6282220953-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6282220953-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="6282220953-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6282220953-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6282220953-8">}</span><span class="p" data-group-id="6282220953-4">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6282220953-1">}</span><span class="p">.</span></code></pre><p><a href="" id="boot"></a></p><h2 id="generating-boot-scripts" class="section-heading">
│ │ │ │ +the <a href="applications.xhtml#ch_app">Applications</a> section:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7027624010-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7027624010-2">[</span><span class="p" data-group-id="7027624010-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="7027624010-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7027624010-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="7027624010-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7027624010-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7027624010-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7027624010-6">]</span><span class="p" data-group-id="7027624010-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7027624010-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7027624010-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="7027624010-8">]</span><span class="p" data-group-id="7027624010-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7027624010-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7027624010-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="7027624010-10">]</span><span class="p" data-group-id="7027624010-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7027624010-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7027624010-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="7027624010-13">[</span><span class="p" data-group-id="7027624010-13">]</span><span class="p" data-group-id="7027624010-12">}</span><span class="p" data-group-id="7027624010-11">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7027624010-2">]</span><span class="p" data-group-id="7027624010-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">.rel</code> file must also contain <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code>, as these
│ │ │ │ +applications are required by <code class="inline">ch_app</code>. The file is called <code class="inline">ch_rel-1.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9519520406-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9519520406-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;A&quot;</span><span class="p" data-group-id="9519520406-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9519520406-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="9519520406-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9519520406-4">[</span><span class="p" data-group-id="9519520406-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="9519520406-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9519520406-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="9519520406-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9519520406-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="9519520406-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9519520406-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9519520406-8">}</span><span class="p" data-group-id="9519520406-4">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9519520406-1">}</span><span class="p">.</span></code></pre><p><a href="" id="boot"></a></p><h2 id="generating-boot-scripts" class="section-heading">
│ │ │ │    <a href="#generating-boot-scripts" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Generating Boot Scripts</span>
│ │ │ │  </h2>
│ │ │ │  <p><a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> in the SASL application includes tools to build and check
│ │ │ │  releases. The functions read the <code class="inline">.rel</code> and <code class="inline">.app</code> files and perform
│ │ │ │ @@ -95,17 +95,17 @@
│ │ │ │    <a href="#creating-a-release-package" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating a Release Package</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <a href="../../../lib/sasl/doc/html/systools.html#make_tar/2"><code class="inline">systools:make_tar/1,2</code></a> function takes a
│ │ │ │  <code class="inline">.rel</code> file as input and creates a zipped tar file with the code for
│ │ │ │ -the specified applications, a <em>release package</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="9711860290-1">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="9711860290-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the specified applications, a <em>release package</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="9499499540-1">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="9499499540-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="9711860290-2">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="9711860290-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="9499499540-2">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="9499499540-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>The release package by default contains:</p><ul><li>The <code class="inline">.app</code> files</li><li>The <code class="inline">.rel</code> file</li><li>The object code for all applications, structured according to the
│ │ │ │  <a href="applications.xhtml#app_dir">application directory structure</a></li><li>The binary boot script renamed to <code class="inline">start.boot</code></li></ul><pre><code class="text">% tar tf ch_rel-1.tar
│ │ │ │  lib/kernel-9.2.4/ebin/kernel.app
│ │ │ │  lib/kernel-9.2.4/ebin/application.beam
│ │ │ │  ...
│ │ │ │  lib/stdlib-5.2.3/ebin/stdlib.app
│ │ │ │  lib/stdlib-5.2.3/ebin/argparse.beam
│ │ │ ├── OEBPS/release_handling.xhtml
│ │ │ │ @@ -128,38 +128,38 @@
│ │ │ │    <span class="text">update</span>
│ │ │ │  </h3>
│ │ │ │  <p>If a more complex change has been made, for example, a change to the format of
│ │ │ │  the internal state of a <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a>, simple code replacement is not sufficient.
│ │ │ │  Instead, it is necessary to:</p><ul><li>Suspend the processes using the module (to avoid that they try to handle any
│ │ │ │  requests before the code replacement is completed).</li><li>Ask them to transform the internal state format and switch to the new version
│ │ │ │  of the module.</li><li>Remove the old version.</li><li>Resume the processes.</li></ul><p>This is called <em>synchronized code replacement</em> and for this the following
│ │ │ │ -instructions are used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8790028609-1">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8790028609-2">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="8790028609-2">}</span><span class="p" data-group-id="8790028609-1">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8790028609-3">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="8790028609-3">}</span></code></pre><p><code class="inline">update</code> with argument <code class="inline">{advanced,Extra}</code> is used when changing the internal
│ │ │ │ +instructions are used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4778700187-1">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4778700187-2">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="4778700187-2">}</span><span class="p" data-group-id="4778700187-1">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4778700187-3">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="4778700187-3">}</span></code></pre><p><code class="inline">update</code> with argument <code class="inline">{advanced,Extra}</code> is used when changing the internal
│ │ │ │  state of a behaviour as described above. It causes behaviour processes to call
│ │ │ │  the callback function <code class="inline">code_change/3</code>, passing the term <code class="inline">Extra</code> and some other
│ │ │ │  information as arguments. See the manual pages for the respective behaviours and
│ │ │ │  <a href="appup_cookbook.xhtml#int_state">Appup Cookbook</a>.</p><p><code class="inline">update</code> with argument <code class="inline">supervisor</code> is used when changing the start
│ │ │ │  specification of a supervisor. See <a href="appup_cookbook.xhtml#sup">Appup Cookbook</a>.</p><p>When a module is to be updated, the release handler finds which processes that
│ │ │ │  are <em>using</em> the module by traversing the supervision tree of each running
│ │ │ │ -application and checking all the child specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8064252776-1">{</span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="n">StartFunc</span><span class="p">,</span><span class="w"> </span><span class="n">Restart</span><span class="p">,</span><span class="w"> </span><span class="n">Shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Modules</span><span class="p" data-group-id="8064252776-1">}</span></code></pre><p>A process uses a module if the name is listed in <code class="inline">Modules</code> in the child
│ │ │ │ +application and checking all the child specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2291494489-1">{</span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="n">StartFunc</span><span class="p">,</span><span class="w"> </span><span class="n">Restart</span><span class="p">,</span><span class="w"> </span><span class="n">Shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Modules</span><span class="p" data-group-id="2291494489-1">}</span></code></pre><p>A process uses a module if the name is listed in <code class="inline">Modules</code> in the child
│ │ │ │  specification for the process.</p><p>If <code class="inline">Modules=dynamic</code>, which is the case for event managers, the event manager
│ │ │ │  process informs the release handler about the list of currently installed event
│ │ │ │  handlers (<code class="inline">gen_event</code>), and it is checked if the module name is in this list
│ │ │ │  instead.</p><p>The release handler suspends, asks for code change, and resumes processes by
│ │ │ │  calling the functions <code class="inline">sys:suspend/1,2</code>, <code class="inline">sys:change_code/4,5</code>, and
│ │ │ │  <code class="inline">sys:resume/1,2</code>, respectively.</p><h3 id="add_module-and-delete_module" class="section-heading">
│ │ │ │    <a href="#add_module-and-delete_module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">add_module and delete_module</span>
│ │ │ │  </h3>
│ │ │ │ -<p>If a new module is introduced, the following instruction is used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7578108551-1">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="7578108551-1">}</span></code></pre><p>This instruction loads module <code class="inline">Module</code>. When running Erlang in
│ │ │ │ +<p>If a new module is introduced, the following instruction is used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3365838630-1">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="3365838630-1">}</span></code></pre><p>This instruction loads module <code class="inline">Module</code>. When running Erlang in
│ │ │ │  embedded mode it is necessary to use this this instruction. It is not
│ │ │ │  strictly required when running Erlang in interactive mode, since the
│ │ │ │ -code server automatically searches for and loads unloaded modules.</p><p>The opposite of <code class="inline">add_module</code> is <code class="inline">delete_module</code>, which unloads a module:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9405732812-1">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="9405732812-1">}</span></code></pre><p>Any process, in any application, with <code class="inline">Module</code> as residence module, is
│ │ │ │ +code server automatically searches for and loads unloaded modules.</p><p>The opposite of <code class="inline">add_module</code> is <code class="inline">delete_module</code>, which unloads a module:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7396514273-1">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="7396514273-1">}</span></code></pre><p>Any process, in any application, with <code class="inline">Module</code> as residence module, is
│ │ │ │  killed when the instruction is evaluated. Therefore, the user must
│ │ │ │  ensure that all such processes are terminated before deleting module
│ │ │ │  <code class="inline">Module</code> to avoid a situation with failing supervisor restarts.</p><h3 id="application-instructions" class="section-heading">
│ │ │ │    <a href="#application-instructions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Application Instructions</span>
│ │ │ │ @@ -232,74 +232,74 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Application Upgrade File</span>
│ │ │ │  </h2>
│ │ │ │  <p>To define how to upgrade/downgrade between the current version and previous
│ │ │ │  versions of an application, an <em>application upgrade file</em>, or in short
│ │ │ │  <code class="inline">.appup</code> file is created. The file is to be called <code class="inline">Application.appup</code>, where
│ │ │ │ -<code class="inline">Application</code> is the application name:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="9898028644-1">{</span><span class="no">Vsn</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9898028644-2">[</span><span class="p" data-group-id="9898028644-3">{</span><span class="no">UpFromVsn1</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsU1</span><span class="p" data-group-id="9898028644-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +<code class="inline">Application</code> is the application name:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="9006754601-1">{</span><span class="no">Vsn</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9006754601-2">[</span><span class="p" data-group-id="9006754601-3">{</span><span class="no">UpFromVsn1</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsU1</span><span class="p" data-group-id="9006754601-3">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9898028644-4">{</span><span class="no">UpFromVsnK</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsUK</span><span class="p" data-group-id="9898028644-4">}</span><span class="p" data-group-id="9898028644-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9898028644-5">[</span><span class="p" data-group-id="9898028644-6">{</span><span class="no">DownToVsn1</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsD1</span><span class="p" data-group-id="9898028644-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="9006754601-4">{</span><span class="no">UpFromVsnK</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsUK</span><span class="p" data-group-id="9006754601-4">}</span><span class="p" data-group-id="9006754601-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="9006754601-5">[</span><span class="p" data-group-id="9006754601-6">{</span><span class="no">DownToVsn1</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsD1</span><span class="p" data-group-id="9006754601-6">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9898028644-7">{</span><span class="no">DownToVsnK</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsDK</span><span class="p" data-group-id="9898028644-7">}</span><span class="p" data-group-id="9898028644-5">]</span><span class="p" data-group-id="9898028644-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">Vsn</code>, a string, is the current version of the application, as defined in the
│ │ │ │ +  </span><span class="p" data-group-id="9006754601-7">{</span><span class="no">DownToVsnK</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsDK</span><span class="p" data-group-id="9006754601-7">}</span><span class="p" data-group-id="9006754601-5">]</span><span class="p" data-group-id="9006754601-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">Vsn</code>, a string, is the current version of the application, as defined in the
│ │ │ │  <code class="inline">.app</code> file.</li><li>Each <code class="inline">UpFromVsn</code> is a previous version of the application to upgrade from.</li><li>Each <code class="inline">DownToVsn</code> is a previous version of the application to downgrade to.</li><li>Each <code class="inline">Instructions</code> is a list of release handling instructions.</li></ul><p><code class="inline">UpFromVsn</code> and <code class="inline">DownToVsn</code> can also be specified as regular expressions. For
│ │ │ │  more information about the syntax and contents of the <code class="inline">.appup</code> file, see
│ │ │ │  <a href="../../../lib/sasl/doc/html/appup.xhtml"><code class="inline">appup</code></a> in SASL.</p><p><a href="appup_cookbook.xhtml">Appup Cookbook</a> includes examples of <code class="inline">.appup</code> files for
│ │ │ │  typical upgrade/downgrade cases.</p><p><em>Example:</em> Consider the release <code class="inline">ch_rel-1</code> from
│ │ │ │  <a href="release_structure.xhtml#ch_rel">Releases</a>. Assume you want to add a function
│ │ │ │  <code class="inline">available/0</code> to server <code class="inline">ch3</code>, which returns the number of available channels
│ │ │ │  (when trying out the example, make the change in a copy of the original
│ │ │ │ -directory, to ensure that the first version is still available):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1072427094-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="1072427094-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1072427094-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="1072427094-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +directory, to ensure that the first version is still available):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1315555534-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="1315555534-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1315555534-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="1315555534-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1072427094-3">(</span><span class="p" data-group-id="1072427094-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1072427094-4">]</span><span class="p" data-group-id="1072427094-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1072427094-5">(</span><span class="p" data-group-id="1072427094-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1072427094-6">]</span><span class="p" data-group-id="1072427094-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1072427094-7">(</span><span class="p" data-group-id="1072427094-8">[</span><span class="ss">available</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1072427094-8">]</span><span class="p" data-group-id="1072427094-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1072427094-9">(</span><span class="p" data-group-id="1072427094-10">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1072427094-10">]</span><span class="p" data-group-id="1072427094-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1315555534-3">(</span><span class="p" data-group-id="1315555534-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1315555534-4">]</span><span class="p" data-group-id="1315555534-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1315555534-5">(</span><span class="p" data-group-id="1315555534-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1315555534-6">]</span><span class="p" data-group-id="1315555534-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1315555534-7">(</span><span class="p" data-group-id="1315555534-8">[</span><span class="ss">available</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1315555534-8">]</span><span class="p" data-group-id="1315555534-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1315555534-9">(</span><span class="p" data-group-id="1315555534-10">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1315555534-10">]</span><span class="p" data-group-id="1315555534-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="1072427094-11">(</span><span class="p" data-group-id="1072427094-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1072427094-12">(</span><span class="p" data-group-id="1072427094-13">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1072427094-13">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1072427094-14">[</span><span class="p" data-group-id="1072427094-14">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1072427094-15">[</span><span class="p" data-group-id="1072427094-15">]</span><span class="p" data-group-id="1072427094-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="1315555534-11">(</span><span class="p" data-group-id="1315555534-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1315555534-12">(</span><span class="p" data-group-id="1315555534-13">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1315555534-13">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1315555534-14">[</span><span class="p" data-group-id="1315555534-14">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1315555534-15">[</span><span class="p" data-group-id="1315555534-15">]</span><span class="p" data-group-id="1315555534-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="1072427094-16">(</span><span class="p" data-group-id="1072427094-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1072427094-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="1072427094-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="1315555534-16">(</span><span class="p" data-group-id="1315555534-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1315555534-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="1315555534-17">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="1072427094-18">(</span><span class="n">Ch</span><span class="p" data-group-id="1072427094-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1072427094-19">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1072427094-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="1072427094-20">}</span><span class="p" data-group-id="1072427094-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="1315555534-18">(</span><span class="n">Ch</span><span class="p" data-group-id="1315555534-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1315555534-19">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1315555534-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="1315555534-20">}</span><span class="p" data-group-id="1315555534-19">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">available</span><span class="p" data-group-id="1072427094-21">(</span><span class="p" data-group-id="1072427094-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1072427094-22">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">available</span><span class="p" data-group-id="1072427094-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">available</span><span class="p" data-group-id="1315555534-21">(</span><span class="p" data-group-id="1315555534-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1315555534-22">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">available</span><span class="p" data-group-id="1315555534-22">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1072427094-23">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="1072427094-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1072427094-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="1072427094-25">(</span><span class="p" data-group-id="1072427094-25">)</span><span class="p" data-group-id="1072427094-24">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="1315555534-23">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="1315555534-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1315555534-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="1315555534-25">(</span><span class="p" data-group-id="1315555534-25">)</span><span class="p" data-group-id="1315555534-24">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="1072427094-26">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1072427094-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1072427094-27">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1072427094-27">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="1072427094-28">(</span><span class="n">Chs</span><span class="p" data-group-id="1072427094-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1072427094-29">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1072427094-29">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="1072427094-30">(</span><span class="ss">available</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1072427094-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">available</span><span class="p" data-group-id="1072427094-31">(</span><span class="n">Chs</span><span class="p" data-group-id="1072427094-31">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1072427094-32">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1072427094-32">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="1315555534-26">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1315555534-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1315555534-27">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1315555534-27">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="1315555534-28">(</span><span class="n">Chs</span><span class="p" data-group-id="1315555534-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1315555534-29">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1315555534-29">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="1315555534-30">(</span><span class="ss">available</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1315555534-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">available</span><span class="p" data-group-id="1315555534-31">(</span><span class="n">Chs</span><span class="p" data-group-id="1315555534-31">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1315555534-32">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1315555534-32">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="1072427094-33">(</span><span class="p" data-group-id="1072427094-34">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="1072427094-34">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1072427094-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="1072427094-35">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1072427094-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1072427094-36">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1072427094-36">}</span><span class="p">.</span></code></pre><p>A new version of the <code class="inline">ch_app.app</code> file must now be created, where the version is
│ │ │ │ -updated:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8589832097-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8589832097-2">[</span><span class="p" data-group-id="8589832097-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="8589832097-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8589832097-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="8589832097-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8589832097-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8589832097-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8589832097-6">]</span><span class="p" data-group-id="8589832097-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8589832097-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8589832097-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="8589832097-8">]</span><span class="p" data-group-id="8589832097-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8589832097-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8589832097-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="8589832097-10">]</span><span class="p" data-group-id="8589832097-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="8589832097-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8589832097-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="8589832097-13">[</span><span class="p" data-group-id="8589832097-13">]</span><span class="p" data-group-id="8589832097-12">}</span><span class="p" data-group-id="8589832097-11">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8589832097-2">]</span><span class="p" data-group-id="8589832097-1">}</span><span class="p">.</span></code></pre><p>To upgrade <code class="inline">ch_app</code> from <code class="inline">&quot;1&quot;</code> to <code class="inline">&quot;2&quot;</code> (and to downgrade from <code class="inline">&quot;2&quot;</code> to <code class="inline">&quot;1&quot;</code>),
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="1315555534-33">(</span><span class="p" data-group-id="1315555534-34">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="1315555534-34">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1315555534-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="1315555534-35">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1315555534-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1315555534-36">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1315555534-36">}</span><span class="p">.</span></code></pre><p>A new version of the <code class="inline">ch_app.app</code> file must now be created, where the version is
│ │ │ │ +updated:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0213360596-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0213360596-2">[</span><span class="p" data-group-id="0213360596-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="0213360596-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0213360596-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="0213360596-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0213360596-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0213360596-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0213360596-6">]</span><span class="p" data-group-id="0213360596-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0213360596-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0213360596-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="0213360596-8">]</span><span class="p" data-group-id="0213360596-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0213360596-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0213360596-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="0213360596-10">]</span><span class="p" data-group-id="0213360596-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0213360596-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0213360596-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="0213360596-13">[</span><span class="p" data-group-id="0213360596-13">]</span><span class="p" data-group-id="0213360596-12">}</span><span class="p" data-group-id="0213360596-11">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0213360596-2">]</span><span class="p" data-group-id="0213360596-1">}</span><span class="p">.</span></code></pre><p>To upgrade <code class="inline">ch_app</code> from <code class="inline">&quot;1&quot;</code> to <code class="inline">&quot;2&quot;</code> (and to downgrade from <code class="inline">&quot;2&quot;</code> to <code class="inline">&quot;1&quot;</code>),
│ │ │ │  you only need to load the new (old) version of the <code class="inline">ch3</code> callback module. Create
│ │ │ │ -the application upgrade file <code class="inline">ch_app.appup</code> in the <code class="inline">ebin</code> directory:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6067355296-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6067355296-2">[</span><span class="p" data-group-id="6067355296-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6067355296-4">[</span><span class="p" data-group-id="6067355296-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6067355296-5">}</span><span class="p" data-group-id="6067355296-4">]</span><span class="p" data-group-id="6067355296-3">}</span><span class="p" data-group-id="6067355296-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6067355296-6">[</span><span class="p" data-group-id="6067355296-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6067355296-8">[</span><span class="p" data-group-id="6067355296-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6067355296-9">}</span><span class="p" data-group-id="6067355296-8">]</span><span class="p" data-group-id="6067355296-7">}</span><span class="p" data-group-id="6067355296-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6067355296-1">}</span><span class="p">.</span></code></pre><p><a href="" id="relup"></a></p><h2 id="release-upgrade-file" class="section-heading">
│ │ │ │ +the application upgrade file <code class="inline">ch_app.appup</code> in the <code class="inline">ebin</code> directory:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5492737769-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5492737769-2">[</span><span class="p" data-group-id="5492737769-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5492737769-4">[</span><span class="p" data-group-id="5492737769-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="5492737769-5">}</span><span class="p" data-group-id="5492737769-4">]</span><span class="p" data-group-id="5492737769-3">}</span><span class="p" data-group-id="5492737769-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5492737769-6">[</span><span class="p" data-group-id="5492737769-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5492737769-8">[</span><span class="p" data-group-id="5492737769-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="5492737769-9">}</span><span class="p" data-group-id="5492737769-8">]</span><span class="p" data-group-id="5492737769-7">}</span><span class="p" data-group-id="5492737769-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5492737769-1">}</span><span class="p">.</span></code></pre><p><a href="" id="relup"></a></p><h2 id="release-upgrade-file" class="section-heading">
│ │ │ │    <a href="#release-upgrade-file" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Release Upgrade File</span>
│ │ │ │  </h2>
│ │ │ │  <p>To define how to upgrade/downgrade between the new version and previous versions
│ │ │ │  of a release, a <em>release upgrade file</em>, or in short <code class="inline">.relup</code> file, is to be
│ │ │ │ @@ -310,22 +310,22 @@
│ │ │ │  are to be added and deleted, and which applications that must be upgraded and/or
│ │ │ │  downgraded. The instructions for this are fetched from the <code class="inline">.appup</code> files and
│ │ │ │  transformed into a single list of low-level instructions in the right order.</p><p>If the <code class="inline">relup</code> file is relatively simple, it can be created manually. It is only
│ │ │ │  to contain low-level instructions.</p><p>For details about the syntax and contents of the release upgrade file, see
│ │ │ │  <a href="../../../lib/sasl/doc/html/relup.xhtml"><code class="inline">relup</code></a> in SASL.</p><p><em>Example, continued from the previous section:</em> You have a new version &quot;2&quot; of
│ │ │ │  <code class="inline">ch_app</code> and an <code class="inline">.appup</code> file. A new version of the <code class="inline">.rel</code> file is also needed.
│ │ │ │  This time the file is called <code class="inline">ch_rel-2.rel</code> and the release version string is
│ │ │ │ -changed from &quot;A&quot; to &quot;B&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6333263459-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6333263459-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="6333263459-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6333263459-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="6333263459-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6333263459-4">[</span><span class="p" data-group-id="6333263459-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="6333263459-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6333263459-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="6333263459-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6333263459-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="6333263459-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="6333263459-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="6333263459-8">}</span><span class="p" data-group-id="6333263459-4">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6333263459-1">}</span><span class="p">.</span></code></pre><p>Now the <code class="inline">relup</code> file can be generated:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;]).
│ │ │ │ +changed from &quot;A&quot; to &quot;B&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7664828558-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7664828558-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="7664828558-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7664828558-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="7664828558-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7664828558-4">[</span><span class="p" data-group-id="7664828558-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="7664828558-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7664828558-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="7664828558-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7664828558-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="7664828558-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7664828558-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="7664828558-8">}</span><span class="p" data-group-id="7664828558-4">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7664828558-1">}</span><span class="p">.</span></code></pre><p>Now the <code class="inline">relup</code> file can be generated:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;]).
│ │ │ │  ok</code></pre><p>This generates a <code class="inline">relup</code> file with instructions for how to upgrade from version
│ │ │ │  &quot;A&quot; (&quot;ch_rel-1&quot;) to version &quot;B&quot; (&quot;ch_rel-2&quot;) and how to downgrade from version
│ │ │ │  &quot;B&quot; to version &quot;A&quot;.</p><p>Both the old and new versions of the <code class="inline">.app</code> and <code class="inline">.rel</code> files must be in the code
│ │ │ │  path, as well as the <code class="inline">.appup</code> and (new) <code class="inline">.beam</code> files. The code path can be
│ │ │ │  extended by using the option <code class="inline">path</code>:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;],
│ │ │ │  [{path,[&quot;../ch_rel-1&quot;,
│ │ │ │  &quot;../ch_rel-1/lib/ch_app-1/ebin&quot;]}]).
│ │ │ │ @@ -338,25 +338,25 @@
│ │ │ │  <p>When you have made a new version of a release, a release package can be created
│ │ │ │  with this new version and transferred to the target environment.</p><p>To install the new version of the release in runtime, the <em>release
│ │ │ │  handler</em> is used. This is a process belonging to the SASL application,
│ │ │ │  which handles unpacking, installation, and removal of release
│ │ │ │  packages. The <a href="../../../lib/sasl/doc/html/release_handler.html"><code class="inline">release_handler</code></a> module communicates with this process.</p><p>Assuming there is an operational target system with installation root directory
│ │ │ │  <code class="inline">$ROOT</code>, the release package with the new version of the release is to be copied
│ │ │ │  to <code class="inline">$ROOT/releases</code>.</p><p>First, <em>unpack</em> the release package. The files are then extracted from the
│ │ │ │ -package:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="8992337726-1">(</span><span class="n">ReleaseName</span><span class="p" data-group-id="8992337726-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8992337726-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p" data-group-id="8992337726-2">}</span></code></pre><ul><li><code class="inline">ReleaseName</code> is the name of the release package except the <code class="inline">.tar.gz</code>
│ │ │ │ +package:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="8062393637-1">(</span><span class="n">ReleaseName</span><span class="p" data-group-id="8062393637-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8062393637-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p" data-group-id="8062393637-2">}</span></code></pre><ul><li><code class="inline">ReleaseName</code> is the name of the release package except the <code class="inline">.tar.gz</code>
│ │ │ │  extension.</li><li><code class="inline">Vsn</code> is the version of the unpacked release, as defined in its <code class="inline">.rel</code> file.</li></ul><p>A directory <code class="inline">$ROOT/lib/releases/Vsn</code> is created, where the <code class="inline">.rel</code> file, the boot
│ │ │ │  script <code class="inline">start.boot</code>, the system configuration file <code class="inline">sys.config</code>, and <code class="inline">relup</code> are
│ │ │ │  placed. For applications with new version numbers, the application directories
│ │ │ │  are placed under <code class="inline">$ROOT/lib</code>. Unchanged applications are not affected.</p><p>An unpacked release can be <em>installed</em>. The release handler then evaluates the
│ │ │ │ -instructions in <code class="inline">relup</code>, step by step:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="8647268471-1">(</span><span class="n">Vsn</span><span class="p" data-group-id="8647268471-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8647268471-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FromVsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8647268471-3">[</span><span class="p" data-group-id="8647268471-3">]</span><span class="p" data-group-id="8647268471-2">}</span></code></pre><p>If an error occurs during the installation, the system is rebooted using the old
│ │ │ │ +instructions in <code class="inline">relup</code>, step by step:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="2734683002-1">(</span><span class="n">Vsn</span><span class="p" data-group-id="2734683002-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2734683002-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FromVsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2734683002-3">[</span><span class="p" data-group-id="2734683002-3">]</span><span class="p" data-group-id="2734683002-2">}</span></code></pre><p>If an error occurs during the installation, the system is rebooted using the old
│ │ │ │  version of the release. If installation succeeds, the system is afterwards using
│ │ │ │  the new version of the release, but if anything happens and the system is
│ │ │ │  rebooted, it starts using the previous version again.</p><p>To be made the default version, the newly installed release must be made
│ │ │ │  <em>permanent</em>, which means the previous version becomes <em>old</em>:</p><pre><code class="text">release_handler:make_permanent(Vsn) =&gt; ok</code></pre><p>The system keeps information about which versions are old and permanent in the
│ │ │ │ -files <code class="inline">$ROOT/releases/RELEASES</code> and <code class="inline">$ROOT/releases/start_erl.data</code>.</p><p>To downgrade from <code class="inline">Vsn</code> to <code class="inline">FromVsn</code>, <code class="inline">install_release</code> must be called again:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="1803806475-1">(</span><span class="n">FromVsn</span><span class="p" data-group-id="1803806475-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1803806475-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1803806475-3">[</span><span class="p" data-group-id="1803806475-3">]</span><span class="p" data-group-id="1803806475-2">}</span></code></pre><p>An installed, but not permanent, release can be <em>removed</em>. Information about the
│ │ │ │ +files <code class="inline">$ROOT/releases/RELEASES</code> and <code class="inline">$ROOT/releases/start_erl.data</code>.</p><p>To downgrade from <code class="inline">Vsn</code> to <code class="inline">FromVsn</code>, <code class="inline">install_release</code> must be called again:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="4691297193-1">(</span><span class="n">FromVsn</span><span class="p" data-group-id="4691297193-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4691297193-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4691297193-3">[</span><span class="p" data-group-id="4691297193-3">]</span><span class="p" data-group-id="4691297193-2">}</span></code></pre><p>An installed, but not permanent, release can be <em>removed</em>. Information about the
│ │ │ │  release is then deleted from <code class="inline">$ROOT/releases/RELEASES</code> and the release-specific
│ │ │ │  code, that is, the new application directories and the <code class="inline">$ROOT/releases/Vsn</code>
│ │ │ │  directory, are removed.</p><pre><code class="text">release_handler:remove_release(Vsn) =&gt; ok</code></pre><h3 id="example-continued-from-the-previous-sections" class="section-heading">
│ │ │ │    <a href="#example-continued-from-the-previous-sections" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example (continued from the previous sections)</span>
│ │ │ │ @@ -367,17 +367,17 @@
│ │ │ │  is needed, the file is to contain the empty list:</p><pre><code class="text">[].</code></pre><p><em>Step 2)</em> Start the system as a simple target system. In reality, it is to be
│ │ │ │  started as an embedded system. However, using <code class="inline">erl</code> with the correct boot script
│ │ │ │  and config file is enough for illustration purposes:</p><pre><code class="text">% cd $ROOT
│ │ │ │  % bin/erl -boot $ROOT/releases/A/start -config $ROOT/releases/A/sys
│ │ │ │  ...</code></pre><p><code class="inline">$ROOT</code> is the installation directory of the target system.</p><p><em>Step 3)</em> In another Erlang shell, generate start scripts and create a release
│ │ │ │  package for the new version <code class="inline">&quot;B&quot;</code>. Remember to include (a possible updated)
│ │ │ │  <code class="inline">sys.config</code> and the <code class="inline">relup</code> file. For more information, see
│ │ │ │ -<a href="release_handling.xhtml#relup">Release Upgrade File</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="9701748015-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="9701748015-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<a href="release_handling.xhtml#relup">Release Upgrade File</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="7621747933-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="7621747933-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="9701748015-2">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="9701748015-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="7621747933-2">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="7621747933-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>The new release package now also contains version &quot;2&quot; of <code class="inline">ch_app</code> and the
│ │ │ │  <code class="inline">relup</code> file:</p><pre><code class="text">% tar tf ch_rel-2.tar
│ │ │ │  lib/kernel-9.2.4/ebin/kernel.app
│ │ │ │  lib/kernel-9.2.4/ebin/application.beam
│ │ │ │  ...
│ │ │ │  lib/stdlib-5.2.3/ebin/stdlib.app
│ │ │ │  lib/stdlib-5.2.3/ebin/argparse.beam
│ │ │ │ @@ -390,31 +390,31 @@
│ │ │ │  lib/ch_app-2/ebin/ch_sup.beam
│ │ │ │  lib/ch_app-2/ebin/ch3.beam
│ │ │ │  releases/B/start.boot
│ │ │ │  releases/B/relup
│ │ │ │  releases/B/sys.config
│ │ │ │  releases/B/ch_rel-2.rel
│ │ │ │  releases/ch_rel-2.rel</code></pre><p><em>Step 4)</em> Copy the release package <code class="inline">ch_rel-2.tar.gz</code> to the <code class="inline">$ROOT/releases</code>
│ │ │ │ -directory.</p><p><em>Step 5)</em> In the running target system, unpack the release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="0510970129-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="0510970129-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0510970129-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="0510970129-2">}</span></code></pre><p>The new application version <code class="inline">ch_app-2</code> is installed under <code class="inline">$ROOT/lib</code> next to
│ │ │ │ +directory.</p><p><em>Step 5)</em> In the running target system, unpack the release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="3010671614-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="3010671614-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3010671614-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="3010671614-2">}</span></code></pre><p>The new application version <code class="inline">ch_app-2</code> is installed under <code class="inline">$ROOT/lib</code> next to
│ │ │ │  <code class="inline">ch_app-1</code>. The <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code> directories are not affected, as
│ │ │ │  they have not changed.</p><p>Under <code class="inline">$ROOT/releases</code>, a new directory <code class="inline">B</code> is created, containing
│ │ │ │ -<code class="inline">ch_rel-2.rel</code>, <code class="inline">start.boot</code>, <code class="inline">sys.config</code>, and <code class="inline">relup</code>.</p><p><em>Step 6)</em> Check if the function <code class="inline">ch3:available/0</code> is available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="7525194756-1">(</span><span class="p" data-group-id="7525194756-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">ch_rel-2.rel</code>, <code class="inline">start.boot</code>, <code class="inline">sys.config</code>, and <code class="inline">relup</code>.</p><p><em>Step 6)</em> Check if the function <code class="inline">ch3:available/0</code> is available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="9834924616-1">(</span><span class="p" data-group-id="9834924616-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: undefined function ch3:available/0</span></code></pre><p><em>Step 7)</em> Install the new release. The instructions in <code class="inline">$ROOT/releases/B/relup</code>
│ │ │ │  are executed one by one, resulting in the new version of <code class="inline">ch3</code> being loaded. The
│ │ │ │ -function <code class="inline">ch3:available/0</code> is now available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="6657650121-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="6657650121-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6657650121-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="p" data-group-id="6657650121-3">[</span><span class="p" data-group-id="6657650121-3">]</span><span class="p" data-group-id="6657650121-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="6657650121-4">(</span><span class="p" data-group-id="6657650121-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +function <code class="inline">ch3:available/0</code> is now available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="8153687155-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="8153687155-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8153687155-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="p" data-group-id="8153687155-3">[</span><span class="p" data-group-id="8153687155-3">]</span><span class="p" data-group-id="8153687155-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="8153687155-4">(</span><span class="p" data-group-id="8153687155-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="6657650121-5">(</span><span class="ss">ch3</span><span class="p" data-group-id="6657650121-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="8153687155-5">(</span><span class="ss">ch3</span><span class="p" data-group-id="8153687155-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;.../lib/ch_app-2/ebin/ch3.beam&quot;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="6657650121-6">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="6657650121-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="8153687155-6">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="8153687155-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;.../lib/ch_app-1/ebin/ch_sup.beam&quot;</span></code></pre><p>Processes in <code class="inline">ch_app</code> for which code have not been updated, for example, the
│ │ │ │  supervisor, are still evaluating code from <code class="inline">ch_app-1</code>.</p><p><em>Step 8)</em> If the target system is now rebooted, it uses version &quot;A&quot; again. The
│ │ │ │ -&quot;B&quot; version must be made permanent, to be used when the system is rebooted.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">make_permanent</span><span class="p" data-group-id="7633064803-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="7633064803-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +&quot;B&quot; version must be made permanent, to be used when the system is rebooted.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">make_permanent</span><span class="p" data-group-id="1449996855-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="1449996855-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p><a href="" id="sys"></a></p><h2 id="updating-application-specifications" class="section-heading">
│ │ │ │    <a href="#updating-application-specifications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Updating Application Specifications</span>
│ │ │ │  </h2>
│ │ │ │  <p>When a new version of a release is installed, the application specifications are
│ │ │ │ @@ -423,14 +423,14 @@
│ │ │ │  boot script is generated from the same <code class="inline">.rel</code> file as is used to build the
│ │ │ │  release package itself.</p></section><p>Specifically, the application configuration parameters are automatically updated
│ │ │ │  according to (in increasing priority order):</p><ul><li>The data in the boot script, fetched from the new application resource file
│ │ │ │  <code class="inline">App.app</code></li><li>The new <code class="inline">sys.config</code></li><li>Command-line arguments <code class="inline">-App Par Val</code></li></ul><p>This means that parameter values set in the other system configuration files and
│ │ │ │  values set using <a href="../../../lib/kernel/doc/html/application.html#set_env/3"><code class="inline">application:set_env/3</code></a> are disregarded.</p><p>When an installed release is made permanent, the system process <code class="inline">init</code> is set to
│ │ │ │  point out the new <code class="inline">sys.config</code>.</p><p>After the installation, the application controller compares the old and new
│ │ │ │  configuration parameters for all running applications and call the callback
│ │ │ │ -function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">config_change</span><span class="p" data-group-id="0118592077-1">(</span><span class="n">Changed</span><span class="p">,</span><span class="w"> </span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Removed</span><span class="p" data-group-id="0118592077-1">)</span></code></pre><ul><li><code class="inline">Module</code> is the application callback module as defined by the <code class="inline">mod</code> key in the
│ │ │ │ +function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">config_change</span><span class="p" data-group-id="6030842799-1">(</span><span class="n">Changed</span><span class="p">,</span><span class="w"> </span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Removed</span><span class="p" data-group-id="6030842799-1">)</span></code></pre><ul><li><code class="inline">Module</code> is the application callback module as defined by the <code class="inline">mod</code> key in the
│ │ │ │  <code class="inline">.app</code> file.</li><li><code class="inline">Changed</code> and <code class="inline">New</code> are lists of <code class="inline">{Par,Val}</code> for all changed and added
│ │ │ │  configuration parameters, respectively.</li><li><code class="inline">Removed</code> is a list of all parameters <code class="inline">Par</code> that have been removed.</li></ul><p>The function is optional and can be omitted when implementing an application
│ │ │ │  callback module.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/ref_man_records.xhtml
│ │ │ │ @@ -28,17 +28,17 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Defining Records</span>
│ │ │ │  </h2>
│ │ │ │  <p>A record definition consists of the name of the record, followed by the field
│ │ │ │  names of the record. Record and field names must be atoms. Each field can be
│ │ │ │  given an optional default value. If no default value is supplied, <code class="inline">undefined</code> is
│ │ │ │ -used.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1646236029-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1646236029-2">{</span><span class="n">Field1</span><span class="w"> </span><span class="p" data-group-id="1646236029-3">[</span><span class="o">=</span><span class="w"> </span><span class="n">Expr1</span><span class="p" data-group-id="1646236029-3">]</span><span class="p">,</span><span class="w">
│ │ │ │ +used.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1067666367-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1067666367-2">{</span><span class="n">Field1</span><span class="w"> </span><span class="p" data-group-id="1067666367-3">[</span><span class="o">=</span><span class="w"> </span><span class="n">Expr1</span><span class="p" data-group-id="1067666367-3">]</span><span class="p">,</span><span class="w">
│ │ │ │                 </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -               </span><span class="n">FieldN</span><span class="w"> </span><span class="p" data-group-id="1646236029-4">[</span><span class="o">=</span><span class="w"> </span><span class="n">ExprN</span><span class="p" data-group-id="1646236029-4">]</span><span class="p" data-group-id="1646236029-2">}</span><span class="p" data-group-id="1646236029-1">)</span><span class="p">.</span></code></pre><p>The default value for a field is an arbitrary expression, except that it must
│ │ │ │ +               </span><span class="n">FieldN</span><span class="w"> </span><span class="p" data-group-id="1067666367-4">[</span><span class="o">=</span><span class="w"> </span><span class="n">ExprN</span><span class="p" data-group-id="1067666367-4">]</span><span class="p" data-group-id="1067666367-2">}</span><span class="p" data-group-id="1067666367-1">)</span><span class="p">.</span></code></pre><p>The default value for a field is an arbitrary expression, except that it must
│ │ │ │  not use any variables.</p><p>A record definition can be placed anywhere among the attributes and function
│ │ │ │  declarations of a module, but the definition must come before any usage of the
│ │ │ │  record.</p><p>If a record is used in several modules, it is recommended that the record
│ │ │ │  definition is placed in an include file.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Starting from Erlang/OTP 26, records can be defined in the Erlang shell
│ │ │ │  using the syntax described in this section. In earlier releases, it was
│ │ │ │  necessary to use the <a href="../../../lib/stdlib/doc/html/shell.html"><code class="inline">shell</code></a> built-in function <code class="inline">rd/2</code>.</p></section><h2 id="creating-records" class="section-heading">
│ │ │ │    <a href="#creating-records" class="hover-link">
│ │ │ │ @@ -48,32 +48,32 @@
│ │ │ │  </h2>
│ │ │ │  <p>The following expression creates a new <code class="inline">Name</code> record where the value of each
│ │ │ │  field <code class="inline">FieldI</code> is the value of evaluating the corresponding expression <code class="inline">ExprI</code>:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p>The fields can be in any order, not necessarily the same order as in the record
│ │ │ │  definition, and fields can be omitted. Omitted fields get their respective
│ │ │ │  default value instead.</p><p>If several fields are to be assigned the same value, the following construction
│ │ │ │  can be used:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK, _=ExprL}</code></pre><p>Omitted fields then get the value of evaluating <code class="inline">ExprL</code> instead of their default
│ │ │ │  values. This feature is primarily intended to be used to create patterns for ETS
│ │ │ │ -and Mnesia match functions.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5641955214-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5641955214-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="5641955214-2">}</span><span class="p" data-group-id="5641955214-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +and Mnesia match functions.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7767298572-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7767298572-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="7767298572-2">}</span><span class="p" data-group-id="7767298572-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="5641955214-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="5641955214-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="5641955214-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5641955214-5">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="5641955214-5">}</span><span class="p" data-group-id="5641955214-4">)</span><span class="p">.</span></code></pre><h2 id="accessing-record-fields" class="section-heading">
│ │ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="7767298572-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="7767298572-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="7767298572-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7767298572-5">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="7767298572-5">}</span><span class="p" data-group-id="7767298572-4">)</span><span class="p">.</span></code></pre><h2 id="accessing-record-fields" class="section-heading">
│ │ │ │    <a href="#accessing-record-fields" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Accessing Record Fields</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="text">Expr#Name.Field</code></pre><p>Returns the value of the specified field. <code class="inline">Expr</code> is to evaluate to a <code class="inline">Name</code>
│ │ │ │ -record.</p><p><em>Example</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0705080745-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0705080745-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="0705080745-2">}</span><span class="p" data-group-id="0705080745-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +record.</p><p><em>Example</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3563161215-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3563161215-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="3563161215-2">}</span><span class="p" data-group-id="3563161215-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">get_person_name</span><span class="p" data-group-id="0705080745-3">(</span><span class="n">Person</span><span class="p" data-group-id="0705080745-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">get_person_name</span><span class="p" data-group-id="3563161215-3">(</span><span class="n">Person</span><span class="p" data-group-id="3563161215-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">.</span></code></pre><p>The following expression returns the position of the specified field in the
│ │ │ │ -tuple representation of the record:</p><pre><code class="text">#Name.Field</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6803974189-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6803974189-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="6803974189-2">}</span><span class="p" data-group-id="6803974189-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +tuple representation of the record:</p><pre><code class="text">#Name.Field</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8742848418-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8742848418-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="8742848418-2">}</span><span class="p" data-group-id="8742848418-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="6803974189-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6803974189-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="6803974189-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6803974189-4">)</span><span class="p">.</span></code></pre><h2 id="updating-records" class="section-heading">
│ │ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="8742848418-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="8742848418-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="8742848418-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="8742848418-4">)</span><span class="p">.</span></code></pre><h2 id="updating-records" class="section-heading">
│ │ │ │    <a href="#updating-records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Updating Records</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="text">Expr#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p><code class="inline">Expr</code> is to evaluate to a <code class="inline">Name</code> record. A copy of this record is returned,
│ │ │ │  with the value of each specified field <code class="inline">FieldI</code> changed to the value of
│ │ │ │ @@ -83,48 +83,48 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Records in Guards</span>
│ │ │ │  </h2>
│ │ │ │  <p>Since record expressions are expanded to tuple expressions, creating
│ │ │ │  records and accessing record fields are allowed in guards. However,
│ │ │ │  all subexpressions (for initializing fields), must be valid guard
│ │ │ │ -expressions as well.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="4533777063-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4533777063-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Msg</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">#</span><span class="ss">msg</span><span class="p" data-group-id="4533777063-2">{</span><span class="ss">to</span><span class="o">=</span><span class="ss">void</span><span class="p">,</span><span class="w"> </span><span class="ss">no</span><span class="o">=</span><span class="mi">3</span><span class="p" data-group-id="4533777063-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +expressions as well.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="5085919990-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5085919990-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Msg</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">#</span><span class="ss">msg</span><span class="p" data-group-id="5085919990-2">{</span><span class="ss">to</span><span class="o">=</span><span class="ss">void</span><span class="p">,</span><span class="w"> </span><span class="ss">no</span><span class="o">=</span><span class="mi">3</span><span class="p" data-group-id="5085919990-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle</span><span class="p" data-group-id="4533777063-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4533777063-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">running</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>There is also a type test BIF <a href="../../../lib/../erts/doc/html/erlang.html#is_record/2"><code class="inline">is_record(Term, RecordTag)</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_person</span><span class="p" data-group-id="7200113665-1">(</span><span class="n">P</span><span class="p" data-group-id="7200113665-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="7200113665-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="7200113665-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle</span><span class="p" data-group-id="5085919990-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5085919990-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">running</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>There is also a type test BIF <a href="../../../lib/../erts/doc/html/erlang.html#is_record/2"><code class="inline">is_record(Term, RecordTag)</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_person</span><span class="p" data-group-id="3870474565-1">(</span><span class="n">P</span><span class="p" data-group-id="3870474565-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="3870474565-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="3870474565-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">is_person</span><span class="p" data-group-id="7200113665-3">(</span><span class="p">_</span><span class="n">P</span><span class="p" data-group-id="7200113665-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">is_person</span><span class="p" data-group-id="3870474565-3">(</span><span class="p">_</span><span class="n">P</span><span class="p" data-group-id="3870474565-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">false</span><span class="p">.</span></code></pre><h2 id="records-in-patterns" class="section-heading">
│ │ │ │    <a href="#records-in-patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Records in Patterns</span>
│ │ │ │  </h2>
│ │ │ │  <p>A pattern that matches a certain record is created in the same way as a record
│ │ │ │  is created:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p>In this case, one or more of <code class="inline">Expr1</code> ... <code class="inline">ExprK</code> can be unbound variables.</p><h2 id="nested-records" class="section-heading">
│ │ │ │    <a href="#nested-records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Nested Records</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Assume the following record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3443216790-1">(</span><span class="ss">nrec0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3443216790-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested0&quot;</span><span class="p" data-group-id="3443216790-2">}</span><span class="p" data-group-id="3443216790-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3443216790-3">(</span><span class="ss">nrec1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3443216790-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec0</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec0</span><span class="p" data-group-id="3443216790-5">{</span><span class="p" data-group-id="3443216790-5">}</span><span class="p" data-group-id="3443216790-4">}</span><span class="p" data-group-id="3443216790-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3443216790-6">(</span><span class="ss">nrec2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3443216790-7">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested2&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec1</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec1</span><span class="p" data-group-id="3443216790-8">{</span><span class="p" data-group-id="3443216790-8">}</span><span class="p" data-group-id="3443216790-7">}</span><span class="p" data-group-id="3443216790-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>Assume the following record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8572706141-1">(</span><span class="ss">nrec0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8572706141-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested0&quot;</span><span class="p" data-group-id="8572706141-2">}</span><span class="p" data-group-id="8572706141-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8572706141-3">(</span><span class="ss">nrec1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8572706141-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec0</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec0</span><span class="p" data-group-id="8572706141-5">{</span><span class="p" data-group-id="8572706141-5">}</span><span class="p" data-group-id="8572706141-4">}</span><span class="p" data-group-id="8572706141-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8572706141-6">(</span><span class="ss">nrec2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8572706141-7">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested2&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec1</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec1</span><span class="p" data-group-id="8572706141-8">{</span><span class="p" data-group-id="8572706141-8">}</span><span class="p" data-group-id="8572706141-7">}</span><span class="p" data-group-id="8572706141-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">N2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">nrec2</span><span class="p" data-group-id="3443216790-9">{</span><span class="p" data-group-id="3443216790-9">}</span><span class="p">,</span></code></pre><p>Accessing or updating nested records can be written without parentheses:</p><pre><code class="text">&quot;nested0&quot; = N2#nrec2.nrec1#nrec1.nrec0#nrec0.name,
│ │ │ │ +</span><span class="n">N2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">nrec2</span><span class="p" data-group-id="8572706141-9">{</span><span class="p" data-group-id="8572706141-9">}</span><span class="p">,</span></code></pre><p>Accessing or updating nested records can be written without parentheses:</p><pre><code class="text">&quot;nested0&quot; = N2#nrec2.nrec1#nrec1.nrec0#nrec0.name,
│ │ │ │      N0n = N2#nrec2.nrec1#nrec1.nrec0#nrec0{name = &quot;nested0a&quot;},</code></pre><p>which is equivalent to:</p><pre><code class="text">&quot;nested0&quot; = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0.name,
│ │ │ │  N0n = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0{name = &quot;nested0a&quot;},</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R14, parentheses were necessary when accessing or updating
│ │ │ │  nested records.</p></section><h2 id="internal-representation-of-records" class="section-heading">
│ │ │ │    <a href="#internal-representation-of-records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Internal Representation of Records</span>
│ │ │ │  </h2>
│ │ │ │  <p>Record expressions are translated to tuple expressions during compilation. A
│ │ │ │ -record defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8059668870-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8059668870-2">{</span><span class="n">Field1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">FieldN</span><span class="p" data-group-id="8059668870-2">}</span><span class="p" data-group-id="8059668870-1">)</span><span class="p">.</span></code></pre><p>is internally represented by the tuple:</p><pre><code class="text">{Name, Value1, ..., ValueN}</code></pre><p>Here each <code class="inline">ValueI</code> is the default value for <code class="inline">FieldI</code>.</p><p>To each module using records, a pseudo function is added during compilation to
│ │ │ │ -obtain information about records:</p><pre><code class="makeup erlang" translate="no"><span class="nf">record_info</span><span class="p" data-group-id="8037417058-1">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="8037417058-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8037417058-2">[</span><span class="n">Field</span><span class="p" data-group-id="8037417058-2">]</span><span class="w">
│ │ │ │ -</span><span class="nf">record_info</span><span class="p" data-group-id="8037417058-3">(</span><span class="nb">size</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="8037417058-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Size</span></code></pre><p><code class="inline">Size</code> is the size of the tuple representation, that is, one more than the
│ │ │ │ +record defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6141706480-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6141706480-2">{</span><span class="n">Field1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">FieldN</span><span class="p" data-group-id="6141706480-2">}</span><span class="p" data-group-id="6141706480-1">)</span><span class="p">.</span></code></pre><p>is internally represented by the tuple:</p><pre><code class="text">{Name, Value1, ..., ValueN}</code></pre><p>Here each <code class="inline">ValueI</code> is the default value for <code class="inline">FieldI</code>.</p><p>To each module using records, a pseudo function is added during compilation to
│ │ │ │ +obtain information about records:</p><pre><code class="makeup erlang" translate="no"><span class="nf">record_info</span><span class="p" data-group-id="0433985633-1">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="0433985633-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0433985633-2">[</span><span class="n">Field</span><span class="p" data-group-id="0433985633-2">]</span><span class="w">
│ │ │ │ +</span><span class="nf">record_info</span><span class="p" data-group-id="0433985633-3">(</span><span class="nb">size</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="0433985633-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Size</span></code></pre><p><code class="inline">Size</code> is the size of the tuple representation, that is, one more than the
│ │ │ │  number of fields.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/ref_man_processes.xhtml
│ │ │ │ @@ -30,18 +30,18 @@
│ │ │ │  (grow and shrink dynamically) with small memory footprint, fast to create and
│ │ │ │  terminate, and the scheduling overhead is low.</p><h2 id="process-creation" class="section-heading">
│ │ │ │    <a href="#process-creation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Process Creation</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A process is created by calling <a href="../../../lib/../erts/doc/html/erlang.html#spawn/3"><code class="inline">spawn()</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="9030359381-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="9030359381-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pid</span><span class="p" data-group-id="9030359381-2">(</span><span class="p" data-group-id="9030359381-2">)</span><span class="w">
│ │ │ │ -  </span><span class="n">Module</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="9030359381-3">(</span><span class="p" data-group-id="9030359381-3">)</span><span class="w">
│ │ │ │ -  </span><span class="n">Args</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9030359381-4">[</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="9030359381-4">]</span><span class="w">
│ │ │ │ -    </span><span class="n">ArgI</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="9030359381-5">(</span><span class="p" data-group-id="9030359381-5">)</span></code></pre><p><code class="inline">spawn()</code> creates a new process and returns the pid.</p><p>The new process starts executing in <code class="inline">Module:Name(Arg1,...,ArgN)</code> where the
│ │ │ │ +<p>A process is created by calling <a href="../../../lib/../erts/doc/html/erlang.html#spawn/3"><code class="inline">spawn()</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="2358555913-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="2358555913-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pid</span><span class="p" data-group-id="2358555913-2">(</span><span class="p" data-group-id="2358555913-2">)</span><span class="w">
│ │ │ │ +  </span><span class="n">Module</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="2358555913-3">(</span><span class="p" data-group-id="2358555913-3">)</span><span class="w">
│ │ │ │ +  </span><span class="n">Args</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2358555913-4">[</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="2358555913-4">]</span><span class="w">
│ │ │ │ +    </span><span class="n">ArgI</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2358555913-5">(</span><span class="p" data-group-id="2358555913-5">)</span></code></pre><p><code class="inline">spawn()</code> creates a new process and returns the pid.</p><p>The new process starts executing in <code class="inline">Module:Name(Arg1,...,ArgN)</code> where the
│ │ │ │  arguments are the elements of the (possible empty) <code class="inline">Args</code> argument list.</p><p>There exist a number of different <code class="inline">spawn</code> BIFs:</p><ul><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn/4"><code class="inline">spawn/1,2,3,4</code></a></li><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn_link/4"><code class="inline">spawn_link/1,2,3,4</code></a></li><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn_monitor/4"><code class="inline">spawn_monitor/1,2,3,4</code></a></li><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn_opt/5"><code class="inline">spawn_opt/2,3,4,5</code></a></li><li><a href="../../../lib/../erts/doc/html/erlang.html#spawn_request/5"><code class="inline">spawn_request/1,2,3,4,5</code></a></li></ul><h2 id="registered-processes" class="section-heading">
│ │ │ │    <a href="#registered-processes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Registered Processes</span>
│ │ │ │  </h2>
│ │ │ │  <p>Besides addressing a process by using its pid, there are also BIFs for
│ │ │ ├── OEBPS/ref_man_functions.xhtml
│ │ │ │ @@ -25,51 +25,51 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Function Declaration Syntax</span>
│ │ │ │  </h2>
│ │ │ │  <p>A <em>function declaration</em> is a sequence of function clauses separated by
│ │ │ │  semicolons, and terminated by a period (<code class="inline">.</code>).</p><p>A <em>function clause</em> consists of a <em>clause head</em> and a <em>clause body</em>, separated by
│ │ │ │  <code class="inline">-&gt;</code>.</p><p>A clause <em>head</em> consists of the function name, an argument list, and an optional
│ │ │ │ -guard sequence beginning with the keyword <code class="inline">when</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="p" data-group-id="9662691931-1">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="9662691931-1">)</span><span class="w"> </span><span class="p" data-group-id="9662691931-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9662691931-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +guard sequence beginning with the keyword <code class="inline">when</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="p" data-group-id="0718499942-1">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="0718499942-1">)</span><span class="w"> </span><span class="p" data-group-id="0718499942-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="0718499942-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="n">Name</span><span class="p" data-group-id="9662691931-3">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="9662691931-3">)</span><span class="w"> </span><span class="p" data-group-id="9662691931-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="9662691931-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="n">Name</span><span class="p" data-group-id="0718499942-3">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="0718499942-3">)</span><span class="w"> </span><span class="p" data-group-id="0718499942-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="0718499942-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">BodyK</span><span class="p">.</span></code></pre><p>The function name is an atom. Each argument is a pattern.</p><p>The number of arguments <code class="inline">N</code> is the <em>arity</em> of the function. A function is
│ │ │ │  uniquely defined by the module name, function name, and arity. That is, two
│ │ │ │  functions with the same name and in the same module, but with different arities
│ │ │ │  are two different functions.</p><p>A function named <code class="inline">f</code> in module <code class="inline">mod</code> and with arity <code class="inline">N</code> is often denoted as
│ │ │ │  <code class="inline">mod:f/N</code>.</p><p>A clause <em>body</em> consists of a sequence of expressions separated by comma (<code class="inline">,</code>):</p><pre><code class="text">Expr1,
│ │ │ │  ...,
│ │ │ │  ExprN</code></pre><p>Valid Erlang expressions and guard sequences are described in
│ │ │ │ -<a href="expressions.xhtml">Expressions</a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">fact</span><span class="p" data-group-id="0016966627-1">(</span><span class="n">N</span><span class="p" data-group-id="0016966627-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% first clause head</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="0016966627-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0016966627-2">)</span><span class="p">;</span><span class="w">     </span><span class="c1">% first clause body</span><span class="w">
│ │ │ │ +<a href="expressions.xhtml">Expressions</a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">fact</span><span class="p" data-group-id="5214966645-1">(</span><span class="n">N</span><span class="p" data-group-id="5214966645-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% first clause head</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="5214966645-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5214966645-2">)</span><span class="p">;</span><span class="w">     </span><span class="c1">% first clause body</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="0016966627-3">(</span><span class="mi">0</span><span class="p" data-group-id="0016966627-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">             </span><span class="c1">% second clause head</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="5214966645-3">(</span><span class="mi">0</span><span class="p" data-group-id="5214966645-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">             </span><span class="c1">% second clause head</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">.</span><span class="w">                 </span><span class="c1">% second clause body</span></code></pre><p><a href="" id="eval"></a></p><h2 id="function-evaluation" class="section-heading">
│ │ │ │    <a href="#function-evaluation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Function Evaluation</span>
│ │ │ │  </h2>
│ │ │ │  <p>When a function <code class="inline">M:F/N</code> is called, first the code for the function is located.
│ │ │ │  If the function cannot be found, an <code class="inline">undef</code> runtime error occurs. Notice that
│ │ │ │  the function must be exported to be visible outside the module it is defined in.</p><p>If the function is found, the function clauses are scanned sequentially until a
│ │ │ │  clause is found that fulfills both of the following two conditions:</p><ol><li>The patterns in the clause head can be successfully matched against the given
│ │ │ │  arguments.</li><li>The guard sequence, if any, is true.</li></ol><p>If such a clause cannot be found, a <code class="inline">function_clause</code> runtime error occurs.</p><p>If such a clause is found, the corresponding clause body is evaluated. That is,
│ │ │ │  the expressions in the body are evaluated sequentially and the value of the last
│ │ │ │ -expression is returned.</p><p>Consider the function <code class="inline">fact</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7202625796-1">(</span><span class="ss">mod</span><span class="p" data-group-id="7202625796-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7202625796-2">(</span><span class="p" data-group-id="7202625796-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7202625796-3">]</span><span class="p" data-group-id="7202625796-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +expression is returned.</p><p>Consider the function <code class="inline">fact</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0403954128-1">(</span><span class="ss">mod</span><span class="p" data-group-id="0403954128-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0403954128-2">(</span><span class="p" data-group-id="0403954128-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0403954128-3">]</span><span class="p" data-group-id="0403954128-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="7202625796-4">(</span><span class="n">N</span><span class="p" data-group-id="7202625796-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="7202625796-5">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7202625796-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="7202625796-6">(</span><span class="mi">0</span><span class="p" data-group-id="7202625796-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="0403954128-4">(</span><span class="n">N</span><span class="p" data-group-id="0403954128-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="0403954128-5">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0403954128-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="0403954128-6">(</span><span class="mi">0</span><span class="p" data-group-id="0403954128-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">.</span></code></pre><p>Assume that you want to calculate the factorial for 1:</p><pre><code class="text">1&gt; mod:fact(1).</code></pre><p>Evaluation starts at the first clause. The pattern <code class="inline">N</code> is matched against
│ │ │ │  argument 1. The matching succeeds and the guard (<code class="inline">N &gt; 0</code>) is true, thus <code class="inline">N</code> is
│ │ │ │ -bound to 1, and the corresponding body is evaluated:</p><pre><code class="makeup erlang" translate="no"><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="6837967668-1">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="6837967668-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6837967668-2">(</span><span class="n">N</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">bound</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6837967668-2">)</span><span class="w">
│ │ │ │ -</span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="6837967668-3">(</span><span class="mi">0</span><span class="p" data-group-id="6837967668-3">)</span></code></pre><p>Now, <code class="inline">fact(0)</code> is called, and the function clauses are scanned
│ │ │ │ +bound to 1, and the corresponding body is evaluated:</p><pre><code class="makeup erlang" translate="no"><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="8044223451-1">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="8044223451-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8044223451-2">(</span><span class="n">N</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">bound</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8044223451-2">)</span><span class="w">
│ │ │ │ +</span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="8044223451-3">(</span><span class="mi">0</span><span class="p" data-group-id="8044223451-3">)</span></code></pre><p>Now, <code class="inline">fact(0)</code> is called, and the function clauses are scanned
│ │ │ │  sequentially again. First, the pattern <code class="inline">N</code> is matched against 0. The
│ │ │ │  matching succeeds, but the guard (<code class="inline">N &gt; 0</code>) is false. Second, the
│ │ │ │  pattern <code class="inline">0</code> is matched against the argument <code class="inline">0</code>. The matching succeeds
│ │ │ │  and the body is evaluated:</p><pre><code class="text">1 * fact(0) =&gt;
│ │ │ │  1 * 1 =&gt;
│ │ │ │  1</code></pre><p>Evaluation has succeed and <code class="inline">mod:fact(1)</code> returns 1.</p><p>If <code class="inline">mod:fact/1</code> is called with a negative number as argument, no clause head
│ │ │ │  matches. A <code class="inline">function_clause</code> runtime error occurs.</p><h2 id="tail-recursion" class="section-heading">
│ │ │ │ @@ -78,17 +78,17 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Tail recursion</span>
│ │ │ │  </h2>
│ │ │ │  <p>If the last expression of a function body is a function call, a
│ │ │ │  <em>tail-recursive call</em> is done. This is to ensure that no system
│ │ │ │  resources, for example, call stack, are consumed. This means that an
│ │ │ │  infinite loop using tail-recursive calls will not exhaust the call
│ │ │ │ -stack and can (in principle) run forever.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="6829847430-1">(</span><span class="n">N</span><span class="p" data-group-id="6829847430-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6829847430-2">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6829847430-3">[</span><span class="n">N</span><span class="p" data-group-id="6829847430-3">]</span><span class="p" data-group-id="6829847430-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="6829847430-4">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="6829847430-4">)</span><span class="p">.</span></code></pre><p>The earlier factorial example is a counter-example. It is not
│ │ │ │ +stack and can (in principle) run forever.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="8816583868-1">(</span><span class="n">N</span><span class="p" data-group-id="8816583868-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8816583868-2">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8816583868-3">[</span><span class="n">N</span><span class="p" data-group-id="8816583868-3">]</span><span class="p" data-group-id="8816583868-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="8816583868-4">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="8816583868-4">)</span><span class="p">.</span></code></pre><p>The earlier factorial example is a counter-example. It is not
│ │ │ │  tail-recursive, since a multiplication is done on the result of the recursive
│ │ │ │  call to <code class="inline">fact(N-1)</code>.</p><h2 id="built-in-functions-bifs" class="section-heading">
│ │ │ │    <a href="#built-in-functions-bifs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Built-In Functions (BIFs)</span>
│ │ │ │  </h2>
│ │ │ │ @@ -96,14 +96,14 @@
│ │ │ │  system. BIFs do things that are difficult or impossible to implement
│ │ │ │  in Erlang. Most of the BIFs belong to module <a href="../../../lib/../erts/doc/html/erlang.html"><code class="inline">erlang</code></a>, but there
│ │ │ │  are also BIFs belonging to a few other modules, for example <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a>
│ │ │ │  and <a href="../../../lib/stdlib/doc/html/ets.html"><code class="inline">ets</code></a>.</p><p>The most commonly used BIFs belonging to <a href="../../../lib/../erts/doc/html/erlang.html"><code class="inline">erlang</code></a> are <em>auto-imported</em>. They do
│ │ │ │  not need to be prefixed with the module name. Which BIFs that are auto-imported
│ │ │ │  is specified in the <a href="../../../lib/../erts/doc/html/erlang.html"><code class="inline">erlang</code></a> module in ERTS. For example, standard-type
│ │ │ │  conversion BIFs like <code class="inline">atom_to_list</code> and BIFs allowed in guards can be called
│ │ │ │ -without specifying the module name.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="2092987350-1">(</span><span class="p" data-group-id="2092987350-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="2092987350-2">}</span><span class="p" data-group-id="2092987350-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +without specifying the module name.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="8153549188-1">(</span><span class="p" data-group-id="8153549188-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8153549188-2">}</span><span class="p" data-group-id="8153549188-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="2092987350-3">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="2092987350-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="8153549188-3">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="8153549188-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;Erlang&quot;</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/records_macros.xhtml
│ │ │ │ @@ -29,40 +29,40 @@
│ │ │ │  </h2>
│ │ │ │  <p>To illustrate this, the messenger example from the previous section is divided
│ │ │ │  into the following five files:</p><ul><li><p><code class="inline">mess_config.hrl</code></p><p>Header file for configuration data</p></li><li><p><code class="inline">mess_interface.hrl</code></p><p>Interface definitions between the client and the messenger</p></li><li><p><code class="inline">user_interface.erl</code></p><p>Functions for the user interface</p></li><li><p><code class="inline">mess_client.erl</code></p><p>Functions for the client side of the messenger</p></li><li><p><code class="inline">mess_server.erl</code></p><p>Functions for the server side of the messenger</p></li></ul><p>While doing this, the message passing interface between the shell, the client,
│ │ │ │  and the server is cleaned up and is defined using <em>records</em>. Also, <em>macros</em> are
│ │ │ │  introduced:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_config.hrl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Configure the location of the server node,</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4002219660-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="4002219660-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="7429231284-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="7429231284-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_interface.hrl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Message interface between client and server and client shell for</span><span class="w">
│ │ │ │  </span><span class="c1">%%% messenger program</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%Messages from Client to server received in server/1 function.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0677458771-1">(</span><span class="ss">logon</span><span class="p">,</span><span class="p" data-group-id="0677458771-2">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="p" data-group-id="0677458771-2">}</span><span class="p" data-group-id="0677458771-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0677458771-3">(</span><span class="ss">message</span><span class="p">,</span><span class="p" data-group-id="0677458771-4">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="0677458771-4">}</span><span class="p" data-group-id="0677458771-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6966114126-1">(</span><span class="ss">logon</span><span class="p">,</span><span class="p" data-group-id="6966114126-2">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="p" data-group-id="6966114126-2">}</span><span class="p" data-group-id="6966114126-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6966114126-3">(</span><span class="ss">message</span><span class="p">,</span><span class="p" data-group-id="6966114126-4">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="6966114126-4">}</span><span class="p" data-group-id="6966114126-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% {&#39;EXIT&#39;, ClientPid, Reason}  (client terminated or unreachable.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Messages from Server to Client, received in await_result/0 function</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0677458771-5">(</span><span class="ss">abort_client</span><span class="p">,</span><span class="p" data-group-id="0677458771-6">{</span><span class="ss">message</span><span class="p" data-group-id="0677458771-6">}</span><span class="p" data-group-id="0677458771-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6966114126-5">(</span><span class="ss">abort_client</span><span class="p">,</span><span class="p" data-group-id="6966114126-6">{</span><span class="ss">message</span><span class="p" data-group-id="6966114126-6">}</span><span class="p" data-group-id="6966114126-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Messages are: user_exists_at_other_node,</span><span class="w">
│ │ │ │  </span><span class="c1">%%%               you_are_not_logged_on</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0677458771-7">(</span><span class="ss">server_reply</span><span class="p">,</span><span class="p" data-group-id="0677458771-8">{</span><span class="ss">message</span><span class="p" data-group-id="0677458771-8">}</span><span class="p" data-group-id="0677458771-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6966114126-7">(</span><span class="ss">server_reply</span><span class="p">,</span><span class="p" data-group-id="6966114126-8">{</span><span class="ss">message</span><span class="p" data-group-id="6966114126-8">}</span><span class="p" data-group-id="6966114126-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Messages are: logged_on</span><span class="w">
│ │ │ │  </span><span class="c1">%%%               receiver_not_found</span><span class="w">
│ │ │ │  </span><span class="c1">%%%               sent  (Message has been sent (no guarantee)</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Messages from Server to Client received in client/1 function</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0677458771-9">(</span><span class="ss">message_from</span><span class="p">,</span><span class="p" data-group-id="0677458771-10">{</span><span class="ss">from_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="0677458771-10">}</span><span class="p" data-group-id="0677458771-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6966114126-9">(</span><span class="ss">message_from</span><span class="p">,</span><span class="p" data-group-id="6966114126-10">{</span><span class="ss">from_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="6966114126-10">}</span><span class="p" data-group-id="6966114126-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Messages from shell to Client received in client/1 function</span><span class="w">
│ │ │ │  </span><span class="c1">%%% spawn(mess_client, client, [server_node(), Name])</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0677458771-11">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="0677458771-12">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="0677458771-12">}</span><span class="p" data-group-id="0677458771-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6966114126-11">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="6966114126-12">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="6966114126-12">}</span><span class="p" data-group-id="6966114126-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% logoff</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE user_interface.erl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% User interface to the messenger program</span><span class="w">
│ │ │ │  </span><span class="c1">%%% login(Name)</span><span class="w">
│ │ │ │  </span><span class="c1">%%%     One user at a time can log in from each Erlang node in the</span><span class="w">
│ │ │ │ @@ -75,177 +75,177 @@
│ │ │ │  </span><span class="c1">%%%     Logs off anybody at that node</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% message(ToName, Message)</span><span class="w">
│ │ │ │  </span><span class="c1">%%%     sends Message to ToName. Error messages if the user of this</span><span class="w">
│ │ │ │  </span><span class="c1">%%%     function is not logged on or if ToName is not logged on at</span><span class="w">
│ │ │ │  </span><span class="c1">%%%     any node.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4357270114-1">(</span><span class="ss">user_interface</span><span class="p" data-group-id="4357270114-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4357270114-2">(</span><span class="p" data-group-id="4357270114-3">[</span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4357270114-3">]</span><span class="p" data-group-id="4357270114-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4357270114-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="4357270114-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4357270114-5">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="4357270114-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0808927611-1">(</span><span class="ss">user_interface</span><span class="p" data-group-id="0808927611-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0808927611-2">(</span><span class="p" data-group-id="0808927611-3">[</span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0808927611-3">]</span><span class="p" data-group-id="0808927611-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="0808927611-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="0808927611-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="0808927611-5">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="0808927611-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="4357270114-6">(</span><span class="n">Name</span><span class="p" data-group-id="4357270114-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="4357270114-7">(</span><span class="ss">mess_client</span><span class="p" data-group-id="4357270114-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="0808927611-6">(</span><span class="n">Name</span><span class="p" data-group-id="0808927611-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="0808927611-7">(</span><span class="ss">mess_client</span><span class="p" data-group-id="0808927611-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="4357270114-8">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="4357270114-9">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4357270114-10">[</span><span class="o">?</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4357270114-10">]</span><span class="p" data-group-id="4357270114-9">)</span><span class="p" data-group-id="4357270114-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="0808927611-8">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="0808927611-9">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808927611-10">[</span><span class="o">?</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0808927611-10">]</span><span class="p" data-group-id="0808927611-9">)</span><span class="p" data-group-id="0808927611-8">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="4357270114-11">(</span><span class="p" data-group-id="4357270114-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="0808927611-11">(</span><span class="p" data-group-id="0808927611-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="4357270114-12">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4357270114-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="4357270114-13">(</span><span class="ss">mess_client</span><span class="p" data-group-id="4357270114-13">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="0808927611-12">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0808927611-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="0808927611-13">(</span><span class="ss">mess_client</span><span class="p" data-group-id="0808927611-13">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="4357270114-14">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="4357270114-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="0808927611-14">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="0808927611-14">}</span><span class="p">,</span><span class="w">
│ │ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_client.erl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% The client process which runs on each user node</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7948461030-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="7948461030-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7948461030-2">(</span><span class="p" data-group-id="7948461030-3">[</span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7948461030-3">]</span><span class="p" data-group-id="7948461030-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="7948461030-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="7948461030-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="7948461030-5">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7948461030-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7948461030-6">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="7948461030-6">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="7948461030-7">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="7948461030-8">(</span><span class="p" data-group-id="7948461030-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="7948461030-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="7948461030-9">(</span><span class="p" data-group-id="7948461030-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="7948461030-10">(</span><span class="n">Server_Node</span><span class="p" data-group-id="7948461030-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6606610866-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="6606610866-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6606610866-2">(</span><span class="p" data-group-id="6606610866-3">[</span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6606610866-3">]</span><span class="p" data-group-id="6606610866-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6606610866-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="6606610866-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="6606610866-5">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6606610866-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6606610866-6">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6606610866-6">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="6606610866-7">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="6606610866-8">(</span><span class="p" data-group-id="6606610866-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="6606610866-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="6606610866-9">(</span><span class="p" data-group-id="6606610866-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="6606610866-10">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6606610866-10">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="7948461030-11">(</span><span class="n">Server_Node</span><span class="p" data-group-id="7948461030-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="6606610866-11">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6606610866-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="7948461030-12">(</span><span class="ss">normal</span><span class="p" data-group-id="7948461030-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="7948461030-13">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="7948461030-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="7948461030-14">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="7948461030-14">}</span><span class="w"> </span><span class="o">!</span><span class="w">
│ │ │ │ -                </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="7948461030-15">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="7948461030-16">(</span><span class="p" data-group-id="7948461030-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="7948461030-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="7948461030-17">(</span><span class="p" data-group-id="7948461030-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="7948461030-18">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7948461030-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7948461030-19">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7948461030-20">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7948461030-20">]</span><span class="p" data-group-id="7948461030-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="6606610866-12">(</span><span class="ss">normal</span><span class="p" data-group-id="6606610866-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="6606610866-13">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="6606610866-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6606610866-14">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6606610866-14">}</span><span class="w"> </span><span class="o">!</span><span class="w">
│ │ │ │ +                </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="6606610866-15">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="6606610866-16">(</span><span class="p" data-group-id="6606610866-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="6606610866-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="6606610866-17">(</span><span class="p" data-group-id="6606610866-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6606610866-18">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6606610866-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6606610866-19">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6606610866-20">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6606610866-20">]</span><span class="p" data-group-id="6606610866-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="7948461030-21">(</span><span class="n">Server_Node</span><span class="p" data-group-id="7948461030-21">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="6606610866-21">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6606610866-21">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="7948461030-22">(</span><span class="p" data-group-id="7948461030-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="6606610866-22">(</span><span class="p" data-group-id="6606610866-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="7948461030-23">{</span><span class="ss">message</span><span class="o">=</span><span class="n">Why</span><span class="p" data-group-id="7948461030-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7948461030-24">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7948461030-25">[</span><span class="n">Why</span><span class="p" data-group-id="7948461030-25">]</span><span class="p" data-group-id="7948461030-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="7948461030-26">(</span><span class="ss">normal</span><span class="p" data-group-id="7948461030-26">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="7948461030-27">{</span><span class="ss">message</span><span class="o">=</span><span class="n">What</span><span class="p" data-group-id="7948461030-27">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7948461030-28">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7948461030-29">[</span><span class="n">What</span><span class="p" data-group-id="7948461030-29">]</span><span class="p" data-group-id="7948461030-28">)</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="6606610866-23">{</span><span class="ss">message</span><span class="o">=</span><span class="n">Why</span><span class="p" data-group-id="6606610866-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6606610866-24">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6606610866-25">[</span><span class="n">Why</span><span class="p" data-group-id="6606610866-25">]</span><span class="p" data-group-id="6606610866-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="6606610866-26">(</span><span class="ss">normal</span><span class="p" data-group-id="6606610866-26">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="6606610866-27">{</span><span class="ss">message</span><span class="o">=</span><span class="n">What</span><span class="p" data-group-id="6606610866-27">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6606610866-28">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6606610866-29">[</span><span class="n">What</span><span class="p" data-group-id="6606610866-29">]</span><span class="p" data-group-id="6606610866-28">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7948461030-30">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7948461030-31">[</span><span class="p" data-group-id="7948461030-31">]</span><span class="p" data-group-id="7948461030-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="7948461030-32">(</span><span class="ss">timeout</span><span class="p" data-group-id="7948461030-32">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6606610866-30">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6606610866-31">[</span><span class="p" data-group-id="6606610866-31">]</span><span class="p" data-group-id="6606610866-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="6606610866-32">(</span><span class="ss">timeout</span><span class="p" data-group-id="6606610866-32">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE---</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_server.erl----</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% This is the server process of the messenger service</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9901692151-1">(</span><span class="ss">mess_server</span><span class="p" data-group-id="9901692151-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9901692151-2">(</span><span class="p" data-group-id="9901692151-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9901692151-3">]</span><span class="p" data-group-id="9901692151-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="9901692151-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="9901692151-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9901692151-5">(</span><span class="p" data-group-id="9901692151-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9901692151-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9901692151-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="9901692151-7">(</span><span class="p" data-group-id="9901692151-8">[</span><span class="p" data-group-id="9901692151-8">]</span><span class="p" data-group-id="9901692151-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8057449265-1">(</span><span class="ss">mess_server</span><span class="p" data-group-id="8057449265-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8057449265-2">(</span><span class="p" data-group-id="8057449265-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8057449265-3">]</span><span class="p" data-group-id="8057449265-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="8057449265-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="8057449265-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="8057449265-5">(</span><span class="p" data-group-id="8057449265-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="8057449265-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8057449265-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="8057449265-7">(</span><span class="p" data-group-id="8057449265-8">[</span><span class="p" data-group-id="8057449265-8">]</span><span class="p" data-group-id="8057449265-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9901692151-9">(</span><span class="n">User_List</span><span class="p" data-group-id="9901692151-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9901692151-10">(</span><span class="s">&quot;User list = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9901692151-11">[</span><span class="n">User_List</span><span class="p" data-group-id="9901692151-11">]</span><span class="p" data-group-id="9901692151-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="8057449265-9">(</span><span class="n">User_List</span><span class="p" data-group-id="8057449265-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8057449265-10">(</span><span class="s">&quot;User list = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8057449265-11">[</span><span class="n">User_List</span><span class="p" data-group-id="8057449265-11">]</span><span class="p" data-group-id="8057449265-10">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="9901692151-12">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="9901692151-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="9901692151-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9901692151-14">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9901692151-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9901692151-15">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9901692151-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="9901692151-16">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9901692151-17">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9901692151-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="9901692151-18">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="9901692151-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9901692151-19">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9901692151-20">(</span><span class="n">User_List</span><span class="p" data-group-id="9901692151-20">)</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="8057449265-12">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="8057449265-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="8057449265-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="8057449265-14">(</span><span class="n">New_User_List</span><span class="p" data-group-id="8057449265-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8057449265-15">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="8057449265-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="8057449265-16">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="8057449265-17">(</span><span class="n">New_User_List</span><span class="p" data-group-id="8057449265-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="8057449265-18">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="8057449265-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="8057449265-19">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="8057449265-20">(</span><span class="n">User_List</span><span class="p" data-group-id="8057449265-20">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="9901692151-21">(</span><span class="p" data-group-id="9901692151-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9901692151-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9901692151-23">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9901692151-24">[</span><span class="p" data-group-id="9901692151-24">]</span><span class="p" data-group-id="9901692151-23">)</span><span class="p" data-group-id="9901692151-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="8057449265-21">(</span><span class="p" data-group-id="8057449265-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="8057449265-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="8057449265-23">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8057449265-24">[</span><span class="p" data-group-id="8057449265-24">]</span><span class="p" data-group-id="8057449265-23">)</span><span class="p" data-group-id="8057449265-22">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="9901692151-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="8057449265-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="9901692151-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="8057449265-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="9901692151-27">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="9901692151-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="8057449265-27">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="8057449265-27">}</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9901692151-28">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">logged_on</span><span class="p" data-group-id="9901692151-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">link</span><span class="p" data-group-id="9901692151-29">(</span><span class="n">From</span><span class="p" data-group-id="9901692151-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9901692151-30">[</span><span class="p" data-group-id="9901692151-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9901692151-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="8057449265-28">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">logged_on</span><span class="p" data-group-id="8057449265-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">link</span><span class="p" data-group-id="8057449265-29">(</span><span class="n">From</span><span class="p" data-group-id="8057449265-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="8057449265-30">[</span><span class="p" data-group-id="8057449265-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8057449265-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="9901692151-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="9901692151-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-33">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="8057449265-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="8057449265-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-33">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9901692151-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="8057449265-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9901692151-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="8057449265-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="9901692151-36">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="9901692151-36">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9901692151-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9901692151-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9901692151-38">}</span><span class="p" data-group-id="9901692151-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9901692151-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-39">)</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="8057449265-36">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="8057449265-36">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8057449265-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8057449265-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8057449265-38">}</span><span class="p" data-group-id="8057449265-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="8057449265-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-39">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9901692151-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="8057449265-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9901692151-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9901692151-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="8057449265-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8057449265-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9901692151-42">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">receiver_not_found</span><span class="p" data-group-id="9901692151-42">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9901692151-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9901692151-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="9901692151-44">}</span><span class="p" data-group-id="9901692151-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_from</span><span class="p" data-group-id="9901692151-45">{</span><span class="ss">from_name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="9901692151-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9901692151-46">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">sent</span><span class="p" data-group-id="9901692151-46">}</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="8057449265-42">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">receiver_not_found</span><span class="p" data-group-id="8057449265-42">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8057449265-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8057449265-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="8057449265-44">}</span><span class="p" data-group-id="8057449265-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_from</span><span class="p" data-group-id="8057449265-45">{</span><span class="ss">from_name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="8057449265-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="8057449265-46">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">sent</span><span class="p" data-group-id="8057449265-46">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%%----END FILE---</span></code></pre><h2 id="header-files" class="section-heading">
│ │ │ │    <a href="#header-files" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Header Files</span>
│ │ │ │  </h2>
│ │ │ │  <p>As shown above, some files have extension <code class="inline">.hrl</code>. These are header files that
│ │ │ │ -are included in the <code class="inline">.erl</code> files by:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5418560476-1">(</span><span class="s">&quot;File_Name&quot;</span><span class="p" data-group-id="5418560476-1">)</span><span class="p">.</span></code></pre><p>for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3801063869-1">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="3801063869-1">)</span><span class="p">.</span></code></pre><p>In the case above the file is fetched from the same directory as all the other
│ │ │ │ +are included in the <code class="inline">.erl</code> files by:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="7353675070-1">(</span><span class="s">&quot;File_Name&quot;</span><span class="p" data-group-id="7353675070-1">)</span><span class="p">.</span></code></pre><p>for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4028881289-1">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="4028881289-1">)</span><span class="p">.</span></code></pre><p>In the case above the file is fetched from the same directory as all the other
│ │ │ │  files in the messenger example. (<em>manual</em>).</p><p>.hrl files can contain any valid Erlang code but are most often used for record
│ │ │ │  and macro definitions.</p><h2 id="records" class="section-heading">
│ │ │ │    <a href="#records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Records</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A record is defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8300357492-1">(</span><span class="ss">name_of_record</span><span class="p">,</span><span class="p" data-group-id="8300357492-2">{</span><span class="ss">field_name1</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name2</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8300357492-2">}</span><span class="p" data-group-id="8300357492-1">)</span><span class="p">.</span></code></pre><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2980428501-1">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="2980428501-2">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="2980428501-2">}</span><span class="p" data-group-id="2980428501-1">)</span><span class="p">.</span></code></pre><p>This is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1768273477-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To_Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="1768273477-1">}</span></code></pre><p>Creating a record is best illustrated by an example:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="7418483049-1">{</span><span class="ss">message</span><span class="o">=</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="ss">fred</span><span class="p">)</span></code></pre><p>This creates:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7252170152-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7252170152-1">}</span></code></pre><p>Notice that you do not have to worry about the order you assign values to the
│ │ │ │ +<p>A record is defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4318340361-1">(</span><span class="ss">name_of_record</span><span class="p">,</span><span class="p" data-group-id="4318340361-2">{</span><span class="ss">field_name1</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name2</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4318340361-2">}</span><span class="p" data-group-id="4318340361-1">)</span><span class="p">.</span></code></pre><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9977764364-1">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="9977764364-2">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="9977764364-2">}</span><span class="p" data-group-id="9977764364-1">)</span><span class="p">.</span></code></pre><p>This is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8785510910-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To_Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8785510910-1">}</span></code></pre><p>Creating a record is best illustrated by an example:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="9595844625-1">{</span><span class="ss">message</span><span class="o">=</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="ss">fred</span><span class="p">)</span></code></pre><p>This creates:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7982086032-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7982086032-1">}</span></code></pre><p>Notice that you do not have to worry about the order you assign values to the
│ │ │ │  various parts of the records when you create it. The advantage of using records
│ │ │ │  is that by placing their definitions in header files you can conveniently define
│ │ │ │  interfaces that are easy to change. For example, if you want to add a new field
│ │ │ │  to the record, you only have to change the code where the new field is used and
│ │ │ │  not at every place the record is referred to. If you leave out a field when
│ │ │ │  creating a record, it gets the value of the atom <code class="inline">undefined</code>. (<em>manual</em>)</p><p>Pattern matching with records is very similar to creating records. For example,
│ │ │ │ -inside a <code class="inline">case</code> or <code class="inline">receive</code>:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="7489389987-1">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="7489389987-1">}</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>This is the same as:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0981243022-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0981243022-1">}</span></code></pre><h2 id="macros" class="section-heading">
│ │ │ │ +inside a <code class="inline">case</code> or <code class="inline">receive</code>:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="5975179109-1">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="5975179109-1">}</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>This is the same as:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9147910754-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9147910754-1">}</span></code></pre><h2 id="macros" class="section-heading">
│ │ │ │    <a href="#macros" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Macros</span>
│ │ │ │  </h2>
│ │ │ │  <p>Another thing that has been added to the messenger is a macro. The file
│ │ │ │  <code class="inline">mess_config.hrl</code> contains the definition:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Configure the location of the server node,</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0186031342-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="0186031342-1">)</span><span class="p">.</span></code></pre><p>This file is included in <code class="inline">mess_server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="9490373060-1">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="9490373060-1">)</span><span class="p">.</span></code></pre><p>Every occurrence of <code class="inline">?server_node</code> in <code class="inline">mess_server.erl</code> is now replaced by
│ │ │ │ -<code class="inline">messenger@super</code>.</p><p>A macro is also used when spawning the server process:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="3486546225-1">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3486546225-2">[</span><span class="p" data-group-id="3486546225-2">]</span><span class="p" data-group-id="3486546225-1">)</span></code></pre><p>This is a standard macro (that is, defined by the system, not by the user).
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4699986930-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="4699986930-1">)</span><span class="p">.</span></code></pre><p>This file is included in <code class="inline">mess_server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="0038451230-1">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="0038451230-1">)</span><span class="p">.</span></code></pre><p>Every occurrence of <code class="inline">?server_node</code> in <code class="inline">mess_server.erl</code> is now replaced by
│ │ │ │ +<code class="inline">messenger@super</code>.</p><p>A macro is also used when spawning the server process:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="2948332052-1">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2948332052-2">[</span><span class="p" data-group-id="2948332052-2">]</span><span class="p" data-group-id="2948332052-1">)</span></code></pre><p>This is a standard macro (that is, defined by the system, not by the user).
│ │ │ │  <code class="inline">?MODULE</code> is always replaced by the name of the current module (that is, the
│ │ │ │  <code class="inline">-module</code> definition near the start of the file). There are more advanced ways
│ │ │ │  of using macros with, for example, <a href="macros.xhtml#defining-and-using-macros">parameters</a>.</p><p>The three Erlang (<code class="inline">.erl</code>) files in the messenger example are individually
│ │ │ │  compiled into object code file (<code class="inline">.beam</code>). The Erlang system loads and links
│ │ │ │  these files into the system when they are referred to during execution of the
│ │ │ │  code. In this case, they are simply put in our current working directory (that
│ │ │ │  is, the place you have done &quot;cd&quot; to). There are ways of putting the <code class="inline">.beam</code>
│ │ │ ├── OEBPS/prog_ex_records.xhtml
│ │ │ │ @@ -27,105 +27,105 @@
│ │ │ │    <span class="text">Records and Tuples</span>
│ │ │ │  </h2>
│ │ │ │  <p>The main advantage of using records rather than tuples is that fields in a
│ │ │ │  record are accessed by name, whereas fields in a tuple are accessed by position.
│ │ │ │  To illustrate these differences, suppose that you want to represent a person
│ │ │ │  with the tuple <code class="inline">{Name, Address, Phone}</code>.</p><p>To write functions that manipulate this data, remember the following:</p><ul><li>The <code class="inline">Name</code> field is the first element of the tuple.</li><li>The <code class="inline">Address</code> field is the second element.</li><li>The <code class="inline">Phone</code> field is the third element.</li></ul><p>For example, to extract data from a variable <code class="inline">P</code> that contains such a tuple, you
│ │ │ │  can write the following code and then use pattern matching to extract the
│ │ │ │ -relevant fields:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="7920203636-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="7920203636-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="7920203636-2">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="7920203636-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +relevant fields:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="0826333811-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="0826333811-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="0826333811-2">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="0826333811-2">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Such code is difficult to read and understand, and errors occur if the numbering
│ │ │ │  of the elements in the tuple is wrong. If the data representation of the fields
│ │ │ │  is changed, by re-ordering, adding, or removing fields, all references to the
│ │ │ │  person tuple must be checked and possibly modified.</p><p>Records allow references to the fields by name, instead of by position. In the
│ │ │ │ -following example, a record instead of a tuple is used to store the data:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7821037078-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7821037078-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="7821037078-2">}</span><span class="p" data-group-id="7821037078-1">)</span><span class="p">.</span></code></pre><p>This enables references to the fields of the record by name. For example, if <code class="inline">P</code>
│ │ │ │ +following example, a record instead of a tuple is used to store the data:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1872032142-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1872032142-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="1872032142-2">}</span><span class="p" data-group-id="1872032142-1">)</span><span class="p">.</span></code></pre><p>This enables references to the fields of the record by name. For example, if <code class="inline">P</code>
│ │ │ │  is a variable whose value is a <code class="inline">person</code> record, the following code access the
│ │ │ │  name and address fields of the records:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">address</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Internally, records are represented using tagged tuples:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0919828037-1">{</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p" data-group-id="0919828037-1">}</span></code></pre><h2 id="defining-a-record" class="section-heading">
│ │ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Internally, records are represented using tagged tuples:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9676919737-1">{</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p" data-group-id="9676919737-1">}</span></code></pre><h2 id="defining-a-record" class="section-heading">
│ │ │ │    <a href="#defining-a-record" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Defining a Record</span>
│ │ │ │  </h2>
│ │ │ │  <p>This following definition of a <code class="inline">person</code> is used in several examples in this
│ │ │ │  section. Three fields are included, <code class="inline">name</code>, <code class="inline">phone</code>, and <code class="inline">address</code>. The default
│ │ │ │  values for <code class="inline">name</code> and <code class="inline">phone</code> is &quot;&quot; and [], respectively. The default value for
│ │ │ │  <code class="inline">address</code> is the atom <code class="inline">undefined</code>, since no default value is supplied for this
│ │ │ │ -field:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1369910386-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1369910386-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1369910386-3">[</span><span class="p" data-group-id="1369910386-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="1369910386-2">}</span><span class="p" data-group-id="1369910386-1">)</span><span class="p">.</span></code></pre><p>The record must be defined in the shell to enable use of the record syntax in
│ │ │ │ -the examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">rd</span><span class="p" data-group-id="9571960233-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9571960233-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9571960233-3">[</span><span class="p" data-group-id="9571960233-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="9571960233-2">}</span><span class="p" data-group-id="9571960233-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +field:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6409732120-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6409732120-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6409732120-3">[</span><span class="p" data-group-id="6409732120-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="6409732120-2">}</span><span class="p" data-group-id="6409732120-1">)</span><span class="p">.</span></code></pre><p>The record must be defined in the shell to enable use of the record syntax in
│ │ │ │ +the examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">rd</span><span class="p" data-group-id="6403904924-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6403904924-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6403904924-3">[</span><span class="p" data-group-id="6403904924-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="6403904924-2">}</span><span class="p" data-group-id="6403904924-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">person</span></code></pre><p>This is because record definitions are only available at compile time, not at
│ │ │ │  runtime. For details on records in the shell, see the <a href="../../../lib/stdlib/doc/html/shell.html"><code class="inline">shell</code></a> manual page in
│ │ │ │  STDLIB.</p><h2 id="creating-a-record" class="section-heading">
│ │ │ │    <a href="#creating-a-record" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating a Record</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A new <code class="inline">person</code> record is created as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4652249159-1">{</span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="4652249159-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4652249159-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="4652249159-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4652249159-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4652249159-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4652249159-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="4652249159-3">}</span></code></pre><p>As the <code class="inline">address</code> field was omitted, its default value is used.</p><p>From Erlang 5.1/OTP R8B, a value to all fields in a record can be set with the
│ │ │ │ -special field <code class="inline">_</code>. <code class="inline">_</code> means &quot;all fields not explicitly specified&quot;.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6648460776-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6648460776-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6648460776-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6648460776-2">}</span></code></pre><p>It is primarily intended to be used in <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a> and
│ │ │ │ +<p>A new <code class="inline">person</code> record is created as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9253989200-1">{</span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="9253989200-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9253989200-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="9253989200-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9253989200-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9253989200-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9253989200-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="9253989200-3">}</span></code></pre><p>As the <code class="inline">address</code> field was omitted, its default value is used.</p><p>From Erlang 5.1/OTP R8B, a value to all fields in a record can be set with the
│ │ │ │ +special field <code class="inline">_</code>. <code class="inline">_</code> means &quot;all fields not explicitly specified&quot;.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6476186920-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6476186920-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6476186920-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6476186920-2">}</span></code></pre><p>It is primarily intended to be used in <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a> and
│ │ │ │  <a href="../../../lib/mnesia/doc/html/mnesia.html#match_object/3"><code class="inline">mnesia:match_object/3</code></a>, to set record fields to the atom <code class="inline">'_'</code>. (This is a
│ │ │ │  wildcard in <a href="../../../lib/stdlib/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>.)</p><h2 id="accessing-a-record-field" class="section-heading">
│ │ │ │    <a href="#accessing-a-record-field" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Accessing a Record Field</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The following example shows how to access a record field:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5291507103-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5291507103-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5291507103-2">]</span><span class="p" data-group-id="5291507103-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5291507103-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5291507103-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5291507103-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="5291507103-3">}</span><span class="w">
│ │ │ │ +<p>The following example shows how to access a record field:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7397570668-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7397570668-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7397570668-2">]</span><span class="p" data-group-id="7397570668-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7397570668-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7397570668-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7397570668-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="7397570668-3">}</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;Joe&quot;</span></code></pre><h2 id="updating-a-record" class="section-heading">
│ │ │ │    <a href="#updating-a-record" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Updating a Record</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The following example shows how to update a record:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1842322437-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="1842322437-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1842322437-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1842322437-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1842322437-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1842322437-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1842322437-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1842322437-3">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P1</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1842322437-5">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="1842322437-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1842322437-6">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1842322437-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1842322437-7">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1842322437-6">}</span></code></pre><h2 id="type-testing" class="section-heading">
│ │ │ │ +<p>The following example shows how to update a record:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1395060358-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="1395060358-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1395060358-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1395060358-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1395060358-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1395060358-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1395060358-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1395060358-3">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P1</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1395060358-5">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="1395060358-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1395060358-6">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1395060358-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1395060358-7">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1395060358-6">}</span></code></pre><h2 id="type-testing" class="section-heading">
│ │ │ │    <a href="#type-testing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Type Testing</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following example shows that the guard succeeds if <code class="inline">P</code> is record of type
│ │ │ │ -<code class="inline">person</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="1010205430-1">(</span><span class="n">P</span><span class="p" data-group-id="1010205430-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="1010205430-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="1010205430-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">a_person</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="1010205430-3">(</span><span class="p">_</span><span class="p" data-group-id="1010205430-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">not_a_person</span><span class="p">.</span></code></pre><h2 id="pattern-matching" class="section-heading">
│ │ │ │ +<code class="inline">person</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="3107888027-1">(</span><span class="n">P</span><span class="p" data-group-id="3107888027-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="3107888027-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="3107888027-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">a_person</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="3107888027-3">(</span><span class="p">_</span><span class="p" data-group-id="3107888027-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">not_a_person</span><span class="p">.</span></code></pre><h2 id="pattern-matching" class="section-heading">
│ │ │ │    <a href="#pattern-matching" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Pattern Matching</span>
│ │ │ │  </h2>
│ │ │ │  <p>Matching can be used in combination with records, as shown in the following
│ │ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6955643654-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="6955643654-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="6955643654-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="6955643654-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6955643654-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6955643654-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="6955643654-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="6955643654-3">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6955643654-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6955643654-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P3</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">.</span><span class="w">
│ │ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7146890733-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="7146890733-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7146890733-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="7146890733-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7146890733-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7146890733-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7146890733-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="7146890733-3">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7146890733-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7146890733-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P3</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;Joe&quot;</span></code></pre><p>The following function takes a list of <code class="inline">person</code> records and searches for the
│ │ │ │ -phone number of a person with a particular name:</p><pre><code class="makeup erlang" translate="no"><span class="nf">find_phone</span><span class="p" data-group-id="6850217681-1">(</span><span class="p" data-group-id="6850217681-2">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6850217681-3">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="n">Phone</span><span class="p" data-group-id="6850217681-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="6850217681-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6850217681-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6850217681-4">{</span><span class="ss">found</span><span class="p">,</span><span class="w">  </span><span class="n">Phone</span><span class="p" data-group-id="6850217681-4">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">find_phone</span><span class="p" data-group-id="6850217681-5">(</span><span class="p" data-group-id="6850217681-6">[</span><span class="p">_</span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6850217681-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6850217681-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">find_phone</span><span class="p" data-group-id="6850217681-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6850217681-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">find_phone</span><span class="p" data-group-id="6850217681-8">(</span><span class="p" data-group-id="6850217681-9">[</span><span class="p" data-group-id="6850217681-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6850217681-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +phone number of a person with a particular name:</p><pre><code class="makeup erlang" translate="no"><span class="nf">find_phone</span><span class="p" data-group-id="7220574793-1">(</span><span class="p" data-group-id="7220574793-2">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7220574793-3">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="n">Phone</span><span class="p" data-group-id="7220574793-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7220574793-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7220574793-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7220574793-4">{</span><span class="ss">found</span><span class="p">,</span><span class="w">  </span><span class="n">Phone</span><span class="p" data-group-id="7220574793-4">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">find_phone</span><span class="p" data-group-id="7220574793-5">(</span><span class="p" data-group-id="7220574793-6">[</span><span class="p">_</span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="7220574793-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7220574793-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">find_phone</span><span class="p" data-group-id="7220574793-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7220574793-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">find_phone</span><span class="p" data-group-id="7220574793-8">(</span><span class="p" data-group-id="7220574793-9">[</span><span class="p" data-group-id="7220574793-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7220574793-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">not_found</span><span class="p">.</span></code></pre><p>The fields referred to in the pattern can be given in any order.</p><h2 id="nested-records" class="section-heading">
│ │ │ │    <a href="#nested-records" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Nested Records</span>
│ │ │ │  </h2>
│ │ │ │  <p>The value of a field in a record can be an instance of a record. Retrieval of
│ │ │ │  nested data can be done stepwise, or in a single step, as shown in the following
│ │ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3315708507-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3315708507-2">{</span><span class="ss">first</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">last</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Ericsson&quot;</span><span class="p" data-group-id="3315708507-2">}</span><span class="p" data-group-id="3315708507-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3315708507-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3315708507-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="3315708507-5">{</span><span class="p" data-group-id="3315708507-5">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p" data-group-id="3315708507-4">}</span><span class="p" data-group-id="3315708507-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6395930413-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6395930413-2">{</span><span class="ss">first</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">last</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Ericsson&quot;</span><span class="p" data-group-id="6395930413-2">}</span><span class="p" data-group-id="6395930413-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6395930413-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6395930413-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="6395930413-5">{</span><span class="p" data-group-id="6395930413-5">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p" data-group-id="6395930413-4">}</span><span class="p" data-group-id="6395930413-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">demo</span><span class="p" data-group-id="3315708507-6">(</span><span class="p" data-group-id="3315708507-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3315708507-7">{</span><span class="ss">name</span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="3315708507-8">{</span><span class="ss">first</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">last</span><span class="o">=</span><span class="s">&quot;Virding&quot;</span><span class="p" data-group-id="3315708507-8">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="mi">123</span><span class="p" data-group-id="3315708507-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="n">First</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3315708507-9">(</span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="3315708507-9">)</span><span class="o">#</span><span class="ss">name</span><span class="p">.</span><span class="ss">first</span><span class="p">.</span></code></pre><p>Here, <code class="inline">demo()</code> evaluates to <code class="inline">&quot;Robert&quot;</code>.</p><h2 id="a-longer-example" class="section-heading">
│ │ │ │ +</span><span class="nf">demo</span><span class="p" data-group-id="6395930413-6">(</span><span class="p" data-group-id="6395930413-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6395930413-7">{</span><span class="ss">name</span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="6395930413-8">{</span><span class="ss">first</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">last</span><span class="o">=</span><span class="s">&quot;Virding&quot;</span><span class="p" data-group-id="6395930413-8">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="mi">123</span><span class="p" data-group-id="6395930413-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="n">First</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6395930413-9">(</span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="6395930413-9">)</span><span class="o">#</span><span class="ss">name</span><span class="p">.</span><span class="ss">first</span><span class="p">.</span></code></pre><p>Here, <code class="inline">demo()</code> evaluates to <code class="inline">&quot;Robert&quot;</code>.</p><h2 id="a-longer-example" class="section-heading">
│ │ │ │    <a href="#a-longer-example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">A Longer Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>Comments are embedded in the following example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% File: person.hrl</span><span class="w">
│ │ │ │  
│ │ │ │ @@ -135,44 +135,44 @@
│ │ │ │  </span><span class="c1">%%    name:  A string (default is undefined).</span><span class="w">
│ │ │ │  </span><span class="c1">%%    age:   An integer (default is undefined).</span><span class="w">
│ │ │ │  </span><span class="c1">%%    phone: A list of integers (default is []).</span><span class="w">
│ │ │ │  </span><span class="c1">%%    dict:  A dictionary containing various information</span><span class="w">
│ │ │ │  </span><span class="c1">%%           about the person.</span><span class="w">
│ │ │ │  </span><span class="c1">%%           A {Key, Value} list (default is the empty list).</span><span class="w">
│ │ │ │  </span><span class="c1">%%------------------------------------------------------------</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1322526648-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1322526648-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1322526648-3">[</span><span class="p" data-group-id="1322526648-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1322526648-4">[</span><span class="p" data-group-id="1322526648-4">]</span><span class="p" data-group-id="1322526648-2">}</span><span class="p" data-group-id="1322526648-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6188422419-1">(</span><span class="ss">person</span><span class="p" data-group-id="6188422419-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6188422419-2">(</span><span class="s">&quot;person.hrl&quot;</span><span class="p" data-group-id="6188422419-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="6188422419-3">(</span><span class="ss">export_all</span><span class="p" data-group-id="6188422419-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% For test purposes only.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5489897302-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5489897302-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5489897302-3">[</span><span class="p" data-group-id="5489897302-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5489897302-4">[</span><span class="p" data-group-id="5489897302-4">]</span><span class="p" data-group-id="5489897302-2">}</span><span class="p" data-group-id="5489897302-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8945594667-1">(</span><span class="ss">person</span><span class="p" data-group-id="8945594667-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="8945594667-2">(</span><span class="s">&quot;person.hrl&quot;</span><span class="p" data-group-id="8945594667-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="8945594667-3">(</span><span class="ss">export_all</span><span class="p" data-group-id="8945594667-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% For test purposes only.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% This creates an instance of a person.</span><span class="w">
│ │ │ │  </span><span class="c1">%%   Note: The phone number is not supplied so the</span><span class="w">
│ │ │ │  </span><span class="c1">%%         default value [] will be used.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="6188422419-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="6188422419-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6188422419-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ │ -           </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6188422419-6">[</span><span class="p" data-group-id="6188422419-7">{</span><span class="ss">computer_knowledge</span><span class="p">,</span><span class="w"> </span><span class="ss">excellent</span><span class="p" data-group-id="6188422419-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                   </span><span class="p" data-group-id="6188422419-8">{</span><span class="ss">drinks</span><span class="p">,</span><span class="w"> </span><span class="ss">coke</span><span class="p" data-group-id="6188422419-8">}</span><span class="p" data-group-id="6188422419-6">]</span><span class="p" data-group-id="6188422419-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="8945594667-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="8945594667-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8945594667-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ │ +           </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8945594667-6">[</span><span class="p" data-group-id="8945594667-7">{</span><span class="ss">computer_knowledge</span><span class="p">,</span><span class="w"> </span><span class="ss">excellent</span><span class="p" data-group-id="8945594667-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                   </span><span class="p" data-group-id="8945594667-8">{</span><span class="ss">drinks</span><span class="p">,</span><span class="w"> </span><span class="ss">coke</span><span class="p" data-group-id="8945594667-8">}</span><span class="p" data-group-id="8945594667-6">]</span><span class="p" data-group-id="8945594667-5">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% This demonstrates matching in arguments</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">print</span><span class="p" data-group-id="6188422419-9">(</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6188422419-10">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="6188422419-10">}</span><span class="p" data-group-id="6188422419-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6188422419-11">(</span><span class="s">&quot;Name: </span><span class="si">~s</span><span class="s">, Age: </span><span class="si">~w</span><span class="s">, Phone: </span><span class="si">~w</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="w">
│ │ │ │ -            </span><span class="s">&quot;Dictionary: </span><span class="si">~w</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6188422419-12">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="6188422419-12">]</span><span class="p" data-group-id="6188422419-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">print</span><span class="p" data-group-id="8945594667-9">(</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8945594667-10">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="8945594667-10">}</span><span class="p" data-group-id="8945594667-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8945594667-11">(</span><span class="s">&quot;Name: </span><span class="si">~s</span><span class="s">, Age: </span><span class="si">~w</span><span class="s">, Phone: </span><span class="si">~w</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="w">
│ │ │ │ +            </span><span class="s">&quot;Dictionary: </span><span class="si">~w</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8945594667-12">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="8945594667-12">]</span><span class="p" data-group-id="8945594667-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Demonstrates type testing, selector, updating.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">birthday</span><span class="p" data-group-id="6188422419-13">(</span><span class="n">P</span><span class="p" data-group-id="6188422419-13">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="6188422419-14">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="6188422419-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6188422419-15">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6188422419-15">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">birthday</span><span class="p" data-group-id="8945594667-13">(</span><span class="n">P</span><span class="p" data-group-id="8945594667-13">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="8945594667-14">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="8945594667-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8945594667-15">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8945594667-15">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">register_two_hackers</span><span class="p" data-group-id="6188422419-16">(</span><span class="p" data-group-id="6188422419-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="n">Hacker1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="6188422419-17">(</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">29</span><span class="p" data-group-id="6188422419-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="n">OldHacker</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">birthday</span><span class="p" data-group-id="6188422419-18">(</span><span class="n">Hacker1</span><span class="p" data-group-id="6188422419-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">register_two_hackers</span><span class="p" data-group-id="8945594667-16">(</span><span class="p" data-group-id="8945594667-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="n">Hacker1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="8945594667-17">(</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">29</span><span class="p" data-group-id="8945594667-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="n">OldHacker</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">birthday</span><span class="p" data-group-id="8945594667-18">(</span><span class="n">Hacker1</span><span class="p" data-group-id="8945594667-18">)</span><span class="p">,</span><span class="w">
│ │ │ │     </span><span class="c1">% The central_register_server should have</span><span class="w">
│ │ │ │     </span><span class="c1">% an interface function for this.</span><span class="w">
│ │ │ │ -   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6188422419-19">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w"> </span><span class="n">Hacker1</span><span class="p" data-group-id="6188422419-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6188422419-20">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w">
│ │ │ │ -             </span><span class="n">OldHacker</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6188422419-21">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -                              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6188422419-22">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6188422419-22">]</span><span class="p" data-group-id="6188422419-21">}</span><span class="p" data-group-id="6188422419-20">}</span><span class="p">.</span></code></pre>
│ │ │ │ +   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8945594667-19">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w"> </span><span class="n">Hacker1</span><span class="p" data-group-id="8945594667-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8945594667-20">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w">
│ │ │ │ +             </span><span class="n">OldHacker</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8945594667-21">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +                              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8945594667-22">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8945594667-22">]</span><span class="p" data-group-id="8945594667-21">}</span><span class="p" data-group-id="8945594667-20">}</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/patterns.xhtml
│ │ │ │ @@ -33,16 +33,16 @@
│ │ │ │  succeeds, any unbound variables in the pattern become bound. If the matching
│ │ │ │  fails, an exception is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** 1:1: variable &#39;X&#39; is unbound **</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">2</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="6204724790-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6204724790-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6204724790-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6204724790-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="1493374650-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1493374650-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1493374650-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1493374650-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value {1,2}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="6204724790-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6204724790-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6204724790-4">{</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6204724790-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6204724790-5">{</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6204724790-5">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="1493374650-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1493374650-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1493374650-4">{</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1493374650-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1493374650-5">{</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1493374650-5">}</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">6&gt; </span><span class="n">Y</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/otp-patch-apply.xhtml
│ │ │ │ @@ -106,13 +106,13 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Sanity check</span>
│ │ │ │  </h2>
│ │ │ │  <p>The application dependencies can be checked using the Erlang shell.
│ │ │ │  Application dependencies are verified among installed applications by
│ │ │ │  <code class="inline">otp_patch_apply</code>, but these are not necessarily those actually loaded.
│ │ │ │  By calling <code class="inline">system_information:sanity_check()</code> one can validate
│ │ │ │ -dependencies among applications actually loaded.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">system_information</span><span class="p">:</span><span class="nf">sanity_check</span><span class="p" data-group-id="3118750785-1">(</span><span class="p" data-group-id="3118750785-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +dependencies among applications actually loaded.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">system_information</span><span class="p">:</span><span class="nf">sanity_check</span><span class="p" data-group-id="2031491948-1">(</span><span class="p" data-group-id="2031491948-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>Please take a look at the reference of <a href="../../../lib/runtime_tools/doc/html/system_information.html#sanity_check/0" title="">sanity_check()</a> for more
│ │ │ │  information.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/opaques.xhtml
│ │ │ │ @@ -27,24 +27,24 @@
│ │ │ │    <span class="text">Opaque Type Aliases</span>
│ │ │ │  </h2>
│ │ │ │  <p>The main use case for opacity in Erlang is to hide the implementation of a data
│ │ │ │  type, enabling evolving the API while minimizing the risk of breaking consumers.
│ │ │ │  The runtime does not check opacity. Dialyzer provides some opacity-checking, but
│ │ │ │  the rest is up to convention.</p><p>This document explains what Erlang opacity is (and the trade-offs involved) via
│ │ │ │  the example of the <a href="../../../lib/stdlib/doc/html/sets.html#t:set/0"><code class="inline">sets:set()</code></a> data type. This type <em>was</em>
│ │ │ │ -defined in the <code class="inline">sets</code> module like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="4233208950-1">(</span><span class="n">Element</span><span class="p" data-group-id="4233208950-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="4233208950-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="4233208950-3">(</span><span class="n">Element</span><span class="p" data-group-id="4233208950-3">)</span><span class="p" data-group-id="4233208950-2">}</span><span class="p">.</span></code></pre><p>OTP 24 changed the definition to the following in
│ │ │ │ -<a href="https://github.com/erlang/otp/commit/e66941e8d7c47b973dff94c0308ea85a6be1958e">this commit</a>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="2492319925-1">(</span><span class="n">Element</span><span class="p" data-group-id="2492319925-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="2492319925-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="2492319925-3">(</span><span class="n">Element</span><span class="p" data-group-id="2492319925-3">)</span><span class="p" data-group-id="2492319925-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="2492319925-4">#{</span><span class="n">Element</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VALUE</span><span class="p" data-group-id="2492319925-4">}</span><span class="p">.</span></code></pre><p>And this change was safer and more backwards-compatible than if the type had
│ │ │ │ +defined in the <code class="inline">sets</code> module like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="6400323529-1">(</span><span class="n">Element</span><span class="p" data-group-id="6400323529-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="6400323529-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="6400323529-3">(</span><span class="n">Element</span><span class="p" data-group-id="6400323529-3">)</span><span class="p" data-group-id="6400323529-2">}</span><span class="p">.</span></code></pre><p>OTP 24 changed the definition to the following in
│ │ │ │ +<a href="https://github.com/erlang/otp/commit/e66941e8d7c47b973dff94c0308ea85a6be1958e">this commit</a>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="7996910642-1">(</span><span class="n">Element</span><span class="p" data-group-id="7996910642-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="7996910642-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="7996910642-3">(</span><span class="n">Element</span><span class="p" data-group-id="7996910642-3">)</span><span class="p" data-group-id="7996910642-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="7996910642-4">#{</span><span class="n">Element</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VALUE</span><span class="p" data-group-id="7996910642-4">}</span><span class="p">.</span></code></pre><p>And this change was safer and more backwards-compatible than if the type had
│ │ │ │  been defined with <code class="inline">-type</code> instead of <code class="inline">-opaque</code>. Here is why: when a module
│ │ │ │  defines an <code class="inline">-opaque</code>, the contract is that only the defining module should rely
│ │ │ │  on the definition of the type: no other modules should rely on the definition.</p><p>This means that code that pattern-matched on <code class="inline">set</code> as a record/tuple technically
│ │ │ │  broke the contract, and opted in to being potentially broken when the definition
│ │ │ │  of <code class="inline">set()</code> changed. Before OTP 24, this code printed <code class="inline">ok</code>. In OTP 24 it may
│ │ │ │ -error:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="7729154249-1">(</span><span class="p" data-group-id="7729154249-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="n">Set</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_tuple</span><span class="p" data-group-id="7729154249-2">(</span><span class="n">Set</span><span class="p" data-group-id="7729154249-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7729154249-3">(</span><span class="s">&quot;ok&quot;</span><span class="p" data-group-id="7729154249-3">)</span><span class="w">
│ │ │ │ +error:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0718250152-1">(</span><span class="p" data-group-id="0718250152-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="n">Set</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_tuple</span><span class="p" data-group-id="0718250152-2">(</span><span class="n">Set</span><span class="p" data-group-id="0718250152-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0718250152-3">(</span><span class="s">&quot;ok&quot;</span><span class="p" data-group-id="0718250152-3">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p><strong>When working with an opaque defined in another module, here are some
│ │ │ │  recommendations:</strong></p><ul><li>Don't examine the underlying type using pattern-matching, guards, or functions
│ │ │ │  that reveal the type, such as <a href="../../../lib/../erts/doc/html/erlang.html#tuple_size/1"><code class="inline">tuple_size/1</code></a> .</li><li>Instead, use functions provided by the module for working with the type. For
│ │ │ │  example, <code class="inline">sets</code> module provides <a href="../../../lib/stdlib/doc/html/sets.html#new/0"><code class="inline">sets:new/0</code></a>, <a href="../../../lib/stdlib/doc/html/sets.html#add_element/2"><code class="inline">sets:add_element/2</code></a>,
│ │ │ │  <a href="../../../lib/stdlib/doc/html/sets.html#is_element/2"><code class="inline">sets:is_element/2</code></a>, and so on.</li><li><p><a href="../../../lib/stdlib/doc/html/sets.html#t:set/1"><code class="inline">sets:set(a)</code></a> is a subtype of <code class="inline">sets:set(a | b)</code> and not the
│ │ │ │  other way around. Generally, you can rely on the property that <code class="inline">the_opaque(T)</code>
│ │ │ │  is a subtype of <code class="inline">the_opaque(U)</code> when T is a subtype of U.</p></li></ul><p><strong>When defining your own opaques, here are some recommendations:</strong></p><ul><li>Since consumers are expected to not rely on the definition of the opaque type,
│ │ │ ├── OEBPS/nif.xhtml
│ │ │ │ @@ -38,26 +38,26 @@
│ │ │ │    <span class="text">Erlang Program</span>
│ │ │ │  </h2>
│ │ │ │  <p>Even if all functions of a module are NIFs, an Erlang module is still needed for
│ │ │ │  two reasons:</p><ul><li>The NIF library must be explicitly loaded by Erlang code in the same module.</li><li>All NIFs of a module must have an Erlang implementation as well.</li></ul><p>Normally these are minimal stub implementations that throw an exception. But
│ │ │ │  they can also be used as fallback implementations for functions that do not have
│ │ │ │  native implementations on some architectures.</p><p>NIF libraries are loaded by calling <a href="../../../lib/../erts/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a>, with the name of the
│ │ │ │  shared library as argument. The second argument can be any term that will be
│ │ │ │ -passed on to the library and used for initialization:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0184088701-1">(</span><span class="ss">complex6</span><span class="p" data-group-id="0184088701-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0184088701-2">(</span><span class="p" data-group-id="0184088701-3">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0184088701-3">]</span><span class="p" data-group-id="0184088701-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="0184088701-4">(</span><span class="p" data-group-id="0184088701-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0184088701-5">]</span><span class="p" data-group-id="0184088701-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="0184088701-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0184088701-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="0184088701-7">(</span><span class="p" data-group-id="0184088701-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="0184088701-8">(</span><span class="s">&quot;./complex6_nif&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0184088701-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="0184088701-9">(</span><span class="p">_</span><span class="n">X</span><span class="p" data-group-id="0184088701-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="0184088701-10">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="0184088701-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="0184088701-11">(</span><span class="p">_</span><span class="n">Y</span><span class="p" data-group-id="0184088701-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="0184088701-12">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="0184088701-12">)</span><span class="p">.</span></code></pre><p>Here, the directive <code class="inline">on_load</code> is used to get function <code class="inline">init</code> to be automatically
│ │ │ │ +passed on to the library and used for initialization:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6770053224-1">(</span><span class="ss">complex6</span><span class="p" data-group-id="6770053224-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6770053224-2">(</span><span class="p" data-group-id="6770053224-3">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6770053224-3">]</span><span class="p" data-group-id="6770053224-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="6770053224-4">(</span><span class="p" data-group-id="6770053224-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6770053224-5">]</span><span class="p" data-group-id="6770053224-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="6770053224-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6770053224-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="6770053224-7">(</span><span class="p" data-group-id="6770053224-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="6770053224-8">(</span><span class="s">&quot;./complex6_nif&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6770053224-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="6770053224-9">(</span><span class="p">_</span><span class="n">X</span><span class="p" data-group-id="6770053224-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="6770053224-10">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="6770053224-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="6770053224-11">(</span><span class="p">_</span><span class="n">Y</span><span class="p" data-group-id="6770053224-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="6770053224-12">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="6770053224-12">)</span><span class="p">.</span></code></pre><p>Here, the directive <code class="inline">on_load</code> is used to get function <code class="inline">init</code> to be automatically
│ │ │ │  called when the module is loaded. If <code class="inline">init</code> returns anything other than <code class="inline">ok</code>,
│ │ │ │  such when the loading of the NIF library fails in this example, the module is
│ │ │ │  unloaded and calls to functions within it, fail.</p><p>Loading the NIF library overrides the stub implementations and cause calls to
│ │ │ │  <code class="inline">foo</code> and <code class="inline">bar</code> to be dispatched to the NIF implementations instead.</p><h2 id="nif-library-code" class="section-heading">
│ │ │ │    <a href="#nif-library-code" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -70,43 +70,43 @@
│ │ │ │  is a shared module, not a program, no main function is to be present.</p><p>The function arguments passed to a NIF appears in an array <code class="inline">argv</code>, with <code class="inline">argc</code>
│ │ │ │  as the length of the array, and thus the arity of the function. The Nth argument
│ │ │ │  of the function can be accessed as <code class="inline">argv[N-1]</code>. NIFs also take an environment
│ │ │ │  argument that serves as an opaque handle that is needed to be passed on to most
│ │ │ │  API functions. The environment contains information about the calling Erlang
│ │ │ │  process:</p><pre><code class="makeup c" translate="no"><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">erl_nif</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="k">extern</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="9282596448-1">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="9282596448-1">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="k">extern</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="9282596448-2">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="9282596448-2">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="k">extern</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="9111896585-1">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="9111896585-1">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="k">extern</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="9111896585-2">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="9111896585-2">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="nf">foo_nif</span><span class="p" data-group-id="9282596448-3">(</span><span class="no">ErlNifEnv</span><span class="o">*</span><span class="w"> </span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9282596448-4">[</span><span class="p" data-group-id="9282596448-4">]</span><span class="p" data-group-id="9282596448-3">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9282596448-5">{</span><span class="w">
│ │ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="nf">foo_nif</span><span class="p" data-group-id="9111896585-3">(</span><span class="no">ErlNifEnv</span><span class="o">*</span><span class="w"> </span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9111896585-4">[</span><span class="p" data-group-id="9111896585-4">]</span><span class="p" data-group-id="9111896585-3">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9111896585-5">{</span><span class="w">
│ │ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9282596448-6">(</span><span class="o">!</span><span class="nf">enif_get_int</span><span class="p" data-group-id="9282596448-7">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9282596448-8">[</span><span class="mi">0</span><span class="p" data-group-id="9282596448-8">]</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="9282596448-7">)</span><span class="p" data-group-id="9282596448-6">)</span><span class="w"> </span><span class="p" data-group-id="9282596448-9">{</span><span class="w">
│ │ │ │ -</span><span class="err">	</span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_badarg</span><span class="p" data-group-id="9282596448-10">(</span><span class="n">env</span><span class="p" data-group-id="9282596448-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9282596448-9">}</span><span class="w">
│ │ │ │ -    </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="9282596448-11">(</span><span class="n">x</span><span class="p" data-group-id="9282596448-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_int</span><span class="p" data-group-id="9282596448-12">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p" data-group-id="9282596448-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9282596448-5">}</span><span class="w">
│ │ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9111896585-6">(</span><span class="o">!</span><span class="nf">enif_get_int</span><span class="p" data-group-id="9111896585-7">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9111896585-8">[</span><span class="mi">0</span><span class="p" data-group-id="9111896585-8">]</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="9111896585-7">)</span><span class="p" data-group-id="9111896585-6">)</span><span class="w"> </span><span class="p" data-group-id="9111896585-9">{</span><span class="w">
│ │ │ │ +</span><span class="err">	</span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_badarg</span><span class="p" data-group-id="9111896585-10">(</span><span class="n">env</span><span class="p" data-group-id="9111896585-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9111896585-9">}</span><span class="w">
│ │ │ │ +    </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="9111896585-11">(</span><span class="n">x</span><span class="p" data-group-id="9111896585-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_int</span><span class="p" data-group-id="9111896585-12">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p" data-group-id="9111896585-12">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9111896585-5">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="nf">bar_nif</span><span class="p" data-group-id="9282596448-13">(</span><span class="no">ErlNifEnv</span><span class="o">*</span><span class="w"> </span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9282596448-14">[</span><span class="p" data-group-id="9282596448-14">]</span><span class="p" data-group-id="9282596448-13">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9282596448-15">{</span><span class="w">
│ │ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="nf">bar_nif</span><span class="p" data-group-id="9111896585-13">(</span><span class="no">ErlNifEnv</span><span class="o">*</span><span class="w"> </span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9111896585-14">[</span><span class="p" data-group-id="9111896585-14">]</span><span class="p" data-group-id="9111896585-13">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9111896585-15">{</span><span class="w">
│ │ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9282596448-16">(</span><span class="o">!</span><span class="nf">enif_get_int</span><span class="p" data-group-id="9282596448-17">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9282596448-18">[</span><span class="mi">0</span><span class="p" data-group-id="9282596448-18">]</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">y</span><span class="p" data-group-id="9282596448-17">)</span><span class="p" data-group-id="9282596448-16">)</span><span class="w"> </span><span class="p" data-group-id="9282596448-19">{</span><span class="w">
│ │ │ │ -</span><span class="err">	</span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_badarg</span><span class="p" data-group-id="9282596448-20">(</span><span class="n">env</span><span class="p" data-group-id="9282596448-20">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9282596448-19">}</span><span class="w">
│ │ │ │ -    </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="9282596448-21">(</span><span class="n">y</span><span class="p" data-group-id="9282596448-21">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_int</span><span class="p" data-group-id="9282596448-22">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p" data-group-id="9282596448-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9282596448-15">}</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ErlNifFunc</span><span class="w"> </span><span class="n">nif_funcs</span><span class="p" data-group-id="9282596448-23">[</span><span class="p" data-group-id="9282596448-23">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9282596448-24">{</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9282596448-25">{</span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">foo_nif</span><span class="p" data-group-id="9282596448-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9282596448-26">{</span><span class="s">&quot;bar&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">bar_nif</span><span class="p" data-group-id="9282596448-26">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9282596448-24">}</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9111896585-16">(</span><span class="o">!</span><span class="nf">enif_get_int</span><span class="p" data-group-id="9111896585-17">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9111896585-18">[</span><span class="mi">0</span><span class="p" data-group-id="9111896585-18">]</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">y</span><span class="p" data-group-id="9111896585-17">)</span><span class="p" data-group-id="9111896585-16">)</span><span class="w"> </span><span class="p" data-group-id="9111896585-19">{</span><span class="w">
│ │ │ │ +</span><span class="err">	</span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_badarg</span><span class="p" data-group-id="9111896585-20">(</span><span class="n">env</span><span class="p" data-group-id="9111896585-20">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9111896585-19">}</span><span class="w">
│ │ │ │ +    </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="9111896585-21">(</span><span class="n">y</span><span class="p" data-group-id="9111896585-21">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_int</span><span class="p" data-group-id="9111896585-22">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p" data-group-id="9111896585-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9111896585-15">}</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ErlNifFunc</span><span class="w"> </span><span class="n">nif_funcs</span><span class="p" data-group-id="9111896585-23">[</span><span class="p" data-group-id="9111896585-23">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9111896585-24">{</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9111896585-25">{</span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">foo_nif</span><span class="p" data-group-id="9111896585-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9111896585-26">{</span><span class="s">&quot;bar&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">bar_nif</span><span class="p" data-group-id="9111896585-26">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9111896585-24">}</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="no">ERL_NIF_INIT</span><span class="p" data-group-id="9282596448-27">(</span><span class="n">complex6</span><span class="p">,</span><span class="w"> </span><span class="n">nif_funcs</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="9282596448-27">)</span></code></pre><p>Here, <code class="inline">ERL_NIF_INIT</code> has the following arguments:</p><ul><li>The first argument must be the name of the Erlang module as a C-identifier. It
│ │ │ │ +</span><span class="no">ERL_NIF_INIT</span><span class="p" data-group-id="9111896585-27">(</span><span class="n">complex6</span><span class="p">,</span><span class="w"> </span><span class="n">nif_funcs</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="9111896585-27">)</span></code></pre><p>Here, <code class="inline">ERL_NIF_INIT</code> has the following arguments:</p><ul><li>The first argument must be the name of the Erlang module as a C-identifier. It
│ │ │ │  will be stringified by the macro.</li><li>The second argument is the array of <code class="inline">ErlNifFunc</code> structures containing name,
│ │ │ │  arity, and function pointer of each NIF.</li><li>The remaining arguments are pointers to callback functions that can be used to
│ │ │ │  initialize the library. They are not used in this simple example, hence they
│ │ │ │  are all set to <code class="inline">NULL</code>.</li></ul><p>Function arguments and return values are represented as values of type
│ │ │ │  <code class="inline">ERL_NIF_TERM</code>. Here, functions like <code class="inline">enif_get_int</code> and <code class="inline">enif_make_int</code> are used
│ │ │ │  to convert between Erlang term and C-type. If the function argument <code class="inline">argv[0]</code> is
│ │ │ │  not an integer, <code class="inline">enif_get_int</code> returns false, in which case it returns by
│ │ │ │ @@ -114,22 +114,22 @@
│ │ │ │    <a href="#running-the-example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Running the Example</span>
│ │ │ │  </h2>
│ │ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">unix&gt; gcc -o complex6_nif.so -fpic -shared complex.c complex6_nif.c
│ │ │ │  windows&gt; cl -LD -MD -Fe complex6_nif.dll complex.c complex6_nif.c</code></pre><p><em>Step 2:</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="ss">erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="n">R13B04</span><span class="w"> </span><span class="p" data-group-id="7351605412-1">(</span><span class="ss">erts</span><span class="o">-</span><span class="mf">5.7</span><span class="p">.</span><span class="mi">5</span><span class="p" data-group-id="7351605412-1">)</span><span class="w"> </span><span class="p" data-group-id="7351605412-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="7351605412-2">]</span><span class="w"> </span><span class="p" data-group-id="7351605412-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="7351605412-3">]</span><span class="w"> </span><span class="p" data-group-id="7351605412-4">[</span><span class="nc">rq</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="7351605412-4">]</span><span class="w"> </span><span class="p" data-group-id="7351605412-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="7351605412-5">]</span><span class="w"> </span><span class="p" data-group-id="7351605412-6">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="7351605412-6">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="n">R13B04</span><span class="w"> </span><span class="p" data-group-id="2620410021-1">(</span><span class="ss">erts</span><span class="o">-</span><span class="mf">5.7</span><span class="p">.</span><span class="mi">5</span><span class="p" data-group-id="2620410021-1">)</span><span class="w"> </span><span class="p" data-group-id="2620410021-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="2620410021-2">]</span><span class="w"> </span><span class="p" data-group-id="2620410021-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="2620410021-3">]</span><span class="w"> </span><span class="p" data-group-id="2620410021-4">[</span><span class="nc">rq</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="2620410021-4">]</span><span class="w"> </span><span class="p" data-group-id="2620410021-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="2620410021-5">]</span><span class="w"> </span><span class="p" data-group-id="2620410021-6">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="2620410021-6">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">7.5</span><span class="w">  </span><span class="p" data-group-id="7351605412-7">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="7351605412-7">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="7351605412-8">(</span><span class="ss">complex6</span><span class="p" data-group-id="7351605412-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7351605412-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex6</span><span class="p" data-group-id="7351605412-9">}</span></code></pre><p><em>Step 3:</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="1564375351-1">(</span><span class="mi">3</span><span class="p" data-group-id="1564375351-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">7.5</span><span class="w">  </span><span class="p" data-group-id="2620410021-7">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="2620410021-7">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="2620410021-8">(</span><span class="ss">complex6</span><span class="p" data-group-id="2620410021-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2620410021-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex6</span><span class="p" data-group-id="2620410021-9">}</span></code></pre><p><em>Step 3:</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="3001077258-1">(</span><span class="mi">3</span><span class="p" data-group-id="3001077258-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="1564375351-2">(</span><span class="mi">5</span><span class="p" data-group-id="1564375351-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="3001077258-2">(</span><span class="mi">5</span><span class="p" data-group-id="3001077258-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="1564375351-3">(</span><span class="s">&quot;not an integer&quot;</span><span class="p" data-group-id="1564375351-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="3001077258-3">(</span><span class="s">&quot;not an integer&quot;</span><span class="p" data-group-id="3001077258-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: bad argument
│ │ │ │       in function  complex6:foo/1
│ │ │ │          called as comlpex6:foo(&quot;not an integer&quot;)</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/modules.xhtml
│ │ │ │ @@ -23,20 +23,20 @@
│ │ │ │  <h2 id="module-syntax" class="section-heading">
│ │ │ │    <a href="#module-syntax" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Module Syntax</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang code is divided into <em>modules</em>. A module consists of a sequence of
│ │ │ │ -attributes and function declarations, each terminated by a period (<code class="inline">.</code>).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2269176923-1">(</span><span class="ss">m</span><span class="p" data-group-id="2269176923-1">)</span><span class="p">.</span><span class="w">          </span><span class="c1">% module attribute</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2269176923-2">(</span><span class="p" data-group-id="2269176923-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2269176923-3">]</span><span class="p" data-group-id="2269176923-2">)</span><span class="p">.</span><span class="w">   </span><span class="c1">% module attribute</span><span class="w">
│ │ │ │ +attributes and function declarations, each terminated by a period (<code class="inline">.</code>).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0920972597-1">(</span><span class="ss">m</span><span class="p" data-group-id="0920972597-1">)</span><span class="p">.</span><span class="w">          </span><span class="c1">% module attribute</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0920972597-2">(</span><span class="p" data-group-id="0920972597-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0920972597-3">]</span><span class="p" data-group-id="0920972597-2">)</span><span class="p">.</span><span class="w">   </span><span class="c1">% module attribute</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="2269176923-4">(</span><span class="n">N</span><span class="p" data-group-id="2269176923-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% beginning of function declaration</span><span class="w">
│ │ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="2269176923-5">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="2269176923-5">)</span><span class="p">;</span><span class="w">   </span><span class="c1">%  |</span><span class="w">
│ │ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="2269176923-6">(</span><span class="mi">0</span><span class="p" data-group-id="2269176923-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">           </span><span class="c1">%  |</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="0920972597-4">(</span><span class="n">N</span><span class="p" data-group-id="0920972597-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% beginning of function declaration</span><span class="w">
│ │ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="0920972597-5">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0920972597-5">)</span><span class="p">;</span><span class="w">   </span><span class="c1">%  |</span><span class="w">
│ │ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="0920972597-6">(</span><span class="mi">0</span><span class="p" data-group-id="0920972597-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">           </span><span class="c1">%  |</span><span class="w">
│ │ │ │      </span><span class="mi">1</span><span class="p">.</span><span class="w">               </span><span class="c1">% end of function declaration</span></code></pre><p>For a description of function declarations, see
│ │ │ │  <a href="ref_man_functions.xhtml">Function Declaration Syntax</a>.</p><h2 id="module-attributes" class="section-heading">
│ │ │ │    <a href="#module-attributes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Module Attributes</span>
│ │ │ │  </h2>
│ │ │ │ @@ -81,71 +81,71 @@
│ │ │ │  meaning.</p></section></li></ul><h3 id="behaviour-module-attribute" class="section-heading">
│ │ │ │    <a href="#behaviour-module-attribute" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Behaviour Module Attribute</span>
│ │ │ │  </h3>
│ │ │ │  <p>It is possible to specify that the module is the callback module for a
│ │ │ │ -<em>behaviour</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5820715417-1">(</span><span class="n">Behaviour</span><span class="p" data-group-id="5820715417-1">)</span><span class="p">.</span></code></pre><p>The atom <code class="inline">Behaviour</code> gives the name of the behaviour, which can be a
│ │ │ │ +<em>behaviour</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4521734348-1">(</span><span class="n">Behaviour</span><span class="p" data-group-id="4521734348-1">)</span><span class="p">.</span></code></pre><p>The atom <code class="inline">Behaviour</code> gives the name of the behaviour, which can be a
│ │ │ │  user-defined behaviour or one of the following OTP standard behaviours:</p><ul><li><code class="inline">gen_server</code></li><li><code class="inline">gen_statem</code></li><li><code class="inline">gen_event</code></li><li><code class="inline">supervisor</code></li></ul><p>The spelling <code class="inline">behavior</code> is also accepted.</p><p>The callback functions of the module can be specified either directly by the
│ │ │ │ -exported function <code class="inline">behaviour_info/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="6039612459-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="6039612459-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Callbacks</span><span class="p">.</span></code></pre><p>or by a <code class="inline">-callback</code> attribute for each callback function:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8822739051-1">(</span><span class="n">Arguments</span><span class="p" data-group-id="8822739051-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="p">.</span></code></pre><p>Here, <code class="inline">Arguments</code> is a list of zero or more arguments. The <code class="inline">-callback</code> attribute
│ │ │ │ +exported function <code class="inline">behaviour_info/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="1284335179-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="1284335179-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Callbacks</span><span class="p">.</span></code></pre><p>or by a <code class="inline">-callback</code> attribute for each callback function:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9435174298-1">(</span><span class="n">Arguments</span><span class="p" data-group-id="9435174298-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="p">.</span></code></pre><p>Here, <code class="inline">Arguments</code> is a list of zero or more arguments. The <code class="inline">-callback</code> attribute
│ │ │ │  is to be preferred since the extra type information can be used by tools to
│ │ │ │  produce documentation or find discrepancies.</p><p>Read more about behaviours and callback modules in
│ │ │ │  <a href="../../../lib/../system/doc/html/spec_proc.xhtml#behaviours">OTP Design Principles</a>.</p><h3 id="record-definitions" class="section-heading">
│ │ │ │    <a href="#record-definitions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Record Definitions</span>
│ │ │ │  </h3>
│ │ │ │ -<p>The same syntax as for module attributes is used for record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2632829792-1">(</span><span class="n">Record</span><span class="p">,</span><span class="w"> </span><span class="n">Fields</span><span class="p" data-group-id="2632829792-1">)</span><span class="p">.</span></code></pre><p>Record definitions are allowed anywhere in a module, also among the function
│ │ │ │ +<p>The same syntax as for module attributes is used for record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4775039277-1">(</span><span class="n">Record</span><span class="p">,</span><span class="w"> </span><span class="n">Fields</span><span class="p" data-group-id="4775039277-1">)</span><span class="p">.</span></code></pre><p>Record definitions are allowed anywhere in a module, also among the function
│ │ │ │  declarations. Read more in <a href="ref_man_records.xhtml">Records</a>.</p><h3 id="preprocessor" class="section-heading">
│ │ │ │    <a href="#preprocessor" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Preprocessor</span>
│ │ │ │  </h3>
│ │ │ │  <p>The same syntax as for module attributes is used by the preprocessor, which
│ │ │ │ -supports file inclusion, macros, and conditional compilation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1219102100-1">(</span><span class="s">&quot;SomeFile.hrl&quot;</span><span class="p" data-group-id="1219102100-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1219102100-2">(</span><span class="n">Macro</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="1219102100-2">)</span><span class="p">.</span></code></pre><p>Read more in <a href="macros.xhtml">Preprocessor</a>.</p><h3 id="setting-file-and-line" class="section-heading">
│ │ │ │ +supports file inclusion, macros, and conditional compilation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="8161123175-1">(</span><span class="s">&quot;SomeFile.hrl&quot;</span><span class="p" data-group-id="8161123175-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8161123175-2">(</span><span class="n">Macro</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="8161123175-2">)</span><span class="p">.</span></code></pre><p>Read more in <a href="macros.xhtml">Preprocessor</a>.</p><h3 id="setting-file-and-line" class="section-heading">
│ │ │ │    <a href="#setting-file-and-line" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Setting File and Line</span>
│ │ │ │  </h3>
│ │ │ │  <p>The same syntax as for module attributes is used for changing the pre-defined
│ │ │ │ -macros <code class="inline">?FILE</code> and <code class="inline">?LINE</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">file</span><span class="p" data-group-id="3627954551-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">Line</span><span class="p" data-group-id="3627954551-1">)</span><span class="p">.</span></code></pre><p>This attribute is used by tools, such as Yecc, to inform the compiler that the
│ │ │ │ +macros <code class="inline">?FILE</code> and <code class="inline">?LINE</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">file</span><span class="p" data-group-id="3178131772-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">Line</span><span class="p" data-group-id="3178131772-1">)</span><span class="p">.</span></code></pre><p>This attribute is used by tools, such as Yecc, to inform the compiler that the
│ │ │ │  source program is generated by another tool. It also indicates the
│ │ │ │  correspondence of source files to lines of the original user-written file, from
│ │ │ │  which the source program is produced.</p><h3 id="types-and-function-specifications" class="section-heading">
│ │ │ │    <a href="#types-and-function-specifications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Types and function specifications</span>
│ │ │ │  </h3>
│ │ │ │  <p>A similar syntax as for module attributes is used for specifying types and
│ │ │ │ -function specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_type</span><span class="p" data-group-id="4704385616-1">(</span><span class="p" data-group-id="4704385616-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="4704385616-2">(</span><span class="p" data-group-id="4704385616-2">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4704385616-3">(</span><span class="p" data-group-id="4704385616-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">my_function</span><span class="p" data-group-id="4704385616-4">(</span><span class="nf">integer</span><span class="p" data-group-id="4704385616-5">(</span><span class="p" data-group-id="4704385616-5">)</span><span class="p" data-group-id="4704385616-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4704385616-6">(</span><span class="p" data-group-id="4704385616-6">)</span><span class="p">.</span></code></pre><p>Read more in <a href="typespec.xhtml">Types and Function specifications</a>.</p><p>The description is based on
│ │ │ │ +function specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_type</span><span class="p" data-group-id="2880114975-1">(</span><span class="p" data-group-id="2880114975-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="2880114975-2">(</span><span class="p" data-group-id="2880114975-2">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="2880114975-3">(</span><span class="p" data-group-id="2880114975-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">my_function</span><span class="p" data-group-id="2880114975-4">(</span><span class="nf">integer</span><span class="p" data-group-id="2880114975-5">(</span><span class="p" data-group-id="2880114975-5">)</span><span class="p" data-group-id="2880114975-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="2880114975-6">(</span><span class="p" data-group-id="2880114975-6">)</span><span class="p">.</span></code></pre><p>Read more in <a href="typespec.xhtml">Types and Function specifications</a>.</p><p>The description is based on
│ │ │ │  <a href="http://www.erlang.org/eeps/eep-0008.html">EEP8 - Types and function specifications</a>,
│ │ │ │  which is not to be further updated.</p><h3 id="documentation-attributes" class="section-heading">
│ │ │ │    <a href="#documentation-attributes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Documentation attributes</span>
│ │ │ │  </h3>
│ │ │ │  <p>The module attribute <code class="inline">-doc(Documentation)</code> is used to provide user documentation
│ │ │ │ -for a function/type/callback:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="1224606623-1">(</span><span class="s">&quot;Example documentation&quot;</span><span class="p" data-group-id="1224606623-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="1224606623-2">(</span><span class="p" data-group-id="1224606623-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The attribute should be placed just before the entity it documents.The
│ │ │ │ +for a function/type/callback:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="1351796445-1">(</span><span class="s">&quot;Example documentation&quot;</span><span class="p" data-group-id="1351796445-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="1351796445-2">(</span><span class="p" data-group-id="1351796445-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The attribute should be placed just before the entity it documents.The
│ │ │ │  parenthesis are optional around <code class="inline">Documentation</code>. The allowed values for
│ │ │ │  <code class="inline">Documentation</code> are:</p><ul><li><p><strong><a href="data_types.xhtml#string">literal string</a> or
│ │ │ │  <a href="expressions.xhtml#unicode-segments">utf-8 encoded binary string</a></strong> - The string
│ │ │ │  documenting the entity. Any literal string is allowed, so both
│ │ │ │  <a href="data_types.xhtml#tqstring">triple quoted strings</a> and
│ │ │ │  <a href="data_types.xhtml#sigil">sigils</a> that translate to literal strings can be used.
│ │ │ │ -The following examples are equivalent:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7229070932-1">(</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="p" data-group-id="7229070932-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7229070932-2">(</span><span class="p" data-group-id="7229070932-3">&lt;&lt;</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="7229070932-3">&gt;&gt;</span><span class="p" data-group-id="7229070932-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +The following examples are equivalent:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="6387805863-1">(</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="p" data-group-id="6387805863-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="6387805863-2">(</span><span class="p" data-group-id="6387805863-3">&lt;&lt;</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="6387805863-3">&gt;&gt;</span><span class="p" data-group-id="6387805863-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">~S/Example &quot;docs&quot;/</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="s">&quot;
│ │ │ │     Example &quot;</span><span class="ss">docs</span><span class="s">&quot;
│ │ │ │     &quot;</span><span class="s">&quot;&quot;</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">~B|Example &quot;docs&quot;|</span><span class="p">.</span></code></pre><p>For clarity it is recommended to use either normal <code class="inline">&quot;strings&quot;</code> or triple
│ │ │ │  quoted strings for documentation attributes.</p></li><li><p><strong><code class="inline">{file,</code> <a href="../../../lib/kernel/doc/html/file.html#t:name/0"><code class="inline">file:name/0</code></a> <code class="inline">}</code></strong> - Read the contents of filename and use
│ │ │ │  that as the documentation string.</p></li><li><p><strong><code class="inline">false</code></strong> - Set the current entity as hidden, that is, it should not be
│ │ │ │ @@ -158,15 +158,15 @@
│ │ │ │    <a href="#the-feature-directive" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">The feature directive</span>
│ │ │ │  </h2>
│ │ │ │  <p>While not a module attribute, but rather a directive (since it might affect
│ │ │ │  syntax), there is the <code class="inline">-feature(..)</code> directive used for enabling and disabling
│ │ │ │ -<a href="../../../lib/../system/doc/html/features.xhtml#features">features</a>.</p><p>The syntax is similar to that of an attribute, but has two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">feature</span><span class="p" data-group-id="7444124099-1">(</span><span class="n">FeatureName</span><span class="p">,</span><span class="w"> </span><span class="ss">enable</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">disable</span><span class="p" data-group-id="7444124099-1">)</span><span class="p">.</span></code></pre><p>Note that the <a href="macros.xhtml#feature-directive">feature directive</a> can only appear
│ │ │ │ +<a href="../../../lib/../system/doc/html/features.xhtml#features">features</a>.</p><p>The syntax is similar to that of an attribute, but has two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">feature</span><span class="p" data-group-id="6783576236-1">(</span><span class="n">FeatureName</span><span class="p">,</span><span class="w"> </span><span class="ss">enable</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">disable</span><span class="p" data-group-id="6783576236-1">)</span><span class="p">.</span></code></pre><p>Note that the <a href="macros.xhtml#feature-directive">feature directive</a> can only appear
│ │ │ │  in a prefix of the module.</p><h2 id="comments" class="section-heading">
│ │ │ │    <a href="#comments" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Comments</span>
│ │ │ │  </h2>
│ │ │ │  <p>Comments can be placed anywhere in a module except within strings and
│ │ │ ├── OEBPS/maps.xhtml
│ │ │ │ @@ -53,16 +53,16 @@
│ │ │ │  single function that constructs the map using the map syntax and always use
│ │ │ │  it.</p></li><li><p>Always update the map using the <code class="inline">:=</code> operator (that is, requiring that an
│ │ │ │  element with that key already exists). The <code class="inline">:=</code> operator is slightly more
│ │ │ │  efficient, and it helps catching mispellings of keys.</p></li><li><p>Whenever possible, match multiple map elements at once.</p></li><li><p>Whenever possible, update multiple map elements at once.</p></li><li><p>Avoid default values and the <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> function. If there are default
│ │ │ │  values, sharing of keys between different instances of the map will be less
│ │ │ │  effective, and it is not possible to match multiple elements having default
│ │ │ │  values in one go.</p></li><li><p>To avoid having to deal with a map that may lack some keys, <a href="../../../lib/stdlib/doc/html/maps.html#merge/2"><code class="inline">maps:merge/2</code></a> can
│ │ │ │ -efficiently add multiple default values. For example:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8225356746-1">#{</span><span class="ss">shoe_size</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="ss">editor</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">emacs</span><span class="p" data-group-id="8225356746-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="8225356746-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="8225356746-2">)</span></code></pre></li></ul><h2 id="using-maps-as-dictionaries" class="section-heading">
│ │ │ │ +efficiently add multiple default values. For example:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4388479852-1">#{</span><span class="ss">shoe_size</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="ss">editor</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">emacs</span><span class="p" data-group-id="4388479852-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="4388479852-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="4388479852-2">)</span></code></pre></li></ul><h2 id="using-maps-as-dictionaries" class="section-heading">
│ │ │ │    <a href="#using-maps-as-dictionaries" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Using Maps as Dictionaries</span>
│ │ │ │  </h2>
│ │ │ │  <p>Using a map as a dictionary implies the following usage pattern:</p><ul><li>Keys are usually variables not known at compile-time.</li><li>There can be any number of elements in the map.</li><li>Usually, no more than one element is looked up or updated at once.</li></ul><p>Given that usage pattern, the difference in performance between using the map
│ │ │ │  syntax and the maps module is usually small. Therefore, which one to use is
│ │ │ │ @@ -72,18 +72,18 @@
│ │ │ │  choice.</li></ul><h2 id="using-maps-as-sets" class="section-heading">
│ │ │ │    <a href="#using-maps-as-sets" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Using Maps as Sets</span>
│ │ │ │  </h2>
│ │ │ │  <p>Starting in OTP 24, the <a href="../../../lib/stdlib/doc/html/sets.html"><code class="inline">sets</code></a> module has an option to represent sets as maps.
│ │ │ │ -Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="6123339611-1">(</span><span class="p" data-group-id="6123339611-2">[</span><span class="p" data-group-id="6123339611-3">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6123339611-3">}</span><span class="p" data-group-id="6123339611-2">]</span><span class="p" data-group-id="6123339611-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6123339611-4">#{</span><span class="p" data-group-id="6123339611-4">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">from_list</span><span class="p" data-group-id="6123339611-5">(</span><span class="p" data-group-id="6123339611-6">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="6123339611-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6123339611-7">[</span><span class="p" data-group-id="6123339611-8">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6123339611-8">}</span><span class="p" data-group-id="6123339611-7">]</span><span class="p" data-group-id="6123339611-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6123339611-9">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6123339611-10">[</span><span class="p" data-group-id="6123339611-10">]</span><span class="p">,</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6123339611-11">[</span><span class="p" data-group-id="6123339611-11">]</span><span class="p">,</span><span class="ss">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6123339611-12">[</span><span class="p" data-group-id="6123339611-12">]</span><span class="p" data-group-id="6123339611-9">}</span></code></pre><p><code class="inline">sets</code> backed by maps is generally the most efficient set representation, with a
│ │ │ │ +Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="7243013236-1">(</span><span class="p" data-group-id="7243013236-2">[</span><span class="p" data-group-id="7243013236-3">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7243013236-3">}</span><span class="p" data-group-id="7243013236-2">]</span><span class="p" data-group-id="7243013236-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7243013236-4">#{</span><span class="p" data-group-id="7243013236-4">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">from_list</span><span class="p" data-group-id="7243013236-5">(</span><span class="p" data-group-id="7243013236-6">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="7243013236-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7243013236-7">[</span><span class="p" data-group-id="7243013236-8">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7243013236-8">}</span><span class="p" data-group-id="7243013236-7">]</span><span class="p" data-group-id="7243013236-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7243013236-9">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7243013236-10">[</span><span class="p" data-group-id="7243013236-10">]</span><span class="p">,</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7243013236-11">[</span><span class="p" data-group-id="7243013236-11">]</span><span class="p">,</span><span class="ss">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7243013236-12">[</span><span class="p" data-group-id="7243013236-12">]</span><span class="p" data-group-id="7243013236-9">}</span></code></pre><p><code class="inline">sets</code> backed by maps is generally the most efficient set representation, with a
│ │ │ │  few possible exceptions:</p><ul><li><a href="../../../lib/stdlib/doc/html/ordsets.html#intersection/2"><code class="inline">ordsets:intersection/2</code></a> can be more efficient than <a href="../../../lib/stdlib/doc/html/sets.html#intersection/2"><code class="inline">sets:intersection/2</code></a>. If
│ │ │ │  the intersection operation is frequently used and operations that operate on a
│ │ │ │  single element in a set (such as <code class="inline">is_element/2</code>) are avoided, <a href="../../../lib/stdlib/doc/html/ordsets.html"><code class="inline">ordsets</code></a> can
│ │ │ │  be a better choice than <a href="../../../lib/stdlib/doc/html/sets.html"><code class="inline">sets</code></a>.</li><li>If the intersection operation is frequently used and operations that operate
│ │ │ │  on a single element in a set (such as <code class="inline">is_element/2</code>) must also be efficient,
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gb_sets.html"><code class="inline">gb_sets</code></a> can potentially be a better choice than <a href="../../../lib/stdlib/doc/html/sets.html"><code class="inline">sets</code></a>.</li><li>If the elements of the set are integers in a fairly compact range, the set can
│ │ │ │  be represented as an integer where each bit represents an element in the set.
│ │ │ │ @@ -108,18 +108,18 @@
│ │ │ │  for the runtime system).</p></li><li><p><strong>N</strong> - The number of elements in the map.</p></li><li><p><strong>Keys</strong> - A tuple with keys of the map: <code class="inline">{Key1,...,KeyN}</code>. The keys are
│ │ │ │  sorted.</p></li><li><p><strong>Value1</strong> - The value corresponding to the first key in the key tuple.</p></li><li><p><strong>ValueN</strong> - The value corresponding to the last key in the key tuple.</p></li></ul><p>As an example, let us look at how the map <code class="inline">#{a =&gt; foo, z =&gt; bar}</code> is
│ │ │ │  represented:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: left;">4</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>2</em></td><td style="text-align: center;"><code class="inline">{a,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: left;"><code class="inline">bar</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, z =&gt; bar}</em></p><p>Let us update the map: <code class="inline">M#{q =&gt; baz}</code>. The map now looks like this:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: center;">4</th><th style="text-align: center;">5</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>3</em></td><td style="text-align: center;"><code class="inline">{a,q,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: center;"><code class="inline">baz</code></td><td style="text-align: center;"><code class="inline">bar</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, q =&gt; baz, z =&gt; bar}</em></p><p>Finally, change the value of one element: <code class="inline">M#{z := bird}</code>. The map now looks
│ │ │ │  like this:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: center;">4</th><th style="text-align: center;">5</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>3</em></td><td style="text-align: center;"><code class="inline">{a,q,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: center;"><code class="inline">baz</code></td><td style="text-align: center;"><code class="inline">bird</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, q =&gt; baz, z =&gt; bird}</em></p><p>When the value for an existing key is updated, the key tuple is not updated,
│ │ │ │  allowing the key tuple to be shared with other instances of the map that have
│ │ │ │  the same keys. In fact, the key tuple can be shared between all maps with the
│ │ │ │  same keys with some care. To arrange that, define a function that returns a map.
│ │ │ │ -For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="0878526940-1">(</span><span class="p" data-group-id="0878526940-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0878526940-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p" data-group-id="0878526940-2">}</span><span class="p">.</span></code></pre><p>Defined like this, the key tuple <code class="inline">{a,b,c}</code> will be a global literal. To ensure
│ │ │ │ +For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="2772730604-1">(</span><span class="p" data-group-id="2772730604-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2772730604-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p" data-group-id="2772730604-2">}</span><span class="p">.</span></code></pre><p>Defined like this, the key tuple <code class="inline">{a,b,c}</code> will be a global literal. To ensure
│ │ │ │  that the key tuple is shared when creating an instance of the map, always call
│ │ │ │ -<code class="inline">new()</code> and modify the returned map:</p><pre><code class="makeup erlang" translate="no"><span class="w">    </span><span class="p" data-group-id="0249634368-1">(</span><span class="n">SOME_MODULE</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0249634368-2">(</span><span class="p" data-group-id="0249634368-2">)</span><span class="p" data-group-id="0249634368-1">)</span><span class="p" data-group-id="0249634368-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="0249634368-3">}</span><span class="p">.</span></code></pre><p>Using the map syntax with small maps is particularly efficient. As long as the
│ │ │ │ +<code class="inline">new()</code> and modify the returned map:</p><pre><code class="makeup erlang" translate="no"><span class="w">    </span><span class="p" data-group-id="7954958824-1">(</span><span class="n">SOME_MODULE</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="7954958824-2">(</span><span class="p" data-group-id="7954958824-2">)</span><span class="p" data-group-id="7954958824-1">)</span><span class="p" data-group-id="7954958824-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="7954958824-3">}</span><span class="p">.</span></code></pre><p>Using the map syntax with small maps is particularly efficient. As long as the
│ │ │ │  keys are known at compile-time, the map is updated in one go, making the time to
│ │ │ │  update a map essentially constant regardless of the number of keys updated. The
│ │ │ │  same goes for matching. (When the keys are variables, one or more of the keys
│ │ │ │  could be identical, so the operations need to be performed sequentially from
│ │ │ │  left to right.)</p><p>The memory size for a small map is the size of all keys and values plus 5 words.
│ │ │ │  See <a href="memory.xhtml">Memory</a> for more information about memory sizes.</p><h3 id="how-large-maps-are-implemented" class="section-heading">
│ │ │ │    <a href="#how-large-maps-are-implemented" class="hover-link">
│ │ │ │ @@ -146,21 +146,21 @@
│ │ │ │    <a href="#using-the-map-syntax" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Using the Map Syntax</span>
│ │ │ │  </h2>
│ │ │ │  <p>Using the map syntax is usually slightly more efficient than using the
│ │ │ │  corresponding function in the <a href="../../../lib/stdlib/doc/html/maps.html"><code class="inline">maps</code></a> module.</p><p>The gain in efficiency for the map syntax is more noticeable for the following
│ │ │ │ -operations that can only be achieved using the map syntax:</p><ul><li>Matching multiple literal keys</li><li>Updating multiple literal keys</li><li>Adding multiple literal keys to a map</li></ul><p>For example:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="1351418653-1">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="ss">z</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="1351418653-1">}</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="5390116976-1">(</span><span class="ss">x</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="5390116976-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="5390116976-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="5390116976-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="5390116976-3">(</span><span class="ss">z</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">,</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="5390116976-3">)</span></code></pre><p>If the map is a small map, the first example runs roughly three times as fast.</p><p>Note that for variable keys, the elements are updated sequentially from left to
│ │ │ │ -right. For example, given the following update with variable keys:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="4426623797-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="4426623797-1">}</span></code></pre><p>the compiler rewrites it like this to ensure that the updates are applied from
│ │ │ │ -left to right:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="2950694548-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2950694548-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="2950694548-2">#{</span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2950694548-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="2950694548-3">#{</span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="2950694548-3">}</span></code></pre><p>If a key is known to exist in a map, using the <code class="inline">:=</code> operator is slightly more
│ │ │ │ +operations that can only be achieved using the map syntax:</p><ul><li>Matching multiple literal keys</li><li>Updating multiple literal keys</li><li>Adding multiple literal keys to a map</li></ul><p>For example:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="3632594906-1">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="ss">z</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="3632594906-1">}</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="2362012178-1">(</span><span class="ss">x</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="2362012178-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="2362012178-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="2362012178-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="2362012178-3">(</span><span class="ss">z</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">,</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="2362012178-3">)</span></code></pre><p>If the map is a small map, the first example runs roughly three times as fast.</p><p>Note that for variable keys, the elements are updated sequentially from left to
│ │ │ │ +right. For example, given the following update with variable keys:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="9703550447-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="9703550447-1">}</span></code></pre><p>the compiler rewrites it like this to ensure that the updates are applied from
│ │ │ │ +left to right:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="5452281912-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5452281912-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="5452281912-2">#{</span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5452281912-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="5452281912-3">#{</span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="5452281912-3">}</span></code></pre><p>If a key is known to exist in a map, using the <code class="inline">:=</code> operator is slightly more
│ │ │ │  efficient than using the <code class="inline">=&gt;</code> operator for a small map.</p><h2 id="using-the-functions-in-the-maps-module" class="section-heading">
│ │ │ │    <a href="#using-the-functions-in-the-maps-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Using the Functions in the maps Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>Here follows some notes about most of the functions in the <code class="inline">maps</code> module. For
│ │ │ │ @@ -211,23 +211,23 @@
│ │ │ │    <a href="#maps-get-3" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">maps:get/3</span>
│ │ │ │  </h3>
│ │ │ │  <p>As an optimization, the compiler will rewrite a call to <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> to Erlang
│ │ │ │  code similar to the following:</p><pre><code class="makeup erlang" translate="no"><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">Map</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="2203366557-1">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="2203366557-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="p">;</span><span class="w">
│ │ │ │ -             </span><span class="p" data-group-id="2203366557-2">#{</span><span class="p" data-group-id="2203366557-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Default</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="0739071713-1">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="0739071713-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="p">;</span><span class="w">
│ │ │ │ +             </span><span class="p" data-group-id="0739071713-2">#{</span><span class="p" data-group-id="0739071713-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Default</span><span class="w">
│ │ │ │           </span><span class="k">end</span></code></pre><p>This is reasonably efficient, but if a small map is used as an alternative to
│ │ │ │  using a record it is often better not to rely on default values as it prevents
│ │ │ │  sharing of keys, which may in the end use more memory than what you save from
│ │ │ │  not storing default values in the map.</p><p>If default values are nevertheless required, instead of calling <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a>
│ │ │ │  multiple times, consider putting the default values in a map and merging that
│ │ │ │ -map with the other map:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8360271284-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">KeyN</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueN</span><span class="p" data-group-id="8360271284-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="8360271284-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="8360271284-2">)</span></code></pre><p>This helps share keys between the default map and the one you applied defaults
│ │ │ │ +map with the other map:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0108897966-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">KeyN</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueN</span><span class="p" data-group-id="0108897966-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="0108897966-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="0108897966-2">)</span></code></pre><p>This helps share keys between the default map and the one you applied defaults
│ │ │ │  to, as long as the default map contains <em>all</em> the keys that will ever be used
│ │ │ │  and not just the ones with default values. Whether this is faster than calling
│ │ │ │  <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> multiple times depends on the size of the map and the number of
│ │ │ │  default values.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before OTP 26.0 <a href="../../../lib/stdlib/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> was implemented by calling the function instead
│ │ │ │  of rewriting it as an Erlang expression. It is now slightly faster but can no
│ │ │ │  longer be traced.</p></section><h3 id="maps-intersect-2-maps-intersect_with-3" class="section-heading">
│ │ │ │    <a href="#maps-intersect-2-maps-intersect_with-3" class="hover-link">
│ │ │ ├── OEBPS/macros.xhtml
│ │ │ │ @@ -22,56 +22,56 @@
│ │ │ │      </h1>
│ │ │ │  <h2 id="file-inclusion" class="section-heading">
│ │ │ │    <a href="#file-inclusion" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">File Inclusion</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A file can be included as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3654479015-1">(</span><span class="n">File</span><span class="p" data-group-id="3654479015-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="3654479015-2">(</span><span class="n">File</span><span class="p" data-group-id="3654479015-2">)</span><span class="p">.</span></code></pre><p><code class="inline">File</code>, a string, is to point out a file. The contents of this file are included
│ │ │ │ +<p>A file can be included as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6731583566-1">(</span><span class="n">File</span><span class="p" data-group-id="6731583566-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="6731583566-2">(</span><span class="n">File</span><span class="p" data-group-id="6731583566-2">)</span><span class="p">.</span></code></pre><p><code class="inline">File</code>, a string, is to point out a file. The contents of this file are included
│ │ │ │  as is, at the position of the directive.</p><p>Include files are typically used for record and macro definitions that are
│ │ │ │  shared by several modules. It is recommended to use the file name extension
│ │ │ │  <code class="inline">.hrl</code> for include files.</p><p><code class="inline">File</code> can start with a path component <code class="inline">$VAR</code>, for some string <code class="inline">VAR</code>. If that is
│ │ │ │  the case, the value of the environment variable <code class="inline">VAR</code> as returned by
│ │ │ │  <code class="inline">os:getenv(VAR)</code> is substituted for <code class="inline">$VAR</code>. If <code class="inline">os:getenv(VAR)</code> returns <code class="inline">false</code>,
│ │ │ │  <code class="inline">$VAR</code> is left as is.</p><p>If the filename <code class="inline">File</code> is absolute (possibly after variable substitution), the
│ │ │ │  include file with that name is included. Otherwise, the specified file is
│ │ │ │  searched for in the following directories, and in this order:</p><ol><li>The current working directory</li><li>The directory where the module is being compiled</li><li>The directories given by the <code class="inline">include</code> option</li></ol><p>For details, see <a href="../../../lib/../erts/doc/html/erlc_cmd.xhtml">erlc</a> in ERTS and
│ │ │ │ -<a href="../../../lib/compiler/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2172713855-1">(</span><span class="s">&quot;my_records.hrl&quot;</span><span class="p" data-group-id="2172713855-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2172713855-2">(</span><span class="s">&quot;incdir/my_records.hrl&quot;</span><span class="p" data-group-id="2172713855-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2172713855-3">(</span><span class="s">&quot;/home/user/proj/my_records.hrl&quot;</span><span class="p" data-group-id="2172713855-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2172713855-4">(</span><span class="s">&quot;$PROJ_ROOT/my_records.hrl&quot;</span><span class="p" data-group-id="2172713855-4">)</span><span class="p">.</span></code></pre><p><code class="inline">include_lib</code> is similar to <code class="inline">include</code>, but is not to point out an absolute file.
│ │ │ │ +<a href="../../../lib/compiler/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6336143279-1">(</span><span class="s">&quot;my_records.hrl&quot;</span><span class="p" data-group-id="6336143279-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6336143279-2">(</span><span class="s">&quot;incdir/my_records.hrl&quot;</span><span class="p" data-group-id="6336143279-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6336143279-3">(</span><span class="s">&quot;/home/user/proj/my_records.hrl&quot;</span><span class="p" data-group-id="6336143279-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="6336143279-4">(</span><span class="s">&quot;$PROJ_ROOT/my_records.hrl&quot;</span><span class="p" data-group-id="6336143279-4">)</span><span class="p">.</span></code></pre><p><code class="inline">include_lib</code> is similar to <code class="inline">include</code>, but is not to point out an absolute file.
│ │ │ │  Instead, the first path component (possibly after variable substitution) is
│ │ │ │ -assumed to be the name of an application.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="7823527580-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="7823527580-1">)</span><span class="p">.</span></code></pre><p>The code server uses <code class="inline">code:lib_dir(kernel)</code> to find the directory of the current
│ │ │ │ +assumed to be the name of an application.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="7847371373-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="7847371373-1">)</span><span class="p">.</span></code></pre><p>The code server uses <code class="inline">code:lib_dir(kernel)</code> to find the directory of the current
│ │ │ │  (latest) version of Kernel, and then the subdirectory <code class="inline">include</code> is searched for
│ │ │ │  the file <code class="inline">file.hrl</code>.</p><h2 id="defining-and-using-macros" class="section-heading">
│ │ │ │    <a href="#defining-and-using-macros" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Defining and Using Macros</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A macro is defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4124981838-1">(</span><span class="n">Const</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="4124981838-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4124981838-2">(</span><span class="n">Func</span><span class="p" data-group-id="4124981838-3">(</span><span class="n">Var1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">VarN</span><span class="p" data-group-id="4124981838-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="4124981838-2">)</span><span class="p">.</span></code></pre><p>A macro definition can be placed anywhere among the attributes and function
│ │ │ │ +<p>A macro is defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8068497753-1">(</span><span class="n">Const</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="8068497753-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8068497753-2">(</span><span class="n">Func</span><span class="p" data-group-id="8068497753-3">(</span><span class="n">Var1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">VarN</span><span class="p" data-group-id="8068497753-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="8068497753-2">)</span><span class="p">.</span></code></pre><p>A macro definition can be placed anywhere among the attributes and function
│ │ │ │  declarations of a module, but the definition must come before any usage of the
│ │ │ │  macro.</p><p>If a macro is used in several modules, it is recommended that the macro
│ │ │ │  definition is placed in an include file.</p><p>A macro is used as follows:</p><pre><code class="text">?Const
│ │ │ │  ?Func(Arg1,...,ArgN)</code></pre><p>Macros are expanded during compilation. A simple macro <code class="inline">?Const</code> is replaced with
│ │ │ │ -<code class="inline">Replacement</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="7310669227-1">(</span><span class="n">TIMEOUT</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="7310669227-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">Replacement</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1095415451-1">(</span><span class="n">TIMEOUT</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="1095415451-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">call</span><span class="p" data-group-id="7310669227-2">(</span><span class="n">Request</span><span class="p" data-group-id="7310669227-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="7310669227-3">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">TIMEOUT</span><span class="p" data-group-id="7310669227-3">)</span><span class="p">.</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">call</span><span class="p" data-group-id="5932718263-1">(</span><span class="n">Request</span><span class="p" data-group-id="5932718263-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="5932718263-2">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="5932718263-2">)</span><span class="p">.</span></code></pre><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> is replaced with <code class="inline">Replacement</code>, where all
│ │ │ │ +</span><span class="nf">call</span><span class="p" data-group-id="1095415451-2">(</span><span class="n">Request</span><span class="p" data-group-id="1095415451-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1095415451-3">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">TIMEOUT</span><span class="p" data-group-id="1095415451-3">)</span><span class="p">.</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">call</span><span class="p" data-group-id="5204819928-1">(</span><span class="n">Request</span><span class="p" data-group-id="5204819928-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="5204819928-2">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="5204819928-2">)</span><span class="p">.</span></code></pre><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> is replaced with <code class="inline">Replacement</code>, where all
│ │ │ │  occurrences of a variable <code class="inline">Var</code> from the macro definition are replaced with the
│ │ │ │ -corresponding argument <code class="inline">Arg</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6227957093-1">(</span><span class="n">MACRO1</span><span class="p" data-group-id="6227957093-2">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6227957093-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6227957093-3">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6227957093-3">}</span><span class="p" data-group-id="6227957093-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +corresponding argument <code class="inline">Arg</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3048734988-1">(</span><span class="n">MACRO1</span><span class="p" data-group-id="3048734988-2">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3048734988-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3048734988-3">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3048734988-3">}</span><span class="p" data-group-id="3048734988-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="6227957093-4">(</span><span class="n">X</span><span class="p" data-group-id="6227957093-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="6227957093-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="6227957093-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="6227957093-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="p" data-group-id="6227957093-6">)</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="6367547134-1">(</span><span class="n">X</span><span class="p" data-group-id="6367547134-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6367547134-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6367547134-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6367547134-3">{</span><span class="ss">a</span><span class="p">,</span><span class="n">X</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">123</span><span class="p" data-group-id="6367547134-3">}</span><span class="p">.</span></code></pre><p>It is good programming practice, but not mandatory, to ensure that a macro
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="3048734988-4">(</span><span class="n">X</span><span class="p" data-group-id="3048734988-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="3048734988-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3048734988-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="3048734988-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="p" data-group-id="3048734988-6">)</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="6784604131-1">(</span><span class="n">X</span><span class="p" data-group-id="6784604131-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6784604131-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6784604131-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6784604131-3">{</span><span class="ss">a</span><span class="p">,</span><span class="n">X</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">123</span><span class="p" data-group-id="6784604131-3">}</span><span class="p">.</span></code></pre><p>It is good programming practice, but not mandatory, to ensure that a macro
│ │ │ │  definition is a valid Erlang syntactic form.</p><p>To view the result of macro expansion, a module can be compiled with the <code class="inline">'P'</code>
│ │ │ │  option. <code class="inline">compile:file(File, ['P'])</code>. This produces a listing of the parsed code
│ │ │ │  after preprocessing and parse transforms, in the file <code class="inline">File.P</code>.</p><h2 id="predefined-macros" class="section-heading">
│ │ │ │    <a href="#predefined-macros" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Predefined Macros</span>
│ │ │ │ @@ -90,29 +90,29 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Macros Overloading</span>
│ │ │ │  </h2>
│ │ │ │  <p>It is possible to overload macros, except for predefined macros. An overloaded
│ │ │ │  macro has more than one definition, each with a different number of arguments.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Support for overloading of macros was added in Erlang 5.7.5/OTP R13B04.</p></section><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> with a (possibly empty) list of arguments results
│ │ │ │  in an error message if there is at least one definition of <code class="inline">Func</code> with
│ │ │ │ -arguments, but none with N arguments.</p><p>Assuming these definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1345563999-1">(</span><span class="n">F0</span><span class="p" data-group-id="1345563999-2">(</span><span class="p" data-group-id="1345563999-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="1345563999-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1345563999-3">(</span><span class="n">F1</span><span class="p" data-group-id="1345563999-4">(</span><span class="n">A</span><span class="p" data-group-id="1345563999-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="1345563999-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1345563999-5">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="nc">m</span><span class="p">:</span><span class="ss">f</span><span class="p" data-group-id="1345563999-5">)</span><span class="p">.</span></code></pre><p>the following does not work:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f0</span><span class="p" data-group-id="5296460424-1">(</span><span class="p" data-group-id="5296460424-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +arguments, but none with N arguments.</p><p>Assuming these definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0110541908-1">(</span><span class="n">F0</span><span class="p" data-group-id="0110541908-2">(</span><span class="p" data-group-id="0110541908-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="0110541908-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0110541908-3">(</span><span class="n">F1</span><span class="p" data-group-id="0110541908-4">(</span><span class="n">A</span><span class="p" data-group-id="0110541908-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="0110541908-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0110541908-5">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="nc">m</span><span class="p">:</span><span class="ss">f</span><span class="p" data-group-id="0110541908-5">)</span><span class="p">.</span></code></pre><p>the following does not work:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f0</span><span class="p" data-group-id="4406564602-1">(</span><span class="p" data-group-id="4406564602-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="o">?</span><span class="n">F0</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, an empty list of arguments expected.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">f1</span><span class="p" data-group-id="5296460424-2">(</span><span class="n">A</span><span class="p" data-group-id="5296460424-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">?</span><span class="n">F1</span><span class="p" data-group-id="5296460424-3">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="5296460424-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, exactly one argument expected.</span></code></pre><p>On the other hand,</p><pre><code class="text">f() -&gt;
│ │ │ │ -    ?C().</code></pre><p>is expanded to</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="3604406620-1">(</span><span class="p" data-group-id="3604406620-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">m</span><span class="p">:</span><span class="nf">f</span><span class="p" data-group-id="3604406620-2">(</span><span class="p" data-group-id="3604406620-2">)</span><span class="p">.</span></code></pre><h2 id="removing-a-macro-definition" class="section-heading">
│ │ │ │ +</span><span class="nf">f1</span><span class="p" data-group-id="4406564602-2">(</span><span class="n">A</span><span class="p" data-group-id="4406564602-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">?</span><span class="n">F1</span><span class="p" data-group-id="4406564602-3">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="4406564602-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, exactly one argument expected.</span></code></pre><p>On the other hand,</p><pre><code class="text">f() -&gt;
│ │ │ │ +    ?C().</code></pre><p>is expanded to</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="1695414897-1">(</span><span class="p" data-group-id="1695414897-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">m</span><span class="p">:</span><span class="nf">f</span><span class="p" data-group-id="1695414897-2">(</span><span class="p" data-group-id="1695414897-2">)</span><span class="p">.</span></code></pre><h2 id="removing-a-macro-definition" class="section-heading">
│ │ │ │    <a href="#removing-a-macro-definition" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Removing a macro definition</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A definition of macro can be removed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">undef</span><span class="p" data-group-id="1336202860-1">(</span><span class="n">Macro</span><span class="p" data-group-id="1336202860-1">)</span><span class="p">.</span></code></pre><h2 id="conditional-compilation" class="section-heading">
│ │ │ │ +<p>A definition of macro can be removed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">undef</span><span class="p" data-group-id="8010555821-1">(</span><span class="n">Macro</span><span class="p" data-group-id="8010555821-1">)</span><span class="p">.</span></code></pre><h2 id="conditional-compilation" class="section-heading">
│ │ │ │    <a href="#conditional-compilation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Conditional Compilation</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following macro directives support conditional compilation:</p><ul><li><p><strong><code class="inline">-ifdef(Macro).</code></strong> - Evaluate the following lines only if <code class="inline">Macro</code> is
│ │ │ │  defined.</p></li><li><p><strong><code class="inline">-ifndef(Macro).</code></strong> - Evaluate the following lines only if <code class="inline">Macro</code> is not
│ │ │ │ @@ -124,43 +124,43 @@
│ │ │ │  true, and the <code class="inline">Condition</code> evaluates to true, the lines following the <code class="inline">elif</code>
│ │ │ │  are evaluated instead.</p></li><li><p><strong><code class="inline">-endif.</code></strong> - Specifies the end of a series of control flow directives.</p></li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Macro directives cannot be used inside functions.</p></section><p>Syntactically, the <code class="inline">Condition</code> in <code class="inline">if</code> and <code class="inline">elif</code> must be a
│ │ │ │  <a href="expressions.xhtml#guard-expressions">guard expression</a>. Other constructs (such as
│ │ │ │  a <code class="inline">case</code> expression) result in a compilation error.</p><p>As opposed to the standard guard expressions, an expression in an <code class="inline">if</code> and
│ │ │ │  <code class="inline">elif</code> also supports calling the psuedo-function <code class="inline">defined(Name)</code>, which tests
│ │ │ │  whether the <code class="inline">Name</code> argument is the name of a previously defined macro.
│ │ │ │  <code class="inline">defined(Name)</code> evaluates to <code class="inline">true</code> if the macro is defined and <code class="inline">false</code>
│ │ │ │ -otherwise. An attempt to call other functions results in a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2724268758-1">(</span><span class="ss">m</span><span class="p" data-group-id="2724268758-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +otherwise. An attempt to call other functions results in a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2646481835-1">(</span><span class="ss">m</span><span class="p" data-group-id="2646481835-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="2724268758-2">(</span><span class="ss">debug</span><span class="p" data-group-id="2724268758-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2724268758-3">(</span><span class="n">LOG</span><span class="p" data-group-id="2724268758-4">(</span><span class="n">X</span><span class="p" data-group-id="2724268758-4">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2724268758-5">(</span><span class="s">&quot;{</span><span class="si">~p</span><span class="s">,</span><span class="si">~p</span><span class="s">}: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2724268758-6">[</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="o">?</span><span class="n">LINE</span><span class="p">,</span><span class="n">X</span><span class="p" data-group-id="2724268758-6">]</span><span class="p" data-group-id="2724268758-5">)</span><span class="p" data-group-id="2724268758-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="2646481835-2">(</span><span class="ss">debug</span><span class="p" data-group-id="2646481835-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2646481835-3">(</span><span class="n">LOG</span><span class="p" data-group-id="2646481835-4">(</span><span class="n">X</span><span class="p" data-group-id="2646481835-4">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2646481835-5">(</span><span class="s">&quot;{</span><span class="si">~p</span><span class="s">,</span><span class="si">~p</span><span class="s">}: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2646481835-6">[</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="o">?</span><span class="n">LINE</span><span class="p">,</span><span class="n">X</span><span class="p" data-group-id="2646481835-6">]</span><span class="p" data-group-id="2646481835-5">)</span><span class="p" data-group-id="2646481835-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2724268758-7">(</span><span class="n">LOG</span><span class="p" data-group-id="2724268758-8">(</span><span class="n">X</span><span class="p" data-group-id="2724268758-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2724268758-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2646481835-7">(</span><span class="n">LOG</span><span class="p" data-group-id="2646481835-8">(</span><span class="n">X</span><span class="p" data-group-id="2646481835-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2646481835-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>When trace output is desired, <code class="inline">debug</code> is to be defined when the module <code class="inline">m</code> is
│ │ │ │  compiled:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erlc -Ddebug m.erl</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="ow">or</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="0234647680-1">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0234647680-2">{</span><span class="ss">d</span><span class="p">,</span><span class="w"> </span><span class="ss">debug</span><span class="p" data-group-id="0234647680-2">}</span><span class="p" data-group-id="0234647680-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0234647680-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">m</span><span class="p" data-group-id="0234647680-3">}</span></code></pre><p><code class="inline">?LOG(Arg)</code> is then expanded to a call to <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> and provide the user
│ │ │ │ -with some simple trace output.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9880039712-1">(</span><span class="ss">m</span><span class="p" data-group-id="9880039712-1">)</span><span class="w">
│ │ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="6575565823-1">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6575565823-2">{</span><span class="ss">d</span><span class="p">,</span><span class="w"> </span><span class="ss">debug</span><span class="p" data-group-id="6575565823-2">}</span><span class="p" data-group-id="6575565823-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6575565823-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">m</span><span class="p" data-group-id="6575565823-3">}</span></code></pre><p><code class="inline">?LOG(Arg)</code> is then expanded to a call to <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> and provide the user
│ │ │ │ +with some simple trace output.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9157303515-1">(</span><span class="ss">m</span><span class="p" data-group-id="9157303515-1">)</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="9880039712-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">25</span><span class="p" data-group-id="9880039712-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="9157303515-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">25</span><span class="p" data-group-id="9157303515-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Code that will work in OTP 25 or higher</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">elif</span><span class="p" data-group-id="9880039712-3">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="p" data-group-id="9880039712-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">elif</span><span class="p" data-group-id="9157303515-3">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="p" data-group-id="9157303515-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Code that will work in OTP 26 or higher</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Code that will work in OTP 24 or lower.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This code uses the <code class="inline">OTP_RELEASE</code> macro to conditionally select code depending on
│ │ │ │ -release.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6318882001-1">(</span><span class="ss">m</span><span class="p" data-group-id="6318882001-1">)</span><span class="w">
│ │ │ │ +release.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5414712898-1">(</span><span class="ss">m</span><span class="p" data-group-id="5414712898-1">)</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="6318882001-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">defined</span><span class="p" data-group-id="6318882001-3">(</span><span class="ss">debug</span><span class="p" data-group-id="6318882001-3">)</span><span class="p" data-group-id="6318882001-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="5414712898-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">defined</span><span class="p" data-group-id="5414712898-3">(</span><span class="ss">debug</span><span class="p" data-group-id="5414712898-3">)</span><span class="p" data-group-id="5414712898-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Debugging code that requires OTP 26 or later.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% Non-debug code that works in any release.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This code uses the <code class="inline">OTP_RELEASE</code> macro and <code class="inline">defined(debug)</code> to compile debug
│ │ │ │  code only for OTP 26 or later.</p><h2 id="the-feature-directive" class="section-heading">
│ │ │ │    <a href="#the-feature-directive" class="hover-link">
│ │ │ │ @@ -175,40 +175,40 @@
│ │ │ │  used. In practice this means it should appear before any <code class="inline">-export(..)</code> or record
│ │ │ │  definitions.</p><h2 id="error-and-warning-directives" class="section-heading">
│ │ │ │    <a href="#error-and-warning-directives" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">-error() and -warning() directives</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The directive <code class="inline">-error(Term)</code> causes a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9626635193-1">(</span><span class="ss">t</span><span class="p" data-group-id="9626635193-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9626635193-2">(</span><span class="p" data-group-id="9626635193-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9626635193-3">]</span><span class="p" data-group-id="9626635193-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>The directive <code class="inline">-error(Term)</code> causes a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3693606966-1">(</span><span class="ss">t</span><span class="p" data-group-id="3693606966-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3693606966-2">(</span><span class="p" data-group-id="3693606966-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3693606966-3">]</span><span class="p" data-group-id="3693606966-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="9626635193-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="9626635193-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="9626635193-5">(</span><span class="p" data-group-id="9626635193-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="3693606966-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="3693606966-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="3693606966-5">(</span><span class="p" data-group-id="3693606966-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">error</span><span class="p" data-group-id="9626635193-6">(</span><span class="s">&quot;Macro VERSION must be defined.&quot;</span><span class="p" data-group-id="9626635193-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="9626635193-7">(</span><span class="p" data-group-id="9626635193-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">error</span><span class="p" data-group-id="3693606966-6">(</span><span class="s">&quot;Macro VERSION must be defined.&quot;</span><span class="p" data-group-id="3693606966-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="3693606966-7">(</span><span class="p" data-group-id="3693606966-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span></code></pre><p>The error message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ │ -t.erl:7: -error(&quot;Macro VERSION must be defined.&quot;).</code></pre><p>The directive <code class="inline">-warning(Term)</code> causes a compilation warning.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1925697330-1">(</span><span class="ss">t</span><span class="p" data-group-id="1925697330-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1925697330-2">(</span><span class="p" data-group-id="1925697330-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1925697330-3">]</span><span class="p" data-group-id="1925697330-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +t.erl:7: -error(&quot;Macro VERSION must be defined.&quot;).</code></pre><p>The directive <code class="inline">-warning(Term)</code> causes a compilation warning.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9082181671-1">(</span><span class="ss">t</span><span class="p" data-group-id="9082181671-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9082181671-2">(</span><span class="p" data-group-id="9082181671-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9082181671-3">]</span><span class="p" data-group-id="9082181671-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">ifndef</span><span class="p" data-group-id="1925697330-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="1925697330-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">warning</span><span class="p" data-group-id="1925697330-5">(</span><span class="s">&quot;Macro VERSION not defined -- using default version.&quot;</span><span class="p" data-group-id="1925697330-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1925697330-6">(</span><span class="n">VERSION</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;0&quot;</span><span class="p" data-group-id="1925697330-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">ifndef</span><span class="p" data-group-id="9082181671-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="9082181671-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">warning</span><span class="p" data-group-id="9082181671-5">(</span><span class="s">&quot;Macro VERSION not defined -- using default version.&quot;</span><span class="p" data-group-id="9082181671-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9082181671-6">(</span><span class="n">VERSION</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;0&quot;</span><span class="p" data-group-id="9082181671-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="1925697330-7">(</span><span class="p" data-group-id="1925697330-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span></code></pre><p>The warning message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="9082181671-7">(</span><span class="p" data-group-id="9082181671-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span></code></pre><p>The warning message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ │  t.erl:5: Warning: -warning(&quot;Macro VERSION not defined -- using default version.&quot;).</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>The <code class="inline">-error()</code> and <code class="inline">-warning()</code> directives were added in Erlang/OTP 19.</p></section><h2 id="stringifying-macro-arguments" class="section-heading">
│ │ │ │    <a href="#stringifying-macro-arguments" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Stringifying Macro Arguments</span>
│ │ │ │  </h2>
│ │ │ │  <p>The construction <code class="inline">??Arg</code>, where <code class="inline">Arg</code> is a macro argument, is expanded to a
│ │ │ │  string containing the tokens of the argument. This is similar to the <code class="inline">#arg</code>
│ │ │ │ -stringifying construction in C.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3748272176-1">(</span><span class="n">TESTCALL</span><span class="p" data-group-id="3748272176-2">(</span><span class="n">Call</span><span class="p" data-group-id="3748272176-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3748272176-3">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3748272176-4">[</span><span class="o">?</span><span class="o">?</span><span class="n">Call</span><span class="p">,</span><span class="w"> </span><span class="n">Call</span><span class="p" data-group-id="3748272176-4">]</span><span class="p" data-group-id="3748272176-3">)</span><span class="p" data-group-id="3748272176-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +stringifying construction in C.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6040626459-1">(</span><span class="n">TESTCALL</span><span class="p" data-group-id="6040626459-2">(</span><span class="n">Call</span><span class="p" data-group-id="6040626459-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6040626459-3">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6040626459-4">[</span><span class="o">?</span><span class="o">?</span><span class="n">Call</span><span class="p">,</span><span class="w"> </span><span class="n">Call</span><span class="p" data-group-id="6040626459-4">]</span><span class="p" data-group-id="6040626459-3">)</span><span class="p" data-group-id="6040626459-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="3748272176-5">(</span><span class="nf">myfunction</span><span class="p" data-group-id="3748272176-6">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3748272176-6">)</span><span class="p" data-group-id="3748272176-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="3748272176-7">(</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="3748272176-8">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3748272176-8">)</span><span class="p" data-group-id="3748272176-7">)</span><span class="p">.</span></code></pre><p>results in</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3158939321-1">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3158939321-2">[</span><span class="s">&quot;myfunction ( 1 , 2 )&quot;</span><span class="p">,</span><span class="nf">myfunction</span><span class="p" data-group-id="3158939321-3">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3158939321-3">)</span><span class="p" data-group-id="3158939321-2">]</span><span class="p" data-group-id="3158939321-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3158939321-4">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3158939321-5">[</span><span class="s">&quot;you : function ( 2 , 1 )&quot;</span><span class="p">,</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="3158939321-6">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3158939321-6">)</span><span class="p" data-group-id="3158939321-5">]</span><span class="p" data-group-id="3158939321-4">)</span><span class="p">.</span></code></pre><p>That is, a trace output, with both the function called and the resulting value.</p>
│ │ │ │ +</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="6040626459-5">(</span><span class="nf">myfunction</span><span class="p" data-group-id="6040626459-6">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6040626459-6">)</span><span class="p" data-group-id="6040626459-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="6040626459-7">(</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="6040626459-8">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6040626459-8">)</span><span class="p" data-group-id="6040626459-7">)</span><span class="p">.</span></code></pre><p>results in</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5433717961-1">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="5433717961-2">[</span><span class="s">&quot;myfunction ( 1 , 2 )&quot;</span><span class="p">,</span><span class="nf">myfunction</span><span class="p" data-group-id="5433717961-3">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5433717961-3">)</span><span class="p" data-group-id="5433717961-2">]</span><span class="p" data-group-id="5433717961-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5433717961-4">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="5433717961-5">[</span><span class="s">&quot;you : function ( 2 , 1 )&quot;</span><span class="p">,</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="5433717961-6">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5433717961-6">)</span><span class="p" data-group-id="5433717961-5">]</span><span class="p" data-group-id="5433717961-4">)</span><span class="p">.</span></code></pre><p>That is, a trace output, with both the function called and the resulting value.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/listhandling.xhtml
│ │ │ │ @@ -25,101 +25,101 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating a List</span>
│ │ │ │  </h2>
│ │ │ │  <p>Lists can only be built starting from the end and attaching list elements at the
│ │ │ │  beginning. If you use the <code class="inline">++</code> operator as follows, a new list is created that
│ │ │ │  is a copy of the elements in <code class="inline">List1</code>, followed by <code class="inline">List2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">List1</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">List2</span></code></pre><p>Looking at how <a href="../../../lib/stdlib/doc/html/lists.html#append/2"><code class="inline">lists:append/2</code></a> or <code class="inline">++</code> would be implemented in plain Erlang,
│ │ │ │ -clearly the first list is copied:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="1508796949-1">(</span><span class="p" data-group-id="1508796949-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1508796949-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1508796949-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1508796949-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">append</span><span class="p" data-group-id="1508796949-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1508796949-4">)</span><span class="p" data-group-id="1508796949-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">append</span><span class="p" data-group-id="1508796949-5">(</span><span class="p" data-group-id="1508796949-6">[</span><span class="p" data-group-id="1508796949-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1508796949-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +clearly the first list is copied:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="6646244000-1">(</span><span class="p" data-group-id="6646244000-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6646244000-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6646244000-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6646244000-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">append</span><span class="p" data-group-id="6646244000-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6646244000-4">)</span><span class="p" data-group-id="6646244000-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">append</span><span class="p" data-group-id="6646244000-5">(</span><span class="p" data-group-id="6646244000-6">[</span><span class="p" data-group-id="6646244000-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6646244000-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>When recursing and building a list, it is important to ensure that you attach
│ │ │ │  the new elements to the beginning of the list. In this way, you will build <em>one</em>
│ │ │ │ -list, not hundreds or thousands of copies of the growing result list.</p><p>Let us first see how it is not to be done:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">bad_fib</span><span class="p" data-group-id="1392482457-1">(</span><span class="n">N</span><span class="p" data-group-id="1392482457-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">bad_fib</span><span class="p" data-group-id="1392482457-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1392482457-3">[</span><span class="p" data-group-id="1392482457-3">]</span><span class="p" data-group-id="1392482457-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +list, not hundreds or thousands of copies of the growing result list.</p><p>Let us first see how it is not to be done:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">bad_fib</span><span class="p" data-group-id="4703761979-1">(</span><span class="n">N</span><span class="p" data-group-id="4703761979-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">bad_fib</span><span class="p" data-group-id="4703761979-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4703761979-3">[</span><span class="p" data-group-id="4703761979-3">]</span><span class="p" data-group-id="4703761979-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">bad_fib</span><span class="p" data-group-id="1392482457-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="1392482457-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">bad_fib</span><span class="p" data-group-id="4703761979-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="4703761979-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Fibs</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">bad_fib</span><span class="p" data-group-id="1392482457-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="1392482457-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">bad_fib</span><span class="p" data-group-id="1392482457-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1392482457-7">[</span><span class="n">Current</span><span class="p" data-group-id="1392482457-7">]</span><span class="p" data-group-id="1392482457-6">)</span><span class="p">.</span></code></pre><p>Here more than one list is built. In each iteration step a new list is created
│ │ │ │ +</span><span class="nf">bad_fib</span><span class="p" data-group-id="4703761979-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="4703761979-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">bad_fib</span><span class="p" data-group-id="4703761979-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4703761979-7">[</span><span class="n">Current</span><span class="p" data-group-id="4703761979-7">]</span><span class="p" data-group-id="4703761979-6">)</span><span class="p">.</span></code></pre><p>Here more than one list is built. In each iteration step a new list is created
│ │ │ │  that is one element longer than the new previous list.</p><p>To avoid copying the result in each iteration, build the list in reverse order
│ │ │ │ -and reverse the list when you are done:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9878516842-1">(</span><span class="n">N</span><span class="p" data-group-id="9878516842-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9878516842-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9878516842-3">[</span><span class="p" data-group-id="9878516842-3">]</span><span class="p" data-group-id="9878516842-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +and reverse the list when you are done:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9465908752-1">(</span><span class="n">N</span><span class="p" data-group-id="9465908752-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9465908752-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9465908752-3">[</span><span class="p" data-group-id="9465908752-3">]</span><span class="p" data-group-id="9465908752-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9878516842-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="9878516842-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9878516842-5">(</span><span class="n">Fibs</span><span class="p" data-group-id="9878516842-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9878516842-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="9878516842-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9878516842-7">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9878516842-8">[</span><span class="n">Current</span><span class="p">|</span><span class="n">Fibs</span><span class="p" data-group-id="9878516842-8">]</span><span class="p" data-group-id="9878516842-7">)</span><span class="p">.</span></code></pre><h2 id="list-comprehensions" class="section-heading">
│ │ │ │ +</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9465908752-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="9465908752-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9465908752-5">(</span><span class="n">Fibs</span><span class="p" data-group-id="9465908752-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9465908752-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="9465908752-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="9465908752-7">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9465908752-8">[</span><span class="n">Current</span><span class="p">|</span><span class="n">Fibs</span><span class="p" data-group-id="9465908752-8">]</span><span class="p" data-group-id="9465908752-7">)</span><span class="p">.</span></code></pre><h2 id="list-comprehensions" class="section-heading">
│ │ │ │    <a href="#list-comprehensions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">List Comprehensions</span>
│ │ │ │  </h2>
│ │ │ │ -<p>A list comprehension:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9749145565-1">[</span><span class="n">Expr</span><span class="p" data-group-id="9749145565-2">(</span><span class="n">E</span><span class="p" data-group-id="9749145565-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9749145565-1">]</span></code></pre><p>is basically translated to a local function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="2432553100-1">(</span><span class="p" data-group-id="2432553100-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="2432553100-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="2432553100-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2432553100-3">[</span><span class="n">Expr</span><span class="p" data-group-id="2432553100-4">(</span><span class="n">E</span><span class="p" data-group-id="2432553100-4">)</span><span class="p">|</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="2432553100-5">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="2432553100-5">)</span><span class="p" data-group-id="2432553100-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="2432553100-6">(</span><span class="p" data-group-id="2432553100-7">[</span><span class="p" data-group-id="2432553100-7">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="2432553100-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2432553100-8">[</span><span class="p" data-group-id="2432553100-8">]</span><span class="p">.</span></code></pre><p>If the result of the list comprehension will <em>obviously</em> not be used, a list
│ │ │ │ -will not be constructed. For example, in this code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7813720369-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="7813720369-2">(</span><span class="n">E</span><span class="p" data-group-id="7813720369-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7813720369-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +<p>A list comprehension:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7555128323-1">[</span><span class="n">Expr</span><span class="p" data-group-id="7555128323-2">(</span><span class="n">E</span><span class="p" data-group-id="7555128323-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7555128323-1">]</span></code></pre><p>is basically translated to a local function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5147718796-1">(</span><span class="p" data-group-id="5147718796-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="5147718796-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="5147718796-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5147718796-3">[</span><span class="n">Expr</span><span class="p" data-group-id="5147718796-4">(</span><span class="n">E</span><span class="p" data-group-id="5147718796-4">)</span><span class="p">|</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5147718796-5">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="5147718796-5">)</span><span class="p" data-group-id="5147718796-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5147718796-6">(</span><span class="p" data-group-id="5147718796-7">[</span><span class="p" data-group-id="5147718796-7">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="5147718796-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5147718796-8">[</span><span class="p" data-group-id="5147718796-8">]</span><span class="p">.</span></code></pre><p>If the result of the list comprehension will <em>obviously</em> not be used, a list
│ │ │ │ +will not be constructed. For example, in this code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0483804632-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="0483804632-2">(</span><span class="n">E</span><span class="p" data-group-id="0483804632-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="0483804632-1">]</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>or in this code:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">Var</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6445957395-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="6445957395-2">(</span><span class="n">E</span><span class="p" data-group-id="6445957395-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6445957395-1">]</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0039388420-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="0039388420-2">(</span><span class="n">E</span><span class="p" data-group-id="0039388420-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="0039388420-1">]</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nf">some_function</span><span class="p" data-group-id="6445957395-3">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6445957395-3">)</span><span class="p">,</span></code></pre><p>the value is not assigned to a variable, not passed to another function, and not
│ │ │ │ +</span><span class="nf">some_function</span><span class="p" data-group-id="0039388420-3">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0039388420-3">)</span><span class="p">,</span></code></pre><p>the value is not assigned to a variable, not passed to another function, and not
│ │ │ │  returned. This means that there is no need to construct a list and the compiler
│ │ │ │ -will simplify the code for the list comprehension to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="8712528249-1">(</span><span class="p" data-group-id="8712528249-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="8712528249-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="8712528249-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Expr</span><span class="p" data-group-id="8712528249-3">(</span><span class="n">E</span><span class="p" data-group-id="8712528249-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="8712528249-4">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="8712528249-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="8712528249-5">(</span><span class="p" data-group-id="8712528249-6">[</span><span class="p" data-group-id="8712528249-6">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="8712528249-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8712528249-7">[</span><span class="p" data-group-id="8712528249-7">]</span><span class="p">.</span></code></pre><p>The compiler also understands that assigning to <code class="inline">_</code> means that the value will
│ │ │ │ -not be used. Therefore, the code in the following example will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9356760383-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="9356760383-2">(</span><span class="n">E</span><span class="p" data-group-id="9356760383-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9356760383-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +will simplify the code for the list comprehension to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="4987937639-1">(</span><span class="p" data-group-id="4987937639-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="4987937639-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="4987937639-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Expr</span><span class="p" data-group-id="4987937639-3">(</span><span class="n">E</span><span class="p" data-group-id="4987937639-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="4987937639-4">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="4987937639-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="4987937639-5">(</span><span class="p" data-group-id="4987937639-6">[</span><span class="p" data-group-id="4987937639-6">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="4987937639-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4987937639-7">[</span><span class="p" data-group-id="4987937639-7">]</span><span class="p">.</span></code></pre><p>The compiler also understands that assigning to <code class="inline">_</code> means that the value will
│ │ │ │ +not be used. Therefore, the code in the following example will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6761618062-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="6761618062-2">(</span><span class="n">E</span><span class="p" data-group-id="6761618062-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6761618062-1">]</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="p">.</span></code></pre><h2 id="deep-and-flat-lists" class="section-heading">
│ │ │ │    <a href="#deep-and-flat-lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Deep and Flat Lists</span>
│ │ │ │  </h2>
│ │ │ │  <p><a href="../../../lib/stdlib/doc/html/lists.html#flatten/1"><code class="inline">lists:flatten/1</code></a> builds an entirely new list. It is therefore expensive, and
│ │ │ │  even <em>more</em> expensive than the <code class="inline">++</code> operator (which copies its left argument,
│ │ │ │  but not its right argument).</p><p>In the following situations it is unnecessary to call <a href="../../../lib/stdlib/doc/html/lists.html#flatten/1"><code class="inline">lists:flatten/1</code></a>:</p><ul><li>When sending data to a port. Ports understand deep lists so there is no reason
│ │ │ │  to flatten the list before sending it to the port.</li><li>When calling BIFs that accept deep lists, such as
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a> or
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#iolist_to_binary/1"><code class="inline">iolist_to_binary/1</code></a>.</li><li>When you know that your list is only one level deep. Use <a href="../../../lib/stdlib/doc/html/lists.html#append/1"><code class="inline">lists:append/1</code></a>
│ │ │ │ -instead.</li></ul><p><em>Examples:</em></p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="2781335951-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">DeepList</span><span class="p" data-group-id="2781335951-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="9691293257-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="9691293257-2">(</span><span class="n">DeepList</span><span class="p" data-group-id="9691293257-2">)</span><span class="p" data-group-id="9691293257-1">)</span></code></pre><p>A common way to send a zero-terminated string to a port is the following:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="8185645012-1">[</span><span class="mi">0</span><span class="p" data-group-id="8185645012-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nf">port_command</span><span class="p" data-group-id="8185645012-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="8185645012-2">)</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2061858082-1">[</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2061858082-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nf">port_command</span><span class="p" data-group-id="2061858082-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="2061858082-2">)</span></code></pre><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">append</span><span class="p" data-group-id="7622533648-1">(</span><span class="p" data-group-id="7622533648-2">[</span><span class="p" data-group-id="7622533648-3">[</span><span class="mi">1</span><span class="p" data-group-id="7622533648-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7622533648-4">[</span><span class="mi">2</span><span class="p" data-group-id="7622533648-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7622533648-5">[</span><span class="mi">3</span><span class="p" data-group-id="7622533648-5">]</span><span class="p" data-group-id="7622533648-2">]</span><span class="p" data-group-id="7622533648-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7622533648-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7622533648-6">]</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="0541099959-1">(</span><span class="p" data-group-id="0541099959-2">[</span><span class="p" data-group-id="0541099959-3">[</span><span class="mi">1</span><span class="p" data-group-id="0541099959-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0541099959-4">[</span><span class="mi">2</span><span class="p" data-group-id="0541099959-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0541099959-5">[</span><span class="mi">3</span><span class="p" data-group-id="0541099959-5">]</span><span class="p" data-group-id="0541099959-2">]</span><span class="p" data-group-id="0541099959-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0541099959-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0541099959-6">]</span></code></pre><h2 id="recursive-list-functions" class="section-heading">
│ │ │ │ +instead.</li></ul><p><em>Examples:</em></p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="9647628725-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">DeepList</span><span class="p" data-group-id="9647628725-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="0083893259-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="0083893259-2">(</span><span class="n">DeepList</span><span class="p" data-group-id="0083893259-2">)</span><span class="p" data-group-id="0083893259-1">)</span></code></pre><p>A common way to send a zero-terminated string to a port is the following:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9531294533-1">[</span><span class="mi">0</span><span class="p" data-group-id="9531294533-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">port_command</span><span class="p" data-group-id="9531294533-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="9531294533-2">)</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5328836047-1">[</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5328836047-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">port_command</span><span class="p" data-group-id="5328836047-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="5328836047-2">)</span></code></pre><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">append</span><span class="p" data-group-id="8289143789-1">(</span><span class="p" data-group-id="8289143789-2">[</span><span class="p" data-group-id="8289143789-3">[</span><span class="mi">1</span><span class="p" data-group-id="8289143789-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8289143789-4">[</span><span class="mi">2</span><span class="p" data-group-id="8289143789-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8289143789-5">[</span><span class="mi">3</span><span class="p" data-group-id="8289143789-5">]</span><span class="p" data-group-id="8289143789-2">]</span><span class="p" data-group-id="8289143789-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8289143789-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8289143789-6">]</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="5377495951-1">(</span><span class="p" data-group-id="5377495951-2">[</span><span class="p" data-group-id="5377495951-3">[</span><span class="mi">1</span><span class="p" data-group-id="5377495951-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5377495951-4">[</span><span class="mi">2</span><span class="p" data-group-id="5377495951-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5377495951-5">[</span><span class="mi">3</span><span class="p" data-group-id="5377495951-5">]</span><span class="p" data-group-id="5377495951-2">]</span><span class="p" data-group-id="5377495951-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5377495951-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5377495951-6">]</span></code></pre><h2 id="recursive-list-functions" class="section-heading">
│ │ │ │    <a href="#recursive-list-functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Recursive List Functions</span>
│ │ │ │  </h2>
│ │ │ │  <p>There are two basic ways to write a function that traverses a list and
│ │ │ │  produces a new list.</p><p>The first way is writing a <em>body-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ │ -</span><span class="nf">add_42_body</span><span class="p" data-group-id="0792296946-1">(</span><span class="p" data-group-id="0792296946-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0792296946-2">]</span><span class="p" data-group-id="0792296946-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0792296946-3">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">add_42_body</span><span class="p" data-group-id="0792296946-4">(</span><span class="n">T</span><span class="p" data-group-id="0792296946-4">)</span><span class="p" data-group-id="0792296946-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">add_42_body</span><span class="p" data-group-id="0792296946-5">(</span><span class="p" data-group-id="0792296946-6">[</span><span class="p" data-group-id="0792296946-6">]</span><span class="p" data-group-id="0792296946-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0792296946-7">[</span><span class="p" data-group-id="0792296946-7">]</span><span class="p">.</span></code></pre><p>The second way is writing a <em>tail-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="0472359149-1">(</span><span class="n">List</span><span class="p" data-group-id="0472359149-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="0472359149-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0472359149-3">[</span><span class="p" data-group-id="0472359149-3">]</span><span class="p" data-group-id="0472359149-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add_42_body</span><span class="p" data-group-id="2258672766-1">(</span><span class="p" data-group-id="2258672766-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2258672766-2">]</span><span class="p" data-group-id="2258672766-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2258672766-3">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">add_42_body</span><span class="p" data-group-id="2258672766-4">(</span><span class="n">T</span><span class="p" data-group-id="2258672766-4">)</span><span class="p" data-group-id="2258672766-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">add_42_body</span><span class="p" data-group-id="2258672766-5">(</span><span class="p" data-group-id="2258672766-6">[</span><span class="p" data-group-id="2258672766-6">]</span><span class="p" data-group-id="2258672766-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2258672766-7">[</span><span class="p" data-group-id="2258672766-7">]</span><span class="p">.</span></code></pre><p>The second way is writing a <em>tail-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="0684061694-1">(</span><span class="n">List</span><span class="p" data-group-id="0684061694-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="0684061694-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0684061694-3">[</span><span class="p" data-group-id="0684061694-3">]</span><span class="p" data-group-id="0684061694-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="0472359149-4">(</span><span class="p" data-group-id="0472359149-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0472359149-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0472359149-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="0472359149-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0472359149-7">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0472359149-7">]</span><span class="p" data-group-id="0472359149-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="0472359149-8">(</span><span class="p" data-group-id="0472359149-9">[</span><span class="p" data-group-id="0472359149-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0472359149-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="0472359149-10">(</span><span class="n">Acc</span><span class="p" data-group-id="0472359149-10">)</span><span class="p">.</span></code></pre><p>In early version of Erlang the tail-recursive function would typically
│ │ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="0684061694-4">(</span><span class="p" data-group-id="0684061694-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0684061694-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0684061694-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="0684061694-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0684061694-7">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0684061694-7">]</span><span class="p" data-group-id="0684061694-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="0684061694-8">(</span><span class="p" data-group-id="0684061694-9">[</span><span class="p" data-group-id="0684061694-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0684061694-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="0684061694-10">(</span><span class="n">Acc</span><span class="p" data-group-id="0684061694-10">)</span><span class="p">.</span></code></pre><p>In early version of Erlang the tail-recursive function would typically
│ │ │ │  be more efficient. In modern versions of Erlang, there is usually not
│ │ │ │  much difference in performance between a body-recursive list function and
│ │ │ │  tail-recursive function that reverses the list at the end. Therefore,
│ │ │ │  concentrate on writing beautiful code and forget about the performance
│ │ │ │  of your list functions. In the time-critical parts of your code,
│ │ │ │  <em>measure</em> before rewriting your code.</p><p>For a thorough discussion about tail and body recursion, see
│ │ │ │  <a href="http://ferd.ca/erlang-s-tail-recursion-is-not-a-silver-bullet.html">Erlang's Tail Recursion is Not a Silver Bullet</a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>This section is about list functions that <em>construct</em> lists. A tail-recursive
│ │ │ │  function that does not construct a list runs in constant space, while the
│ │ │ │  corresponding body-recursive function uses stack space proportional to the
│ │ │ │  length of the list.</p></section><p>For example, a function that sums a list of integers, is <em>not</em> to be written as
│ │ │ │ -follows:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">recursive_sum</span><span class="p" data-group-id="6505926727-1">(</span><span class="p" data-group-id="6505926727-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6505926727-2">]</span><span class="p" data-group-id="6505926727-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">H</span><span class="o">+</span><span class="nf">recursive_sum</span><span class="p" data-group-id="6505926727-3">(</span><span class="n">T</span><span class="p" data-group-id="6505926727-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">recursive_sum</span><span class="p" data-group-id="6505926727-4">(</span><span class="p" data-group-id="6505926727-5">[</span><span class="p" data-group-id="6505926727-5">]</span><span class="p" data-group-id="6505926727-4">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">sum</span><span class="p" data-group-id="3376865046-1">(</span><span class="n">L</span><span class="p" data-group-id="3376865046-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="3376865046-2">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3376865046-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +follows:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">recursive_sum</span><span class="p" data-group-id="3167164491-1">(</span><span class="p" data-group-id="3167164491-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3167164491-2">]</span><span class="p" data-group-id="3167164491-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">H</span><span class="o">+</span><span class="nf">recursive_sum</span><span class="p" data-group-id="3167164491-3">(</span><span class="n">T</span><span class="p" data-group-id="3167164491-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">recursive_sum</span><span class="p" data-group-id="3167164491-4">(</span><span class="p" data-group-id="3167164491-5">[</span><span class="p" data-group-id="3167164491-5">]</span><span class="p" data-group-id="3167164491-4">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">sum</span><span class="p" data-group-id="4797534608-1">(</span><span class="n">L</span><span class="p" data-group-id="4797534608-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="4797534608-2">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4797534608-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">sum</span><span class="p" data-group-id="3376865046-3">(</span><span class="p" data-group-id="3376865046-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3376865046-4">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="3376865046-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="3376865046-5">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">H</span><span class="p" data-group-id="3376865046-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">sum</span><span class="p" data-group-id="3376865046-6">(</span><span class="p" data-group-id="3376865046-7">[</span><span class="p" data-group-id="3376865046-7">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="3376865046-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Sum</span><span class="p">.</span></code></pre>
│ │ │ │ +</span><span class="nf">sum</span><span class="p" data-group-id="4797534608-3">(</span><span class="p" data-group-id="4797534608-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4797534608-4">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="4797534608-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="4797534608-5">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">H</span><span class="p" data-group-id="4797534608-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">sum</span><span class="p" data-group-id="4797534608-6">(</span><span class="p" data-group-id="4797534608-7">[</span><span class="p" data-group-id="4797534608-7">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="4797534608-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Sum</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/list_comprehensions.xhtml
│ │ │ │ @@ -22,33 +22,33 @@
│ │ │ │      </h1>
│ │ │ │  <h2 id="simple-examples" class="section-heading">
│ │ │ │    <a href="#simple-examples" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simple Examples</span>
│ │ │ │  </h2>
│ │ │ │ -<p>This section starts with a simple example, showing a generator and a filter:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="4445530386-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4445530386-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4445530386-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4445530386-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4445530386-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4445530386-3">]</span></code></pre><p>This is read as follows: The list of X such that X is taken from the list
│ │ │ │ +<p>This section starts with a simple example, showing a generator and a filter:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="1429935331-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1429935331-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1429935331-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1429935331-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1429935331-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1429935331-3">]</span></code></pre><p>This is read as follows: The list of X such that X is taken from the list
│ │ │ │  <code class="inline">[1,2,a,...]</code> and X is greater than 3.</p><p>The notation <code class="inline">X &lt;- [1,2,a,...]</code> is a generator and the expression <code class="inline">X &gt; 3</code> is a
│ │ │ │  filter.</p><p>An additional filter, <a href="../../../lib/../erts/doc/html/erlang.html#is_integer/1"><code class="inline">is_integer(X)</code></a>, can be added to
│ │ │ │ -restrict the result to integers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="4533089592-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4533089592-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4533089592-2">]</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="4533089592-3">(</span><span class="n">X</span><span class="p" data-group-id="4533089592-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4533089592-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4533089592-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4533089592-4">]</span></code></pre><p>Generators can be combined. For example, the Cartesian product of two lists can
│ │ │ │ -be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="7352665637-1">[</span><span class="p" data-group-id="7352665637-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7352665637-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7352665637-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7352665637-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7352665637-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7352665637-4">]</span><span class="p" data-group-id="7352665637-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7352665637-5">[</span><span class="p" data-group-id="7352665637-6">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7352665637-6">}</span><span class="p">,</span><span class="p" data-group-id="7352665637-7">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7352665637-7">}</span><span class="p">,</span><span class="p" data-group-id="7352665637-8">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7352665637-8">}</span><span class="p">,</span><span class="p" data-group-id="7352665637-9">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7352665637-9">}</span><span class="p">,</span><span class="p" data-group-id="7352665637-10">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7352665637-10">}</span><span class="p">,</span><span class="p" data-group-id="7352665637-11">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7352665637-11">}</span><span class="p" data-group-id="7352665637-5">]</span></code></pre><h2 id="quick-sort" class="section-heading">
│ │ │ │ +restrict the result to integers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="6429583223-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6429583223-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6429583223-2">]</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6429583223-3">(</span><span class="n">X</span><span class="p" data-group-id="6429583223-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6429583223-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6429583223-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6429583223-4">]</span></code></pre><p>Generators can be combined. For example, the Cartesian product of two lists can
│ │ │ │ +be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="8423004622-1">[</span><span class="p" data-group-id="8423004622-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8423004622-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8423004622-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8423004622-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8423004622-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8423004622-4">]</span><span class="p" data-group-id="8423004622-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8423004622-5">[</span><span class="p" data-group-id="8423004622-6">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="8423004622-6">}</span><span class="p">,</span><span class="p" data-group-id="8423004622-7">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8423004622-7">}</span><span class="p">,</span><span class="p" data-group-id="8423004622-8">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="8423004622-8">}</span><span class="p">,</span><span class="p" data-group-id="8423004622-9">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8423004622-9">}</span><span class="p">,</span><span class="p" data-group-id="8423004622-10">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="8423004622-10">}</span><span class="p">,</span><span class="p" data-group-id="8423004622-11">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8423004622-11">}</span><span class="p" data-group-id="8423004622-5">]</span></code></pre><h2 id="quick-sort" class="section-heading">
│ │ │ │    <a href="#quick-sort" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Quick Sort</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The well-known quick sort routine can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sort</span><span class="p" data-group-id="8802470770-1">(</span><span class="p" data-group-id="8802470770-2">[</span><span class="p" data-group-id="8802470770-2">]</span><span class="p" data-group-id="8802470770-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8802470770-3">[</span><span class="p" data-group-id="8802470770-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">sort</span><span class="p" data-group-id="8802470770-4">(</span><span class="p" data-group-id="8802470770-5">[</span><span class="p">_</span><span class="p" data-group-id="8802470770-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="8802470770-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">L</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">sort</span><span class="p" data-group-id="8802470770-6">(</span><span class="p" data-group-id="8802470770-7">[</span><span class="n">Pivot</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8802470770-7">]</span><span class="p" data-group-id="8802470770-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">sort</span><span class="p" data-group-id="8802470770-8">(</span><span class="p" data-group-id="8802470770-9">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="8802470770-9">]</span><span class="p" data-group-id="8802470770-8">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8802470770-10">[</span><span class="n">Pivot</span><span class="p" data-group-id="8802470770-10">]</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ │ -    </span><span class="nf">sort</span><span class="p" data-group-id="8802470770-11">(</span><span class="p" data-group-id="8802470770-12">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="8802470770-12">]</span><span class="p" data-group-id="8802470770-11">)</span><span class="p">.</span></code></pre><p>The expression <code class="inline">[X || X &lt;- T, X &lt; Pivot]</code> is the list of all elements in <code class="inline">T</code>
│ │ │ │ +<p>The well-known quick sort routine can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sort</span><span class="p" data-group-id="0332240787-1">(</span><span class="p" data-group-id="0332240787-2">[</span><span class="p" data-group-id="0332240787-2">]</span><span class="p" data-group-id="0332240787-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0332240787-3">[</span><span class="p" data-group-id="0332240787-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">sort</span><span class="p" data-group-id="0332240787-4">(</span><span class="p" data-group-id="0332240787-5">[</span><span class="p">_</span><span class="p" data-group-id="0332240787-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0332240787-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">L</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">sort</span><span class="p" data-group-id="0332240787-6">(</span><span class="p" data-group-id="0332240787-7">[</span><span class="n">Pivot</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0332240787-7">]</span><span class="p" data-group-id="0332240787-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">sort</span><span class="p" data-group-id="0332240787-8">(</span><span class="p" data-group-id="0332240787-9">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="0332240787-9">]</span><span class="p" data-group-id="0332240787-8">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0332240787-10">[</span><span class="n">Pivot</span><span class="p" data-group-id="0332240787-10">]</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ │ +    </span><span class="nf">sort</span><span class="p" data-group-id="0332240787-11">(</span><span class="p" data-group-id="0332240787-12">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="0332240787-12">]</span><span class="p" data-group-id="0332240787-11">)</span><span class="p">.</span></code></pre><p>The expression <code class="inline">[X || X &lt;- T, X &lt; Pivot]</code> is the list of all elements in <code class="inline">T</code>
│ │ │ │  that are less than <code class="inline">Pivot</code>.</p><p><code class="inline">[X || X &lt;- T, X &gt;= Pivot]</code> is the list of all elements in <code class="inline">T</code> that are greater
│ │ │ │  than or equal to <code class="inline">Pivot</code>.</p><p>With the algorithm above, a list is sorted as follows:</p><ul><li>A list with zero or one element is trivially sorted.</li><li>For lists with more than one element:<ol><li>The first element in the list is isolated as the pivot element.</li><li>The remaining list is partitioned into two sublists, such that:</li></ol><ul><li>The first sublist contains all elements that are smaller than the pivot
│ │ │ │  element.</li><li>The second sublist contains all elements that are greater than or equal to
│ │ │ │  the pivot element.</li></ul><ol><li>The sublists are recursively sorted by the same algorithm and the results
│ │ │ │  are combined, resulting in a list consisting of:</li></ol><ul><li>All elements from the first sublist, that is all elements smaller than the
│ │ │ │  pivot element, in sorted order.</li><li>The pivot element.</li><li>All elements from the second sublist, that is all elements greater than or
│ │ │ │  equal to the pivot element, in sorted order.</li></ul></li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>While the sorting algorithm as shown above serves as a nice example to
│ │ │ │ @@ -56,90 +56,90 @@
│ │ │ │  <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a> module contains sorting functions that are implemented in a more
│ │ │ │  efficient way.</p></section><h2 id="permutations" class="section-heading">
│ │ │ │    <a href="#permutations" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Permutations</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The following example generates all permutations of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">perms</span><span class="p" data-group-id="2452050184-1">(</span><span class="p" data-group-id="2452050184-2">[</span><span class="p" data-group-id="2452050184-2">]</span><span class="p" data-group-id="2452050184-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2452050184-3">[</span><span class="p" data-group-id="2452050184-4">[</span><span class="p" data-group-id="2452050184-4">]</span><span class="p" data-group-id="2452050184-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">perms</span><span class="p" data-group-id="2452050184-5">(</span><span class="n">L</span><span class="p" data-group-id="2452050184-5">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2452050184-6">[</span><span class="p" data-group-id="2452050184-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2452050184-7">]</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nf">perms</span><span class="p" data-group-id="2452050184-8">(</span><span class="n">L</span><span class="o">--</span><span class="p" data-group-id="2452050184-9">[</span><span class="n">H</span><span class="p" data-group-id="2452050184-9">]</span><span class="p" data-group-id="2452050184-8">)</span><span class="p" data-group-id="2452050184-6">]</span><span class="p">.</span></code></pre><p>This takes <code class="inline">H</code> from <code class="inline">L</code> in all possible ways. The result is the set of all lists
│ │ │ │ +<p>The following example generates all permutations of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">perms</span><span class="p" data-group-id="4346473761-1">(</span><span class="p" data-group-id="4346473761-2">[</span><span class="p" data-group-id="4346473761-2">]</span><span class="p" data-group-id="4346473761-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4346473761-3">[</span><span class="p" data-group-id="4346473761-4">[</span><span class="p" data-group-id="4346473761-4">]</span><span class="p" data-group-id="4346473761-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">perms</span><span class="p" data-group-id="4346473761-5">(</span><span class="n">L</span><span class="p" data-group-id="4346473761-5">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4346473761-6">[</span><span class="p" data-group-id="4346473761-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4346473761-7">]</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nf">perms</span><span class="p" data-group-id="4346473761-8">(</span><span class="n">L</span><span class="o">--</span><span class="p" data-group-id="4346473761-9">[</span><span class="n">H</span><span class="p" data-group-id="4346473761-9">]</span><span class="p" data-group-id="4346473761-8">)</span><span class="p" data-group-id="4346473761-6">]</span><span class="p">.</span></code></pre><p>This takes <code class="inline">H</code> from <code class="inline">L</code> in all possible ways. The result is the set of all lists
│ │ │ │  <code class="inline">[H|T]</code>, where <code class="inline">T</code> is the set of all possible permutations of <code class="inline">L</code>, with <code class="inline">H</code>
│ │ │ │ -removed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">perms</span><span class="p" data-group-id="6845670606-1">(</span><span class="p" data-group-id="6845670606-2">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="6845670606-2">]</span><span class="p" data-group-id="6845670606-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6845670606-3">[</span><span class="p" data-group-id="6845670606-4">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="6845670606-4">]</span><span class="p">,</span><span class="p" data-group-id="6845670606-5">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="6845670606-5">]</span><span class="p">,</span><span class="p" data-group-id="6845670606-6">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="6845670606-6">]</span><span class="p">,</span><span class="p" data-group-id="6845670606-7">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6845670606-7">]</span><span class="p">,</span><span class="p" data-group-id="6845670606-8">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="6845670606-8">]</span><span class="p">,</span><span class="p" data-group-id="6845670606-9">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6845670606-9">]</span><span class="p" data-group-id="6845670606-3">]</span></code></pre><h2 id="pythagorean-triplets" class="section-heading">
│ │ │ │ +removed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">perms</span><span class="p" data-group-id="5250016689-1">(</span><span class="p" data-group-id="5250016689-2">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="5250016689-2">]</span><span class="p" data-group-id="5250016689-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5250016689-3">[</span><span class="p" data-group-id="5250016689-4">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="5250016689-4">]</span><span class="p">,</span><span class="p" data-group-id="5250016689-5">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="5250016689-5">]</span><span class="p">,</span><span class="p" data-group-id="5250016689-6">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="5250016689-6">]</span><span class="p">,</span><span class="p" data-group-id="5250016689-7">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5250016689-7">]</span><span class="p">,</span><span class="p" data-group-id="5250016689-8">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="5250016689-8">]</span><span class="p">,</span><span class="p" data-group-id="5250016689-9">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5250016689-9">]</span><span class="p" data-group-id="5250016689-3">]</span></code></pre><h2 id="pythagorean-triplets" class="section-heading">
│ │ │ │    <a href="#pythagorean-triplets" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Pythagorean Triplets</span>
│ │ │ │  </h2>
│ │ │ │  <p>Pythagorean triplets are sets of integers <code class="inline">{A,B,C}</code> such that
│ │ │ │  <code class="inline">A**2 + B**2 = C**2</code>.</p><p>The function <code class="inline">pyth(N)</code> generates a list of all integers <code class="inline">{A,B,C}</code> such that
│ │ │ │  <code class="inline">A**2 + B**2 = C**2</code> and where the sum of the sides is equal to, or less than,
│ │ │ │ -<code class="inline">N</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth</span><span class="p" data-group-id="2473548028-1">(</span><span class="n">N</span><span class="p" data-group-id="2473548028-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2473548028-2">[</span><span class="w"> </span><span class="p" data-group-id="2473548028-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="2473548028-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ │ -        </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2473548028-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="2473548028-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2473548028-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="2473548028-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2473548028-6">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="2473548028-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +<code class="inline">N</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth</span><span class="p" data-group-id="2969809091-1">(</span><span class="n">N</span><span class="p" data-group-id="2969809091-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2969809091-2">[</span><span class="w"> </span><span class="p" data-group-id="2969809091-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="2969809091-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ │ +        </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2969809091-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="2969809091-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2969809091-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="2969809091-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2969809091-6">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="2969809091-6">)</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">+</span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2473548028-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="7072990149-1">(</span><span class="mi">3</span><span class="p" data-group-id="7072990149-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7072990149-2">[</span><span class="p" data-group-id="7072990149-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="7072990149-3">(</span><span class="mi">11</span><span class="p" data-group-id="7072990149-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7072990149-4">[</span><span class="p" data-group-id="7072990149-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="7072990149-5">(</span><span class="mi">12</span><span class="p" data-group-id="7072990149-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7072990149-6">[</span><span class="p" data-group-id="7072990149-7">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7072990149-7">}</span><span class="p">,</span><span class="p" data-group-id="7072990149-8">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7072990149-8">}</span><span class="p" data-group-id="7072990149-6">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="7072990149-9">(</span><span class="mi">50</span><span class="p" data-group-id="7072990149-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7072990149-10">[</span><span class="p" data-group-id="7072990149-11">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7072990149-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-12">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7072990149-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-13">{</span><span class="mi">5</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="7072990149-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-14">{</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="7072990149-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-15">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="7072990149-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-16">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="7072990149-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-17">{</span><span class="mi">9</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="7072990149-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-18">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="7072990149-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-19">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="7072990149-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-20">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="7072990149-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-21">{</span><span class="mi">15</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="7072990149-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7072990149-22">{</span><span class="mi">16</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="7072990149-22">}</span><span class="p" data-group-id="7072990149-10">]</span></code></pre><p>The following code reduces the search space and is more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth1</span><span class="p" data-group-id="1782139025-1">(</span><span class="n">N</span><span class="p" data-group-id="1782139025-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="1782139025-2">[</span><span class="p" data-group-id="1782139025-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="1782139025-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ │ -       </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1782139025-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="1782139025-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -       </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1782139025-5">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="1782139025-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -       </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1782139025-6">(</span><span class="n">B</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="1782139025-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2969809091-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="1403916881-1">(</span><span class="mi">3</span><span class="p" data-group-id="1403916881-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1403916881-2">[</span><span class="p" data-group-id="1403916881-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="1403916881-3">(</span><span class="mi">11</span><span class="p" data-group-id="1403916881-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1403916881-4">[</span><span class="p" data-group-id="1403916881-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="1403916881-5">(</span><span class="mi">12</span><span class="p" data-group-id="1403916881-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1403916881-6">[</span><span class="p" data-group-id="1403916881-7">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1403916881-7">}</span><span class="p">,</span><span class="p" data-group-id="1403916881-8">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1403916881-8">}</span><span class="p" data-group-id="1403916881-6">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="1403916881-9">(</span><span class="mi">50</span><span class="p" data-group-id="1403916881-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1403916881-10">[</span><span class="p" data-group-id="1403916881-11">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1403916881-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-12">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1403916881-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-13">{</span><span class="mi">5</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="1403916881-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-14">{</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="1403916881-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-15">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="1403916881-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-16">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="1403916881-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-17">{</span><span class="mi">9</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="1403916881-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-18">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="1403916881-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-19">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="1403916881-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-20">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="1403916881-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-21">{</span><span class="mi">15</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="1403916881-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1403916881-22">{</span><span class="mi">16</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="1403916881-22">}</span><span class="p" data-group-id="1403916881-10">]</span></code></pre><p>The following code reduces the search space and is more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth1</span><span class="p" data-group-id="9943745543-1">(</span><span class="n">N</span><span class="p" data-group-id="9943745543-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="9943745543-2">[</span><span class="p" data-group-id="9943745543-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="9943745543-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ │ +       </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="9943745543-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="9943745543-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +       </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="9943745543-5">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="9943745543-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +       </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="9943745543-6">(</span><span class="n">B</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="9943745543-6">)</span><span class="p">,</span><span class="w">
│ │ │ │         </span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">+</span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w">
│ │ │ │ -       </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w"> </span><span class="p" data-group-id="1782139025-2">]</span><span class="p">.</span></code></pre><h2 id="simplifications-with-list-comprehensions" class="section-heading">
│ │ │ │ +       </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w"> </span><span class="p" data-group-id="9943745543-2">]</span><span class="p">.</span></code></pre><h2 id="simplifications-with-list-comprehensions" class="section-heading">
│ │ │ │    <a href="#simplifications-with-list-comprehensions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simplifications With List Comprehensions</span>
│ │ │ │  </h2>
│ │ │ │  <p>As an example, list comprehensions can be used to simplify some of the functions
│ │ │ │ -in <code class="inline">lists.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="2437675719-1">(</span><span class="n">L</span><span class="p" data-group-id="2437675719-1">)</span><span class="w">   </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="2437675719-2">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">L1</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="2437675719-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="2437675719-3">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2437675719-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2437675719-4">[</span><span class="n">Fun</span><span class="p" data-group-id="2437675719-5">(</span><span class="n">X</span><span class="p" data-group-id="2437675719-5">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2437675719-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">filter</span><span class="p" data-group-id="2437675719-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2437675719-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2437675719-7">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="2437675719-8">(</span><span class="n">X</span><span class="p" data-group-id="2437675719-8">)</span><span class="p" data-group-id="2437675719-7">]</span><span class="p">.</span></code></pre><h2 id="variable-bindings-in-list-comprehensions" class="section-heading">
│ │ │ │ +in <code class="inline">lists.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="1601165375-1">(</span><span class="n">L</span><span class="p" data-group-id="1601165375-1">)</span><span class="w">   </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="1601165375-2">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">L1</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="1601165375-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="1601165375-3">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1601165375-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1601165375-4">[</span><span class="n">Fun</span><span class="p" data-group-id="1601165375-5">(</span><span class="n">X</span><span class="p" data-group-id="1601165375-5">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1601165375-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">filter</span><span class="p" data-group-id="1601165375-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1601165375-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1601165375-7">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="1601165375-8">(</span><span class="n">X</span><span class="p" data-group-id="1601165375-8">)</span><span class="p" data-group-id="1601165375-7">]</span><span class="p">.</span></code></pre><h2 id="variable-bindings-in-list-comprehensions" class="section-heading">
│ │ │ │    <a href="#variable-bindings-in-list-comprehensions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Variable Bindings in List Comprehensions</span>
│ │ │ │  </h2>
│ │ │ │  <p>The scope rules for variables that occur in list comprehensions are as follows:</p><ul><li>All variables that occur in a generator pattern are assumed to be &quot;fresh&quot;
│ │ │ │  variables.</li><li>Any variables that are defined before the list comprehension, and that are
│ │ │ │  used in filters, have the values they had before the list comprehension.</li><li>Variables cannot be exported from a list comprehension.</li></ul><p>As an example of these rules, suppose you want to write the function <code class="inline">select</code>,
│ │ │ │  which selects certain elements from a list of tuples. Suppose you write
│ │ │ │  <code class="inline">select(X, L) -&gt; [Y || {X, Y} &lt;- L].</code> with the intention of extracting all
│ │ │ │  tuples from <code class="inline">L</code>, where the first item is <code class="inline">X</code>.</p><p>Compiling this gives the following diagnostic:</p><pre><code class="text">./FileName.erl:Line: Warning: variable 'X' shadowed in generate</code></pre><p>This diagnostic warns that the variable <code class="inline">X</code> in the pattern is not the same as
│ │ │ │ -the variable <code class="inline">X</code> that occurs in the function head.</p><p>Evaluating <code class="inline">select</code> gives the following result:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="9937503111-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="9937503111-2">[</span><span class="p" data-group-id="9937503111-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="9937503111-3">}</span><span class="p">,</span><span class="p" data-group-id="9937503111-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9937503111-4">}</span><span class="p">,</span><span class="p" data-group-id="9937503111-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9937503111-5">}</span><span class="p">,</span><span class="p" data-group-id="9937503111-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="9937503111-6">}</span><span class="p" data-group-id="9937503111-2">]</span><span class="p" data-group-id="9937503111-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9937503111-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="9937503111-7">]</span></code></pre><p>This is not the wanted result. To achieve the desired effect, <code class="inline">select</code> must be
│ │ │ │ -written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="9810741003-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="9810741003-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="9810741003-2">[</span><span class="n">Y</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="9810741003-3">{</span><span class="n">X1</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9810741003-3">}</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">X1</span><span class="p" data-group-id="9810741003-2">]</span><span class="p">.</span></code></pre><p>The generator now contains unbound variables and the test has been moved into
│ │ │ │ -the filter.</p><p>This now works as expected:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="4137053227-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="4137053227-2">[</span><span class="p" data-group-id="4137053227-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4137053227-3">}</span><span class="p">,</span><span class="p" data-group-id="4137053227-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4137053227-4">}</span><span class="p">,</span><span class="p" data-group-id="4137053227-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4137053227-5">}</span><span class="p">,</span><span class="p" data-group-id="4137053227-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4137053227-6">}</span><span class="p" data-group-id="4137053227-2">]</span><span class="p" data-group-id="4137053227-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4137053227-7">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4137053227-7">]</span></code></pre><p>Also note that a variable in a generator pattern will shadow a variable with the
│ │ │ │ -same name bound in a previous generator pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="9274831078-1">[</span><span class="p" data-group-id="9274831078-2">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p" data-group-id="9274831078-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9274831078-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9274831078-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="o">=</span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9274831078-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9274831078-4">]</span><span class="p" data-group-id="9274831078-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9274831078-5">[</span><span class="p" data-group-id="9274831078-6">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="9274831078-6">}</span><span class="p">,</span><span class="p" data-group-id="9274831078-7">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9274831078-7">}</span><span class="p">,</span><span class="p" data-group-id="9274831078-8">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9274831078-8">}</span><span class="p">,</span><span class="p" data-group-id="9274831078-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="9274831078-9">}</span><span class="p">,</span><span class="p" data-group-id="9274831078-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9274831078-10">}</span><span class="p">,</span><span class="p" data-group-id="9274831078-11">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9274831078-11">}</span><span class="p">,</span><span class="p" data-group-id="9274831078-12">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="9274831078-12">}</span><span class="p">,</span><span class="p" data-group-id="9274831078-13">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9274831078-13">}</span><span class="p">,</span><span class="p" data-group-id="9274831078-14">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9274831078-14">}</span><span class="p" data-group-id="9274831078-5">]</span></code></pre><p>A consequence of the rules for importing variables into a list comprehensions is
│ │ │ │ +the variable <code class="inline">X</code> that occurs in the function head.</p><p>Evaluating <code class="inline">select</code> gives the following result:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="3148101286-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="3148101286-2">[</span><span class="p" data-group-id="3148101286-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3148101286-3">}</span><span class="p">,</span><span class="p" data-group-id="3148101286-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3148101286-4">}</span><span class="p">,</span><span class="p" data-group-id="3148101286-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3148101286-5">}</span><span class="p">,</span><span class="p" data-group-id="3148101286-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3148101286-6">}</span><span class="p" data-group-id="3148101286-2">]</span><span class="p" data-group-id="3148101286-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3148101286-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3148101286-7">]</span></code></pre><p>This is not the wanted result. To achieve the desired effect, <code class="inline">select</code> must be
│ │ │ │ +written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="2593922466-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2593922466-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="2593922466-2">[</span><span class="n">Y</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="2593922466-3">{</span><span class="n">X1</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2593922466-3">}</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">X1</span><span class="p" data-group-id="2593922466-2">]</span><span class="p">.</span></code></pre><p>The generator now contains unbound variables and the test has been moved into
│ │ │ │ +the filter.</p><p>This now works as expected:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="6911445371-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="6911445371-2">[</span><span class="p" data-group-id="6911445371-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6911445371-3">}</span><span class="p">,</span><span class="p" data-group-id="6911445371-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6911445371-4">}</span><span class="p">,</span><span class="p" data-group-id="6911445371-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6911445371-5">}</span><span class="p">,</span><span class="p" data-group-id="6911445371-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="6911445371-6">}</span><span class="p" data-group-id="6911445371-2">]</span><span class="p" data-group-id="6911445371-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6911445371-7">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="6911445371-7">]</span></code></pre><p>Also note that a variable in a generator pattern will shadow a variable with the
│ │ │ │ +same name bound in a previous generator pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="9700346407-1">[</span><span class="p" data-group-id="9700346407-2">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p" data-group-id="9700346407-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9700346407-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9700346407-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="o">=</span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9700346407-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9700346407-4">]</span><span class="p" data-group-id="9700346407-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9700346407-5">[</span><span class="p" data-group-id="9700346407-6">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="9700346407-6">}</span><span class="p">,</span><span class="p" data-group-id="9700346407-7">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9700346407-7">}</span><span class="p">,</span><span class="p" data-group-id="9700346407-8">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9700346407-8">}</span><span class="p">,</span><span class="p" data-group-id="9700346407-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="9700346407-9">}</span><span class="p">,</span><span class="p" data-group-id="9700346407-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9700346407-10">}</span><span class="p">,</span><span class="p" data-group-id="9700346407-11">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9700346407-11">}</span><span class="p">,</span><span class="p" data-group-id="9700346407-12">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="9700346407-12">}</span><span class="p">,</span><span class="p" data-group-id="9700346407-13">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9700346407-13">}</span><span class="p">,</span><span class="p" data-group-id="9700346407-14">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9700346407-14">}</span><span class="p" data-group-id="9700346407-5">]</span></code></pre><p>A consequence of the rules for importing variables into a list comprehensions is
│ │ │ │  that certain pattern matching operations must be moved into the filters and
│ │ │ │ -cannot be written directly in the generators.</p><p>To illustrate this, do <em>not</em> write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="8434821001-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8434821001-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +cannot be written directly in the generators.</p><p>To illustrate this, do <em>not</em> write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0612045786-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0612045786-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8434821001-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8434821001-2">]</span><span class="w">
│ │ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Instead, write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0097285124-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0097285124-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0612045786-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0612045786-2">]</span><span class="w">
│ │ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Instead, write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="6890475747-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6890475747-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0097285124-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y1</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0097285124-2">]</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6890475747-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y1</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6890475747-2">]</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/install-win32.xhtml
│ │ │ │ @@ -200,15 +200,15 @@
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">cd erts/emulator
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make debug
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">cd ../etc
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make debug
│ │ │ │  </span></code></pre><p>and sometimes</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make local_setup
│ │ │ │  </span></code></pre><p>So now when you run <code class="inline">$ERL_TOP/erl.exe</code>, you should have a debug compiled
│ │ │ │ -emulator, which you will see if you do a:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="8803180533-1">(</span><span class="ss">system_version</span><span class="p" data-group-id="8803180533-1">)</span><span class="p">.</span></code></pre><p>in the erlang shell. If the returned string contains <code class="inline">[debug]</code>, you
│ │ │ │ +emulator, which you will see if you do a:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="7009367675-1">(</span><span class="ss">system_version</span><span class="p" data-group-id="7009367675-1">)</span><span class="p">.</span></code></pre><p>in the erlang shell. If the returned string contains <code class="inline">[debug]</code>, you
│ │ │ │  got a debug compiled emulator.</p><p>To hack the erlang libraries, you simply do a <code class="inline">make opt</code> in the
│ │ │ │  specific &quot;applications&quot; directory, like:</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make opt
│ │ │ │  </span></code></pre><p>or even in the source directory...</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib/src
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make opt
│ │ │ │  </span></code></pre><p>Note that you're expected to have a fresh Erlang in your path when
│ │ │ │  doing this, preferably the plain 27 you have built in the previous
│ │ │ │ @@ -223,19 +223,19 @@
│ │ │ │  </span><span class="">:$ERL_TOP/erts/etc/win32/wsl_tools:$ERL_TOP/bootstrap/bin:$PATH
│ │ │ │  </span></code></pre><p>That should make it possible to rebuild any library without hassle...</p><p>If you want to copy a library (an application) newly built, to a
│ │ │ │  release area, you do like with the emulator:</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib
│ │ │ │  </span><span class="gp unselectable">$ </span><span class="">make TESTROOT=/tmp/erlang_release release
│ │ │ │  </span></code></pre><p>Remember that:</p><ul><li><p>  Windows specific C-code goes in the <code class="inline">$ERL_TOP/erts/emulator/sys/win32</code>,
│ │ │ │  <code class="inline">$ERL_TOP/erts/emulator/drivers/win32</code> or <code class="inline">$ERL_TOP/erts/etc/win32</code>.</p></li><li><p>  Windows specific erlang code should be used conditionally and the
│ │ │ │  host OS tested in <em>runtime</em>, the exactly same beam files should be
│ │ │ │ -distributed for every platform! So write code like:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">os</span><span class="p">:</span><span class="nf">type</span><span class="p" data-group-id="4605487127-1">(</span><span class="p" data-group-id="4605487127-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4605487127-2">{</span><span class="ss">win32</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4605487127-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nf">do_windows_specific</span><span class="p" data-group-id="4605487127-3">(</span><span class="p" data-group-id="4605487127-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +distributed for every platform! So write code like:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">os</span><span class="p">:</span><span class="nf">type</span><span class="p" data-group-id="6474553741-1">(</span><span class="p" data-group-id="6474553741-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6474553741-2">{</span><span class="ss">win32</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6474553741-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">do_windows_specific</span><span class="p" data-group-id="6474553741-3">(</span><span class="p" data-group-id="6474553741-3">)</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">Other</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nf">do_fallback_or_exit</span><span class="p" data-group-id="4605487127-4">(</span><span class="p" data-group-id="4605487127-4">)</span><span class="w">
│ │ │ │ +        </span><span class="nf">do_fallback_or_exit</span><span class="p" data-group-id="6474553741-4">(</span><span class="p" data-group-id="6474553741-4">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre></li></ul><p>That's basically all you need to get going.</p><h2 id="frequently-asked-questions" class="section-heading">
│ │ │ │    <a href="#frequently-asked-questions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Frequently Asked Questions</span>
│ │ │ │  </h2>
│ │ │ │  <ul><li><p>  Q: So, now I can build Erlang using GCC on Windows?</p><p>A: No, unfortunately not. You'll need Microsoft's Visual C++
│ │ │ ├── OEBPS/included_applications.xhtml
│ │ │ │ @@ -66,72 +66,72 @@
│ │ │ │  belonging to the primary application.</p><h2 id="specifying-included-applications" class="section-heading">
│ │ │ │    <a href="#specifying-included-applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Specifying Included Applications</span>
│ │ │ │  </h2>
│ │ │ │  <p>Which applications to include is defined by the <code class="inline">included_applications</code> key in
│ │ │ │ -the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5305888113-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5305888113-2">[</span><span class="p" data-group-id="5305888113-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="5305888113-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5305888113-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="5305888113-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5305888113-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5305888113-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="5305888113-6">]</span><span class="p" data-group-id="5305888113-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5305888113-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5305888113-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="5305888113-8">]</span><span class="p" data-group-id="5305888113-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5305888113-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5305888113-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="5305888113-10">]</span><span class="p" data-group-id="5305888113-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5305888113-11">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5305888113-12">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="5305888113-12">]</span><span class="p" data-group-id="5305888113-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5305888113-13">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5305888113-14">{</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="5305888113-15">[</span><span class="p" data-group-id="5305888113-15">]</span><span class="p" data-group-id="5305888113-14">}</span><span class="p" data-group-id="5305888113-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="5305888113-16">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5305888113-17">[</span><span class="p" data-group-id="5305888113-18">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="5305888113-18">}</span><span class="p" data-group-id="5305888113-17">]</span><span class="p" data-group-id="5305888113-16">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5305888113-2">]</span><span class="p" data-group-id="5305888113-1">}</span><span class="p">.</span></code></pre><h2 id="synchronizing-processes-during-startup" class="section-heading">
│ │ │ │ +the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4179024809-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4179024809-2">[</span><span class="p" data-group-id="4179024809-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="4179024809-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4179024809-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="4179024809-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4179024809-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4179024809-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="4179024809-6">]</span><span class="p" data-group-id="4179024809-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4179024809-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4179024809-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="4179024809-8">]</span><span class="p" data-group-id="4179024809-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4179024809-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4179024809-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="4179024809-10">]</span><span class="p" data-group-id="4179024809-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4179024809-11">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4179024809-12">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="4179024809-12">]</span><span class="p" data-group-id="4179024809-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4179024809-13">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4179024809-14">{</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="4179024809-15">[</span><span class="p" data-group-id="4179024809-15">]</span><span class="p" data-group-id="4179024809-14">}</span><span class="p" data-group-id="4179024809-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4179024809-16">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4179024809-17">[</span><span class="p" data-group-id="4179024809-18">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="4179024809-18">}</span><span class="p" data-group-id="4179024809-17">]</span><span class="p" data-group-id="4179024809-16">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4179024809-2">]</span><span class="p" data-group-id="4179024809-1">}</span><span class="p">.</span></code></pre><h2 id="synchronizing-processes-during-startup" class="section-heading">
│ │ │ │    <a href="#synchronizing-processes-during-startup" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Synchronizing Processes during Startup</span>
│ │ │ │  </h2>
│ │ │ │  <p>The supervisor tree of an included application is started as part of the
│ │ │ │  supervisor tree of the including application. If there is a need for
│ │ │ │  synchronization between processes in the including and included applications,
│ │ │ │  this can be achieved by using <em>start phases</em>.</p><p>Start phases are defined by the <code class="inline">start_phases</code> key in the <code class="inline">.app</code> file as a list
│ │ │ │  of tuples <code class="inline">{Phase,PhaseArgs}</code>, where <code class="inline">Phase</code> is an atom and <code class="inline">PhaseArgs</code> is a
│ │ │ │  term.</p><p>The value of the <code class="inline">mod</code> key of the including application must be set to
│ │ │ │  <code class="inline">{application_starter,[Module,StartArgs]}</code>, where <code class="inline">Module</code> as usual is the
│ │ │ │  application callback module. <code class="inline">StartArgs</code> is a term provided as argument to the
│ │ │ │ -callback function <code class="inline">Module:start/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9543669804-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9543669804-2">[</span><span class="p" data-group-id="9543669804-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="9543669804-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9543669804-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="9543669804-6">]</span><span class="p" data-group-id="9543669804-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="9543669804-8">]</span><span class="p" data-group-id="9543669804-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="9543669804-10">]</span><span class="p" data-group-id="9543669804-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-11">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-12">[</span><span class="p" data-group-id="9543669804-13">{</span><span class="ss">init</span><span class="p">,</span><span class="p" data-group-id="9543669804-14">[</span><span class="p" data-group-id="9543669804-14">]</span><span class="p" data-group-id="9543669804-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-15">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="9543669804-16">[</span><span class="p" data-group-id="9543669804-16">]</span><span class="p" data-group-id="9543669804-15">}</span><span class="p" data-group-id="9543669804-12">]</span><span class="p" data-group-id="9543669804-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-17">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-18">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="9543669804-18">]</span><span class="p" data-group-id="9543669804-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-19">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-20">{</span><span class="ss">application_starter</span><span class="p">,</span><span class="p" data-group-id="9543669804-21">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="9543669804-22">[</span><span class="p" data-group-id="9543669804-22">]</span><span class="p" data-group-id="9543669804-21">]</span><span class="p" data-group-id="9543669804-20">}</span><span class="p" data-group-id="9543669804-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-23">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-24">[</span><span class="p" data-group-id="9543669804-25">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="9543669804-25">}</span><span class="p" data-group-id="9543669804-24">]</span><span class="p" data-group-id="9543669804-23">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9543669804-2">]</span><span class="p" data-group-id="9543669804-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +callback function <code class="inline">Module:start/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6927553938-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6927553938-2">[</span><span class="p" data-group-id="6927553938-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="6927553938-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6927553938-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="6927553938-6">]</span><span class="p" data-group-id="6927553938-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="6927553938-8">]</span><span class="p" data-group-id="6927553938-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="6927553938-10">]</span><span class="p" data-group-id="6927553938-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-11">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-12">[</span><span class="p" data-group-id="6927553938-13">{</span><span class="ss">init</span><span class="p">,</span><span class="p" data-group-id="6927553938-14">[</span><span class="p" data-group-id="6927553938-14">]</span><span class="p" data-group-id="6927553938-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-15">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="6927553938-16">[</span><span class="p" data-group-id="6927553938-16">]</span><span class="p" data-group-id="6927553938-15">}</span><span class="p" data-group-id="6927553938-12">]</span><span class="p" data-group-id="6927553938-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-17">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-18">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="6927553938-18">]</span><span class="p" data-group-id="6927553938-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-19">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-20">{</span><span class="ss">application_starter</span><span class="p">,</span><span class="p" data-group-id="6927553938-21">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="6927553938-22">[</span><span class="p" data-group-id="6927553938-22">]</span><span class="p" data-group-id="6927553938-21">]</span><span class="p" data-group-id="6927553938-20">}</span><span class="p" data-group-id="6927553938-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-23">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-24">[</span><span class="p" data-group-id="6927553938-25">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="6927553938-25">}</span><span class="p" data-group-id="6927553938-24">]</span><span class="p" data-group-id="6927553938-23">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6927553938-2">]</span><span class="p" data-group-id="6927553938-1">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="9543669804-26">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9543669804-27">[</span><span class="p" data-group-id="9543669804-28">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Included application&quot;</span><span class="p" data-group-id="9543669804-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-29">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9543669804-29">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-30">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-31">[</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_server</span><span class="p" data-group-id="9543669804-31">]</span><span class="p" data-group-id="9543669804-30">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-32">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-33">[</span><span class="p" data-group-id="9543669804-33">]</span><span class="p" data-group-id="9543669804-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-34">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-35">[</span><span class="p" data-group-id="9543669804-36">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="9543669804-37">[</span><span class="p" data-group-id="9543669804-37">]</span><span class="p" data-group-id="9543669804-36">}</span><span class="p" data-group-id="9543669804-35">]</span><span class="p" data-group-id="9543669804-34">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-38">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-39">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="9543669804-39">]</span><span class="p" data-group-id="9543669804-38">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9543669804-40">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9543669804-41">{</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="p" data-group-id="9543669804-42">[</span><span class="p" data-group-id="9543669804-42">]</span><span class="p" data-group-id="9543669804-41">}</span><span class="p" data-group-id="9543669804-40">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9543669804-27">]</span><span class="p" data-group-id="9543669804-26">}</span><span class="p">.</span></code></pre><p>When starting a primary application with included applications, the primary
│ │ │ │ +</span><span class="p" data-group-id="6927553938-26">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6927553938-27">[</span><span class="p" data-group-id="6927553938-28">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Included application&quot;</span><span class="p" data-group-id="6927553938-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-29">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6927553938-29">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-30">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-31">[</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_server</span><span class="p" data-group-id="6927553938-31">]</span><span class="p" data-group-id="6927553938-30">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-32">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-33">[</span><span class="p" data-group-id="6927553938-33">]</span><span class="p" data-group-id="6927553938-32">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-34">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-35">[</span><span class="p" data-group-id="6927553938-36">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="6927553938-37">[</span><span class="p" data-group-id="6927553938-37">]</span><span class="p" data-group-id="6927553938-36">}</span><span class="p" data-group-id="6927553938-35">]</span><span class="p" data-group-id="6927553938-34">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-38">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-39">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="6927553938-39">]</span><span class="p" data-group-id="6927553938-38">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6927553938-40">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6927553938-41">{</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="p" data-group-id="6927553938-42">[</span><span class="p" data-group-id="6927553938-42">]</span><span class="p" data-group-id="6927553938-41">}</span><span class="p" data-group-id="6927553938-40">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6927553938-27">]</span><span class="p" data-group-id="6927553938-26">}</span><span class="p">.</span></code></pre><p>When starting a primary application with included applications, the primary
│ │ │ │  application is started the normal way, that is:</p><ul><li>The application controller creates an application master for the application</li><li>The application master calls <code class="inline">Module:start(normal, StartArgs)</code> to start the
│ │ │ │  top supervisor.</li></ul><p>Then, for the primary application and each included application in top-down,
│ │ │ │  left-to-right order, the application master calls
│ │ │ │  <code class="inline">Module:start_phase(Phase, Type, PhaseArgs)</code> for each phase defined for the
│ │ │ │  primary application, in that order. If a phase is not defined for an included
│ │ │ │  application, the function is not called for this phase and application.</p><p>The following requirements apply to the <code class="inline">.app</code> file for an included application:</p><ul><li>The <code class="inline">{mod, {Module,StartArgs}}</code> option must be included. This option is used
│ │ │ │  to find the callback module <code class="inline">Module</code> of the application. <code class="inline">StartArgs</code> is
│ │ │ │  ignored, as <code class="inline">Module:start/2</code> is called only for the primary application.</li><li>If the included application itself contains included applications, instead the
│ │ │ │  <code class="inline">{mod, {application_starter, [Module,StartArgs]}}</code> option must be included.</li><li>The <code class="inline">{start_phases, [{Phase,PhaseArgs}]}</code> option must be included, and the set
│ │ │ │  of specified phases must be a subset of the set of phases specified for the
│ │ │ │  primary application.</li></ul><p>When starting <code class="inline">prim_app</code> as defined above, the application controller calls the
│ │ │ │  following callback functions before <code class="inline">application:start(prim_app)</code> returns a
│ │ │ │ -value:</p><pre><code class="makeup erlang" translate="no"><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4977980953-1">(</span><span class="ss">prim_app</span><span class="p" data-group-id="4977980953-1">)</span><span class="w">
│ │ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4977980953-2">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4977980953-3">[</span><span class="p" data-group-id="4977980953-3">]</span><span class="p" data-group-id="4977980953-2">)</span><span class="w">
│ │ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="4977980953-4">(</span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4977980953-5">[</span><span class="p" data-group-id="4977980953-5">]</span><span class="p" data-group-id="4977980953-4">)</span><span class="w">
│ │ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="4977980953-6">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4977980953-7">[</span><span class="p" data-group-id="4977980953-7">]</span><span class="p" data-group-id="4977980953-6">)</span><span class="w">
│ │ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">incl_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="4977980953-8">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4977980953-9">[</span><span class="p" data-group-id="4977980953-9">]</span><span class="p" data-group-id="4977980953-8">)</span><span class="w">
│ │ │ │ +value:</p><pre><code class="makeup erlang" translate="no"><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7401679153-1">(</span><span class="ss">prim_app</span><span class="p" data-group-id="7401679153-1">)</span><span class="w">
│ │ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7401679153-2">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7401679153-3">[</span><span class="p" data-group-id="7401679153-3">]</span><span class="p" data-group-id="7401679153-2">)</span><span class="w">
│ │ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="7401679153-4">(</span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7401679153-5">[</span><span class="p" data-group-id="7401679153-5">]</span><span class="p" data-group-id="7401679153-4">)</span><span class="w">
│ │ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="7401679153-6">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7401679153-7">[</span><span class="p" data-group-id="7401679153-7">]</span><span class="p" data-group-id="7401679153-6">)</span><span class="w">
│ │ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">incl_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="7401679153-8">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7401679153-9">[</span><span class="p" data-group-id="7401679153-9">]</span><span class="p" data-group-id="7401679153-8">)</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/gen_server_concepts.xhtml
│ │ │ │ @@ -62,63 +62,63 @@
│ │ │ │    <a href="#example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>An example of a simple server written in plain Erlang is provided in
│ │ │ │  <a href="design_principles.xhtml#ch1">Overview</a>. The server can be reimplemented using
│ │ │ │ -<code class="inline">gen_server</code>, resulting in this callback module:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5727641331-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="5727641331-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5727641331-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="5727641331-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">gen_server</code>, resulting in this callback module:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3605991220-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="3605991220-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3605991220-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="3605991220-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5727641331-3">(</span><span class="p" data-group-id="5727641331-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5727641331-4">]</span><span class="p" data-group-id="5727641331-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5727641331-5">(</span><span class="p" data-group-id="5727641331-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5727641331-6">]</span><span class="p" data-group-id="5727641331-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5727641331-7">(</span><span class="p" data-group-id="5727641331-8">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5727641331-8">]</span><span class="p" data-group-id="5727641331-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3605991220-3">(</span><span class="p" data-group-id="3605991220-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3605991220-4">]</span><span class="p" data-group-id="3605991220-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3605991220-5">(</span><span class="p" data-group-id="3605991220-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3605991220-6">]</span><span class="p" data-group-id="3605991220-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3605991220-7">(</span><span class="p" data-group-id="3605991220-8">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3605991220-8">]</span><span class="p" data-group-id="3605991220-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="5727641331-9">(</span><span class="p" data-group-id="5727641331-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5727641331-10">(</span><span class="p" data-group-id="5727641331-11">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="5727641331-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5727641331-12">[</span><span class="p" data-group-id="5727641331-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5727641331-13">[</span><span class="p" data-group-id="5727641331-13">]</span><span class="p" data-group-id="5727641331-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="3605991220-9">(</span><span class="p" data-group-id="3605991220-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3605991220-10">(</span><span class="p" data-group-id="3605991220-11">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3605991220-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3605991220-12">[</span><span class="p" data-group-id="3605991220-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3605991220-13">[</span><span class="p" data-group-id="3605991220-13">]</span><span class="p" data-group-id="3605991220-10">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="5727641331-14">(</span><span class="p" data-group-id="5727641331-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="5727641331-15">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="5727641331-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="3605991220-14">(</span><span class="p" data-group-id="3605991220-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3605991220-15">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="3605991220-15">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="5727641331-16">(</span><span class="n">Ch</span><span class="p" data-group-id="5727641331-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="5727641331-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5727641331-18">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5727641331-18">}</span><span class="p" data-group-id="5727641331-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="3605991220-16">(</span><span class="n">Ch</span><span class="p" data-group-id="3605991220-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="3605991220-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3605991220-18">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3605991220-18">}</span><span class="p" data-group-id="3605991220-17">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="5727641331-19">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5727641331-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5727641331-20">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="5727641331-21">(</span><span class="p" data-group-id="5727641331-21">)</span><span class="p" data-group-id="5727641331-20">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3605991220-19">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="3605991220-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3605991220-20">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="3605991220-21">(</span><span class="p" data-group-id="3605991220-21">)</span><span class="p" data-group-id="3605991220-20">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="5727641331-22">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5727641331-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5727641331-23">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="5727641331-23">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="5727641331-24">(</span><span class="n">Chs</span><span class="p" data-group-id="5727641331-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5727641331-25">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="5727641331-25">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="3605991220-22">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3605991220-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3605991220-23">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3605991220-23">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="3605991220-24">(</span><span class="n">Chs</span><span class="p" data-group-id="3605991220-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3605991220-25">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3605991220-25">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="5727641331-26">(</span><span class="p" data-group-id="5727641331-27">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5727641331-27">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5727641331-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="5727641331-28">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5727641331-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5727641331-29">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="5727641331-29">}</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-a-gen_server" class="section-heading">
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="3605991220-26">(</span><span class="p" data-group-id="3605991220-27">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="3605991220-27">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3605991220-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="3605991220-28">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3605991220-28">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3605991220-29">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3605991220-29">}</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-a-gen_server" class="section-heading">
│ │ │ │    <a href="#starting-a-gen_server" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting a Gen_Server</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the example in the previous section, <code class="inline">gen_server</code> is started by calling
│ │ │ │ -<code class="inline">ch3:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="6224905957-1">(</span><span class="p" data-group-id="6224905957-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6224905957-2">(</span><span class="p" data-group-id="6224905957-3">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6224905957-3">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6224905957-4">[</span><span class="p" data-group-id="6224905957-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6224905957-5">[</span><span class="p" data-group-id="6224905957-5">]</span><span class="p" data-group-id="6224905957-2">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6224905957-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="6224905957-6">}</span></code></pre><p><code class="inline">start_link/0</code> calls function <a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a>.  This function
│ │ │ │ +<code class="inline">ch3:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="6346115151-1">(</span><span class="p" data-group-id="6346115151-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6346115151-2">(</span><span class="p" data-group-id="6346115151-3">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6346115151-3">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6346115151-4">[</span><span class="p" data-group-id="6346115151-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6346115151-5">[</span><span class="p" data-group-id="6346115151-5">]</span><span class="p" data-group-id="6346115151-2">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6346115151-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="6346115151-6">}</span></code></pre><p><code class="inline">start_link/0</code> calls function <a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a>.  This function
│ │ │ │  spawns and links to a new process, a <code class="inline">gen_server</code>.</p><ul><li><p>The first argument, <code class="inline">{local, ch3}</code>, specifies the name.
│ │ │ │  The gen_server is then locally registered as <code class="inline">ch3</code>.</p><p>If the name is omitted, the <code class="inline">gen_server</code> is not registered. Instead its pid
│ │ │ │  must be used. The name can also be given as <code class="inline">{global, Name}</code>, in which case
│ │ │ │  the <code class="inline">gen_server</code> is registered using <a href="../../../lib/kernel/doc/html/global.html#register_name/2"><code class="inline">global:register_name/2</code></a>.</p></li><li><p>The second argument, <code class="inline">ch3</code>, is the name of the callback module, which is
│ │ │ │  the module where the callback functions are located.</p><p>The interface functions (<code class="inline">start_link/0</code>, <code class="inline">alloc/0</code>, and <code class="inline">free/1</code>) are located
│ │ │ │  in the same module as the callback functions (<code class="inline">init/1</code>, <code class="inline">handle_call/3</code>, and
│ │ │ │  <code class="inline">handle_cast/2</code>). It is usually good programming practice to have the code
│ │ │ │  corresponding to one process contained in a single module.</p></li><li><p>The third argument, <code class="inline">[]</code>, is a term that is passed as is to the callback
│ │ │ │  function <code class="inline">init</code>. Here, <code class="inline">init</code> does not need any indata and ignores the
│ │ │ │  argument.</p></li><li><p>The fourth argument, <code class="inline">[]</code>, is a list of options. See <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ │  for the available options.</p></li></ul><p>If name registration succeeds, the new <code class="inline">gen_server</code> process calls the callback
│ │ │ │  function <code class="inline">ch3:init([])</code>. <code class="inline">init</code> is expected to return <code class="inline">{ok, State}</code>, where
│ │ │ │  <code class="inline">State</code> is the internal state of the <code class="inline">gen_server</code>. In this case, the state is
│ │ │ │ -the available channels.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9164903081-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="9164903081-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9164903081-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="9164903081-3">(</span><span class="p" data-group-id="9164903081-3">)</span><span class="p" data-group-id="9164903081-2">}</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> is synchronous. It does not return until the
│ │ │ │ +the available channels.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7670387692-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="7670387692-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7670387692-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="7670387692-3">(</span><span class="p" data-group-id="7670387692-3">)</span><span class="p" data-group-id="7670387692-2">}</span><span class="p">.</span></code></pre><p><a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> is synchronous. It does not return until the
│ │ │ │  <code class="inline">gen_server</code> has been initialized and is ready to receive requests.</p><p><a href="../../../lib/stdlib/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> must be used if the <code class="inline">gen_server</code> is part of
│ │ │ │  a supervision tree, meaning that it was started by a supervisor. There
│ │ │ │  is another function, <a href="../../../lib/stdlib/doc/html/gen_server.html#start/4"><code class="inline">gen_server:start/4</code></a>, to start a standalone
│ │ │ │  <code class="inline">gen_server</code> that is not part of a supervision tree.</p><h2 id="synchronous-requests-call" class="section-heading">
│ │ │ │    <a href="#synchronous-requests-call" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -126,32 +126,32 @@
│ │ │ │  </h2>
│ │ │ │  <p>The synchronous request <code class="inline">alloc()</code> is implemented using <a href="../../../lib/stdlib/doc/html/gen_server.html#call/2"><code class="inline">gen_server:call/2</code></a>:</p><pre><code class="text">alloc() -&gt;
│ │ │ │      gen_server:call(ch3, alloc).</code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code> and must agree with the name
│ │ │ │  used to start it. <code class="inline">alloc</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │ │  When the request is received, the <code class="inline">gen_server</code> calls
│ │ │ │  <code class="inline">handle_call(Request, From, State)</code>, which is expected to return
│ │ │ │  a tuple <code class="inline">{reply,Reply,State1}</code>. <code class="inline">Reply</code> is the reply that is to be sent back
│ │ │ │ -to the client, and <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="3972960828-1">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="3972960828-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3972960828-2">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3972960828-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="3972960828-3">(</span><span class="n">Chs</span><span class="p" data-group-id="3972960828-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3972960828-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="3972960828-4">}</span><span class="p">.</span></code></pre><p>In this case, the reply is the allocated channel <code class="inline">Ch</code> and the new state is the
│ │ │ │ +to the client, and <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="4436463912-1">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4436463912-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4436463912-2">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="4436463912-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="4436463912-3">(</span><span class="n">Chs</span><span class="p" data-group-id="4436463912-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4436463912-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="4436463912-4">}</span><span class="p">.</span></code></pre><p>In this case, the reply is the allocated channel <code class="inline">Ch</code> and the new state is the
│ │ │ │  set of remaining available channels <code class="inline">Chs2</code>.</p><p>Thus, the call <code class="inline">ch3:alloc()</code> returns the allocated channel <code class="inline">Ch</code> and the
│ │ │ │  <code class="inline">gen_server</code> then waits for new requests, now with an updated list of
│ │ │ │  available channels.</p><h2 id="asynchronous-requests-cast" class="section-heading">
│ │ │ │    <a href="#asynchronous-requests-cast" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Asynchronous Requests - Cast</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The asynchronous request <code class="inline">free(Ch)</code> is implemented using <a href="../../../lib/stdlib/doc/html/gen_server.html#cast/2"><code class="inline">gen_server:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">free</span><span class="p" data-group-id="6340049232-1">(</span><span class="n">Ch</span><span class="p" data-group-id="6340049232-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6340049232-2">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6340049232-3">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6340049232-3">}</span><span class="p" data-group-id="6340049232-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code>. <code class="inline">{free, Ch}</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │ │ +<p>The asynchronous request <code class="inline">free(Ch)</code> is implemented using <a href="../../../lib/stdlib/doc/html/gen_server.html#cast/2"><code class="inline">gen_server:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">free</span><span class="p" data-group-id="2810117156-1">(</span><span class="n">Ch</span><span class="p" data-group-id="2810117156-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="2810117156-2">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2810117156-3">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="2810117156-3">}</span><span class="p" data-group-id="2810117156-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code>. <code class="inline">{free, Ch}</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │ │  <code class="inline">cast</code>, and thus <code class="inline">free</code>, then returns <code class="inline">ok</code>.</p><p>When the request is received, the <code class="inline">gen_server</code> calls
│ │ │ │  <code class="inline">handle_cast(Request, State)</code>, which is expected to return a tuple
│ │ │ │ -<code class="inline">{noreply,State1}</code>. <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_cast</span><span class="p" data-group-id="5185609153-1">(</span><span class="p" data-group-id="5185609153-2">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5185609153-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5185609153-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="5185609153-3">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5185609153-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5185609153-4">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="5185609153-4">}</span><span class="p">.</span></code></pre><p>In this case, the new state is the updated list of available channels <code class="inline">Chs2</code>.
│ │ │ │ +<code class="inline">{noreply,State1}</code>. <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_cast</span><span class="p" data-group-id="7524943676-1">(</span><span class="p" data-group-id="7524943676-2">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7524943676-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7524943676-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="7524943676-3">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7524943676-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7524943676-4">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="7524943676-4">}</span><span class="p">.</span></code></pre><p>In this case, the new state is the updated list of available channels <code class="inline">Chs2</code>.
│ │ │ │  The <code class="inline">gen_server</code> is now ready for new requests.</p><h2 id="stopping" class="section-heading">
│ │ │ │    <a href="#stopping" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Stopping</span>
│ │ │ │  </h2>
│ │ │ │  <h3 id="in-a-supervision-tree" class="section-heading">
│ │ │ │ @@ -162,65 +162,65 @@
│ │ │ │  </h3>
│ │ │ │  <p>If the <code class="inline">gen_server</code> is part of a supervision tree, no stop function is needed.
│ │ │ │  The <code class="inline">gen_server</code> is automatically terminated by its supervisor.  Exactly how
│ │ │ │  this is done is defined by a <a href="sup_princ.xhtml#shutdown">shutdown strategy</a>
│ │ │ │  set in the supervisor.</p><p>If it is necessary to clean up before termination, the shutdown strategy
│ │ │ │  must be a time-out value and the <code class="inline">gen_server</code> must be set to trap exit signals
│ │ │ │  in function <code class="inline">init</code>. When ordered to shutdown, the <code class="inline">gen_server</code> then calls
│ │ │ │ -the callback function <code class="inline">terminate(shutdown, State)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="2395018189-1">(</span><span class="n">Args</span><span class="p" data-group-id="2395018189-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +the callback function <code class="inline">terminate(shutdown, State)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7594991072-1">(</span><span class="n">Args</span><span class="p" data-group-id="7594991072-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="2395018189-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2395018189-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="7594991072-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7594991072-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2395018189-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2395018189-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7594991072-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7594991072-3">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="2395018189-4">(</span><span class="ss">shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="2395018189-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="7594991072-4">(</span><span class="ss">shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7594991072-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code for cleaning up here</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="standalone-gen_servers" class="section-heading">
│ │ │ │    <a href="#standalone-gen_servers" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Standalone Gen_Servers</span>
│ │ │ │  </h3>
│ │ │ │  <p>If the <code class="inline">gen_server</code> is not part of a supervision tree, a stop function
│ │ │ │  can be useful, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">export</span><span class="p" data-group-id="6415991784-1">(</span><span class="p" data-group-id="6415991784-2">[</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6415991784-2">]</span><span class="p" data-group-id="6415991784-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">export</span><span class="p" data-group-id="4665354887-1">(</span><span class="p" data-group-id="4665354887-2">[</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4665354887-2">]</span><span class="p" data-group-id="4665354887-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="6415991784-3">(</span><span class="p" data-group-id="6415991784-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6415991784-4">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p" data-group-id="6415991784-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="4665354887-3">(</span><span class="p" data-group-id="4665354887-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4665354887-4">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p" data-group-id="4665354887-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="6415991784-5">(</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6415991784-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6415991784-6">{</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6415991784-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="6415991784-7">(</span><span class="p" data-group-id="6415991784-8">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6415991784-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6415991784-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="4665354887-5">(</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4665354887-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4665354887-6">{</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4665354887-6">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="4665354887-7">(</span><span class="p" data-group-id="4665354887-8">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4665354887-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4665354887-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="6415991784-9">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6415991784-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="4665354887-9">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4665354887-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The callback function handling the <code class="inline">stop</code> request returns a tuple
│ │ │ │  <code class="inline">{stop,normal,State1}</code>, where <code class="inline">normal</code> specifies that it is
│ │ │ │  a normal termination and <code class="inline">State1</code> is a new value for the state
│ │ │ │  of the <code class="inline">gen_server</code>.  This causes the <code class="inline">gen_server</code> to call
│ │ │ │  <code class="inline">terminate(normal, State1)</code> and then it terminates gracefully.</p><h2 id="handling-other-messages" class="section-heading">
│ │ │ │    <a href="#handling-other-messages" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Handling Other Messages</span>
│ │ │ │  </h2>
│ │ │ │  <p>If the <code class="inline">gen_server</code> is to be able to receive other messages than requests,
│ │ │ │  the callback function <code class="inline">handle_info(Info, State)</code> must be implemented
│ │ │ │  to handle them.  Examples of other messages are exit messages,
│ │ │ │  if the <code class="inline">gen_server</code> is linked to other processes than the supervisor
│ │ │ │ -and it is trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="1169063701-1">(</span><span class="p" data-group-id="1169063701-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1169063701-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1169063701-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +and it is trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="1684867220-1">(</span><span class="p" data-group-id="1684867220-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1684867220-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1684867220-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code to handle exits here.</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1169063701-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="1169063701-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="7140326125-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="7140326125-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1684867220-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="1684867220-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="6244911763-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="6244911763-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code to convert state (and more) during code change.</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7140326125-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="7140326125-2">}</span><span class="p">.</span></code></pre>
│ │ │ │ +    </span><span class="p" data-group-id="6244911763-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="6244911763-2">}</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/funs.xhtml
│ │ │ │ @@ -22,399 +22,399 @@
│ │ │ │      </h1>
│ │ │ │  <h2 id="map" class="section-heading">
│ │ │ │    <a href="#map" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">map</span>
│ │ │ │  </h2>
│ │ │ │ -<p>The following function, <code class="inline">double</code>, doubles every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="8797363454-1">(</span><span class="p" data-group-id="8797363454-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8797363454-2">]</span><span class="p" data-group-id="8797363454-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8797363454-3">[</span><span class="mi">2</span><span class="o">*</span><span class="n">H</span><span class="p">|</span><span class="nf">double</span><span class="p" data-group-id="8797363454-4">(</span><span class="n">T</span><span class="p" data-group-id="8797363454-4">)</span><span class="p" data-group-id="8797363454-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="8797363454-5">(</span><span class="p" data-group-id="8797363454-6">[</span><span class="p" data-group-id="8797363454-6">]</span><span class="p" data-group-id="8797363454-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8797363454-7">[</span><span class="p" data-group-id="8797363454-7">]</span><span class="p">.</span></code></pre><p>Hence, the argument entered as input is doubled as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">double</span><span class="p" data-group-id="4605324082-1">(</span><span class="p" data-group-id="4605324082-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4605324082-2">]</span><span class="p" data-group-id="4605324082-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4605324082-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p" data-group-id="4605324082-3">]</span></code></pre><p>The following function, <code class="inline">add_one</code>, adds one to every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add_one</span><span class="p" data-group-id="5395426095-1">(</span><span class="p" data-group-id="5395426095-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5395426095-2">]</span><span class="p" data-group-id="5395426095-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5395426095-3">[</span><span class="n">H</span><span class="o">+</span><span class="mi">1</span><span class="p">|</span><span class="nf">add_one</span><span class="p" data-group-id="5395426095-4">(</span><span class="n">T</span><span class="p" data-group-id="5395426095-4">)</span><span class="p" data-group-id="5395426095-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">add_one</span><span class="p" data-group-id="5395426095-5">(</span><span class="p" data-group-id="5395426095-6">[</span><span class="p" data-group-id="5395426095-6">]</span><span class="p" data-group-id="5395426095-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5395426095-7">[</span><span class="p" data-group-id="5395426095-7">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> have a similar structure. This can be used
│ │ │ │ -by writing a function <code class="inline">map</code> that expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="4600068361-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4600068361-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4600068361-2">]</span><span class="p" data-group-id="4600068361-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4600068361-3">[</span><span class="n">F</span><span class="p" data-group-id="4600068361-4">(</span><span class="n">H</span><span class="p" data-group-id="4600068361-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="4600068361-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4600068361-5">)</span><span class="p" data-group-id="4600068361-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="4600068361-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4600068361-7">[</span><span class="p" data-group-id="4600068361-7">]</span><span class="p" data-group-id="4600068361-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4600068361-8">[</span><span class="p" data-group-id="4600068361-8">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> can now be expressed in terms of <code class="inline">map</code> as
│ │ │ │ -follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="5097799991-1">(</span><span class="n">L</span><span class="p" data-group-id="5097799991-1">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="5097799991-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5097799991-3">(</span><span class="n">X</span><span class="p" data-group-id="5097799991-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5097799991-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add_one</span><span class="p" data-group-id="5097799991-4">(</span><span class="n">L</span><span class="p" data-group-id="5097799991-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="5097799991-5">(</span><span class="nf">fun</span><span class="p" data-group-id="5097799991-6">(</span><span class="n">X</span><span class="p" data-group-id="5097799991-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5097799991-5">)</span><span class="p">.</span></code></pre><p><code class="inline">map(F, List)</code> is a function that takes a function <code class="inline">F</code> and a list <code class="inline">L</code> as
│ │ │ │ +<p>The following function, <code class="inline">double</code>, doubles every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="4028043235-1">(</span><span class="p" data-group-id="4028043235-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4028043235-2">]</span><span class="p" data-group-id="4028043235-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4028043235-3">[</span><span class="mi">2</span><span class="o">*</span><span class="n">H</span><span class="p">|</span><span class="nf">double</span><span class="p" data-group-id="4028043235-4">(</span><span class="n">T</span><span class="p" data-group-id="4028043235-4">)</span><span class="p" data-group-id="4028043235-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="4028043235-5">(</span><span class="p" data-group-id="4028043235-6">[</span><span class="p" data-group-id="4028043235-6">]</span><span class="p" data-group-id="4028043235-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4028043235-7">[</span><span class="p" data-group-id="4028043235-7">]</span><span class="p">.</span></code></pre><p>Hence, the argument entered as input is doubled as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">double</span><span class="p" data-group-id="3735324513-1">(</span><span class="p" data-group-id="3735324513-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3735324513-2">]</span><span class="p" data-group-id="3735324513-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3735324513-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p" data-group-id="3735324513-3">]</span></code></pre><p>The following function, <code class="inline">add_one</code>, adds one to every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add_one</span><span class="p" data-group-id="8022265123-1">(</span><span class="p" data-group-id="8022265123-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8022265123-2">]</span><span class="p" data-group-id="8022265123-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8022265123-3">[</span><span class="n">H</span><span class="o">+</span><span class="mi">1</span><span class="p">|</span><span class="nf">add_one</span><span class="p" data-group-id="8022265123-4">(</span><span class="n">T</span><span class="p" data-group-id="8022265123-4">)</span><span class="p" data-group-id="8022265123-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">add_one</span><span class="p" data-group-id="8022265123-5">(</span><span class="p" data-group-id="8022265123-6">[</span><span class="p" data-group-id="8022265123-6">]</span><span class="p" data-group-id="8022265123-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8022265123-7">[</span><span class="p" data-group-id="8022265123-7">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> have a similar structure. This can be used
│ │ │ │ +by writing a function <code class="inline">map</code> that expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="2373405061-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2373405061-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2373405061-2">]</span><span class="p" data-group-id="2373405061-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2373405061-3">[</span><span class="n">F</span><span class="p" data-group-id="2373405061-4">(</span><span class="n">H</span><span class="p" data-group-id="2373405061-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="2373405061-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2373405061-5">)</span><span class="p" data-group-id="2373405061-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="2373405061-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2373405061-7">[</span><span class="p" data-group-id="2373405061-7">]</span><span class="p" data-group-id="2373405061-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2373405061-8">[</span><span class="p" data-group-id="2373405061-8">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> can now be expressed in terms of <code class="inline">map</code> as
│ │ │ │ +follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="2355140328-1">(</span><span class="n">L</span><span class="p" data-group-id="2355140328-1">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="2355140328-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2355140328-3">(</span><span class="n">X</span><span class="p" data-group-id="2355140328-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2355140328-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add_one</span><span class="p" data-group-id="2355140328-4">(</span><span class="n">L</span><span class="p" data-group-id="2355140328-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="2355140328-5">(</span><span class="nf">fun</span><span class="p" data-group-id="2355140328-6">(</span><span class="n">X</span><span class="p" data-group-id="2355140328-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2355140328-5">)</span><span class="p">.</span></code></pre><p><code class="inline">map(F, List)</code> is a function that takes a function <code class="inline">F</code> and a list <code class="inline">L</code> as
│ │ │ │  arguments and returns a new list, obtained by applying <code class="inline">F</code> to each of the
│ │ │ │  elements in <code class="inline">L</code>.</p><p>The process of abstracting out the common features of a number of different
│ │ │ │  programs is called <em>procedural abstraction</em>. Procedural abstraction can be used
│ │ │ │  to write several different functions that have a similar structure, but differ
│ │ │ │  in some minor detail. This is done as follows:</p><ol><li><em>Step 1.</em> Write one function that represents the common features of these
│ │ │ │  functions.</li><li><em>Step 2.</em> Parameterize the difference in terms of functions that are passed
│ │ │ │  as arguments to the common function.</li></ol><h2 id="foreach" class="section-heading">
│ │ │ │    <a href="#foreach" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">foreach</span>
│ │ │ │  </h2>
│ │ │ │  <p>This section illustrates procedural abstraction. Initially, the following two
│ │ │ │ -examples are written as conventional functions.</p><p>This function prints all elements of a list onto a stream:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="4142187403-1">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4142187403-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4142187403-2">]</span><span class="p" data-group-id="4142187403-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4142187403-3">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4142187403-4">[</span><span class="n">H</span><span class="p" data-group-id="4142187403-4">]</span><span class="p" data-group-id="4142187403-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">print_list</span><span class="p" data-group-id="4142187403-5">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4142187403-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">print_list</span><span class="p" data-group-id="4142187403-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4142187403-7">[</span><span class="p" data-group-id="4142187403-7">]</span><span class="p" data-group-id="4142187403-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>This function broadcasts a message to a list of processes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">broadcast</span><span class="p" data-group-id="3380868850-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3380868850-2">[</span><span class="n">Pid</span><span class="p">|</span><span class="n">Pids</span><span class="p" data-group-id="3380868850-2">]</span><span class="p" data-group-id="3380868850-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +examples are written as conventional functions.</p><p>This function prints all elements of a list onto a stream:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="3908644544-1">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3908644544-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3908644544-2">]</span><span class="p" data-group-id="3908644544-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3908644544-3">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3908644544-4">[</span><span class="n">H</span><span class="p" data-group-id="3908644544-4">]</span><span class="p" data-group-id="3908644544-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">print_list</span><span class="p" data-group-id="3908644544-5">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3908644544-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">print_list</span><span class="p" data-group-id="3908644544-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3908644544-7">[</span><span class="p" data-group-id="3908644544-7">]</span><span class="p" data-group-id="3908644544-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>This function broadcasts a message to a list of processes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">broadcast</span><span class="p" data-group-id="4687778426-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4687778426-2">[</span><span class="n">Pid</span><span class="p">|</span><span class="n">Pids</span><span class="p" data-group-id="4687778426-2">]</span><span class="p" data-group-id="4687778426-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Msg</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">broadcast</span><span class="p" data-group-id="3380868850-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">Pids</span><span class="p" data-group-id="3380868850-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">broadcast</span><span class="p" data-group-id="3380868850-4">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3380868850-5">[</span><span class="p" data-group-id="3380868850-5">]</span><span class="p" data-group-id="3380868850-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">broadcast</span><span class="p" data-group-id="4687778426-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">Pids</span><span class="p" data-group-id="4687778426-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">broadcast</span><span class="p" data-group-id="4687778426-4">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4687778426-5">[</span><span class="p" data-group-id="4687778426-5">]</span><span class="p" data-group-id="4687778426-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="p">.</span></code></pre><p>These two functions have a similar structure. They both iterate over a list and
│ │ │ │  do something to each element in the list. The &quot;something&quot; is passed on as an
│ │ │ │ -extra argument to the function that does this.</p><p>The function <code class="inline">foreach</code> expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="2381642277-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2381642277-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2381642277-2">]</span><span class="p" data-group-id="2381642277-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">F</span><span class="p" data-group-id="2381642277-3">(</span><span class="n">H</span><span class="p" data-group-id="2381642277-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="2381642277-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2381642277-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="2381642277-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2381642277-6">[</span><span class="p" data-group-id="2381642277-6">]</span><span class="p" data-group-id="2381642277-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">print_list</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="5715821086-1">(</span><span class="nf">fun</span><span class="p" data-group-id="5715821086-2">(</span><span class="n">H</span><span class="p" data-group-id="5715821086-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5715821086-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="5715821086-4">[</span><span class="n">H</span><span class="p" data-group-id="5715821086-4">]</span><span class="p" data-group-id="5715821086-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5715821086-1">)</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">broadcast</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="0832699254-1">(</span><span class="nf">fun</span><span class="p" data-group-id="0832699254-2">(</span><span class="n">Pid</span><span class="p" data-group-id="0832699254-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0832699254-1">)</span></code></pre><p><code class="inline">foreach</code> is evaluated for its side-effect and not its value. <code class="inline">foreach(Fun ,L)</code>
│ │ │ │ +extra argument to the function that does this.</p><p>The function <code class="inline">foreach</code> expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="8306517633-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8306517633-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8306517633-2">]</span><span class="p" data-group-id="8306517633-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">F</span><span class="p" data-group-id="8306517633-3">(</span><span class="n">H</span><span class="p" data-group-id="8306517633-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="8306517633-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8306517633-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="8306517633-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8306517633-6">[</span><span class="p" data-group-id="8306517633-6">]</span><span class="p" data-group-id="8306517633-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">print_list</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="0521629283-1">(</span><span class="nf">fun</span><span class="p" data-group-id="0521629283-2">(</span><span class="n">H</span><span class="p" data-group-id="0521629283-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0521629283-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="0521629283-4">[</span><span class="n">H</span><span class="p" data-group-id="0521629283-4">]</span><span class="p" data-group-id="0521629283-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0521629283-1">)</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">broadcast</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="4910697451-1">(</span><span class="nf">fun</span><span class="p" data-group-id="4910697451-2">(</span><span class="n">Pid</span><span class="p" data-group-id="4910697451-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4910697451-1">)</span></code></pre><p><code class="inline">foreach</code> is evaluated for its side-effect and not its value. <code class="inline">foreach(Fun ,L)</code>
│ │ │ │  calls <code class="inline">Fun(X)</code> for each element <code class="inline">X</code> in <code class="inline">L</code> and the processing occurs in the
│ │ │ │  order that the elements were defined in <code class="inline">L</code>. <code class="inline">map</code> does not define the order in
│ │ │ │  which its elements are processed.</p><h2 id="syntax-of-funs" class="section-heading">
│ │ │ │    <a href="#syntax-of-funs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Syntax of Funs</span>
│ │ │ │  </h2>
│ │ │ │  <p>Funs are written with the following syntax (see
│ │ │ │ -<a href="../../../lib/../system/doc/html/expressions.xhtml#fun-expressions">Fun Expressions </a>for full description):</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1743559960-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">ArgN</span><span class="p" data-group-id="1743559960-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<a href="../../../lib/../system/doc/html/expressions.xhtml#fun-expressions">Fun Expressions </a>for full description):</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8559671765-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">ArgN</span><span class="p" data-group-id="8559671765-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │      </span><span class="k">end</span></code></pre><p>This creates an anonymous function of <code class="inline">N</code> arguments and binds it to the variable
│ │ │ │  <code class="inline">F</code>.</p><p>Another function, <code class="inline">FunctionName</code>, written in the same module, can be passed as
│ │ │ │  an argument, using the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>With this form of function reference, the function that is referred to does not
│ │ │ │  need to be exported from the module.</p><p>It is also possible to refer to a function defined in a different module, with
│ │ │ │ -the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In this case, the function must be exported from the module in question.</p><p>The following program illustrates the different ways of creating funs:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5081479979-1">(</span><span class="ss">fun_test</span><span class="p" data-group-id="5081479979-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5081479979-2">(</span><span class="p" data-group-id="5081479979-3">[</span><span class="ss">t1</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">t2</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5081479979-3">]</span><span class="p" data-group-id="5081479979-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="5081479979-4">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5081479979-5">[</span><span class="ss">map</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5081479979-5">]</span><span class="p" data-group-id="5081479979-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In this case, the function must be exported from the module in question.</p><p>The following program illustrates the different ways of creating funs:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2411864555-1">(</span><span class="ss">fun_test</span><span class="p" data-group-id="2411864555-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2411864555-2">(</span><span class="p" data-group-id="2411864555-3">[</span><span class="ss">t1</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">t2</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2411864555-3">]</span><span class="p" data-group-id="2411864555-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="2411864555-4">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2411864555-5">[</span><span class="ss">map</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2411864555-5">]</span><span class="p" data-group-id="2411864555-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">t1</span><span class="p" data-group-id="5081479979-6">(</span><span class="p" data-group-id="5081479979-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="5081479979-7">(</span><span class="nf">fun</span><span class="p" data-group-id="5081479979-8">(</span><span class="n">X</span><span class="p" data-group-id="5081479979-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5081479979-9">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5081479979-9">]</span><span class="p" data-group-id="5081479979-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">t1</span><span class="p" data-group-id="2411864555-6">(</span><span class="p" data-group-id="2411864555-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="2411864555-7">(</span><span class="nf">fun</span><span class="p" data-group-id="2411864555-8">(</span><span class="n">X</span><span class="p" data-group-id="2411864555-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2411864555-9">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2411864555-9">]</span><span class="p" data-group-id="2411864555-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">t2</span><span class="p" data-group-id="5081479979-10">(</span><span class="p" data-group-id="5081479979-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="5081479979-11">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5081479979-12">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5081479979-12">]</span><span class="p" data-group-id="5081479979-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">t2</span><span class="p" data-group-id="2411864555-10">(</span><span class="p" data-group-id="2411864555-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="2411864555-11">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2411864555-12">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2411864555-12">]</span><span class="p" data-group-id="2411864555-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="5081479979-13">(</span><span class="n">X</span><span class="p" data-group-id="5081479979-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span></code></pre><p>The fun <code class="inline">F</code> can be evaluated with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="p" data-group-id="7098575163-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Argn</span><span class="p" data-group-id="7098575163-1">)</span></code></pre><p>To check whether a term is a fun, use the test
│ │ │ │ -<a href="../../../lib/../erts/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> in a guard.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0983391631-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="0983391631-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_function</span><span class="p" data-group-id="0983391631-2">(</span><span class="n">F</span><span class="p" data-group-id="0983391631-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="nf">apply</span><span class="p" data-group-id="0983391631-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="0983391631-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="0983391631-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="0983391631-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="0983391631-5">(</span><span class="n">N</span><span class="p" data-group-id="0983391631-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="2411864555-13">(</span><span class="n">X</span><span class="p" data-group-id="2411864555-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span></code></pre><p>The fun <code class="inline">F</code> can be evaluated with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="p" data-group-id="4443895333-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Argn</span><span class="p" data-group-id="4443895333-1">)</span></code></pre><p>To check whether a term is a fun, use the test
│ │ │ │ +<a href="../../../lib/../erts/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> in a guard.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="7864953316-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="7864953316-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_function</span><span class="p" data-group-id="7864953316-2">(</span><span class="n">F</span><span class="p" data-group-id="7864953316-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="nf">apply</span><span class="p" data-group-id="7864953316-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="7864953316-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="7864953316-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7864953316-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="7864953316-5">(</span><span class="n">N</span><span class="p" data-group-id="7864953316-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │     </span><span class="n">N</span><span class="p">.</span></code></pre><p>Funs are a distinct type. The BIFs <code class="inline">erlang:fun_info/1,2</code> can be used to retrieve
│ │ │ │  information about a fun, and the BIF <a href="../../../lib/../erts/doc/html/erlang.html#fun_to_list/1"><code class="inline">erlang:fun_to_list/1</code></a> returns a textual
│ │ │ │  representation of a fun. The <a href="../../../lib/../erts/doc/html/erlang.html#check_process_code/2"><code class="inline">check_process_code/2</code></a>
│ │ │ │  BIF returns <code class="inline">true</code> if the process contains funs that depend on the old version
│ │ │ │  of a module.</p><h2 id="variable-bindings-within-a-fun" class="section-heading">
│ │ │ │    <a href="#variable-bindings-within-a-fun" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Variable Bindings Within a Fun</span>
│ │ │ │  </h2>
│ │ │ │  <p>The scope rules for variables that occur in funs are as follows:</p><ul><li>All variables that occur in the head of a fun are assumed to be &quot;fresh&quot;
│ │ │ │  variables.</li><li>Variables that are defined before the fun, and that occur in function calls or
│ │ │ │ -guard tests within the fun, have the values they had outside the fun.</li><li>Variables cannot be exported from a fun.</li></ul><p>The following examples illustrate these rules:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="3312592138-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3312592138-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3312592138-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="3312592138-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="3312592138-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="3312592138-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="3312592138-4">(</span><span class="nf">fun</span><span class="p" data-group-id="3312592138-5">(</span><span class="n">X</span><span class="p" data-group-id="3312592138-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3312592138-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3312592138-7">[</span><span class="n">X</span><span class="p" data-group-id="3312592138-7">]</span><span class="p" data-group-id="3312592138-6">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3312592138-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="3312592138-8">(</span><span class="n">Stream</span><span class="p" data-group-id="3312592138-8">)</span><span class="p">.</span></code></pre><p>Here, the variable <code class="inline">X</code>, defined in the head of the fun, is a new variable. The
│ │ │ │ +guard tests within the fun, have the values they had outside the fun.</li><li>Variables cannot be exported from a fun.</li></ul><p>The following examples illustrate these rules:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="7251901787-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7251901787-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7251901787-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="7251901787-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="7251901787-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="7251901787-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="7251901787-4">(</span><span class="nf">fun</span><span class="p" data-group-id="7251901787-5">(</span><span class="n">X</span><span class="p" data-group-id="7251901787-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7251901787-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="7251901787-7">[</span><span class="n">X</span><span class="p" data-group-id="7251901787-7">]</span><span class="p" data-group-id="7251901787-6">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7251901787-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="7251901787-8">(</span><span class="n">Stream</span><span class="p" data-group-id="7251901787-8">)</span><span class="p">.</span></code></pre><p>Here, the variable <code class="inline">X</code>, defined in the head of the fun, is a new variable. The
│ │ │ │  variable <code class="inline">Stream</code>, which is used within the fun, gets its value from the
│ │ │ │  <code class="inline">file:open</code> line.</p><p>As any variable that occurs in the head of a fun is considered a new variable,
│ │ │ │ -it is equally valid to write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="4551136598-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4551136598-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4551136598-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="4551136598-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="4551136598-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="4551136598-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="4551136598-4">(</span><span class="nf">fun</span><span class="p" data-group-id="4551136598-5">(</span><span class="n">File</span><span class="p" data-group-id="4551136598-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4551136598-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="4551136598-7">[</span><span class="n">File</span><span class="p" data-group-id="4551136598-7">]</span><span class="p" data-group-id="4551136598-6">)</span><span class="w">
│ │ │ │ -            </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4551136598-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="4551136598-8">(</span><span class="n">Stream</span><span class="p" data-group-id="4551136598-8">)</span><span class="p">.</span></code></pre><p>Here, <code class="inline">File</code> is used as the new variable instead of <code class="inline">X</code>. This is not so wise
│ │ │ │ +it is equally valid to write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="5728335705-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="5728335705-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5728335705-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="5728335705-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="5728335705-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="5728335705-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="5728335705-4">(</span><span class="nf">fun</span><span class="p" data-group-id="5728335705-5">(</span><span class="n">File</span><span class="p" data-group-id="5728335705-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5728335705-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="5728335705-7">[</span><span class="n">File</span><span class="p" data-group-id="5728335705-7">]</span><span class="p" data-group-id="5728335705-6">)</span><span class="w">
│ │ │ │ +            </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="5728335705-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="5728335705-8">(</span><span class="n">Stream</span><span class="p" data-group-id="5728335705-8">)</span><span class="p">.</span></code></pre><p>Here, <code class="inline">File</code> is used as the new variable instead of <code class="inline">X</code>. This is not so wise
│ │ │ │  because code in the fun body cannot refer to the variable <code class="inline">File</code>, which is
│ │ │ │  defined outside of the fun. Compiling this example gives the following
│ │ │ │  diagnostic:</p><pre><code class="text">./FileName.erl:Line: Warning: variable 'File'
│ │ │ │        shadowed in 'fun'</code></pre><p>This indicates that the variable <code class="inline">File</code>, which is defined inside the fun,
│ │ │ │  collides with the variable <code class="inline">File</code>, which is defined outside the fun.</p><p>The rules for importing variables into a fun has the consequence that certain
│ │ │ │  pattern matching operations must be moved into guard expressions and cannot be
│ │ │ │  written in the head of the fun. For example, you might write the following code
│ │ │ │  if you intend the first clause of <code class="inline">F</code> to be evaluated when the value of its
│ │ │ │ -argument is <code class="inline">Y</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="5372180922-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5372180922-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +argument is <code class="inline">Y</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4809316774-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4809316774-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="nf">map</span><span class="p" data-group-id="5372180922-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5372180922-3">(</span><span class="n">X</span><span class="p" data-group-id="5372180922-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">map</span><span class="p" data-group-id="4809316774-2">(</span><span class="nf">fun</span><span class="p" data-group-id="4809316774-3">(</span><span class="n">X</span><span class="p" data-group-id="4809316774-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │               </span><span class="p">;</span><span class="w">
│ │ │ │ -           </span><span class="p" data-group-id="5372180922-4">(</span><span class="p">_</span><span class="p" data-group-id="5372180922-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +           </span><span class="p" data-group-id="4809316774-4">(</span><span class="p">_</span><span class="p" data-group-id="4809316774-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │               </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5372180922-2">)</span><span class="w">
│ │ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>instead of writing the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="8803579907-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8803579907-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4809316774-2">)</span><span class="w">
│ │ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>instead of writing the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0202234197-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0202234197-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="nf">map</span><span class="p" data-group-id="8803579907-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8803579907-3">(</span><span class="n">Y</span><span class="p" data-group-id="8803579907-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">map</span><span class="p" data-group-id="0202234197-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0202234197-3">(</span><span class="n">Y</span><span class="p" data-group-id="0202234197-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │               </span><span class="p">;</span><span class="w">
│ │ │ │ -           </span><span class="p" data-group-id="8803579907-4">(</span><span class="p">_</span><span class="p" data-group-id="8803579907-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +           </span><span class="p" data-group-id="0202234197-4">(</span><span class="p">_</span><span class="p" data-group-id="0202234197-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │               </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8803579907-2">)</span><span class="w">
│ │ │ │ +        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0202234197-2">)</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="funs-and-module-lists" class="section-heading">
│ │ │ │    <a href="#funs-and-module-lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Funs and Module Lists</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following examples show a dialogue with the Erlang shell. All the higher
│ │ │ │  order functions discussed are exported from the module <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a>.</p><h3 id="map-1" class="section-heading">
│ │ │ │    <a href="#map-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">map</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="9138371452-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9138371452-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9138371452-2">]</span><span class="p" data-group-id="9138371452-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9138371452-3">[</span><span class="n">F</span><span class="p" data-group-id="9138371452-4">(</span><span class="n">H</span><span class="p" data-group-id="9138371452-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="9138371452-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9138371452-5">)</span><span class="p" data-group-id="9138371452-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="9138371452-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9138371452-7">[</span><span class="p" data-group-id="9138371452-7">]</span><span class="p" data-group-id="9138371452-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9138371452-8">[</span><span class="p" data-group-id="9138371452-8">]</span><span class="p">.</span></code></pre><p>It returns the list obtained by applying the function to every argument in the
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="1039881706-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1039881706-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1039881706-2">]</span><span class="p" data-group-id="1039881706-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1039881706-3">[</span><span class="n">F</span><span class="p" data-group-id="1039881706-4">(</span><span class="n">H</span><span class="p" data-group-id="1039881706-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="1039881706-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="1039881706-5">)</span><span class="p" data-group-id="1039881706-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="1039881706-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1039881706-7">[</span><span class="p" data-group-id="1039881706-7">]</span><span class="p" data-group-id="1039881706-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1039881706-8">[</span><span class="p" data-group-id="1039881706-8">]</span><span class="p">.</span></code></pre><p>It returns the list obtained by applying the function to every argument in the
│ │ │ │  list.</p><p>When a new fun is defined in the shell, the value of the fun is printed as
│ │ │ │ -<code class="inline">Fun#&lt;erl_eval&gt;</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Double</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9112377043-1">(</span><span class="n">X</span><span class="p" data-group-id="9112377043-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">Fun#&lt;erl_eval&gt;</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Double</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1393021705-1">(</span><span class="n">X</span><span class="p" data-group-id="1393021705-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="9112377043-2">(</span><span class="n">Double</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9112377043-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9112377043-3">]</span><span class="p" data-group-id="9112377043-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9112377043-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="9112377043-4">]</span></code></pre><h3 id="any" class="section-heading">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1393021705-2">(</span><span class="n">Double</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1393021705-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1393021705-3">]</span><span class="p" data-group-id="1393021705-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1393021705-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="1393021705-4">]</span></code></pre><h3 id="any" class="section-heading">
│ │ │ │    <a href="#any" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">any</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#any/2"><code class="inline">lists:any/2</code></a> takes a predicate <code class="inline">P</code> of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">any</span><span class="p" data-group-id="8077871964-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8077871964-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8077871964-2">]</span><span class="p" data-group-id="8077871964-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="8077871964-3">(</span><span class="n">H</span><span class="p" data-group-id="8077871964-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#any/2"><code class="inline">lists:any/2</code></a> takes a predicate <code class="inline">P</code> of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">any</span><span class="p" data-group-id="3142609561-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3142609561-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3142609561-2">]</span><span class="p" data-group-id="3142609561-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="3142609561-3">(</span><span class="n">H</span><span class="p" data-group-id="3142609561-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">any</span><span class="p" data-group-id="8077871964-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8077871964-4">)</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">any</span><span class="p" data-group-id="3142609561-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3142609561-4">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">any</span><span class="p" data-group-id="8077871964-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8077871964-6">[</span><span class="p" data-group-id="8077871964-6">]</span><span class="p" data-group-id="8077871964-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">any</span><span class="p" data-group-id="3142609561-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3142609561-6">[</span><span class="p" data-group-id="3142609561-6">]</span><span class="p" data-group-id="3142609561-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">false</span><span class="p">.</span></code></pre><p>A predicate is a function that returns <code class="inline">true</code> or <code class="inline">false</code>. <code class="inline">any</code> is <code class="inline">true</code> if
│ │ │ │  there is a term <code class="inline">X</code> in the list such that <code class="inline">P(X)</code> is <code class="inline">true</code>.</p><p>A predicate <code class="inline">Big(X)</code> is defined, which is <code class="inline">true</code> if its argument is greater that
│ │ │ │ -10:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Big</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="8484921160-1">(</span><span class="n">X</span><span class="p" data-group-id="8484921160-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="p">;</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +10:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Big</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="7159543773-1">(</span><span class="n">X</span><span class="p" data-group-id="7159543773-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="p">;</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="8484921160-2">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8484921160-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8484921160-3">]</span><span class="p" data-group-id="8484921160-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="7159543773-2">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7159543773-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7159543773-3">]</span><span class="p" data-group-id="7159543773-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="8484921160-4">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8484921160-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8484921160-5">]</span><span class="p" data-group-id="8484921160-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="7159543773-4">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7159543773-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7159543773-5">]</span><span class="p" data-group-id="7159543773-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><h3 id="all" class="section-heading">
│ │ │ │    <a href="#all" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">all</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#all/2"><code class="inline">lists:all/2</code></a> has the same arguments as <code class="inline">any</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="5698895491-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5698895491-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5698895491-2">]</span><span class="p" data-group-id="5698895491-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="5698895491-3">(</span><span class="n">H</span><span class="p" data-group-id="5698895491-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">all</span><span class="p" data-group-id="5698895491-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5698895491-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#all/2"><code class="inline">lists:all/2</code></a> has the same arguments as <code class="inline">any</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="7440678280-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7440678280-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7440678280-2">]</span><span class="p" data-group-id="7440678280-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="7440678280-3">(</span><span class="n">H</span><span class="p" data-group-id="7440678280-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">all</span><span class="p" data-group-id="7440678280-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="7440678280-4">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="ss">false</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">all</span><span class="p" data-group-id="5698895491-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5698895491-6">[</span><span class="p" data-group-id="5698895491-6">]</span><span class="p" data-group-id="5698895491-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>It is <code class="inline">true</code> if the predicate applied to all elements in the list is <code class="inline">true</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="5202555481-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5202555481-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5202555481-2">]</span><span class="p" data-group-id="5202555481-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">all</span><span class="p" data-group-id="7440678280-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7440678280-6">[</span><span class="p" data-group-id="7440678280-6">]</span><span class="p" data-group-id="7440678280-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>It is <code class="inline">true</code> if the predicate applied to all elements in the list is <code class="inline">true</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="6681755627-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6681755627-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6681755627-2">]</span><span class="p" data-group-id="6681755627-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="5202555481-3">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5202555481-4">[</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="5202555481-4">]</span><span class="p" data-group-id="5202555481-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="6681755627-3">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6681755627-4">[</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="6681755627-4">]</span><span class="p" data-group-id="6681755627-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><h3 id="foreach-1" class="section-heading">
│ │ │ │    <a href="#foreach-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">foreach</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#foreach/2"><code class="inline">lists:foreach/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="6037851348-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6037851348-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6037851348-2">]</span><span class="p" data-group-id="6037851348-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">F</span><span class="p" data-group-id="6037851348-3">(</span><span class="n">H</span><span class="p" data-group-id="6037851348-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="6037851348-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6037851348-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="6037851348-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6037851348-6">[</span><span class="p" data-group-id="6037851348-6">]</span><span class="p" data-group-id="6037851348-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#foreach/2"><code class="inline">lists:foreach/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="1850987801-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1850987801-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1850987801-2">]</span><span class="p" data-group-id="1850987801-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">F</span><span class="p" data-group-id="1850987801-3">(</span><span class="n">H</span><span class="p" data-group-id="1850987801-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="1850987801-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="1850987801-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="1850987801-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1850987801-6">[</span><span class="p" data-group-id="1850987801-6">]</span><span class="p" data-group-id="1850987801-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The function is applied to each argument in the list. <code class="inline">foreach</code> returns <code class="inline">ok</code>. It
│ │ │ │ -is only used for its side-effect:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="0108549811-1">(</span><span class="nf">fun</span><span class="p" data-group-id="0108549811-2">(</span><span class="n">X</span><span class="p" data-group-id="0108549811-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0108549811-3">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="0108549811-4">[</span><span class="n">X</span><span class="p" data-group-id="0108549811-4">]</span><span class="p" data-group-id="0108549811-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0108549811-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0108549811-5">]</span><span class="p" data-group-id="0108549811-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +is only used for its side-effect:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="5667386260-1">(</span><span class="nf">fun</span><span class="p" data-group-id="5667386260-2">(</span><span class="n">X</span><span class="p" data-group-id="5667386260-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5667386260-3">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="5667386260-4">[</span><span class="n">X</span><span class="p" data-group-id="5667386260-4">]</span><span class="p" data-group-id="5667386260-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5667386260-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5667386260-5">]</span><span class="p" data-group-id="5667386260-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="w">
│ │ │ │  </span><span class="mi">2</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><h3 id="foldl" class="section-heading">
│ │ │ │    <a href="#foldl" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">foldl</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> takes a function of two arguments, an accumulator and a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foldl</span><span class="p" data-group-id="1905724370-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1905724370-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="1905724370-2">]</span><span class="p" data-group-id="1905724370-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">foldl</span><span class="p" data-group-id="1905724370-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="1905724370-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="1905724370-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1905724370-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">foldl</span><span class="p" data-group-id="1905724370-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1905724370-6">[</span><span class="p" data-group-id="1905724370-6">]</span><span class="p" data-group-id="1905724370-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Accu</span><span class="p">.</span></code></pre><p>The function is called with two arguments. The first argument is the successive
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> takes a function of two arguments, an accumulator and a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foldl</span><span class="p" data-group-id="9887123217-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9887123217-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="9887123217-2">]</span><span class="p" data-group-id="9887123217-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">foldl</span><span class="p" data-group-id="9887123217-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="9887123217-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="9887123217-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="9887123217-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">foldl</span><span class="p" data-group-id="9887123217-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9887123217-6">[</span><span class="p" data-group-id="9887123217-6">]</span><span class="p" data-group-id="9887123217-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Accu</span><span class="p">.</span></code></pre><p>The function is called with two arguments. The first argument is the successive
│ │ │ │  elements in the list. The second argument is the accumulator. The function must
│ │ │ │  return a new accumulator, which is used the next time the function is called.</p><p>If you have a list of lists <code class="inline">L = [&quot;I&quot;,&quot;like&quot;,&quot;Erlang&quot;]</code>, then you can sum the
│ │ │ │ -lengths of all the strings in <code class="inline">L</code> as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7047253971-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="7047253971-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7047253971-2">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="7047253971-2">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="7047253971-3">(</span><span class="nf">fun</span><span class="p" data-group-id="7047253971-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="7047253971-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7047253971-5">(</span><span class="n">X</span><span class="p" data-group-id="7047253971-5">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7047253971-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mi">11</span></code></pre><p><a href="../../../lib/stdlib/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> works like a <code class="inline">while</code> loop in an imperative language:</p><pre><code class="makeup erlang" translate="no"><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="p" data-group-id="5541685117-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="5541685117-1">]</span><span class="p">,</span><span class="w">
│ │ │ │ +lengths of all the strings in <code class="inline">L</code> as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7338351563-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="7338351563-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7338351563-2">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="7338351563-2">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="7338351563-3">(</span><span class="nf">fun</span><span class="p" data-group-id="7338351563-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="7338351563-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7338351563-5">(</span><span class="n">X</span><span class="p" data-group-id="7338351563-5">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7338351563-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="mi">11</span></code></pre><p><a href="../../../lib/stdlib/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> works like a <code class="inline">while</code> loop in an imperative language:</p><pre><code class="makeup erlang" translate="no"><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="p" data-group-id="3213702715-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="3213702715-1">]</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">Sum</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="nf">while</span><span class="p" data-group-id="5541685117-2">(</span><span class="w"> </span><span class="n">L</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5541685117-3">[</span><span class="p" data-group-id="5541685117-3">]</span><span class="p" data-group-id="5541685117-2">)</span><span class="p" data-group-id="5541685117-4">{</span><span class="w">
│ │ │ │ -    </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="5541685117-5">(</span><span class="nf">head</span><span class="p" data-group-id="5541685117-6">(</span><span class="n">L</span><span class="p" data-group-id="5541685117-6">)</span><span class="p" data-group-id="5541685117-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tail</span><span class="p" data-group-id="5541685117-7">(</span><span class="n">L</span><span class="p" data-group-id="5541685117-7">)</span><span class="w">
│ │ │ │ +</span><span class="nf">while</span><span class="p" data-group-id="3213702715-2">(</span><span class="w"> </span><span class="n">L</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3213702715-3">[</span><span class="p" data-group-id="3213702715-3">]</span><span class="p" data-group-id="3213702715-2">)</span><span class="p" data-group-id="3213702715-4">{</span><span class="w">
│ │ │ │ +    </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="3213702715-5">(</span><span class="nf">head</span><span class="p" data-group-id="3213702715-6">(</span><span class="n">L</span><span class="p" data-group-id="3213702715-6">)</span><span class="p" data-group-id="3213702715-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tail</span><span class="p" data-group-id="3213702715-7">(</span><span class="n">L</span><span class="p" data-group-id="3213702715-7">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><h3 id="mapfoldl" class="section-heading">
│ │ │ │    <a href="#mapfoldl" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">mapfoldl</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#mapfoldl/3"><code class="inline">lists:mapfoldl/3</code></a> simultaneously maps and folds over a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mapfoldl</span><span class="p" data-group-id="2189511564-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2189511564-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="2189511564-2">]</span><span class="p" data-group-id="2189511564-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2189511564-3">{</span><span class="n">R</span><span class="p">,</span><span class="n">Accu1</span><span class="p" data-group-id="2189511564-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="2189511564-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p" data-group-id="2189511564-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2189511564-5">{</span><span class="n">Rs</span><span class="p">,</span><span class="n">Accu2</span><span class="p" data-group-id="2189511564-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">mapfoldl</span><span class="p" data-group-id="2189511564-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu1</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="2189511564-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2189511564-7">{</span><span class="p" data-group-id="2189511564-8">[</span><span class="n">R</span><span class="p">|</span><span class="n">Rs</span><span class="p" data-group-id="2189511564-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu2</span><span class="p" data-group-id="2189511564-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">mapfoldl</span><span class="p" data-group-id="2189511564-9">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2189511564-10">[</span><span class="p" data-group-id="2189511564-10">]</span><span class="p" data-group-id="2189511564-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2189511564-11">{</span><span class="p" data-group-id="2189511564-12">[</span><span class="p" data-group-id="2189511564-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="2189511564-11">}</span><span class="p">.</span></code></pre><p>The following example shows how to change all letters in <code class="inline">L</code> to upper case and
│ │ │ │ -then count them.</p><p>First the change to upper case:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Upcase</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="0139018044-1">(</span><span class="n">X</span><span class="p" data-group-id="0139018044-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w">  </span><span class="n">X</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="sc">$a</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0139018044-2">(</span><span class="n">X</span><span class="p" data-group-id="0139018044-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#mapfoldl/3"><code class="inline">lists:mapfoldl/3</code></a> simultaneously maps and folds over a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mapfoldl</span><span class="p" data-group-id="6932083612-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6932083612-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="6932083612-2">]</span><span class="p" data-group-id="6932083612-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6932083612-3">{</span><span class="n">R</span><span class="p">,</span><span class="n">Accu1</span><span class="p" data-group-id="6932083612-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="6932083612-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p" data-group-id="6932083612-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6932083612-5">{</span><span class="n">Rs</span><span class="p">,</span><span class="n">Accu2</span><span class="p" data-group-id="6932083612-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">mapfoldl</span><span class="p" data-group-id="6932083612-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu1</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6932083612-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6932083612-7">{</span><span class="p" data-group-id="6932083612-8">[</span><span class="n">R</span><span class="p">|</span><span class="n">Rs</span><span class="p" data-group-id="6932083612-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu2</span><span class="p" data-group-id="6932083612-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">mapfoldl</span><span class="p" data-group-id="6932083612-9">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6932083612-10">[</span><span class="p" data-group-id="6932083612-10">]</span><span class="p" data-group-id="6932083612-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6932083612-11">{</span><span class="p" data-group-id="6932083612-12">[</span><span class="p" data-group-id="6932083612-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="6932083612-11">}</span><span class="p">.</span></code></pre><p>The following example shows how to change all letters in <code class="inline">L</code> to upper case and
│ │ │ │ +then count them.</p><p>First the change to upper case:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Upcase</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="7400882776-1">(</span><span class="n">X</span><span class="p" data-group-id="7400882776-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w">  </span><span class="n">X</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="sc">$a</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7400882776-2">(</span><span class="n">X</span><span class="p" data-group-id="7400882776-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">&gt; </span><span class="n">Upcase_word</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ │ -</span><span class="nf">fun</span><span class="p" data-group-id="0139018044-3">(</span><span class="n">X</span><span class="p" data-group-id="0139018044-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0139018044-4">(</span><span class="n">Upcase</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0139018044-4">)</span><span class="w">
│ │ │ │ +</span><span class="nf">fun</span><span class="p" data-group-id="7400882776-3">(</span><span class="n">X</span><span class="p" data-group-id="7400882776-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7400882776-4">(</span><span class="n">Upcase</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7400882776-4">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">Upcase_word</span><span class="p" data-group-id="0139018044-5">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="0139018044-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">Upcase_word</span><span class="p" data-group-id="7400882776-5">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="7400882776-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;ERLANG&quot;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="0139018044-6">(</span><span class="n">Upcase_word</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0139018044-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0139018044-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="0139018044-7">]</span></code></pre><p>Now, the fold and the map can be done at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">mapfoldl</span><span class="p" data-group-id="0021010437-1">(</span><span class="nf">fun</span><span class="p" data-group-id="0021010437-2">(</span><span class="n">Word</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="0021010437-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0021010437-3">{</span><span class="n">Upcase_word</span><span class="p" data-group-id="0021010437-4">(</span><span class="n">Word</span><span class="p" data-group-id="0021010437-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0021010437-5">(</span><span class="n">Word</span><span class="p" data-group-id="0021010437-5">)</span><span class="p" data-group-id="0021010437-3">}</span><span class="w">
│ │ │ │ -</span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0021010437-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0021010437-6">{</span><span class="p" data-group-id="0021010437-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="0021010437-7">]</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="0021010437-6">}</span></code></pre><h3 id="filter" class="section-heading">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7400882776-6">(</span><span class="n">Upcase_word</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7400882776-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7400882776-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="7400882776-7">]</span></code></pre><p>Now, the fold and the map can be done at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">mapfoldl</span><span class="p" data-group-id="0637146159-1">(</span><span class="nf">fun</span><span class="p" data-group-id="0637146159-2">(</span><span class="n">Word</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="0637146159-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0637146159-3">{</span><span class="n">Upcase_word</span><span class="p" data-group-id="0637146159-4">(</span><span class="n">Word</span><span class="p" data-group-id="0637146159-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0637146159-5">(</span><span class="n">Word</span><span class="p" data-group-id="0637146159-5">)</span><span class="p" data-group-id="0637146159-3">}</span><span class="w">
│ │ │ │ +</span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0637146159-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0637146159-6">{</span><span class="p" data-group-id="0637146159-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="0637146159-7">]</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="0637146159-6">}</span></code></pre><h3 id="filter" class="section-heading">
│ │ │ │    <a href="#filter" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">filter</span>
│ │ │ │  </h3>
│ │ │ │  <p><a href="../../../lib/stdlib/doc/html/lists.html#filter/2"><code class="inline">lists:filter/2</code></a> takes a predicate of one argument and a list and returns all elements
│ │ │ │ -in the list that satisfy the predicate:</p><pre><code class="makeup erlang" translate="no"><span class="nf">filter</span><span class="p" data-group-id="5635766329-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5635766329-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5635766329-2">]</span><span class="p" data-group-id="5635766329-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="5635766329-3">(</span><span class="n">H</span><span class="p" data-group-id="5635766329-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5635766329-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">filter</span><span class="p" data-group-id="5635766329-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5635766329-5">)</span><span class="p" data-group-id="5635766329-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="5635766329-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5635766329-6">)</span><span class="w">
│ │ │ │ +in the list that satisfy the predicate:</p><pre><code class="makeup erlang" translate="no"><span class="nf">filter</span><span class="p" data-group-id="2863443447-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2863443447-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2863443447-2">]</span><span class="p" data-group-id="2863443447-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="2863443447-3">(</span><span class="n">H</span><span class="p" data-group-id="2863443447-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2863443447-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">filter</span><span class="p" data-group-id="2863443447-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2863443447-5">)</span><span class="p" data-group-id="2863443447-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="2863443447-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2863443447-6">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">filter</span><span class="p" data-group-id="5635766329-7">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5635766329-8">[</span><span class="p" data-group-id="5635766329-8">]</span><span class="p" data-group-id="5635766329-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5635766329-9">[</span><span class="p" data-group-id="5635766329-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="0028485840-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0028485840-2">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="0028485840-2">]</span><span class="p" data-group-id="0028485840-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0028485840-3">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="0028485840-3">]</span></code></pre><p>Combining maps and filters enables writing of very succinct code. For example,
│ │ │ │ +</span><span class="nf">filter</span><span class="p" data-group-id="2863443447-7">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2863443447-8">[</span><span class="p" data-group-id="2863443447-8">]</span><span class="p" data-group-id="2863443447-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2863443447-9">[</span><span class="p" data-group-id="2863443447-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="9654703720-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9654703720-2">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="9654703720-2">]</span><span class="p" data-group-id="9654703720-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9654703720-3">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="9654703720-3">]</span></code></pre><p>Combining maps and filters enables writing of very succinct code. For example,
│ │ │ │  to define a set difference function <code class="inline">diff(L1, L2)</code> to be the difference between
│ │ │ │ -the lists <code class="inline">L1</code> and <code class="inline">L2</code>, the code can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">diff</span><span class="p" data-group-id="9342831997-1">(</span><span class="n">L1</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="9342831997-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">filter</span><span class="p" data-group-id="9342831997-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9342831997-3">(</span><span class="n">X</span><span class="p" data-group-id="9342831997-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="9342831997-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="9342831997-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="9342831997-2">)</span><span class="p">.</span></code></pre><p>This gives the list of all elements in L1 that are not contained in L2.</p><p>The AND intersection of the list <code class="inline">L1</code> and <code class="inline">L2</code> is also easily defined:</p><pre><code class="makeup erlang" translate="no"><span class="nf">intersection</span><span class="p" data-group-id="7279121058-1">(</span><span class="n">L1</span><span class="p">,</span><span class="n">L2</span><span class="p" data-group-id="7279121058-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="7279121058-2">(</span><span class="nf">fun</span><span class="p" data-group-id="7279121058-3">(</span><span class="n">X</span><span class="p" data-group-id="7279121058-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="7279121058-4">(</span><span class="n">X</span><span class="p">,</span><span class="n">L1</span><span class="p" data-group-id="7279121058-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="7279121058-2">)</span><span class="p">.</span></code></pre><h3 id="takewhile" class="section-heading">
│ │ │ │ +the lists <code class="inline">L1</code> and <code class="inline">L2</code>, the code can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">diff</span><span class="p" data-group-id="4943559298-1">(</span><span class="n">L1</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="4943559298-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">filter</span><span class="p" data-group-id="4943559298-2">(</span><span class="nf">fun</span><span class="p" data-group-id="4943559298-3">(</span><span class="n">X</span><span class="p" data-group-id="4943559298-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="4943559298-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="4943559298-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="4943559298-2">)</span><span class="p">.</span></code></pre><p>This gives the list of all elements in L1 that are not contained in L2.</p><p>The AND intersection of the list <code class="inline">L1</code> and <code class="inline">L2</code> is also easily defined:</p><pre><code class="makeup erlang" translate="no"><span class="nf">intersection</span><span class="p" data-group-id="2170780317-1">(</span><span class="n">L1</span><span class="p">,</span><span class="n">L2</span><span class="p" data-group-id="2170780317-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="2170780317-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2170780317-3">(</span><span class="n">X</span><span class="p" data-group-id="2170780317-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="2170780317-4">(</span><span class="n">X</span><span class="p">,</span><span class="n">L1</span><span class="p" data-group-id="2170780317-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="2170780317-2">)</span><span class="p">.</span></code></pre><h3 id="takewhile" class="section-heading">
│ │ │ │    <a href="#takewhile" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">takewhile</span>
│ │ │ │  </h3>
│ │ │ │  <p><a href="../../../lib/stdlib/doc/html/lists.html#takewhile/2"><code class="inline">lists:takewhile/2</code></a> takes elements <code class="inline">X</code> from a list <code class="inline">L</code> as long as the predicate
│ │ │ │ -<code class="inline">P(X)</code> is true:</p><pre><code class="makeup erlang" translate="no"><span class="nf">takewhile</span><span class="p" data-group-id="7930256963-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7930256963-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7930256963-2">]</span><span class="p" data-group-id="7930256963-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="7930256963-3">(</span><span class="n">H</span><span class="p" data-group-id="7930256963-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7930256963-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">takewhile</span><span class="p" data-group-id="7930256963-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="7930256963-5">)</span><span class="p" data-group-id="7930256963-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7930256963-6">[</span><span class="p" data-group-id="7930256963-6">]</span><span class="w">
│ │ │ │ +<code class="inline">P(X)</code> is true:</p><pre><code class="makeup erlang" translate="no"><span class="nf">takewhile</span><span class="p" data-group-id="0544140268-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0544140268-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0544140268-2">]</span><span class="p" data-group-id="0544140268-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="0544140268-3">(</span><span class="n">H</span><span class="p" data-group-id="0544140268-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0544140268-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">takewhile</span><span class="p" data-group-id="0544140268-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="0544140268-5">)</span><span class="p" data-group-id="0544140268-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0544140268-6">[</span><span class="p" data-group-id="0544140268-6">]</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">takewhile</span><span class="p" data-group-id="7930256963-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7930256963-8">[</span><span class="p" data-group-id="7930256963-8">]</span><span class="p" data-group-id="7930256963-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7930256963-9">[</span><span class="p" data-group-id="7930256963-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">takewhile</span><span class="p" data-group-id="9992201071-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9992201071-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9992201071-2">]</span><span class="p" data-group-id="9992201071-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9992201071-3">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="9992201071-3">]</span></code></pre><h3 id="dropwhile" class="section-heading">
│ │ │ │ +</span><span class="nf">takewhile</span><span class="p" data-group-id="0544140268-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0544140268-8">[</span><span class="p" data-group-id="0544140268-8">]</span><span class="p" data-group-id="0544140268-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0544140268-9">[</span><span class="p" data-group-id="0544140268-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">takewhile</span><span class="p" data-group-id="2644306971-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2644306971-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2644306971-2">]</span><span class="p" data-group-id="2644306971-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2644306971-3">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="2644306971-3">]</span></code></pre><h3 id="dropwhile" class="section-heading">
│ │ │ │    <a href="#dropwhile" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">dropwhile</span>
│ │ │ │  </h3>
│ │ │ │ -<p><a href="../../../lib/stdlib/doc/html/lists.html#dropwhile/2"><code class="inline">lists:dropwhile/2</code></a> is the complement of <code class="inline">takewhile</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">dropwhile</span><span class="p" data-group-id="9291845449-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9291845449-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9291845449-2">]</span><span class="p" data-group-id="9291845449-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="9291845449-3">(</span><span class="n">H</span><span class="p" data-group-id="9291845449-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">dropwhile</span><span class="p" data-group-id="9291845449-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9291845449-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9291845449-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9291845449-5">]</span><span class="w">
│ │ │ │ +<p><a href="../../../lib/stdlib/doc/html/lists.html#dropwhile/2"><code class="inline">lists:dropwhile/2</code></a> is the complement of <code class="inline">takewhile</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">dropwhile</span><span class="p" data-group-id="3293347323-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3293347323-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3293347323-2">]</span><span class="p" data-group-id="3293347323-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="3293347323-3">(</span><span class="n">H</span><span class="p" data-group-id="3293347323-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">dropwhile</span><span class="p" data-group-id="3293347323-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3293347323-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3293347323-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3293347323-5">]</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">dropwhile</span><span class="p" data-group-id="9291845449-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9291845449-7">[</span><span class="p" data-group-id="9291845449-7">]</span><span class="p" data-group-id="9291845449-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9291845449-8">[</span><span class="p" data-group-id="9291845449-8">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">dropwhile</span><span class="p" data-group-id="5595120005-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5595120005-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5595120005-2">]</span><span class="p" data-group-id="5595120005-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5595120005-3">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5595120005-3">]</span></code></pre><h3 id="splitwith" class="section-heading">
│ │ │ │ +</span><span class="nf">dropwhile</span><span class="p" data-group-id="3293347323-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3293347323-7">[</span><span class="p" data-group-id="3293347323-7">]</span><span class="p" data-group-id="3293347323-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3293347323-8">[</span><span class="p" data-group-id="3293347323-8">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">dropwhile</span><span class="p" data-group-id="1274961700-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1274961700-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1274961700-2">]</span><span class="p" data-group-id="1274961700-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1274961700-3">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1274961700-3">]</span></code></pre><h3 id="splitwith" class="section-heading">
│ │ │ │    <a href="#splitwith" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">splitwith</span>
│ │ │ │  </h3>
│ │ │ │  <p><a href="../../../lib/stdlib/doc/html/lists.html#splitwith/2"><code class="inline">lists:splitwith/2</code></a> splits the list <code class="inline">L</code> into the two sublists <code class="inline">{L1, L2}</code>, where
│ │ │ │ -<code class="inline">L = takewhile(P, L)</code> and <code class="inline">L2 = dropwhile(P, L)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">splitwith</span><span class="p" data-group-id="6710309996-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6710309996-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">splitwith</span><span class="p" data-group-id="6710309996-2">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6710309996-3">[</span><span class="p" data-group-id="6710309996-3">]</span><span class="p" data-group-id="6710309996-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">L = takewhile(P, L)</code> and <code class="inline">L2 = dropwhile(P, L)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">splitwith</span><span class="p" data-group-id="6313316424-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6313316424-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">splitwith</span><span class="p" data-group-id="6313316424-2">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6313316424-3">[</span><span class="p" data-group-id="6313316424-3">]</span><span class="p" data-group-id="6313316424-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">splitwith</span><span class="p" data-group-id="6710309996-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6710309996-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6710309996-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6710309996-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="6710309996-6">(</span><span class="n">H</span><span class="p" data-group-id="6710309996-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">splitwith</span><span class="p" data-group-id="6710309996-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6710309996-8">[</span><span class="n">H</span><span class="p">|</span><span class="n">L</span><span class="p" data-group-id="6710309996-8">]</span><span class="p" data-group-id="6710309996-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6710309996-9">{</span><span class="nf">reverse</span><span class="p" data-group-id="6710309996-10">(</span><span class="n">L</span><span class="p" data-group-id="6710309996-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6710309996-11">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6710309996-11">]</span><span class="p" data-group-id="6710309996-9">}</span><span class="w">
│ │ │ │ +</span><span class="nf">splitwith</span><span class="p" data-group-id="6313316424-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6313316424-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6313316424-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6313316424-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="6313316424-6">(</span><span class="n">H</span><span class="p" data-group-id="6313316424-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">splitwith</span><span class="p" data-group-id="6313316424-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6313316424-8">[</span><span class="n">H</span><span class="p">|</span><span class="n">L</span><span class="p" data-group-id="6313316424-8">]</span><span class="p" data-group-id="6313316424-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6313316424-9">{</span><span class="nf">reverse</span><span class="p" data-group-id="6313316424-10">(</span><span class="n">L</span><span class="p" data-group-id="6313316424-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6313316424-11">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6313316424-11">]</span><span class="p" data-group-id="6313316424-9">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">splitwith</span><span class="p" data-group-id="6710309996-12">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6710309996-13">[</span><span class="p" data-group-id="6710309996-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6710309996-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6710309996-14">{</span><span class="nf">reverse</span><span class="p" data-group-id="6710309996-15">(</span><span class="n">L</span><span class="p" data-group-id="6710309996-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6710309996-16">[</span><span class="p" data-group-id="6710309996-16">]</span><span class="p" data-group-id="6710309996-14">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">splitwith</span><span class="p" data-group-id="1364939630-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1364939630-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1364939630-2">]</span><span class="p" data-group-id="1364939630-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1364939630-3">{</span><span class="p" data-group-id="1364939630-4">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="1364939630-4">]</span><span class="p">,</span><span class="p" data-group-id="1364939630-5">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1364939630-5">]</span><span class="p" data-group-id="1364939630-3">}</span></code></pre><h2 id="funs-returning-funs" class="section-heading">
│ │ │ │ +</span><span class="nf">splitwith</span><span class="p" data-group-id="6313316424-12">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6313316424-13">[</span><span class="p" data-group-id="6313316424-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6313316424-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6313316424-14">{</span><span class="nf">reverse</span><span class="p" data-group-id="6313316424-15">(</span><span class="n">L</span><span class="p" data-group-id="6313316424-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6313316424-16">[</span><span class="p" data-group-id="6313316424-16">]</span><span class="p" data-group-id="6313316424-14">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">splitwith</span><span class="p" data-group-id="2837712515-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2837712515-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2837712515-2">]</span><span class="p" data-group-id="2837712515-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2837712515-3">{</span><span class="p" data-group-id="2837712515-4">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="2837712515-4">]</span><span class="p">,</span><span class="p" data-group-id="2837712515-5">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2837712515-5">]</span><span class="p" data-group-id="2837712515-3">}</span></code></pre><h2 id="funs-returning-funs" class="section-heading">
│ │ │ │    <a href="#funs-returning-funs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Funs Returning Funs</span>
│ │ │ │  </h2>
│ │ │ │  <p>So far, only functions that take funs as arguments have been described. More
│ │ │ │  powerful functions, that themselves return funs, can also be written. The
│ │ │ │  following examples illustrate these type of functions.</p><h3 id="simple-higher-order-functions" class="section-heading">
│ │ │ │    <a href="#simple-higher-order-functions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Simple Higher Order Functions</span>
│ │ │ │  </h3>
│ │ │ │  <p><code class="inline">Adder(X)</code> is a function that given <code class="inline">X</code>, returns a new function <code class="inline">G</code> such that
│ │ │ │ -<code class="inline">G(K)</code> returns <code class="inline">K + X</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Adder</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3872362369-1">(</span><span class="n">X</span><span class="p" data-group-id="3872362369-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3872362369-2">(</span><span class="n">Y</span><span class="p" data-group-id="3872362369-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">G(K)</code> returns <code class="inline">K + X</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Adder</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9249565976-1">(</span><span class="n">X</span><span class="p" data-group-id="9249565976-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9249565976-2">(</span><span class="n">Y</span><span class="p" data-group-id="9249565976-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">Add6</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Adder</span><span class="p" data-group-id="3872362369-3">(</span><span class="mi">6</span><span class="p" data-group-id="3872362369-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">Add6</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Adder</span><span class="p" data-group-id="9249565976-3">(</span><span class="mi">6</span><span class="p" data-group-id="9249565976-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">Add6</span><span class="p" data-group-id="3872362369-4">(</span><span class="mi">10</span><span class="p" data-group-id="3872362369-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">Add6</span><span class="p" data-group-id="9249565976-4">(</span><span class="mi">10</span><span class="p" data-group-id="9249565976-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">16</span></code></pre><h3 id="infinite-lists" class="section-heading">
│ │ │ │    <a href="#infinite-lists" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Infinite Lists</span>
│ │ │ │  </h3>
│ │ │ │ -<p>The idea is to write something like:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1474584046-1">(</span><span class="ss">lazy</span><span class="p" data-group-id="1474584046-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1474584046-2">(</span><span class="p" data-group-id="1474584046-3">[</span><span class="ss">ints_from</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1474584046-3">]</span><span class="p" data-group-id="1474584046-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">ints_from</span><span class="p" data-group-id="1474584046-4">(</span><span class="n">N</span><span class="p" data-group-id="1474584046-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">fun</span><span class="p" data-group-id="1474584046-5">(</span><span class="p" data-group-id="1474584046-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="1474584046-6">[</span><span class="n">N</span><span class="p">|</span><span class="nf">ints_from</span><span class="p" data-group-id="1474584046-7">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="1474584046-7">)</span><span class="p" data-group-id="1474584046-6">]</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Then proceed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lazy</span><span class="p">:</span><span class="nf">ints_from</span><span class="p" data-group-id="4572769584-1">(</span><span class="mi">1</span><span class="p" data-group-id="4572769584-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>The idea is to write something like:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8601345820-1">(</span><span class="ss">lazy</span><span class="p" data-group-id="8601345820-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8601345820-2">(</span><span class="p" data-group-id="8601345820-3">[</span><span class="ss">ints_from</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8601345820-3">]</span><span class="p" data-group-id="8601345820-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">ints_from</span><span class="p" data-group-id="8601345820-4">(</span><span class="n">N</span><span class="p" data-group-id="8601345820-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">fun</span><span class="p" data-group-id="8601345820-5">(</span><span class="p" data-group-id="8601345820-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="8601345820-6">[</span><span class="n">N</span><span class="p">|</span><span class="nf">ints_from</span><span class="p" data-group-id="8601345820-7">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="8601345820-7">)</span><span class="p" data-group-id="8601345820-6">]</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Then proceed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lazy</span><span class="p">:</span><span class="nf">ints_from</span><span class="p" data-group-id="7714364330-1">(</span><span class="mi">1</span><span class="p" data-group-id="7714364330-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="p" data-group-id="4572769584-2">(</span><span class="p" data-group-id="4572769584-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4572769584-3">[</span><span class="mi">1</span><span class="p">|</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="p" data-group-id="4572769584-3">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="4572769584-4">(</span><span class="n">XX</span><span class="p" data-group-id="4572769584-5">(</span><span class="p" data-group-id="4572769584-5">)</span><span class="p" data-group-id="4572769584-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="p" data-group-id="7714364330-2">(</span><span class="p" data-group-id="7714364330-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7714364330-3">[</span><span class="mi">1</span><span class="p">|</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="p" data-group-id="7714364330-3">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="7714364330-4">(</span><span class="n">XX</span><span class="p" data-group-id="7714364330-5">(</span><span class="p" data-group-id="7714364330-5">)</span><span class="p" data-group-id="7714364330-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tl</span><span class="p" data-group-id="4572769584-6">(</span><span class="n">XX</span><span class="p" data-group-id="4572769584-7">(</span><span class="p" data-group-id="4572769584-7">)</span><span class="p" data-group-id="4572769584-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tl</span><span class="p" data-group-id="7714364330-6">(</span><span class="n">XX</span><span class="p" data-group-id="7714364330-7">(</span><span class="p" data-group-id="7714364330-7">)</span><span class="p" data-group-id="7714364330-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="4572769584-8">(</span><span class="n">Y</span><span class="p" data-group-id="4572769584-9">(</span><span class="p" data-group-id="4572769584-9">)</span><span class="p" data-group-id="4572769584-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="7714364330-8">(</span><span class="n">Y</span><span class="p" data-group-id="7714364330-9">(</span><span class="p" data-group-id="7714364330-9">)</span><span class="p" data-group-id="7714364330-8">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">2</span></code></pre><p>And so on. This is an example of &quot;lazy embedding&quot;.</p><h3 id="parsing" class="section-heading">
│ │ │ │    <a href="#parsing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Parsing</span>
│ │ │ │  </h3>
│ │ │ │ -<p>The following examples show parsers of the following type:</p><pre><code class="makeup erlang" translate="no"><span class="n">Parser</span><span class="p" data-group-id="9959978344-1">(</span><span class="n">Toks</span><span class="p" data-group-id="9959978344-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9959978344-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tree</span><span class="p">,</span><span class="w"> </span><span class="n">Toks1</span><span class="p" data-group-id="9959978344-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">fail</span></code></pre><p><code class="inline">Toks</code> is the list of tokens to be parsed. A successful parse returns
│ │ │ │ +<p>The following examples show parsers of the following type:</p><pre><code class="makeup erlang" translate="no"><span class="n">Parser</span><span class="p" data-group-id="4873648950-1">(</span><span class="n">Toks</span><span class="p" data-group-id="4873648950-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4873648950-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tree</span><span class="p">,</span><span class="w"> </span><span class="n">Toks1</span><span class="p" data-group-id="4873648950-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">fail</span></code></pre><p><code class="inline">Toks</code> is the list of tokens to be parsed. A successful parse returns
│ │ │ │  <code class="inline">{ok, Tree, Toks1}</code>.</p><ul><li><code class="inline">Tree</code> is a parse tree.</li><li><code class="inline">Toks1</code> is a tail of <code class="inline">Tree</code> that contains symbols encountered after the
│ │ │ │  structure that was correctly parsed.</li></ul><p>An unsuccessful parse returns <code class="inline">fail</code>.</p><p>The following example illustrates a simple, functional parser that parses the
│ │ │ │  grammar:</p><pre><code class="text">(a | b) &amp; (c | d)</code></pre><p>The following code defines a function <code class="inline">pconst(X)</code> in the module <code class="inline">funparse</code>,
│ │ │ │ -which returns a fun that parses a list of tokens:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pconst</span><span class="p" data-group-id="8296167689-1">(</span><span class="n">X</span><span class="p" data-group-id="8296167689-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8296167689-2">(</span><span class="n">T</span><span class="p" data-group-id="8296167689-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +which returns a fun that parses a list of tokens:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pconst</span><span class="p" data-group-id="0546316062-1">(</span><span class="n">X</span><span class="p" data-group-id="0546316062-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0546316062-2">(</span><span class="n">T</span><span class="p" data-group-id="0546316062-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │         </span><span class="k">case</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -           </span><span class="p" data-group-id="8296167689-3">[</span><span class="n">X</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="8296167689-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8296167689-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8296167689-5">{</span><span class="ss">const</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8296167689-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="8296167689-4">}</span><span class="p">;</span><span class="w">
│ │ │ │ +           </span><span class="p" data-group-id="0546316062-3">[</span><span class="n">X</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="0546316062-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0546316062-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0546316062-5">{</span><span class="ss">const</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0546316062-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="0546316062-4">}</span><span class="p">;</span><span class="w">
│ │ │ │             </span><span class="p">_</span><span class="w">      </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">fail</span><span class="w">
│ │ │ │         </span><span class="k">end</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>This function can be used as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">pconst</span><span class="p" data-group-id="0791553181-1">(</span><span class="ss">a</span><span class="p" data-group-id="0791553181-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>This function can be used as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">pconst</span><span class="p" data-group-id="1990480274-1">(</span><span class="ss">a</span><span class="p" data-group-id="1990480274-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">funparse</span><span class="p">.</span><span class="mf">0.22674075</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="p" data-group-id="0791553181-2">(</span><span class="p" data-group-id="0791553181-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0791553181-3">]</span><span class="p" data-group-id="0791553181-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0791553181-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="0791553181-5">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="0791553181-5">}</span><span class="p">,</span><span class="p" data-group-id="0791553181-6">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0791553181-6">]</span><span class="p" data-group-id="0791553181-4">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="p" data-group-id="0791553181-7">(</span><span class="p" data-group-id="0791553181-8">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="0791553181-8">]</span><span class="p" data-group-id="0791553181-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="p" data-group-id="1990480274-2">(</span><span class="p" data-group-id="1990480274-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1990480274-3">]</span><span class="p" data-group-id="1990480274-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1990480274-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="1990480274-5">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1990480274-5">}</span><span class="p">,</span><span class="p" data-group-id="1990480274-6">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1990480274-6">]</span><span class="p" data-group-id="1990480274-4">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="p" data-group-id="1990480274-7">(</span><span class="p" data-group-id="1990480274-8">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="1990480274-8">]</span><span class="p" data-group-id="1990480274-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">fail</span></code></pre><p>Next, the two higher order functions <code class="inline">pand</code> and <code class="inline">por</code> are defined. They combine
│ │ │ │ -primitive parsers to produce more complex parsers.</p><p>First <code class="inline">pand</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pand</span><span class="p" data-group-id="0167931030-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="0167931030-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0167931030-2">(</span><span class="n">T</span><span class="p" data-group-id="0167931030-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="0167931030-3">(</span><span class="n">T</span><span class="p" data-group-id="0167931030-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="0167931030-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="0167931030-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="0167931030-5">(</span><span class="n">T1</span><span class="p" data-group-id="0167931030-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="0167931030-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="0167931030-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                        </span><span class="p" data-group-id="0167931030-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0167931030-8">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="0167931030-8">}</span><span class="p" data-group-id="0167931030-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +primitive parsers to produce more complex parsers.</p><p>First <code class="inline">pand</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pand</span><span class="p" data-group-id="9809347347-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="9809347347-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="9809347347-2">(</span><span class="n">T</span><span class="p" data-group-id="9809347347-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="9809347347-3">(</span><span class="n">T</span><span class="p" data-group-id="9809347347-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9809347347-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="9809347347-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="9809347347-5">(</span><span class="n">T1</span><span class="p" data-group-id="9809347347-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="9809347347-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="9809347347-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                        </span><span class="p" data-group-id="9809347347-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9809347347-8">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="9809347347-8">}</span><span class="p" data-group-id="9809347347-7">}</span><span class="p">;</span><span class="w">
│ │ │ │                      </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                          </span><span class="ss">fail</span><span class="w">
│ │ │ │                  </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="ss">fail</span><span class="w">
│ │ │ │          </span><span class="k">end</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Given a parser <code class="inline">P1</code> for grammar <code class="inline">G1</code>, and a parser <code class="inline">P2</code> for grammar <code class="inline">G2</code>,
│ │ │ │  <code class="inline">pand(P1, P2)</code> returns a parser for the grammar, which consists of sequences of
│ │ │ │  tokens that satisfy <code class="inline">G1</code>, followed by sequences of tokens that satisfy <code class="inline">G2</code>.</p><p><code class="inline">por(P1, P2)</code> returns a parser for the language described by the grammar <code class="inline">G1</code> or
│ │ │ │ -<code class="inline">G2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">por</span><span class="p" data-group-id="3244259746-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="3244259746-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3244259746-2">(</span><span class="n">T</span><span class="p" data-group-id="3244259746-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="3244259746-3">(</span><span class="n">T</span><span class="p" data-group-id="3244259746-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="3244259746-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3244259746-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="3244259746-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3244259746-6">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="n">R</span><span class="p" data-group-id="3244259746-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3244259746-5">}</span><span class="p">;</span><span class="w">
│ │ │ │ +<code class="inline">G2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">por</span><span class="p" data-group-id="4279070042-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="4279070042-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4279070042-2">(</span><span class="n">T</span><span class="p" data-group-id="4279070042-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="4279070042-3">(</span><span class="n">T</span><span class="p" data-group-id="4279070042-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="4279070042-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4279070042-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="4279070042-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4279070042-6">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="n">R</span><span class="p" data-group-id="4279070042-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4279070042-5">}</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="3244259746-7">(</span><span class="n">T</span><span class="p" data-group-id="3244259746-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="3244259746-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3244259746-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                        </span><span class="p" data-group-id="3244259746-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3244259746-10">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="n">R1</span><span class="p" data-group-id="3244259746-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3244259746-9">}</span><span class="p">;</span><span class="w">
│ │ │ │ +                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="4279070042-7">(</span><span class="n">T</span><span class="p" data-group-id="4279070042-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="4279070042-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4279070042-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                        </span><span class="p" data-group-id="4279070042-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4279070042-10">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="n">R1</span><span class="p" data-group-id="4279070042-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4279070042-9">}</span><span class="p">;</span><span class="w">
│ │ │ │                      </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                          </span><span class="ss">fail</span><span class="w">
│ │ │ │                  </span><span class="k">end</span><span class="w">
│ │ │ │          </span><span class="k">end</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The original problem was to parse the grammar <code class="inline">(a | b) &amp; (c | d)</code>. The following
│ │ │ │ -code addresses this problem:</p><pre><code class="makeup erlang" translate="no"><span class="nf">grammar</span><span class="p" data-group-id="0913730025-1">(</span><span class="p" data-group-id="0913730025-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">pand</span><span class="p" data-group-id="0913730025-2">(</span><span class="w">
│ │ │ │ -         </span><span class="nf">por</span><span class="p" data-group-id="0913730025-3">(</span><span class="nf">pconst</span><span class="p" data-group-id="0913730025-4">(</span><span class="ss">a</span><span class="p" data-group-id="0913730025-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="0913730025-5">(</span><span class="ss">b</span><span class="p" data-group-id="0913730025-5">)</span><span class="p" data-group-id="0913730025-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="nf">por</span><span class="p" data-group-id="0913730025-6">(</span><span class="nf">pconst</span><span class="p" data-group-id="0913730025-7">(</span><span class="ss">c</span><span class="p" data-group-id="0913730025-7">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="0913730025-8">(</span><span class="ss">d</span><span class="p" data-group-id="0913730025-8">)</span><span class="p" data-group-id="0913730025-6">)</span><span class="p" data-group-id="0913730025-2">)</span><span class="p">.</span></code></pre><p>The following code adds a parser interface to the grammar:</p><pre><code class="makeup erlang" translate="no"><span class="nf">parse</span><span class="p" data-group-id="7278526696-1">(</span><span class="n">List</span><span class="p" data-group-id="7278526696-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7278526696-2">(</span><span class="nf">grammar</span><span class="p" data-group-id="7278526696-3">(</span><span class="p" data-group-id="7278526696-3">)</span><span class="p" data-group-id="7278526696-2">)</span><span class="p" data-group-id="7278526696-4">(</span><span class="n">List</span><span class="p" data-group-id="7278526696-4">)</span><span class="p">.</span></code></pre><p>The parser can be tested as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="7448062307-1">(</span><span class="p" data-group-id="7448062307-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7448062307-2">]</span><span class="p" data-group-id="7448062307-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7448062307-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="7448062307-4">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="7448062307-5">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="7448062307-6">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7448062307-6">}</span><span class="p" data-group-id="7448062307-5">}</span><span class="p">,</span><span class="p" data-group-id="7448062307-7">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="7448062307-8">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7448062307-8">}</span><span class="p" data-group-id="7448062307-7">}</span><span class="p" data-group-id="7448062307-4">}</span><span class="p" data-group-id="7448062307-3">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="7448062307-9">(</span><span class="p" data-group-id="7448062307-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="7448062307-10">]</span><span class="p" data-group-id="7448062307-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7448062307-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="7448062307-12">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="7448062307-13">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="7448062307-14">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="7448062307-14">}</span><span class="p" data-group-id="7448062307-13">}</span><span class="p">,</span><span class="p" data-group-id="7448062307-15">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="7448062307-16">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="7448062307-16">}</span><span class="p" data-group-id="7448062307-15">}</span><span class="p" data-group-id="7448062307-12">}</span><span class="p" data-group-id="7448062307-11">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="7448062307-17">(</span><span class="p" data-group-id="7448062307-18">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7448062307-18">]</span><span class="p" data-group-id="7448062307-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7448062307-19">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="7448062307-20">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="7448062307-21">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="7448062307-22">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7448062307-22">}</span><span class="p" data-group-id="7448062307-21">}</span><span class="p">,</span><span class="p" data-group-id="7448062307-23">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="7448062307-24">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7448062307-24">}</span><span class="p" data-group-id="7448062307-23">}</span><span class="p" data-group-id="7448062307-20">}</span><span class="p" data-group-id="7448062307-19">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="7448062307-25">(</span><span class="p" data-group-id="7448062307-26">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="7448062307-26">]</span><span class="p" data-group-id="7448062307-25">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7448062307-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="7448062307-28">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="7448062307-29">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="7448062307-30">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7448062307-30">}</span><span class="p" data-group-id="7448062307-29">}</span><span class="p">,</span><span class="p" data-group-id="7448062307-31">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="7448062307-32">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="7448062307-32">}</span><span class="p" data-group-id="7448062307-31">}</span><span class="p" data-group-id="7448062307-28">}</span><span class="p" data-group-id="7448062307-27">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="7448062307-33">(</span><span class="p" data-group-id="7448062307-34">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7448062307-34">]</span><span class="p" data-group-id="7448062307-33">)</span><span class="p">.</span><span class="w">
│ │ │ │ +code addresses this problem:</p><pre><code class="makeup erlang" translate="no"><span class="nf">grammar</span><span class="p" data-group-id="3229655563-1">(</span><span class="p" data-group-id="3229655563-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">pand</span><span class="p" data-group-id="3229655563-2">(</span><span class="w">
│ │ │ │ +         </span><span class="nf">por</span><span class="p" data-group-id="3229655563-3">(</span><span class="nf">pconst</span><span class="p" data-group-id="3229655563-4">(</span><span class="ss">a</span><span class="p" data-group-id="3229655563-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="3229655563-5">(</span><span class="ss">b</span><span class="p" data-group-id="3229655563-5">)</span><span class="p" data-group-id="3229655563-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="nf">por</span><span class="p" data-group-id="3229655563-6">(</span><span class="nf">pconst</span><span class="p" data-group-id="3229655563-7">(</span><span class="ss">c</span><span class="p" data-group-id="3229655563-7">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="3229655563-8">(</span><span class="ss">d</span><span class="p" data-group-id="3229655563-8">)</span><span class="p" data-group-id="3229655563-6">)</span><span class="p" data-group-id="3229655563-2">)</span><span class="p">.</span></code></pre><p>The following code adds a parser interface to the grammar:</p><pre><code class="makeup erlang" translate="no"><span class="nf">parse</span><span class="p" data-group-id="8963046408-1">(</span><span class="n">List</span><span class="p" data-group-id="8963046408-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8963046408-2">(</span><span class="nf">grammar</span><span class="p" data-group-id="8963046408-3">(</span><span class="p" data-group-id="8963046408-3">)</span><span class="p" data-group-id="8963046408-2">)</span><span class="p" data-group-id="8963046408-4">(</span><span class="n">List</span><span class="p" data-group-id="8963046408-4">)</span><span class="p">.</span></code></pre><p>The parser can be tested as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="9704667230-1">(</span><span class="p" data-group-id="9704667230-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9704667230-2">]</span><span class="p" data-group-id="9704667230-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9704667230-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="9704667230-4">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="9704667230-5">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="9704667230-6">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="9704667230-6">}</span><span class="p" data-group-id="9704667230-5">}</span><span class="p">,</span><span class="p" data-group-id="9704667230-7">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="9704667230-8">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9704667230-8">}</span><span class="p" data-group-id="9704667230-7">}</span><span class="p" data-group-id="9704667230-4">}</span><span class="p" data-group-id="9704667230-3">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="9704667230-9">(</span><span class="p" data-group-id="9704667230-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="9704667230-10">]</span><span class="p" data-group-id="9704667230-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9704667230-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="9704667230-12">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="9704667230-13">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="9704667230-14">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="9704667230-14">}</span><span class="p" data-group-id="9704667230-13">}</span><span class="p">,</span><span class="p" data-group-id="9704667230-15">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="9704667230-16">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="9704667230-16">}</span><span class="p" data-group-id="9704667230-15">}</span><span class="p" data-group-id="9704667230-12">}</span><span class="p" data-group-id="9704667230-11">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="9704667230-17">(</span><span class="p" data-group-id="9704667230-18">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9704667230-18">]</span><span class="p" data-group-id="9704667230-17">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9704667230-19">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="9704667230-20">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="9704667230-21">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="9704667230-22">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9704667230-22">}</span><span class="p" data-group-id="9704667230-21">}</span><span class="p">,</span><span class="p" data-group-id="9704667230-23">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="9704667230-24">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9704667230-24">}</span><span class="p" data-group-id="9704667230-23">}</span><span class="p" data-group-id="9704667230-20">}</span><span class="p" data-group-id="9704667230-19">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="9704667230-25">(</span><span class="p" data-group-id="9704667230-26">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="9704667230-26">]</span><span class="p" data-group-id="9704667230-25">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9704667230-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="9704667230-28">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="9704667230-29">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="9704667230-30">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9704667230-30">}</span><span class="p" data-group-id="9704667230-29">}</span><span class="p">,</span><span class="p" data-group-id="9704667230-31">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="9704667230-32">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="9704667230-32">}</span><span class="p" data-group-id="9704667230-31">}</span><span class="p" data-group-id="9704667230-28">}</span><span class="p" data-group-id="9704667230-27">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="9704667230-33">(</span><span class="p" data-group-id="9704667230-34">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9704667230-34">]</span><span class="p" data-group-id="9704667230-33">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">fail</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/expressions.xhtml
│ │ │ │ @@ -56,81 +56,81 @@
│ │ │ │  </span><span class="n">Phone_number</span><span class="w">
│ │ │ │  </span><span class="p">_</span><span class="w">
│ │ │ │  </span><span class="p">_</span><span class="n">Height</span><span class="w">
│ │ │ │  </span><span class="ss">name@node</span></code></pre><p>Variables are bound to values using <a href="patterns.xhtml">pattern matching</a>. Erlang uses
│ │ │ │  <em>single assignment</em>, that is, a variable can only be bound once.</p><p>The <em>anonymous variable</em> is denoted by underscore (_) and can be used when a
│ │ │ │  variable is required but its value can be ignored.</p><p><em>Example:</em></p><pre><code class="text">[H|_] = [1,2,3]</code></pre><p>Variables starting with underscore (<code class="inline">_</code>), for example, <code class="inline">_Height</code>, are normal
│ │ │ │  variables, not anonymous. However, they are ignored by the compiler in the sense
│ │ │ │ -that they do not generate warnings.</p><p><em>Example:</em></p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="5981754430-1">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5981754430-2">[</span><span class="p" data-group-id="5981754430-2">]</span><span class="p" data-group-id="5981754430-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5981754430-3">[</span><span class="p" data-group-id="5981754430-3">]</span><span class="p">.</span></code></pre><p>can be rewritten to be more readable:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="9260967766-1">(</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9260967766-2">[</span><span class="p" data-group-id="9260967766-2">]</span><span class="p" data-group-id="9260967766-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9260967766-3">[</span><span class="p" data-group-id="9260967766-3">]</span><span class="p">.</span></code></pre><p>This causes a warning for an unused variable, <code class="inline">Elem</code>. To avoid the warning,
│ │ │ │ -the code can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="6795713196-1">(</span><span class="p">_</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6795713196-2">[</span><span class="p" data-group-id="6795713196-2">]</span><span class="p" data-group-id="6795713196-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6795713196-3">[</span><span class="p" data-group-id="6795713196-3">]</span><span class="p">.</span></code></pre><p>Notice that since variables starting with an underscore are not anonymous, the
│ │ │ │ -following example matches:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5061886140-1">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5061886140-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5061886140-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5061886140-2">}</span></code></pre><p>But this example fails:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8749422890-1">{</span><span class="p">_</span><span class="n">N</span><span class="p">,</span><span class="p">_</span><span class="n">N</span><span class="p" data-group-id="8749422890-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8749422890-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8749422890-2">}</span></code></pre><p>The scope for a variable is its function clause. Variables bound in a branch of
│ │ │ │ +that they do not generate warnings.</p><p><em>Example:</em></p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="3145184022-1">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3145184022-2">[</span><span class="p" data-group-id="3145184022-2">]</span><span class="p" data-group-id="3145184022-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3145184022-3">[</span><span class="p" data-group-id="3145184022-3">]</span><span class="p">.</span></code></pre><p>can be rewritten to be more readable:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="1218865106-1">(</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1218865106-2">[</span><span class="p" data-group-id="1218865106-2">]</span><span class="p" data-group-id="1218865106-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1218865106-3">[</span><span class="p" data-group-id="1218865106-3">]</span><span class="p">.</span></code></pre><p>This causes a warning for an unused variable, <code class="inline">Elem</code>. To avoid the warning,
│ │ │ │ +the code can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="0001852360-1">(</span><span class="p">_</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0001852360-2">[</span><span class="p" data-group-id="0001852360-2">]</span><span class="p" data-group-id="0001852360-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0001852360-3">[</span><span class="p" data-group-id="0001852360-3">]</span><span class="p">.</span></code></pre><p>Notice that since variables starting with an underscore are not anonymous, the
│ │ │ │ +following example matches:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0933830964-1">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0933830964-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0933830964-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0933830964-2">}</span></code></pre><p>But this example fails:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7516629587-1">{</span><span class="p">_</span><span class="n">N</span><span class="p">,</span><span class="p">_</span><span class="n">N</span><span class="p" data-group-id="7516629587-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7516629587-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7516629587-2">}</span></code></pre><p>The scope for a variable is its function clause. Variables bound in a branch of
│ │ │ │  an <code class="inline">if</code>, <code class="inline">case</code>, or <code class="inline">receive</code> expression must be bound in all branches to have a
│ │ │ │  value outside the expression. Otherwise they are regarded as unsafe outside
│ │ │ │  the expression.</p><p>For the <code class="inline">try</code> expression variable scoping is limited so that variables bound in
│ │ │ │  the expression are always unsafe outside the expression.</p><h2 id="patterns" class="section-heading">
│ │ │ │    <a href="#patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Patterns</span>
│ │ │ │  </h2>
│ │ │ │  <p>A pattern has the same structure as a term but can contain unbound variables.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">Name1</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3045261518-1">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3045261518-1">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3045261518-2">{</span><span class="ss">error</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="3045261518-2">}</span></code></pre><p>Patterns are allowed in clause heads, <a href="expressions.xhtml#case">case expressions</a>,
│ │ │ │ +</span><span class="p" data-group-id="6694568887-1">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6694568887-1">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6694568887-2">{</span><span class="ss">error</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="6694568887-2">}</span></code></pre><p>Patterns are allowed in clause heads, <a href="expressions.xhtml#case">case expressions</a>,
│ │ │ │  <a href="expressions.xhtml#receive">receive expressions</a>, and
│ │ │ │  <a href="expressions.xhtml#the-match-operator">match expressions</a>.</p><h3 id="the-compound-pattern-operator" class="section-heading">
│ │ │ │    <a href="#the-compound-pattern-operator" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">The Compound Pattern Operator</span>
│ │ │ │  </h3>
│ │ │ │  <p>If <code class="inline">Pattern1</code> and <code class="inline">Pattern2</code> are valid patterns, the following is also a valid
│ │ │ │  pattern:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Pattern2</span></code></pre><p>When matched against a term, both <code class="inline">Pattern1</code> and <code class="inline">Pattern2</code> are matched against
│ │ │ │ -the term. The idea behind this feature is to avoid reconstruction of terms.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4692913475-1">(</span><span class="p" data-group-id="4692913475-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="4692913475-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="4692913475-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Signal</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4692913475-3">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="4692913475-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +the term. The idea behind this feature is to avoid reconstruction of terms.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="9221738787-1">(</span><span class="p" data-group-id="9221738787-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="9221738787-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="9221738787-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Signal</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9221738787-3">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="9221738787-3">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="4692913475-4">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="4692913475-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>can instead be written as</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="5695591247-1">(</span><span class="p" data-group-id="5695591247-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5695591247-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="5695591247-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="9221738787-4">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="9221738787-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>can instead be written as</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0121444170-1">(</span><span class="p" data-group-id="0121444170-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0121444170-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="0121444170-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="5695591247-3">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="5695591247-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="0121444170-3">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="0121444170-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>The compound pattern operator does not imply that its operands are matched in
│ │ │ │  any particular order. That means that it is not legal to bind a variable in
│ │ │ │  <code class="inline">Pattern1</code> and use it in <code class="inline">Pattern2</code>, or vice versa.</p><h3 id="string-prefix-in-patterns" class="section-heading">
│ │ │ │    <a href="#string-prefix-in-patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">String Prefix in Patterns</span>
│ │ │ │  </h3>
│ │ │ │ -<p>When matching strings, the following is a valid pattern:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="7795265838-1">(</span><span class="s">&quot;prefix&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="7795265838-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This is syntactic sugar for the equivalent, but harder to read:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="5439412684-1">(</span><span class="p" data-group-id="5439412684-2">[</span><span class="sc">$p</span><span class="p">,</span><span class="sc">$r</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$f</span><span class="p">,</span><span class="sc">$i</span><span class="p">,</span><span class="sc">$x</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="5439412684-2">]</span><span class="p" data-group-id="5439412684-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h3 id="expressions-in-patterns" class="section-heading">
│ │ │ │ +<p>When matching strings, the following is a valid pattern:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="2125973405-1">(</span><span class="s">&quot;prefix&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="2125973405-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This is syntactic sugar for the equivalent, but harder to read:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="1743454881-1">(</span><span class="p" data-group-id="1743454881-2">[</span><span class="sc">$p</span><span class="p">,</span><span class="sc">$r</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$f</span><span class="p">,</span><span class="sc">$i</span><span class="p">,</span><span class="sc">$x</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="1743454881-2">]</span><span class="p" data-group-id="1743454881-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h3 id="expressions-in-patterns" class="section-heading">
│ │ │ │    <a href="#expressions-in-patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Expressions in Patterns</span>
│ │ │ │  </h3>
│ │ │ │  <p>An arithmetic expression can be used within a pattern if it meets both of the
│ │ │ │ -following two conditions:</p><ul><li>It uses only numeric or bitwise operators.</li><li>Its value can be evaluated to a constant when complied.</li></ul><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="p" data-group-id="4344158471-1">{</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="4344158471-1">}</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4344158471-2">{</span><span class="o">?</span><span class="n">THRESHOLD</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="4344158471-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="the-match-operator" class="section-heading">
│ │ │ │ +following two conditions:</p><ul><li>It uses only numeric or bitwise operators.</li><li>Its value can be evaluated to a constant when complied.</li></ul><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="p" data-group-id="0536244412-1">{</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0536244412-1">}</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0536244412-2">{</span><span class="o">?</span><span class="n">THRESHOLD</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="0536244412-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="the-match-operator" class="section-heading">
│ │ │ │    <a href="#the-match-operator" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">The Match Operator</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following matches <code class="inline">Pattern</code> against <code class="inline">Expr</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>If the matching succeeds, any unbound variable in the pattern becomes bound and
│ │ │ │  the value of <code class="inline">Expr</code> is returned.</p><p>If multiple match operators are applied in sequence, they will be evaluated from
│ │ │ │ -right to left.</p><p>If the matching fails, a <code class="inline">badmatch</code> run-time error occurs.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4618438185-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4618438185-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4618438185-2">{</span><span class="ss">answer</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="4618438185-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4618438185-3">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="4618438185-3">}</span><span class="w">
│ │ │ │ +right to left.</p><p>If the matching fails, a <code class="inline">badmatch</code> run-time error occurs.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7793852359-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="7793852359-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7793852359-2">{</span><span class="ss">answer</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="7793852359-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7793852359-3">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7793852359-3">}</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">answer</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4618438185-4">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="4618438185-4">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="4618438185-5">{</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="4618438185-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4618438185-6">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4618438185-6">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7793852359-4">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="7793852359-4">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="7793852359-5">{</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="7793852359-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7793852359-6">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7793852359-6">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right-hand side value [1,2]</span></code></pre><p>Because multiple match operators are evaluated from right to left, it means
│ │ │ │  that:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Pattern2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PatternN</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expression</span></code></pre><p>is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="n">Temporary</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expression</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">PatternN</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Temporary</span><span class="p">,</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">Pattern2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Temporary</span><span class="p">,</span><span class="w">
│ │ │ │ @@ -144,30 +144,30 @@
│ │ │ │  can safely be skipped on a first reading.</p></section><p>The <code class="inline">=</code> character is used to denote two similar but distinct operators: the
│ │ │ │  match operator and the compound pattern operator. Which one is meant is
│ │ │ │  determined by context.</p><p>The <em>compound pattern operator</em> is used to construct a compound pattern from two
│ │ │ │  patterns. Compound patterns are accepted everywhere a pattern is accepted. A
│ │ │ │  compound pattern matches if all of its constituent patterns match. It is not
│ │ │ │  legal for a pattern that is part of a compound pattern to use variables (as keys
│ │ │ │  in map patterns or sizes in binary patterns) bound in other sub patterns of the
│ │ │ │ -same compound pattern.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">fun</span><span class="p" data-group-id="5740451867-1">(</span><span class="p" data-group-id="5740451867-2">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="5740451867-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5740451867-3">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5740451867-3">}</span><span class="p" data-group-id="5740451867-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +same compound pattern.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">fun</span><span class="p" data-group-id="6013943946-1">(</span><span class="p" data-group-id="6013943946-2">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="6013943946-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6013943946-3">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="6013943946-3">}</span><span class="p" data-group-id="6013943946-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">* 1:7: variable &#39;Key&#39; is unbound</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5740451867-4">(</span><span class="p" data-group-id="5740451867-5">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="5740451867-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="5740451867-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5740451867-6">{</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="5740451867-6">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="5740451867-7">(</span><span class="p" data-group-id="5740451867-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5740451867-8">}</span><span class="p" data-group-id="5740451867-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5740451867-9">{</span><span class="p" data-group-id="5740451867-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5740451867-10">}</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5740451867-9">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="n">G</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5740451867-11">(</span><span class="p" data-group-id="5740451867-12">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">B</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="5740451867-12">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5740451867-13">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5740451867-13">&gt;&gt;</span><span class="p" data-group-id="5740451867-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5740451867-14">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="5740451867-14">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">G</span><span class="p" data-group-id="5740451867-15">(</span><span class="p" data-group-id="5740451867-16">&lt;&lt;</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p" data-group-id="5740451867-16">&gt;&gt;</span><span class="p" data-group-id="5740451867-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5740451867-17">{</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p">,</span><span class="mi">10795</span><span class="p" data-group-id="5740451867-17">}</span></code></pre><p>The <em>match operator</em> is allowed everywhere an expression is allowed. It is used
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6013943946-4">(</span><span class="p" data-group-id="6013943946-5">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="6013943946-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="6013943946-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6013943946-6">{</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="6013943946-6">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="6013943946-7">(</span><span class="p" data-group-id="6013943946-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6013943946-8">}</span><span class="p" data-group-id="6013943946-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6013943946-9">{</span><span class="p" data-group-id="6013943946-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6013943946-10">}</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6013943946-9">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="n">G</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6013943946-11">(</span><span class="p" data-group-id="6013943946-12">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">B</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="6013943946-12">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6013943946-13">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6013943946-13">&gt;&gt;</span><span class="p" data-group-id="6013943946-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6013943946-14">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="6013943946-14">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">G</span><span class="p" data-group-id="6013943946-15">(</span><span class="p" data-group-id="6013943946-16">&lt;&lt;</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p" data-group-id="6013943946-16">&gt;&gt;</span><span class="p" data-group-id="6013943946-15">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6013943946-17">{</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p">,</span><span class="mi">10795</span><span class="p" data-group-id="6013943946-17">}</span></code></pre><p>The <em>match operator</em> is allowed everywhere an expression is allowed. It is used
│ │ │ │  to match the value of an expression to a pattern. If multiple match operators
│ │ │ │ -are applied in sequence, they will be evaluated from right to left.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9237672929-1">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="9237672929-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9237672929-2">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="9237672929-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">f</span><span class="p" data-group-id="9237672929-3">(</span><span class="n">Key</span><span class="p" data-group-id="9237672929-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9237672929-4">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9237672929-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9237672929-5">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9237672929-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │ +are applied in sequence, they will be evaluated from right to left.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7008131937-1">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="7008131937-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7008131937-2">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="7008131937-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">f</span><span class="p" data-group-id="7008131937-3">(</span><span class="n">Key</span><span class="p" data-group-id="7008131937-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7008131937-4">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="7008131937-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7008131937-5">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="7008131937-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">value</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">f</span><span class="p" data-group-id="9237672929-6">(</span><span class="n">Key</span><span class="p" data-group-id="9237672929-6">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9237672929-7">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9237672929-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9237672929-8">(</span><span class="p" data-group-id="9237672929-9">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9237672929-9">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="9237672929-8">)</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">f</span><span class="p" data-group-id="7008131937-6">(</span><span class="n">Key</span><span class="p" data-group-id="7008131937-6">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7008131937-7">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="7008131937-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7008131937-8">(</span><span class="p" data-group-id="7008131937-9">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="7008131937-9">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="7008131937-8">)</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">value</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nf">f</span><span class="p" data-group-id="9237672929-10">(</span><span class="n">Key</span><span class="p" data-group-id="9237672929-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9237672929-11">(</span><span class="p" data-group-id="9237672929-12">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9237672929-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9237672929-13">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9237672929-13">}</span><span class="p" data-group-id="9237672929-11">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nf">f</span><span class="p" data-group-id="7008131937-10">(</span><span class="n">Key</span><span class="p" data-group-id="7008131937-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7008131937-11">(</span><span class="p" data-group-id="7008131937-12">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="7008131937-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7008131937-13">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="7008131937-13">}</span><span class="p" data-group-id="7008131937-11">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">* 1:12: variable &#39;Key&#39; is unbound</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="9237672929-14">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">Y</span><span class="p" data-group-id="9237672929-14">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">begin</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9237672929-15">&lt;&lt;</span><span class="mi">42</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="9237672929-15">&gt;&gt;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="7008131937-14">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">Y</span><span class="p" data-group-id="7008131937-14">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">begin</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7008131937-15">&lt;&lt;</span><span class="mi">42</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="7008131937-15">&gt;&gt;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span></code></pre><p>The expression at prompt <code class="inline">2&gt;</code> first matches the value of variable <code class="inline">M</code> against
│ │ │ │  pattern <code class="inline">#{key := Key}</code>, binding variable <code class="inline">Key</code>. It then matches the value of
│ │ │ │  <code class="inline">M</code> against pattern <code class="inline">#{Key := Value}</code> using variable <code class="inline">Key</code> as the key, binding
│ │ │ │  variable <code class="inline">Value</code>.</p><p>The expression at prompt <code class="inline">3&gt;</code> matches expression <code class="inline">(#{key := Key} = M)</code> against
│ │ │ │  pattern <code class="inline">#{Key := Value}</code>. The expression inside the parentheses is evaluated
│ │ │ │  first. That is, <code class="inline">M</code> is matched against <code class="inline">#{key := Key}</code>, and then the value of
│ │ │ │  <code class="inline">M</code> is matched against pattern <code class="inline">#{Key := Value}</code>. That is the same evaluation
│ │ │ │ @@ -181,30 +181,30 @@
│ │ │ │  binding variable <code class="inline">Y</code> and creating a binary. The binary is then matched against
│ │ │ │  pattern <code class="inline">&lt;&lt;X:Y&gt;&gt;</code> using the value of <code class="inline">Y</code> as the size of the segment.</p><h2 id="function-calls" class="section-heading">
│ │ │ │    <a href="#function-calls" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Function Calls</span>
│ │ │ │  </h2>
│ │ │ │ -<pre><code class="makeup erlang" translate="no"><span class="n">ExprF</span><span class="p" data-group-id="5754671300-1">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="5754671300-1">)</span><span class="w">
│ │ │ │ -</span><span class="n">ExprM</span><span class="p">:</span><span class="n">ExprF</span><span class="p" data-group-id="5754671300-2">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="5754671300-2">)</span></code></pre><p>In the first form of function calls, <code class="inline">ExprM:ExprF(Expr1,...,ExprN)</code>, each of
│ │ │ │ +<pre><code class="makeup erlang" translate="no"><span class="n">ExprF</span><span class="p" data-group-id="1737749129-1">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="1737749129-1">)</span><span class="w">
│ │ │ │ +</span><span class="n">ExprM</span><span class="p">:</span><span class="n">ExprF</span><span class="p" data-group-id="1737749129-2">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="1737749129-2">)</span></code></pre><p>In the first form of function calls, <code class="inline">ExprM:ExprF(Expr1,...,ExprN)</code>, each of
│ │ │ │  <code class="inline">ExprM</code> and <code class="inline">ExprF</code> must be an atom or an expression that evaluates to an atom.
│ │ │ │  The function is said to be called by using the <em>fully qualified function name</em>.
│ │ │ │ -This is often referred to as a <em>remote</em> or <em>external function call</em>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="0869232719-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="0869232719-1">)</span></code></pre><p>In the second form of function calls, <code class="inline">ExprF(Expr1,...,ExprN)</code>, <code class="inline">ExprF</code> must be
│ │ │ │ +This is often referred to as a <em>remote</em> or <em>external function call</em>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="7298260962-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7298260962-1">)</span></code></pre><p>In the second form of function calls, <code class="inline">ExprF(Expr1,...,ExprN)</code>, <code class="inline">ExprF</code> must be
│ │ │ │  an atom or evaluate to a fun.</p><p>If <code class="inline">ExprF</code> is an atom, the function is said to be called by using the
│ │ │ │  <em>implicitly qualified function name</em>. If the function <code class="inline">ExprF</code> is locally
│ │ │ │  defined, it is called. Alternatively, if <code class="inline">ExprF</code> is explicitly imported from the
│ │ │ │  <code class="inline">M</code> module, <code class="inline">M:ExprF(Expr1,...,ExprN)</code> is called. If <code class="inline">ExprF</code> is neither declared
│ │ │ │  locally nor explicitly imported, <code class="inline">ExprF</code> must be the name of an automatically
│ │ │ │ -imported BIF.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="9589175140-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9589175140-1">)</span><span class="w">
│ │ │ │ -</span><span class="nf">spawn</span><span class="p" data-group-id="9589175140-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9589175140-3">[</span><span class="p" data-group-id="9589175140-3">]</span><span class="p" data-group-id="9589175140-2">)</span></code></pre><p><em>Examples</em> where <code class="inline">ExprF</code> is a fun:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9605698485-1">(</span><span class="n">X</span><span class="p" data-group-id="9605698485-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Fun1</span><span class="p" data-group-id="9605698485-2">(</span><span class="mi">3</span><span class="p" data-group-id="9605698485-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +imported BIF.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="3817344519-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3817344519-1">)</span><span class="w">
│ │ │ │ +</span><span class="nf">spawn</span><span class="p" data-group-id="3817344519-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3817344519-3">[</span><span class="p" data-group-id="3817344519-3">]</span><span class="p" data-group-id="3817344519-2">)</span></code></pre><p><em>Examples</em> where <code class="inline">ExprF</code> is a fun:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1145544904-1">(</span><span class="n">X</span><span class="p" data-group-id="1145544904-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Fun1</span><span class="p" data-group-id="1145544904-2">(</span><span class="mi">3</span><span class="p" data-group-id="1145544904-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="k">fun</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="ss">append</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9605698485-3">(</span><span class="p" data-group-id="9605698485-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9605698485-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9605698485-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="9605698485-5">]</span><span class="p" data-group-id="9605698485-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9605698485-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="9605698485-6">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="k">fun</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="ss">append</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1145544904-3">(</span><span class="p" data-group-id="1145544904-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1145544904-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1145544904-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1145544904-5">]</span><span class="p" data-group-id="1145544904-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1145544904-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1145544904-6">]</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="o">&gt;</span></code></pre><p>Notice that when calling a local function, there is a difference between using
│ │ │ │  the implicitly or fully qualified function name. The latter always refers to the
│ │ │ │  latest version of the module. See
│ │ │ │  <a href="code_loading.xhtml">Compilation and Code Loading </a>and
│ │ │ │  <a href="ref_man_functions.xhtml#eval">Function Evaluation</a>.</p><h3 id="local-function-names-clashing-with-auto-imported-bifs" class="section-heading">
│ │ │ │    <a href="#local-function-names-clashing-with-auto-imported-bifs" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -221,40 +221,40 @@
│ │ │ │  called instead. This is to avoid that future additions to the set of
│ │ │ │  auto-imported BIFs do not silently change the behavior of old code.</p></section><p>However, to avoid that old (pre R14) code changed its behavior when compiled
│ │ │ │  with Erlang/OTP version R14A or later, the following restriction applies: If you
│ │ │ │  override the name of a BIF that was auto-imported in OTP versions prior to R14A
│ │ │ │  (ERTS version 5.8) and have an implicitly qualified call to that function in
│ │ │ │  your code, you either need to explicitly remove the auto-import using a compiler
│ │ │ │  directive, or replace the call with a fully qualified function call. Otherwise
│ │ │ │ -you get a compilation error. See the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9514657742-1">(</span><span class="p" data-group-id="9514657742-2">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9514657742-2">]</span><span class="p" data-group-id="9514657742-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +you get a compilation error. See the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1952188896-1">(</span><span class="p" data-group-id="1952188896-2">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1952188896-2">]</span><span class="p" data-group-id="1952188896-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="9514657742-3">(</span><span class="p" data-group-id="9514657742-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="9514657742-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9514657742-5">]</span><span class="p" data-group-id="9514657742-4">}</span><span class="p" data-group-id="9514657742-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="1952188896-3">(</span><span class="p" data-group-id="1952188896-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="1952188896-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1952188896-5">]</span><span class="p" data-group-id="1952188896-4">}</span><span class="p" data-group-id="1952188896-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">length</span><span class="p" data-group-id="9514657742-6">(</span><span class="p" data-group-id="9514657742-7">[</span><span class="p" data-group-id="9514657742-7">]</span><span class="p" data-group-id="9514657742-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">length</span><span class="p" data-group-id="1952188896-6">(</span><span class="p" data-group-id="1952188896-7">[</span><span class="p" data-group-id="1952188896-7">]</span><span class="p" data-group-id="1952188896-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">length</span><span class="p" data-group-id="9514657742-8">(</span><span class="p" data-group-id="9514657742-9">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9514657742-9">]</span><span class="p" data-group-id="9514657742-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9514657742-10">(</span><span class="n">T</span><span class="p" data-group-id="9514657742-10">)</span><span class="p">.</span><span class="w"> </span><span class="c1">%% Calls the local function length/1</span><span class="w">
│ │ │ │ +</span><span class="nf">length</span><span class="p" data-group-id="1952188896-8">(</span><span class="p" data-group-id="1952188896-9">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1952188896-9">]</span><span class="p" data-group-id="1952188896-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1952188896-10">(</span><span class="n">T</span><span class="p" data-group-id="1952188896-10">)</span><span class="p">.</span><span class="w"> </span><span class="c1">%% Calls the local function length/1</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="9514657742-11">(</span><span class="n">X</span><span class="p" data-group-id="9514657742-11">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="9514657742-12">(</span><span class="n">X</span><span class="p" data-group-id="9514657742-12">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="1952188896-11">(</span><span class="n">X</span><span class="p" data-group-id="1952188896-11">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="1952188896-12">(</span><span class="n">X</span><span class="p" data-group-id="1952188896-12">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ │                                    </span><span class="c1">%% which is allowed in guards</span><span class="w">
│ │ │ │      </span><span class="ss">long</span><span class="p">.</span></code></pre><p>The same logic applies to explicitly imported functions from other modules, as
│ │ │ │  to locally defined functions. It is not allowed to both import a function from
│ │ │ │ -another module and have the function declared in the module at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5907585143-1">(</span><span class="p" data-group-id="5907585143-2">[</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5907585143-2">]</span><span class="p" data-group-id="5907585143-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +another module and have the function declared in the module at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0115522460-1">(</span><span class="p" data-group-id="0115522460-2">[</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0115522460-2">]</span><span class="p" data-group-id="0115522460-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="5907585143-3">(</span><span class="p" data-group-id="5907585143-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="5907585143-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5907585143-5">]</span><span class="p" data-group-id="5907585143-4">}</span><span class="p" data-group-id="5907585143-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="0115522460-3">(</span><span class="p" data-group-id="0115522460-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="0115522460-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0115522460-5">]</span><span class="p" data-group-id="0115522460-4">}</span><span class="p" data-group-id="0115522460-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="5907585143-6">(</span><span class="ss">mod</span><span class="p">,</span><span class="p" data-group-id="5907585143-7">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5907585143-7">]</span><span class="p" data-group-id="5907585143-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="0115522460-6">(</span><span class="ss">mod</span><span class="p">,</span><span class="p" data-group-id="0115522460-7">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0115522460-7">]</span><span class="p" data-group-id="0115522460-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="5907585143-8">(</span><span class="n">X</span><span class="p" data-group-id="5907585143-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="5907585143-9">(</span><span class="n">X</span><span class="p" data-group-id="5907585143-9">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">33</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="0115522460-8">(</span><span class="n">X</span><span class="p" data-group-id="0115522460-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="0115522460-9">(</span><span class="n">X</span><span class="p" data-group-id="0115522460-9">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">33</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ │                                     </span><span class="c1">%% which is allowed in guards</span><span class="w">
│ │ │ │  
│ │ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="5907585143-10">(</span><span class="n">X</span><span class="p" data-group-id="5907585143-10">)</span><span class="p">;</span><span class="w">              </span><span class="c1">%% Explicit call to erlang:length in body</span><span class="w">
│ │ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="0115522460-10">(</span><span class="n">X</span><span class="p" data-group-id="0115522460-10">)</span><span class="p">;</span><span class="w">              </span><span class="c1">%% Explicit call to erlang:length in body</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="5907585143-11">(</span><span class="n">X</span><span class="p" data-group-id="5907585143-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">length</span><span class="p" data-group-id="5907585143-12">(</span><span class="n">X</span><span class="p" data-group-id="5907585143-12">)</span><span class="p">.</span><span class="w">                     </span><span class="c1">%% mod:length/1 is called</span></code></pre><p>For auto-imported BIFs added in Erlang/OTP R14A and thereafter, overriding the
│ │ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="0115522460-11">(</span><span class="n">X</span><span class="p" data-group-id="0115522460-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">length</span><span class="p" data-group-id="0115522460-12">(</span><span class="n">X</span><span class="p" data-group-id="0115522460-12">)</span><span class="p">.</span><span class="w">                     </span><span class="c1">%% mod:length/1 is called</span></code></pre><p>For auto-imported BIFs added in Erlang/OTP R14A and thereafter, overriding the
│ │ │ │  name with a local function or explicit import is always allowed. However, if the
│ │ │ │  <code class="inline">-compile({no_auto_import,[F/A])</code> directive is not used, the compiler issues a
│ │ │ │  warning whenever the function is called in the module using the implicitly
│ │ │ │  qualified function name.</p><h2 id="if" class="section-heading">
│ │ │ │    <a href="#if" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -266,40 +266,40 @@
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">GuardSeqN</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The branches of an <code class="inline">if</code>-expression are scanned sequentially until a guard
│ │ │ │  sequence <code class="inline">GuardSeq</code> that evaluates to true is found. Then the corresponding
│ │ │ │  <code class="inline">Body</code> (a sequence of expressions separated by <code class="inline">,</code>) is evaluated.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">if</code> expression.</p><p>If no guard sequence is evaluated as true, an <code class="inline">if_clause</code> run-time error occurs.
│ │ │ │  If necessary, the guard expression <code class="inline">true</code> can be used in the last branch, as
│ │ │ │ -that guard sequence is always true.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_greater_than</span><span class="p" data-group-id="8759269453-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8759269453-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +that guard sequence is always true.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_greater_than</span><span class="p" data-group-id="9259577486-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9259577486-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">if</span><span class="w">
│ │ │ │          </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% works as an &#39;else&#39; branch</span><span class="w">
│ │ │ │              </span><span class="ss">false</span><span class="w">
│ │ │ │      </span><span class="k">end</span></code></pre><h2 id="case" class="section-heading">
│ │ │ │    <a href="#case" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Case</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">Expr</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="7726381846-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="7726381846-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="3982483444-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="3982483444-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="7726381846-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="7726381846-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="3982483444-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="3982483444-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The expression <code class="inline">Expr</code> is evaluated and the patterns <code class="inline">Pattern</code> are sequentially
│ │ │ │  matched against the result. If a match succeeds and the optional guard sequence
│ │ │ │  <code class="inline">GuardSeq</code> is true, the corresponding <code class="inline">Body</code> is evaluated.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">case</code> expression.</p><p>If there is no matching pattern with a true guard sequence, a <code class="inline">case_clause</code>
│ │ │ │ -run-time error occurs.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_valid_signal</span><span class="p" data-group-id="2551933795-1">(</span><span class="n">Signal</span><span class="p" data-group-id="2551933795-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +run-time error occurs.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_valid_signal</span><span class="p" data-group-id="2319656706-1">(</span><span class="n">Signal</span><span class="p" data-group-id="2319656706-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Signal</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2551933795-2">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="2551933795-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2319656706-2">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="2319656706-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2551933795-3">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="2551933795-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2319656706-3">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="2319656706-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">_</span><span class="n">Else</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">false</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="maybe" class="section-heading">
│ │ │ │    <a href="#maybe" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -317,57 +317,57 @@
│ │ │ │  the top-level of a <code class="inline">maybe</code> block. It matches the pattern <code class="inline">Expr1</code> against
│ │ │ │  <code class="inline">Expr2</code>. If the matching succeeds, any unbound variable in the pattern becomes
│ │ │ │  bound. If the expression is the last expression in the <code class="inline">maybe</code> block, it also
│ │ │ │  returns the value of <code class="inline">Expr2</code>. If the matching is unsuccessful, the rest of the
│ │ │ │  expressions in the <code class="inline">maybe</code> block are skipped and the return value of the <code class="inline">maybe</code>
│ │ │ │  block is <code class="inline">Expr2</code>.</p><p>None of the variables bound in a <code class="inline">maybe</code> block must be used in the code that
│ │ │ │  follows the block.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2725504500-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2725504500-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="2725504500-2">(</span><span class="p" data-group-id="2725504500-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2086916983-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2086916983-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="2086916983-2">(</span><span class="p" data-group-id="2086916983-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2725504500-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2725504500-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="2725504500-4">(</span><span class="p" data-group-id="2725504500-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2086916983-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2086916983-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="2086916983-4">(</span><span class="p" data-group-id="2086916983-4">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>Let us first assume that <code class="inline">a()</code> returns <code class="inline">{ok,42}</code> and <code class="inline">b()</code> returns <code class="inline">{ok,58}</code>.
│ │ │ │  With those return values, all of the match operators will succeed, and the
│ │ │ │  return value of the <code class="inline">maybe</code> block is <code class="inline">A + B</code>, which is equal to <code class="inline">42 + 58 = 100</code>.</p><p>Now let us assume that <code class="inline">a()</code> returns <code class="inline">error</code>. The conditional match operator in
│ │ │ │  <code class="inline">{ok, A} ?= a()</code> fails to match, and the return value of the <code class="inline">maybe</code> block is
│ │ │ │  the value of the expression that failed to match, namely <code class="inline">error</code>. Similarly, if
│ │ │ │  <code class="inline">b()</code> returns <code class="inline">wrong</code>, the return value of the <code class="inline">maybe</code> block is <code class="inline">wrong</code>.</p><p>Finally, let us assume that <code class="inline">a()</code> returns <code class="inline">{ok,-1}</code>. Because <code class="inline">true = A &gt;= 0</code> uses
│ │ │ │  the match operator <code class="inline">=</code>, a <code class="inline">{badmatch,false}</code> run-time error occurs when the
│ │ │ │ -expression fails to match the pattern.</p><p>The example can be written in a less succient way using nested case expressions:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="4630213896-1">(</span><span class="p" data-group-id="4630213896-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4630213896-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="4630213896-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +expression fails to match the pattern.</p><p>The example can be written in a less succient way using nested case expressions:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="2290996036-1">(</span><span class="p" data-group-id="2290996036-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2290996036-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2290996036-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="4630213896-3">(</span><span class="p" data-group-id="4630213896-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="4630213896-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4630213896-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="2290996036-3">(</span><span class="p" data-group-id="2290996036-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="2290996036-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2290996036-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">;</span><span class="w">
│ │ │ │              </span><span class="n">Other1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                  </span><span class="n">Other1</span><span class="w">
│ │ │ │          </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">Other2</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Other2</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">maybe</code> block can be augmented with <code class="inline">else</code> clauses:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ │      </span><span class="n">Expr1</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">ExprN</span><span class="w">
│ │ │ │  </span><span class="k">else</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="9447567890-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9447567890-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="2769466391-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="2769466391-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="9447567890-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="9447567890-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="2769466391-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="2769466391-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>If a conditional match operator fails, the failed expression is matched against
│ │ │ │  the patterns in all clauses between the <code class="inline">else</code> and <code class="inline">end</code> keywords. If a match
│ │ │ │  succeeds and the optional guard sequence <code class="inline">GuardSeq</code> is true, the corresponding
│ │ │ │  <code class="inline">Body</code> is evaluated. The value returned from the body is the return value of the
│ │ │ │  <code class="inline">maybe</code> block.</p><p>If there is no matching pattern with a true guard sequence, an <code class="inline">else_clause</code>
│ │ │ │  run-time error occurs.</p><p>None of the variables bound in a <code class="inline">maybe</code> block must be used in the <code class="inline">else</code>
│ │ │ │  clauses. None of the variables bound in the <code class="inline">else</code> clauses must be used in the
│ │ │ │  code that follows the <code class="inline">maybe</code> block.</p><p>Here is the previous example augmented with <code class="inline">else</code> clauses:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8443974881-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="8443974881-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="8443974881-2">(</span><span class="p" data-group-id="8443974881-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0855607770-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="0855607770-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="0855607770-2">(</span><span class="p" data-group-id="0855607770-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8443974881-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="8443974881-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="8443974881-4">(</span><span class="p" data-group-id="8443974881-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0855607770-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="0855607770-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="0855607770-4">(</span><span class="p" data-group-id="0855607770-4">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w">
│ │ │ │  </span><span class="k">else</span><span class="w">
│ │ │ │      </span><span class="ss">error</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="ss">wrong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">else</code> clauses translate the failing value from the conditional match
│ │ │ │  operators to the value <code class="inline">error</code>. If the failing value is not one of the
│ │ │ │  recognized values, a <code class="inline">else_clause</code> run-time error occurs.</p><h2 id="send" class="section-heading">
│ │ │ │ @@ -386,75 +386,75 @@
│ │ │ │  <code class="inline">{Name,Node}</code> (or a pid located at another node), also never fails.</li></ul><h2 id="receive" class="section-heading">
│ │ │ │    <a href="#receive" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Receive</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="2114933823-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="2114933823-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="8463670060-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="8463670060-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="2114933823-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="2114933823-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="8463670060-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="8463670060-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>Fetches a received message present in the message queue of the process. The
│ │ │ │  first message in the message queue is matched sequentially against the patterns
│ │ │ │  from top to bottom. If no match was found, the matching sequence is repeated for
│ │ │ │  the second message in the queue, and so on. Messages are queued in the
│ │ │ │  <a href="ref_man_processes.xhtml#message-queue-order">order they were received</a>. If a match
│ │ │ │  succeeds, that is, if the <code class="inline">Pattern</code> matches and the optional guard sequence
│ │ │ │  <code class="inline">GuardSeq</code> is true, then the message is removed from the message queue and the
│ │ │ │  corresponding <code class="inline">Body</code> is evaluated. All other messages in the message queue
│ │ │ │  remain unchanged.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">receive</code> expression.</p><p><code class="inline">receive</code> never fails. The execution is suspended, possibly indefinitely, until
│ │ │ │  a message arrives that matches one of the patterns and with a true guard
│ │ │ │ -sequence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9951310610-1">(</span><span class="p" data-group-id="9951310610-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +sequence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="2144692060-1">(</span><span class="p" data-group-id="2144692060-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">onhook</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="9951310610-2">(</span><span class="p" data-group-id="9951310610-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">idle</span><span class="p" data-group-id="9951310610-3">(</span><span class="p" data-group-id="9951310610-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9951310610-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9951310610-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9951310610-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9951310610-6">(</span><span class="p" data-group-id="9951310610-6">)</span><span class="p" data-group-id="9951310610-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9951310610-7">(</span><span class="p" data-group-id="9951310610-7">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="2144692060-2">(</span><span class="p" data-group-id="2144692060-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">idle</span><span class="p" data-group-id="2144692060-3">(</span><span class="p" data-group-id="2144692060-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2144692060-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2144692060-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2144692060-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2144692060-6">(</span><span class="p" data-group-id="2144692060-6">)</span><span class="p" data-group-id="2144692060-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="2144692060-7">(</span><span class="p" data-group-id="2144692060-7">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">receive</code> expression can be augmented with a timeout:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="3624148202-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="3624148202-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="8480455751-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="8480455751-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="3624148202-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="3624148202-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="8480455751-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="8480455751-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">after</span><span class="w">
│ │ │ │      </span><span class="n">ExprT</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyT</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p><code class="inline">receive...after</code> works exactly as <code class="inline">receive</code>, except that if no matching message
│ │ │ │  has arrived within <code class="inline">ExprT</code> milliseconds, then <code class="inline">BodyT</code> is evaluated instead. The
│ │ │ │  return value of <code class="inline">BodyT</code> then becomes the return value of the <code class="inline">receive...after</code>
│ │ │ │  expression. <code class="inline">ExprT</code> is to evaluate to an integer, or the atom <code class="inline">infinity</code>. The
│ │ │ │  allowed integer range is from 0 to 4294967295, that is, the longest possible
│ │ │ │  timeout is almost 50 days. With a zero value the timeout occurs immediately if
│ │ │ │  there is no matching message in the message queue.</p><p>The atom <code class="inline">infinity</code> will make the process wait indefinitely for a matching
│ │ │ │  message. This is the same as not using a timeout. It can be useful for timeout
│ │ │ │ -values that are calculated at runtime.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9926742484-1">(</span><span class="p" data-group-id="9926742484-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +values that are calculated at runtime.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="0536107092-1">(</span><span class="p" data-group-id="0536107092-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">onhook</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="9926742484-2">(</span><span class="p" data-group-id="9926742484-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">idle</span><span class="p" data-group-id="9926742484-3">(</span><span class="p" data-group-id="9926742484-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9926742484-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9926742484-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9926742484-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9926742484-6">(</span><span class="p" data-group-id="9926742484-6">)</span><span class="p" data-group-id="9926742484-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="9926742484-7">(</span><span class="p" data-group-id="9926742484-7">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="0536107092-2">(</span><span class="p" data-group-id="0536107092-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">idle</span><span class="p" data-group-id="0536107092-3">(</span><span class="p" data-group-id="0536107092-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0536107092-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="0536107092-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0536107092-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0536107092-6">(</span><span class="p" data-group-id="0536107092-6">)</span><span class="p" data-group-id="0536107092-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="0536107092-7">(</span><span class="p" data-group-id="0536107092-7">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w">
│ │ │ │          </span><span class="mi">60000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="9926742484-8">(</span><span class="p" data-group-id="9926742484-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">error</span><span class="p" data-group-id="9926742484-9">(</span><span class="p" data-group-id="9926742484-9">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="0536107092-8">(</span><span class="p" data-group-id="0536107092-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">error</span><span class="p" data-group-id="0536107092-9">(</span><span class="p" data-group-id="0536107092-9">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>It is legal to use a <code class="inline">receive...after</code> expression with no branches:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │  </span><span class="k">after</span><span class="w">
│ │ │ │      </span><span class="n">ExprT</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyT</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>This construction does not consume any messages, only suspends execution in the
│ │ │ │ -process for <code class="inline">ExprT</code> milliseconds. This can be used to implement simple timers.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">timer</span><span class="p" data-group-id="9780231940-1">(</span><span class="p" data-group-id="9780231940-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9780231940-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9780231940-3">[</span><span class="nf">self</span><span class="p" data-group-id="9780231940-4">(</span><span class="p" data-group-id="9780231940-4">)</span><span class="p" data-group-id="9780231940-3">]</span><span class="p" data-group-id="9780231940-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +process for <code class="inline">ExprT</code> milliseconds. This can be used to implement simple timers.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">timer</span><span class="p" data-group-id="9469249173-1">(</span><span class="p" data-group-id="9469249173-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9469249173-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9469249173-3">[</span><span class="nf">self</span><span class="p" data-group-id="9469249173-4">(</span><span class="p" data-group-id="9469249173-4">)</span><span class="p" data-group-id="9469249173-3">]</span><span class="p" data-group-id="9469249173-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">timer</span><span class="p" data-group-id="9780231940-5">(</span><span class="n">Pid</span><span class="p" data-group-id="9780231940-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">timer</span><span class="p" data-group-id="9469249173-5">(</span><span class="n">Pid</span><span class="p" data-group-id="9469249173-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w">
│ │ │ │          </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">timeout</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>For more information on timers in Erlang in general, see the
│ │ │ │  <a href="../../../lib/../erts/doc/html/time_correction.xhtml#timers"><em>Timers</em></a> section of the
│ │ │ │  <a href="../../../lib/../erts/doc/html/time_correction.xhtml"><em>Time and Time Correction in Erlang</em></a>
│ │ │ │ @@ -496,21 +496,21 @@
│ │ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">4&gt; </span><span class="mf">0.0</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">-</span><span class="mf">0.0</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">5&gt; </span><span class="mf">0.0</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">+</span><span class="mf">0.0</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">6&gt; </span><span class="mi">1</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="p" data-group-id="8658408501-1">#{</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8658408501-1">}</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="8658408501-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8658408501-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="p" data-group-id="6940976494-1">#{</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6940976494-1">}</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="6940976494-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6940976494-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">8&gt; </span><span class="p" data-group-id="8658408501-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8658408501-3">}</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="p" data-group-id="8658408501-4">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">2.0</span><span class="p" data-group-id="8658408501-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">8&gt; </span><span class="p" data-group-id="6940976494-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6940976494-3">}</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="p" data-group-id="6940976494-4">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">2.0</span><span class="p" data-group-id="6940976494-4">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="p" data-group-id="8658408501-5">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="8658408501-5">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="8658408501-6">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="8658408501-6">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="p" data-group-id="6940976494-5">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="6940976494-5">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="6940976494-6">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="6940976494-6">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="p" data-group-id="8658408501-7">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="8658408501-7">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="8658408501-8">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="8658408501-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="p" data-group-id="6940976494-7">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="6940976494-7">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="6940976494-8">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="6940976494-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Prior to OTP 27, the term equivalence operators considered <code class="inline">0.0</code>
│ │ │ │  and <code class="inline">-0.0</code> to be the same term.</p><p>This was changed in OTP 27 but legacy code may have expected them to be
│ │ │ │  considered the same. To help users catch errors that may arise from an
│ │ │ │  upgrade, the compiler raises a warning when <code class="inline">0.0</code> is pattern-matched or used
│ │ │ │  in a term equivalence test.</p><p>If you need to match <code class="inline">0.0</code> specifically, the warning can be silenced by
│ │ │ │  writing <code class="inline">+0.0</code> instead, which produces the same term but makes the compiler
│ │ │ │  interpret the match as being done on purpose.</p></section><h2 id="arithmetic-expressions" class="section-heading">
│ │ │ │ @@ -536,15 +536,15 @@
│ │ │ │  </span><span class="mi">0</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">8&gt; </span><span class="mi">2#10</span><span class="w"> </span><span class="ow">bor</span><span class="w"> </span><span class="mi">2#01</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">9&gt; </span><span class="ss">a</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: an error occurred when evaluating an arithmetic expression
│ │ │ │       in operator  +/2
│ │ │ │          called as a + 10</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="mi">1</span><span class="w"> </span><span class="nf">bsl</span><span class="w"> </span><span class="p" data-group-id="4046830206-1">(</span><span class="mi">1</span><span class="w"> </span><span class="ow">bsl</span><span class="w"> </span><span class="mi">64</span><span class="p" data-group-id="4046830206-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="mi">1</span><span class="w"> </span><span class="nf">bsl</span><span class="w"> </span><span class="p" data-group-id="1551463617-1">(</span><span class="mi">1</span><span class="w"> </span><span class="ow">bsl</span><span class="w"> </span><span class="mi">64</span><span class="p" data-group-id="1551463617-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: a system limit has been reached
│ │ │ │       in operator  bsl/2
│ │ │ │          called as 1 bsl 18446744073709551616</span></code></pre><h2 id="boolean-expressions" class="section-heading">
│ │ │ │    <a href="#boolean-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Boolean Expressions</span>
│ │ │ │ @@ -563,136 +563,136 @@
│ │ │ │    <a href="#short-circuit-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Short-Circuit Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="n">Expr1</span><span class="w"> </span><span class="ow">orelse</span><span class="w"> </span><span class="n">Expr2</span><span class="w">
│ │ │ │  </span><span class="n">Expr1</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">Expr2</span></code></pre><p><code class="inline">Expr2</code> is evaluated only if necessary. That is, <code class="inline">Expr2</code> is evaluated only if:</p><ul><li><code class="inline">Expr1</code> evaluates to <code class="inline">false</code> in an <code class="inline">orelse</code> expression.</li></ul><p>or</p><ul><li><code class="inline">Expr1</code> evaluates to <code class="inline">true</code> in an <code class="inline">andalso</code> expression.</li></ul><p>Returns either the value of <code class="inline">Expr1</code> (that is, <code class="inline">true</code> or <code class="inline">false</code>) or the value of
│ │ │ │ -<code class="inline">Expr2</code> (if <code class="inline">Expr2</code> is evaluated).</p><p><em>Example 1:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="o">-</span><span class="mf">1.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nc">math</span><span class="p">:</span><span class="nf">sqrt</span><span class="p" data-group-id="1929242535-1">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="1929242535-1">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span></code></pre><p>This works even if <code class="inline">A</code> is less than <code class="inline">-1.0</code>, since in that case, <a href="../../../lib/stdlib/doc/html/math.html#sqrt/1"><code class="inline">math:sqrt/1</code></a> is
│ │ │ │ -never evaluated.</p><p><em>Example 2:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">OnlyOne</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">is_atom</span><span class="p" data-group-id="4493252825-1">(</span><span class="n">L</span><span class="p" data-group-id="4493252825-1">)</span><span class="w"> </span><span class="nf">orelse</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="4493252825-2">(</span><span class="nf">is_list</span><span class="p" data-group-id="4493252825-3">(</span><span class="n">L</span><span class="p" data-group-id="4493252825-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="4493252825-4">(</span><span class="n">L</span><span class="p" data-group-id="4493252825-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4493252825-2">)</span><span class="p">,</span></code></pre><p><code class="inline">Expr2</code> is not required to evaluate to a Boolean value. Because of that,
│ │ │ │ -<code class="inline">andalso</code> and <code class="inline">orelse</code> are tail-recursive.</p><p><em>Example 3 (tail-recursive function):</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="3799483708-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3799483708-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="3799483708-2">]</span><span class="p" data-group-id="3799483708-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pred</span><span class="p" data-group-id="3799483708-3">(</span><span class="n">Hd</span><span class="p" data-group-id="3799483708-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">all</span><span class="p" data-group-id="3799483708-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="3799483708-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">all</span><span class="p" data-group-id="3799483708-5">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3799483708-6">[</span><span class="p" data-group-id="3799483708-6">]</span><span class="p" data-group-id="3799483708-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +<code class="inline">Expr2</code> (if <code class="inline">Expr2</code> is evaluated).</p><p><em>Example 1:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="o">-</span><span class="mf">1.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nc">math</span><span class="p">:</span><span class="nf">sqrt</span><span class="p" data-group-id="6842013764-1">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="6842013764-1">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span></code></pre><p>This works even if <code class="inline">A</code> is less than <code class="inline">-1.0</code>, since in that case, <a href="../../../lib/stdlib/doc/html/math.html#sqrt/1"><code class="inline">math:sqrt/1</code></a> is
│ │ │ │ +never evaluated.</p><p><em>Example 2:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">OnlyOne</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">is_atom</span><span class="p" data-group-id="6237201878-1">(</span><span class="n">L</span><span class="p" data-group-id="6237201878-1">)</span><span class="w"> </span><span class="nf">orelse</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="6237201878-2">(</span><span class="nf">is_list</span><span class="p" data-group-id="6237201878-3">(</span><span class="n">L</span><span class="p" data-group-id="6237201878-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="6237201878-4">(</span><span class="n">L</span><span class="p" data-group-id="6237201878-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6237201878-2">)</span><span class="p">,</span></code></pre><p><code class="inline">Expr2</code> is not required to evaluate to a Boolean value. Because of that,
│ │ │ │ +<code class="inline">andalso</code> and <code class="inline">orelse</code> are tail-recursive.</p><p><em>Example 3 (tail-recursive function):</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="0049657033-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0049657033-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="0049657033-2">]</span><span class="p" data-group-id="0049657033-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pred</span><span class="p" data-group-id="0049657033-3">(</span><span class="n">Hd</span><span class="p" data-group-id="0049657033-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">all</span><span class="p" data-group-id="0049657033-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0049657033-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">all</span><span class="p" data-group-id="0049657033-5">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0049657033-6">[</span><span class="p" data-group-id="0049657033-6">]</span><span class="p" data-group-id="0049657033-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">true</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R13A, <code class="inline">Expr2</code> was required to evaluate to a Boolean value,
│ │ │ │  and as consequence, <code class="inline">andalso</code> and <code class="inline">orelse</code> were <strong>not</strong> tail-recursive.</p></section><h2 id="list-operations" class="section-heading">
│ │ │ │    <a href="#list-operations" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">List Operations</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="n">Expr1</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Expr2</span><span class="w">
│ │ │ │  </span><span class="n">Expr1</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="n">Expr2</span></code></pre><p>The list concatenation operator <code class="inline">++</code> appends its second argument to its first
│ │ │ │  and returns the resulting list.</p><p>The list subtraction operator <code class="inline">--</code> produces a list that is a copy of the first
│ │ │ │  argument. The procedure is as follows: for each element in the second argument,
│ │ │ │ -the first occurrence of this element (if any) is removed.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2555320734-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2555320734-1">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2555320734-2">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2555320734-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2555320734-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2555320734-3">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="2555320734-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2555320734-4">]</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="p" data-group-id="2555320734-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2555320734-5">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2555320734-6">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2555320734-6">]</span></code></pre><h2 id="map-expressions" class="section-heading">
│ │ │ │ +the first occurrence of this element (if any) is removed.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4760787928-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4760787928-1">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4760787928-2">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4760787928-2">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4760787928-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4760787928-3">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4760787928-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4760787928-4">]</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="p" data-group-id="4760787928-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4760787928-5">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4760787928-6">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4760787928-6">]</span></code></pre><h2 id="map-expressions" class="section-heading">
│ │ │ │    <a href="#map-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Map Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <h3 id="creating-maps" class="section-heading">
│ │ │ │    <a href="#creating-maps" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating Maps</span>
│ │ │ │  </h3>
│ │ │ │  <p>Constructing a new map is done by letting an expression <code class="inline">K</code> be associated with
│ │ │ │ -another expression <code class="inline">V</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8177742676-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="8177742676-1">}</span></code></pre><p>New maps can include multiple associations at construction by listing every
│ │ │ │ -association:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6636300999-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="6636300999-1">}</span></code></pre><p>An empty map is constructed by not associating any terms with each other:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8167819920-1">#{</span><span class="p" data-group-id="8167819920-1">}</span></code></pre><p>All keys and values in the map are terms. Any expression is first evaluated and
│ │ │ │ +another expression <code class="inline">V</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7010162855-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="7010162855-1">}</span></code></pre><p>New maps can include multiple associations at construction by listing every
│ │ │ │ +association:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0620167667-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="0620167667-1">}</span></code></pre><p>An empty map is constructed by not associating any terms with each other:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3329523277-1">#{</span><span class="p" data-group-id="3329523277-1">}</span></code></pre><p>All keys and values in the map are terms. Any expression is first evaluated and
│ │ │ │  then the resulting terms are used as <em>key</em> and <em>value</em> respectively.</p><p>Keys and values are separated by the <code class="inline">=&gt;</code> arrow and associations are separated
│ │ │ │ -by a comma (<code class="inline">,</code>).</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5946396202-1">#{</span><span class="p" data-group-id="5946396202-1">}</span><span class="p">,</span><span class="w">                 </span><span class="c1">% empty map</span><span class="w">
│ │ │ │ -</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5946396202-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5946396202-3">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5946396202-3">&gt;&gt;</span><span class="p" data-group-id="5946396202-2">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% single association with literals</span><span class="w">
│ │ │ │ -</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5946396202-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="5946396202-4">}</span><span class="p">,</span><span class="w">   </span><span class="c1">% multiple associations with literals</span><span class="w">
│ │ │ │ -</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5946396202-5">#{</span><span class="ss">k</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5946396202-6">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="5946396202-6">}</span><span class="p" data-group-id="5946396202-5">}</span><span class="p">,</span><span class="w">       </span><span class="c1">% single association with variables</span><span class="w">
│ │ │ │ -</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5946396202-7">#{</span><span class="p" data-group-id="5946396202-8">{</span><span class="s">&quot;w&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5946396202-8">}</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="5946396202-9">(</span><span class="p" data-group-id="5946396202-9">)</span><span class="p" data-group-id="5946396202-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% compound key associated with an evaluated expression</span></code></pre><p>Here, <code class="inline">A</code> and <code class="inline">B</code> are any expressions and <code class="inline">M0</code> through <code class="inline">M4</code> are the resulting
│ │ │ │ -map terms.</p><p>If two matching keys are declared, the latter key takes precedence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6407292814-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="6407292814-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6407292814-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p" data-group-id="6407292814-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="6407292814-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="6407292814-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6407292814-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="6407292814-4">}</span></code></pre><p>The order in which the expressions constructing the keys (and their associated
│ │ │ │ +by a comma (<code class="inline">,</code>).</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7645547495-1">#{</span><span class="p" data-group-id="7645547495-1">}</span><span class="p">,</span><span class="w">                 </span><span class="c1">% empty map</span><span class="w">
│ │ │ │ +</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7645547495-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7645547495-3">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7645547495-3">&gt;&gt;</span><span class="p" data-group-id="7645547495-2">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% single association with literals</span><span class="w">
│ │ │ │ +</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7645547495-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7645547495-4">}</span><span class="p">,</span><span class="w">   </span><span class="c1">% multiple associations with literals</span><span class="w">
│ │ │ │ +</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7645547495-5">#{</span><span class="ss">k</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7645547495-6">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="7645547495-6">}</span><span class="p" data-group-id="7645547495-5">}</span><span class="p">,</span><span class="w">       </span><span class="c1">% single association with variables</span><span class="w">
│ │ │ │ +</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7645547495-7">#{</span><span class="p" data-group-id="7645547495-8">{</span><span class="s">&quot;w&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7645547495-8">}</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="7645547495-9">(</span><span class="p" data-group-id="7645547495-9">)</span><span class="p" data-group-id="7645547495-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% compound key associated with an evaluated expression</span></code></pre><p>Here, <code class="inline">A</code> and <code class="inline">B</code> are any expressions and <code class="inline">M0</code> through <code class="inline">M4</code> are the resulting
│ │ │ │ +map terms.</p><p>If two matching keys are declared, the latter key takes precedence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0948283141-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="0948283141-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0948283141-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p" data-group-id="0948283141-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="0948283141-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="0948283141-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0948283141-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="0948283141-4">}</span></code></pre><p>The order in which the expressions constructing the keys (and their associated
│ │ │ │  values) are evaluated is not defined. The syntactic order of the key-value pairs
│ │ │ │  in the construction is of no relevance, except in the recently mentioned case of
│ │ │ │  two matching keys.</p><h3 id="updating-maps" class="section-heading">
│ │ │ │    <a href="#updating-maps" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Updating Maps</span>
│ │ │ │  </h3>
│ │ │ │  <p>Updating a map has a similar syntax as constructing it.</p><p>An expression defining the map to be updated is put in front of the expression
│ │ │ │ -defining the keys to be updated and their respective values:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="8699585425-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="8699585425-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map and <code class="inline">K</code> and <code class="inline">V</code> are any expression.</p><p>If key <code class="inline">K</code> does not match any existing key in the map, a new association is
│ │ │ │ +defining the keys to be updated and their respective values:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="3577133573-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="3577133573-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map and <code class="inline">K</code> and <code class="inline">V</code> are any expression.</p><p>If key <code class="inline">K</code> does not match any existing key in the map, a new association is
│ │ │ │  created from key <code class="inline">K</code> to value <code class="inline">V</code>.</p><p>If key <code class="inline">K</code> matches an existing key in map <code class="inline">M</code>, its associated value is replaced
│ │ │ │  by the new value <code class="inline">V</code>. In both cases, the evaluated map expression returns a new
│ │ │ │ -map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p>To only update an existing value, the following syntax is used:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="3492109200-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="3492109200-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map, <code class="inline">V</code> is an expression and <code class="inline">K</code> is an expression
│ │ │ │ +map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p>To only update an existing value, the following syntax is used:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="1662222867-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="1662222867-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map, <code class="inline">V</code> is an expression and <code class="inline">K</code> is an expression
│ │ │ │  that evaluates to an existing key in <code class="inline">M</code>.</p><p>If key <code class="inline">K</code> does not match any existing keys in map <code class="inline">M</code>, an exception of type
│ │ │ │  <code class="inline">badkey</code> is raised at runtime. If a matching key <code class="inline">K</code> is present in map <code class="inline">M</code>,
│ │ │ │  its associated value is replaced by the new value <code class="inline">V</code>, and the evaluated map
│ │ │ │ -expression returns a new map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5132929623-1">#{</span><span class="p" data-group-id="5132929623-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M0</span><span class="p" data-group-id="5132929623-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5132929623-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="5132929623-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5132929623-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M2</span><span class="p" data-group-id="5132929623-4">#{</span><span class="s">&quot;function&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5132929623-5">(</span><span class="p" data-group-id="5132929623-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="5132929623-6">(</span><span class="p" data-group-id="5132929623-6">)</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="5132929623-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M3</span><span class="p" data-group-id="5132929623-7">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5132929623-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% &#39;a&#39; and &#39;b&#39; was added in `M1` and `M2`.</span></code></pre><p>Here <code class="inline">M0</code> is any map. It follows that <code class="inline">M1</code> through <code class="inline">M4</code> are maps as well.</p><p><em>More examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6752278642-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="6752278642-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6752278642-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="p" data-group-id="6752278642-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">M</span><span class="p" data-group-id="6752278642-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="6752278642-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6752278642-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="6752278642-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="n">M</span><span class="p" data-group-id="6752278642-5">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="6752278642-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6752278642-6">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="6752278642-6">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">M</span><span class="p" data-group-id="6752278642-7">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="6752278642-7">}</span><span class="p">.</span><span class="w">
│ │ │ │ +expression returns a new map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3477214365-1">#{</span><span class="p" data-group-id="3477214365-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M0</span><span class="p" data-group-id="3477214365-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3477214365-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="3477214365-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3477214365-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M2</span><span class="p" data-group-id="3477214365-4">#{</span><span class="s">&quot;function&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3477214365-5">(</span><span class="p" data-group-id="3477214365-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="3477214365-6">(</span><span class="p" data-group-id="3477214365-6">)</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="3477214365-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M3</span><span class="p" data-group-id="3477214365-7">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3477214365-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% &#39;a&#39; and &#39;b&#39; was added in `M1` and `M2`.</span></code></pre><p>Here <code class="inline">M0</code> is any map. It follows that <code class="inline">M1</code> through <code class="inline">M4</code> are maps as well.</p><p><em>More examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7750984192-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="7750984192-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7750984192-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="p" data-group-id="7750984192-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">M</span><span class="p" data-group-id="7750984192-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7750984192-3">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7750984192-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7750984192-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="n">M</span><span class="p" data-group-id="7750984192-5">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7750984192-5">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7750984192-6">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7750984192-6">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">M</span><span class="p" data-group-id="7750984192-7">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7750984192-7">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: bad argument</span></code></pre><p>As in construction, the order in which the key and value expressions are
│ │ │ │  evaluated is not defined. The syntactic order of the key-value pairs in the
│ │ │ │  update is of no relevance, except in the case where two keys match. In that
│ │ │ │  case, the latter value is used.</p><h3 id="maps-in-patterns" class="section-heading">
│ │ │ │    <a href="#maps-in-patterns" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Maps in Patterns</span>
│ │ │ │  </h3>
│ │ │ │ -<p>Matching of key-value associations from maps is done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8410218400-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="8410218400-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here <code class="inline">M</code> is any map. The key <code class="inline">K</code> must be a
│ │ │ │ +<p>Matching of key-value associations from maps is done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6338883485-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="6338883485-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here <code class="inline">M</code> is any map. The key <code class="inline">K</code> must be a
│ │ │ │  <a href="expressions.xhtml#guard-expressions">guard expression</a>, with all variables already
│ │ │ │  bound. <code class="inline">V</code> can be any pattern with either bound or unbound variables.</p><p>If the variable <code class="inline">V</code> is unbound, it becomes bound to the value associated with
│ │ │ │  the key <code class="inline">K</code>, which must exist in the map <code class="inline">M</code>. If the variable <code class="inline">V</code> is bound, it
│ │ │ │  must match the value associated with <code class="inline">K</code> in <code class="inline">M</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 23, the expression defining the key <code class="inline">K</code> was restricted to be
│ │ │ │ -either a single variable or a literal.</p></section><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0440629822-1">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0440629822-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0440629822-2">}</span><span class="p" data-group-id="0440629822-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0440629822-3">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0440629822-4">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0440629822-4">}</span><span class="p" data-group-id="0440629822-3">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="0440629822-5">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="0440629822-6">{</span><span class="mi">1</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="0440629822-6">}</span><span class="p" data-group-id="0440629822-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0440629822-7">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0440629822-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0440629822-8">}</span><span class="p" data-group-id="0440629822-7">}</span><span class="w">
│ │ │ │ +either a single variable or a literal.</p></section><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2342094903-1">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2342094903-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2342094903-2">}</span><span class="p" data-group-id="2342094903-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2342094903-3">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2342094903-4">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2342094903-4">}</span><span class="p" data-group-id="2342094903-3">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="2342094903-5">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2342094903-6">{</span><span class="mi">1</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="2342094903-6">}</span><span class="p" data-group-id="2342094903-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2342094903-7">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2342094903-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2342094903-8">}</span><span class="p" data-group-id="2342094903-7">}</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mi">2</span><span class="p">.</span></code></pre><p>This binds variable <code class="inline">B</code> to integer <code class="inline">2</code>.</p><p>Similarly, multiple values from the map can be matched:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2208301823-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="2208301823-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here keys <code class="inline">K1</code> through <code class="inline">Kn</code> are any expressions with literals or bound
│ │ │ │ +</span><span class="mi">2</span><span class="p">.</span></code></pre><p>This binds variable <code class="inline">B</code> to integer <code class="inline">2</code>.</p><p>Similarly, multiple values from the map can be matched:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2594460831-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="2594460831-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here keys <code class="inline">K1</code> through <code class="inline">Kn</code> are any expressions with literals or bound
│ │ │ │  variables. If all key expressions evaluate successfully and all keys
│ │ │ │  exist in map <code class="inline">M</code>, all variables in <code class="inline">V1 .. Vn</code> is matched to the
│ │ │ │  associated values of their respective keys.</p><p>If the matching conditions are not met the match fails.</p><p>Note that when matching a map, only the <code class="inline">:=</code> operator (not the <code class="inline">=&gt;</code>) is allowed
│ │ │ │  as a delimiter for the associations.</p><p>The order in which keys are declared in matching has no relevance.</p><p>Duplicate keys are allowed in matching and match each pattern associated to the
│ │ │ │ -keys:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8444143914-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V2</span><span class="p" data-group-id="8444143914-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>The empty map literal (<code class="inline">#{}</code>) matches any map when used as a pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1673794253-1">#{</span><span class="p" data-group-id="1673794253-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>This expression matches if the expression <code class="inline">Expr</code> is of type map, otherwise it
│ │ │ │ -fails with an exception <code class="inline">badmatch</code>.</p><p>Here the key to be retrieved is constructed from an expression:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9869486180-1">#{</span><span class="p" data-group-id="9869486180-2">{</span><span class="ss">tag</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="9869486180-3">(</span><span class="n">List</span><span class="p" data-group-id="9869486180-3">)</span><span class="p" data-group-id="9869486180-2">}</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="9869486180-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map</span></code></pre><p><code class="inline">List</code> must be an already bound variable.</p><h4>Matching Syntax</h4><p>Matching of literals as keys are allowed in function heads:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% only start if not_started</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="2313615386-1">(</span><span class="ss">start</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2313615386-2">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">not_started</span><span class="p" data-group-id="2313615386-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="2313615386-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +keys:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8933935133-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V2</span><span class="p" data-group-id="8933935133-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>The empty map literal (<code class="inline">#{}</code>) matches any map when used as a pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2339530837-1">#{</span><span class="p" data-group-id="2339530837-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>This expression matches if the expression <code class="inline">Expr</code> is of type map, otherwise it
│ │ │ │ +fails with an exception <code class="inline">badmatch</code>.</p><p>Here the key to be retrieved is constructed from an expression:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3380299833-1">#{</span><span class="p" data-group-id="3380299833-2">{</span><span class="ss">tag</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="3380299833-3">(</span><span class="n">List</span><span class="p" data-group-id="3380299833-3">)</span><span class="p" data-group-id="3380299833-2">}</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="3380299833-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map</span></code></pre><p><code class="inline">List</code> must be an already bound variable.</p><h4>Matching Syntax</h4><p>Matching of literals as keys are allowed in function heads:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% only start if not_started</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="7048287423-1">(</span><span class="ss">start</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7048287423-2">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">not_started</span><span class="p" data-group-id="7048287423-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7048287423-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2313615386-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="2313615386-4">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="2313615386-4">}</span><span class="p" data-group-id="2313615386-3">}</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="7048287423-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7048287423-4">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="7048287423-4">}</span><span class="p" data-group-id="7048287423-3">}</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% only change if started</span><span class="w">
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="2313615386-5">(</span><span class="ss">change</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2313615386-6">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="2313615386-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="2313615386-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="7048287423-5">(</span><span class="ss">change</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7048287423-6">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="7048287423-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7048287423-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2313615386-7">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="2313615386-8">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">changed</span><span class="p" data-group-id="2313615386-8">}</span><span class="p" data-group-id="2313615386-7">}</span><span class="p">;</span></code></pre><h3 id="maps-in-guards" class="section-heading">
│ │ │ │ +    </span><span class="p" data-group-id="7048287423-7">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7048287423-8">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">changed</span><span class="p" data-group-id="7048287423-8">}</span><span class="p" data-group-id="7048287423-7">}</span><span class="p">;</span></code></pre><h3 id="maps-in-guards" class="section-heading">
│ │ │ │    <a href="#maps-in-guards" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Maps in Guards</span>
│ │ │ │  </h3>
│ │ │ │  <p>Maps are allowed in guards as long as all subexpressions are valid guard
│ │ │ │  expressions.</p><p>The following guard BIFs handle maps:</p><ul><li><a href="../../../lib/../erts/doc/html/erlang.html#is_map/1">is_map/1</a> in the <code class="inline">erlang</code> module</li><li><a href="../../../lib/../erts/doc/html/erlang.html#is_map_key/2">is_map_key/2</a> in the <code class="inline">erlang</code> module</li><li><a href="../../../lib/../erts/doc/html/erlang.html#map_get/2">map_get/2</a> in the <code class="inline">erlang</code> module</li><li><a href="../../../lib/../erts/doc/html/erlang.html#map_size/1">map_size/1</a> in the <code class="inline">erlang</code> module</li></ul><h2 id="bit-syntax-expressions" class="section-heading">
│ │ │ │    <a href="#bit-syntax-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Bit Syntax Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <p>The bit syntax operates on <em>bit strings</em>. A bit string is a sequence of bits
│ │ │ │ -ordered from the most significant bit to the least significant bit.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2107495508-1">&lt;&lt;</span><span class="p" data-group-id="2107495508-1">&gt;&gt;</span><span class="w">  </span><span class="c1">% The empty bit string, zero length</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2107495508-2">&lt;&lt;</span><span class="n">E1</span><span class="p" data-group-id="2107495508-2">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2107495508-3">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">En</span><span class="p" data-group-id="2107495508-3">&gt;&gt;</span></code></pre><p>Each element <code class="inline">Ei</code> specifies a <em>segment</em> of the bit string. The segments are
│ │ │ │ +ordered from the most significant bit to the least significant bit.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8375286021-1">&lt;&lt;</span><span class="p" data-group-id="8375286021-1">&gt;&gt;</span><span class="w">  </span><span class="c1">% The empty bit string, zero length</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8375286021-2">&lt;&lt;</span><span class="n">E1</span><span class="p" data-group-id="8375286021-2">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8375286021-3">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">En</span><span class="p" data-group-id="8375286021-3">&gt;&gt;</span></code></pre><p>Each element <code class="inline">Ei</code> specifies a <em>segment</em> of the bit string. The segments are
│ │ │ │  ordered left to right from the most significant bit to the least significant bit
│ │ │ │  of the bit string.</p><p>Each segment specification <code class="inline">Ei</code> is a value, whose default type is <code class="inline">integer</code>,
│ │ │ │  followed by an optional <em>size expression</em> and an optional <em>type specifier list</em>.</p><pre><code class="makeup erlang" translate="no"><span class="n">Ei</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ │       </span><span class="n">Value</span><span class="p">:</span><span class="n">Size</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ │       </span><span class="n">Value</span><span class="o">/</span><span class="n">TypeSpecifierList</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ │       </span><span class="n">Value</span><span class="p">:</span><span class="n">Size</span><span class="o">/</span><span class="n">TypeSpecifierList</span></code></pre><p>When used in a bit string construction, <code class="inline">Value</code> is an expression that is to
│ │ │ │  evaluate to an integer, float, or bit string. If the expression is not a single
│ │ │ │ @@ -703,34 +703,34 @@
│ │ │ │  <a href="expressions.xhtml#guard-expressions">guard expression</a> that evaluates to an
│ │ │ │  integer. All variables in the guard expression must be already bound.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable
│ │ │ │  bound to an integer.</p></section><p>The value of <code class="inline">Size</code> specifies the size of the segment in units (see below). The
│ │ │ │  default value depends on the type (see below):</p><ul><li>For <code class="inline">integer</code> it is 8.</li><li>For <code class="inline">float</code> it is 64.</li><li>For <code class="inline">binary</code> and <code class="inline">bitstring</code> it is the whole binary or bit string.</li></ul><p>In matching, the default value for a binary or bit string segment is only valid
│ │ │ │  for the last element. All other bit string or binary elements in the matching
│ │ │ │  must have a size specification.</p><p><a href="" id="binaries"></a></p><p><strong>Binaries</strong></p><p>A bit string with a length that is a multiple of 8 bits is known as a <em>binary</em>,
│ │ │ │  which is the most common and useful type of bit string.</p><p>A binary has a canonical representation in memory. Here follows a sequence of
│ │ │ │ -bytes where each byte's value is its sequence number:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5028319236-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p" data-group-id="5028319236-1">&gt;&gt;</span></code></pre><p>Bit strings are a later generalization of binaries, so many texts and much
│ │ │ │ -information about binaries apply just as well for bit strings.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8060529751-1">&lt;&lt;</span><span class="n">A</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8060529751-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8060529751-2">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="8060529751-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +bytes where each byte's value is its sequence number:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4373630194-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p" data-group-id="4373630194-1">&gt;&gt;</span></code></pre><p>Bit strings are a later generalization of binaries, so many texts and much
│ │ │ │ +information about binaries apply just as well for bit strings.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3464766481-1">&lt;&lt;</span><span class="n">A</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3464766481-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3464766481-2">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="3464766481-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">* 1:3: a binary field without size is only allowed at the end of a binary pattern</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="8060529751-3">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">3</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8060529751-3">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8060529751-4">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="8060529751-4">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8060529751-5">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="8060529751-5">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="3464766481-3">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">3</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3464766481-3">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3464766481-4">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="3464766481-4">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3464766481-5">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="3464766481-5">&gt;&gt;</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8060529751-6">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="8060529751-6">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3464766481-6">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3464766481-6">&gt;&gt;</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">4&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8060529751-7">&lt;&lt;</span><span class="s">&quot;de&quot;</span><span class="p" data-group-id="8060529751-7">&gt;&gt;</span></code></pre><p>For the <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code> types, <code class="inline">Size</code> must not be given. The size
│ │ │ │ +</span><span class="p" data-group-id="3464766481-7">&lt;&lt;</span><span class="s">&quot;de&quot;</span><span class="p" data-group-id="3464766481-7">&gt;&gt;</span></code></pre><p>For the <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code> types, <code class="inline">Size</code> must not be given. The size
│ │ │ │  of the segment is implicitly determined by the type and value itself.</p><p><code class="inline">TypeSpecifierList</code> is a list of type specifiers, in any order, separated by
│ │ │ │  hyphens (-). Default values are used for any omitted type specifiers.</p><ul><li><p><strong><code class="inline">Type</code>= <code class="inline">integer</code> | <code class="inline">float</code> | <code class="inline">binary</code> | <code class="inline">bytes</code> | <code class="inline">bitstring</code> | <code class="inline">bits</code> |
│ │ │ │  <code class="inline">utf8</code> | <code class="inline">utf16</code> | <code class="inline">utf32</code></strong> - The default is <code class="inline">integer</code>. <code class="inline">bytes</code> is a
│ │ │ │  shorthand for <code class="inline">binary</code> and <code class="inline">bits</code> is a shorthand for <code class="inline">bitstring</code>. See below
│ │ │ │  for more information about the <code class="inline">utf</code> types.</p></li><li><p><strong><code class="inline">Signedness</code>= <code class="inline">signed</code> | <code class="inline">unsigned</code></strong> - Only matters for matching and when
│ │ │ │  the type is <code class="inline">integer</code>. The default is <code class="inline">unsigned</code>.</p></li><li><p><strong><code class="inline">Endianness</code>= <code class="inline">big</code> | <code class="inline">little</code> | <code class="inline">native</code></strong> - Specifies byte level (octet
│ │ │ │  level) endianness (byte order). Native-endian means that the endianness is
│ │ │ │  resolved at load time to be either big-endian or little-endian, depending on
│ │ │ │  what is native for the CPU that the Erlang machine is run on. Endianness only
│ │ │ │  matters when the <strong>Type</strong> is either <code class="inline">integer</code>, <code class="inline">utf16</code>, <code class="inline">utf32</code>, or <code class="inline">float</code>. The
│ │ │ │ -default is <code class="inline">big</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1986261396-1">&lt;&lt;</span><span class="mi">16#1234</span><span class="p">:</span><span class="mi">16</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="1986261396-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1986261396-2">&lt;&lt;</span><span class="mi">16#3412</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1986261396-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1986261396-3">&lt;&lt;</span><span class="mi">16#34</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">16#12</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="1986261396-3">&gt;&gt;</span></code></pre></li><li><p><strong><code class="inline">Unit</code>= <code class="inline">unit:IntegerLiteral</code></strong> - The allowed range is 1 through 256.
│ │ │ │ +default is <code class="inline">big</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0308035249-1">&lt;&lt;</span><span class="mi">16#1234</span><span class="p">:</span><span class="mi">16</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="0308035249-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0308035249-2">&lt;&lt;</span><span class="mi">16#3412</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0308035249-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0308035249-3">&lt;&lt;</span><span class="mi">16#34</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">16#12</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0308035249-3">&gt;&gt;</span></code></pre></li><li><p><strong><code class="inline">Unit</code>= <code class="inline">unit:IntegerLiteral</code></strong> - The allowed range is 1 through 256.
│ │ │ │  Defaults to 1 for <code class="inline">integer</code>, <code class="inline">float</code>, and <code class="inline">bitstring</code>, and to 8 for <code class="inline">binary</code>.
│ │ │ │  For types <code class="inline">bitstring</code>, <code class="inline">bits</code>, and <code class="inline">bytes</code>, it is not allowed to specify a
│ │ │ │  unit value different from the default value. No unit specifier must be given
│ │ │ │  for the types <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code>.</p></li></ul><h3 id="integer-segments" class="section-heading">
│ │ │ │    <a href="#integer-segments" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -755,41 +755,41 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Binary segments</span>
│ │ │ │  </h3>
│ │ │ │  <p>In this section, the phrase &quot;binary segment&quot; refers to any one of the segment
│ │ │ │  types <code class="inline">binary</code>, <code class="inline">bitstring</code>, <code class="inline">bytes</code>, and <code class="inline">bits</code>.</p><p>See also the paragraphs about <a href="expressions.xhtml#binaries">Binaries</a>.</p><p>When constructing binaries and no size is specified for a binary segment, the
│ │ │ │  entire binary value is interpolated into the binary being constructed. However,
│ │ │ │  the size in bits of the binary being interpolated must be evenly divisible by
│ │ │ │ -the unit value for the segment; otherwise an exception is raised.</p><p>For example, the following examples all succeed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6108023806-1">&lt;&lt;</span><span class="p" data-group-id="6108023806-2">(</span><span class="p" data-group-id="6108023806-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6108023806-3">&gt;&gt;</span><span class="p" data-group-id="6108023806-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="6108023806-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6108023806-4">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6108023806-4">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="6108023806-5">&lt;&lt;</span><span class="p" data-group-id="6108023806-6">(</span><span class="p" data-group-id="6108023806-7">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6108023806-7">&gt;&gt;</span><span class="p" data-group-id="6108023806-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6108023806-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6108023806-8">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6108023806-8">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="6108023806-9">&lt;&lt;</span><span class="p" data-group-id="6108023806-10">(</span><span class="p" data-group-id="6108023806-11">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6108023806-11">&gt;&gt;</span><span class="p" data-group-id="6108023806-10">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6108023806-9">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6108023806-12">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6108023806-12">&gt;&gt;</span></code></pre><p>The first two examples have a unit value of 1 for the segment, while the third
│ │ │ │ +the unit value for the segment; otherwise an exception is raised.</p><p>For example, the following examples all succeed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9302129265-1">&lt;&lt;</span><span class="p" data-group-id="9302129265-2">(</span><span class="p" data-group-id="9302129265-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9302129265-3">&gt;&gt;</span><span class="p" data-group-id="9302129265-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="9302129265-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9302129265-4">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9302129265-4">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="9302129265-5">&lt;&lt;</span><span class="p" data-group-id="9302129265-6">(</span><span class="p" data-group-id="9302129265-7">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9302129265-7">&gt;&gt;</span><span class="p" data-group-id="9302129265-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="9302129265-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9302129265-8">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9302129265-8">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="9302129265-9">&lt;&lt;</span><span class="p" data-group-id="9302129265-10">(</span><span class="p" data-group-id="9302129265-11">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9302129265-11">&gt;&gt;</span><span class="p" data-group-id="9302129265-10">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9302129265-9">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9302129265-12">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9302129265-12">&gt;&gt;</span></code></pre><p>The first two examples have a unit value of 1 for the segment, while the third
│ │ │ │  segment has a unit value of 8.</p><p>Attempting to interpolate a bit string of size 1 into a binary segment with unit
│ │ │ │ -8 (the default unit for <code class="inline">binary</code>) fails as shown in this example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1801166654-1">&lt;&lt;</span><span class="p" data-group-id="1801166654-2">(</span><span class="p" data-group-id="1801166654-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1801166654-3">&gt;&gt;</span><span class="p" data-group-id="1801166654-2">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1801166654-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="gt">** exception error: bad argument</span></code></pre><p>For the construction to succeed, the unit value of the segment must be 1:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="6443636041-1">&lt;&lt;</span><span class="p" data-group-id="6443636041-2">(</span><span class="p" data-group-id="6443636041-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6443636041-3">&gt;&gt;</span><span class="p" data-group-id="6443636041-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="6443636041-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6443636041-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6443636041-4">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="6443636041-5">&lt;&lt;</span><span class="p" data-group-id="6443636041-6">(</span><span class="p" data-group-id="6443636041-7">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6443636041-7">&gt;&gt;</span><span class="p" data-group-id="6443636041-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6443636041-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6443636041-8">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6443636041-8">&gt;&gt;</span></code></pre><p>Similarly, when matching a binary segment with no size specified, the match
│ │ │ │ +8 (the default unit for <code class="inline">binary</code>) fails as shown in this example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0437825418-1">&lt;&lt;</span><span class="p" data-group-id="0437825418-2">(</span><span class="p" data-group-id="0437825418-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0437825418-3">&gt;&gt;</span><span class="p" data-group-id="0437825418-2">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0437825418-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gt">** exception error: bad argument</span></code></pre><p>For the construction to succeed, the unit value of the segment must be 1:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4978204289-1">&lt;&lt;</span><span class="p" data-group-id="4978204289-2">(</span><span class="p" data-group-id="4978204289-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4978204289-3">&gt;&gt;</span><span class="p" data-group-id="4978204289-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="4978204289-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4978204289-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4978204289-4">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="4978204289-5">&lt;&lt;</span><span class="p" data-group-id="4978204289-6">(</span><span class="p" data-group-id="4978204289-7">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4978204289-7">&gt;&gt;</span><span class="p" data-group-id="4978204289-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4978204289-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4978204289-8">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4978204289-8">&gt;&gt;</span></code></pre><p>Similarly, when matching a binary segment with no size specified, the match
│ │ │ │  succeeds if and only if the size in bits of the rest of the binary is evenly
│ │ │ │ -divisible by the unit value:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0139247048-1">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0139247048-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0139247048-2">&lt;&lt;</span><span class="s">&quot;&quot;</span><span class="p" data-group-id="0139247048-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0139247048-3">&lt;&lt;</span><span class="p" data-group-id="0139247048-3">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="0139247048-4">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0139247048-4">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0139247048-5">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="0139247048-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +divisible by the unit value:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0773156531-1">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0773156531-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0773156531-2">&lt;&lt;</span><span class="s">&quot;&quot;</span><span class="p" data-group-id="0773156531-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0773156531-3">&lt;&lt;</span><span class="p" data-group-id="0773156531-3">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="0773156531-4">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0773156531-4">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0773156531-5">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="0773156531-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value &lt;&lt;&quot;a&quot;&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="0139247048-6">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0139247048-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0139247048-7">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="0139247048-7">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0139247048-8">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="0139247048-8">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="0139247048-9">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0139247048-9">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0139247048-10">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0139247048-10">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="0773156531-6">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0773156531-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0773156531-7">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="0773156531-7">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0773156531-8">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="0773156531-8">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="0773156531-9">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0773156531-9">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0773156531-10">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="0773156531-10">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: no match of right hand side value &lt;&lt;&quot;abc&quot;&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="0139247048-11">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0139247048-11">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0139247048-12">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="0139247048-12">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0139247048-13">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="0139247048-13">&gt;&gt;</span></code></pre><p>When a size is explicitly specified for a binary segment, the segment size in
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="0773156531-11">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0773156531-11">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0773156531-12">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="0773156531-12">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0773156531-13">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="0773156531-13">&gt;&gt;</span></code></pre><p>When a size is explicitly specified for a binary segment, the segment size in
│ │ │ │  bits is the value of <code class="inline">Size</code> multiplied by the default or explicit unit value.</p><p>When constructing binaries, the size of the binary being interpolated into the
│ │ │ │ -constructed binary must be at least as large as the size of the binary segment.</p><p><strong>Examples:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2348344503-1">&lt;&lt;</span><span class="p" data-group-id="2348344503-2">(</span><span class="p" data-group-id="2348344503-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2348344503-3">&gt;&gt;</span><span class="p" data-group-id="2348344503-2">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2348344503-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2348344503-4">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="2348344503-4">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="2348344503-5">&lt;&lt;</span><span class="p" data-group-id="2348344503-6">(</span><span class="p" data-group-id="2348344503-7">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="2348344503-7">&gt;&gt;</span><span class="p" data-group-id="2348344503-6">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2348344503-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +constructed binary must be at least as large as the size of the binary segment.</p><p><strong>Examples:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7955153915-1">&lt;&lt;</span><span class="p" data-group-id="7955153915-2">(</span><span class="p" data-group-id="7955153915-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="7955153915-3">&gt;&gt;</span><span class="p" data-group-id="7955153915-2">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7955153915-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7955153915-4">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="7955153915-4">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="7955153915-5">&lt;&lt;</span><span class="p" data-group-id="7955153915-6">(</span><span class="p" data-group-id="7955153915-7">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="7955153915-7">&gt;&gt;</span><span class="p" data-group-id="7955153915-6">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7955153915-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: construction of binary failed
│ │ │ │          *** segment 1 of type &#39;binary&#39;: the value &lt;&lt;&quot;a&quot;&gt;&gt; is shorter than the size of the segment</span></code></pre><h3 id="unicode-segments" class="section-heading">
│ │ │ │    <a href="#unicode-segments" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Unicode segments</span>
│ │ │ │  </h3>
│ │ │ │ @@ -805,78 +805,78 @@
│ │ │ │  range <code class="inline">0</code> through <code class="inline">16#D7FF</code> or <code class="inline">16#E000</code> through <code class="inline">16#10FFFF</code>. The match fails if the
│ │ │ │  returned value falls outside those ranges.</p><p>A segment of type <code class="inline">utf8</code> matches 1-4 bytes in the bit string, if the bit string
│ │ │ │  at the match position contains a valid UTF-8 sequence. (See RFC-3629 or the
│ │ │ │  Unicode standard.)</p><p>A segment of type <code class="inline">utf16</code> can match 2 or 4 bytes in the bit string. The match
│ │ │ │  fails if the bit string at the match position does not contain a legal UTF-16
│ │ │ │  encoding of a Unicode code point. (See RFC-2781 or the Unicode standard.)</p><p>A segment of type <code class="inline">utf32</code> can match 4 bytes in the bit string in the same way as
│ │ │ │  an <code class="inline">integer</code> segment matches 32 bits. The match fails if the resulting integer
│ │ │ │ -is outside the legal ranges previously mentioned.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3353423026-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="3353423026-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="3353423026-2">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3353423026-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3353423026-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-4">&lt;&lt;</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="3353423026-4">&gt;&gt;</span><span class="w">
│ │ │ │ +is outside the legal ranges previously mentioned.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1676997917-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="1676997917-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="1676997917-2">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1676997917-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="1676997917-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-4">&lt;&lt;</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="1676997917-4">&gt;&gt;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3353423026-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="3353423026-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-6">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="3353423026-6">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="3353423026-7">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="3353423026-7">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3353423026-8">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="3353423026-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-9">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="3353423026-9">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1676997917-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1676997917-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-6">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="1676997917-6">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="1676997917-7">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1676997917-7">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1676997917-8">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1676997917-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-9">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="1676997917-9">&gt;&gt;</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">5&gt; </span><span class="n">C</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="p" data-group-id="3353423026-10">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="n">E</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="3353423026-10">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3353423026-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="3353423026-11">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-12">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="3353423026-12">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="p" data-group-id="1676997917-10">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="n">E</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="1676997917-10">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1676997917-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1676997917-11">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-12">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="1676997917-12">&gt;&gt;</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">7&gt; </span><span class="n">D</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">273</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">8&gt; </span><span class="n">F</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="p" data-group-id="3353423026-13">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">H</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3353423026-13">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3353423026-14">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="3353423026-14">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-15">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="3353423026-15">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="p" data-group-id="1676997917-13">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">H</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1676997917-13">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1676997917-14">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1676997917-14">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-15">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="1676997917-15">&gt;&gt;</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">10&gt; </span><span class="n">H</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-16">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="3353423026-16">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">11&gt; </span><span class="p" data-group-id="3353423026-17">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">J</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="3353423026-17">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3353423026-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="3353423026-18">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-19">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="3353423026-19">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-16">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="1676997917-16">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">11&gt; </span><span class="p" data-group-id="1676997917-17">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">J</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="1676997917-17">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1676997917-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="1676997917-18">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-19">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="1676997917-19">&gt;&gt;</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">12&gt; </span><span class="n">J</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-20">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="3353423026-20">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-20">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="1676997917-20">&gt;&gt;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">13</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="3353423026-21">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="3353423026-21">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-22">&lt;&lt;</span><span class="mi">208</span><span class="p">,</span><span class="mi">128</span><span class="p" data-group-id="3353423026-22">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="mi">13</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="1676997917-21">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="1676997917-21">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-22">&lt;&lt;</span><span class="mi">208</span><span class="p">,</span><span class="mi">128</span><span class="p" data-group-id="1676997917-22">&gt;&gt;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">14</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="3353423026-23">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">:</span><span class="mi">7</span><span class="p" data-group-id="3353423026-23">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-24">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="3353423026-24">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">15&gt; </span><span class="p" data-group-id="3353423026-25">&lt;&lt;</span><span class="mi">16#123</span><span class="p">:</span><span class="mi">12</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="3353423026-25">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3353423026-26">&lt;&lt;</span><span class="mi">16#231</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="3353423026-26">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3353423026-27">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="3353423026-27">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3353423026-28">&lt;&lt;</span><span class="mi">35</span><span class="p">,</span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="3353423026-28">&gt;&gt;</span></code></pre><p>Notice that bit string patterns cannot be nested.</p><p>Notice also that &quot;<code class="inline">B=&lt;&lt;1&gt;&gt;</code>&quot; is interpreted as &quot;<code class="inline">B =&lt; &lt;1&gt;&gt;</code>&quot; which is a syntax
│ │ │ │ +</span><span class="mi">14</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="1676997917-23">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">:</span><span class="mi">7</span><span class="p" data-group-id="1676997917-23">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-24">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="1676997917-24">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">15&gt; </span><span class="p" data-group-id="1676997917-25">&lt;&lt;</span><span class="mi">16#123</span><span class="p">:</span><span class="mi">12</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="1676997917-25">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1676997917-26">&lt;&lt;</span><span class="mi">16#231</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="1676997917-26">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1676997917-27">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="1676997917-27">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1676997917-28">&lt;&lt;</span><span class="mi">35</span><span class="p">,</span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="1676997917-28">&gt;&gt;</span></code></pre><p>Notice that bit string patterns cannot be nested.</p><p>Notice also that &quot;<code class="inline">B=&lt;&lt;1&gt;&gt;</code>&quot; is interpreted as &quot;<code class="inline">B =&lt; &lt;1&gt;&gt;</code>&quot; which is a syntax
│ │ │ │  error. The correct way is to write a space after <code class="inline">=</code>: &quot;<code class="inline">B = &lt;&lt;1&gt;&gt;</code>.</p><p>More examples are provided in <a href="../../../lib/../system/doc/html/bit_syntax.xhtml">Programming Examples</a>.</p><h2 id="fun-expressions" class="section-heading">
│ │ │ │    <a href="#fun-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Fun Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">fun</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9811119268-1">[</span><span class="n">Name</span><span class="p" data-group-id="9811119268-1">]</span><span class="p" data-group-id="9811119268-2">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="9811119268-2">)</span><span class="w"> </span><span class="p" data-group-id="9811119268-3">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9811119268-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5451464862-1">[</span><span class="n">Name</span><span class="p" data-group-id="5451464862-1">]</span><span class="p" data-group-id="5451464862-2">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="5451464862-2">)</span><span class="w"> </span><span class="p" data-group-id="5451464862-3">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="5451464862-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9811119268-4">[</span><span class="n">Name</span><span class="p" data-group-id="9811119268-4">]</span><span class="p" data-group-id="9811119268-5">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="9811119268-5">)</span><span class="w"> </span><span class="p" data-group-id="9811119268-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="9811119268-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5451464862-4">[</span><span class="n">Name</span><span class="p" data-group-id="5451464862-4">]</span><span class="p" data-group-id="5451464862-5">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="5451464862-5">)</span><span class="w"> </span><span class="p" data-group-id="5451464862-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="5451464862-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                </span><span class="n">BodyK</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>A fun expression begins with the keyword <code class="inline">fun</code> and ends with the keyword <code class="inline">end</code>.
│ │ │ │  Between them is to be a function declaration, similar to a
│ │ │ │  <a href="ref_man_functions.xhtml#function-declaration-syntax">regular function declaration</a>,
│ │ │ │  except that the function name is optional and is to be a variable, if any.</p><p>Variables in a fun head shadow the function name and both shadow variables in
│ │ │ │  the function clause surrounding the fun expression. Variables bound in a fun
│ │ │ │ -body are local to the fun body.</p><p>The return value of the expression is the resulting fun.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7060243533-1">(</span><span class="n">X</span><span class="p" data-group-id="7060243533-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +body are local to the fun body.</p><p>The return value of the expression is the resulting fun.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5019383488-1">(</span><span class="n">X</span><span class="p" data-group-id="5019383488-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="7060243533-2">(</span><span class="mi">2</span><span class="p" data-group-id="7060243533-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="5019383488-2">(</span><span class="mi">2</span><span class="p" data-group-id="5019383488-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="n">Fun2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7060243533-3">(</span><span class="n">X</span><span class="p" data-group-id="7060243533-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="o">&gt;=</span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">gt</span><span class="p">;</span><span class="w"> </span><span class="p" data-group-id="7060243533-4">(</span><span class="n">X</span><span class="p" data-group-id="7060243533-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">lt</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="n">Fun2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5019383488-3">(</span><span class="n">X</span><span class="p" data-group-id="5019383488-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="o">&gt;=</span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">gt</span><span class="p">;</span><span class="w"> </span><span class="p" data-group-id="5019383488-4">(</span><span class="n">X</span><span class="p" data-group-id="5019383488-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">lt</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">Fun2</span><span class="p" data-group-id="7060243533-5">(</span><span class="mi">7</span><span class="p" data-group-id="7060243533-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">Fun2</span><span class="p" data-group-id="5019383488-5">(</span><span class="mi">7</span><span class="p" data-group-id="5019383488-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">gt</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="n">Fun3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="7060243533-6">(</span><span class="mi">1</span><span class="p" data-group-id="7060243533-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="7060243533-7">(</span><span class="n">X</span><span class="p" data-group-id="7060243533-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="7060243533-8">(</span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7060243533-8">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="n">Fun3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="5019383488-6">(</span><span class="mi">1</span><span class="p" data-group-id="5019383488-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="5019383488-7">(</span><span class="n">X</span><span class="p" data-group-id="5019383488-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="5019383488-8">(</span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5019383488-8">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="n">Fun3</span><span class="p" data-group-id="7060243533-9">(</span><span class="mi">4</span><span class="p" data-group-id="7060243533-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="n">Fun3</span><span class="p" data-group-id="5019383488-9">(</span><span class="mi">4</span><span class="p" data-group-id="5019383488-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">24</span></code></pre><p>The following fun expressions are also allowed:</p><pre><code class="makeup erlang" translate="no"><span class="k">fun</span><span class="w"> </span><span class="n">Name</span><span class="o">/</span><span class="n">Arity</span><span class="w">
│ │ │ │  </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">Name</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In <code class="inline">Name/Arity</code>, <code class="inline">Name</code> is an atom and <code class="inline">Arity</code> is an integer. <code class="inline">Name/Arity</code> must
│ │ │ │ -specify an existing local function. The expression is syntactic sugar for:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="9348083045-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="9348083045-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9348083045-2">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="9348083045-2">)</span><span class="w"> </span><span class="k">end</span></code></pre><p>In <code class="inline">Module:Name/Arity</code>, <code class="inline">Module</code>, and <code class="inline">Name</code> are atoms and <code class="inline">Arity</code> is an
│ │ │ │ +specify an existing local function. The expression is syntactic sugar for:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1356820329-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="1356820329-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="1356820329-2">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="1356820329-2">)</span><span class="w"> </span><span class="k">end</span></code></pre><p>In <code class="inline">Module:Name/Arity</code>, <code class="inline">Module</code>, and <code class="inline">Name</code> are atoms and <code class="inline">Arity</code> is an
│ │ │ │  integer. <code class="inline">Module</code>, <code class="inline">Name</code>, and <code class="inline">Arity</code> can also be variables. A fun defined in
│ │ │ │  this way refers to the function <code class="inline">Name</code> with arity <code class="inline">Arity</code> in the <em>latest</em>
│ │ │ │  version of module <code class="inline">Module</code>. A fun defined in this way is not dependent on the
│ │ │ │  code for the module in which it is defined.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R15, <code class="inline">Module</code>, <code class="inline">Name</code>, and <code class="inline">Arity</code> were not allowed to be
│ │ │ │  variables.</p></section><p>More examples are provided in <a href="../../../lib/../system/doc/html/funs.xhtml">Programming Examples</a>.</p><h2 id="catch-and-throw" class="section-heading">
│ │ │ │    <a href="#catch-and-throw" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -886,35 +886,35 @@
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">catch</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>Returns the value of <code class="inline">Expr</code> unless an exception is raised during the evaluation. In
│ │ │ │  that case, the exception is caught. The return value depends on the class of the
│ │ │ │  exception:</p><ul><li><p><strong><code class="inline">error</code></strong> (a run-time error or the code called <a href="../../../lib/../erts/doc/html/erlang.html#error/1"><code class="inline">error(Term)</code></a>) -
│ │ │ │  <code class="inline">{'EXIT',{Reason,Stack}}</code> is returned.</p></li><li><p><strong><code class="inline">exit</code></strong> (the code called <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(Term)</code></a>) - <code class="inline">{'EXIT',Term}</code> is returned.</p></li><li><p><strong><code class="inline">throw</code></strong> (the code called <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw(Term)</code></a>): <code class="inline">Term</code> is returned.</p></li></ul><p><code class="inline">Reason</code> depends on the type of error that occurred, and <code class="inline">Stack</code> is the stack of
│ │ │ │  recent function calls, see <a href="errors.xhtml#exit_reasons">Exit Reasons</a>.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="k">catch</span><span class="w"> </span><span class="mi">1</span><span class="o">+</span><span class="mi">2</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">2&gt; </span><span class="k">catch</span><span class="w"> </span><span class="mi">1</span><span class="o">+</span><span class="ss">a</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2189244444-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="2189244444-2">{</span><span class="ss">badarith</span><span class="p">,</span><span class="p" data-group-id="2189244444-3">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2189244444-3">]</span><span class="p" data-group-id="2189244444-2">}</span><span class="p" data-group-id="2189244444-1">}</span></code></pre><p>The BIF <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw(Any)</code></a> can be used for non-local return from a
│ │ │ │ -function. It must be evaluated within a <code class="inline">catch</code>, which returns the value <code class="inline">Any</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="8432739846-1">(</span><span class="ss">hello</span><span class="p" data-group-id="8432739846-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4259050418-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="4259050418-2">{</span><span class="ss">badarith</span><span class="p">,</span><span class="p" data-group-id="4259050418-3">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4259050418-3">]</span><span class="p" data-group-id="4259050418-2">}</span><span class="p" data-group-id="4259050418-1">}</span></code></pre><p>The BIF <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw(Any)</code></a> can be used for non-local return from a
│ │ │ │ +function. It must be evaluated within a <code class="inline">catch</code>, which returns the value <code class="inline">Any</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="8653168957-1">(</span><span class="ss">hello</span><span class="p" data-group-id="8653168957-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span></code></pre><p>If <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw/1</code></a> is not evaluated within a catch, a <code class="inline">nocatch</code> run-time
│ │ │ │  error occurs.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 24, the <code class="inline">catch</code> operator had the lowest precedence, making
│ │ │ │ -it necessary to add parentheses when combining it with the <code class="inline">match</code> operator:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8888534964-1">(</span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="8888534964-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +it necessary to add parentheses when combining it with the <code class="inline">match</code> operator:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2524821023-1">(</span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="2524821023-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span></code></pre><p>Starting from Erlang/OTP 24, the parentheses can be omitted:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">42</span></code></pre></section><h2 id="try" class="section-heading">
│ │ │ │    <a href="#try" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Try</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="9804790082-1">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="9804790082-1">]</span><span class="w"> </span><span class="p" data-group-id="9804790082-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="9804790082-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="8565787631-1">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="8565787631-1">]</span><span class="w"> </span><span class="p" data-group-id="8565787631-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="8565787631-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="9804790082-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="9804790082-3">]</span><span class="w"> </span><span class="p" data-group-id="9804790082-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="9804790082-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="8565787631-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="8565787631-3">]</span><span class="w"> </span><span class="p" data-group-id="8565787631-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="8565787631-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>This is an enhancement of <a href="expressions.xhtml#catch-and-throw">catch</a>. It gives the
│ │ │ │  possibility to:</p><ul><li>Distinguish between different exception classes.</li><li>Choose to handle only the desired ones.</li><li>Passing the others on to an enclosing <code class="inline">try</code> or <code class="inline">catch</code>, or to default error
│ │ │ │  handling.</li></ul><p>Notice that although the keyword <code class="inline">catch</code> is used in the <code class="inline">try</code> expression, there
│ │ │ │  is not a <code class="inline">catch</code> expression within the <code class="inline">try</code> expression.</p><p>It returns the value of <code class="inline">Exprs</code> (a sequence of expressions <code class="inline">Expr1, ..., ExprN</code>)
│ │ │ │  unless an exception occurs during the evaluation. In that case the exception is
│ │ │ │  caught and the patterns <code class="inline">ExceptionPattern</code> with the right exception class
│ │ │ │ @@ -924,47 +924,47 @@
│ │ │ │  stack trace is bound to the variable when the corresponding <code class="inline">ExceptionPattern</code>
│ │ │ │  matches.</p><p>If an exception occurs during evaluation of <code class="inline">Exprs</code> but there is no matching
│ │ │ │  <code class="inline">ExceptionPattern</code> of the right <code class="inline">Class</code> with a true guard sequence, the
│ │ │ │  exception is passed on as if <code class="inline">Exprs</code> had not been enclosed in a <code class="inline">try</code>
│ │ │ │  expression.</p><p>If an exception occurs during evaluation of <code class="inline">ExceptionBody</code>, it is not caught.</p><p>It is allowed to omit <code class="inline">Class</code> and <code class="inline">Stacktrace</code>. An omitted <code class="inline">Class</code> is shorthand
│ │ │ │  for <code class="inline">throw</code>:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │ -    </span><span class="n">ExceptionPattern1</span><span class="w"> </span><span class="p" data-group-id="1439435809-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="1439435809-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ExceptionPattern1</span><span class="w"> </span><span class="p" data-group-id="3379746144-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="3379746144-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">ExceptionPatternN</span><span class="w"> </span><span class="p" data-group-id="1439435809-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="1439435809-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ExceptionPatternN</span><span class="w"> </span><span class="p" data-group-id="3379746144-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="3379746144-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">try</code> expression can have an <code class="inline">of</code> section:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="7116599147-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="7116599147-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="9075241812-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9075241812-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="7116599147-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="7116599147-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="9075241812-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="9075241812-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="7116599147-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="7116599147-3">]</span><span class="w"> </span><span class="p" data-group-id="7116599147-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="7116599147-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="9075241812-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="9075241812-3">]</span><span class="w"> </span><span class="p" data-group-id="9075241812-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="9075241812-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="7116599147-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="7116599147-5">]</span><span class="w"> </span><span class="p" data-group-id="7116599147-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="7116599147-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="9075241812-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="9075241812-5">]</span><span class="w"> </span><span class="p" data-group-id="9075241812-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="9075241812-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>If the evaluation of <code class="inline">Exprs</code> succeeds without an exception, the patterns
│ │ │ │  <code class="inline">Pattern</code> are sequentially matched against the result in the same way as for a
│ │ │ │  <a href="expressions.xhtml#case">case</a> expression, except that if the matching fails, a
│ │ │ │  <code class="inline">try_clause</code> run-time error occurs instead of a <code class="inline">case_clause</code>.</p><p>Only exceptions occurring during the evaluation of <code class="inline">Exprs</code> can be caught by the
│ │ │ │  <code class="inline">catch</code> section. Exceptions occurring in a <code class="inline">Body</code> or due to a failed match are
│ │ │ │  not caught.</p><p>The <code class="inline">try</code> expression can also be augmented with an <code class="inline">after</code> section, intended to
│ │ │ │  be used for cleanup with side effects:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="8891013026-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="8891013026-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="4268013221-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="4268013221-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="8891013026-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="8891013026-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="4268013221-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="4268013221-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="8891013026-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="8891013026-3">]</span><span class="w"> </span><span class="p" data-group-id="8891013026-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="8891013026-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="4268013221-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="4268013221-3">]</span><span class="w"> </span><span class="p" data-group-id="4268013221-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="4268013221-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="8891013026-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="8891013026-5">]</span><span class="w"> </span><span class="p" data-group-id="8891013026-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="8891013026-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="4268013221-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="4268013221-5">]</span><span class="w"> </span><span class="p" data-group-id="4268013221-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="4268013221-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │ │  </span><span class="k">after</span><span class="w">
│ │ │ │      </span><span class="n">AfterBody</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p><code class="inline">AfterBody</code> is evaluated after either <code class="inline">Body</code> or <code class="inline">ExceptionBody</code>, no matter which
│ │ │ │  one. The evaluated value of <code class="inline">AfterBody</code> is lost; the return value of the <code class="inline">try</code>
│ │ │ │  expression is the same with an <code class="inline">after</code> section as without.</p><p>Even if an exception occurs during evaluation of <code class="inline">Body</code> or <code class="inline">ExceptionBody</code>,
│ │ │ │  <code class="inline">AfterBody</code> is evaluated. In this case the exception is passed on after
│ │ │ │ @@ -987,40 +987,40 @@
│ │ │ │          </span><span class="n">ExpressionBody</span><span class="w">
│ │ │ │  </span><span class="k">after</span><span class="w">
│ │ │ │      </span><span class="n">AfterBody</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="n">AfterBody</span><span class="w"> </span><span class="k">end</span></code></pre><p>Next is an example of using <code class="inline">after</code>. This closes the file, even in the event of
│ │ │ │  exceptions in <a href="../../../lib/kernel/doc/html/file.html#read/2"><code class="inline">file:read/2</code></a> or in <a href="../../../lib/../erts/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>. The
│ │ │ │ -exceptions are the same as without the <code class="inline">try</code>...<code class="inline">after</code>...<code class="inline">end</code> expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">termize_file</span><span class="p" data-group-id="8991681797-1">(</span><span class="n">Name</span><span class="p" data-group-id="8991681797-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8991681797-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="8991681797-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="8991681797-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8991681797-4">[</span><span class="ss">read</span><span class="p">,</span><span class="ss">binary</span><span class="p" data-group-id="8991681797-4">]</span><span class="p" data-group-id="8991681797-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +exceptions are the same as without the <code class="inline">try</code>...<code class="inline">after</code>...<code class="inline">end</code> expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">termize_file</span><span class="p" data-group-id="1962167580-1">(</span><span class="n">Name</span><span class="p" data-group-id="1962167580-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1962167580-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="1962167580-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="1962167580-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1962167580-4">[</span><span class="ss">read</span><span class="p">,</span><span class="ss">binary</span><span class="p" data-group-id="1962167580-4">]</span><span class="p" data-group-id="1962167580-3">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">try</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8991681797-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">Bin</span><span class="p" data-group-id="8991681797-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="8991681797-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p" data-group-id="8991681797-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="nf">binary_to_term</span><span class="p" data-group-id="8991681797-7">(</span><span class="n">Bin</span><span class="p" data-group-id="8991681797-7">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="1962167580-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">Bin</span><span class="p" data-group-id="1962167580-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="1962167580-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p" data-group-id="1962167580-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="nf">binary_to_term</span><span class="p" data-group-id="1962167580-7">(</span><span class="n">Bin</span><span class="p" data-group-id="1962167580-7">)</span><span class="w">
│ │ │ │      </span><span class="k">after</span><span class="w">
│ │ │ │ -        </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="8991681797-8">(</span><span class="n">F</span><span class="p" data-group-id="8991681797-8">)</span><span class="w">
│ │ │ │ +        </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="1962167580-8">(</span><span class="n">F</span><span class="p" data-group-id="1962167580-8">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Next is an example of using <code class="inline">try</code> to emulate <code class="inline">catch Expr</code>:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Expr</span><span class="w">
│ │ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ │      </span><span class="nc">throw</span><span class="p">:</span><span class="n">Term</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Term</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="nc">exit</span><span class="p">:</span><span class="n">Reason</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8955435835-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="8955435835-1">}</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="nc">error</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stk</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8955435835-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="8955435835-3">{</span><span class="n">Reason</span><span class="p">,</span><span class="n">Stk</span><span class="p" data-group-id="8955435835-3">}</span><span class="p" data-group-id="8955435835-2">}</span><span class="w">
│ │ │ │ +    </span><span class="nc">exit</span><span class="p">:</span><span class="n">Reason</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7655984868-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="7655984868-1">}</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nc">error</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stk</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7655984868-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="7655984868-3">{</span><span class="n">Reason</span><span class="p">,</span><span class="n">Stk</span><span class="p" data-group-id="7655984868-3">}</span><span class="p" data-group-id="7655984868-2">}</span><span class="w">
│ │ │ │  </span><span class="k">end</span></code></pre><p>Variables bound in the various parts of these expressions have different scopes.
│ │ │ │  Variables bound just after the <code class="inline">try</code> keyword are:</p><ul><li>bound in the <code class="inline">of</code> section</li><li>unsafe in both the <code class="inline">catch</code> and <code class="inline">after</code> sections, as well as after the whole
│ │ │ │  construct</li></ul><p>Variables bound in <code class="inline">of</code> section are:</p><ul><li>unbound in the <code class="inline">catch</code> section</li><li>unsafe in both the <code class="inline">after</code> section, as well as after the whole construct</li></ul><p>Variables bound in the <code class="inline">catch</code> section are unsafe in the <code class="inline">after</code> section, as
│ │ │ │  well as after the whole construct.</p><p>Variables bound in the <code class="inline">after</code> section are unsafe after the whole construct.</p><h2 id="parenthesized-expressions" class="section-heading">
│ │ │ │    <a href="#parenthesized-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Parenthesized Expressions</span>
│ │ │ │  </h2>
│ │ │ │ -<pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6841410557-1">(</span><span class="n">Expr</span><span class="p" data-group-id="6841410557-1">)</span></code></pre><p>Parenthesized expressions are useful to override
│ │ │ │ +<pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2218652160-1">(</span><span class="n">Expr</span><span class="p" data-group-id="2218652160-1">)</span></code></pre><p>Parenthesized expressions are useful to override
│ │ │ │  <a href="expressions.xhtml#prec">operator precedences</a>, for example, in arithmetic
│ │ │ │  expressions:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">7</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4272451593-1">(</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4272451593-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="8711512028-1">(</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8711512028-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">9</span></code></pre><h2 id="block-expressions" class="section-heading">
│ │ │ │    <a href="#block-expressions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Block Expressions</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">begin</span><span class="w">
│ │ │ │ @@ -1032,71 +1032,71 @@
│ │ │ │    <a href="#comprehensions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Comprehensions</span>
│ │ │ │  </h2>
│ │ │ │  <p>Comprehensions provide a succinct notation for iterating over one or more terms
│ │ │ │  and constructing a new term. Comprehensions come in three different flavors,
│ │ │ │ -depending on the type of term they build.</p><p>List comprehensions construct lists. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2140552425-1">[</span><span class="n">Expr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="2140552425-1">]</span></code></pre><p>Here, <code class="inline">Expr</code> is an arbitrary expression, and each <code class="inline">Qualifier</code> is either a
│ │ │ │ +depending on the type of term they build.</p><p>List comprehensions construct lists. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4363436970-1">[</span><span class="n">Expr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="4363436970-1">]</span></code></pre><p>Here, <code class="inline">Expr</code> is an arbitrary expression, and each <code class="inline">Qualifier</code> is either a
│ │ │ │  <strong>generator</strong> or a <strong>filter</strong>.</p><p>Bit string comprehensions construct bit strings or binaries. They have the
│ │ │ │ -following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4602561023-1">&lt;&lt;</span><span class="w"> </span><span class="n">BitStringExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="w"> </span><span class="p" data-group-id="4602561023-1">&gt;&gt;</span></code></pre><p><code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string. If
│ │ │ │ +following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5464186763-1">&lt;&lt;</span><span class="w"> </span><span class="n">BitStringExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="w"> </span><span class="p" data-group-id="5464186763-1">&gt;&gt;</span></code></pre><p><code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string. If
│ │ │ │  <code class="inline">BitStringExpr</code> is a function call, it must be enclosed in parentheses. Each
│ │ │ │ -<code class="inline">Qualifier</code> is either a <strong>generator</strong> or a <strong>filter</strong>.</p><p>Map comprehensions construct maps. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9062161436-1">#{</span><span class="n">KeyExpr</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="9062161436-1">}</span></code></pre><p>Here, <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> are arbitrary expressions, and each <code class="inline">Qualifier</code>
│ │ │ │ +<code class="inline">Qualifier</code> is either a <strong>generator</strong> or a <strong>filter</strong>.</p><p>Map comprehensions construct maps. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2801907038-1">#{</span><span class="n">KeyExpr</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="2801907038-1">}</span></code></pre><p>Here, <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> are arbitrary expressions, and each <code class="inline">Qualifier</code>
│ │ │ │  is either a <strong>generator</strong> or a <strong>filter</strong>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Map comprehensions and map generators were introduced in Erlang/OTP 26.</p></section><p>There are three kinds of generators.</p><p>A <em>list generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">ListExpr</span></code></pre><p>where <code class="inline">ListExpr</code> is an expression that evaluates to a list of terms.</p><p>A <em>bit string generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">BitstringPattern</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="n">BitStringExpr</span></code></pre><p>where <code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string.</p><p>A <em>map generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">KeyPattern</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">ValuePattern</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">MapExpression</span></code></pre><p>where <code class="inline">MapExpr</code> is an expression that evaluates to a map, or a map iterator
│ │ │ │  obtained by calling <a href="../../../lib/stdlib/doc/html/maps.html#iterator/1"><code class="inline">maps:iterator/1</code></a> or <a href="../../../lib/stdlib/doc/html/maps.html#iterator/2"><code class="inline">maps:iterator/2</code></a>.</p><p>A <em>filter</em> is an expression that evaluates to <code class="inline">true</code> or <code class="inline">false</code>.</p><p>The variables in the generator patterns shadow previously bound variables,
│ │ │ │  including variables bound in a previous generator pattern.</p><p>Variables bound in a generator expression are not visible outside the
│ │ │ │ -expression:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5785373186-1">[</span><span class="p" data-group-id="5785373186-2">{</span><span class="n">E</span><span class="p">,</span><span class="n">L</span><span class="p" data-group-id="5785373186-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="o">=</span><span class="p" data-group-id="5785373186-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5785373186-3">]</span><span class="p" data-group-id="5785373186-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +expression:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7266661477-1">[</span><span class="p" data-group-id="7266661477-2">{</span><span class="n">E</span><span class="p">,</span><span class="n">L</span><span class="p" data-group-id="7266661477-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="o">=</span><span class="p" data-group-id="7266661477-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7266661477-3">]</span><span class="p" data-group-id="7266661477-1">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">* 1:5: variable &#39;L&#39; is unbound</span></code></pre><p>A <strong>list comprehension</strong> returns a list, where the list elements are the result
│ │ │ │  of evaluating <code class="inline">Expr</code> for each combination of generator elements for which all
│ │ │ │  filters are true.</p><p>A <strong>bit string comprehension</strong> returns a bit string, which is created by
│ │ │ │  concatenating the results of evaluating <code class="inline">BitStringExpr</code> for each combination of
│ │ │ │  bit string generator elements for which all filters are true.</p><p>A <strong>map comprehension</strong> returns a map, where the map elements are the result of
│ │ │ │  evaluating <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> for each combination of generator elements
│ │ │ │  for which all filters are true. If the key expressions are not unique, the last
│ │ │ │ -occurrence is stored in the map.</p><p><strong>Examples:</strong></p><p>Multiplying each element in a list by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5301957450-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5301957450-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5301957450-2">]</span><span class="p" data-group-id="5301957450-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5301957450-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5301957450-3">]</span></code></pre><p>Multiplying each byte in a binary by two, returning a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6429684417-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="6429684417-2">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="6429684417-2">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="6429684417-3">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6429684417-3">&gt;&gt;</span><span class="p" data-group-id="6429684417-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6429684417-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6429684417-4">]</span></code></pre><p>Multiplying each byte in a binary by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8111554470-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="8111554470-2">&lt;&lt;</span><span class="p" data-group-id="8111554470-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="8111554470-3">)</span><span class="p" data-group-id="8111554470-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="8111554470-4">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="8111554470-4">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="8111554470-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8111554470-5">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="8111554470-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8111554470-6">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8111554470-6">&gt;&gt;</span></code></pre><p>Multiplying each element in a list by two, returning a binary:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0175920759-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="0175920759-2">&lt;&lt;</span><span class="p" data-group-id="0175920759-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="0175920759-3">)</span><span class="p" data-group-id="0175920759-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0175920759-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0175920759-4">]</span><span class="w"> </span><span class="p" data-group-id="0175920759-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0175920759-5">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="0175920759-5">&gt;&gt;</span></code></pre><p>Creating a mapping from an integer to its square:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3560074781-1">#{</span><span class="n">X</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="3560074781-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3560074781-2">]</span><span class="p" data-group-id="3560074781-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3560074781-3">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="3560074781-3">}</span></code></pre><p>Multiplying the value of each element in a map by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2182369529-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">V</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="2182369529-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2182369529-2">}</span><span class="p" data-group-id="2182369529-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2182369529-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="2182369529-3">}</span></code></pre><p>Filtering a list, keeping odd numbers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6265785011-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6265785011-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="6265785011-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6265785011-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6265785011-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="6265785011-3">]</span></code></pre><p>Filtering a list, keeping only elements that match:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7428937064-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="7428937064-2">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7428937064-2">}</span><span class="o">=</span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7428937064-3">[</span><span class="p" data-group-id="7428937064-4">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7428937064-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7428937064-5">[</span><span class="ss">a</span><span class="p" data-group-id="7428937064-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7428937064-6">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="7428937064-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7428937064-7">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7428937064-7">}</span><span class="p" data-group-id="7428937064-3">]</span><span class="p" data-group-id="7428937064-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7428937064-8">[</span><span class="p" data-group-id="7428937064-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="7428937064-9">}</span><span class="p">,</span><span class="p" data-group-id="7428937064-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7428937064-10">}</span><span class="p" data-group-id="7428937064-8">]</span></code></pre><p>Combining elements from two list generators:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0697208475-1">[</span><span class="p" data-group-id="0697208475-2">{</span><span class="n">P</span><span class="p">,</span><span class="n">Q</span><span class="p" data-group-id="0697208475-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0697208475-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0697208475-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0697208475-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0697208475-4">]</span><span class="p" data-group-id="0697208475-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0697208475-5">[</span><span class="p" data-group-id="0697208475-6">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0697208475-6">}</span><span class="p">,</span><span class="p" data-group-id="0697208475-7">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0697208475-7">}</span><span class="p">,</span><span class="p" data-group-id="0697208475-8">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0697208475-8">}</span><span class="p">,</span><span class="p" data-group-id="0697208475-9">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0697208475-9">}</span><span class="p">,</span><span class="p" data-group-id="0697208475-10">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0697208475-10">}</span><span class="p">,</span><span class="p" data-group-id="0697208475-11">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0697208475-11">}</span><span class="p" data-group-id="0697208475-5">]</span></code></pre><p>More examples are provided in
│ │ │ │ +occurrence is stored in the map.</p><p><strong>Examples:</strong></p><p>Multiplying each element in a list by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9635075216-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9635075216-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9635075216-2">]</span><span class="p" data-group-id="9635075216-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9635075216-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9635075216-3">]</span></code></pre><p>Multiplying each byte in a binary by two, returning a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2080946509-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="2080946509-2">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="2080946509-2">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="2080946509-3">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2080946509-3">&gt;&gt;</span><span class="p" data-group-id="2080946509-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2080946509-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2080946509-4">]</span></code></pre><p>Multiplying each byte in a binary by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9517522236-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="9517522236-2">&lt;&lt;</span><span class="p" data-group-id="9517522236-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="9517522236-3">)</span><span class="p" data-group-id="9517522236-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="9517522236-4">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="9517522236-4">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="9517522236-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9517522236-5">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="9517522236-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9517522236-6">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9517522236-6">&gt;&gt;</span></code></pre><p>Multiplying each element in a list by two, returning a binary:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2409758753-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="2409758753-2">&lt;&lt;</span><span class="p" data-group-id="2409758753-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="2409758753-3">)</span><span class="p" data-group-id="2409758753-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="2409758753-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2409758753-4">]</span><span class="w"> </span><span class="p" data-group-id="2409758753-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2409758753-5">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2409758753-5">&gt;&gt;</span></code></pre><p>Creating a mapping from an integer to its square:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9960560606-1">#{</span><span class="n">X</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9960560606-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9960560606-2">]</span><span class="p" data-group-id="9960560606-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9960560606-3">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9960560606-3">}</span></code></pre><p>Multiplying the value of each element in a map by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0320384729-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">V</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0320384729-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="0320384729-2">}</span><span class="p" data-group-id="0320384729-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0320384729-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="0320384729-3">}</span></code></pre><p>Filtering a list, keeping odd numbers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7601203755-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7601203755-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7601203755-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7601203755-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7601203755-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7601203755-3">]</span></code></pre><p>Filtering a list, keeping only elements that match:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6880728106-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="6880728106-2">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6880728106-2">}</span><span class="o">=</span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6880728106-3">[</span><span class="p" data-group-id="6880728106-4">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6880728106-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6880728106-5">[</span><span class="ss">a</span><span class="p" data-group-id="6880728106-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6880728106-6">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="6880728106-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6880728106-7">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6880728106-7">}</span><span class="p" data-group-id="6880728106-3">]</span><span class="p" data-group-id="6880728106-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="6880728106-8">[</span><span class="p" data-group-id="6880728106-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6880728106-9">}</span><span class="p">,</span><span class="p" data-group-id="6880728106-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6880728106-10">}</span><span class="p" data-group-id="6880728106-8">]</span></code></pre><p>Combining elements from two list generators:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1372276899-1">[</span><span class="p" data-group-id="1372276899-2">{</span><span class="n">P</span><span class="p">,</span><span class="n">Q</span><span class="p" data-group-id="1372276899-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1372276899-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1372276899-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1372276899-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1372276899-4">]</span><span class="p" data-group-id="1372276899-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1372276899-5">[</span><span class="p" data-group-id="1372276899-6">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1372276899-6">}</span><span class="p">,</span><span class="p" data-group-id="1372276899-7">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1372276899-7">}</span><span class="p">,</span><span class="p" data-group-id="1372276899-8">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1372276899-8">}</span><span class="p">,</span><span class="p" data-group-id="1372276899-9">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1372276899-9">}</span><span class="p">,</span><span class="p" data-group-id="1372276899-10">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1372276899-10">}</span><span class="p">,</span><span class="p" data-group-id="1372276899-11">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1372276899-11">}</span><span class="p" data-group-id="1372276899-5">]</span></code></pre><p>More examples are provided in
│ │ │ │  <a href="../../../lib/../system/doc/html/list_comprehensions.xhtml">Programming Examples.</a></p><p>When there are no generators, a comprehension returns either a term constructed
│ │ │ │  from a single element (the result of evaluating <code class="inline">Expr</code>) if all filters are true,
│ │ │ │  or a term constructed from no elements (that is, <code class="inline">[]</code> for list comprehension,
│ │ │ │ -<code class="inline">&lt;&lt;&gt;&gt;</code> for a bit string comprehension, and <code class="inline">#{}</code> for a map comprehension).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4012566170-1">[</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="4012566170-2">(</span><span class="mi">2</span><span class="p" data-group-id="4012566170-2">)</span><span class="p" data-group-id="4012566170-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4012566170-3">[</span><span class="mi">2</span><span class="p" data-group-id="4012566170-3">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4012566170-4">[</span><span class="ss">x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="4012566170-5">(</span><span class="ss">x</span><span class="p" data-group-id="4012566170-5">)</span><span class="p" data-group-id="4012566170-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4012566170-6">[</span><span class="p" data-group-id="4012566170-6">]</span></code></pre><p>What happens when the filter expression does not evaluate to a boolean value
│ │ │ │ +<code class="inline">&lt;&lt;&gt;&gt;</code> for a bit string comprehension, and <code class="inline">#{}</code> for a map comprehension).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3565604422-1">[</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="3565604422-2">(</span><span class="mi">2</span><span class="p" data-group-id="3565604422-2">)</span><span class="p" data-group-id="3565604422-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3565604422-3">[</span><span class="mi">2</span><span class="p" data-group-id="3565604422-3">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="3565604422-4">[</span><span class="ss">x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="3565604422-5">(</span><span class="ss">x</span><span class="p" data-group-id="3565604422-5">)</span><span class="p" data-group-id="3565604422-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3565604422-6">[</span><span class="p" data-group-id="3565604422-6">]</span></code></pre><p>What happens when the filter expression does not evaluate to a boolean value
│ │ │ │  depends on the expression:</p><ul><li>If the expression is a <a href="expressions.xhtml#guard-expressions">guard expression</a>,
│ │ │ │  failure to evaluate or evaluating to a non-boolean value is equivalent to
│ │ │ │  evaluating to <code class="inline">false</code>.</li><li>If the expression is not a guard expression and evaluates to a non-Boolean
│ │ │ │  value <code class="inline">Val</code>, an exception <code class="inline">{bad_filter, Val}</code> is triggered at runtime. If the
│ │ │ │  evaluation of the expression raises an exception, it is not caught by the
│ │ │ │ -comprehension.</li></ul><p><strong>Examples</strong> (using a guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5744916002-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5744916002-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5744916002-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5744916002-2">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="5744916002-3">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5744916002-3">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5744916002-4">[</span><span class="p" data-group-id="5744916002-4">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="5744916002-5">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5744916002-5">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5744916002-6">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5744916002-6">]</span></code></pre><p><strong>Examples</strong> (using a non-guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0425420972-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0425420972-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0425420972-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0425420972-2">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">FaultyIsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0425420972-3">(</span><span class="n">E</span><span class="p" data-group-id="0425420972-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +comprehension.</li></ul><p><strong>Examples</strong> (using a guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8632519266-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8632519266-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8632519266-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8632519266-2">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="8632519266-3">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8632519266-3">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8632519266-4">[</span><span class="p" data-group-id="8632519266-4">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="8632519266-5">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8632519266-5">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8632519266-6">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8632519266-6">]</span></code></pre><p><strong>Examples</strong> (using a non-guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7292560394-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7292560394-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7292560394-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7292560394-2">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">FaultyIsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7292560394-3">(</span><span class="n">E</span><span class="p" data-group-id="7292560394-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">42.17316486</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="0425420972-4">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">FaultyIsEven</span><span class="p" data-group-id="0425420972-5">(</span><span class="n">E</span><span class="p" data-group-id="0425420972-5">)</span><span class="p" data-group-id="0425420972-4">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="7292560394-4">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">FaultyIsEven</span><span class="p" data-group-id="7292560394-5">(</span><span class="n">E</span><span class="p" data-group-id="7292560394-5">)</span><span class="p" data-group-id="7292560394-4">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: bad filter 1</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">IsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0425420972-6">(</span><span class="n">E</span><span class="p" data-group-id="0425420972-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">IsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7292560394-6">(</span><span class="n">E</span><span class="p" data-group-id="7292560394-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">42.17316486</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="0425420972-7">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="0425420972-8">(</span><span class="n">E</span><span class="p" data-group-id="0425420972-8">)</span><span class="p" data-group-id="0425420972-7">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="7292560394-7">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="7292560394-8">(</span><span class="n">E</span><span class="p" data-group-id="7292560394-8">)</span><span class="p" data-group-id="7292560394-7">]</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="gt">** exception error: an error occurred when evaluating an arithmetic expression
│ │ │ │       in operator  rem/2
│ │ │ │          called as a rem 2</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="p" data-group-id="0425420972-9">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="0425420972-10">(</span><span class="n">E</span><span class="p" data-group-id="0425420972-10">)</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="0425420972-11">(</span><span class="n">E</span><span class="p" data-group-id="0425420972-11">)</span><span class="p" data-group-id="0425420972-9">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0425420972-12">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0425420972-12">]</span></code></pre><p><a href="" id="guards"></a></p><h2 id="guard-sequences" class="section-heading">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="p" data-group-id="7292560394-9">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="7292560394-10">(</span><span class="n">E</span><span class="p" data-group-id="7292560394-10">)</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="7292560394-11">(</span><span class="n">E</span><span class="p" data-group-id="7292560394-11">)</span><span class="p" data-group-id="7292560394-9">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7292560394-12">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7292560394-12">]</span></code></pre><p><a href="" id="guards"></a></p><h2 id="guard-sequences" class="section-heading">
│ │ │ │    <a href="#guard-sequences" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Guard Sequences</span>
│ │ │ │  </h2>
│ │ │ │  <p>A <em>guard sequence</em> is a sequence of guards, separated by semicolon (<code class="inline">;</code>). The
│ │ │ │  guard sequence is true if at least one of the guards is true. (The remaining
│ │ │ ├── OEBPS/example.xhtml
│ │ │ │ @@ -26,24 +26,24 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Description</span>
│ │ │ │  </h2>
│ │ │ │  <p>A common interoperability situation is when you want to incorporate a piece of
│ │ │ │  code, solving a complex problem, in your Erlang program. Suppose for example,
│ │ │ │  that you have the following C functions that you would like to call from Erlang:</p><pre><code class="makeup c" translate="no"><span class="cm">/* complex.c */</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="6126087698-1">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="6126087698-1">)</span><span class="w"> </span><span class="p" data-group-id="6126087698-2">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="7811166325-1">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="7811166325-1">)</span><span class="w"> </span><span class="p" data-group-id="7811166325-2">{</span><span class="w">
│ │ │ │    </span><span class="k">return</span><span class="w"> </span><span class="n">x</span><span class="o">+</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6126087698-2">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7811166325-2">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="6126087698-3">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="6126087698-3">)</span><span class="w"> </span><span class="p" data-group-id="6126087698-4">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="7811166325-3">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="7811166325-3">)</span><span class="w"> </span><span class="p" data-group-id="7811166325-4">{</span><span class="w">
│ │ │ │    </span><span class="k">return</span><span class="w"> </span><span class="n">y</span><span class="o">*</span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6126087698-4">}</span></code></pre><p>The functions are deliberately kept as simple as possible, for readability
│ │ │ │ +</span><span class="p" data-group-id="7811166325-4">}</span></code></pre><p>The functions are deliberately kept as simple as possible, for readability
│ │ │ │  reasons.</p><p>From an Erlang perspective, it is preferable to be able to call <code class="inline">foo</code> and <code class="inline">bar</code>
│ │ │ │  without having to bother about that they are C functions:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% Erlang code</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="n">Res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">complex</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="8863765636-1">(</span><span class="n">X</span><span class="p" data-group-id="8863765636-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">complex</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="9509996481-1">(</span><span class="n">X</span><span class="p" data-group-id="9509996481-1">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Here, the communication with C is hidden in the implementation of <code class="inline">complex.erl</code>.
│ │ │ │  In the following sections, it is shown how this module can be implemented using
│ │ │ │  the different interoperability mechanisms.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/events.xhtml
│ │ │ │ @@ -40,43 +40,43 @@
│ │ │ │  event handler.</p><h2 id="example" class="section-heading">
│ │ │ │    <a href="#example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Example</span>
│ │ │ │  </h2>
│ │ │ │  <p>The callback module for the event handler writing error messages to the terminal
│ │ │ │ -can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5682373678-1">(</span><span class="ss">terminal_logger</span><span class="p" data-group-id="5682373678-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5682373678-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="5682373678-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5684458005-1">(</span><span class="ss">terminal_logger</span><span class="p" data-group-id="5684458005-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5684458005-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="5684458005-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5682373678-3">(</span><span class="p" data-group-id="5682373678-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5682373678-4">]</span><span class="p" data-group-id="5682373678-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5684458005-3">(</span><span class="p" data-group-id="5684458005-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5684458005-4">]</span><span class="p" data-group-id="5684458005-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="5682373678-5">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5682373678-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5682373678-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5682373678-7">[</span><span class="p" data-group-id="5682373678-7">]</span><span class="p" data-group-id="5682373678-6">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="5684458005-5">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5684458005-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5684458005-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5684458005-7">[</span><span class="p" data-group-id="5684458005-7">]</span><span class="p" data-group-id="5684458005-6">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5682373678-8">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5682373678-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5682373678-9">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5682373678-10">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="5682373678-10">]</span><span class="p" data-group-id="5682373678-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5682373678-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5682373678-11">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="5684458005-8">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5684458005-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5684458005-9">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5684458005-10">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="5684458005-10">]</span><span class="p" data-group-id="5684458005-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5684458005-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5684458005-11">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="5682373678-12">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="5682373678-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="5684458005-12">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="5684458005-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The callback module for the event handler writing error messages to a file can
│ │ │ │ -look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5827328028-1">(</span><span class="ss">file_logger</span><span class="p" data-group-id="5827328028-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5827328028-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="5827328028-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5296672327-1">(</span><span class="ss">file_logger</span><span class="p" data-group-id="5296672327-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5296672327-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="5296672327-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5827328028-3">(</span><span class="p" data-group-id="5827328028-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5827328028-4">]</span><span class="p" data-group-id="5827328028-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5296672327-3">(</span><span class="p" data-group-id="5296672327-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5296672327-4">]</span><span class="p" data-group-id="5296672327-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="5827328028-5">(</span><span class="n">File</span><span class="p" data-group-id="5827328028-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5827328028-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5827328028-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="5827328028-7">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="5827328028-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5827328028-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5827328028-8">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5827328028-9">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5827328028-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5827328028-10">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5827328028-11">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="5827328028-11">]</span><span class="p" data-group-id="5827328028-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5827328028-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5827328028-12">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="5296672327-5">(</span><span class="n">File</span><span class="p" data-group-id="5296672327-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5296672327-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5296672327-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="5296672327-7">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="5296672327-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5296672327-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5296672327-8">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="5296672327-9">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5296672327-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5296672327-10">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5296672327-11">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="5296672327-11">]</span><span class="p" data-group-id="5296672327-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5296672327-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5296672327-12">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="5827328028-13">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5827328028-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="5827328028-14">(</span><span class="n">Fd</span><span class="p" data-group-id="5827328028-14">)</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><p><a href="" id="mgr"></a></p><h2 id="starting-an-event-manager" class="section-heading">
│ │ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="5296672327-13">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5296672327-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="5296672327-14">(</span><span class="n">Fd</span><span class="p" data-group-id="5296672327-14">)</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><p><a href="" id="mgr"></a></p><h2 id="starting-an-event-manager" class="section-heading">
│ │ │ │    <a href="#starting-an-event-manager" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting an Event Manager</span>
│ │ │ │  </h2>
│ │ │ │  <p>To start an event manager for handling errors, as described in the previous
│ │ │ │  example, call the following function:</p><pre><code class="text">gen_event:start_link({local, error_man})</code></pre><p><a href="../../../lib/stdlib/doc/html/gen_event.html#start_link/1"><code class="inline">gen_event:start_link/1</code></a> spawns and links to a new event manager process.</p><p>The argument, <code class="inline">{local, error_man}</code>, specifies the name under which the
│ │ │ │ @@ -89,57 +89,57 @@
│ │ │ │  manager that is not part of a supervision tree.</p><h2 id="adding-an-event-handler" class="section-heading">
│ │ │ │    <a href="#adding-an-event-handler" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Adding an Event Handler</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following example shows how to start an event manager and add an event
│ │ │ │ -handler to it by using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1651410191-1">(</span><span class="p" data-group-id="1651410191-2">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="1651410191-2">}</span><span class="p" data-group-id="1651410191-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1651410191-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.31</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="1651410191-3">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">add_handler</span><span class="p" data-group-id="1651410191-4">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1651410191-5">[</span><span class="p" data-group-id="1651410191-5">]</span><span class="p" data-group-id="1651410191-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +handler to it by using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7431432349-1">(</span><span class="p" data-group-id="7431432349-2">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="7431432349-2">}</span><span class="p" data-group-id="7431432349-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7431432349-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.31</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7431432349-3">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">add_handler</span><span class="p" data-group-id="7431432349-4">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7431432349-5">[</span><span class="p" data-group-id="7431432349-5">]</span><span class="p" data-group-id="7431432349-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>This function sends a message to the event manager registered as <code class="inline">error_man</code>,
│ │ │ │  telling it to add the event handler <code class="inline">terminal_logger</code>. The event manager calls
│ │ │ │  the callback function <code class="inline">terminal_logger:init([])</code>, where the argument <code class="inline">[]</code> is the
│ │ │ │  third argument to <code class="inline">add_handler</code>. <code class="inline">init/1</code> is expected to return <code class="inline">{ok, State}</code>,
│ │ │ │ -where <code class="inline">State</code> is the internal state of the event handler.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="2985712042-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="2985712042-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2985712042-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2985712042-3">[</span><span class="p" data-group-id="2985712042-3">]</span><span class="p" data-group-id="2985712042-2">}</span><span class="p">.</span></code></pre><p>Here, <code class="inline">init/1</code> does not need any input data and ignores its argument. For
│ │ │ │ +where <code class="inline">State</code> is the internal state of the event handler.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5592916559-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5592916559-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5592916559-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5592916559-3">[</span><span class="p" data-group-id="5592916559-3">]</span><span class="p" data-group-id="5592916559-2">}</span><span class="p">.</span></code></pre><p>Here, <code class="inline">init/1</code> does not need any input data and ignores its argument. For
│ │ │ │  <code class="inline">terminal_logger</code>, the internal state is not used. For <code class="inline">file_logger</code>, the
│ │ │ │ -internal state is used to save the open file descriptor.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4460484501-1">(</span><span class="n">File</span><span class="p" data-group-id="4460484501-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4460484501-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="4460484501-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="4460484501-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="4460484501-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4460484501-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="4460484501-4">}</span><span class="p">.</span></code></pre><h2 id="notifying-about-events" class="section-heading">
│ │ │ │ +internal state is used to save the open file descriptor.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="3377613303-1">(</span><span class="n">File</span><span class="p" data-group-id="3377613303-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3377613303-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="3377613303-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="3377613303-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="3377613303-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3377613303-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="3377613303-4">}</span><span class="p">.</span></code></pre><h2 id="notifying-about-events" class="section-heading">
│ │ │ │    <a href="#notifying-about-events" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Notifying about Events</span>
│ │ │ │  </h2>
│ │ │ │  <pre><code class="text">3&gt; gen_event:notify(error_man, no_reply).
│ │ │ │  ***Error*** no_reply
│ │ │ │  ok</code></pre><p><code class="inline">error_man</code> is the name of the event manager and <code class="inline">no_reply</code> is the event.</p><p>The event is made into a message and sent to the event manager. When the event
│ │ │ │  is received, the event manager calls <code class="inline">handle_event(Event, State)</code> for each
│ │ │ │  installed event handler, in the same order as they were added. The function is
│ │ │ │  expected to return a tuple <code class="inline">{ok,State1}</code>, where <code class="inline">State1</code> is a new value for the
│ │ │ │ -state of the event handler.</p><p>In <code class="inline">terminal_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="8493923352-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8493923352-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8493923352-2">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8493923352-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="8493923352-3">]</span><span class="p" data-group-id="8493923352-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8493923352-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8493923352-4">}</span><span class="p">.</span></code></pre><p>In <code class="inline">file_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="2355678913-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2355678913-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2355678913-2">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2355678913-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="2355678913-3">]</span><span class="p" data-group-id="2355678913-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2355678913-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2355678913-4">}</span><span class="p">.</span></code></pre><h2 id="deleting-an-event-handler" class="section-heading">
│ │ │ │ +state of the event handler.</p><p>In <code class="inline">terminal_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="8133813288-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8133813288-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8133813288-2">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8133813288-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="8133813288-3">]</span><span class="p" data-group-id="8133813288-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8133813288-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8133813288-4">}</span><span class="p">.</span></code></pre><p>In <code class="inline">file_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="5998026848-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5998026848-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5998026848-2">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5998026848-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="5998026848-3">]</span><span class="p" data-group-id="5998026848-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5998026848-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5998026848-4">}</span><span class="p">.</span></code></pre><h2 id="deleting-an-event-handler" class="section-heading">
│ │ │ │    <a href="#deleting-an-event-handler" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Deleting an Event Handler</span>
│ │ │ │  </h2>
│ │ │ │ -<pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">delete_handler</span><span class="p" data-group-id="4759108543-1">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4759108543-2">[</span><span class="p" data-group-id="4759108543-2">]</span><span class="p" data-group-id="4759108543-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">delete_handler</span><span class="p" data-group-id="1037639413-1">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1037639413-2">[</span><span class="p" data-group-id="1037639413-2">]</span><span class="p" data-group-id="1037639413-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><p>This function sends a message to the event manager registered as <code class="inline">error_man</code>,
│ │ │ │  telling it to delete the event handler <code class="inline">terminal_logger</code>. The event manager
│ │ │ │  calls the callback function <code class="inline">terminal_logger:terminate([], State)</code>, where the
│ │ │ │  argument <code class="inline">[]</code> is the third argument to <code class="inline">delete_handler</code>. <code class="inline">terminate/2</code> is to be
│ │ │ │  the opposite of <code class="inline">init/1</code> and do any necessary cleaning up. Its return value is
│ │ │ │ -ignored.</p><p>For <code class="inline">terminal_logger</code>, no cleaning up is necessary:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="0143607113-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="0143607113-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>For <code class="inline">file_logger</code>, the file descriptor opened in <code class="inline">init</code> must be closed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="8102481298-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8102481298-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="8102481298-2">(</span><span class="n">Fd</span><span class="p" data-group-id="8102481298-2">)</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │ │ +ignored.</p><p>For <code class="inline">terminal_logger</code>, no cleaning up is necessary:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="1298219128-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="1298219128-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>For <code class="inline">file_logger</code>, the file descriptor opened in <code class="inline">init</code> must be closed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="5481949592-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5481949592-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="5481949592-2">(</span><span class="n">Fd</span><span class="p" data-group-id="5481949592-2">)</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │ │    <a href="#stopping" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Stopping</span>
│ │ │ │  </h2>
│ │ │ │  <p>When an event manager is stopped, it gives each of the installed event handlers
│ │ │ │  the chance to clean up by calling <code class="inline">terminate/2</code>, the same way as when deleting a
│ │ │ │ @@ -154,29 +154,29 @@
│ │ │ │  this is done is defined by a <a href="sup_princ.xhtml#shutdown">shutdown strategy</a> set in
│ │ │ │  the supervisor.</p><h3 id="standalone-event-managers" class="section-heading">
│ │ │ │    <a href="#standalone-event-managers" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Standalone Event Managers</span>
│ │ │ │  </h3>
│ │ │ │ -<p>An event manager can also be stopped by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="2047733548-1">(</span><span class="ss">error_man</span><span class="p" data-group-id="2047733548-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>An event manager can also be stopped by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="5046176794-1">(</span><span class="ss">error_man</span><span class="p" data-group-id="5046176794-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span></code></pre><h2 id="handling-other-messages" class="section-heading">
│ │ │ │    <a href="#handling-other-messages" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Handling Other Messages</span>
│ │ │ │  </h2>
│ │ │ │  <p>If the <code class="inline">gen_event</code> process is to be able to receive other messages
│ │ │ │  than events, the callback function <code class="inline">handle_info(Info, State)</code> must be
│ │ │ │  implemented to handle them. Examples of other messages are exit
│ │ │ │  messages if the event manager is linked to other processes than the
│ │ │ │  supervisor (for example via <a href="../../../lib/stdlib/doc/html/gen_event.html#add_sup_handler/3"><code class="inline">gen_event:add_sup_handler/3</code></a>) and is
│ │ │ │ -trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="3499673186-1">(</span><span class="p" data-group-id="3499673186-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="3499673186-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3499673186-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="5719816738-1">(</span><span class="p" data-group-id="5719816738-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5719816738-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5719816738-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code to handle exits here.</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3499673186-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="3499673186-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="6871834346-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="6871834346-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5719816738-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="5719816738-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="9407411190-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="9407411190-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Code to convert state (and more) during code change.</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6871834346-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="6871834346-2">}</span><span class="p">.</span></code></pre>
│ │ │ │ +    </span><span class="p" data-group-id="9407411190-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="9407411190-2">}</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/errors.xhtml
│ │ │ │ @@ -56,22 +56,22 @@
│ │ │ │  classes, with different origins. The <a href="expressions.xhtml#try">try</a> expression can
│ │ │ │  distinguish between the different classes, whereas the
│ │ │ │  <a href="expressions.xhtml#catch-and-throw">catch</a> expression cannot. <code class="inline">try</code> and <code class="inline">catch</code> are described
│ │ │ │  in <a href="expressions.xhtml">Expressions</a>.</p><table><thead><tr><th style="text-align: left;"><em>Class</em></th><th style="text-align: left;"><em>Origin</em></th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">error</code></td><td style="text-align: left;">Run-time error, for example, <code class="inline">1+a</code>, or the process called <a href="../../../lib/../erts/doc/html/erlang.html#error/1"><code class="inline">error/1</code></a></td></tr><tr><td style="text-align: left;"><code class="inline">exit</code></td><td style="text-align: left;">The process called <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a></td></tr><tr><td style="text-align: left;"><code class="inline">throw</code></td><td style="text-align: left;">The process called <a href="../../../lib/../erts/doc/html/erlang.html#throw/1"><code class="inline">throw/1</code></a></td></tr></tbody></table><p><em>Table: Exception Classes.</em></p><p>All of the above exceptions can also be generated by calling <a href="../../../lib/../erts/doc/html/erlang.html#raise/3"><code class="inline">erlang:raise/3</code></a>.</p><p>An exception consists of its class, an exit reason (see
│ │ │ │  <a href="errors.xhtml#exit_reasons">Exit Reason</a>), and a stack trace (which aids in finding
│ │ │ │  the code location of the exception).</p><p>The stack trace can be bound to a variable from within a <code class="inline">try</code> expression for
│ │ │ │  any exception class, or as part of the exit reason when a run-time error is
│ │ │ │ -caught by a <code class="inline">catch</code>. Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="8301579780-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="8301579780-2">{</span><span class="ss">test</span><span class="p">,</span><span class="n">Stacktrace</span><span class="p" data-group-id="8301579780-2">}</span><span class="p" data-group-id="8301579780-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8301579780-3">(</span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="8301579780-4">(</span><span class="ss">test</span><span class="p" data-group-id="8301579780-4">)</span><span class="p" data-group-id="8301579780-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Stacktrace</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8301579780-5">[</span><span class="p" data-group-id="8301579780-6">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="8301579780-7">[</span><span class="p" data-group-id="8301579780-7">]</span><span class="p" data-group-id="8301579780-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8301579780-8">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="8301579780-9">[</span><span class="p" data-group-id="8301579780-9">]</span><span class="p" data-group-id="8301579780-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8301579780-5">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">&gt; </span><span class="k">try</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="8301579780-10">(</span><span class="ss">test</span><span class="p" data-group-id="8301579780-10">)</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="n">Class</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stacktrace</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Stacktrace</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8301579780-11">[</span><span class="p" data-group-id="8301579780-12">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="8301579780-13">[</span><span class="p" data-group-id="8301579780-13">]</span><span class="p" data-group-id="8301579780-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8301579780-14">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="8301579780-15">[</span><span class="p" data-group-id="8301579780-15">]</span><span class="p" data-group-id="8301579780-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8301579780-11">]</span></code></pre><p><a href="" id="stacktrace"></a></p><h3 id="the-call-stack-back-trace-stacktrace" class="section-heading">
│ │ │ │ +caught by a <code class="inline">catch</code>. Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="8892115492-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="8892115492-2">{</span><span class="ss">test</span><span class="p">,</span><span class="n">Stacktrace</span><span class="p" data-group-id="8892115492-2">}</span><span class="p" data-group-id="8892115492-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8892115492-3">(</span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="8892115492-4">(</span><span class="ss">test</span><span class="p" data-group-id="8892115492-4">)</span><span class="p" data-group-id="8892115492-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Stacktrace</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8892115492-5">[</span><span class="p" data-group-id="8892115492-6">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="8892115492-7">[</span><span class="p" data-group-id="8892115492-7">]</span><span class="p" data-group-id="8892115492-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8892115492-8">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="8892115492-9">[</span><span class="p" data-group-id="8892115492-9">]</span><span class="p" data-group-id="8892115492-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8892115492-5">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">&gt; </span><span class="k">try</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="8892115492-10">(</span><span class="ss">test</span><span class="p" data-group-id="8892115492-10">)</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="n">Class</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stacktrace</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Stacktrace</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8892115492-11">[</span><span class="p" data-group-id="8892115492-12">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="8892115492-13">[</span><span class="p" data-group-id="8892115492-13">]</span><span class="p" data-group-id="8892115492-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8892115492-14">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="8892115492-15">[</span><span class="p" data-group-id="8892115492-15">]</span><span class="p" data-group-id="8892115492-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8892115492-11">]</span></code></pre><p><a href="" id="stacktrace"></a></p><h3 id="the-call-stack-back-trace-stacktrace" class="section-heading">
│ │ │ │    <a href="#the-call-stack-back-trace-stacktrace" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">The call-stack back trace (stacktrace)</span>
│ │ │ │  </h3>
│ │ │ │  <p>The stack back-trace (<a href="../../../lib/../erts/doc/html/erlang.html#t:stacktrace/0"><em>stacktrace</em></a>) is a list that
│ │ │ │  contains <code class="inline">{Module, Function, Arity, ExtraInfo}</code> and/or <code class="inline">{Fun, Arity, ExtraInfo}</code>
│ │ │ ├── OEBPS/error_logging.xhtml
│ │ │ │ @@ -48,36 +48,36 @@
│ │ │ │  reports and other error and information reports are by default logged through
│ │ │ │  the log handler which is set up when the Kernel application is started.</p><p>Prior to Erlang/OTP 21.0, supervisor, crash, and progress reports were only
│ │ │ │  logged when the SASL application was running. This behaviour can, for backwards
│ │ │ │  compatibility, be enabled by setting the Kernel configuration parameter
│ │ │ │  <a href="../../../lib/kernel/doc/html/kernel_app.xhtml#logger_sasl_compatible"><code class="inline">logger_sasl_compatible</code></a> to
│ │ │ │  <code class="inline">true</code>. For more information, see
│ │ │ │  <a href="../../../lib/sasl/doc/html/error_logging.xhtml">SASL Error Logging</a> in the SASL User's Guide.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -kernel logger_level info</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">21</span><span class="w"> </span><span class="p" data-group-id="6291763953-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">10.0</span><span class="p" data-group-id="6291763953-1">]</span><span class="w"> </span><span class="p" data-group-id="6291763953-2">[</span><span class="ss">source</span><span class="o">-</span><span class="mi">13</span><span class="ss">c50db</span><span class="p" data-group-id="6291763953-2">]</span><span class="w"> </span><span class="p" data-group-id="6291763953-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="6291763953-3">]</span><span class="w"> </span><span class="p" data-group-id="6291763953-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="6291763953-4">]</span><span class="w"> </span><span class="p" data-group-id="6291763953-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="6291763953-5">]</span><span class="w"> </span><span class="p" data-group-id="6291763953-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="6291763953-6">]</span><span class="w"> </span><span class="p" data-group-id="6291763953-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="6291763953-7">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">21</span><span class="w"> </span><span class="p" data-group-id="4831025010-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">10.0</span><span class="p" data-group-id="4831025010-1">]</span><span class="w"> </span><span class="p" data-group-id="4831025010-2">[</span><span class="ss">source</span><span class="o">-</span><span class="mi">13</span><span class="ss">c50db</span><span class="p" data-group-id="4831025010-2">]</span><span class="w"> </span><span class="p" data-group-id="4831025010-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4831025010-3">]</span><span class="w"> </span><span class="p" data-group-id="4831025010-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="4831025010-4">]</span><span class="w"> </span><span class="p" data-group-id="4831025010-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4831025010-5">]</span><span class="w"> </span><span class="p" data-group-id="4831025010-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4831025010-6">]</span><span class="w"> </span><span class="p" data-group-id="4831025010-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="4831025010-7">]</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.916404</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ │      </span><span class="nc">application</span><span class="p">:</span><span class="w"> </span><span class="ss">kernel</span><span class="w">
│ │ │ │      </span><span class="nc">started_at</span><span class="p">:</span><span class="w"> </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.922908</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ │      </span><span class="nc">application</span><span class="p">:</span><span class="w"> </span><span class="ss">stdlib</span><span class="w">
│ │ │ │      </span><span class="nc">started_at</span><span class="p">:</span><span class="w"> </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.925755</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6291763953-8">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="6291763953-8">}</span><span class="w">
│ │ │ │ -    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6291763953-9">[</span><span class="p" data-group-id="6291763953-10">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.74</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6291763953-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-11">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_sup</span><span class="p" data-group-id="6291763953-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-12">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="6291763953-13">{</span><span class="ss">disk_log_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="6291763953-14">[</span><span class="p" data-group-id="6291763953-14">]</span><span class="p" data-group-id="6291763953-13">}</span><span class="p" data-group-id="6291763953-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-15">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="6291763953-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-16">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">1000</span><span class="p" data-group-id="6291763953-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-17">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">supervisor</span><span class="p" data-group-id="6291763953-17">}</span><span class="p" data-group-id="6291763953-9">]</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4831025010-8">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="4831025010-8">}</span><span class="w">
│ │ │ │ +    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4831025010-9">[</span><span class="p" data-group-id="4831025010-10">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.74</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4831025010-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-11">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_sup</span><span class="p" data-group-id="4831025010-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-12">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="4831025010-13">{</span><span class="ss">disk_log_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="4831025010-14">[</span><span class="p" data-group-id="4831025010-14">]</span><span class="p" data-group-id="4831025010-13">}</span><span class="p" data-group-id="4831025010-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-15">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="4831025010-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-16">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">1000</span><span class="p" data-group-id="4831025010-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-17">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">supervisor</span><span class="p" data-group-id="4831025010-17">}</span><span class="p" data-group-id="4831025010-9">]</span><span class="w">
│ │ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.926056</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6291763953-18">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="6291763953-18">}</span><span class="w">
│ │ │ │ -    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="6291763953-19">[</span><span class="p" data-group-id="6291763953-20">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.75</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6291763953-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-21">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_server</span><span class="p" data-group-id="6291763953-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-22">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="6291763953-23">{</span><span class="ss">disk_log_server</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="6291763953-24">[</span><span class="p" data-group-id="6291763953-24">]</span><span class="p" data-group-id="6291763953-23">}</span><span class="p" data-group-id="6291763953-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-25">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="6291763953-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-26">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">2000</span><span class="p" data-group-id="6291763953-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="6291763953-27">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">worker</span><span class="p" data-group-id="6291763953-27">}</span><span class="p" data-group-id="6291763953-19">]</span><span class="w">
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V10</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="6291763953-28">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="6291763953-28">)</span><span class="w">
│ │ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4831025010-18">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="4831025010-18">}</span><span class="w">
│ │ │ │ +    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4831025010-19">[</span><span class="p" data-group-id="4831025010-20">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.75</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4831025010-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-21">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_server</span><span class="p" data-group-id="4831025010-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-22">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="4831025010-23">{</span><span class="ss">disk_log_server</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="4831025010-24">[</span><span class="p" data-group-id="4831025010-24">]</span><span class="p" data-group-id="4831025010-23">}</span><span class="p" data-group-id="4831025010-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-25">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="4831025010-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-26">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">2000</span><span class="p" data-group-id="4831025010-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="4831025010-27">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">worker</span><span class="p" data-group-id="4831025010-27">}</span><span class="p" data-group-id="4831025010-19">]</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V10</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="4831025010-28">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="4831025010-28">)</span><span class="w">
│ │ │ │  </span><span class="mi">1</span><span class="o">&gt;</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/erl_interface.xhtml
│ │ │ │ @@ -25,119 +25,119 @@
│ │ │ │  to read the port example in <a href="c_port.xhtml">Ports</a> before reading this section.</p><h2 id="erlang-program" class="section-heading">
│ │ │ │    <a href="#erlang-program" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Erlang Program</span>
│ │ │ │  </h2>
│ │ │ │  <p>The following example shows an Erlang program communicating with a C program
│ │ │ │ -over a plain port with home made encoding:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4246579761-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="4246579761-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4246579761-2">(</span><span class="p" data-group-id="4246579761-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4246579761-3">]</span><span class="p" data-group-id="4246579761-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4246579761-4">(</span><span class="p" data-group-id="4246579761-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4246579761-5">]</span><span class="p" data-group-id="4246579761-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="4246579761-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="4246579761-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="4246579761-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4246579761-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="4246579761-8">]</span><span class="p" data-group-id="4246579761-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="4246579761-9">(</span><span class="p" data-group-id="4246579761-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +over a plain port with home made encoding:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8343630387-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="8343630387-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8343630387-2">(</span><span class="p" data-group-id="8343630387-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8343630387-3">]</span><span class="p" data-group-id="8343630387-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8343630387-4">(</span><span class="p" data-group-id="8343630387-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8343630387-5">]</span><span class="p" data-group-id="8343630387-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8343630387-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="8343630387-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="8343630387-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8343630387-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="8343630387-8">]</span><span class="p" data-group-id="8343630387-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="8343630387-9">(</span><span class="p" data-group-id="8343630387-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="4246579761-10">(</span><span class="n">X</span><span class="p" data-group-id="4246579761-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="4246579761-11">(</span><span class="p" data-group-id="4246579761-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4246579761-12">}</span><span class="p" data-group-id="4246579761-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="4246579761-13">(</span><span class="n">Y</span><span class="p" data-group-id="4246579761-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="4246579761-14">(</span><span class="p" data-group-id="4246579761-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4246579761-15">}</span><span class="p" data-group-id="4246579761-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="8343630387-10">(</span><span class="n">X</span><span class="p" data-group-id="8343630387-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="8343630387-11">(</span><span class="p" data-group-id="8343630387-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8343630387-12">}</span><span class="p" data-group-id="8343630387-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="8343630387-13">(</span><span class="n">Y</span><span class="p" data-group-id="8343630387-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="8343630387-14">(</span><span class="p" data-group-id="8343630387-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8343630387-15">}</span><span class="p" data-group-id="8343630387-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="4246579761-16">(</span><span class="n">Msg</span><span class="p" data-group-id="4246579761-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4246579761-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4246579761-18">(</span><span class="p" data-group-id="4246579761-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4246579761-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="8343630387-16">(</span><span class="n">Msg</span><span class="p" data-group-id="8343630387-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8343630387-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8343630387-18">(</span><span class="p" data-group-id="8343630387-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8343630387-17">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="4246579761-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="4246579761-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="8343630387-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8343630387-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="4246579761-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="4246579761-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="4246579761-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4246579761-22">(</span><span class="p" data-group-id="4246579761-22">)</span><span class="p" data-group-id="4246579761-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="4246579761-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4246579761-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="4246579761-24">(</span><span class="p" data-group-id="4246579761-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="4246579761-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4246579761-26">[</span><span class="p" data-group-id="4246579761-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4246579761-27">}</span><span class="p" data-group-id="4246579761-26">]</span><span class="p" data-group-id="4246579761-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="4246579761-28">(</span><span class="n">Port</span><span class="p" data-group-id="4246579761-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8343630387-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="8343630387-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="8343630387-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8343630387-22">(</span><span class="p" data-group-id="8343630387-22">)</span><span class="p" data-group-id="8343630387-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="8343630387-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8343630387-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8343630387-24">(</span><span class="p" data-group-id="8343630387-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="8343630387-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8343630387-26">[</span><span class="p" data-group-id="8343630387-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8343630387-27">}</span><span class="p" data-group-id="8343630387-26">]</span><span class="p" data-group-id="8343630387-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="8343630387-28">(</span><span class="n">Port</span><span class="p" data-group-id="8343630387-28">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="4246579761-29">(</span><span class="n">Port</span><span class="p" data-group-id="4246579761-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="8343630387-29">(</span><span class="n">Port</span><span class="p" data-group-id="8343630387-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="4246579761-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4246579761-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4246579761-31">{</span><span class="nf">self</span><span class="p" data-group-id="4246579761-32">(</span><span class="p" data-group-id="4246579761-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4246579761-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="4246579761-34">(</span><span class="n">Msg</span><span class="p" data-group-id="4246579761-34">)</span><span class="p" data-group-id="4246579761-33">}</span><span class="p" data-group-id="4246579761-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="8343630387-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8343630387-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8343630387-31">{</span><span class="nf">self</span><span class="p" data-group-id="8343630387-32">(</span><span class="p" data-group-id="8343630387-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8343630387-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="8343630387-34">(</span><span class="n">Msg</span><span class="p" data-group-id="8343630387-34">)</span><span class="p" data-group-id="8343630387-33">}</span><span class="p" data-group-id="8343630387-31">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="4246579761-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4246579761-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4246579761-36">}</span><span class="p" data-group-id="4246579761-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4246579761-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="4246579761-38">(</span><span class="n">Data</span><span class="p" data-group-id="4246579761-38">)</span><span class="p" data-group-id="4246579761-37">}</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="8343630387-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8343630387-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8343630387-36">}</span><span class="p" data-group-id="8343630387-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8343630387-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="8343630387-38">(</span><span class="n">Data</span><span class="p" data-group-id="8343630387-38">)</span><span class="p" data-group-id="8343630387-37">}</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="4246579761-39">(</span><span class="n">Port</span><span class="p" data-group-id="4246579761-39">)</span><span class="p">;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="8343630387-39">(</span><span class="n">Port</span><span class="p" data-group-id="8343630387-39">)</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4246579761-40">{</span><span class="nf">self</span><span class="p" data-group-id="4246579761-41">(</span><span class="p" data-group-id="4246579761-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="4246579761-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8343630387-40">{</span><span class="nf">self</span><span class="p" data-group-id="8343630387-41">(</span><span class="p" data-group-id="8343630387-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="8343630387-40">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="4246579761-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="4246579761-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="4246579761-43">(</span><span class="ss">normal</span><span class="p" data-group-id="4246579761-43">)</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="8343630387-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="8343630387-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="8343630387-43">(</span><span class="ss">normal</span><span class="p" data-group-id="8343630387-43">)</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="4246579761-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="4246579761-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="4246579761-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="4246579761-45">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="8343630387-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="8343630387-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="8343630387-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="8343630387-45">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="4246579761-46">(</span><span class="p" data-group-id="4246579761-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4246579761-47">}</span><span class="p" data-group-id="4246579761-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4246579761-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4246579761-48">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="4246579761-49">(</span><span class="p" data-group-id="4246579761-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4246579761-50">}</span><span class="p" data-group-id="4246579761-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4246579761-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4246579761-51">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="8343630387-46">(</span><span class="p" data-group-id="8343630387-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8343630387-47">}</span><span class="p" data-group-id="8343630387-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8343630387-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8343630387-48">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="8343630387-49">(</span><span class="p" data-group-id="8343630387-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8343630387-50">}</span><span class="p" data-group-id="8343630387-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8343630387-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8343630387-51">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="4246579761-52">(</span><span class="p" data-group-id="4246579761-53">[</span><span class="n">Int</span><span class="p" data-group-id="4246579761-53">]</span><span class="p" data-group-id="4246579761-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>There are two differences when using Erl_Interface on the C side compared to the
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="8343630387-52">(</span><span class="p" data-group-id="8343630387-53">[</span><span class="n">Int</span><span class="p" data-group-id="8343630387-53">]</span><span class="p" data-group-id="8343630387-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>There are two differences when using Erl_Interface on the C side compared to the
│ │ │ │  example in <a href="c_port.xhtml">Ports</a>, using only the plain port:</p><ul><li>As Erl_Interface operates on the Erlang external term format, the port must be
│ │ │ │  set to use binaries.</li><li>Instead of inventing an encoding/decoding scheme, the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#term_to_binary/1"><code class="inline">term_to_binary/1</code></a> and
│ │ │ │ -<a href="../../../lib/../erts/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a> BIFs are to be used.</li></ul><p>That is:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="7430939627-1">(</span><span class="p" data-group-id="7430939627-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="7430939627-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7430939627-3">[</span><span class="p" data-group-id="7430939627-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7430939627-4">}</span><span class="p" data-group-id="7430939627-3">]</span><span class="p" data-group-id="7430939627-1">)</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="7209019459-1">(</span><span class="p" data-group-id="7209019459-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="7209019459-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7209019459-3">[</span><span class="p" data-group-id="7209019459-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7209019459-4">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="7209019459-3">]</span><span class="p" data-group-id="7209019459-1">)</span></code></pre><p>And:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2411139206-1">{</span><span class="nf">self</span><span class="p" data-group-id="2411139206-2">(</span><span class="p" data-group-id="2411139206-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2411139206-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="2411139206-4">(</span><span class="n">Msg</span><span class="p" data-group-id="2411139206-4">)</span><span class="p" data-group-id="2411139206-3">}</span><span class="p" data-group-id="2411139206-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +<a href="../../../lib/../erts/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a> BIFs are to be used.</li></ul><p>That is:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="0581193788-1">(</span><span class="p" data-group-id="0581193788-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="0581193788-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0581193788-3">[</span><span class="p" data-group-id="0581193788-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0581193788-4">}</span><span class="p" data-group-id="0581193788-3">]</span><span class="p" data-group-id="0581193788-1">)</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="6536416888-1">(</span><span class="p" data-group-id="6536416888-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="6536416888-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6536416888-3">[</span><span class="p" data-group-id="6536416888-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6536416888-4">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="6536416888-3">]</span><span class="p" data-group-id="6536416888-1">)</span></code></pre><p>And:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5338499924-1">{</span><span class="nf">self</span><span class="p" data-group-id="5338499924-2">(</span><span class="p" data-group-id="5338499924-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5338499924-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="5338499924-4">(</span><span class="n">Msg</span><span class="p" data-group-id="5338499924-4">)</span><span class="p" data-group-id="5338499924-3">}</span><span class="p" data-group-id="5338499924-1">}</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2411139206-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2411139206-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2411139206-6">}</span><span class="p" data-group-id="2411139206-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2411139206-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="2411139206-8">(</span><span class="n">Data</span><span class="p" data-group-id="2411139206-8">)</span><span class="p" data-group-id="2411139206-7">}</span><span class="w">
│ │ │ │ -</span><span class="k">end</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7021722252-1">{</span><span class="nf">self</span><span class="p" data-group-id="7021722252-2">(</span><span class="p" data-group-id="7021722252-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7021722252-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="7021722252-4">(</span><span class="n">Msg</span><span class="p" data-group-id="7021722252-4">)</span><span class="p" data-group-id="7021722252-3">}</span><span class="p" data-group-id="7021722252-1">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5338499924-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5338499924-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5338499924-6">}</span><span class="p" data-group-id="5338499924-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5338499924-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="5338499924-8">(</span><span class="n">Data</span><span class="p" data-group-id="5338499924-8">)</span><span class="p" data-group-id="5338499924-7">}</span><span class="w">
│ │ │ │ +</span><span class="k">end</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3578129530-1">{</span><span class="nf">self</span><span class="p" data-group-id="3578129530-2">(</span><span class="p" data-group-id="3578129530-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3578129530-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="3578129530-4">(</span><span class="n">Msg</span><span class="p" data-group-id="3578129530-4">)</span><span class="p" data-group-id="3578129530-3">}</span><span class="p" data-group-id="3578129530-1">}</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="7021722252-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7021722252-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7021722252-6">}</span><span class="p" data-group-id="7021722252-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7021722252-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="7021722252-8">(</span><span class="n">Data</span><span class="p" data-group-id="7021722252-8">)</span><span class="p" data-group-id="7021722252-7">}</span><span class="w">
│ │ │ │ -</span><span class="k">end</span></code></pre><p>The resulting Erlang program is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1779374678-1">(</span><span class="ss">complex2</span><span class="p" data-group-id="1779374678-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1779374678-2">(</span><span class="p" data-group-id="1779374678-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1779374678-3">]</span><span class="p" data-group-id="1779374678-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1779374678-4">(</span><span class="p" data-group-id="1779374678-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1779374678-5">]</span><span class="p" data-group-id="1779374678-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="1779374678-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1779374678-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1779374678-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1779374678-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="1779374678-8">]</span><span class="p" data-group-id="1779374678-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="1779374678-9">(</span><span class="p" data-group-id="1779374678-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3578129530-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3578129530-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3578129530-6">}</span><span class="p" data-group-id="3578129530-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3578129530-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="3578129530-8">(</span><span class="n">Data</span><span class="p" data-group-id="3578129530-8">)</span><span class="p" data-group-id="3578129530-7">}</span><span class="w">
│ │ │ │ +</span><span class="k">end</span></code></pre><p>The resulting Erlang program is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1296504389-1">(</span><span class="ss">complex2</span><span class="p" data-group-id="1296504389-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1296504389-2">(</span><span class="p" data-group-id="1296504389-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1296504389-3">]</span><span class="p" data-group-id="1296504389-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1296504389-4">(</span><span class="p" data-group-id="1296504389-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1296504389-5">]</span><span class="p" data-group-id="1296504389-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="1296504389-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1296504389-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="1296504389-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1296504389-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="1296504389-8">]</span><span class="p" data-group-id="1296504389-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="1296504389-9">(</span><span class="p" data-group-id="1296504389-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="1779374678-10">(</span><span class="n">X</span><span class="p" data-group-id="1779374678-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="1779374678-11">(</span><span class="p" data-group-id="1779374678-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1779374678-12">}</span><span class="p" data-group-id="1779374678-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="1779374678-13">(</span><span class="n">Y</span><span class="p" data-group-id="1779374678-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="1779374678-14">(</span><span class="p" data-group-id="1779374678-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1779374678-15">}</span><span class="p" data-group-id="1779374678-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="1296504389-10">(</span><span class="n">X</span><span class="p" data-group-id="1296504389-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="1296504389-11">(</span><span class="p" data-group-id="1296504389-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1296504389-12">}</span><span class="p" data-group-id="1296504389-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="1296504389-13">(</span><span class="n">Y</span><span class="p" data-group-id="1296504389-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="1296504389-14">(</span><span class="p" data-group-id="1296504389-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1296504389-15">}</span><span class="p" data-group-id="1296504389-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="1779374678-16">(</span><span class="n">Msg</span><span class="p" data-group-id="1779374678-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1779374678-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1779374678-18">(</span><span class="p" data-group-id="1779374678-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1779374678-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="1296504389-16">(</span><span class="n">Msg</span><span class="p" data-group-id="1296504389-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1296504389-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1296504389-18">(</span><span class="p" data-group-id="1296504389-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1296504389-17">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1779374678-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1779374678-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="1296504389-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1296504389-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1779374678-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1779374678-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="1779374678-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1779374678-22">(</span><span class="p" data-group-id="1779374678-22">)</span><span class="p" data-group-id="1779374678-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="1779374678-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1779374678-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="1779374678-24">(</span><span class="p" data-group-id="1779374678-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="1779374678-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1779374678-26">[</span><span class="p" data-group-id="1779374678-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1779374678-27">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="1779374678-26">]</span><span class="p" data-group-id="1779374678-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="1779374678-28">(</span><span class="n">Port</span><span class="p" data-group-id="1779374678-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="1296504389-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1296504389-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="1296504389-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1296504389-22">(</span><span class="p" data-group-id="1296504389-22">)</span><span class="p" data-group-id="1296504389-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="1296504389-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1296504389-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="1296504389-24">(</span><span class="p" data-group-id="1296504389-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="1296504389-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1296504389-26">[</span><span class="p" data-group-id="1296504389-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1296504389-27">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="1296504389-26">]</span><span class="p" data-group-id="1296504389-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="1296504389-28">(</span><span class="n">Port</span><span class="p" data-group-id="1296504389-28">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="1779374678-29">(</span><span class="n">Port</span><span class="p" data-group-id="1779374678-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="1296504389-29">(</span><span class="n">Port</span><span class="p" data-group-id="1296504389-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1779374678-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1779374678-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1779374678-31">{</span><span class="nf">self</span><span class="p" data-group-id="1779374678-32">(</span><span class="p" data-group-id="1779374678-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1779374678-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="1779374678-34">(</span><span class="n">Msg</span><span class="p" data-group-id="1779374678-34">)</span><span class="p" data-group-id="1779374678-33">}</span><span class="p" data-group-id="1779374678-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="1296504389-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1296504389-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1296504389-31">{</span><span class="nf">self</span><span class="p" data-group-id="1296504389-32">(</span><span class="p" data-group-id="1296504389-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1296504389-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="1296504389-34">(</span><span class="n">Msg</span><span class="p" data-group-id="1296504389-34">)</span><span class="p" data-group-id="1296504389-33">}</span><span class="p" data-group-id="1296504389-31">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="1779374678-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1779374678-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1779374678-36">}</span><span class="p" data-group-id="1779374678-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1779374678-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="1779374678-38">(</span><span class="n">Data</span><span class="p" data-group-id="1779374678-38">)</span><span class="p" data-group-id="1779374678-37">}</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="1296504389-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1296504389-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1296504389-36">}</span><span class="p" data-group-id="1296504389-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1296504389-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="1296504389-38">(</span><span class="n">Data</span><span class="p" data-group-id="1296504389-38">)</span><span class="p" data-group-id="1296504389-37">}</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="1779374678-39">(</span><span class="n">Port</span><span class="p" data-group-id="1779374678-39">)</span><span class="p">;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="1296504389-39">(</span><span class="n">Port</span><span class="p" data-group-id="1296504389-39">)</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1779374678-40">{</span><span class="nf">self</span><span class="p" data-group-id="1779374678-41">(</span><span class="p" data-group-id="1779374678-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="1779374678-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1296504389-40">{</span><span class="nf">self</span><span class="p" data-group-id="1296504389-41">(</span><span class="p" data-group-id="1296504389-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="1296504389-40">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="1779374678-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="1779374678-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="1779374678-43">(</span><span class="ss">normal</span><span class="p" data-group-id="1779374678-43">)</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="1296504389-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="1296504389-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="1296504389-43">(</span><span class="ss">normal</span><span class="p" data-group-id="1296504389-43">)</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1779374678-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1779374678-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="1779374678-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="1779374678-45">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="1296504389-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1296504389-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="1296504389-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="1296504389-45">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Notice that calling <code class="inline">complex2:foo/1</code> and <code class="inline">complex2:bar/1</code> results in the tuple
│ │ │ │  <code class="inline">{foo,X}</code> or <code class="inline">{bar,Y}</code> being sent to the <code class="inline">complex</code> process, which codes them as
│ │ │ │  binaries and sends them to the port. This means that the C program must be able
│ │ │ │  to handle these two tuples.</p><h2 id="c-program" class="section-heading">
│ │ │ │    <a href="#c-program" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │ @@ -149,142 +149,142 @@
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="s">&quot;ei.h&quot;</span><span class="w">
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">unistd</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">string</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdlib</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="kt">byte</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="0742806470-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="0742806470-1">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="0742806470-2">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0742806470-2">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0742806470-3">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="0742806470-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="0742806470-4">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="0742806470-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">fail</span><span class="p" data-group-id="0742806470-5">(</span><span class="kt">int</span><span class="w"> </span><span class="n">place</span><span class="p" data-group-id="0742806470-5">)</span><span class="w"> </span><span class="p" data-group-id="0742806470-6">{</span><span class="w">
│ │ │ │ -    </span><span class="nf">fprintf</span><span class="p" data-group-id="0742806470-7">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Something went wrong %d</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">place</span><span class="p" data-group-id="0742806470-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="0742806470-8">(</span><span class="mi">1</span><span class="p" data-group-id="0742806470-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0742806470-6">}</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="2447157169-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="2447157169-1">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="2447157169-2">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="2447157169-2">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="2447157169-3">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="2447157169-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="2447157169-4">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="2447157169-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">fail</span><span class="p" data-group-id="2447157169-5">(</span><span class="kt">int</span><span class="w"> </span><span class="n">place</span><span class="p" data-group-id="2447157169-5">)</span><span class="w"> </span><span class="p" data-group-id="2447157169-6">{</span><span class="w">
│ │ │ │ +    </span><span class="nf">fprintf</span><span class="p" data-group-id="2447157169-7">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Something went wrong %d</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">place</span><span class="p" data-group-id="2447157169-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="2447157169-8">(</span><span class="mi">1</span><span class="p" data-group-id="2447157169-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2447157169-6">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p" data-group-id="0742806470-9">(</span><span class="p" data-group-id="0742806470-9">)</span><span class="w"> </span><span class="p" data-group-id="0742806470-10">{</span><span class="w">
│ │ │ │ -    </span><span class="kt">byte</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="0742806470-11">[</span><span class="mi">100</span><span class="p" data-group-id="0742806470-11">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p" data-group-id="2447157169-9">(</span><span class="p" data-group-id="2447157169-9">)</span><span class="w"> </span><span class="p" data-group-id="2447157169-10">{</span><span class="w">
│ │ │ │ +    </span><span class="kt">byte</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="2447157169-11">[</span><span class="mi">100</span><span class="p" data-group-id="2447157169-11">]</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">index</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">version</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">arity</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="kt">char</span><span class="w"> </span><span class="n">atom</span><span class="p" data-group-id="0742806470-12">[</span><span class="mi">128</span><span class="p" data-group-id="0742806470-12">]</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="kt">char</span><span class="w"> </span><span class="n">atom</span><span class="p" data-group-id="2447157169-12">[</span><span class="mi">128</span><span class="p" data-group-id="2447157169-12">]</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="kt">long</span><span class="w"> </span><span class="n">in</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">ei_x_buff</span><span class="w"> </span><span class="n">res_buf</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="nf">ei_init</span><span class="p" data-group-id="0742806470-13">(</span><span class="p" data-group-id="0742806470-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="0742806470-14">(</span><span class="nf">read_cmd</span><span class="p" data-group-id="0742806470-15">(</span><span class="n">buf</span><span class="p" data-group-id="0742806470-15">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-14">)</span><span class="w"> </span><span class="p" data-group-id="0742806470-16">{</span><span class="w">
│ │ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-17">(</span><span class="nf">ei_decode_version</span><span class="p" data-group-id="0742806470-18">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">version</span><span class="p" data-group-id="0742806470-18">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-17">)</span><span class="w">
│ │ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="0742806470-19">(</span><span class="mi">1</span><span class="p" data-group-id="0742806470-19">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-20">(</span><span class="nf">ei_decode_tuple_header</span><span class="p" data-group-id="0742806470-21">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">arity</span><span class="p" data-group-id="0742806470-21">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-20">)</span><span class="w">
│ │ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="0742806470-22">(</span><span class="mi">2</span><span class="p" data-group-id="0742806470-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-23">(</span><span class="n">arity</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0742806470-23">)</span><span class="w">
│ │ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="0742806470-24">(</span><span class="mi">3</span><span class="p" data-group-id="0742806470-24">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-25">(</span><span class="nf">ei_decode_atom</span><span class="p" data-group-id="0742806470-26">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="n">atom</span><span class="p" data-group-id="0742806470-26">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-25">)</span><span class="w">
│ │ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="0742806470-27">(</span><span class="mi">4</span><span class="p" data-group-id="0742806470-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-28">(</span><span class="nf">ei_decode_long</span><span class="p" data-group-id="0742806470-29">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">in</span><span class="p" data-group-id="0742806470-29">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-28">)</span><span class="w">
│ │ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="0742806470-30">(</span><span class="mi">5</span><span class="p" data-group-id="0742806470-30">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-31">(</span><span class="nf">strncmp</span><span class="p" data-group-id="0742806470-32">(</span><span class="n">atom</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="0742806470-32">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-31">)</span><span class="w"> </span><span class="p" data-group-id="0742806470-33">{</span><span class="w">
│ │ │ │ -            </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0742806470-34">(</span><span class="p" data-group-id="0742806470-35">(</span><span class="kt">int</span><span class="p" data-group-id="0742806470-35">)</span><span class="n">in</span><span class="p" data-group-id="0742806470-34">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0742806470-33">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-36">(</span><span class="nf">strncmp</span><span class="p" data-group-id="0742806470-37">(</span><span class="n">atom</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bar&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="0742806470-37">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-36">)</span><span class="w"> </span><span class="p" data-group-id="0742806470-38">{</span><span class="w">
│ │ │ │ -            </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="0742806470-39">(</span><span class="p" data-group-id="0742806470-40">(</span><span class="kt">int</span><span class="p" data-group-id="0742806470-40">)</span><span class="n">in</span><span class="p" data-group-id="0742806470-39">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0742806470-38">}</span><span class="w">
│ │ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-41">(</span><span class="nf">ei_x_new_with_version</span><span class="p" data-group-id="0742806470-42">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p" data-group-id="0742806470-42">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-41">)</span><span class="w">
│ │ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="0742806470-43">(</span><span class="mi">6</span><span class="p" data-group-id="0742806470-43">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-44">(</span><span class="nf">ei_x_encode_long</span><span class="p" data-group-id="0742806470-45">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p" data-group-id="0742806470-45">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-44">)</span><span class="w">
│ │ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="0742806470-46">(</span><span class="mi">7</span><span class="p" data-group-id="0742806470-46">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="nf">write_cmd</span><span class="p" data-group-id="0742806470-47">(</span><span class="n">res_buf</span><span class="p">.</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="n">res_buf</span><span class="p">.</span><span class="n">index</span><span class="p" data-group-id="0742806470-47">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nf">ei_init</span><span class="p" data-group-id="2447157169-13">(</span><span class="p" data-group-id="2447157169-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="2447157169-14">(</span><span class="nf">read_cmd</span><span class="p" data-group-id="2447157169-15">(</span><span class="n">buf</span><span class="p" data-group-id="2447157169-15">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-14">)</span><span class="w"> </span><span class="p" data-group-id="2447157169-16">{</span><span class="w">
│ │ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-17">(</span><span class="nf">ei_decode_version</span><span class="p" data-group-id="2447157169-18">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">version</span><span class="p" data-group-id="2447157169-18">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-17">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2447157169-19">(</span><span class="mi">1</span><span class="p" data-group-id="2447157169-19">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-20">(</span><span class="nf">ei_decode_tuple_header</span><span class="p" data-group-id="2447157169-21">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">arity</span><span class="p" data-group-id="2447157169-21">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-20">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2447157169-22">(</span><span class="mi">2</span><span class="p" data-group-id="2447157169-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-23">(</span><span class="n">arity</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2447157169-23">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2447157169-24">(</span><span class="mi">3</span><span class="p" data-group-id="2447157169-24">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-25">(</span><span class="nf">ei_decode_atom</span><span class="p" data-group-id="2447157169-26">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="n">atom</span><span class="p" data-group-id="2447157169-26">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-25">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2447157169-27">(</span><span class="mi">4</span><span class="p" data-group-id="2447157169-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-28">(</span><span class="nf">ei_decode_long</span><span class="p" data-group-id="2447157169-29">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">in</span><span class="p" data-group-id="2447157169-29">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-28">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2447157169-30">(</span><span class="mi">5</span><span class="p" data-group-id="2447157169-30">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-31">(</span><span class="nf">strncmp</span><span class="p" data-group-id="2447157169-32">(</span><span class="n">atom</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2447157169-32">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-31">)</span><span class="w"> </span><span class="p" data-group-id="2447157169-33">{</span><span class="w">
│ │ │ │ +            </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="2447157169-34">(</span><span class="p" data-group-id="2447157169-35">(</span><span class="kt">int</span><span class="p" data-group-id="2447157169-35">)</span><span class="n">in</span><span class="p" data-group-id="2447157169-34">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2447157169-33">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-36">(</span><span class="nf">strncmp</span><span class="p" data-group-id="2447157169-37">(</span><span class="n">atom</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bar&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2447157169-37">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-36">)</span><span class="w"> </span><span class="p" data-group-id="2447157169-38">{</span><span class="w">
│ │ │ │ +            </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="2447157169-39">(</span><span class="p" data-group-id="2447157169-40">(</span><span class="kt">int</span><span class="p" data-group-id="2447157169-40">)</span><span class="n">in</span><span class="p" data-group-id="2447157169-39">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2447157169-38">}</span><span class="w">
│ │ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-41">(</span><span class="nf">ei_x_new_with_version</span><span class="p" data-group-id="2447157169-42">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p" data-group-id="2447157169-42">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-41">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2447157169-43">(</span><span class="mi">6</span><span class="p" data-group-id="2447157169-43">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-44">(</span><span class="nf">ei_x_encode_long</span><span class="p" data-group-id="2447157169-45">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p" data-group-id="2447157169-45">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-44">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2447157169-46">(</span><span class="mi">7</span><span class="p" data-group-id="2447157169-46">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="nf">write_cmd</span><span class="p" data-group-id="2447157169-47">(</span><span class="n">res_buf</span><span class="p">.</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="n">res_buf</span><span class="p">.</span><span class="n">index</span><span class="p" data-group-id="2447157169-47">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0742806470-48">(</span><span class="nf">ei_x_free</span><span class="p" data-group-id="0742806470-49">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p" data-group-id="0742806470-49">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0742806470-48">)</span><span class="w">
│ │ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="0742806470-50">(</span><span class="mi">8</span><span class="p" data-group-id="0742806470-50">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2447157169-48">(</span><span class="nf">ei_x_free</span><span class="p" data-group-id="2447157169-49">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p" data-group-id="2447157169-49">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2447157169-48">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2447157169-50">(</span><span class="mi">8</span><span class="p" data-group-id="2447157169-50">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="n">index</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0742806470-16">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0742806470-10">}</span></code></pre><p>The following functions, <code class="inline">read_cmd()</code> and <code class="inline">write_cmd()</code>, from the <code class="inline">erl_comm.c</code>
│ │ │ │ +    </span><span class="p" data-group-id="2447157169-16">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2447157169-10">}</span></code></pre><p>The following functions, <code class="inline">read_cmd()</code> and <code class="inline">write_cmd()</code>, from the <code class="inline">erl_comm.c</code>
│ │ │ │  example in <a href="c_port.xhtml">Ports</a> can still be used for reading from and writing to
│ │ │ │  the port:</p><pre><code class="makeup c" translate="no"><span class="cm">/* erl_comm.c */</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdio</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">unistd</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="kt">byte</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="0377805234-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0377805234-1">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0377805234-2">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="4990450458-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="4990450458-1">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4990450458-2">{</span><span class="w">
│ │ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">got</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="0377805234-3">{</span><span class="w">
│ │ │ │ -      </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0377805234-4">(</span><span class="p" data-group-id="0377805234-5">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read</span><span class="p" data-group-id="0377805234-6">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">got</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">got</span><span class="p" data-group-id="0377805234-6">)</span><span class="p" data-group-id="0377805234-5">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0377805234-4">)</span><span class="p" data-group-id="0377805234-7">{</span><span class="w">
│ │ │ │ -          </span><span class="nf">return</span><span class="p" data-group-id="0377805234-8">(</span><span class="n">i</span><span class="p" data-group-id="0377805234-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ -      </span><span class="p" data-group-id="0377805234-7">}</span><span class="w">
│ │ │ │ +  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="4990450458-3">{</span><span class="w">
│ │ │ │ +      </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4990450458-4">(</span><span class="p" data-group-id="4990450458-5">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read</span><span class="p" data-group-id="4990450458-6">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">got</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">got</span><span class="p" data-group-id="4990450458-6">)</span><span class="p" data-group-id="4990450458-5">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4990450458-4">)</span><span class="p" data-group-id="4990450458-7">{</span><span class="w">
│ │ │ │ +          </span><span class="nf">return</span><span class="p" data-group-id="4990450458-8">(</span><span class="n">i</span><span class="p" data-group-id="4990450458-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +      </span><span class="p" data-group-id="4990450458-7">}</span><span class="w">
│ │ │ │      </span><span class="n">got</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0377805234-3">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="0377805234-9">(</span><span class="n">got</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="0377805234-9">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4990450458-3">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="4990450458-9">(</span><span class="n">got</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="4990450458-9">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="nf">return</span><span class="p" data-group-id="0377805234-10">(</span><span class="n">len</span><span class="p" data-group-id="0377805234-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0377805234-2">}</span><span class="w">
│ │ │ │ +  </span><span class="nf">return</span><span class="p" data-group-id="4990450458-10">(</span><span class="n">len</span><span class="p" data-group-id="4990450458-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4990450458-2">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="0377805234-11">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0377805234-11">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0377805234-12">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="4990450458-11">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="4990450458-11">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4990450458-12">{</span><span class="w">
│ │ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">wrote</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="0377805234-13">{</span><span class="w">
│ │ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0377805234-14">(</span><span class="p" data-group-id="0377805234-15">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">write</span><span class="p" data-group-id="0377805234-16">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">wrote</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">wrote</span><span class="p" data-group-id="0377805234-16">)</span><span class="p" data-group-id="0377805234-15">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0377805234-14">)</span><span class="w">
│ │ │ │ -      </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="0377805234-17">(</span><span class="n">i</span><span class="p" data-group-id="0377805234-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="4990450458-13">{</span><span class="w">
│ │ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4990450458-14">(</span><span class="p" data-group-id="4990450458-15">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">write</span><span class="p" data-group-id="4990450458-16">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">wrote</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">wrote</span><span class="p" data-group-id="4990450458-16">)</span><span class="p" data-group-id="4990450458-15">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4990450458-14">)</span><span class="w">
│ │ │ │ +      </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="4990450458-17">(</span><span class="n">i</span><span class="p" data-group-id="4990450458-17">)</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">wrote</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0377805234-13">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="0377805234-18">(</span><span class="n">wrote</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="0377805234-18">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="4990450458-13">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="4990450458-18">(</span><span class="n">wrote</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="4990450458-18">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="0377805234-19">(</span><span class="n">len</span><span class="p" data-group-id="0377805234-19">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0377805234-12">}</span><span class="w">
│ │ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="4990450458-19">(</span><span class="n">len</span><span class="p" data-group-id="4990450458-19">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4990450458-12">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="0377805234-20">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="0377805234-20">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0377805234-21">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="4990450458-20">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="4990450458-20">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4990450458-21">{</span><span class="w">
│ │ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0377805234-22">(</span><span class="nf">read_exact</span><span class="p" data-group-id="0377805234-23">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0377805234-23">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0377805234-22">)</span><span class="w">
│ │ │ │ -    </span><span class="nf">return</span><span class="p" data-group-id="0377805234-24">(</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0377805234-24">)</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="n">len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0377805234-25">(</span><span class="n">buf</span><span class="p" data-group-id="0377805234-26">[</span><span class="mi">0</span><span class="p" data-group-id="0377805234-26">]</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="0377805234-25">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="0377805234-27">[</span><span class="mi">1</span><span class="p" data-group-id="0377805234-27">]</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="0377805234-28">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0377805234-28">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0377805234-21">}</span><span class="w">
│ │ │ │ +  </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4990450458-22">(</span><span class="nf">read_exact</span><span class="p" data-group-id="4990450458-23">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4990450458-23">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4990450458-22">)</span><span class="w">
│ │ │ │ +    </span><span class="nf">return</span><span class="p" data-group-id="4990450458-24">(</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="4990450458-24">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="n">len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4990450458-25">(</span><span class="n">buf</span><span class="p" data-group-id="4990450458-26">[</span><span class="mi">0</span><span class="p" data-group-id="4990450458-26">]</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="4990450458-25">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="4990450458-27">[</span><span class="mi">1</span><span class="p" data-group-id="4990450458-27">]</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="4990450458-28">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="4990450458-28">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4990450458-21">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="0377805234-29">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0377805234-29">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0377805234-30">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="4990450458-29">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="4990450458-29">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4990450458-30">{</span><span class="w">
│ │ │ │    </span><span class="kt">byte</span><span class="w"> </span><span class="n">li</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0377805234-31">(</span><span class="n">len</span><span class="w"> </span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="0377805234-31">)</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="nf">write_exact</span><span class="p" data-group-id="0377805234-32">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0377805234-32">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4990450458-31">(</span><span class="n">len</span><span class="w"> </span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="4990450458-31">)</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="nf">write_exact</span><span class="p" data-group-id="4990450458-32">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4990450458-32">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │    </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">len</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="nf">write_exact</span><span class="p" data-group-id="0377805234-33">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0377805234-33">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="nf">write_exact</span><span class="p" data-group-id="4990450458-33">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4990450458-33">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="0377805234-34">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0377805234-34">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0377805234-30">}</span></code></pre><h2 id="running-the-example" class="section-heading">
│ │ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="4990450458-34">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="4990450458-34">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4990450458-30">}</span></code></pre><h2 id="running-the-example" class="section-heading">
│ │ │ │    <a href="#running-the-example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Running the Example</span>
│ │ │ │  </h2>
│ │ │ │  <p><em>Step 1.</em> Compile the C code. This provides the paths to the include file
│ │ │ │  <code class="inline">ei.h</code>, and also to the library <code class="inline">ei</code>:</p><pre><code class="text">$ gcc -o extprg -I/usr/local/otp/lib/erl_interface-3.9.2/include \
│ │ │ │      -L/usr/local/otp/lib/erl_interface-3.9.2/lib \
│ │ │ │      complex.c erl_comm.c ei.c -lei -lpthread</code></pre><p>In Erlang/OTP R5B and later versions of OTP, the <code class="inline">include</code> and <code class="inline">lib</code> directories
│ │ │ │  are situated under <code class="inline">$OTPROOT/lib/erl_interface-VSN</code>, where <code class="inline">$OTPROOT</code> is the
│ │ │ │  root directory of the OTP installation (<code class="inline">/usr/local/otp</code> in the recent example)
│ │ │ │  and <code class="inline">VSN</code> is the version of the Erl_interface application (3.2.1 in the recent
│ │ │ │  example).</p><p>In R4B and earlier versions of OTP, <code class="inline">include</code> and <code class="inline">lib</code> are situated under
│ │ │ │  <code class="inline">$OTPROOT/usr</code>.</p><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$ </span><span class="ss">erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="1020114596-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="1020114596-1">]</span><span class="w"> </span><span class="p" data-group-id="1020114596-2">[</span><span class="ss">source</span><span class="p" data-group-id="1020114596-2">]</span><span class="w"> </span><span class="p" data-group-id="1020114596-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="1020114596-3">]</span><span class="w"> </span><span class="p" data-group-id="1020114596-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="1020114596-4">]</span><span class="w"> </span><span class="p" data-group-id="1020114596-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="1020114596-5">]</span><span class="w"> </span><span class="p" data-group-id="1020114596-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1020114596-6">]</span><span class="w"> </span><span class="p" data-group-id="1020114596-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="1020114596-7">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="8020076880-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="8020076880-1">]</span><span class="w"> </span><span class="p" data-group-id="8020076880-2">[</span><span class="ss">source</span><span class="p" data-group-id="8020076880-2">]</span><span class="w"> </span><span class="p" data-group-id="8020076880-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="8020076880-3">]</span><span class="w"> </span><span class="p" data-group-id="8020076880-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="8020076880-4">]</span><span class="w"> </span><span class="p" data-group-id="8020076880-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="8020076880-5">]</span><span class="w"> </span><span class="p" data-group-id="8020076880-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8020076880-6">]</span><span class="w"> </span><span class="p" data-group-id="8020076880-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="8020076880-7">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="1020114596-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="1020114596-9">(</span><span class="p" data-group-id="1020114596-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="1020114596-8">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="1020114596-10">(</span><span class="ss">complex2</span><span class="p" data-group-id="1020114596-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1020114596-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex2</span><span class="p" data-group-id="1020114596-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8951078127-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="8951078127-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="8020076880-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="8020076880-9">(</span><span class="p" data-group-id="8020076880-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="8020076880-8">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="8020076880-10">(</span><span class="ss">complex2</span><span class="p" data-group-id="8020076880-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8020076880-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex2</span><span class="p" data-group-id="8020076880-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3502125210-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="3502125210-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="8951078127-2">(</span><span class="mi">3</span><span class="p" data-group-id="8951078127-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="3502125210-2">(</span><span class="mi">3</span><span class="p" data-group-id="3502125210-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="8951078127-3">(</span><span class="mi">5</span><span class="p" data-group-id="8951078127-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="3502125210-3">(</span><span class="mi">5</span><span class="p" data-group-id="3502125210-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="8951078127-4">(</span><span class="mi">352</span><span class="p" data-group-id="8951078127-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="3502125210-4">(</span><span class="mi">352</span><span class="p" data-group-id="3502125210-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">704</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="8951078127-5">(</span><span class="p" data-group-id="8951078127-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="3502125210-5">(</span><span class="p" data-group-id="3502125210-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/eff_guide_processes.xhtml
│ │ │ │ @@ -24,45 +24,45 @@
│ │ │ │    <a href="#creating-an-erlang-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating an Erlang Process</span>
│ │ │ │  </h2>
│ │ │ │  <p>An Erlang process is lightweight compared to threads and processes in operating
│ │ │ │  systems.</p><p>A newly spawned Erlang process uses 327 words of memory. The size can be found
│ │ │ │ -as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="4257777487-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p">.</span><span class="mi">3</span><span class="p" data-group-id="4257777487-1">]</span><span class="w"> </span><span class="p" data-group-id="4257777487-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4257777487-2">]</span><span class="w"> </span><span class="p" data-group-id="4257777487-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4257777487-3">]</span><span class="w"> </span><span class="p" data-group-id="4257777487-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4257777487-4">]</span><span class="w"> </span><span class="p" data-group-id="4257777487-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4257777487-5">]</span><span class="w"> </span><span class="p" data-group-id="4257777487-6">[</span><span class="ss">jit</span><span class="p" data-group-id="4257777487-6">]</span><span class="w">
│ │ │ │ +as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="4006630175-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p">.</span><span class="mi">3</span><span class="p" data-group-id="4006630175-1">]</span><span class="w"> </span><span class="p" data-group-id="4006630175-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4006630175-2">]</span><span class="w"> </span><span class="p" data-group-id="4006630175-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4006630175-3">]</span><span class="w"> </span><span class="p" data-group-id="4006630175-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4006630175-4">]</span><span class="w"> </span><span class="p" data-group-id="4006630175-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4006630175-5">]</span><span class="w"> </span><span class="p" data-group-id="4006630175-6">[</span><span class="ss">jit</span><span class="p" data-group-id="4006630175-6">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mf">2.3</span><span class="w"> </span><span class="p" data-group-id="4257777487-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4257777487-8">(</span><span class="p" data-group-id="4257777487-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4257777487-7">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4257777487-9">(</span><span class="p" data-group-id="4257777487-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="ss">infinity</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mf">2.3</span><span class="w"> </span><span class="p" data-group-id="4006630175-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4006630175-8">(</span><span class="p" data-group-id="4006630175-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4006630175-7">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4006630175-9">(</span><span class="p" data-group-id="4006630175-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="ss">infinity</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">43.39164016</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4257777487-10">{</span><span class="p">_</span><span class="p">,</span><span class="n">Bytes</span><span class="p" data-group-id="4257777487-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">process_info</span><span class="p" data-group-id="4257777487-11">(</span><span class="nf">spawn</span><span class="p" data-group-id="4257777487-12">(</span><span class="n">Fun</span><span class="p" data-group-id="4257777487-12">)</span><span class="p">,</span><span class="w"> </span><span class="nb">memory</span><span class="p" data-group-id="4257777487-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4257777487-13">{</span><span class="nb">memory</span><span class="p">,</span><span class="mi">2616</span><span class="p" data-group-id="4257777487-13">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="n">Bytes</span><span class="w"> </span><span class="ow">div</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="4257777487-14">(</span><span class="ss">wordsize</span><span class="p" data-group-id="4257777487-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4006630175-10">{</span><span class="p">_</span><span class="p">,</span><span class="n">Bytes</span><span class="p" data-group-id="4006630175-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">process_info</span><span class="p" data-group-id="4006630175-11">(</span><span class="nf">spawn</span><span class="p" data-group-id="4006630175-12">(</span><span class="n">Fun</span><span class="p" data-group-id="4006630175-12">)</span><span class="p">,</span><span class="w"> </span><span class="nb">memory</span><span class="p" data-group-id="4006630175-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4006630175-13">{</span><span class="nb">memory</span><span class="p">,</span><span class="mi">2616</span><span class="p" data-group-id="4006630175-13">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="n">Bytes</span><span class="w"> </span><span class="ow">div</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="4006630175-14">(</span><span class="ss">wordsize</span><span class="p" data-group-id="4006630175-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">327</span></code></pre><p>The size includes 233 words for the heap area (which includes the stack). The
│ │ │ │  garbage collector increases the heap as needed.</p><p>The main (outer) loop for a process <em>must</em> be tail-recursive. Otherwise, the
│ │ │ │ -stack grows until the process terminates.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="0230600466-1">(</span><span class="p" data-group-id="0230600466-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +stack grows until the process terminates.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="7695856862-1">(</span><span class="p" data-group-id="7695856862-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0230600466-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="0230600466-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="0230600466-3">(</span><span class="n">Msg</span><span class="p" data-group-id="0230600466-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="0230600466-4">(</span><span class="p" data-group-id="0230600466-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="0230600466-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="0230600466-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -          </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="0230600466-6">(</span><span class="n">Msg</span><span class="p" data-group-id="0230600466-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7695856862-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7695856862-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="7695856862-3">(</span><span class="n">Msg</span><span class="p" data-group-id="7695856862-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="7695856862-4">(</span><span class="p" data-group-id="7695856862-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="7695856862-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7695856862-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +          </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7695856862-6">(</span><span class="n">Msg</span><span class="p" data-group-id="7695856862-6">)</span><span class="p">,</span><span class="w">
│ │ │ │            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Reply</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="nf">loop</span><span class="p" data-group-id="0230600466-7">(</span><span class="p" data-group-id="0230600466-7">)</span><span class="w">
│ │ │ │ +          </span><span class="nf">loop</span><span class="p" data-group-id="7695856862-7">(</span><span class="p" data-group-id="7695856862-7">)</span><span class="w">
│ │ │ │    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0230600466-8">(</span><span class="s">&quot;Message is processed</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0230600466-9">[</span><span class="p" data-group-id="0230600466-9">]</span><span class="p" data-group-id="0230600466-8">)</span><span class="p">.</span></code></pre><p>The call to <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> will never be executed, but a return address will
│ │ │ │ +  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7695856862-8">(</span><span class="s">&quot;Message is processed</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7695856862-9">[</span><span class="p" data-group-id="7695856862-9">]</span><span class="p" data-group-id="7695856862-8">)</span><span class="p">.</span></code></pre><p>The call to <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> will never be executed, but a return address will
│ │ │ │  still be pushed to the stack each time <code class="inline">loop/0</code> is called recursively. The
│ │ │ │ -correct tail-recursive version of the function looks as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="8620031491-1">(</span><span class="p" data-group-id="8620031491-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +correct tail-recursive version of the function looks as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="7120881776-1">(</span><span class="p" data-group-id="7120881776-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │     </span><span class="k">receive</span><span class="w">
│ │ │ │ -      </span><span class="p" data-group-id="8620031491-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8620031491-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="8620031491-3">(</span><span class="n">Msg</span><span class="p" data-group-id="8620031491-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="8620031491-4">(</span><span class="p" data-group-id="8620031491-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ -      </span><span class="p" data-group-id="8620031491-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8620031491-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -         </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8620031491-6">(</span><span class="n">Msg</span><span class="p" data-group-id="8620031491-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +      </span><span class="p" data-group-id="7120881776-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7120881776-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="7120881776-3">(</span><span class="n">Msg</span><span class="p" data-group-id="7120881776-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="7120881776-4">(</span><span class="p" data-group-id="7120881776-4">)</span><span class="p">;</span><span class="w">
│ │ │ │ +      </span><span class="p" data-group-id="7120881776-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7120881776-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +         </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7120881776-6">(</span><span class="n">Msg</span><span class="p" data-group-id="7120881776-6">)</span><span class="p">,</span><span class="w">
│ │ │ │           </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Reply</span><span class="p">,</span><span class="w">
│ │ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="8620031491-7">(</span><span class="p" data-group-id="8620031491-7">)</span><span class="w">
│ │ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="7120881776-7">(</span><span class="p" data-group-id="7120881776-7">)</span><span class="w">
│ │ │ │   </span><span class="k">end</span><span class="p">.</span></code></pre><h3 id="initial-heap-size" class="section-heading">
│ │ │ │    <a href="#initial-heap-size" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Initial Heap Size</span>
│ │ │ │  </h3>
│ │ │ │  <p>The default initial heap size of 233 words is quite conservative to support
│ │ │ │ @@ -94,30 +94,30 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Receiving messages</span>
│ │ │ │  </h2>
│ │ │ │  <p>The cost of receiving messages depends on how complicated the <code class="inline">receive</code>
│ │ │ │  expression is. A simple expression that matches any message is very cheap
│ │ │ │  because it retrieves the first message in the message queue:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="1577663839-1">(</span><span class="n">Message</span><span class="p" data-group-id="1577663839-1">)</span><span class="w">
│ │ │ │ +    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="1457978620-1">(</span><span class="n">Message</span><span class="p" data-group-id="1457978620-1">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>However, this is not always convenient: we can receive a message that we do not
│ │ │ │  know how to handle at this point, so it is common to only match the messages we
│ │ │ │  expect:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1485307972-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="1485307972-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="1485307972-2">(</span><span class="n">Message</span><span class="p" data-group-id="1485307972-2">)</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1469724446-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="1469724446-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="1469724446-2">(</span><span class="n">Message</span><span class="p" data-group-id="1469724446-2">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>While this is convenient it means that the entire message queue must be searched
│ │ │ │  until it finds a matching message. This is very expensive for processes with
│ │ │ │  long message queues, so there is an optimization for the common case of
│ │ │ │ -sending a request and waiting for a response shortly after:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="9134439054-1">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="9134439054-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9134439054-2">{</span><span class="nf">self</span><span class="p" data-group-id="9134439054-3">(</span><span class="p" data-group-id="9134439054-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="9134439054-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +sending a request and waiting for a response shortly after:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="1705478399-1">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="1705478399-1">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1705478399-2">{</span><span class="nf">self</span><span class="p" data-group-id="1705478399-3">(</span><span class="p" data-group-id="1705478399-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="1705478399-2">}</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9134439054-4">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="9134439054-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="9134439054-5">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9134439054-6">[</span><span class="ss">flush</span><span class="p" data-group-id="9134439054-6">]</span><span class="p" data-group-id="9134439054-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="nf">handle_reply</span><span class="p" data-group-id="9134439054-7">(</span><span class="n">Reply</span><span class="p" data-group-id="9134439054-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9134439054-8">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9134439054-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nf">handle_error</span><span class="p" data-group-id="9134439054-9">(</span><span class="n">Reason</span><span class="p" data-group-id="9134439054-9">)</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1705478399-4">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="1705478399-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="1705478399-5">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1705478399-6">[</span><span class="ss">flush</span><span class="p" data-group-id="1705478399-6">]</span><span class="p" data-group-id="1705478399-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="nf">handle_reply</span><span class="p" data-group-id="1705478399-7">(</span><span class="n">Reply</span><span class="p" data-group-id="1705478399-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1705478399-8">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1705478399-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nf">handle_error</span><span class="p" data-group-id="1705478399-9">(</span><span class="n">Reason</span><span class="p" data-group-id="1705478399-9">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>Since the compiler knows that the reference created by
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#monitor/2"><code class="inline">monitor/2</code></a> cannot exist before the call (since it is a globally
│ │ │ │  unique identifier), and that the <code class="inline">receive</code> only matches messages that contain
│ │ │ │  said reference, it will tell the emulator to search only the messages that
│ │ │ │  arrived after the call to <a href="../../../lib/../erts/doc/html/erlang.html#monitor/2"><code class="inline">monitor/2</code></a>.</p><p>The above is a simple example where one is but guaranteed that the optimization
│ │ │ │  will take, but what about more complicated code?</p><p><a href="" id="recv_opt_info"></a></p><h3 id="option-recv_opt_info" class="section-heading">
│ │ │ │    <a href="#option-recv_opt_info" class="hover-link">
│ │ │ │ @@ -133,101 +133,101 @@
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">200</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">NOT</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">do</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">suitable</span><span class="w"> </span><span class="ss">reference</span><span class="w">
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">206</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">used</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">mark</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">message</span><span class="w"> </span><span class="ss">queue</span><span class="w"> </span><span class="ss">position</span><span class="w">
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">208</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">created</span><span class="w"> </span><span class="ss">by</span><span class="w"> </span><span class="nb">monitor</span><span class="p">/</span><span class="mi">2</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">206</span><span class="w">
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">219</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">INFO</span><span class="p">:</span><span class="w"> </span><span class="ss">passing</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">created</span><span class="w"> </span><span class="ss">by</span><span class="w"> </span><span class="ss">make_ref</span><span class="p">/</span><span class="mi">0</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">218</span><span class="w">
│ │ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">222</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">function</span><span class="w"> </span><span class="ss">parameter</span><span class="w"> </span><span class="mi">1</span></code></pre><p>To make it clearer exactly what code the warnings refer to, the warnings in the
│ │ │ │  following examples are inserted as comments after the clause they refer to, for
│ │ │ │  example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% DO</span><span class="w">
│ │ │ │ -</span><span class="nf">simple_receive</span><span class="p" data-group-id="0408646461-1">(</span><span class="p" data-group-id="0408646461-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">simple_receive</span><span class="p" data-group-id="8849138652-1">(</span><span class="p" data-group-id="8849138652-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%% efficiency_guide.erl:194: Warning: INFO: not a selective receive, this is always fast</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="0408646461-2">(</span><span class="n">Message</span><span class="p" data-group-id="0408646461-2">)</span><span class="w">
│ │ │ │ +    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8849138652-2">(</span><span class="n">Message</span><span class="p" data-group-id="8849138652-2">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% DO NOT, unless Tag is known to be a suitable reference: see</span><span class="w">
│ │ │ │  </span><span class="c1">%% cross_function_receive/0 further down.</span><span class="w">
│ │ │ │ -</span><span class="nf">selective_receive</span><span class="p" data-group-id="0408646461-3">(</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0408646461-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">selective_receive</span><span class="p" data-group-id="8849138652-3">(</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8849138652-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%% efficiency_guide.erl:200: Warning: NOT OPTIMIZED: all clauses do not match a suitable reference</span><span class="w">
│ │ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0408646461-4">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0408646461-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="0408646461-5">(</span><span class="n">Message</span><span class="p" data-group-id="0408646461-5">)</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8849138652-4">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8849138652-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8849138652-5">(</span><span class="n">Message</span><span class="p" data-group-id="8849138652-5">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% DO</span><span class="w">
│ │ │ │ -</span><span class="nf">optimized_receive</span><span class="p" data-group-id="0408646461-6">(</span><span class="n">Process</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0408646461-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">optimized_receive</span><span class="p" data-group-id="8849138652-6">(</span><span class="n">Process</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8849138652-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%% efficiency_guide.erl:206: Warning: OPTIMIZED: reference used to mark a message queue position</span><span class="w">
│ │ │ │ -    </span><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="0408646461-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="0408646461-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0408646461-8">{</span><span class="nf">self</span><span class="p" data-group-id="0408646461-9">(</span><span class="p" data-group-id="0408646461-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="0408646461-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="8849138652-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="8849138652-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8849138652-8">{</span><span class="nf">self</span><span class="p" data-group-id="8849138652-9">(</span><span class="p" data-group-id="8849138652-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="8849138652-8">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%% efficiency_guide.erl:208: Warning: OPTIMIZED: matches reference created by monitor/2 at efficiency_guide.erl:206</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0408646461-10">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="0408646461-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="0408646461-11">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0408646461-12">[</span><span class="ss">flush</span><span class="p" data-group-id="0408646461-12">]</span><span class="p" data-group-id="0408646461-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="nf">handle_reply</span><span class="p" data-group-id="0408646461-13">(</span><span class="n">Reply</span><span class="p" data-group-id="0408646461-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0408646461-14">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="0408646461-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">handle_error</span><span class="p" data-group-id="0408646461-15">(</span><span class="n">Reason</span><span class="p" data-group-id="0408646461-15">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8849138652-10">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="8849138652-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="8849138652-11">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8849138652-12">[</span><span class="ss">flush</span><span class="p" data-group-id="8849138652-12">]</span><span class="p" data-group-id="8849138652-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="nf">handle_reply</span><span class="p" data-group-id="8849138652-13">(</span><span class="n">Reply</span><span class="p" data-group-id="8849138652-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8849138652-14">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="8849138652-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">handle_error</span><span class="p" data-group-id="8849138652-15">(</span><span class="n">Reason</span><span class="p" data-group-id="8849138652-15">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% DO</span><span class="w">
│ │ │ │ -</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="0408646461-16">(</span><span class="p" data-group-id="0408646461-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="8849138652-16">(</span><span class="p" data-group-id="8849138652-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% efficiency_guide.erl:218: Warning: OPTIMIZED: reference used to mark a message queue position</span><span class="w">
│ │ │ │ -    </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="0408646461-17">(</span><span class="p" data-group-id="0408646461-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="8849138652-17">(</span><span class="p" data-group-id="8849138652-17">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%% efficiency_guide.erl:219: Warning: INFO: passing reference created by make_ref/0 at efficiency_guide.erl:218</span><span class="w">
│ │ │ │ -    </span><span class="nf">cross_function_receive</span><span class="p" data-group-id="0408646461-18">(</span><span class="n">Ref</span><span class="p" data-group-id="0408646461-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">cross_function_receive</span><span class="p" data-group-id="8849138652-18">(</span><span class="n">Ref</span><span class="p" data-group-id="8849138652-18">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="0408646461-19">(</span><span class="n">Ref</span><span class="p" data-group-id="0408646461-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="8849138652-19">(</span><span class="n">Ref</span><span class="p" data-group-id="8849138652-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% efficiency_guide.erl:222: Warning: OPTIMIZED: all clauses match reference in function parameter 1</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="0408646461-20">{</span><span class="n">Ref</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0408646461-20">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="0408646461-21">(</span><span class="n">Message</span><span class="p" data-group-id="0408646461-21">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="8849138652-20">{</span><span class="n">Ref</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8849138652-20">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8849138652-21">(</span><span class="n">Message</span><span class="p" data-group-id="8849138652-21">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="literal-pool" class="section-heading">
│ │ │ │    <a href="#literal-pool" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Literal Pool</span>
│ │ │ │  </h2>
│ │ │ │  <p>Constant Erlang terms (hereafter called <em>literals</em>) are kept in <em>literal pools</em>;
│ │ │ │  each loaded module has its own pool. The following function does not build the
│ │ │ │  tuple every time it is called (only to have it discarded the next time the
│ │ │ │  garbage collector was run), but the tuple is located in the module's literal
│ │ │ │ -pool:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">days_in_month</span><span class="p" data-group-id="5513226907-1">(</span><span class="n">M</span><span class="p" data-group-id="5513226907-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="5513226907-2">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5513226907-3">{</span><span class="mi">31</span><span class="p">,</span><span class="mi">28</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p" data-group-id="5513226907-3">}</span><span class="p" data-group-id="5513226907-2">)</span><span class="p">.</span></code></pre><p>If a literal, or a term that contains a literal, is inserted into an Ets table,
│ │ │ │ +pool:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">days_in_month</span><span class="p" data-group-id="3028482715-1">(</span><span class="n">M</span><span class="p" data-group-id="3028482715-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="3028482715-2">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3028482715-3">{</span><span class="mi">31</span><span class="p">,</span><span class="mi">28</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p" data-group-id="3028482715-3">}</span><span class="p" data-group-id="3028482715-2">)</span><span class="p">.</span></code></pre><p>If a literal, or a term that contains a literal, is inserted into an Ets table,
│ │ │ │  it is <em>copied</em>. The reason is that the module containing the literal can be
│ │ │ │  unloaded in the future.</p><p>When a literal is sent to another process, it is <em>not</em> copied. When a module
│ │ │ │  holding a literal is unloaded, the literal will be copied to the heap of all
│ │ │ │  processes that hold references to that literal.</p><p>There also exists a global literal pool that is managed by the
│ │ │ │  <a href="../../../lib/../erts/doc/html/persistent_term.html"><code class="inline">persistent_term</code></a> module.</p><p>By default, 1 GB of virtual address space is reserved for all literal pools (in
│ │ │ │  BEAM code and persistent terms). The amount of virtual address space reserved
│ │ │ │  for literals can be changed by using the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erts_alloc.xhtml#MIscs"><code class="inline">+MIscs option</code></a> when starting the emulator.</p><p>Here is an example how the reserved virtual address space for literals can be
│ │ │ │  raised to 2 GB (2048 MB):</p><pre><code class="text">erl +MIscs 2048</code></pre><h2 id="loss-of-sharing" class="section-heading">
│ │ │ │    <a href="#loss-of-sharing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Loss of Sharing</span>
│ │ │ │  </h2>
│ │ │ │ -<p>An Erlang term can have shared subterms. Here is a simple example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2856270261-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="2856270261-1">}</span></code></pre><p>Shared subterms are <em>not</em> preserved in the following cases:</p><ul><li>When a term is sent to another process</li><li>When a term is passed as the initial process arguments in the <code class="inline">spawn</code> call</li><li>When a term is stored in an Ets table</li></ul><p>That is an optimization. Most applications do not send messages with shared
│ │ │ │ -subterms.</p><p>The following example shows how a shared subterm can be created:</p><pre><code class="makeup erlang" translate="no"><span class="nf">kilo_byte</span><span class="p" data-group-id="0423218041-1">(</span><span class="p" data-group-id="0423218041-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="0423218041-2">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0423218041-3">[</span><span class="mi">42</span><span class="p" data-group-id="0423218041-3">]</span><span class="p" data-group-id="0423218041-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>An Erlang term can have shared subterms. Here is a simple example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6423969277-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="6423969277-1">}</span></code></pre><p>Shared subterms are <em>not</em> preserved in the following cases:</p><ul><li>When a term is sent to another process</li><li>When a term is passed as the initial process arguments in the <code class="inline">spawn</code> call</li><li>When a term is stored in an Ets table</li></ul><p>That is an optimization. Most applications do not send messages with shared
│ │ │ │ +subterms.</p><p>The following example shows how a shared subterm can be created:</p><pre><code class="makeup erlang" translate="no"><span class="nf">kilo_byte</span><span class="p" data-group-id="0135665040-1">(</span><span class="p" data-group-id="0135665040-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="0135665040-2">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0135665040-3">[</span><span class="mi">42</span><span class="p" data-group-id="0135665040-3">]</span><span class="p" data-group-id="0135665040-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">kilo_byte</span><span class="p" data-group-id="0423218041-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0423218041-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">kilo_byte</span><span class="p" data-group-id="0135665040-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0135665040-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">kilo_byte</span><span class="p" data-group-id="0423218041-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0423218041-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="0423218041-6">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0423218041-7">[</span><span class="n">Acc</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="0423218041-7">]</span><span class="p" data-group-id="0423218041-6">)</span><span class="p">.</span></code></pre><p><code class="inline">kilo_byte/1</code> creates a deep list. If <a href="../../../lib/../erts/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a>
│ │ │ │ +</span><span class="nf">kilo_byte</span><span class="p" data-group-id="0135665040-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0135665040-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="0135665040-6">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0135665040-7">[</span><span class="n">Acc</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="0135665040-7">]</span><span class="p" data-group-id="0135665040-6">)</span><span class="p">.</span></code></pre><p><code class="inline">kilo_byte/1</code> creates a deep list. If <a href="../../../lib/../erts/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a>
│ │ │ │  is called, the deep list can be converted to a binary of 1024 bytes:</p><pre><code class="text">1&gt; byte_size(list_to_binary(efficiency_guide:kilo_byte())).
│ │ │ │  1024</code></pre><p>Using the <code class="inline">erts_debug:size/1</code> BIF, it can be seen that the deep list only
│ │ │ │ -requires 22 words of heap space:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="4758502224-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="4758502224-2">(</span><span class="p" data-group-id="4758502224-2">)</span><span class="p" data-group-id="4758502224-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +requires 22 words of heap space:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="8286972198-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="8286972198-2">(</span><span class="p" data-group-id="8286972198-2">)</span><span class="p" data-group-id="8286972198-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">22</span></code></pre><p>Using the <code class="inline">erts_debug:flat_size/1</code> BIF, the size of the deep list can be
│ │ │ │  calculated if sharing is ignored. It becomes the size of the list when it has
│ │ │ │ -been sent to another process or stored in an Ets table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="9836587888-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="9836587888-2">(</span><span class="p" data-group-id="9836587888-2">)</span><span class="p" data-group-id="9836587888-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +been sent to another process or stored in an Ets table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="2204774398-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="2204774398-2">(</span><span class="p" data-group-id="2204774398-2">)</span><span class="p" data-group-id="2204774398-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4094</span></code></pre><p>It can be verified that sharing will be lost if the data is inserted into an Ets
│ │ │ │ -table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="1082332068-1">(</span><span class="ss">tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1082332068-2">[</span><span class="p" data-group-id="1082332068-2">]</span><span class="p" data-group-id="1082332068-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="8681331331-1">(</span><span class="ss">tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8681331331-2">[</span><span class="p" data-group-id="8681331331-2">]</span><span class="p" data-group-id="8681331331-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Ref</span><span class="o">&lt;</span><span class="mf">0.1662103692</span><span class="p">.</span><span class="mf">2407923716.214181</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">ets</span><span class="p">:</span><span class="nf">insert</span><span class="p" data-group-id="1082332068-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1082332068-4">{</span><span class="ss">key</span><span class="p">,</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="1082332068-5">(</span><span class="p" data-group-id="1082332068-5">)</span><span class="p" data-group-id="1082332068-4">}</span><span class="p" data-group-id="1082332068-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">ets</span><span class="p">:</span><span class="nf">insert</span><span class="p" data-group-id="8681331331-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8681331331-4">{</span><span class="ss">key</span><span class="p">,</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="8681331331-5">(</span><span class="p" data-group-id="8681331331-5">)</span><span class="p" data-group-id="8681331331-4">}</span><span class="p" data-group-id="8681331331-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="1082332068-6">(</span><span class="nf">element</span><span class="p" data-group-id="1082332068-7">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="1082332068-8">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="1082332068-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="1082332068-9">)</span><span class="p" data-group-id="1082332068-8">)</span><span class="p" data-group-id="1082332068-7">)</span><span class="p" data-group-id="1082332068-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="8681331331-6">(</span><span class="nf">element</span><span class="p" data-group-id="8681331331-7">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="8681331331-8">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="8681331331-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="8681331331-9">)</span><span class="p" data-group-id="8681331331-8">)</span><span class="p" data-group-id="8681331331-7">)</span><span class="p" data-group-id="8681331331-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4094</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="1082332068-10">(</span><span class="nf">element</span><span class="p" data-group-id="1082332068-11">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="1082332068-12">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="1082332068-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="1082332068-13">)</span><span class="p" data-group-id="1082332068-12">)</span><span class="p" data-group-id="1082332068-11">)</span><span class="p" data-group-id="1082332068-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="8681331331-10">(</span><span class="nf">element</span><span class="p" data-group-id="8681331331-11">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="8681331331-12">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="8681331331-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="8681331331-13">)</span><span class="p" data-group-id="8681331331-12">)</span><span class="p" data-group-id="8681331331-11">)</span><span class="p" data-group-id="8681331331-10">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4094</span></code></pre><p>When the data has passed through an Ets table, <code class="inline">erts_debug:size/1</code> and
│ │ │ │  <code class="inline">erts_debug:flat_size/1</code> return the same value. Sharing has been lost.</p><p>It is possible to build an <em>experimental</em> variant of the runtime system that
│ │ │ │  will preserve sharing when copying terms by giving the
│ │ │ │  <code class="inline">--enable-sharing-preserving</code> option to the <code class="inline">configure</code> script.</p><h2 id="smp-run-time-system" class="section-heading">
│ │ │ │    <a href="#smp-run-time-system" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ ├── OEBPS/eff_guide_functions.xhtml
│ │ │ │ @@ -27,67 +27,67 @@
│ │ │ │    <span class="text">Pattern Matching</span>
│ │ │ │  </h2>
│ │ │ │  <p>Pattern matching in function head as well as in <code class="inline">case</code> and <code class="inline">receive</code> clauses are
│ │ │ │  optimized by the compiler. With a few exceptions, there is nothing to gain by
│ │ │ │  rearranging clauses.</p><p>One exception is pattern matching of binaries. The compiler does not rearrange
│ │ │ │  clauses that match binaries. Placing the clause that matches against the empty
│ │ │ │  binary <em>last</em> is usually slightly faster than placing it <em>first</em>.</p><p>The following is a rather unnatural example to show another exception where
│ │ │ │ -rearranging clauses is beneficial:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map1</span><span class="p" data-group-id="2248037692-1">(</span><span class="ss">one</span><span class="p" data-group-id="2248037692-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="2248037692-2">(</span><span class="ss">two</span><span class="p" data-group-id="2248037692-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="2248037692-3">(</span><span class="ss">three</span><span class="p" data-group-id="2248037692-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="2248037692-4">(</span><span class="n">Int</span><span class="p" data-group-id="2248037692-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="2248037692-5">(</span><span class="n">Int</span><span class="p" data-group-id="2248037692-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="2248037692-6">(</span><span class="ss">four</span><span class="p" data-group-id="2248037692-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="2248037692-7">(</span><span class="ss">five</span><span class="p" data-group-id="2248037692-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="2248037692-8">(</span><span class="ss">six</span><span class="p" data-group-id="2248037692-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>The problem is the clause with the variable <code class="inline">Int</code>. As a variable can match
│ │ │ │ +rearranging clauses is beneficial:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map1</span><span class="p" data-group-id="1047497145-1">(</span><span class="ss">one</span><span class="p" data-group-id="1047497145-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="1047497145-2">(</span><span class="ss">two</span><span class="p" data-group-id="1047497145-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="1047497145-3">(</span><span class="ss">three</span><span class="p" data-group-id="1047497145-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="1047497145-4">(</span><span class="n">Int</span><span class="p" data-group-id="1047497145-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="1047497145-5">(</span><span class="n">Int</span><span class="p" data-group-id="1047497145-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="1047497145-6">(</span><span class="ss">four</span><span class="p" data-group-id="1047497145-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="1047497145-7">(</span><span class="ss">five</span><span class="p" data-group-id="1047497145-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="1047497145-8">(</span><span class="ss">six</span><span class="p" data-group-id="1047497145-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>The problem is the clause with the variable <code class="inline">Int</code>. As a variable can match
│ │ │ │  anything, including the atoms <code class="inline">four</code>, <code class="inline">five</code>, and <code class="inline">six</code>, which the following
│ │ │ │  clauses also match, the compiler must generate suboptimal code that executes as
│ │ │ │  follows:</p><ul><li>First, the input value is compared to <code class="inline">one</code>, <code class="inline">two</code>, and <code class="inline">three</code> (using a
│ │ │ │  single instruction that does a binary search; thus, quite efficient even if
│ │ │ │  there are many values) to select which one of the first three clauses to
│ │ │ │  execute (if any).</li><li>If none of the first three clauses match, the fourth clause match as a
│ │ │ │  variable always matches.</li><li>If the guard test <a href="../../../lib/../erts/doc/html/erlang.html#is_integer/1"><code class="inline">is_integer(Int)</code></a> succeeds, the fourth
│ │ │ │  clause is executed.</li><li>If the guard test fails, the input value is compared to <code class="inline">four</code>, <code class="inline">five</code>, and
│ │ │ │  <code class="inline">six</code>, and the appropriate clause is selected. (There is a <code class="inline">function_clause</code>
│ │ │ │ -exception if none of the values matched.)</li></ul><p>Rewriting to either:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map2</span><span class="p" data-group-id="8561173425-1">(</span><span class="ss">one</span><span class="p" data-group-id="8561173425-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="8561173425-2">(</span><span class="ss">two</span><span class="p" data-group-id="8561173425-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="8561173425-3">(</span><span class="ss">three</span><span class="p" data-group-id="8561173425-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="8561173425-4">(</span><span class="ss">four</span><span class="p" data-group-id="8561173425-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="8561173425-5">(</span><span class="ss">five</span><span class="p" data-group-id="8561173425-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="8561173425-6">(</span><span class="ss">six</span><span class="p" data-group-id="8561173425-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="8561173425-7">(</span><span class="n">Int</span><span class="p" data-group-id="8561173425-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="8561173425-8">(</span><span class="n">Int</span><span class="p" data-group-id="8561173425-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>or:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map3</span><span class="p" data-group-id="6534728793-1">(</span><span class="n">Int</span><span class="p" data-group-id="6534728793-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6534728793-2">(</span><span class="n">Int</span><span class="p" data-group-id="6534728793-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="6534728793-3">(</span><span class="ss">one</span><span class="p" data-group-id="6534728793-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="6534728793-4">(</span><span class="ss">two</span><span class="p" data-group-id="6534728793-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="6534728793-5">(</span><span class="ss">three</span><span class="p" data-group-id="6534728793-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="6534728793-6">(</span><span class="ss">four</span><span class="p" data-group-id="6534728793-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="6534728793-7">(</span><span class="ss">five</span><span class="p" data-group-id="6534728793-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="6534728793-8">(</span><span class="ss">six</span><span class="p" data-group-id="6534728793-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>gives slightly more efficient matching code.</p><p>Another example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs1</span><span class="p" data-group-id="3286315246-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3286315246-2">[</span><span class="p" data-group-id="3286315246-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="3286315246-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +exception if none of the values matched.)</li></ul><p>Rewriting to either:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map2</span><span class="p" data-group-id="2561902527-1">(</span><span class="ss">one</span><span class="p" data-group-id="2561902527-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="2561902527-2">(</span><span class="ss">two</span><span class="p" data-group-id="2561902527-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="2561902527-3">(</span><span class="ss">three</span><span class="p" data-group-id="2561902527-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="2561902527-4">(</span><span class="ss">four</span><span class="p" data-group-id="2561902527-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="2561902527-5">(</span><span class="ss">five</span><span class="p" data-group-id="2561902527-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="2561902527-6">(</span><span class="ss">six</span><span class="p" data-group-id="2561902527-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="2561902527-7">(</span><span class="n">Int</span><span class="p" data-group-id="2561902527-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="2561902527-8">(</span><span class="n">Int</span><span class="p" data-group-id="2561902527-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>or:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map3</span><span class="p" data-group-id="7486641320-1">(</span><span class="n">Int</span><span class="p" data-group-id="7486641320-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="7486641320-2">(</span><span class="n">Int</span><span class="p" data-group-id="7486641320-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="7486641320-3">(</span><span class="ss">one</span><span class="p" data-group-id="7486641320-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="7486641320-4">(</span><span class="ss">two</span><span class="p" data-group-id="7486641320-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="7486641320-5">(</span><span class="ss">three</span><span class="p" data-group-id="7486641320-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="7486641320-6">(</span><span class="ss">four</span><span class="p" data-group-id="7486641320-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="7486641320-7">(</span><span class="ss">five</span><span class="p" data-group-id="7486641320-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="7486641320-8">(</span><span class="ss">six</span><span class="p" data-group-id="7486641320-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>gives slightly more efficient matching code.</p><p>Another example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs1</span><span class="p" data-group-id="4827403750-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4827403750-2">[</span><span class="p" data-group-id="4827403750-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="4827403750-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Ys</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map_pairs1</span><span class="p" data-group-id="3286315246-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3286315246-4">[</span><span class="p" data-group-id="3286315246-4">]</span><span class="p" data-group-id="3286315246-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">map_pairs1</span><span class="p" data-group-id="4827403750-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4827403750-4">[</span><span class="p" data-group-id="4827403750-4">]</span><span class="p" data-group-id="4827403750-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Xs</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map_pairs1</span><span class="p" data-group-id="3286315246-5">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3286315246-6">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="3286315246-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3286315246-7">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="3286315246-7">]</span><span class="p" data-group-id="3286315246-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3286315246-8">[</span><span class="n">Map</span><span class="p" data-group-id="3286315246-9">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3286315246-9">)</span><span class="p">|</span><span class="nf">map_pairs1</span><span class="p" data-group-id="3286315246-10">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="3286315246-10">)</span><span class="p" data-group-id="3286315246-8">]</span><span class="p">.</span></code></pre><p>The first argument is <em>not</em> a problem. It is variable, but it is a variable in
│ │ │ │ +</span><span class="nf">map_pairs1</span><span class="p" data-group-id="4827403750-5">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4827403750-6">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="4827403750-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4827403750-7">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="4827403750-7">]</span><span class="p" data-group-id="4827403750-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4827403750-8">[</span><span class="n">Map</span><span class="p" data-group-id="4827403750-9">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4827403750-9">)</span><span class="p">|</span><span class="nf">map_pairs1</span><span class="p" data-group-id="4827403750-10">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="4827403750-10">)</span><span class="p" data-group-id="4827403750-8">]</span><span class="p">.</span></code></pre><p>The first argument is <em>not</em> a problem. It is variable, but it is a variable in
│ │ │ │  all clauses. The problem is the variable in the second argument, <code class="inline">Xs</code>, in the
│ │ │ │  middle clause. Because the variable can match anything, the compiler is not
│ │ │ │  allowed to rearrange the clauses, but must generate code that matches them in
│ │ │ │  the order written.</p><p>If the function is rewritten as follows, the compiler is free to rearrange the
│ │ │ │ -clauses:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs2</span><span class="p" data-group-id="5984940937-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5984940937-2">[</span><span class="p" data-group-id="5984940937-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5984940937-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +clauses:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs2</span><span class="p" data-group-id="1539300458-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1539300458-2">[</span><span class="p" data-group-id="1539300458-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="1539300458-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Ys</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map_pairs2</span><span class="p" data-group-id="5984940937-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5984940937-4">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="5984940937-4">]</span><span class="o">=</span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5984940937-5">[</span><span class="p" data-group-id="5984940937-5">]</span><span class="w"> </span><span class="p" data-group-id="5984940937-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">map_pairs2</span><span class="p" data-group-id="1539300458-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1539300458-4">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="1539300458-4">]</span><span class="o">=</span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1539300458-5">[</span><span class="p" data-group-id="1539300458-5">]</span><span class="w"> </span><span class="p" data-group-id="1539300458-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Xs</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">map_pairs2</span><span class="p" data-group-id="5984940937-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5984940937-7">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="5984940937-7">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5984940937-8">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="5984940937-8">]</span><span class="p" data-group-id="5984940937-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5984940937-9">[</span><span class="n">Map</span><span class="p" data-group-id="5984940937-10">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5984940937-10">)</span><span class="p">|</span><span class="nf">map_pairs2</span><span class="p" data-group-id="5984940937-11">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5984940937-11">)</span><span class="p" data-group-id="5984940937-9">]</span><span class="p">.</span></code></pre><p>The compiler will generate code similar to this:</p><p><strong>DO NOT (already done by the compiler)</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="4840639614-1">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs0</span><span class="p">,</span><span class="w"> </span><span class="n">Ys0</span><span class="p" data-group-id="4840639614-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">map_pairs2</span><span class="p" data-group-id="1539300458-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1539300458-7">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="1539300458-7">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1539300458-8">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="1539300458-8">]</span><span class="p" data-group-id="1539300458-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1539300458-9">[</span><span class="n">Map</span><span class="p" data-group-id="1539300458-10">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1539300458-10">)</span><span class="p">|</span><span class="nf">map_pairs2</span><span class="p" data-group-id="1539300458-11">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="1539300458-11">)</span><span class="p" data-group-id="1539300458-9">]</span><span class="p">.</span></code></pre><p>The compiler will generate code similar to this:</p><p><strong>DO NOT (already done by the compiler)</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="7363183406-1">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs0</span><span class="p">,</span><span class="w"> </span><span class="n">Ys0</span><span class="p" data-group-id="7363183406-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Xs0</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="4840639614-2">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="4840639614-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="7363183406-2">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="7363183406-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="k">case</span><span class="w"> </span><span class="n">Ys0</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="4840639614-3">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="4840639614-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="p" data-group-id="4840639614-4">[</span><span class="n">Map</span><span class="p" data-group-id="4840639614-5">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4840639614-5">)</span><span class="p">|</span><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="4840639614-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="4840639614-6">)</span><span class="p" data-group-id="4840639614-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="4840639614-7">[</span><span class="p" data-group-id="4840639614-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="7363183406-3">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="7363183406-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="p" data-group-id="7363183406-4">[</span><span class="n">Map</span><span class="p" data-group-id="7363183406-5">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7363183406-5">)</span><span class="p">|</span><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="7363183406-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="7363183406-6">)</span><span class="p" data-group-id="7363183406-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="7363183406-7">[</span><span class="p" data-group-id="7363183406-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  		    </span><span class="n">Xs0</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="4840639614-8">[</span><span class="p" data-group-id="4840639614-8">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="7363183406-8">[</span><span class="p" data-group-id="7363183406-8">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Ys0</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>This is slightly faster for probably the most common case that the input lists
│ │ │ │  are not empty or very short. (Another advantage is that Dialyzer can deduce a
│ │ │ │  better type for the <code class="inline">Xs</code> variable.)</p><h2 id="function-calls" class="section-heading">
│ │ │ │    <a href="#function-calls" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ ├── OEBPS/drivers.xhtml
│ │ │ │ @@ -27,23 +27,23 @@
│ │ │ │    <span class="text">Drivers and Concurrency</span>
│ │ │ │  </h2>
│ │ │ │  <p>The runtime system always takes a lock before running any code in a driver.</p><p>By default, that lock is at the driver level, that is, if several ports have
│ │ │ │  been opened to the same driver, only code for one port at the same time can be
│ │ │ │  running.</p><p>A driver can be configured to have one lock for each port instead.</p><p>If a driver is used in a functional way (that is, holds no state, but only does
│ │ │ │  some heavy calculation and returns a result), several ports with registered
│ │ │ │  names can be opened beforehand, and the port to be used can be chosen based on
│ │ │ │ -the scheduler ID as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9984742048-1">(</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="9984742048-2">(</span><span class="p" data-group-id="9984742048-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="9984742048-3">{</span><span class="ss">some_driver_01</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_02</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_03</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_04</span><span class="p">,</span><span class="w">
│ │ │ │ +the scheduler ID as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3906072582-1">(</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="3906072582-2">(</span><span class="p" data-group-id="3906072582-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="3906072582-3">{</span><span class="ss">some_driver_01</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_02</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_03</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_04</span><span class="p">,</span><span class="w">
│ │ │ │  	 </span><span class="ss">some_driver_05</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_06</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_07</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_08</span><span class="p">,</span><span class="w">
│ │ │ │  	 </span><span class="ss">some_driver_09</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_10</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_11</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_12</span><span class="p">,</span><span class="w">
│ │ │ │ -	 </span><span class="ss">some_driver_13</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_14</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_15</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_16</span><span class="p" data-group-id="9984742048-3">}</span><span class="p" data-group-id="9984742048-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +	 </span><span class="ss">some_driver_13</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_14</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_15</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_16</span><span class="p" data-group-id="3906072582-3">}</span><span class="p" data-group-id="3906072582-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">client_port</span><span class="p" data-group-id="9984742048-4">(</span><span class="p" data-group-id="9984742048-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="9984742048-5">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="9984742048-6">(</span><span class="ss">scheduler_id</span><span class="p" data-group-id="9984742048-6">)</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="9984742048-7">(</span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="9984742048-8">(</span><span class="p" data-group-id="9984742048-8">)</span><span class="p" data-group-id="9984742048-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="9984742048-9">(</span><span class="p" data-group-id="9984742048-9">)</span><span class="p" data-group-id="9984742048-5">)</span><span class="p">.</span></code></pre><p>As long as there are no more than 16 schedulers, there will never be any lock
│ │ │ │ +</span><span class="nf">client_port</span><span class="p" data-group-id="3906072582-4">(</span><span class="p" data-group-id="3906072582-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="3906072582-5">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="3906072582-6">(</span><span class="ss">scheduler_id</span><span class="p" data-group-id="3906072582-6">)</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="3906072582-7">(</span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="3906072582-8">(</span><span class="p" data-group-id="3906072582-8">)</span><span class="p" data-group-id="3906072582-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="3906072582-9">(</span><span class="p" data-group-id="3906072582-9">)</span><span class="p" data-group-id="3906072582-5">)</span><span class="p">.</span></code></pre><p>As long as there are no more than 16 schedulers, there will never be any lock
│ │ │ │  contention on the port lock for the driver.</p><h2 id="avoiding-copying-binaries-when-calling-a-driver" class="section-heading">
│ │ │ │    <a href="#avoiding-copying-binaries-when-calling-a-driver" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Avoiding Copying Binaries When Calling a Driver</span>
│ │ │ │  </h2>
│ │ │ │  <p>There are basically two ways to avoid copying a binary that is sent to a driver:</p><ul><li><p>If the <code class="inline">Data</code> argument for <a href="../../../lib/../erts/doc/html/erlang.html#port_control/3"><code class="inline">port_control/3</code></a> is a
│ │ │ ├── OEBPS/documentation.xhtml
│ │ │ │ @@ -17,23 +17,23 @@
│ │ │ │    </head>
│ │ │ │    <body class="content-inner">
│ │ │ │  
│ │ │ │      <h1 id="content">
│ │ │ │  Documentation
│ │ │ │      </h1>
│ │ │ │  <p>Documentation in Erlang is done through the <code class="inline">-moduledoc</code> and <code class="inline">-doc</code>
│ │ │ │ -<a href="modules.xhtml#module-attributes">attributes</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6979870300-1">(</span><span class="ss">arith</span><span class="p" data-group-id="6979870300-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<a href="modules.xhtml#module-attributes">attributes</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6226315313-1">(</span><span class="ss">arith</span><span class="p" data-group-id="6226315313-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  A module for basic arithmetic.
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6979870300-2">(</span><span class="p" data-group-id="6979870300-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6979870300-3">]</span><span class="p" data-group-id="6979870300-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6226315313-2">(</span><span class="p" data-group-id="6226315313-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6226315313-3">]</span><span class="p" data-group-id="6226315313-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="6979870300-4">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="6979870300-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The <code class="inline">-moduledoc</code> attribute has to be located before the first <code class="inline">-doc</code> attribute
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="6226315313-4">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="6226315313-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The <code class="inline">-moduledoc</code> attribute has to be located before the first <code class="inline">-doc</code> attribute
│ │ │ │  or function declaration. It documents the overall purpose of the module.</p><p>The <code class="inline">-doc</code> attribute always precedes the <a href="ref_man_functions.xhtml">function</a> or
│ │ │ │  <a href="modules.xhtml#module-attributes">attribute</a> it documents. The
│ │ │ │  attributes that can be documented are
│ │ │ │  <a href="typespec.xhtml#type-declarations-of-user-defined-types">user-defined types</a>
│ │ │ │  (<code class="inline">-type</code> and <code class="inline">-opaque</code>) and
│ │ │ │  <a href="modules.xhtml#behaviour-module-attribute">behaviour module attributes</a>
│ │ │ │  (<code class="inline">-callback</code>).</p><p>By default the format used for documentation attributes is
│ │ │ │ @@ -45,55 +45,55 @@
│ │ │ │  <a href="modules.xhtml#documentation-attributes">Documentation Attributes</a>.</p><p><code class="inline">-doc</code> attributes have been available since Erlang/OTP 27.</p><h2 id="documentation-metadata" class="section-heading">
│ │ │ │    <a href="#documentation-metadata" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Documentation metadata</span>
│ │ │ │  </h2>
│ │ │ │  <p>It is possible to add metadata to the documentation entry. You do this by adding
│ │ │ │ -a <code class="inline">-moduledoc</code> or <code class="inline">-doc</code> attribute with a map as argument. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7512260998-1">(</span><span class="ss">arith</span><span class="p" data-group-id="7512260998-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +a <code class="inline">-moduledoc</code> or <code class="inline">-doc</code> attribute with a map as argument. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7212149720-1">(</span><span class="ss">arith</span><span class="p" data-group-id="7212149720-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  A module for basic arithmetic.
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="7512260998-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="7512260998-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="7212149720-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="7212149720-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7512260998-3">(</span><span class="p" data-group-id="7512260998-4">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7512260998-4">]</span><span class="p" data-group-id="7512260998-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7212149720-3">(</span><span class="p" data-group-id="7212149720-4">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7212149720-4">]</span><span class="p" data-group-id="7212149720-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7512260998-5">(</span><span class="p" data-group-id="7512260998-6">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="7512260998-6">}</span><span class="p" data-group-id="7512260998-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="7512260998-7">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="7512260998-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The metadata is used by documentation tools to provide extra information to the
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7212149720-5">(</span><span class="p" data-group-id="7212149720-6">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="7212149720-6">}</span><span class="p" data-group-id="7212149720-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="7212149720-7">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="7212149720-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The metadata is used by documentation tools to provide extra information to the
│ │ │ │  user. There can be multiple metadata documentation entries, in which case the
│ │ │ │  maps will be merged with the latest taking precedence if there are duplicate
│ │ │ │  keys. Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="2161579887-1">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">author</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p" data-group-id="2161579887-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="2161579887-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="2161579887-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="2161579887-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="2161579887-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>This will result in a metadata entry of <code class="inline">#{since =&gt; &quot;2.0&quot;, author =&gt; &quot;Joe&quot;}</code>.</p><p>The keys and values in the metadata map can be any type, but it is recommended
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="3923111072-1">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">author</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p" data-group-id="3923111072-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="3923111072-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="3923111072-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="3923111072-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="3923111072-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>This will result in a metadata entry of <code class="inline">#{since =&gt; &quot;2.0&quot;, author =&gt; &quot;Joe&quot;}</code>.</p><p>The keys and values in the metadata map can be any type, but it is recommended
│ │ │ │  that only <a href="data_types.xhtml#atom">atoms</a> are used for keys and
│ │ │ │  <a href="data_types.xhtml#string">strings</a> for the values.</p><h2 id="external-documentation-files" class="section-heading">
│ │ │ │    <a href="#external-documentation-files" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">External documentation files</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <code class="inline">-moduledoc</code> and <code class="inline">-doc</code> can also be placed in external files. To do so use
│ │ │ │  <code class="inline">-doc {file, &quot;path/to/doc.md&quot;}</code> to point to the documentation. The path used is
│ │ │ │  relative to the file where the <code class="inline">-doc</code> attribute is located. For example:</p><pre><code class="markdown">%% doc/add.md
│ │ │ │  Adds two numbers.</code></pre><p>and</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% src/arith.erl</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="5305364492-1">(</span><span class="p" data-group-id="5305364492-2">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/add.md&quot;</span><span class="p" data-group-id="5305364492-2">}</span><span class="p" data-group-id="5305364492-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="5305364492-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5305364492-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><h2 id="documenting-a-module" class="section-heading">
│ │ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="4384667415-1">(</span><span class="p" data-group-id="4384667415-2">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/add.md&quot;</span><span class="p" data-group-id="4384667415-2">}</span><span class="p" data-group-id="4384667415-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="4384667415-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4384667415-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><h2 id="documenting-a-module" class="section-heading">
│ │ │ │    <a href="#documenting-a-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Documenting a module</span>
│ │ │ │  </h2>
│ │ │ │  <p>The module description should include details on how to use the API and examples
│ │ │ │  of the different functions working together. Here is a good place to use images
│ │ │ │  and other diagrams to better show the usage of the module. Instead of writing a
│ │ │ │  long text in the <code class="inline">moduledoc</code> attribute, it could be better to break it out into
│ │ │ │  an external page.</p><p>The <code class="inline">moduledoc</code> attribute should start with a short paragraph describing the
│ │ │ │ -module and then go into greater details. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1297979446-1">(</span><span class="ss">arith</span><span class="p" data-group-id="1297979446-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +module and then go into greater details. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8583224906-1">(</span><span class="ss">arith</span><span class="p" data-group-id="8583224906-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="s">&quot;
│ │ │ │     A module for basic arithmetic.
│ │ │ │  
│ │ │ │     This module can be used to add and subtract values. For example:
│ │ │ │  
│ │ │ │     ```erlang
│ │ │ │     1&gt; arith:substract(arith:add(2, 3), 1).
│ │ │ │ @@ -108,94 +108,94 @@
│ │ │ │  <p>There are three reserved metadata keys for <code class="inline">-moduledoc</code>:</p><ul><li><code class="inline">since</code> - Shows in which version of the application the module was added.
│ │ │ │  If this is added, all functions, types, and callbacks within will also receive
│ │ │ │  the same <code class="inline">since</code> value unless specified in the metadata of the function, type
│ │ │ │  or callback.</li><li><code class="inline">deprecated</code> - Shows a text in the documentation explaining that it is
│ │ │ │  deprecated and what to use instead.</li><li><code class="inline">format</code> - The format to use for all documentation in this module. The
│ │ │ │  default is <code class="inline">text/markdown</code>. It should be written using the
│ │ │ │  <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types">mime type</a>
│ │ │ │ -of the format.</li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="4373589377-1">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/arith.asciidoc&quot;</span><span class="p" data-group-id="4373589377-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="4373589377-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;0.1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">format</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;text/asciidoc&quot;</span><span class="p" data-group-id="4373589377-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="4373589377-3">#{</span><span class="ss">deprecated</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Use the Erlang arithmetic operators instead.&quot;</span><span class="p" data-group-id="4373589377-3">}</span><span class="p">.</span></code></pre><h2 id="documenting-functions-user-defined-types-and-callbacks" class="section-heading">
│ │ │ │ +of the format.</li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="6260750529-1">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/arith.asciidoc&quot;</span><span class="p" data-group-id="6260750529-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="6260750529-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;0.1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">format</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;text/asciidoc&quot;</span><span class="p" data-group-id="6260750529-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="6260750529-3">#{</span><span class="ss">deprecated</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Use the Erlang arithmetic operators instead.&quot;</span><span class="p" data-group-id="6260750529-3">}</span><span class="p">.</span></code></pre><h2 id="documenting-functions-user-defined-types-and-callbacks" class="section-heading">
│ │ │ │    <a href="#documenting-functions-user-defined-types-and-callbacks" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Documenting functions, user-defined types, and callbacks</span>
│ │ │ │  </h2>
│ │ │ │  <p>Functions, types, and callbacks can be documented using the <code class="inline">-doc</code> attribute.
│ │ │ │  Each entry should start with a short paragraph describing the purpose of entity,
│ │ │ │  and then go into greater detail in needed.</p><p>It is not recommended to include images or diagrams in this documentation as it
│ │ │ │  is used by IDEs and <a href="../../../lib/stdlib/doc/html/c.html#h/1"><code class="inline">c:h/1</code></a> to show the documentation to the user.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  A number that can be used by the arith module.
│ │ │ │  
│ │ │ │  We use a special number here so that we know
│ │ │ │  that this number comes from this module.
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5203697682-1">(</span><span class="p" data-group-id="5203697682-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="5203697682-2">{</span><span class="ss">arith</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">number</span><span class="p" data-group-id="5203697682-3">(</span><span class="p" data-group-id="5203697682-3">)</span><span class="p" data-group-id="5203697682-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="1477634937-1">(</span><span class="p" data-group-id="1477634937-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1477634937-2">{</span><span class="ss">arith</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">number</span><span class="p" data-group-id="1477634937-3">(</span><span class="p" data-group-id="1477634937-3">)</span><span class="p" data-group-id="1477634937-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  Adds two numbers.
│ │ │ │  
│ │ │ │  ### Example:
│ │ │ │  
│ │ │ │  ```
│ │ │ │  1&gt; arith:add(arith:number(1), arith:number(2)). {number, 3}
│ │ │ │  ```
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="5203697682-4">(</span><span class="nf">number</span><span class="p" data-group-id="5203697682-5">(</span><span class="p" data-group-id="5203697682-5">)</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5203697682-6">(</span><span class="p" data-group-id="5203697682-6">)</span><span class="p" data-group-id="5203697682-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5203697682-7">(</span><span class="p" data-group-id="5203697682-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="5203697682-8">(</span><span class="p" data-group-id="5203697682-9">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="p" data-group-id="5203697682-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5203697682-10">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5203697682-10">}</span><span class="p" data-group-id="5203697682-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5203697682-11">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5203697682-11">}</span><span class="p">.</span></code></pre><h3 id="doc-metadata" class="section-heading">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="1477634937-4">(</span><span class="nf">number</span><span class="p" data-group-id="1477634937-5">(</span><span class="p" data-group-id="1477634937-5">)</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="1477634937-6">(</span><span class="p" data-group-id="1477634937-6">)</span><span class="p" data-group-id="1477634937-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="1477634937-7">(</span><span class="p" data-group-id="1477634937-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="1477634937-8">(</span><span class="p" data-group-id="1477634937-9">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="p" data-group-id="1477634937-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1477634937-10">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="1477634937-10">}</span><span class="p" data-group-id="1477634937-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1477634937-11">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="1477634937-11">}</span><span class="p">.</span></code></pre><h3 id="doc-metadata" class="section-heading">
│ │ │ │    <a href="#doc-metadata" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Doc metadata</span>
│ │ │ │  </h3>
│ │ │ │  <p>There are four reserved metadata keys for <code class="inline">-doc</code>:</p><ul><li><p><code class="inline">since =&gt; unicode:chardata()</code> - Shows which version of the application the
│ │ │ │  module was added.</p></li><li><p><code class="inline">deprecated =&gt; unicode:chardata()</code> - Shows a text in the documentation
│ │ │ │  explaining that it is deprecated and what to use instead. The compiler will
│ │ │ │  automatically insert this key if there is a <code class="inline">-deprecated</code> attribute marking a
│ │ │ │  function as deprecated.</p></li><li><p><code class="inline">equiv =&gt; unicode:chardata() | F/A | F(...)</code> - Notes that this function is equivalent to
│ │ │ │  another function in this module. The equivalence can be described using either
│ │ │ │ -<code class="inline">Func/Arity</code>, <code class="inline">Func(Args)</code> or a <a href="../../../lib/stdlib/doc/html/unicode.html#t:chardata/0">unicode string</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="1041127336-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="1041127336-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="1041127336-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="1041127336-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="1041127336-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1041127336-4">[</span><span class="p" data-group-id="1041127336-4">]</span><span class="p" data-group-id="1041127336-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="1041127336-5">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="1041127336-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="5159008305-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="5159008305-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5159008305-3">[</span><span class="p" data-group-id="5159008305-3">]</span><span class="p" data-group-id="5159008305-2">)</span><span class="p" data-group-id="5159008305-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="5159008305-4">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5159008305-5">(</span><span class="p" data-group-id="5159008305-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5159008305-6">(</span><span class="p" data-group-id="5159008305-6">)</span><span class="p" data-group-id="5159008305-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="5159008305-7">(</span><span class="p" data-group-id="5159008305-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="5159008305-8">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5159008305-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="5159008305-9">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5159008305-10">[</span><span class="p" data-group-id="5159008305-10">]</span><span class="p" data-group-id="5159008305-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="5159008305-11">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="5159008305-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The entry into the <a href="../../../lib/kernel/doc/html/eep48_chapter.xhtml">EEP-48</a> doc chunk metadata is
│ │ │ │ +<code class="inline">Func/Arity</code>, <code class="inline">Func(Args)</code> or a <a href="../../../lib/stdlib/doc/html/unicode.html#t:chardata/0">unicode string</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="6804343211-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="6804343211-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="6804343211-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="6804343211-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="6804343211-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6804343211-4">[</span><span class="p" data-group-id="6804343211-4">]</span><span class="p" data-group-id="6804343211-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="6804343211-5">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="6804343211-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="3347802266-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="3347802266-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3347802266-3">[</span><span class="p" data-group-id="3347802266-3">]</span><span class="p" data-group-id="3347802266-2">)</span><span class="p" data-group-id="3347802266-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="3347802266-4">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3347802266-5">(</span><span class="p" data-group-id="3347802266-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3347802266-6">(</span><span class="p" data-group-id="3347802266-6">)</span><span class="p" data-group-id="3347802266-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3347802266-7">(</span><span class="p" data-group-id="3347802266-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="3347802266-8">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="3347802266-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="3347802266-9">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3347802266-10">[</span><span class="p" data-group-id="3347802266-10">]</span><span class="p" data-group-id="3347802266-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="3347802266-11">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="3347802266-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The entry into the <a href="../../../lib/kernel/doc/html/eep48_chapter.xhtml">EEP-48</a> doc chunk metadata is
│ │ │ │  the value converted to a string.</p></li><li><p><code class="inline">exported =&gt; boolean()</code> - A <a href="../../../lib/../erts/doc/html/erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a> signifying if the entry is <code class="inline">exported</code>
│ │ │ │  or not. This value is automatically set by the compiler and should not be set
│ │ │ │  by the user.</p></li></ul><h3 id="doc-signatures" class="section-heading">
│ │ │ │    <a href="#doc-signatures" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Doc signatures</span>
│ │ │ │  </h3>
│ │ │ │  <p>The doc signature is a short text shown to describe the function and its arguments.
│ │ │ │  By default it is determined by looking at the names of the arguments in the
│ │ │ │ -<code class="inline">-spec</code> or function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add</span><span class="p" data-group-id="4617161898-1">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4617161898-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">-spec</code> or function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add</span><span class="p" data-group-id="9557581776-1">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="9557581776-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">sub</span><span class="p" data-group-id="4617161898-2">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4617161898-3">(</span><span class="p" data-group-id="4617161898-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4617161898-4">(</span><span class="p" data-group-id="4617161898-4">)</span><span class="p" data-group-id="4617161898-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="4617161898-5">(</span><span class="p" data-group-id="4617161898-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">sub</span><span class="p" data-group-id="4617161898-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4617161898-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>will have a signature of <code class="inline">add(One, Two)</code> and <code class="inline">sub(One, Two)</code>.</p><p>For types or callbacks, the signature is derived from the type or callback
│ │ │ │ -specification. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3196776061-1">(</span><span class="n">Value</span><span class="p" data-group-id="3196776061-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3196776061-2">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="3196776061-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">sub</span><span class="p" data-group-id="9557581776-2">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="9557581776-3">(</span><span class="p" data-group-id="9557581776-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="9557581776-4">(</span><span class="p" data-group-id="9557581776-4">)</span><span class="p" data-group-id="9557581776-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="9557581776-5">(</span><span class="p" data-group-id="9557581776-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">sub</span><span class="p" data-group-id="9557581776-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9557581776-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>will have a signature of <code class="inline">add(One, Two)</code> and <code class="inline">sub(One, Two)</code>.</p><p>For types or callbacks, the signature is derived from the type or callback
│ │ │ │ +specification. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4614625781-1">(</span><span class="n">Value</span><span class="p" data-group-id="4614625781-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4614625781-2">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="4614625781-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% signature will be `number(Value)`</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3196776061-3">(</span><span class="p" data-group-id="3196776061-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3196776061-4">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3196776061-5">(</span><span class="p" data-group-id="3196776061-5">)</span><span class="p" data-group-id="3196776061-4">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4614625781-3">(</span><span class="p" data-group-id="4614625781-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4614625781-4">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4614625781-5">(</span><span class="p" data-group-id="4614625781-5">)</span><span class="p" data-group-id="4614625781-4">}</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% signature will be `number()`</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="3196776061-6">(</span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3196776061-7">(</span><span class="p" data-group-id="3196776061-7">)</span><span class="p" data-group-id="3196776061-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="4614625781-6">(</span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4614625781-7">(</span><span class="p" data-group-id="4614625781-7">)</span><span class="p" data-group-id="4614625781-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% signature will be `increment(In)`</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="3196776061-8">(</span><span class="n">In</span><span class="p" data-group-id="3196776061-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3196776061-9">(</span><span class="p" data-group-id="3196776061-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="4614625781-8">(</span><span class="n">In</span><span class="p" data-group-id="4614625781-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4614625781-9">(</span><span class="p" data-group-id="4614625781-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%% signature will be `increment(In)`</span></code></pre><p>If it is not possible to &quot;easily&quot; figure out a nice signature from the code, the
│ │ │ │  MFA syntax is used instead. For example: <code class="inline">add/2</code>, <code class="inline">number/1</code>, <code class="inline">increment/1</code></p><p>It is possible to supply a custom signature by placing it as the first line of the
│ │ │ │  <code class="inline">-doc</code> attribute. The provided signature must be in the form of a function
│ │ │ │  declaration up until the <code class="inline">-&gt;</code>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │ │  add(One, Two)
│ │ │ │  
│ │ │ │  Adds two numbers.
│ │ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="1995107948-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="1995107948-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">.</span></code></pre><p>Will create the signature <code class="inline">add(One, Two)</code>. The signature will be removed from the
│ │ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="2586390028-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2586390028-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">.</span></code></pre><p>Will create the signature <code class="inline">add(One, Two)</code>. The signature will be removed from the
│ │ │ │  documentation string, so in the example above only the text <code class="inline">&quot;Adds two numbers&quot;</code>
│ │ │ │  will be part of the documentation. This works for functions, types, and
│ │ │ │  callbacks.</p><h2 id="links-in-markdown" class="section-heading">
│ │ │ │    <a href="#links-in-markdown" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Links in Markdown</span>
│ │ │ │ @@ -233,28 +233,28 @@
│ │ │ │  modules. That is, modules that should be used by other applications and modules
│ │ │ │  that should not. By default all modules in an application are visible, but by
│ │ │ │  setting <code class="inline">-moduledoc false.</code> specific modules can be hidden from being listed as
│ │ │ │  part of the available API.</p><p>An Erlang <a href="modules.xhtml">module</a> consists of public and private functions and type
│ │ │ │  attributes. By default, all exported functions, exported types and callbacks are
│ │ │ │  considered visible and part of the modules public API. In addition, any
│ │ │ │  non-exported type that is referred to by any other visible type attribute is
│ │ │ │ -also visible, but not considered to be part of the public API. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9526543230-1">(</span><span class="p" data-group-id="9526543230-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9526543230-2">]</span><span class="p" data-group-id="9526543230-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +also visible, but not considered to be part of the public API. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4143728468-1">(</span><span class="p" data-group-id="4143728468-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4143728468-2">]</span><span class="p" data-group-id="4143728468-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="9526543230-3">(</span><span class="p" data-group-id="9526543230-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="9526543230-4">(</span><span class="p" data-group-id="9526543230-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="9526543230-5">(</span><span class="p" data-group-id="9526543230-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="9526543230-6">(</span><span class="p" data-group-id="9526543230-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>in the above code, the function <code class="inline">example/0</code> is exported and it referenced the
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="4143728468-3">(</span><span class="p" data-group-id="4143728468-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="4143728468-4">(</span><span class="p" data-group-id="4143728468-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="4143728468-5">(</span><span class="p" data-group-id="4143728468-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="4143728468-6">(</span><span class="p" data-group-id="4143728468-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>in the above code, the function <code class="inline">example/0</code> is exported and it referenced the
│ │ │ │  un-exported type <code class="inline">private/0</code>. Therefore both <code class="inline">example/0</code> and <code class="inline">private/0</code> will be
│ │ │ │  marked as visible. The <code class="inline">private/0</code> type will have the metadata field <code class="inline">exported</code>
│ │ │ │  set to <code class="inline">false</code> to show that it is not part of the public API.</p><p>If you want to make a visible entity hidden you need to set the <code class="inline">-doc</code> attribute
│ │ │ │ -to <code class="inline">false</code>. Let us revisit our previous example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1345243276-1">(</span><span class="p" data-group-id="1345243276-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1345243276-2">]</span><span class="p" data-group-id="1345243276-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +to <code class="inline">false</code>. Let us revisit our previous example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5928999087-1">(</span><span class="p" data-group-id="5928999087-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5928999087-2">]</span><span class="p" data-group-id="5928999087-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="1345243276-3">(</span><span class="p" data-group-id="1345243276-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="1345243276-4">(</span><span class="p" data-group-id="1345243276-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="1345243276-5">(</span><span class="p" data-group-id="1345243276-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="5928999087-3">(</span><span class="p" data-group-id="5928999087-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="5928999087-4">(</span><span class="p" data-group-id="5928999087-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="5928999087-5">(</span><span class="p" data-group-id="5928999087-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="ss">false</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="1345243276-6">(</span><span class="p" data-group-id="1345243276-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>The function <code class="inline">example/0</code> is exported but explicitly marked as hidden; therefore
│ │ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="5928999087-6">(</span><span class="p" data-group-id="5928999087-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>The function <code class="inline">example/0</code> is exported but explicitly marked as hidden; therefore
│ │ │ │  both <code class="inline">example/0</code> and <code class="inline">private/0</code> will be hidden.</p><p>Any documentation added to an automatically hidden entity (non-exported function
│ │ │ │  or type) is ignored and will generate a warning. Such functions can be
│ │ │ │  documented using comments.</p><h2 id="compiling-and-getting-documentation" class="section-heading">
│ │ │ │    <a href="#compiling-and-getting-documentation" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Compiling and getting documentation</span>
│ │ │ │ @@ -280,21 +280,21 @@
│ │ │ │    <span class="text">Using ExDoc to generate HTML/ePub documentation</span>
│ │ │ │  </h2>
│ │ │ │  <p><a href="https://hexdocs.pm/ex_doc/">ExDoc</a> has built-in support to generate
│ │ │ │  documentation from Markdown. The simplest way is by using the
│ │ │ │  <a href="https://hexdocs.pm/rebar3_ex_doc">rebar3_ex_doc</a> plugin. To set up a
│ │ │ │  rebar3 project to use <a href="https://hexdocs.pm/ex_doc/">ExDoc</a> to generate
│ │ │ │  documentation add the following to your <code class="inline">rebar3.config</code>.</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Enable the plugin</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4635414137-1">{</span><span class="ss">plugins</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4635414137-2">[</span><span class="ss">rebar3_ex_doc</span><span class="p" data-group-id="4635414137-2">]</span><span class="p" data-group-id="4635414137-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7036474825-1">{</span><span class="ss">plugins</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7036474825-2">[</span><span class="ss">rebar3_ex_doc</span><span class="p" data-group-id="7036474825-2">]</span><span class="p" data-group-id="7036474825-1">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="4635414137-3">{</span><span class="ss">ex_doc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4635414137-4">[</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4635414137-5">{</span><span class="ss">extras</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4635414137-6">[</span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="4635414137-6">]</span><span class="p" data-group-id="4635414137-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4635414137-7">{</span><span class="ss">main</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="4635414137-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4635414137-8">{</span><span class="ss">source_url</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;https://github.com/namespace/your_app&quot;</span><span class="p" data-group-id="4635414137-8">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4635414137-4">]</span><span class="p" data-group-id="4635414137-3">}</span><span class="p">.</span></code></pre><p>When configured you can run <code class="inline">rebar3 ex_doc</code> to generate the
│ │ │ │ +</span><span class="p" data-group-id="7036474825-3">{</span><span class="ss">ex_doc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7036474825-4">[</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7036474825-5">{</span><span class="ss">extras</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7036474825-6">[</span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="7036474825-6">]</span><span class="p" data-group-id="7036474825-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7036474825-7">{</span><span class="ss">main</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="7036474825-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7036474825-8">{</span><span class="ss">source_url</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;https://github.com/namespace/your_app&quot;</span><span class="p" data-group-id="7036474825-8">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7036474825-4">]</span><span class="p" data-group-id="7036474825-3">}</span><span class="p">.</span></code></pre><p>When configured you can run <code class="inline">rebar3 ex_doc</code> to generate the
│ │ │ │  documentation to <code class="inline">doc/index.html</code>. For more details and options see
│ │ │ │  the <a href="https://hexdocs.pm/rebar3_ex_doc">rebar3_ex_doc</a> documentation.</p><p>You can also download the
│ │ │ │  <a href="https://github.com/elixir/ex_doc/releases/latest">release escript bundle</a> from
│ │ │ │  github and run it from the command line. The documentation for using the escript
│ │ │ │  is found by running <code class="inline">ex_doc --help</code>.</p><p>If you are writing documentation that will be using
│ │ │ │  <a href="https://hexdocs.pm/ex_doc/">ExDoc</a> to generate HTML/ePub it is highly
│ │ │ │  recommended to read its documentation.</p>
│ │ │ ├── OEBPS/distributed_applications.xhtml
│ │ │ │ @@ -55,36 +55,36 @@
│ │ │ │  (within the time-out specified by <code class="inline">sync_nodes_timeout</code>).</li><li><p><code class="inline">sync_nodes_timeout = integer() | infinity</code> - Specifies how many milliseconds
│ │ │ │  to wait for the other nodes to start.</p></li></ul><p>When started, the node waits for all nodes specified by <code class="inline">sync_nodes_mandatory</code>
│ │ │ │  and <code class="inline">sync_nodes_optional</code> to come up. When all nodes are up, or when all
│ │ │ │  mandatory nodes are up and the time specified by <code class="inline">sync_nodes_timeout</code> has
│ │ │ │  elapsed, all applications start. If not all mandatory nodes are up, the node
│ │ │ │  terminates.</p><p><em>Example:</em></p><p>An application <code class="inline">myapp</code> is to run at the node <code class="inline">cp1@cave</code>. If this node goes down,
│ │ │ │  <code class="inline">myapp</code> is to be restarted at <code class="inline">cp2@cave</code> or <code class="inline">cp3@cave</code>. A system configuration
│ │ │ │ -file <code class="inline">cp1.config</code> for <code class="inline">cp1@cave</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4443599407-1">[</span><span class="p" data-group-id="4443599407-2">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4443599407-3">[</span><span class="p" data-group-id="4443599407-4">{</span><span class="ss">distributed</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4443599407-5">[</span><span class="p" data-group-id="4443599407-6">{</span><span class="ss">myapp</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4443599407-7">[</span><span class="ss">cp1@cave</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4443599407-8">{</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="4443599407-8">}</span><span class="p" data-group-id="4443599407-7">]</span><span class="p" data-group-id="4443599407-6">}</span><span class="p" data-group-id="4443599407-5">]</span><span class="p" data-group-id="4443599407-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4443599407-9">{</span><span class="ss">sync_nodes_mandatory</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4443599407-10">[</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="4443599407-10">]</span><span class="p" data-group-id="4443599407-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4443599407-11">{</span><span class="ss">sync_nodes_timeout</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p" data-group-id="4443599407-11">}</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4443599407-3">]</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4443599407-2">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4443599407-1">]</span><span class="p">.</span></code></pre><p>The system configuration files for <code class="inline">cp2@cave</code> and <code class="inline">cp3@cave</code> are identical,
│ │ │ │ +file <code class="inline">cp1.config</code> for <code class="inline">cp1@cave</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1131256017-1">[</span><span class="p" data-group-id="1131256017-2">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="1131256017-3">[</span><span class="p" data-group-id="1131256017-4">{</span><span class="ss">distributed</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1131256017-5">[</span><span class="p" data-group-id="1131256017-6">{</span><span class="ss">myapp</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1131256017-7">[</span><span class="ss">cp1@cave</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1131256017-8">{</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="1131256017-8">}</span><span class="p" data-group-id="1131256017-7">]</span><span class="p" data-group-id="1131256017-6">}</span><span class="p" data-group-id="1131256017-5">]</span><span class="p" data-group-id="1131256017-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1131256017-9">{</span><span class="ss">sync_nodes_mandatory</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1131256017-10">[</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="1131256017-10">]</span><span class="p" data-group-id="1131256017-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1131256017-11">{</span><span class="ss">sync_nodes_timeout</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p" data-group-id="1131256017-11">}</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="1131256017-3">]</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1131256017-2">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1131256017-1">]</span><span class="p">.</span></code></pre><p>The system configuration files for <code class="inline">cp2@cave</code> and <code class="inline">cp3@cave</code> are identical,
│ │ │ │  except for the list of mandatory nodes, which is to be <code class="inline">[cp1@cave, cp3@cave]</code>
│ │ │ │  for <code class="inline">cp2@cave</code> and <code class="inline">[cp1@cave, cp2@cave]</code> for <code class="inline">cp3@cave</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>All involved nodes must have the same value for <code class="inline">distributed</code> and
│ │ │ │  <code class="inline">sync_nodes_timeout</code>. Otherwise the system behavior is undefined.</p></section><h2 id="starting-and-stopping-distributed-applications" class="section-heading">
│ │ │ │    <a href="#starting-and-stopping-distributed-applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting and Stopping Distributed Applications</span>
│ │ │ │  </h2>
│ │ │ │  <p>When all involved (mandatory) nodes have been started, the distributed
│ │ │ │  application can be started by calling <code class="inline">application:start(Application)</code> at <em>all
│ │ │ │  of these nodes.</em></p><p>A boot script (see <a href="release_structure.xhtml">Releases</a>) can be used that
│ │ │ │  automatically starts the application.</p><p>The application is started at the first operational node that is listed in the
│ │ │ │  list of nodes in the <code class="inline">distributed</code> configuration parameter. The application is
│ │ │ │  started as usual. That is, an application master is created and calls the
│ │ │ │ -application callback function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1104631048-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="1104631048-1">)</span></code></pre><p>Example:</p><p>Continuing the example from the previous section, the three nodes are started,
│ │ │ │ +application callback function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5535331240-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="5535331240-1">)</span></code></pre><p>Example:</p><p>Continuing the example from the previous section, the three nodes are started,
│ │ │ │  specifying the system configuration file:</p><pre><code class="text">&gt; erl -sname cp1 -config cp1
│ │ │ │  &gt; erl -sname cp2 -config cp2
│ │ │ │  &gt; erl -sname cp3 -config cp3</code></pre><p>When all nodes are operational, <code class="inline">myapp</code> can be started. This is achieved by
│ │ │ │  calling <code class="inline">application:start(myapp)</code> at all three nodes. It is then started at
│ │ │ │  <code class="inline">cp1</code>, as shown in the following figure:</p><p><a href="" id="dist1"></a></p><p><img src="assets/dist1.gif" alt="Application myapp - Situation 1" title="Application myapp - Situation 1"/></p><p>Similarly, the application must be stopped by calling
│ │ │ │  <code class="inline">application:stop(Application)</code> at all involved nodes.</p><h2 id="failover" class="section-heading">
│ │ │ │    <a href="#failover" class="hover-link">
│ │ │ │ @@ -92,30 +92,30 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Failover</span>
│ │ │ │  </h2>
│ │ │ │  <p>If the node where the application is running goes down, the application is
│ │ │ │  restarted (after the specified time-out) at the first operational node that is
│ │ │ │  listed in the list of nodes in the <code class="inline">distributed</code> configuration parameter. This
│ │ │ │  is called a <em>failover</em>.</p><p>The application is started the normal way at the new node, that is, by the
│ │ │ │ -application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4012638863-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="4012638863-1">)</span></code></pre><p>An exception is if the application has the <code class="inline">start_phases</code> key defined (see
│ │ │ │ +application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8931416443-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="8931416443-1">)</span></code></pre><p>An exception is if the application has the <code class="inline">start_phases</code> key defined (see
│ │ │ │  <a href="included_applications.xhtml">Included Applications</a>). The application is then
│ │ │ │ -instead started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0768923309-1">(</span><span class="p" data-group-id="0768923309-2">{</span><span class="ss">failover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="0768923309-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="0768923309-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the terminated node.</p><p><em>Example:</em></p><p>If <code class="inline">cp1</code> goes down, the system checks which one of the other nodes, <code class="inline">cp2</code> or
│ │ │ │ +instead started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9379423343-1">(</span><span class="p" data-group-id="9379423343-2">{</span><span class="ss">failover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="9379423343-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="9379423343-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the terminated node.</p><p><em>Example:</em></p><p>If <code class="inline">cp1</code> goes down, the system checks which one of the other nodes, <code class="inline">cp2</code> or
│ │ │ │  <code class="inline">cp3</code>, has the least number of running applications, but waits for 5 seconds for
│ │ │ │  <code class="inline">cp1</code> to restart. If <code class="inline">cp1</code> does not restart and <code class="inline">cp2</code> runs fewer applications
│ │ │ │  than <code class="inline">cp3</code>, <code class="inline">myapp</code> is restarted on <code class="inline">cp2</code>.</p><p><a href="" id="dist2"></a></p><p><img src="assets/dist2.gif" alt="Application myapp - Situation 2" title="Application myapp - Situation 2"/></p><p>Suppose now that <code class="inline">cp2</code> goes also down and does not restart within 5 seconds.
│ │ │ │  <code class="inline">myapp</code> is now restarted on <code class="inline">cp3</code>.</p><p><a href="" id="dist3"></a></p><p><img src="assets/dist3.gif" alt="Application myapp - Situation 3" title="Application myapp - Situation 3"/></p><h2 id="takeover" class="section-heading">
│ │ │ │    <a href="#takeover" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Takeover</span>
│ │ │ │  </h2>
│ │ │ │  <p>If a node is started, which has higher priority according to <code class="inline">distributed</code> than
│ │ │ │  the node where a distributed application is running, the application is
│ │ │ │  restarted at the new node and stopped at the old node. This is called a
│ │ │ │ -<em>takeover</em>.</p><p>The application is started by the application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6408491874-1">(</span><span class="p" data-group-id="6408491874-2">{</span><span class="ss">takeover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="6408491874-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="6408491874-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the old node.</p><p><em>Example:</em></p><p>If <code class="inline">myapp</code> is running at <code class="inline">cp3</code>, and if <code class="inline">cp2</code> now restarts, it does not restart
│ │ │ │ +<em>takeover</em>.</p><p>The application is started by the application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0751681820-1">(</span><span class="p" data-group-id="0751681820-2">{</span><span class="ss">takeover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="0751681820-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="0751681820-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the old node.</p><p><em>Example:</em></p><p>If <code class="inline">myapp</code> is running at <code class="inline">cp3</code>, and if <code class="inline">cp2</code> now restarts, it does not restart
│ │ │ │  <code class="inline">myapp</code>, as the order between the <code class="inline">cp2</code> and <code class="inline">cp3</code> nodes is undefined.</p><p><a href="" id="dist4"></a></p><p><img src="assets/dist4.gif" alt="Application myapp - Situation 4" title="Application myapp - Situation 4"/></p><p>However, if <code class="inline">cp1</code> also restarts, the function <a href="../../../lib/kernel/doc/html/application.html#takeover/2"><code class="inline">application:takeover/2</code></a> moves
│ │ │ │  <code class="inline">myapp</code> to <code class="inline">cp1</code>, as <code class="inline">cp1</code> has a higher priority than <code class="inline">cp3</code> for this
│ │ │ │  application. In this case, <code class="inline">Module:start({takeover, cp3@cave}, StartArgs)</code> is
│ │ │ │  executed at <code class="inline">cp1</code> to start the application.</p><p><a href="" id="dist5"></a></p><p><img src="assets/dist5.gif" alt="Application myapp - Situation 5" title="Application myapp - Situation 5"/></p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/distributed.xhtml
│ │ │ │ @@ -47,25 +47,25 @@
│ │ │ │  </h2>
│ │ │ │  <p>A <em>node</em> is an executing Erlang runtime system that has been given a name, using
│ │ │ │  the command-line flag <a href="../../../lib/../erts/doc/html/erl_cmd.xhtml#name"><code class="inline">-name</code></a> (long names) or
│ │ │ │  <a href="../../../lib/../erts/doc/html/erl_cmd.xhtml#sname"><code class="inline">-sname</code></a> (short names).</p><p>The format of the node name is an atom <code class="inline">name@host</code>. <code class="inline">name</code> is the name given by
│ │ │ │  the user. <code class="inline">host</code> is the full host name if long names are used, or the first part
│ │ │ │  of the host name if short names are used. Function <a href="../../../lib/../erts/doc/html/erlang.html#node/0"><code class="inline">node()</code></a>
│ │ │ │  returns the name of the node.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -name dilbert</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8976911150-1">(</span><span class="ss">dilbert@uab</span><span class="p">.</span><span class="ss">ericsson</span><span class="p">.</span><span class="ss">se</span><span class="p" data-group-id="8976911150-1">)</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="8976911150-2">(</span><span class="p" data-group-id="8976911150-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0062973516-1">(</span><span class="ss">dilbert@uab</span><span class="p">.</span><span class="ss">ericsson</span><span class="p">.</span><span class="ss">se</span><span class="p" data-group-id="0062973516-1">)</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="0062973516-2">(</span><span class="p" data-group-id="0062973516-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">&#39;dilbert@uab.ericsson.se&#39;</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">% erl -sname dilbert</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">(dilbert@uab)1&gt; </span><span class="nf">node</span><span class="p" data-group-id="8976911150-3">(</span><span class="p" data-group-id="8976911150-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">(dilbert@uab)1&gt; </span><span class="nf">node</span><span class="p" data-group-id="0062973516-3">(</span><span class="p" data-group-id="0062973516-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">dilbert@uab</span></code></pre><p>The node name can also be given in runtime by calling <a href="../../../lib/kernel/doc/html/net_kernel.html#start/1"><code class="inline">net_kernel:start/1</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">node</span><span class="p" data-group-id="0268571782-1">(</span><span class="p" data-group-id="0268571782-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">node</span><span class="p" data-group-id="4552114318-1">(</span><span class="p" data-group-id="4552114318-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">net_kernel</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0268571782-2">(</span><span class="p" data-group-id="0268571782-3">[</span><span class="ss">dilbert</span><span class="p">,</span><span class="ss">shortnames</span><span class="p" data-group-id="0268571782-3">]</span><span class="p" data-group-id="0268571782-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0268571782-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.102</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0268571782-4">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">(dilbert@uab)3&gt; </span><span class="nf">node</span><span class="p" data-group-id="0268571782-5">(</span><span class="p" data-group-id="0268571782-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">net_kernel</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4552114318-2">(</span><span class="p" data-group-id="4552114318-3">[</span><span class="ss">dilbert</span><span class="p">,</span><span class="ss">shortnames</span><span class="p" data-group-id="4552114318-3">]</span><span class="p" data-group-id="4552114318-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4552114318-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.102</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4552114318-4">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">(dilbert@uab)3&gt; </span><span class="nf">node</span><span class="p" data-group-id="4552114318-5">(</span><span class="p" data-group-id="4552114318-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">dilbert@uab</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>A node with a long node name cannot communicate with a node with a short node
│ │ │ │  name.</p></section><h2 id="node-connections" class="section-heading">
│ │ │ │    <a href="#node-connections" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Node Connections</span>
│ │ │ │  </h2>
│ │ │ ├── OEBPS/design_principles.xhtml
│ │ │ │ @@ -57,135 +57,135 @@
│ │ │ │  the code for a process in a generic part (a behaviour module) and a specific
│ │ │ │  part (a <em>callback module</em>).</p><p>The behaviour module is part of Erlang/OTP. To implement a process such as a
│ │ │ │  supervisor, the user only needs to implement the callback module, which is to
│ │ │ │  export a pre-defined set of functions, the <em>callback functions</em>.</p><p>The following example illustrate how code can be divided into a generic and a
│ │ │ │  specific part. Consider the following code (written in plain Erlang) for a
│ │ │ │  simple server, which keeps track of a number of &quot;channels&quot;. Other processes can
│ │ │ │  allocate and free the channels by calling the functions <code class="inline">alloc/0</code> and <code class="inline">free/1</code>,
│ │ │ │ -respectively.</p><p><a href="" id="ch1"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2038235185-1">(</span><span class="ss">ch1</span><span class="p" data-group-id="2038235185-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2038235185-2">(</span><span class="p" data-group-id="2038235185-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2038235185-3">]</span><span class="p" data-group-id="2038235185-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2038235185-4">(</span><span class="p" data-group-id="2038235185-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2038235185-5">]</span><span class="p" data-group-id="2038235185-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2038235185-6">(</span><span class="p" data-group-id="2038235185-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2038235185-7">]</span><span class="p" data-group-id="2038235185-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +respectively.</p><p><a href="" id="ch1"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0665442307-1">(</span><span class="ss">ch1</span><span class="p" data-group-id="0665442307-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0665442307-2">(</span><span class="p" data-group-id="0665442307-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0665442307-3">]</span><span class="p" data-group-id="0665442307-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0665442307-4">(</span><span class="p" data-group-id="0665442307-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0665442307-5">]</span><span class="p" data-group-id="0665442307-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0665442307-6">(</span><span class="p" data-group-id="0665442307-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0665442307-7">]</span><span class="p" data-group-id="0665442307-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2038235185-8">(</span><span class="p" data-group-id="2038235185-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2038235185-9">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2038235185-10">[</span><span class="p" data-group-id="2038235185-10">]</span><span class="p" data-group-id="2038235185-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="0665442307-8">(</span><span class="p" data-group-id="0665442307-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="0665442307-9">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0665442307-10">[</span><span class="p" data-group-id="0665442307-10">]</span><span class="p" data-group-id="0665442307-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="2038235185-11">(</span><span class="p" data-group-id="2038235185-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2038235185-12">{</span><span class="nf">self</span><span class="p" data-group-id="2038235185-13">(</span><span class="p" data-group-id="2038235185-13">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="2038235185-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="0665442307-11">(</span><span class="p" data-group-id="0665442307-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0665442307-12">{</span><span class="nf">self</span><span class="p" data-group-id="0665442307-13">(</span><span class="p" data-group-id="0665442307-13">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0665442307-12">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2038235185-14">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="2038235185-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0665442307-14">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="0665442307-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Res</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="2038235185-15">(</span><span class="n">Ch</span><span class="p" data-group-id="2038235185-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2038235185-16">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="2038235185-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="0665442307-15">(</span><span class="n">Ch</span><span class="p" data-group-id="0665442307-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0665442307-16">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0665442307-16">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="2038235185-17">(</span><span class="p" data-group-id="2038235185-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="2038235185-18">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2038235185-19">(</span><span class="p" data-group-id="2038235185-19">)</span><span class="p" data-group-id="2038235185-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="2038235185-20">(</span><span class="p" data-group-id="2038235185-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="2038235185-21">(</span><span class="n">Chs</span><span class="p" data-group-id="2038235185-21">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="0665442307-17">(</span><span class="p" data-group-id="0665442307-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="0665442307-18">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0665442307-19">(</span><span class="p" data-group-id="0665442307-19">)</span><span class="p" data-group-id="0665442307-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="0665442307-20">(</span><span class="p" data-group-id="0665442307-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="0665442307-21">(</span><span class="n">Chs</span><span class="p" data-group-id="0665442307-21">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="2038235185-22">(</span><span class="n">Chs</span><span class="p" data-group-id="2038235185-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="0665442307-22">(</span><span class="n">Chs</span><span class="p" data-group-id="0665442307-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2038235185-23">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="2038235185-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="2038235185-24">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="2038235185-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="2038235185-25">(</span><span class="n">Chs</span><span class="p" data-group-id="2038235185-25">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2038235185-26">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="2038235185-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="2038235185-27">(</span><span class="n">Chs2</span><span class="p" data-group-id="2038235185-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2038235185-28">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="2038235185-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="2038235185-29">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2038235185-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="2038235185-30">(</span><span class="n">Chs2</span><span class="p" data-group-id="2038235185-30">)</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The code for the server can be rewritten into a generic part <code class="inline">server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9272415123-1">(</span><span class="ss">server</span><span class="p" data-group-id="9272415123-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9272415123-2">(</span><span class="p" data-group-id="9272415123-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9272415123-3">]</span><span class="p" data-group-id="9272415123-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9272415123-4">(</span><span class="p" data-group-id="9272415123-5">[</span><span class="ss">call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9272415123-5">]</span><span class="p" data-group-id="9272415123-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9272415123-6">(</span><span class="p" data-group-id="9272415123-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9272415123-7">]</span><span class="p" data-group-id="9272415123-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0665442307-23">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0665442307-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="0665442307-24">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="0665442307-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="0665442307-25">(</span><span class="n">Chs</span><span class="p" data-group-id="0665442307-25">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0665442307-26">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0665442307-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0665442307-27">(</span><span class="n">Chs2</span><span class="p" data-group-id="0665442307-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0665442307-28">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0665442307-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="0665442307-29">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0665442307-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0665442307-30">(</span><span class="n">Chs2</span><span class="p" data-group-id="0665442307-30">)</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The code for the server can be rewritten into a generic part <code class="inline">server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9444911843-1">(</span><span class="ss">server</span><span class="p" data-group-id="9444911843-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9444911843-2">(</span><span class="p" data-group-id="9444911843-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9444911843-3">]</span><span class="p" data-group-id="9444911843-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9444911843-4">(</span><span class="p" data-group-id="9444911843-5">[</span><span class="ss">call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9444911843-5">]</span><span class="p" data-group-id="9444911843-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9444911843-6">(</span><span class="p" data-group-id="9444911843-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9444911843-7">]</span><span class="p" data-group-id="9444911843-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9272415123-8">(</span><span class="n">Mod</span><span class="p" data-group-id="9272415123-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9272415123-9">(</span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9272415123-10">[</span><span class="n">Mod</span><span class="p" data-group-id="9272415123-10">]</span><span class="p" data-group-id="9272415123-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="9444911843-8">(</span><span class="n">Mod</span><span class="p" data-group-id="9444911843-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9444911843-9">(</span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9444911843-10">[</span><span class="n">Mod</span><span class="p" data-group-id="9444911843-10">]</span><span class="p" data-group-id="9444911843-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call</span><span class="p" data-group-id="9272415123-11">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9272415123-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9272415123-12">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9272415123-13">(</span><span class="p" data-group-id="9272415123-13">)</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9272415123-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call</span><span class="p" data-group-id="9444911843-11">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9444911843-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9444911843-12">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9444911843-13">(</span><span class="p" data-group-id="9444911843-13">)</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9444911843-12">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9272415123-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="9272415123-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9444911843-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="9444911843-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Res</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">cast</span><span class="p" data-group-id="9272415123-15">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9272415123-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9272415123-16">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9272415123-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">cast</span><span class="p" data-group-id="9444911843-15">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9444911843-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9444911843-16">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9444911843-16">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="9272415123-17">(</span><span class="n">Mod</span><span class="p" data-group-id="9272415123-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9272415123-18">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9272415123-19">(</span><span class="p" data-group-id="9272415123-19">)</span><span class="p" data-group-id="9272415123-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">init</span><span class="p" data-group-id="9272415123-20">(</span><span class="p" data-group-id="9272415123-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="9272415123-21">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9272415123-21">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="9444911843-17">(</span><span class="n">Mod</span><span class="p" data-group-id="9444911843-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="9444911843-18">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9444911843-19">(</span><span class="p" data-group-id="9444911843-19">)</span><span class="p" data-group-id="9444911843-18">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">init</span><span class="p" data-group-id="9444911843-20">(</span><span class="p" data-group-id="9444911843-20">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="9444911843-21">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9444911843-21">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="9272415123-22">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9272415123-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="9444911843-22">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9444911843-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9272415123-23">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9272415123-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="9272415123-24">{</span><span class="n">Res</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="9272415123-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_call</span><span class="p" data-group-id="9272415123-25">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9272415123-25">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9272415123-26">{</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="9272415123-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="9272415123-27">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="9272415123-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9272415123-28">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9272415123-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">State2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_cast</span><span class="p" data-group-id="9272415123-29">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9272415123-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="9272415123-30">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="9272415123-30">)</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>And a callback module <code class="inline">ch2.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6601903288-1">(</span><span class="ss">ch2</span><span class="p" data-group-id="6601903288-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6601903288-2">(</span><span class="p" data-group-id="6601903288-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6601903288-3">]</span><span class="p" data-group-id="6601903288-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6601903288-4">(</span><span class="p" data-group-id="6601903288-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6601903288-5">]</span><span class="p" data-group-id="6601903288-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6601903288-6">(</span><span class="p" data-group-id="6601903288-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6601903288-7">]</span><span class="p" data-group-id="6601903288-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="6601903288-8">(</span><span class="p" data-group-id="6601903288-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6601903288-9">(</span><span class="ss">ch2</span><span class="p" data-group-id="6601903288-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="6601903288-10">(</span><span class="p" data-group-id="6601903288-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="6601903288-11">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="6601903288-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="6601903288-12">(</span><span class="n">Ch</span><span class="p" data-group-id="6601903288-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6601903288-13">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6601903288-14">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6601903288-14">}</span><span class="p" data-group-id="6601903288-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9444911843-23">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9444911843-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="9444911843-24">{</span><span class="n">Res</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="9444911843-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_call</span><span class="p" data-group-id="9444911843-25">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9444911843-25">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9444911843-26">{</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="9444911843-26">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="9444911843-27">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="9444911843-27">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9444911843-28">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="9444911843-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">State2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_cast</span><span class="p" data-group-id="9444911843-29">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9444911843-29">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="9444911843-30">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="9444911843-30">)</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>And a callback module <code class="inline">ch2.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8477761431-1">(</span><span class="ss">ch2</span><span class="p" data-group-id="8477761431-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8477761431-2">(</span><span class="p" data-group-id="8477761431-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8477761431-3">]</span><span class="p" data-group-id="8477761431-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8477761431-4">(</span><span class="p" data-group-id="8477761431-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8477761431-5">]</span><span class="p" data-group-id="8477761431-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8477761431-6">(</span><span class="p" data-group-id="8477761431-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8477761431-7">]</span><span class="p" data-group-id="8477761431-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8477761431-8">(</span><span class="p" data-group-id="8477761431-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8477761431-9">(</span><span class="ss">ch2</span><span class="p" data-group-id="8477761431-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="8477761431-10">(</span><span class="p" data-group-id="8477761431-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="8477761431-11">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8477761431-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="8477761431-12">(</span><span class="n">Ch</span><span class="p" data-group-id="8477761431-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8477761431-13">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8477761431-14">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8477761431-14">}</span><span class="p" data-group-id="8477761431-13">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6601903288-15">(</span><span class="p" data-group-id="6601903288-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">channels</span><span class="p" data-group-id="6601903288-16">(</span><span class="p" data-group-id="6601903288-16">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8477761431-15">(</span><span class="p" data-group-id="8477761431-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">channels</span><span class="p" data-group-id="8477761431-16">(</span><span class="p" data-group-id="8477761431-16">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="6601903288-17">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6601903288-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">alloc</span><span class="p" data-group-id="6601903288-18">(</span><span class="n">Chs</span><span class="p" data-group-id="6601903288-18">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; {Ch,Chs2}</span><span class="w">
│ │ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="8477761431-17">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8477761431-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">alloc</span><span class="p" data-group-id="8477761431-18">(</span><span class="n">Chs</span><span class="p" data-group-id="8477761431-18">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; {Ch,Chs2}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="6601903288-19">(</span><span class="p" data-group-id="6601903288-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6601903288-20">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6601903288-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">free</span><span class="p" data-group-id="6601903288-21">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6601903288-21">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; Chs2</span></code></pre><p>Notice the following:</p><ul><li>The code in <code class="inline">server</code> can be reused to build many different servers.</li><li>The server name, in this example the atom <code class="inline">ch2</code>, is hidden from the users of
│ │ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="8477761431-19">(</span><span class="p" data-group-id="8477761431-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8477761431-20">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8477761431-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">free</span><span class="p" data-group-id="8477761431-21">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8477761431-21">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; Chs2</span></code></pre><p>Notice the following:</p><ul><li>The code in <code class="inline">server</code> can be reused to build many different servers.</li><li>The server name, in this example the atom <code class="inline">ch2</code>, is hidden from the users of
│ │ │ │  the client functions. This means that the name can be changed without
│ │ │ │  affecting them.</li><li>The protocol (messages sent to and received from the server) is also hidden.
│ │ │ │  This is good programming practice and allows one to change the protocol
│ │ │ │  without changing the code using the interface functions.</li><li>The functionality of <code class="inline">server</code> can be extended without having to change <code class="inline">ch2</code>
│ │ │ │  or any other callback module.</li></ul><p>In <code class="inline">ch1.erl</code> and <code class="inline">ch2.erl</code> above, the implementation of <code class="inline">channels/0</code>, <code class="inline">alloc/1</code>,
│ │ │ │  and <code class="inline">free/2</code> has been intentionally left out, as it is not relevant to the
│ │ │ │  example. For completeness, one way to write these functions is given below. This
│ │ │ │  is an example only, a realistic implementation must be able to handle situations
│ │ │ │ -like running out of channels to allocate, and so on.</p><p><a href="" id="channels-implementation"></a></p><pre><code class="makeup erlang" translate="no"><span class="nf">channels</span><span class="p" data-group-id="6120355190-1">(</span><span class="p" data-group-id="6120355190-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="6120355190-2">{</span><span class="p">_</span><span class="n">Allocated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6120355190-3">[</span><span class="p" data-group-id="6120355190-3">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="6120355190-4">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="6120355190-4">)</span><span class="p" data-group-id="6120355190-2">}</span><span class="p">.</span><span class="w">
│ │ │ │ +like running out of channels to allocate, and so on.</p><p><a href="" id="channels-implementation"></a></p><pre><code class="makeup erlang" translate="no"><span class="nf">channels</span><span class="p" data-group-id="0927175987-1">(</span><span class="p" data-group-id="0927175987-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="0927175987-2">{</span><span class="p">_</span><span class="n">Allocated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0927175987-3">[</span><span class="p" data-group-id="0927175987-3">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="0927175987-4">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="0927175987-4">)</span><span class="p" data-group-id="0927175987-2">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="6120355190-5">(</span><span class="p" data-group-id="6120355190-6">{</span><span class="n">Allocated</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6120355190-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6120355190-7">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="p" data-group-id="6120355190-6">}</span><span class="p" data-group-id="6120355190-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="6120355190-8">{</span><span class="n">H</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6120355190-9">{</span><span class="p" data-group-id="6120355190-10">[</span><span class="n">H</span><span class="p">|</span><span class="n">Allocated</span><span class="p" data-group-id="6120355190-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6120355190-9">}</span><span class="p" data-group-id="6120355190-8">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="0927175987-5">(</span><span class="p" data-group-id="0927175987-6">{</span><span class="n">Allocated</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0927175987-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0927175987-7">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="p" data-group-id="0927175987-6">}</span><span class="p" data-group-id="0927175987-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="0927175987-8">{</span><span class="n">H</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0927175987-9">{</span><span class="p" data-group-id="0927175987-10">[</span><span class="n">H</span><span class="p">|</span><span class="n">Allocated</span><span class="p" data-group-id="0927175987-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="0927175987-9">}</span><span class="p" data-group-id="0927175987-8">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="6120355190-11">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6120355190-12">{</span><span class="n">Alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Free</span><span class="p" data-group-id="6120355190-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Channels</span><span class="p" data-group-id="6120355190-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="6120355190-13">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="6120355190-13">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="0927175987-11">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0927175987-12">{</span><span class="n">Alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Free</span><span class="p" data-group-id="0927175987-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Channels</span><span class="p" data-group-id="0927175987-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="0927175987-13">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="0927175987-13">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │        </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -         </span><span class="p" data-group-id="6120355190-14">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="6120355190-15">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="6120355190-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6120355190-16">[</span><span class="n">Ch</span><span class="p">|</span><span class="n">Free</span><span class="p" data-group-id="6120355190-16">]</span><span class="p" data-group-id="6120355190-14">}</span><span class="p">;</span><span class="w">
│ │ │ │ +         </span><span class="p" data-group-id="0927175987-14">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="0927175987-15">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="0927175987-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0927175987-16">[</span><span class="n">Ch</span><span class="p">|</span><span class="n">Free</span><span class="p" data-group-id="0927175987-16">]</span><span class="p" data-group-id="0927175987-14">}</span><span class="p">;</span><span class="w">
│ │ │ │        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │           </span><span class="n">Channels</span><span class="w">
│ │ │ │     </span><span class="k">end</span><span class="p">.</span></code></pre><p>Code written without using behaviours can be more efficient, but the increased
│ │ │ │  efficiency is at the expense of generality. The ability to manage all
│ │ │ │  applications in the system in a consistent manner is important.</p><p>Using behaviours also makes it easier to read and understand code written by
│ │ │ │  other programmers. Improvised programming structures, while possibly more
│ │ │ │  efficient, are always more difficult to understand.</p><p>The <code class="inline">server</code> module corresponds, greatly simplified, to the Erlang/OTP behaviour
│ │ │ │  <code class="inline">gen_server</code>.</p><p>The standard Erlang/OTP behaviours are:</p><ul><li><p><a href="gen_server_concepts.xhtml">gen_server</a></p><p>For implementing the server of a client-server relation</p></li><li><p><a href="statem.xhtml">gen_statem</a></p><p>For implementing state machines</p></li><li><p><a href="events.xhtml">gen_event</a></p><p>For implementing event handling functionality</p></li><li><p><a href="sup_princ.xhtml">supervisor</a></p><p>For implementing a supervisor in a supervision tree</p></li></ul><p>The compiler understands the module attribute <code class="inline">-behaviour(Behaviour)</code> and issues
│ │ │ │ -warnings about missing callback functions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1014871771-1">(</span><span class="ss">chs3</span><span class="p" data-group-id="1014871771-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1014871771-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="1014871771-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +warnings about missing callback functions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0842409449-1">(</span><span class="ss">chs3</span><span class="p" data-group-id="0842409449-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0842409449-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="0842409449-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="1014871771-3">(</span><span class="ss">chs3</span><span class="p" data-group-id="1014871771-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="0842409449-3">(</span><span class="ss">chs3</span><span class="p" data-group-id="0842409449-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="o">/</span><span class="ss">chs3</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">10</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="ss">undefined</span><span class="w"> </span><span class="ss">call</span><span class="o">-</span><span class="ss">back</span><span class="w"> </span><span class="ss">function</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1014871771-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">chs3</span><span class="p" data-group-id="1014871771-4">}</span></code></pre><h2 id="applications" class="section-heading">
│ │ │ │ +</span><span class="p" data-group-id="0842409449-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">chs3</span><span class="p" data-group-id="0842409449-4">}</span></code></pre><h2 id="applications" class="section-heading">
│ │ │ │    <a href="#applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Applications</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang/OTP comes with a number of components, each implementing some specific
│ │ │ │  functionality. Components are with Erlang/OTP terminology called <em>applications</em>.
│ │ │ ├── OEBPS/data_types.xhtml
│ │ │ │ @@ -97,18 +97,18 @@
│ │ │ │    </a>
│ │ │ │    <span class="text">Representation of Floating Point Numbers</span>
│ │ │ │  </h3>
│ │ │ │  <p>When working with floats you may not see what you expect when printing or doing
│ │ │ │  arithmetic operations. This is because floats are represented by a fixed number
│ │ │ │  of bits in a base-2 system while printed floats are represented with a base-10
│ │ │ │  system. Erlang uses 64-bit floats. Here are examples of this phenomenon:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="mf">0.30000000000000004</span></code></pre><p>The real numbers <code class="inline">0.1</code> and <code class="inline">0.2</code> cannot be represented exactly as floats.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4682092626-1">{</span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963968</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="mf">36028797018963970.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963970</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963970.0</span><span class="p" data-group-id="4682092626-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4682092626-2">{</span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="4682092626-2">}</span><span class="p">.</span></code></pre><p>The value <code class="inline">36028797018963968</code> can be represented exactly as a float value but
│ │ │ │ +</span><span class="mf">0.30000000000000004</span></code></pre><p>The real numbers <code class="inline">0.1</code> and <code class="inline">0.2</code> cannot be represented exactly as floats.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0815165398-1">{</span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963968</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="mf">36028797018963970.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963970</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963970.0</span><span class="p" data-group-id="0815165398-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0815165398-2">{</span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0815165398-2">}</span><span class="p">.</span></code></pre><p>The value <code class="inline">36028797018963968</code> can be represented exactly as a float value but
│ │ │ │  Erlang's pretty printer rounds <code class="inline">36028797018963968.0</code> to <code class="inline">3.602879701896397e16</code>
│ │ │ │  (<code class="inline">=36028797018963970.0</code>) as all values in the range
│ │ │ │  <code class="inline">[36028797018963966.0, 36028797018963972.0]</code> are represented by
│ │ │ │  <code class="inline">36028797018963968.0</code>.</p><p>For more information about floats and issues with them see:</p><ul><li><a href="https://floating-point-gui.de/">What Every Programmer Should Know About Floating-Point Arithmetic</a></li><li><a href="https://0.30000000000000004.com/">0.30000000000000004.com/</a></li><li><a href="https://docs.python.org/3/tutorial/floatingpoint.html">Floating Point Arithmetic: Issues and Limitations</a></li></ul><p>If you need to work with exact decimal fractions, for instance to represent
│ │ │ │  money, it is recommended to use a library that handles that, or work in
│ │ │ │  cents instead of dollars or euros so that decimal fractions are not needed.</p><p>Also note that Erlang's floats do not exactly match IEEE 754 floats,
│ │ │ │  in that neither <em>Inf</em> nor <em>NaN</em> are supported in Erlang. Any
│ │ │ │ @@ -142,52 +142,52 @@
│ │ │ │  by eight are called <em>binaries</em>.</p><p><em>Examples:</em></p><pre><code class="text">1&gt; &lt;&lt;10,20&gt;&gt;.
│ │ │ │  &lt;&lt;10,20&gt;&gt;
│ │ │ │  2&gt; &lt;&lt;&quot;ABC&quot;&gt;&gt;.
│ │ │ │  &lt;&lt;&quot;ABC&quot;&gt;&gt;
│ │ │ │  3&gt; &lt;&lt;1:1,0:1&gt;&gt;.
│ │ │ │  &lt;&lt;2:2&gt;&gt;</code></pre><p>The <a href="../../../lib/../erts/doc/html/erlang.html#is_bitstring/1"><code class="inline">is_bitstring/1</code></a> BIF tests whether a
│ │ │ │  term is a bit string, and the <a href="../../../lib/../erts/doc/html/erlang.html#is_binary/1"><code class="inline">is_binary/1</code></a>
│ │ │ │ -BIF tests whether a term is a binary.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">is_bitstring</span><span class="p" data-group-id="5414422593-1">(</span><span class="p" data-group-id="5414422593-2">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5414422593-2">&gt;&gt;</span><span class="p" data-group-id="5414422593-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +BIF tests whether a term is a binary.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">is_bitstring</span><span class="p" data-group-id="9376551489-1">(</span><span class="p" data-group-id="9376551489-2">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="9376551489-2">&gt;&gt;</span><span class="p" data-group-id="9376551489-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="5414422593-3">(</span><span class="p" data-group-id="5414422593-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5414422593-4">&gt;&gt;</span><span class="p" data-group-id="5414422593-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="9376551489-3">(</span><span class="p" data-group-id="9376551489-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="9376551489-4">&gt;&gt;</span><span class="p" data-group-id="9376551489-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="5414422593-5">(</span><span class="p" data-group-id="5414422593-6">&lt;&lt;</span><span class="mi">42</span><span class="p" data-group-id="5414422593-6">&gt;&gt;</span><span class="p" data-group-id="5414422593-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="9376551489-5">(</span><span class="p" data-group-id="9376551489-6">&lt;&lt;</span><span class="mi">42</span><span class="p" data-group-id="9376551489-6">&gt;&gt;</span><span class="p" data-group-id="9376551489-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │  </span></code></pre><p>For more examples, see <a href="../../../lib/../system/doc/html/bit_syntax.xhtml">Programming Examples</a>.</p><h2 id="reference" class="section-heading">
│ │ │ │    <a href="#reference" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Reference</span>
│ │ │ │  </h2>
│ │ │ │  <p>A term that is <a href="../../../lib/../system/doc/html/system_limits.xhtml#unique_references">unique</a>
│ │ │ │  among connected nodes. A reference is created by calling the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#make_ref/0"><code class="inline">make_ref/0</code></a> BIF. The
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#is_reference/1"><code class="inline">is_reference/1</code></a> BIF tests whether a term
│ │ │ │ -is a reference.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="0512799844-1">(</span><span class="p" data-group-id="0512799844-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +is a reference.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="9890427607-1">(</span><span class="p" data-group-id="9890427607-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Ref</span><span class="o">&lt;</span><span class="mf">0.76482849</span><span class="p">.</span><span class="mf">3801088007.198204</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">is_reference</span><span class="p" data-group-id="0512799844-2">(</span><span class="n">Ref</span><span class="p" data-group-id="0512799844-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">is_reference</span><span class="p" data-group-id="9890427607-2">(</span><span class="n">Ref</span><span class="p" data-group-id="9890427607-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><h2 id="fun" class="section-heading">
│ │ │ │    <a href="#fun" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Fun</span>
│ │ │ │  </h2>
│ │ │ │  <p>A fun is a functional object. Funs make it possible to create an anonymous
│ │ │ │  function and pass the function itself — not its name — as argument to other
│ │ │ │ -functions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1942677835-1">(</span><span class="n">X</span><span class="p" data-group-id="1942677835-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +functions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0918825553-1">(</span><span class="n">X</span><span class="p" data-group-id="0918825553-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="1942677835-2">(</span><span class="mi">2</span><span class="p" data-group-id="1942677835-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="0918825553-2">(</span><span class="mi">2</span><span class="p" data-group-id="0918825553-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span></code></pre><p>The <a href="../../../lib/../erts/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> and <a href="../../../lib/../erts/doc/html/erlang.html#is_function/2"><code class="inline">is_function/2</code></a>
│ │ │ │ -BIFs tests whether a term is a fun.</p><p><em>Examples</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4542327291-1">(</span><span class="p" data-group-id="4542327291-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │ +BIFs tests whether a term is a fun.</p><p><em>Examples</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9612892386-1">(</span><span class="p" data-group-id="9612892386-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">43.105768164</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="4542327291-2">(</span><span class="n">F</span><span class="p" data-group-id="4542327291-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="9612892386-2">(</span><span class="n">F</span><span class="p" data-group-id="9612892386-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="4542327291-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4542327291-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="9612892386-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="9612892386-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="4542327291-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4542327291-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="9612892386-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9612892386-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><p>Read more about funs in <a href="expressions.xhtml#fun-expressions">Fun Expressions</a>. For more
│ │ │ │  examples, see <a href="../../../lib/../system/doc/html/funs.xhtml">Programming Examples</a>.</p><h2 id="port-identifier" class="section-heading">
│ │ │ │    <a href="#port-identifier" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Port Identifier</span>
│ │ │ │  </h2>
│ │ │ │ @@ -205,94 +205,94 @@
│ │ │ │  for a new process after a while.</p><p>The BIF <a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the Pid of the calling process. When
│ │ │ │  <a href="ref_man_processes.xhtml#process-creation">creating a new process</a>, the parent
│ │ │ │  process will be able to get the Pid of the child process either via the return
│ │ │ │  value, as is the case when calling the <a href="../../../lib/../erts/doc/html/erlang.html#spawn/3"><code class="inline">spawn/3</code></a> BIF, or via
│ │ │ │  a message, which is the case when calling the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#spawn_request/5"><code class="inline">spawn_request/5</code></a> BIF. A Pid is typically used when
│ │ │ │  when sending a process a <a href="ref_man_processes.xhtml#signals">signal</a>. The
│ │ │ │ -<a href="../../../lib/../erts/doc/html/erlang.html#is_pid/1"><code class="inline">is_pid/1</code></a> BIF tests whether a term is a Pid.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1711915056-1">(</span><span class="ss">m</span><span class="p" data-group-id="1711915056-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1711915056-2">(</span><span class="p" data-group-id="1711915056-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1711915056-3">]</span><span class="p" data-group-id="1711915056-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<a href="../../../lib/../erts/doc/html/erlang.html#is_pid/1"><code class="inline">is_pid/1</code></a> BIF tests whether a term is a Pid.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7824398889-1">(</span><span class="ss">m</span><span class="p" data-group-id="7824398889-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7824398889-2">(</span><span class="p" data-group-id="7824398889-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7824398889-3">]</span><span class="p" data-group-id="7824398889-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="1711915056-4">(</span><span class="p" data-group-id="1711915056-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="7824398889-4">(</span><span class="p" data-group-id="7824398889-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">who_are_you</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1711915056-5">(</span><span class="s">&quot;I am </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1711915056-6">[</span><span class="nf">self</span><span class="p" data-group-id="1711915056-7">(</span><span class="p" data-group-id="1711915056-7">)</span><span class="p" data-group-id="1711915056-6">]</span><span class="p" data-group-id="1711915056-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="1711915056-8">(</span><span class="p" data-group-id="1711915056-8">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7824398889-5">(</span><span class="s">&quot;I am </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7824398889-6">[</span><span class="nf">self</span><span class="p" data-group-id="7824398889-7">(</span><span class="p" data-group-id="7824398889-7">)</span><span class="p" data-group-id="7824398889-6">]</span><span class="p" data-group-id="7824398889-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="7824398889-8">(</span><span class="p" data-group-id="7824398889-8">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1711915056-9">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">loop</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1711915056-10">[</span><span class="p" data-group-id="1711915056-10">]</span><span class="p" data-group-id="1711915056-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7824398889-9">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">loop</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7824398889-10">[</span><span class="p" data-group-id="7824398889-10">]</span><span class="p" data-group-id="7824398889-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.58</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">who_are_you</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="n">I</span><span class="w"> </span><span class="ss">am</span><span class="w"> </span><span class="o">&lt;</span><span class="mf">0.58</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="ss">who_are_you</span></code></pre><p>Read more about processes in <a href="ref_man_processes.xhtml">Processes</a>.</p><h2 id="tuple" class="section-heading">
│ │ │ │    <a href="#tuple" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Tuple</span>
│ │ │ │  </h2>
│ │ │ │  <p>A tuple is a compound data type with a fixed number of terms:</p><pre><code class="text">{Term1,...,TermN}</code></pre><p>Each term <code class="inline">Term</code> in the tuple is called an <em>element</em>. The number of elements is
│ │ │ │ -said to be the <em>size</em> of the tuple.</p><p>There exists a number of BIFs to manipulate tuples.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5829856075-1">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="5829856075-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="5829856075-2">}</span><span class="p" data-group-id="5829856075-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5829856075-3">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="5829856075-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="5829856075-4">}</span><span class="p" data-group-id="5829856075-3">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">element</span><span class="p" data-group-id="5829856075-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="5829856075-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +said to be the <em>size</em> of the tuple.</p><p>There exists a number of BIFs to manipulate tuples.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7514802964-1">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="7514802964-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="7514802964-2">}</span><span class="p" data-group-id="7514802964-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7514802964-3">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="7514802964-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="7514802964-4">}</span><span class="p" data-group-id="7514802964-3">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">element</span><span class="p" data-group-id="7514802964-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="7514802964-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">adam</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">element</span><span class="p" data-group-id="5829856075-6">(</span><span class="mi">3</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="5829856075-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5829856075-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="5829856075-7">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="5829856075-8">(</span><span class="mi">2</span><span class="p">,</span><span class="n">P</span><span class="p">,</span><span class="mi">25</span><span class="p" data-group-id="5829856075-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5829856075-9">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">25</span><span class="p">,</span><span class="p" data-group-id="5829856075-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="5829856075-10">}</span><span class="p" data-group-id="5829856075-9">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="5829856075-11">(</span><span class="n">P</span><span class="p" data-group-id="5829856075-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">element</span><span class="p" data-group-id="7514802964-6">(</span><span class="mi">3</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="7514802964-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7514802964-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="7514802964-7">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="7514802964-8">(</span><span class="mi">2</span><span class="p">,</span><span class="n">P</span><span class="p">,</span><span class="mi">25</span><span class="p" data-group-id="7514802964-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7514802964-9">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">25</span><span class="p">,</span><span class="p" data-group-id="7514802964-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="7514802964-10">}</span><span class="p" data-group-id="7514802964-9">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="7514802964-11">(</span><span class="n">P</span><span class="p" data-group-id="7514802964-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="5829856075-12">(</span><span class="p" data-group-id="5829856075-13">{</span><span class="p" data-group-id="5829856075-13">}</span><span class="p" data-group-id="5829856075-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="7514802964-12">(</span><span class="p" data-group-id="7514802964-13">{</span><span class="p" data-group-id="7514802964-13">}</span><span class="p" data-group-id="7514802964-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">0</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="5829856075-14">(</span><span class="p" data-group-id="5829856075-15">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5829856075-15">}</span><span class="p" data-group-id="5829856075-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="7514802964-14">(</span><span class="p" data-group-id="7514802964-15">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="7514802964-15">}</span><span class="p" data-group-id="7514802964-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><h2 id="map" class="section-heading">
│ │ │ │    <a href="#map" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Map</span>
│ │ │ │  </h2>
│ │ │ │  <p>A map is a compound data type with a variable number of key-value associations:</p><pre><code class="text">#{Key1 =&gt; Value1, ..., KeyN =&gt; ValueN}</code></pre><p>Each key-value association in the map is called an <em>association pair</em>. The key
│ │ │ │  and value parts of the pair are called <em>elements</em>. The number of association
│ │ │ │ -pairs is said to be the <em>size</em> of the map.</p><p>There exists a number of BIFs to manipulate maps.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7312102734-1">#{</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="w"> </span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7312102734-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="7312102734-2">}</span><span class="p" data-group-id="7312102734-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7312102734-3">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7312102734-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="7312102734-4">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="7312102734-3">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="7312102734-5">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="7312102734-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +pairs is said to be the <em>size</em> of the map.</p><p>There exists a number of BIFs to manipulate maps.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2192930945-1">#{</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="w"> </span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2192930945-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2192930945-2">}</span><span class="p" data-group-id="2192930945-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2192930945-3">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2192930945-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2192930945-4">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="2192930945-3">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="2192930945-5">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="2192930945-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">adam</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="7312102734-6">(</span><span class="ss">date</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="7312102734-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7312102734-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="7312102734-7">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="7312102734-8">(</span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="7312102734-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7312102734-9">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7312102734-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="7312102734-10">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="7312102734-9">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="7312102734-11">(</span><span class="n">M</span><span class="p" data-group-id="7312102734-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="2192930945-6">(</span><span class="ss">date</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="2192930945-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2192930945-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2192930945-7">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="2192930945-8">(</span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="2192930945-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2192930945-9">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2192930945-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2192930945-10">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="2192930945-9">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="2192930945-11">(</span><span class="n">M</span><span class="p" data-group-id="2192930945-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="7312102734-12">(</span><span class="p" data-group-id="7312102734-13">#{</span><span class="p" data-group-id="7312102734-13">}</span><span class="p" data-group-id="7312102734-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="2192930945-12">(</span><span class="p" data-group-id="2192930945-13">#{</span><span class="p" data-group-id="2192930945-13">}</span><span class="p" data-group-id="2192930945-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">0</span></code></pre><p>A collection of maps processing functions are found in module <a href="../../../lib/stdlib/doc/html/maps.html"><code class="inline">maps</code></a>
│ │ │ │  in STDLIB.</p><p>Read more about maps in <a href="expressions.xhtml#map-expressions">Map Expressions</a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Maps were introduced as an experimental feature in Erlang/OTP R17. Their
│ │ │ │  functionality was extended and became fully supported in Erlang/OTP 18.</p></section><h2 id="list" class="section-heading">
│ │ │ │    <a href="#list" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">List</span>
│ │ │ │  </h2>
│ │ │ │  <p>A list is a compound data type with a variable number of terms.</p><pre><code class="text">[Term1,...,TermN]</code></pre><p>Each term <code class="inline">Term</code> in the list is called an <em>element</em>. The number of elements is
│ │ │ │  said to be the <em>length</em> of the list.</p><p>Formally, a list is either the empty list <code class="inline">[]</code> or consists of a <em>head</em> (first
│ │ │ │  element) and a <em>tail</em> (remainder of the list). The <em>tail</em> is also a list. The
│ │ │ │  latter can be expressed as <code class="inline">[H|T]</code>. The notation <code class="inline">[Term1,...,TermN]</code> above is
│ │ │ │  equivalent with the list <code class="inline">[Term1|[...|[TermN|[]]]]</code>.</p><p><em>Example:</em></p><p><code class="inline">[]</code> is a list, thus<br/><code class="inline">[c|[]]</code> is a list, thus<br/><code class="inline">[b|[c|[]]]</code> is a list, thus<br/><code class="inline">[a|[b|[c|[]]]]</code> is a list, or in short <code class="inline">[a,b,c]</code></p><p>A list where the tail is a list is sometimes called a <em>proper list</em>. It is
│ │ │ │  allowed to have a list where the tail is not a list, for example, <code class="inline">[a|b]</code>.
│ │ │ │ -However, this type of list is of little practical use.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5488115428-1">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5488115428-2">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5488115428-2">}</span><span class="p" data-group-id="5488115428-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5488115428-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5488115428-4">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5488115428-4">}</span><span class="p" data-group-id="5488115428-3">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="5488115428-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5488115428-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5488115428-6">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5488115428-7">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5488115428-7">}</span><span class="p" data-group-id="5488115428-6">]</span><span class="w">
│ │ │ │ +However, this type of list is of little practical use.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8590809286-1">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="8590809286-2">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8590809286-2">}</span><span class="p" data-group-id="8590809286-1">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8590809286-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="8590809286-4">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8590809286-4">}</span><span class="p" data-group-id="8590809286-3">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="8590809286-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8590809286-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8590809286-6">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="8590809286-7">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8590809286-7">}</span><span class="p" data-group-id="8590809286-6">]</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">H</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">a</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5488115428-8">[</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5488115428-9">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5488115428-9">}</span><span class="p" data-group-id="5488115428-8">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="n">L2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5488115428-10">[</span><span class="ss">d</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5488115428-10">]</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5488115428-11">[</span><span class="ss">d</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5488115428-12">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5488115428-12">}</span><span class="p" data-group-id="5488115428-11">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nf">length</span><span class="p" data-group-id="5488115428-13">(</span><span class="n">L1</span><span class="p" data-group-id="5488115428-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8590809286-8">[</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="8590809286-9">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8590809286-9">}</span><span class="p" data-group-id="8590809286-8">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="n">L2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8590809286-10">[</span><span class="ss">d</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8590809286-10">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8590809286-11">[</span><span class="ss">d</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="8590809286-12">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8590809286-12">}</span><span class="p" data-group-id="8590809286-11">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nf">length</span><span class="p" data-group-id="8590809286-13">(</span><span class="n">L1</span><span class="p" data-group-id="8590809286-13">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nf">length</span><span class="p" data-group-id="5488115428-14">(</span><span class="p" data-group-id="5488115428-15">[</span><span class="p" data-group-id="5488115428-15">]</span><span class="p" data-group-id="5488115428-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nf">length</span><span class="p" data-group-id="8590809286-14">(</span><span class="p" data-group-id="8590809286-15">[</span><span class="p" data-group-id="8590809286-15">]</span><span class="p" data-group-id="8590809286-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">0</span></code></pre><p>A collection of list processing functions are found in module
│ │ │ │  <a href="../../../lib/stdlib/doc/html/lists.html"><code class="inline">lists</code></a> in STDLIB.</p><h2 id="string" class="section-heading">
│ │ │ │    <a href="#string" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">String</span>
│ │ │ │  </h2>
│ │ │ │ @@ -412,41 +412,41 @@
│ │ │ │    <span class="text">Record</span>
│ │ │ │  </h2>
│ │ │ │  <p>A record is a data structure for storing a fixed number of elements. It has
│ │ │ │  named fields and is similar to a struct in C. However, a record is not a true
│ │ │ │  data type. Instead, record expressions are translated to tuple expressions
│ │ │ │  during compilation. Therefore, record expressions are not understood by the
│ │ │ │  shell unless special actions are taken. For details, see module <a href="../../../lib/stdlib/doc/html/shell.html"><code class="inline">shell</code></a>
│ │ │ │ -in STDLIB.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9966119135-1">(</span><span class="ss">person</span><span class="p" data-group-id="9966119135-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9966119135-2">(</span><span class="p" data-group-id="9966119135-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9966119135-3">]</span><span class="p" data-group-id="9966119135-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +in STDLIB.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2059900426-1">(</span><span class="ss">person</span><span class="p" data-group-id="2059900426-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2059900426-2">(</span><span class="p" data-group-id="2059900426-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2059900426-3">]</span><span class="p" data-group-id="2059900426-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9966119135-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9966119135-5">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="9966119135-5">}</span><span class="p" data-group-id="9966119135-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2059900426-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2059900426-5">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="2059900426-5">}</span><span class="p" data-group-id="2059900426-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">new</span><span class="p" data-group-id="9966119135-6">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="9966119135-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9966119135-7">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="o">=</span><span class="n">Age</span><span class="p" data-group-id="9966119135-7">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">new</span><span class="p" data-group-id="2059900426-6">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="2059900426-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2059900426-7">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="o">=</span><span class="n">Age</span><span class="p" data-group-id="2059900426-7">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">person</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="9966119135-8">(</span><span class="ss">ernie</span><span class="p">,</span><span class="w"> </span><span class="mi">44</span><span class="p" data-group-id="9966119135-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9966119135-9">{</span><span class="ss">person</span><span class="p">,</span><span class="ss">ernie</span><span class="p">,</span><span class="mi">44</span><span class="p" data-group-id="9966119135-9">}</span></code></pre><p>Read more about records in <a href="ref_man_records.xhtml">Records</a>. More examples are
│ │ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">person</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2059900426-8">(</span><span class="ss">ernie</span><span class="p">,</span><span class="w"> </span><span class="mi">44</span><span class="p" data-group-id="2059900426-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2059900426-9">{</span><span class="ss">person</span><span class="p">,</span><span class="ss">ernie</span><span class="p">,</span><span class="mi">44</span><span class="p" data-group-id="2059900426-9">}</span></code></pre><p>Read more about records in <a href="ref_man_records.xhtml">Records</a>. More examples are
│ │ │ │  found in <a href="../../../lib/../system/doc/html/prog_ex_records.xhtml">Programming Examples</a>.</p><h2 id="boolean" class="section-heading">
│ │ │ │    <a href="#boolean" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Boolean</span>
│ │ │ │  </h2>
│ │ │ │  <p>There is no Boolean data type in Erlang. Instead the atoms <code class="inline">true</code> and <code class="inline">false</code>
│ │ │ │  are used to denote Boolean values. The <a href="../../../lib/../erts/doc/html/erlang.html#is_boolean/1"><code class="inline">is_boolean/1</code></a>
│ │ │ │  BIF tests whether a term is a boolean.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mi">2</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │  </span><span class="gp unselectable">2&gt; </span><span class="ss">true</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="ss">false</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="4100428523-1">(</span><span class="ss">true</span><span class="p" data-group-id="4100428523-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1285117311-1">(</span><span class="ss">true</span><span class="p" data-group-id="1285117311-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="4100428523-2">(</span><span class="ss">false</span><span class="p" data-group-id="4100428523-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1285117311-2">(</span><span class="ss">false</span><span class="p" data-group-id="1285117311-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="4100428523-3">(</span><span class="ss">ok</span><span class="p" data-group-id="4100428523-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1285117311-3">(</span><span class="ss">ok</span><span class="p" data-group-id="1285117311-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><h2 id="escape-sequences" class="section-heading">
│ │ │ │    <a href="#escape-sequences" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Escape Sequences</span>
│ │ │ │  </h2>
│ │ │ │  <p>Within strings (<code class="inline">&quot;</code>-delimited), quoted atoms, and the content of
│ │ │ │ @@ -464,44 +464,44 @@
│ │ │ │  <a href="data_types.xhtml#sigil"><code class="inline">~b</code> or <code class="inline">~s</code> sigils </a>the escape sequences for normal
│ │ │ │  strings, above, are used.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Triple-quoted strings and sigils were introduced in Erlang/OTP 27.</p></section><h2 id="type-conversions" class="section-heading">
│ │ │ │    <a href="#type-conversions" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Type Conversions</span>
│ │ │ │  </h2>
│ │ │ │ -<p>There are a number of BIFs for type conversions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="1851681845-1">(</span><span class="ss">hello</span><span class="p" data-group-id="1851681845-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>There are a number of BIFs for type conversions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="5692666303-1">(</span><span class="ss">hello</span><span class="p" data-group-id="5692666303-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="1851681845-2">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="1851681845-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="5692666303-2">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5692666303-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="1851681845-3">(</span><span class="p" data-group-id="1851681845-4">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="1851681845-4">&gt;&gt;</span><span class="p" data-group-id="1851681845-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="5692666303-3">(</span><span class="p" data-group-id="5692666303-4">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5692666303-4">&gt;&gt;</span><span class="p" data-group-id="5692666303-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="1851681845-5">(</span><span class="p" data-group-id="1851681845-6">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="1851681845-6">&gt;&gt;</span><span class="p" data-group-id="1851681845-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="5692666303-5">(</span><span class="p" data-group-id="5692666303-6">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="5692666303-6">&gt;&gt;</span><span class="p" data-group-id="5692666303-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="1851681845-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="1851681845-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1851681845-8">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="1851681845-8">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="1851681845-9">(</span><span class="mf">7.0</span><span class="p" data-group-id="1851681845-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="5692666303-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5692666303-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692666303-8">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="5692666303-8">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="5692666303-9">(</span><span class="mf">7.0</span><span class="p" data-group-id="5692666303-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="1851681845-10">(</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="1851681845-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="5692666303-10">(</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="5692666303-10">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">7.0</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">8&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="1851681845-11">(</span><span class="mi">77</span><span class="p" data-group-id="1851681845-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">8&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="5692666303-11">(</span><span class="mi">77</span><span class="p" data-group-id="5692666303-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="s">&quot;77&quot;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="1851681845-12">(</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="1851681845-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="5692666303-12">(</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="5692666303-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">77</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="1851681845-13">(</span><span class="p" data-group-id="1851681845-14">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1851681845-14">}</span><span class="p" data-group-id="1851681845-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1851681845-15">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1851681845-15">]</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">11&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="1851681845-16">(</span><span class="p" data-group-id="1851681845-17">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1851681845-17">]</span><span class="p" data-group-id="1851681845-16">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1851681845-18">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1851681845-18">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">12&gt; </span><span class="nf">term_to_binary</span><span class="p" data-group-id="1851681845-19">(</span><span class="p" data-group-id="1851681845-20">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1851681845-20">}</span><span class="p" data-group-id="1851681845-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1851681845-21">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="1851681845-21">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">13&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="1851681845-22">(</span><span class="p" data-group-id="1851681845-23">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="1851681845-23">&gt;&gt;</span><span class="p" data-group-id="1851681845-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1851681845-24">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1851681845-24">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">14&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="1851681845-25">(</span><span class="p" data-group-id="1851681845-26">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="1851681845-26">&gt;&gt;</span><span class="p" data-group-id="1851681845-25">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="5692666303-13">(</span><span class="p" data-group-id="5692666303-14">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5692666303-14">}</span><span class="p" data-group-id="5692666303-13">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692666303-15">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5692666303-15">]</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">11&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="5692666303-16">(</span><span class="p" data-group-id="5692666303-17">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5692666303-17">]</span><span class="p" data-group-id="5692666303-16">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692666303-18">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5692666303-18">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">12&gt; </span><span class="nf">term_to_binary</span><span class="p" data-group-id="5692666303-19">(</span><span class="p" data-group-id="5692666303-20">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5692666303-20">}</span><span class="p" data-group-id="5692666303-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692666303-21">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="5692666303-21">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">13&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="5692666303-22">(</span><span class="p" data-group-id="5692666303-23">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="5692666303-23">&gt;&gt;</span><span class="p" data-group-id="5692666303-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692666303-24">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5692666303-24">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">14&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="5692666303-25">(</span><span class="p" data-group-id="5692666303-26">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="5692666303-26">&gt;&gt;</span><span class="p" data-group-id="5692666303-25">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">77</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">15&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="1851681845-27">(</span><span class="mi">77</span><span class="p" data-group-id="1851681845-27">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1851681845-28">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="1851681845-28">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">16&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="1851681845-29">(</span><span class="mf">7.0</span><span class="p" data-group-id="1851681845-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1851681845-30">&lt;&lt;</span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="p" data-group-id="1851681845-30">&gt;&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">17&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="1851681845-31">(</span><span class="p" data-group-id="1851681845-32">&lt;&lt;</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="1851681845-32">&gt;&gt;</span><span class="p" data-group-id="1851681845-31">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">15&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="5692666303-27">(</span><span class="mi">77</span><span class="p" data-group-id="5692666303-27">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692666303-28">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="5692666303-28">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">16&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="5692666303-29">(</span><span class="mf">7.0</span><span class="p" data-group-id="5692666303-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5692666303-30">&lt;&lt;</span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="p" data-group-id="5692666303-30">&gt;&gt;</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">17&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="5692666303-31">(</span><span class="p" data-group-id="5692666303-32">&lt;&lt;</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="5692666303-32">&gt;&gt;</span><span class="p" data-group-id="5692666303-31">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mf">7.0</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/create_target.xhtml
│ │ │ │ @@ -43,21 +43,21 @@
│ │ │ │    <span class="text">Creating a Target System</span>
│ │ │ │  </h2>
│ │ │ │  <p>It is assumed that you have a working Erlang/OTP system structured according to
│ │ │ │  the OTP design principles.</p><p><em>Step 1.</em> Create a <code class="inline">.rel</code> file (see the <a href="../../../lib/sasl/doc/html/rel.xhtml">rel(4)</a> manual page in
│ │ │ │  SASL), which specifies the ERTS version and lists all applications that are to
│ │ │ │  be included in the new basic target system. An example is the following
│ │ │ │  <code class="inline">mysystem.rel</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% mysystem.rel</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9826066500-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9826066500-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;FIRST&quot;</span><span class="p" data-group-id="9826066500-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9826066500-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.10.4&quot;</span><span class="p" data-group-id="9826066500-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9826066500-4">[</span><span class="p" data-group-id="9826066500-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.16.4&quot;</span><span class="p" data-group-id="9826066500-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9826066500-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.19.4&quot;</span><span class="p" data-group-id="9826066500-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9826066500-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.3.4&quot;</span><span class="p" data-group-id="9826066500-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9826066500-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="9826066500-8">}</span><span class="p" data-group-id="9826066500-4">]</span><span class="p" data-group-id="9826066500-1">}</span><span class="p">.</span></code></pre><p>The listed applications are not only original Erlang/OTP applications but
│ │ │ │ +</span><span class="p" data-group-id="3543521801-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3543521801-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;FIRST&quot;</span><span class="p" data-group-id="3543521801-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3543521801-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.10.4&quot;</span><span class="p" data-group-id="3543521801-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3543521801-4">[</span><span class="p" data-group-id="3543521801-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.16.4&quot;</span><span class="p" data-group-id="3543521801-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3543521801-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.19.4&quot;</span><span class="p" data-group-id="3543521801-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3543521801-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.3.4&quot;</span><span class="p" data-group-id="3543521801-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3543521801-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="3543521801-8">}</span><span class="p" data-group-id="3543521801-4">]</span><span class="p" data-group-id="3543521801-1">}</span><span class="p">.</span></code></pre><p>The listed applications are not only original Erlang/OTP applications but
│ │ │ │  possibly also new applications that you have written (here exemplified by the
│ │ │ │  application Pea (<code class="inline">pea</code>)).</p><p><em>Step 2.</em> Start Erlang/OTP from the directory where the <code class="inline">mysystem.rel</code> file
│ │ │ │  resides:</p><pre><code class="text">% erl -pa /home/user/target_system/myapps/pea-1.0/ebin</code></pre><p>The <code class="inline">-pa</code> argument prepends the path to the <code class="inline">ebin</code> directory for
│ │ │ │  the Pea application to the code path.</p><p><em>Step 3.</em> Create the target system:</p><pre><code class="text">1&gt; target_system:create(&quot;mysystem&quot;).</code></pre><p>The function <code class="inline">target_system:create/1</code> performs the following:</p><ol><li><p>Reads the file <code class="inline">mysystem.rel</code> and creates a new file <code class="inline">plain.rel</code>.
│ │ │ │  The new file is identical to the original, except that it only
│ │ │ │  lists the Kernel and STDLIB applications.</p></li><li><p>From the files <code class="inline">mysystem.rel</code> and <code class="inline">plain.rel</code> creates the files
│ │ │ │  <code class="inline">mysystem.script</code>, <code class="inline">mysystem.boot</code>, <code class="inline">plain.script</code>, and <code class="inline">plain.boot</code>
│ │ │ │ @@ -147,25 +147,25 @@
│ │ │ │    <a href="#creating-the-next-version" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Creating the Next Version</span>
│ │ │ │  </h2>
│ │ │ │  <p>In this example the Pea application has been changed, and so are the
│ │ │ │  applications ERTS, Kernel, STDLIB and SASL.</p><p><em>Step 1.</em> Create the file <code class="inline">.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% mysystem2.rel</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9864247916-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9864247916-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;SECOND&quot;</span><span class="p" data-group-id="9864247916-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9864247916-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;6.0&quot;</span><span class="p" data-group-id="9864247916-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9864247916-4">[</span><span class="p" data-group-id="9864247916-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;3.0&quot;</span><span class="p" data-group-id="9864247916-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9864247916-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="9864247916-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9864247916-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.4&quot;</span><span class="p" data-group-id="9864247916-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="9864247916-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="9864247916-8">}</span><span class="p" data-group-id="9864247916-4">]</span><span class="p" data-group-id="9864247916-1">}</span><span class="p">.</span></code></pre><p><em>Step 2.</em> Create the application upgrade file (see
│ │ │ │ +</span><span class="p" data-group-id="7339056171-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7339056171-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;SECOND&quot;</span><span class="p" data-group-id="7339056171-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7339056171-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;6.0&quot;</span><span class="p" data-group-id="7339056171-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7339056171-4">[</span><span class="p" data-group-id="7339056171-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;3.0&quot;</span><span class="p" data-group-id="7339056171-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7339056171-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="7339056171-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7339056171-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.4&quot;</span><span class="p" data-group-id="7339056171-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7339056171-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="7339056171-8">}</span><span class="p" data-group-id="7339056171-4">]</span><span class="p" data-group-id="7339056171-1">}</span><span class="p">.</span></code></pre><p><em>Step 2.</em> Create the application upgrade file (see
│ │ │ │  <a href="../../../lib/sasl/doc/html/appup.xhtml">appup</a> in SASL) for Pea, for example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% pea.appup</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8608338656-1">{</span><span class="s">&quot;2.0&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8608338656-2">[</span><span class="p" data-group-id="8608338656-3">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="8608338656-4">[</span><span class="p" data-group-id="8608338656-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="8608338656-5">}</span><span class="p" data-group-id="8608338656-4">]</span><span class="p" data-group-id="8608338656-3">}</span><span class="p" data-group-id="8608338656-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="8608338656-6">[</span><span class="p" data-group-id="8608338656-7">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="8608338656-8">[</span><span class="p" data-group-id="8608338656-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="8608338656-9">}</span><span class="p" data-group-id="8608338656-8">]</span><span class="p" data-group-id="8608338656-7">}</span><span class="p" data-group-id="8608338656-6">]</span><span class="p" data-group-id="8608338656-1">}</span><span class="p">.</span></code></pre><p><em>Step 3.</em> From the directory where the file <code class="inline">mysystem2.rel</code> resides, start the
│ │ │ │ +</span><span class="p" data-group-id="8219664023-1">{</span><span class="s">&quot;2.0&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8219664023-2">[</span><span class="p" data-group-id="8219664023-3">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="8219664023-4">[</span><span class="p" data-group-id="8219664023-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="8219664023-5">}</span><span class="p" data-group-id="8219664023-4">]</span><span class="p" data-group-id="8219664023-3">}</span><span class="p" data-group-id="8219664023-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8219664023-6">[</span><span class="p" data-group-id="8219664023-7">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="8219664023-8">[</span><span class="p" data-group-id="8219664023-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="8219664023-9">}</span><span class="p" data-group-id="8219664023-8">]</span><span class="p" data-group-id="8219664023-7">}</span><span class="p" data-group-id="8219664023-6">]</span><span class="p" data-group-id="8219664023-1">}</span><span class="p">.</span></code></pre><p><em>Step 3.</em> From the directory where the file <code class="inline">mysystem2.rel</code> resides, start the
│ │ │ │  Erlang/OTP system, giving the path to the new version of Pea:</p><pre><code class="text">% erl -pa /home/user/target_system/myapps/pea-2.0/ebin</code></pre><p><em>Step 4.</em> Create the release upgrade file (see <a href="../../../lib/sasl/doc/html/relup.xhtml">relup</a>
│ │ │ │  in SASL):</p><pre><code class="text">1&gt; systools:make_relup(&quot;mysystem2&quot;,[&quot;mysystem&quot;],[&quot;mysystem&quot;],
│ │ │ │      [{path,[&quot;/home/user/target_system/myapps/pea-1.0/ebin&quot;,
│ │ │ │      &quot;/my/old/erlang/lib/*/ebin&quot;]}]).</code></pre><p>Here <code class="inline">&quot;mysystem&quot;</code> is the base release and <code class="inline">&quot;mysystem2&quot;</code> is the release to
│ │ │ │  upgrade to.</p><p>The <code class="inline">path</code> option is used for pointing out the old version of all applications.
│ │ │ │  (The new versions are already in the code path - assuming of course that the
│ │ │ │  Erlang node on which this is executed is running the correct version of
│ │ │ │ @@ -197,287 +197,287 @@
│ │ │ │  {continue_after_restart,&quot;FIRST&quot;,[]}
│ │ │ │  heart: Tue Apr  1 12:15:10 2014: Erlang has closed.
│ │ │ │  heart: Tue Apr  1 12:15:11 2014: Executed &quot;/usr/local/erl-target/bin/start /usr/local/erl-target/releases/new_start_erl.data&quot; -&gt; 0. Terminating.
│ │ │ │  [End]</code></pre><p>The above return value and output after the call to
│ │ │ │  <a href="../../../lib/sasl/doc/html/release_handler.html#install_release/1"><code class="inline">release_handler:install_release/1</code></a> means that the <code class="inline">release_handler</code> has
│ │ │ │  restarted the node by using <code class="inline">heart</code>. This is always done when the upgrade
│ │ │ │  involves a change of the applications ERTS, Kernel, STDLIB, or SASL. For more
│ │ │ │ -information, see <a href="upgrade.xhtml">Upgrade when Erlang/OTP has Changed</a>.</p><p>The node is accessible through a new pipe:</p><pre><code class="text">% /usr/local/erl-target/bin/to_erl /tmp/erlang.pipe.2</code></pre><p>List the available releases in the system:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">which_releases</span><span class="p" data-group-id="0353537776-1">(</span><span class="p" data-group-id="0353537776-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0353537776-2">[</span><span class="p" data-group-id="0353537776-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0353537776-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="0353537776-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">current</span><span class="p" data-group-id="0353537776-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0353537776-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0353537776-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="0353537776-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="ss">permanent</span><span class="p" data-group-id="0353537776-5">}</span><span class="p" data-group-id="0353537776-2">]</span></code></pre><p>Our new release, &quot;SECOND&quot;, is now the current release, but we can also see that
│ │ │ │ +information, see <a href="upgrade.xhtml">Upgrade when Erlang/OTP has Changed</a>.</p><p>The node is accessible through a new pipe:</p><pre><code class="text">% /usr/local/erl-target/bin/to_erl /tmp/erlang.pipe.2</code></pre><p>List the available releases in the system:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">which_releases</span><span class="p" data-group-id="0517548256-1">(</span><span class="p" data-group-id="0517548256-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0517548256-2">[</span><span class="p" data-group-id="0517548256-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0517548256-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="0517548256-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">current</span><span class="p" data-group-id="0517548256-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0517548256-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0517548256-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="0517548256-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="ss">permanent</span><span class="p" data-group-id="0517548256-5">}</span><span class="p" data-group-id="0517548256-2">]</span></code></pre><p>Our new release, &quot;SECOND&quot;, is now the current release, but we can also see that
│ │ │ │  our &quot;FIRST&quot; release is still permanent. This means that if the node would be
│ │ │ │ -restarted now, it would come up running the &quot;FIRST&quot; release again.</p><p><em>Step 3.</em> Make the new release permanent:</p><pre><code class="text">2&gt; release_handler:make_permanent(&quot;SECOND&quot;).</code></pre><p>Check the releases again:</p><pre><code class="makeup c" translate="no"><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">release_handler</span><span class="o">:</span><span class="nf">which_releases</span><span class="p" data-group-id="3615904968-1">(</span><span class="p" data-group-id="3615904968-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3615904968-2">[</span><span class="p" data-group-id="3615904968-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="3615904968-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="3615904968-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="n">permanent</span><span class="p" data-group-id="3615904968-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3615904968-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="3615904968-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="3615904968-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="n">old</span><span class="p" data-group-id="3615904968-5">}</span><span class="p" data-group-id="3615904968-2">]</span></code></pre><p>We see that the new release version is <code class="inline">permanent</code>, so it would be safe to
│ │ │ │ +restarted now, it would come up running the &quot;FIRST&quot; release again.</p><p><em>Step 3.</em> Make the new release permanent:</p><pre><code class="text">2&gt; release_handler:make_permanent(&quot;SECOND&quot;).</code></pre><p>Check the releases again:</p><pre><code class="makeup c" translate="no"><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">release_handler</span><span class="o">:</span><span class="nf">which_releases</span><span class="p" data-group-id="7071398808-1">(</span><span class="p" data-group-id="7071398808-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7071398808-2">[</span><span class="p" data-group-id="7071398808-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7071398808-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="7071398808-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="n">permanent</span><span class="p" data-group-id="7071398808-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="7071398808-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="7071398808-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="7071398808-6">]</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="n">old</span><span class="p" data-group-id="7071398808-5">}</span><span class="p" data-group-id="7071398808-2">]</span></code></pre><p>We see that the new release version is <code class="inline">permanent</code>, so it would be safe to
│ │ │ │  restart the node.</p><p><a href="" id="listing-of-target-system"></a></p><h2 id="listing-of-target_system-erl" class="section-heading">
│ │ │ │    <a href="#listing-of-target_system-erl" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Listing of target_system.erl</span>
│ │ │ │  </h2>
│ │ │ │  <p>This module can also be found in the <code class="inline">examples</code> directory of the SASL
│ │ │ │  application.</p><pre><code class="makeup erlang" translate="no"><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2572133318-1">(</span><span class="ss">target_system</span><span class="p" data-group-id="2572133318-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2572133318-2">(</span><span class="p" data-group-id="2572133318-3">[</span><span class="ss">create</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">create</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">install</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2572133318-3">]</span><span class="p" data-group-id="2572133318-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0180395686-1">(</span><span class="ss">target_system</span><span class="p" data-group-id="0180395686-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0180395686-2">(</span><span class="p" data-group-id="0180395686-3">[</span><span class="ss">create</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">create</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">install</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0180395686-3">]</span><span class="p" data-group-id="0180395686-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% Note: RelFileName below is the *stem* without trailing .rel,</span><span class="w">
│ │ │ │  </span><span class="c1">%% .script etc.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% create(RelFileName)</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">create</span><span class="p" data-group-id="2572133318-4">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2572133318-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">create</span><span class="p" data-group-id="2572133318-5">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="p" data-group-id="2572133318-6">[</span><span class="p" data-group-id="2572133318-6">]</span><span class="p" data-group-id="2572133318-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">create</span><span class="p" data-group-id="0180395686-4">(</span><span class="n">RelFileName</span><span class="p" data-group-id="0180395686-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">create</span><span class="p" data-group-id="0180395686-5">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="p" data-group-id="0180395686-6">[</span><span class="p" data-group-id="0180395686-6">]</span><span class="p" data-group-id="0180395686-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">create</span><span class="p" data-group-id="2572133318-7">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2572133318-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">create</span><span class="p" data-group-id="0180395686-7">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="0180395686-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">RelFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="2572133318-8">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2572133318-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-9">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;plain&quot;</span><span class="p" data-group-id="2572133318-9">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="0180395686-8">(</span><span class="n">RelFileName</span><span class="p" data-group-id="0180395686-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-9">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;plain&quot;</span><span class="p" data-group-id="0180395686-9">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">PlainRelFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-10">(</span><span class="s">&quot;Reading file: ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-11">[</span><span class="n">RelFile</span><span class="p" data-group-id="2572133318-11">]</span><span class="p" data-group-id="2572133318-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-13">[</span><span class="n">RelSpec</span><span class="p" data-group-id="2572133318-13">]</span><span class="p" data-group-id="2572133318-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">consult</span><span class="p" data-group-id="2572133318-14">(</span><span class="n">RelFile</span><span class="p" data-group-id="2572133318-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-15">(</span><span class="s">&quot;Creating file: ~ts from ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="2572133318-16">[</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="n">RelFile</span><span class="p" data-group-id="2572133318-16">]</span><span class="p" data-group-id="2572133318-15">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-17">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="2572133318-18">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="2572133318-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="p" data-group-id="2572133318-19">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="2572133318-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -     </span><span class="n">AppVsns</span><span class="p" data-group-id="2572133318-17">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelSpec</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">PlainRelSpec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2572133318-20">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="2572133318-21">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="2572133318-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="p" data-group-id="2572133318-22">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="2572133318-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ -                    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="2572133318-23">(</span><span class="nf">fun</span><span class="p" data-group-id="2572133318-24">(</span><span class="p" data-group-id="2572133318-25">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2572133318-25">}</span><span class="p" data-group-id="2572133318-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-10">(</span><span class="s">&quot;Reading file: ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-11">[</span><span class="n">RelFile</span><span class="p" data-group-id="0180395686-11">]</span><span class="p" data-group-id="0180395686-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-13">[</span><span class="n">RelSpec</span><span class="p" data-group-id="0180395686-13">]</span><span class="p" data-group-id="0180395686-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">consult</span><span class="p" data-group-id="0180395686-14">(</span><span class="n">RelFile</span><span class="p" data-group-id="0180395686-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-15">(</span><span class="s">&quot;Creating file: ~ts from ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="0180395686-16">[</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="n">RelFile</span><span class="p" data-group-id="0180395686-16">]</span><span class="p" data-group-id="0180395686-15">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-17">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="0180395686-18">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="0180395686-18">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="p" data-group-id="0180395686-19">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="0180395686-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +     </span><span class="n">AppVsns</span><span class="p" data-group-id="0180395686-17">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelSpec</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">PlainRelSpec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0180395686-20">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="0180395686-21">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="0180395686-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="p" data-group-id="0180395686-22">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="0180395686-22">}</span><span class="p">,</span><span class="w">
│ │ │ │ +                    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="0180395686-23">(</span><span class="nf">fun</span><span class="p" data-group-id="0180395686-24">(</span><span class="p" data-group-id="0180395686-25">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="0180395686-25">}</span><span class="p" data-group-id="0180395686-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                                           </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -                                    </span><span class="p" data-group-id="2572133318-26">(</span><span class="p" data-group-id="2572133318-27">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2572133318-27">}</span><span class="p" data-group-id="2572133318-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                                    </span><span class="p" data-group-id="0180395686-26">(</span><span class="p" data-group-id="0180395686-27">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="0180395686-27">}</span><span class="p" data-group-id="0180395686-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                                           </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ │ -                                    </span><span class="p" data-group-id="2572133318-28">(</span><span class="p">_</span><span class="p" data-group-id="2572133318-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                                    </span><span class="p" data-group-id="0180395686-28">(</span><span class="p">_</span><span class="p" data-group-id="0180395686-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │                                           </span><span class="ss">false</span><span class="w">
│ │ │ │ -                                 </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsns</span><span class="p" data-group-id="2572133318-23">)</span><span class="w">
│ │ │ │ -                   </span><span class="p" data-group-id="2572133318-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2572133318-29">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2572133318-30">(</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-31">[</span><span class="ss">write</span><span class="p" data-group-id="2572133318-31">]</span><span class="p" data-group-id="2572133318-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-32">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-33">[</span><span class="n">PlainRelSpec</span><span class="p" data-group-id="2572133318-33">]</span><span class="p" data-group-id="2572133318-32">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2572133318-34">(</span><span class="n">Fd</span><span class="p" data-group-id="2572133318-34">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-35">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -	      </span><span class="p" data-group-id="2572133318-36">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">PlainRelFileName</span><span class="p" data-group-id="2572133318-36">]</span><span class="p" data-group-id="2572133318-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">make_script</span><span class="p" data-group-id="2572133318-37">(</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2572133318-37">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-38">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="2572133318-39">[</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="2572133318-39">]</span><span class="p" data-group-id="2572133318-38">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">make_script</span><span class="p" data-group-id="2572133318-40">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2572133318-40">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                                 </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsns</span><span class="p" data-group-id="0180395686-23">)</span><span class="w">
│ │ │ │ +                   </span><span class="p" data-group-id="0180395686-20">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0180395686-29">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="0180395686-30">(</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-31">[</span><span class="ss">write</span><span class="p" data-group-id="0180395686-31">]</span><span class="p" data-group-id="0180395686-30">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-32">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-33">[</span><span class="n">PlainRelSpec</span><span class="p" data-group-id="0180395686-33">]</span><span class="p" data-group-id="0180395686-32">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="0180395686-34">(</span><span class="n">Fd</span><span class="p" data-group-id="0180395686-34">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-35">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +	      </span><span class="p" data-group-id="0180395686-36">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">PlainRelFileName</span><span class="p" data-group-id="0180395686-36">]</span><span class="p" data-group-id="0180395686-35">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">make_script</span><span class="p" data-group-id="0180395686-37">(</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="0180395686-37">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-38">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="0180395686-39">[</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="0180395686-39">]</span><span class="p" data-group-id="0180395686-38">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">make_script</span><span class="p" data-group-id="0180395686-40">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="0180395686-40">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │      </span><span class="n">TarFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.tar.gz&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-41">(</span><span class="s">&quot;Creating tar file ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-42">[</span><span class="n">TarFileName</span><span class="p" data-group-id="2572133318-42">]</span><span class="p" data-group-id="2572133318-41">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">make_tar</span><span class="p" data-group-id="2572133318-43">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2572133318-43">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-41">(</span><span class="s">&quot;Creating tar file ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-42">[</span><span class="n">TarFileName</span><span class="p" data-group-id="0180395686-42">]</span><span class="p" data-group-id="0180395686-41">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">make_tar</span><span class="p" data-group-id="0180395686-43">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="0180395686-43">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │ -    </span><span class="n">TmpDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-44">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;tmp&quot;</span><span class="p" data-group-id="2572133318-44">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-45">(</span><span class="s">&quot;Creating directory ~tp ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2572133318-46">[</span><span class="n">TmpDir</span><span class="p" data-group-id="2572133318-46">]</span><span class="p" data-group-id="2572133318-45">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="2572133318-47">(</span><span class="n">TmpDir</span><span class="p" data-group-id="2572133318-47">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-48">(</span><span class="s">&quot;Extracting ~ts into directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-49">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="2572133318-49">]</span><span class="p" data-group-id="2572133318-48">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">extract_tar</span><span class="p" data-group-id="2572133318-50">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="n">TmpDir</span><span class="p" data-group-id="2572133318-50">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="n">TmpBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-51">(</span><span class="p" data-group-id="2572133318-52">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2572133318-52">]</span><span class="p" data-group-id="2572133318-51">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-53">(</span><span class="p" data-group-id="2572133318-54">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2572133318-54">]</span><span class="p" data-group-id="2572133318-53">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-55">(</span><span class="s">&quot;Deleting \&quot;erl\&quot; and \&quot;start\&quot; in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="2572133318-56">[</span><span class="n">ErtsBinDir</span><span class="p" data-group-id="2572133318-56">]</span><span class="p" data-group-id="2572133318-55">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2572133318-57">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-58">(</span><span class="p" data-group-id="2572133318-59">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erl&quot;</span><span class="p" data-group-id="2572133318-59">]</span><span class="p" data-group-id="2572133318-58">)</span><span class="p" data-group-id="2572133318-57">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2572133318-60">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-61">(</span><span class="p" data-group-id="2572133318-62">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="2572133318-62">]</span><span class="p" data-group-id="2572133318-61">)</span><span class="p" data-group-id="2572133318-60">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-63">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-64">[</span><span class="n">TmpBinDir</span><span class="p" data-group-id="2572133318-64">]</span><span class="p" data-group-id="2572133318-63">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="2572133318-65">(</span><span class="n">TmpBinDir</span><span class="p" data-group-id="2572133318-65">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-66">(</span><span class="s">&quot;Copying file \&quot;~ts.boot\&quot; to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="2572133318-67">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-68">(</span><span class="p" data-group-id="2572133318-69">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="2572133318-69">]</span><span class="p" data-group-id="2572133318-68">)</span><span class="p" data-group-id="2572133318-67">]</span><span class="p" data-group-id="2572133318-66">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="2572133318-70">(</span><span class="n">PlainRelFileName</span><span class="o">++</span><span class="s">&quot;.boot&quot;</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-71">(</span><span class="p" data-group-id="2572133318-72">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="2572133318-72">]</span><span class="p" data-group-id="2572133318-71">)</span><span class="p" data-group-id="2572133318-70">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">TmpDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-44">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;tmp&quot;</span><span class="p" data-group-id="0180395686-44">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-45">(</span><span class="s">&quot;Creating directory ~tp ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="0180395686-46">[</span><span class="n">TmpDir</span><span class="p" data-group-id="0180395686-46">]</span><span class="p" data-group-id="0180395686-45">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="0180395686-47">(</span><span class="n">TmpDir</span><span class="p" data-group-id="0180395686-47">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-48">(</span><span class="s">&quot;Extracting ~ts into directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-49">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="0180395686-49">]</span><span class="p" data-group-id="0180395686-48">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">extract_tar</span><span class="p" data-group-id="0180395686-50">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="n">TmpDir</span><span class="p" data-group-id="0180395686-50">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="n">TmpBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-51">(</span><span class="p" data-group-id="0180395686-52">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="0180395686-52">]</span><span class="p" data-group-id="0180395686-51">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-53">(</span><span class="p" data-group-id="0180395686-54">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="0180395686-54">]</span><span class="p" data-group-id="0180395686-53">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-55">(</span><span class="s">&quot;Deleting \&quot;erl\&quot; and \&quot;start\&quot; in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="0180395686-56">[</span><span class="n">ErtsBinDir</span><span class="p" data-group-id="0180395686-56">]</span><span class="p" data-group-id="0180395686-55">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="0180395686-57">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-58">(</span><span class="p" data-group-id="0180395686-59">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erl&quot;</span><span class="p" data-group-id="0180395686-59">]</span><span class="p" data-group-id="0180395686-58">)</span><span class="p" data-group-id="0180395686-57">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="0180395686-60">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-61">(</span><span class="p" data-group-id="0180395686-62">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="0180395686-62">]</span><span class="p" data-group-id="0180395686-61">)</span><span class="p" data-group-id="0180395686-60">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-63">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-64">[</span><span class="n">TmpBinDir</span><span class="p" data-group-id="0180395686-64">]</span><span class="p" data-group-id="0180395686-63">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="0180395686-65">(</span><span class="n">TmpBinDir</span><span class="p" data-group-id="0180395686-65">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-66">(</span><span class="s">&quot;Copying file \&quot;~ts.boot\&quot; to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="0180395686-67">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-68">(</span><span class="p" data-group-id="0180395686-69">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="0180395686-69">]</span><span class="p" data-group-id="0180395686-68">)</span><span class="p" data-group-id="0180395686-67">]</span><span class="p" data-group-id="0180395686-66">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="0180395686-70">(</span><span class="n">PlainRelFileName</span><span class="o">++</span><span class="s">&quot;.boot&quot;</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-71">(</span><span class="p" data-group-id="0180395686-72">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="0180395686-72">]</span><span class="p" data-group-id="0180395686-71">)</span><span class="p" data-group-id="0180395686-70">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-73">(</span><span class="s">&quot;Copying files \&quot;epmd\&quot;, \&quot;run_erl\&quot; and \&quot;to_erl\&quot; from \n&quot;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-73">(</span><span class="s">&quot;Copying files \&quot;epmd\&quot;, \&quot;run_erl\&quot; and \&quot;to_erl\&quot; from \n&quot;</span><span class="w">
│ │ │ │                </span><span class="s">&quot;~ts to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="p" data-group-id="2572133318-74">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">TmpBinDir</span><span class="p" data-group-id="2572133318-74">]</span><span class="p" data-group-id="2572133318-73">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="2572133318-75">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-76">(</span><span class="p" data-group-id="2572133318-77">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="2572133318-77">]</span><span class="p" data-group-id="2572133318-76">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-78">(</span><span class="p" data-group-id="2572133318-79">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="2572133318-79">]</span><span class="p" data-group-id="2572133318-78">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-80">[</span><span class="ss">preserve</span><span class="p" data-group-id="2572133318-80">]</span><span class="p" data-group-id="2572133318-75">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="2572133318-81">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-82">(</span><span class="p" data-group-id="2572133318-83">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="2572133318-83">]</span><span class="p" data-group-id="2572133318-82">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-84">(</span><span class="p" data-group-id="2572133318-85">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="2572133318-85">]</span><span class="p" data-group-id="2572133318-84">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-86">[</span><span class="ss">preserve</span><span class="p" data-group-id="2572133318-86">]</span><span class="p" data-group-id="2572133318-81">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="2572133318-87">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-88">(</span><span class="p" data-group-id="2572133318-89">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="2572133318-89">]</span><span class="p" data-group-id="2572133318-88">)</span><span class="p">,</span><span class="w">
│ │ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-90">(</span><span class="p" data-group-id="2572133318-91">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="2572133318-91">]</span><span class="p" data-group-id="2572133318-90">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-92">[</span><span class="ss">preserve</span><span class="p" data-group-id="2572133318-92">]</span><span class="p" data-group-id="2572133318-87">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="p" data-group-id="0180395686-74">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">TmpBinDir</span><span class="p" data-group-id="0180395686-74">]</span><span class="p" data-group-id="0180395686-73">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="0180395686-75">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-76">(</span><span class="p" data-group-id="0180395686-77">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="0180395686-77">]</span><span class="p" data-group-id="0180395686-76">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-78">(</span><span class="p" data-group-id="0180395686-79">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="0180395686-79">]</span><span class="p" data-group-id="0180395686-78">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-80">[</span><span class="ss">preserve</span><span class="p" data-group-id="0180395686-80">]</span><span class="p" data-group-id="0180395686-75">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="0180395686-81">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-82">(</span><span class="p" data-group-id="0180395686-83">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="0180395686-83">]</span><span class="p" data-group-id="0180395686-82">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-84">(</span><span class="p" data-group-id="0180395686-85">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="0180395686-85">]</span><span class="p" data-group-id="0180395686-84">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-86">[</span><span class="ss">preserve</span><span class="p" data-group-id="0180395686-86">]</span><span class="p" data-group-id="0180395686-81">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="0180395686-87">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-88">(</span><span class="p" data-group-id="0180395686-89">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="0180395686-89">]</span><span class="p" data-group-id="0180395686-88">)</span><span class="p">,</span><span class="w">
│ │ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-90">(</span><span class="p" data-group-id="0180395686-91">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="0180395686-91">]</span><span class="p" data-group-id="0180395686-90">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-92">[</span><span class="ss">preserve</span><span class="p" data-group-id="0180395686-92">]</span><span class="p" data-group-id="0180395686-87">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │      </span><span class="c1">%% This is needed if &#39;start&#39; script created from &#39;start.src&#39; shall</span><span class="w">
│ │ │ │      </span><span class="c1">%% be used as it points out this directory as log dir for &#39;run_erl&#39;</span><span class="w">
│ │ │ │ -    </span><span class="n">TmpLogDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-93">(</span><span class="p" data-group-id="2572133318-94">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="2572133318-94">]</span><span class="p" data-group-id="2572133318-93">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-95">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-96">[</span><span class="n">TmpLogDir</span><span class="p" data-group-id="2572133318-96">]</span><span class="p" data-group-id="2572133318-95">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="2572133318-97">(</span><span class="n">TmpLogDir</span><span class="p" data-group-id="2572133318-97">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-98">(</span><span class="p" data-group-id="2572133318-99">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="2572133318-99">]</span><span class="p" data-group-id="2572133318-98">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-100">(</span><span class="s">&quot;Creating ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-101">[</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="2572133318-101">]</span><span class="p" data-group-id="2572133318-100">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">StartErlData</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">io_lib</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-102">(</span><span class="s">&quot;</span><span class="si">~s</span><span class="s"> </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-103">[</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="2572133318-103">]</span><span class="p" data-group-id="2572133318-102">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">write_file</span><span class="p" data-group-id="2572133318-104">(</span><span class="n">StartErlDataFile</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="2572133318-104">)</span><span class="p">,</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-105">(</span><span class="s">&quot;Recreating tar file ~ts from contents in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -	      </span><span class="p" data-group-id="2572133318-106">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="2572133318-106">]</span><span class="p" data-group-id="2572133318-105">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-107">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tar</span><span class="p" data-group-id="2572133318-107">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2572133318-108">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-109">[</span><span class="ss">write</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="2572133318-109">]</span><span class="p" data-group-id="2572133318-108">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">TmpLogDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-93">(</span><span class="p" data-group-id="0180395686-94">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="0180395686-94">]</span><span class="p" data-group-id="0180395686-93">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-95">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-96">[</span><span class="n">TmpLogDir</span><span class="p" data-group-id="0180395686-96">]</span><span class="p" data-group-id="0180395686-95">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="0180395686-97">(</span><span class="n">TmpLogDir</span><span class="p" data-group-id="0180395686-97">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-98">(</span><span class="p" data-group-id="0180395686-99">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="0180395686-99">]</span><span class="p" data-group-id="0180395686-98">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-100">(</span><span class="s">&quot;Creating ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-101">[</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="0180395686-101">]</span><span class="p" data-group-id="0180395686-100">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">StartErlData</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">io_lib</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-102">(</span><span class="s">&quot;</span><span class="si">~s</span><span class="s"> </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-103">[</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="0180395686-103">]</span><span class="p" data-group-id="0180395686-102">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">write_file</span><span class="p" data-group-id="0180395686-104">(</span><span class="n">StartErlDataFile</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="0180395686-104">)</span><span class="p">,</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-105">(</span><span class="s">&quot;Recreating tar file ~ts from contents in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +	      </span><span class="p" data-group-id="0180395686-106">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="0180395686-106">]</span><span class="p" data-group-id="0180395686-105">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-107">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tar</span><span class="p" data-group-id="0180395686-107">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="0180395686-108">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-109">[</span><span class="ss">write</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="0180395686-109">]</span><span class="p" data-group-id="0180395686-108">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%% {ok, Cwd} = file:get_cwd(),</span><span class="w">
│ │ │ │      </span><span class="c1">%% file:set_cwd(&quot;tmp&quot;),</span><span class="w">
│ │ │ │      </span><span class="n">ErtsDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="o">++</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2572133318-110">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-111">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2572133318-111">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-112">[</span><span class="p" data-group-id="2572133318-112">]</span><span class="p" data-group-id="2572133318-110">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2572133318-113">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-114">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="n">ErtsDir</span><span class="p" data-group-id="2572133318-114">)</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsDir</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-115">[</span><span class="p" data-group-id="2572133318-115">]</span><span class="p" data-group-id="2572133318-113">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2572133318-116">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-117">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;releases&quot;</span><span class="p" data-group-id="2572133318-117">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-118">[</span><span class="p" data-group-id="2572133318-118">]</span><span class="p" data-group-id="2572133318-116">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2572133318-119">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-120">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;lib&quot;</span><span class="p" data-group-id="2572133318-120">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;lib&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-121">[</span><span class="p" data-group-id="2572133318-121">]</span><span class="p" data-group-id="2572133318-119">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2572133318-122">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-123">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="2572133318-123">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-124">[</span><span class="p" data-group-id="2572133318-124">]</span><span class="p" data-group-id="2572133318-122">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2572133318-125">(</span><span class="n">Tar</span><span class="p" data-group-id="2572133318-125">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="0180395686-110">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-111">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="0180395686-111">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-112">[</span><span class="p" data-group-id="0180395686-112">]</span><span class="p" data-group-id="0180395686-110">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="0180395686-113">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-114">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="n">ErtsDir</span><span class="p" data-group-id="0180395686-114">)</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsDir</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-115">[</span><span class="p" data-group-id="0180395686-115">]</span><span class="p" data-group-id="0180395686-113">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="0180395686-116">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-117">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;releases&quot;</span><span class="p" data-group-id="0180395686-117">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-118">[</span><span class="p" data-group-id="0180395686-118">]</span><span class="p" data-group-id="0180395686-116">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="0180395686-119">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-120">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;lib&quot;</span><span class="p" data-group-id="0180395686-120">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;lib&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-121">[</span><span class="p" data-group-id="0180395686-121">]</span><span class="p" data-group-id="0180395686-119">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="0180395686-122">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-123">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="0180395686-123">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-124">[</span><span class="p" data-group-id="0180395686-124">]</span><span class="p" data-group-id="0180395686-122">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="0180395686-125">(</span><span class="n">Tar</span><span class="p" data-group-id="0180395686-125">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%% file:set_cwd(Cwd),</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-126">(</span><span class="s">&quot;Removing directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2572133318-127">[</span><span class="n">TmpDir</span><span class="p" data-group-id="2572133318-127">]</span><span class="p" data-group-id="2572133318-126">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="2572133318-128">(</span><span class="n">TmpDir</span><span class="p" data-group-id="2572133318-128">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-126">(</span><span class="s">&quot;Removing directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="0180395686-127">[</span><span class="n">TmpDir</span><span class="p" data-group-id="0180395686-127">]</span><span class="p" data-group-id="0180395686-126">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="0180395686-128">(</span><span class="n">TmpDir</span><span class="p" data-group-id="0180395686-128">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │ -</span><span class="nf">install</span><span class="p" data-group-id="2572133318-129">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2572133318-129">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">install</span><span class="p" data-group-id="0180395686-129">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="0180395686-129">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">TarFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.tar.gz&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-130">(</span><span class="s">&quot;Extracting ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-131">[</span><span class="n">TarFile</span><span class="p" data-group-id="2572133318-131">]</span><span class="p" data-group-id="2572133318-130">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">extract_tar</span><span class="p" data-group-id="2572133318-132">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2572133318-132">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-133">(</span><span class="p" data-group-id="2572133318-134">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="2572133318-134">]</span><span class="p" data-group-id="2572133318-133">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-135">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="2572133318-135">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="2572133318-136">(</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="2572133318-136">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-137">[</span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">RelVsn</span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2572133318-137">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">string</span><span class="p">:</span><span class="nf">tokens</span><span class="p" data-group-id="2572133318-138">(</span><span class="n">StartErlData</span><span class="p">,</span><span class="w"> </span><span class="s">&quot; \n&quot;</span><span class="p" data-group-id="2572133318-138">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-139">(</span><span class="p" data-group-id="2572133318-140">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2572133318-140">]</span><span class="p" data-group-id="2572133318-139">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">BinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-141">(</span><span class="p" data-group-id="2572133318-142">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2572133318-142">]</span><span class="p" data-group-id="2572133318-141">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-143">(</span><span class="s">&quot;Substituting in erl.src, start.src and start_erl.src to &quot;</span><span class="w">
│ │ │ │ -              </span><span class="s">&quot;form erl, start and start_erl ...\n&quot;</span><span class="p" data-group-id="2572133318-143">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="2572133318-144">(</span><span class="p" data-group-id="2572133318-145">[</span><span class="s">&quot;erl&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="2572133318-145">]</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">BinDir</span><span class="p">,</span><span class="w">
│ │ │ │ -                      </span><span class="p" data-group-id="2572133318-146">[</span><span class="p" data-group-id="2572133318-147">{</span><span class="s">&quot;FINAL_ROOTDIR&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2572133318-147">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-148">{</span><span class="s">&quot;EMU&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;beam&quot;</span><span class="p" data-group-id="2572133318-148">}</span><span class="p" data-group-id="2572133318-146">]</span><span class="p">,</span><span class="w">
│ │ │ │ -                      </span><span class="p" data-group-id="2572133318-149">[</span><span class="ss">preserve</span><span class="p" data-group-id="2572133318-149">]</span><span class="p" data-group-id="2572133318-144">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-130">(</span><span class="s">&quot;Extracting ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-131">[</span><span class="n">TarFile</span><span class="p" data-group-id="0180395686-131">]</span><span class="p" data-group-id="0180395686-130">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">extract_tar</span><span class="p" data-group-id="0180395686-132">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="0180395686-132">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-133">(</span><span class="p" data-group-id="0180395686-134">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="0180395686-134">]</span><span class="p" data-group-id="0180395686-133">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-135">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="0180395686-135">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="0180395686-136">(</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="0180395686-136">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-137">[</span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">RelVsn</span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="0180395686-137">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">string</span><span class="p">:</span><span class="nf">tokens</span><span class="p" data-group-id="0180395686-138">(</span><span class="n">StartErlData</span><span class="p">,</span><span class="w"> </span><span class="s">&quot; \n&quot;</span><span class="p" data-group-id="0180395686-138">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-139">(</span><span class="p" data-group-id="0180395686-140">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="0180395686-140">]</span><span class="p" data-group-id="0180395686-139">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">BinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-141">(</span><span class="p" data-group-id="0180395686-142">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="0180395686-142">]</span><span class="p" data-group-id="0180395686-141">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-143">(</span><span class="s">&quot;Substituting in erl.src, start.src and start_erl.src to &quot;</span><span class="w">
│ │ │ │ +              </span><span class="s">&quot;form erl, start and start_erl ...\n&quot;</span><span class="p" data-group-id="0180395686-143">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="0180395686-144">(</span><span class="p" data-group-id="0180395686-145">[</span><span class="s">&quot;erl&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="0180395686-145">]</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">BinDir</span><span class="p">,</span><span class="w">
│ │ │ │ +                      </span><span class="p" data-group-id="0180395686-146">[</span><span class="p" data-group-id="0180395686-147">{</span><span class="s">&quot;FINAL_ROOTDIR&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="0180395686-147">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-148">{</span><span class="s">&quot;EMU&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;beam&quot;</span><span class="p" data-group-id="0180395686-148">}</span><span class="p" data-group-id="0180395686-146">]</span><span class="p">,</span><span class="w">
│ │ │ │ +                      </span><span class="p" data-group-id="0180395686-149">[</span><span class="ss">preserve</span><span class="p" data-group-id="0180395686-149">]</span><span class="p" data-group-id="0180395686-144">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="c1">%%! Workaround for pre OTP 17.0: start.src and start_erl.src did</span><span class="w">
│ │ │ │      </span><span class="c1">%%! not have correct permissions, so the above &#39;preserve&#39; option did not help</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="2572133318-150">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-151">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="2572133318-151">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="2572133318-150">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="2572133318-152">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-153">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="2572133318-153">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="2572133318-152">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="0180395686-150">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-151">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="0180395686-151">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="0180395686-150">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="0180395686-152">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-153">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="0180395686-153">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="0180395686-152">)</span><span class="p">,</span><span class="w">
│ │ │ │  
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2572133318-154">(</span><span class="s">&quot;Creating the RELEASES file ...\n&quot;</span><span class="p" data-group-id="2572133318-154">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">create_RELEASES</span><span class="p" data-group-id="2572133318-155">(</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-156">(</span><span class="p" data-group-id="2572133318-157">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -					    </span><span class="nc">filename</span><span class="p">:</span><span class="nf">basename</span><span class="p" data-group-id="2572133318-158">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2572133318-158">)</span><span class="p" data-group-id="2572133318-157">]</span><span class="p" data-group-id="2572133318-156">)</span><span class="p" data-group-id="2572133318-155">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="0180395686-154">(</span><span class="s">&quot;Creating the RELEASES file ...\n&quot;</span><span class="p" data-group-id="0180395686-154">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">create_RELEASES</span><span class="p" data-group-id="0180395686-155">(</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-156">(</span><span class="p" data-group-id="0180395686-157">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +					    </span><span class="nc">filename</span><span class="p">:</span><span class="nf">basename</span><span class="p" data-group-id="0180395686-158">(</span><span class="n">RelFileName</span><span class="p" data-group-id="0180395686-158">)</span><span class="p" data-group-id="0180395686-157">]</span><span class="p" data-group-id="0180395686-156">)</span><span class="p" data-group-id="0180395686-155">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% LOCALS</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% make_script(RelFileName,Opts)</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">make_script</span><span class="p" data-group-id="2572133318-159">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="2572133318-159">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="2572133318-160">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-161">[</span><span class="ss">no_module_tests</span><span class="p">,</span><span class="w">
│ │ │ │ -				       </span><span class="p" data-group-id="2572133318-162">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="2572133318-163">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2572133318-163">)</span><span class="p" data-group-id="2572133318-162">}</span><span class="w">
│ │ │ │ -				       </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="2572133318-161">]</span><span class="p" data-group-id="2572133318-160">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">make_script</span><span class="p" data-group-id="0180395686-159">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="0180395686-159">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="0180395686-160">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-161">[</span><span class="ss">no_module_tests</span><span class="p">,</span><span class="w">
│ │ │ │ +				       </span><span class="p" data-group-id="0180395686-162">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="0180395686-163">(</span><span class="n">RelFileName</span><span class="p" data-group-id="0180395686-163">)</span><span class="p" data-group-id="0180395686-162">}</span><span class="w">
│ │ │ │ +				       </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="0180395686-161">]</span><span class="p" data-group-id="0180395686-160">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% make_tar(RelFileName,Opts)</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">make_tar</span><span class="p" data-group-id="2572133318-164">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="2572133318-164">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">RootDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">code</span><span class="p">:</span><span class="nf">root_dir</span><span class="p" data-group-id="2572133318-165">(</span><span class="p" data-group-id="2572133318-165">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="2572133318-166">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-167">[</span><span class="p" data-group-id="2572133318-168">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2572133318-168">}</span><span class="p">,</span><span class="w">
│ │ │ │ -				    </span><span class="p" data-group-id="2572133318-169">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="2572133318-170">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2572133318-170">)</span><span class="p" data-group-id="2572133318-169">}</span><span class="w">
│ │ │ │ -				    </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="2572133318-167">]</span><span class="p" data-group-id="2572133318-166">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">make_tar</span><span class="p" data-group-id="0180395686-164">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="0180395686-164">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">RootDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">code</span><span class="p">:</span><span class="nf">root_dir</span><span class="p" data-group-id="0180395686-165">(</span><span class="p" data-group-id="0180395686-165">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="0180395686-166">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-167">[</span><span class="p" data-group-id="0180395686-168">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="0180395686-168">}</span><span class="p">,</span><span class="w">
│ │ │ │ +				    </span><span class="p" data-group-id="0180395686-169">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="0180395686-170">(</span><span class="n">RelFileName</span><span class="p" data-group-id="0180395686-170">)</span><span class="p" data-group-id="0180395686-169">}</span><span class="w">
│ │ │ │ +				    </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="0180395686-167">]</span><span class="p" data-group-id="0180395686-166">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% extract_tar(TarFile, DestDir)</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">extract_tar</span><span class="p" data-group-id="2572133318-171">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="2572133318-171">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">extract</span><span class="p" data-group-id="2572133318-172">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-173">[</span><span class="p" data-group-id="2572133318-174">{</span><span class="ss">cwd</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="2572133318-174">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="2572133318-173">]</span><span class="p" data-group-id="2572133318-172">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">extract_tar</span><span class="p" data-group-id="0180395686-171">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="0180395686-171">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">extract</span><span class="p" data-group-id="0180395686-172">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-173">[</span><span class="p" data-group-id="0180395686-174">{</span><span class="ss">cwd</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="0180395686-174">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="0180395686-173">]</span><span class="p" data-group-id="0180395686-172">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="2572133318-175">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="2572133318-175">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="2572133318-176">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p" data-group-id="2572133318-176">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="0180395686-175">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="0180395686-175">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="0180395686-176">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p" data-group-id="0180395686-176">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="2572133318-177">(</span><span class="n">Scripts</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2572133318-177">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="2572133318-178">(</span><span class="nf">fun</span><span class="p" data-group-id="2572133318-179">(</span><span class="n">Script</span><span class="p" data-group-id="2572133318-179">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                          </span><span class="nf">subst_src_script</span><span class="p" data-group-id="2572133318-180">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w">
│ │ │ │ -                                           </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2572133318-180">)</span><span class="w">
│ │ │ │ -                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Scripts</span><span class="p" data-group-id="2572133318-178">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">subst_src_script</span><span class="p" data-group-id="2572133318-181">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2572133318-181">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_file</span><span class="p" data-group-id="2572133318-182">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-183">(</span><span class="p" data-group-id="2572133318-184">[</span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.src&quot;</span><span class="p" data-group-id="2572133318-184">]</span><span class="p" data-group-id="2572133318-183">)</span><span class="p">,</span><span class="w">
│ │ │ │ -               </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-185">(</span><span class="p" data-group-id="2572133318-186">[</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="p" data-group-id="2572133318-186">]</span><span class="p" data-group-id="2572133318-185">)</span><span class="p">,</span><span class="w">
│ │ │ │ -               </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2572133318-182">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">subst_file</span><span class="p" data-group-id="2572133318-187">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2572133318-187">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-188">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="2572133318-188">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="2572133318-189">(</span><span class="n">Src</span><span class="p" data-group-id="2572133318-189">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">NConts</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">subst</span><span class="p" data-group-id="2572133318-190">(</span><span class="n">Conts</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="2572133318-190">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">write_file</span><span class="p" data-group-id="2572133318-191">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">NConts</span><span class="p" data-group-id="2572133318-191">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="2572133318-192">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2572133318-192">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="0180395686-177">(</span><span class="n">Scripts</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="0180395686-177">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="0180395686-178">(</span><span class="nf">fun</span><span class="p" data-group-id="0180395686-179">(</span><span class="n">Script</span><span class="p" data-group-id="0180395686-179">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                          </span><span class="nf">subst_src_script</span><span class="p" data-group-id="0180395686-180">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w">
│ │ │ │ +                                           </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="0180395686-180">)</span><span class="w">
│ │ │ │ +                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Scripts</span><span class="p" data-group-id="0180395686-178">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">subst_src_script</span><span class="p" data-group-id="0180395686-181">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="0180395686-181">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_file</span><span class="p" data-group-id="0180395686-182">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-183">(</span><span class="p" data-group-id="0180395686-184">[</span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.src&quot;</span><span class="p" data-group-id="0180395686-184">]</span><span class="p" data-group-id="0180395686-183">)</span><span class="p">,</span><span class="w">
│ │ │ │ +               </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-185">(</span><span class="p" data-group-id="0180395686-186">[</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="p" data-group-id="0180395686-186">]</span><span class="p" data-group-id="0180395686-185">)</span><span class="p">,</span><span class="w">
│ │ │ │ +               </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="0180395686-182">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">subst_file</span><span class="p" data-group-id="0180395686-187">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="0180395686-187">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-188">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="0180395686-188">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="0180395686-189">(</span><span class="n">Src</span><span class="p" data-group-id="0180395686-189">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">NConts</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">subst</span><span class="p" data-group-id="0180395686-190">(</span><span class="n">Conts</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="0180395686-190">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">write_file</span><span class="p" data-group-id="0180395686-191">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">NConts</span><span class="p" data-group-id="0180395686-191">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="0180395686-192">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="0180395686-192">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="2572133318-193">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2572133318-193">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="2572133318-194">(</span><span class="n">Src</span><span class="p" data-group-id="2572133318-194">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="2572133318-195">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2572133318-195">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="0180395686-193">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="0180395686-193">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="0180395686-194">(</span><span class="n">Src</span><span class="p" data-group-id="0180395686-194">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="0180395686-195">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="0180395686-195">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">ok</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%% subst(Str, Vars)</span><span class="w">
│ │ │ │  </span><span class="c1">%% Vars = [{Var, Val}]</span><span class="w">
│ │ │ │  </span><span class="c1">%% Var = Val = string()</span><span class="w">
│ │ │ │  </span><span class="c1">%% Substitute all occurrences of %Var% for Val in Str, using the list</span><span class="w">
│ │ │ │  </span><span class="c1">%% of variables in Vars.</span><span class="w">
│ │ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="2572133318-196">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="2572133318-196">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="2572133318-197">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-198">[</span><span class="p" data-group-id="2572133318-198">]</span><span class="p" data-group-id="2572133318-197">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="0180395686-196">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="0180395686-196">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="0180395686-197">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-198">[</span><span class="p" data-group-id="0180395686-198">]</span><span class="p" data-group-id="0180395686-197">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="2572133318-199">(</span><span class="p" data-group-id="2572133318-200">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2572133318-200">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2572133318-199">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$Z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="2572133318-201">(</span><span class="p" data-group-id="2572133318-202">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2572133318-202">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-203">[</span><span class="p" data-group-id="2572133318-203">]</span><span class="p" data-group-id="2572133318-201">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="2572133318-204">(</span><span class="p" data-group-id="2572133318-205">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2572133318-205">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2572133318-204">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="2572133318-206">(</span><span class="p" data-group-id="2572133318-207">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2572133318-207">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-208">[</span><span class="p" data-group-id="2572133318-208">]</span><span class="p" data-group-id="2572133318-206">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="2572133318-209">(</span><span class="p" data-group-id="2572133318-210">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2572133318-210">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2572133318-209">)</span><span class="w"> </span><span class="k">when</span><span class="w">  </span><span class="n">C</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">$_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="2572133318-211">(</span><span class="p" data-group-id="2572133318-212">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2572133318-212">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-213">[</span><span class="p" data-group-id="2572133318-213">]</span><span class="p" data-group-id="2572133318-211">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="2572133318-214">(</span><span class="p" data-group-id="2572133318-215">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2572133318-215">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2572133318-214">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="2572133318-216">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-217">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2572133318-217">]</span><span class="p" data-group-id="2572133318-216">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="2572133318-218">(</span><span class="p" data-group-id="2572133318-219">[</span><span class="p" data-group-id="2572133318-219">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2572133318-218">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2572133318-220">(</span><span class="n">Result</span><span class="p" data-group-id="2572133318-220">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="2572133318-221">(</span><span class="p" data-group-id="2572133318-222">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2572133318-222">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2572133318-221">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Key</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2572133318-223">(</span><span class="n">VarAcc</span><span class="p" data-group-id="2572133318-223">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="2572133318-224">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="2572133318-224">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2572133318-225">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-226">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="2572133318-226">}</span><span class="p" data-group-id="2572133318-225">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">subst</span><span class="p" data-group-id="2572133318-227">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2572133318-228">(</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2572133318-228">)</span><span class="p" data-group-id="2572133318-227">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="0180395686-199">(</span><span class="p" data-group-id="0180395686-200">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0180395686-200">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0180395686-199">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$Z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="0180395686-201">(</span><span class="p" data-group-id="0180395686-202">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0180395686-202">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-203">[</span><span class="p" data-group-id="0180395686-203">]</span><span class="p" data-group-id="0180395686-201">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="0180395686-204">(</span><span class="p" data-group-id="0180395686-205">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0180395686-205">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0180395686-204">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="0180395686-206">(</span><span class="p" data-group-id="0180395686-207">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0180395686-207">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-208">[</span><span class="p" data-group-id="0180395686-208">]</span><span class="p" data-group-id="0180395686-206">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="0180395686-209">(</span><span class="p" data-group-id="0180395686-210">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0180395686-210">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0180395686-209">)</span><span class="w"> </span><span class="k">when</span><span class="w">  </span><span class="n">C</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">$_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="0180395686-211">(</span><span class="p" data-group-id="0180395686-212">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0180395686-212">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-213">[</span><span class="p" data-group-id="0180395686-213">]</span><span class="p" data-group-id="0180395686-211">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="0180395686-214">(</span><span class="p" data-group-id="0180395686-215">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0180395686-215">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0180395686-214">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="0180395686-216">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-217">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0180395686-217">]</span><span class="p" data-group-id="0180395686-216">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="0180395686-218">(</span><span class="p" data-group-id="0180395686-219">[</span><span class="p" data-group-id="0180395686-219">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0180395686-218">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="0180395686-220">(</span><span class="n">Result</span><span class="p" data-group-id="0180395686-220">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="0180395686-221">(</span><span class="p" data-group-id="0180395686-222">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0180395686-222">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="0180395686-221">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Key</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="0180395686-223">(</span><span class="n">VarAcc</span><span class="p" data-group-id="0180395686-223">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0180395686-224">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="0180395686-224">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0180395686-225">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-226">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="0180395686-226">}</span><span class="p" data-group-id="0180395686-225">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">subst</span><span class="p" data-group-id="0180395686-227">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="0180395686-228">(</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0180395686-228">)</span><span class="p" data-group-id="0180395686-227">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">subst</span><span class="p" data-group-id="2572133318-229">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-230">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2572133318-231">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2572133318-231">]</span><span class="p" data-group-id="2572133318-230">]</span><span class="p" data-group-id="2572133318-229">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">subst</span><span class="p" data-group-id="0180395686-229">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-230">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0180395686-231">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0180395686-231">]</span><span class="p" data-group-id="0180395686-230">]</span><span class="p" data-group-id="0180395686-229">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="2572133318-232">(</span><span class="p" data-group-id="2572133318-233">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2572133318-233">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2572133318-232">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="2572133318-234">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-235">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2572133318-235">]</span><span class="p" data-group-id="2572133318-234">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="2572133318-236">(</span><span class="p" data-group-id="2572133318-237">[</span><span class="p" data-group-id="2572133318-237">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2572133318-236">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="2572133318-238">(</span><span class="p" data-group-id="2572133318-239">[</span><span class="p" data-group-id="2572133318-239">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-240">[</span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2572133318-241">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2572133318-241">]</span><span class="p" data-group-id="2572133318-240">]</span><span class="p" data-group-id="2572133318-238">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">copy_file</span><span class="p" data-group-id="2572133318-242">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="2572133318-242">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="2572133318-243">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-244">[</span><span class="p" data-group-id="2572133318-244">]</span><span class="p" data-group-id="2572133318-243">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">copy_file</span><span class="p" data-group-id="2572133318-245">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2572133318-245">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-246">{</span><span class="ss">ok</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2572133318-246">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">copy</span><span class="p" data-group-id="2572133318-247">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="2572133318-247">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="2572133318-248">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2572133318-248">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="0180395686-232">(</span><span class="p" data-group-id="0180395686-233">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0180395686-233">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="0180395686-232">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="0180395686-234">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-235">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="0180395686-235">]</span><span class="p" data-group-id="0180395686-234">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="0180395686-236">(</span><span class="p" data-group-id="0180395686-237">[</span><span class="p" data-group-id="0180395686-237">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="0180395686-236">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="0180395686-238">(</span><span class="p" data-group-id="0180395686-239">[</span><span class="p" data-group-id="0180395686-239">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-240">[</span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0180395686-241">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0180395686-241">]</span><span class="p" data-group-id="0180395686-240">]</span><span class="p" data-group-id="0180395686-238">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">copy_file</span><span class="p" data-group-id="0180395686-242">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="0180395686-242">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="0180395686-243">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-244">[</span><span class="p" data-group-id="0180395686-244">]</span><span class="p" data-group-id="0180395686-243">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">copy_file</span><span class="p" data-group-id="0180395686-245">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="0180395686-245">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-246">{</span><span class="ss">ok</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0180395686-246">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">copy</span><span class="p" data-group-id="0180395686-247">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="0180395686-247">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="0180395686-248">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="0180395686-248">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="2572133318-249">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2572133318-249">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="2572133318-250">(</span><span class="n">Src</span><span class="p" data-group-id="2572133318-250">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="2572133318-251">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2572133318-251">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="0180395686-249">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="0180395686-249">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="0180395686-250">(</span><span class="n">Src</span><span class="p" data-group-id="0180395686-250">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="0180395686-251">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="0180395686-251">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">ok</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">write_file</span><span class="p" data-group-id="2572133318-252">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="2572133318-252">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Enc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">native_name_encoding</span><span class="p" data-group-id="2572133318-253">(</span><span class="p" data-group-id="2572133318-253">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-254">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2572133318-254">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2572133318-255">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-256">[</span><span class="ss">write</span><span class="p" data-group-id="2572133318-256">]</span><span class="p" data-group-id="2572133318-255">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">write</span><span class="p" data-group-id="2572133318-257">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="nc">unicode</span><span class="p">:</span><span class="nf">characters_to_binary</span><span class="p" data-group-id="2572133318-258">(</span><span class="n">Conts</span><span class="p">,</span><span class="n">Enc</span><span class="p">,</span><span class="n">Enc</span><span class="p" data-group-id="2572133318-258">)</span><span class="p" data-group-id="2572133318-257">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2572133318-259">(</span><span class="n">Fd</span><span class="p" data-group-id="2572133318-259">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">read_txt_file</span><span class="p" data-group-id="2572133318-260">(</span><span class="n">File</span><span class="p" data-group-id="2572133318-260">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-261">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="2572133318-261">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file</span><span class="p" data-group-id="2572133318-262">(</span><span class="n">File</span><span class="p" data-group-id="2572133318-262">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2572133318-263">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_list</span><span class="p" data-group-id="2572133318-264">(</span><span class="n">Bin</span><span class="p" data-group-id="2572133318-264">)</span><span class="p" data-group-id="2572133318-263">}</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="2572133318-265">(</span><span class="n">Dir</span><span class="p" data-group-id="2572133318-265">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">remove_all_files</span><span class="p" data-group-id="2572133318-266">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2572133318-267">[</span><span class="n">Dir</span><span class="p" data-group-id="2572133318-267">]</span><span class="p" data-group-id="2572133318-266">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">remove_all_files</span><span class="p" data-group-id="2572133318-268">(</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="2572133318-268">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="2572133318-269">(</span><span class="nf">fun</span><span class="p" data-group-id="2572133318-270">(</span><span class="n">File</span><span class="p" data-group-id="2572133318-270">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                          </span><span class="n">FilePath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2572133318-271">(</span><span class="p" data-group-id="2572133318-272">[</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">File</span><span class="p" data-group-id="2572133318-272">]</span><span class="p" data-group-id="2572133318-271">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                          </span><span class="k">case</span><span class="w"> </span><span class="nc">filelib</span><span class="p">:</span><span class="nf">is_dir</span><span class="p" data-group-id="2572133318-273">(</span><span class="n">FilePath</span><span class="p" data-group-id="2572133318-273">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">write_file</span><span class="p" data-group-id="0180395686-252">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="0180395686-252">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Enc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">native_name_encoding</span><span class="p" data-group-id="0180395686-253">(</span><span class="p" data-group-id="0180395686-253">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-254">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="0180395686-254">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="0180395686-255">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-256">[</span><span class="ss">write</span><span class="p" data-group-id="0180395686-256">]</span><span class="p" data-group-id="0180395686-255">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">write</span><span class="p" data-group-id="0180395686-257">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="nc">unicode</span><span class="p">:</span><span class="nf">characters_to_binary</span><span class="p" data-group-id="0180395686-258">(</span><span class="n">Conts</span><span class="p">,</span><span class="n">Enc</span><span class="p">,</span><span class="n">Enc</span><span class="p" data-group-id="0180395686-258">)</span><span class="p" data-group-id="0180395686-257">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="0180395686-259">(</span><span class="n">Fd</span><span class="p" data-group-id="0180395686-259">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">read_txt_file</span><span class="p" data-group-id="0180395686-260">(</span><span class="n">File</span><span class="p" data-group-id="0180395686-260">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-261">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="0180395686-261">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file</span><span class="p" data-group-id="0180395686-262">(</span><span class="n">File</span><span class="p" data-group-id="0180395686-262">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0180395686-263">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_list</span><span class="p" data-group-id="0180395686-264">(</span><span class="n">Bin</span><span class="p" data-group-id="0180395686-264">)</span><span class="p" data-group-id="0180395686-263">}</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="0180395686-265">(</span><span class="n">Dir</span><span class="p" data-group-id="0180395686-265">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">remove_all_files</span><span class="p" data-group-id="0180395686-266">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0180395686-267">[</span><span class="n">Dir</span><span class="p" data-group-id="0180395686-267">]</span><span class="p" data-group-id="0180395686-266">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">remove_all_files</span><span class="p" data-group-id="0180395686-268">(</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="0180395686-268">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="0180395686-269">(</span><span class="nf">fun</span><span class="p" data-group-id="0180395686-270">(</span><span class="n">File</span><span class="p" data-group-id="0180395686-270">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                          </span><span class="n">FilePath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="0180395686-271">(</span><span class="p" data-group-id="0180395686-272">[</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">File</span><span class="p" data-group-id="0180395686-272">]</span><span class="p" data-group-id="0180395686-271">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                          </span><span class="k">case</span><span class="w"> </span><span class="nc">filelib</span><span class="p">:</span><span class="nf">is_dir</span><span class="p" data-group-id="0180395686-273">(</span><span class="n">FilePath</span><span class="p" data-group-id="0180395686-273">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │                                </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                                  </span><span class="p" data-group-id="2572133318-274">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="2572133318-274">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">list_dir</span><span class="p" data-group-id="2572133318-275">(</span><span class="n">FilePath</span><span class="p" data-group-id="2572133318-275">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                                  </span><span class="nf">remove_all_files</span><span class="p" data-group-id="2572133318-276">(</span><span class="n">FilePath</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="2572133318-276">)</span><span class="p">,</span><span class="w">
│ │ │ │ -                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">del_dir</span><span class="p" data-group-id="2572133318-277">(</span><span class="n">FilePath</span><span class="p" data-group-id="2572133318-277">)</span><span class="p">;</span><span class="w">
│ │ │ │ +                                  </span><span class="p" data-group-id="0180395686-274">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="0180395686-274">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">list_dir</span><span class="p" data-group-id="0180395686-275">(</span><span class="n">FilePath</span><span class="p" data-group-id="0180395686-275">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                                  </span><span class="nf">remove_all_files</span><span class="p" data-group-id="0180395686-276">(</span><span class="n">FilePath</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="0180395686-276">)</span><span class="p">,</span><span class="w">
│ │ │ │ +                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">del_dir</span><span class="p" data-group-id="0180395686-277">(</span><span class="n">FilePath</span><span class="p" data-group-id="0180395686-277">)</span><span class="p">;</span><span class="w">
│ │ │ │                                </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2572133318-278">(</span><span class="n">FilePath</span><span class="p" data-group-id="2572133318-278">)</span><span class="w">
│ │ │ │ +                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="0180395686-278">(</span><span class="n">FilePath</span><span class="p" data-group-id="0180395686-278">)</span><span class="w">
│ │ │ │                            </span><span class="k">end</span><span class="w">
│ │ │ │ -                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="2572133318-269">)</span><span class="p">.</span></code></pre>
│ │ │ │ +                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="0180395686-269">)</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/content.opf
│ │ │ │ ├── OEBPS/content.opf
│ │ │ │ │ @@ -1,14 +1,14 @@
│ │ │ │ │  <?xml version="1.0" encoding="utf-8"?>
│ │ │ │ │  <package xmlns="http://www.idpf.org/2007/opf" unique-identifier="project-Erlang System Documentation" version="3.0">
│ │ │ │ │    <metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
│ │ │ │ │      <dc:title>Erlang System Documentation - 27.3.4.11</dc:title>
│ │ │ │ │ -    <dc:identifier id="project-Erlang System Documentation">urn:uuid:d84b0db7-01db-0af1-135f-84af594bbae6</dc:identifier>
│ │ │ │ │ +    <dc:identifier id="project-Erlang System Documentation">urn:uuid:8959efea-3128-ef7e-9e49-5a90ca598aca</dc:identifier>
│ │ │ │ │      <dc:language>en</dc:language>
│ │ │ │ │ -    <meta property="dcterms:modified">2026-05-05T13:52:08Z</meta>
│ │ │ │ │ +    <meta property="dcterms:modified">2026-05-10T23:47:21Z</meta>
│ │ │ │ │    </metadata>
│ │ │ │ │    <manifest>
│ │ │ │ │      <item id="nav" href="nav.xhtml" media-type="application/xhtml+xml" properties="nav scripted"/>
│ │ │ │ │      <item id="cover" href="title.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="readme" href="readme.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="installation_guide" href="installation_guide.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="install" href="install.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │ @@ -82,21 +82,21 @@
│ │ │ │ │      <item id="c_portdriver" href="c_portdriver.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="cnode" href="cnode.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="nif" href="nif.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="debugging" href="debugging.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="embedded" href="embedded.xhtml" media-type="application/xhtml+xml" properties="scripted"/>
│ │ │ │ │      <item id="epub-lsjciytm-js" href="dist/epub-LSJCIYTM.js" media-type="text/javascript"/>
│ │ │ │ │      <item id="epub-erlang-qrovqrm3-css" href="dist/epub-erlang-QROVQRM3.css" media-type="text/css"/>
│ │ │ │ │ +    <item id="dist2-gif" href="assets/dist2.gif" media-type="image/gif"/>
│ │ │ │ │      <item id="erlang-logo-png" href="assets/erlang-logo.png" media-type="image/png"/>
│ │ │ │ │      <item id="dist1-gif" href="assets/dist1.gif" media-type="image/gif"/>
│ │ │ │ │ -    <item id="dist2-gif" href="assets/dist2.gif" media-type="image/gif"/>
│ │ │ │ │      <item id="dist3-gif" href="assets/dist3.gif" media-type="image/gif"/>
│ │ │ │ │      <item id="dist4-gif" href="assets/dist4.gif" media-type="image/gif"/>
│ │ │ │ │ -    <item id="dist5-gif" href="assets/dist5.gif" media-type="image/gif"/>
│ │ │ │ │      <item id="ballpoint-pen-svg" href="assets/ballpoint-pen.svg" media-type="image/svg+xml"/>
│ │ │ │ │ +    <item id="dist5-gif" href="assets/dist5.gif" media-type="image/gif"/>
│ │ │ │ │      <item id="logo" href="assets/logo.png" media-type="image/png"/>
│ │ │ │ │    </manifest>
│ │ │ │ │    <spine>
│ │ │ │ │      <itemref idref="cover"/>
│ │ │ │ │      <itemref idref="nav"/>
│ │ │ │ │      <itemref idref="readme"/>
│ │ │ │ │      <itemref idref="installation_guide"/>
│ │ │ ├── OEBPS/conc_prog.xhtml
│ │ │ │ @@ -37,107 +37,107 @@
│ │ │ │  threads of execution in an Erlang program and to allow these threads to
│ │ │ │  communicate with each other. In Erlang, each thread of execution is called a
│ │ │ │  <em>process</em>.</p><p>(Aside: the term &quot;process&quot; is usually used when the threads of execution share
│ │ │ │  no data with each other and the term &quot;thread&quot; when they share data in some way.
│ │ │ │  Threads of execution in Erlang share no data, that is why they are called
│ │ │ │  processes).</p><p>The Erlang BIF <code class="inline">spawn</code> is used to create a new process:
│ │ │ │  <code class="inline">spawn(Module, Exported_Function, List of Arguments)</code>. Consider the following
│ │ │ │ -module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6663506932-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="6663506932-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4686652237-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="4686652237-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6663506932-2">(</span><span class="p" data-group-id="6663506932-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6663506932-3">]</span><span class="p" data-group-id="6663506932-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4686652237-2">(</span><span class="p" data-group-id="4686652237-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4686652237-3">]</span><span class="p" data-group-id="4686652237-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">say_something</span><span class="p" data-group-id="6663506932-4">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6663506932-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">say_something</span><span class="p" data-group-id="4686652237-4">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4686652237-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">done</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">say_something</span><span class="p" data-group-id="6663506932-5">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="p" data-group-id="6663506932-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6663506932-6">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6663506932-7">[</span><span class="n">What</span><span class="p" data-group-id="6663506932-7">]</span><span class="p" data-group-id="6663506932-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">say_something</span><span class="p" data-group-id="6663506932-8">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6663506932-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="6663506932-9">(</span><span class="p" data-group-id="6663506932-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="6663506932-10">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6663506932-11">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6663506932-11">]</span><span class="p" data-group-id="6663506932-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="6663506932-12">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6663506932-13">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6663506932-13">]</span><span class="p" data-group-id="6663506932-12">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="2630064215-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="2630064215-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2630064215-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut14</span><span class="p" data-group-id="2630064215-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">say_something</span><span class="p" data-group-id="2630064215-3">(</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2630064215-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">say_something</span><span class="p" data-group-id="4686652237-5">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="p" data-group-id="4686652237-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4686652237-6">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4686652237-7">[</span><span class="n">What</span><span class="p" data-group-id="4686652237-7">]</span><span class="p" data-group-id="4686652237-6">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">say_something</span><span class="p" data-group-id="4686652237-8">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4686652237-8">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="4686652237-9">(</span><span class="p" data-group-id="4686652237-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="4686652237-10">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4686652237-11">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4686652237-11">]</span><span class="p" data-group-id="4686652237-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="4686652237-12">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4686652237-13">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4686652237-13">]</span><span class="p" data-group-id="4686652237-12">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="3790833168-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="3790833168-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3790833168-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut14</span><span class="p" data-group-id="3790833168-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">say_something</span><span class="p" data-group-id="3790833168-3">(</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3790833168-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">done</span></code></pre><p>As shown, the function <code class="inline">say_something</code> writes its first argument the number of
│ │ │ │  times specified by second argument. The function <code class="inline">start</code> starts two Erlang
│ │ │ │  processes, one that writes &quot;hello&quot; three times and one that writes &quot;goodbye&quot;
│ │ │ │  three times. Both processes use the function <code class="inline">say_something</code>. Notice that a
│ │ │ │  function used in this way by <code class="inline">spawn</code>, to start a process, must be exported from
│ │ │ │ -the module (that is, in the <code class="inline">-export</code> at the start of the module).</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3065905898-1">(</span><span class="p" data-group-id="3065905898-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +the module (that is, in the <code class="inline">-export</code> at the start of the module).</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6735584417-1">(</span><span class="p" data-group-id="6735584417-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.63</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ │  </span><span class="ss">goodbye</span></code></pre><p>Notice that it did not write &quot;hello&quot; three times and then &quot;goodbye&quot; three times.
│ │ │ │  Instead, the first process wrote a &quot;hello&quot;, the second a &quot;goodbye&quot;, the first
│ │ │ │  another &quot;hello&quot; and so forth. But where did the <code class="inline">&lt;0.63.0&gt;</code> come from? The return
│ │ │ │  value of a function is the return value of the last &quot;thing&quot; in the function. The
│ │ │ │ -last thing in the function <code class="inline">start</code> is</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="4130486978-1">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4130486978-2">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4130486978-2">]</span><span class="p" data-group-id="4130486978-1">)</span><span class="p">.</span></code></pre><p><code class="inline">spawn</code> returns a <em>process identifier</em>, or <em>pid</em>, which uniquely identifies the
│ │ │ │ +last thing in the function <code class="inline">start</code> is</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="6070020663-1">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6070020663-2">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6070020663-2">]</span><span class="p" data-group-id="6070020663-1">)</span><span class="p">.</span></code></pre><p><code class="inline">spawn</code> returns a <em>process identifier</em>, or <em>pid</em>, which uniquely identifies the
│ │ │ │  process. So <code class="inline">&lt;0.63.0&gt;</code> is the pid of the <code class="inline">spawn</code> function call above. The next
│ │ │ │  example shows how to use pids.</p><p>Notice also that ~p is used instead of ~w in <a href="../../../lib/stdlib/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a>. To quote <a href="../../../lib/stdlib/doc/html/io.html#tilde_p">the manual</a>:</p><blockquote><p>~p Writes the data with standard syntax in the same way as ~w, but breaks terms
│ │ │ │  whose printed representation is longer than one line into many lines and indents
│ │ │ │  each line sensibly. It also tries to detect flat lists of printable characters and
│ │ │ │  to output these as strings</p></blockquote><h2 id="message-passing" class="section-heading">
│ │ │ │    <a href="#message-passing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Message Passing</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the following example two processes are created and they send messages to
│ │ │ │ -each other a number of times.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2601619759-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="2601619759-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +each other a number of times.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0007545029-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="0007545029-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2601619759-2">(</span><span class="p" data-group-id="2601619759-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2601619759-3">]</span><span class="p" data-group-id="2601619759-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0007545029-2">(</span><span class="p" data-group-id="0007545029-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0007545029-3">]</span><span class="p" data-group-id="0007545029-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2601619759-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="2601619759-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="0007545029-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0007545029-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2601619759-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2601619759-6">[</span><span class="p" data-group-id="2601619759-6">]</span><span class="p" data-group-id="2601619759-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0007545029-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0007545029-6">[</span><span class="p" data-group-id="0007545029-6">]</span><span class="p" data-group-id="0007545029-5">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2601619759-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="2601619759-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2601619759-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2601619759-9">(</span><span class="p" data-group-id="2601619759-9">)</span><span class="p" data-group-id="2601619759-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="0007545029-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0007545029-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0007545029-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0007545029-9">(</span><span class="p" data-group-id="0007545029-9">)</span><span class="p" data-group-id="0007545029-8">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2601619759-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2601619759-11">[</span><span class="p" data-group-id="2601619759-11">]</span><span class="p" data-group-id="2601619759-10">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0007545029-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0007545029-11">[</span><span class="p" data-group-id="0007545029-11">]</span><span class="p" data-group-id="0007545029-10">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="2601619759-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="2601619759-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="0007545029-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0007545029-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="2601619759-13">(</span><span class="p" data-group-id="2601619759-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="0007545029-13">(</span><span class="p" data-group-id="0007545029-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2601619759-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2601619759-15">[</span><span class="p" data-group-id="2601619759-15">]</span><span class="p" data-group-id="2601619759-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2601619759-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2601619759-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2601619759-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2601619759-18">[</span><span class="p" data-group-id="2601619759-18">]</span><span class="p" data-group-id="2601619759-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0007545029-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0007545029-15">[</span><span class="p" data-group-id="0007545029-15">]</span><span class="p" data-group-id="0007545029-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0007545029-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="0007545029-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0007545029-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0007545029-18">[</span><span class="p" data-group-id="0007545029-18">]</span><span class="p" data-group-id="0007545029-17">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="2601619759-19">(</span><span class="p" data-group-id="2601619759-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="0007545029-19">(</span><span class="p" data-group-id="0007545029-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2601619759-20">(</span><span class="p" data-group-id="2601619759-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2601619759-21">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2601619759-22">[</span><span class="p" data-group-id="2601619759-22">]</span><span class="p" data-group-id="2601619759-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2601619759-23">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2601619759-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="2601619759-24">]</span><span class="p" data-group-id="2601619759-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="8253752188-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="8253752188-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8253752188-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut15</span><span class="p" data-group-id="8253752188-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">tut15</span><span class="p">:</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="8253752188-3">(</span><span class="p" data-group-id="8253752188-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="0007545029-20">(</span><span class="p" data-group-id="0007545029-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0007545029-21">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0007545029-22">[</span><span class="p" data-group-id="0007545029-22">]</span><span class="p" data-group-id="0007545029-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="0007545029-23">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0007545029-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0007545029-24">]</span><span class="p" data-group-id="0007545029-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="2116206183-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="2116206183-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2116206183-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut15</span><span class="p" data-group-id="2116206183-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">tut15</span><span class="p">:</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="2116206183-3">(</span><span class="p" data-group-id="2116206183-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.36</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span><span class="w">
│ │ │ │ -</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>The function <code class="inline">start</code> first creates a process, let us call it &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9929323859-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9929323859-2">[</span><span class="p" data-group-id="9929323859-2">]</span><span class="p" data-group-id="9929323859-1">)</span></code></pre><p>This process executes <code class="inline">tut15:pong()</code>. <code class="inline">Pong_PID</code> is the process identity of the
│ │ │ │ -&quot;pong&quot; process. The function <code class="inline">start</code> now creates another process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="5986807302-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5986807302-2">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="5986807302-2">]</span><span class="p" data-group-id="5986807302-1">)</span><span class="p">,</span></code></pre><p>This process executes:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="7688803172-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="7688803172-1">)</span></code></pre><p><code class="inline">&lt;0.36.0&gt;</code> is the return value from the <code class="inline">start</code> function.</p><p>The process &quot;pong&quot; now does:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │ +</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>The function <code class="inline">start</code> first creates a process, let us call it &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="3902384432-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3902384432-2">[</span><span class="p" data-group-id="3902384432-2">]</span><span class="p" data-group-id="3902384432-1">)</span></code></pre><p>This process executes <code class="inline">tut15:pong()</code>. <code class="inline">Pong_PID</code> is the process identity of the
│ │ │ │ +&quot;pong&quot; process. The function <code class="inline">start</code> now creates another process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="6560437041-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6560437041-2">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="6560437041-2">]</span><span class="p" data-group-id="6560437041-1">)</span><span class="p">,</span></code></pre><p>This process executes:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="4383283704-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="4383283704-1">)</span></code></pre><p><code class="inline">&lt;0.36.0&gt;</code> is the return value from the <code class="inline">start</code> function.</p><p>The process &quot;pong&quot; now does:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │      </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9311831517-1">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9311831517-2">[</span><span class="p" data-group-id="9311831517-2">]</span><span class="p" data-group-id="9311831517-1">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9311831517-3">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9311831517-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9311831517-4">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9311831517-5">[</span><span class="p" data-group-id="9311831517-5">]</span><span class="p" data-group-id="9311831517-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4806026336-1">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4806026336-2">[</span><span class="p" data-group-id="4806026336-2">]</span><span class="p" data-group-id="4806026336-1">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4806026336-3">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="4806026336-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4806026336-4">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4806026336-5">[</span><span class="p" data-group-id="4806026336-5">]</span><span class="p" data-group-id="4806026336-4">)</span><span class="p">,</span><span class="w">
│ │ │ │          </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="nf">pong</span><span class="p" data-group-id="9311831517-6">(</span><span class="p" data-group-id="9311831517-6">)</span><span class="w">
│ │ │ │ +        </span><span class="nf">pong</span><span class="p" data-group-id="4806026336-6">(</span><span class="p" data-group-id="4806026336-6">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">receive</code> construct is used to allow processes to wait for messages from
│ │ │ │  other processes. It has the following format:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │     </span><span class="ss">pattern1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │         </span><span class="ss">actions1</span><span class="p">;</span><span class="w">
│ │ │ │     </span><span class="ss">pattern2</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │         </span><span class="ss">actions2</span><span class="p">;</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ @@ -158,84 +158,84 @@
│ │ │ │  queue (keeping the first message and any other messages in the queue). If the
│ │ │ │  second message does not match, the third message is tried, and so on, until the
│ │ │ │  end of the queue is reached. If the end of the queue is reached, the process
│ │ │ │  blocks (stops execution) and waits until a new message is received and this
│ │ │ │  procedure is repeated.</p><p>The Erlang implementation is &quot;clever&quot; and minimizes the number of times each
│ │ │ │  message is tested against the patterns in each <code class="inline">receive</code>.</p><p>Now back to the ping pong example.</p><p>&quot;Pong&quot; is waiting for messages. If the atom <code class="inline">finished</code> is received, &quot;pong&quot;
│ │ │ │  writes &quot;Pong finished&quot; to the output and, as it has nothing more to do,
│ │ │ │ -terminates. If it receives a message with the format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4532814171-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="4532814171-1">}</span></code></pre><p>it writes &quot;Pong received ping&quot; to the output and sends the atom <code class="inline">pong</code> to the
│ │ │ │ +terminates. If it receives a message with the format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5984142572-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="5984142572-1">}</span></code></pre><p>it writes &quot;Pong received ping&quot; to the output and sends the atom <code class="inline">pong</code> to the
│ │ │ │  process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span></code></pre><p>Notice how the operator &quot;!&quot; is used to send messages. The syntax of &quot;!&quot; is:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Message</span></code></pre><p>That is, <code class="inline">Message</code> (any Erlang term) is sent to the process with identity <code class="inline">Pid</code>.</p><p>After sending the message <code class="inline">pong</code> to the process &quot;ping&quot;, &quot;pong&quot; calls the <code class="inline">pong</code>
│ │ │ │  function again, which causes it to get back to the <code class="inline">receive</code> again and wait for
│ │ │ │ -another message.</p><p>Now let us look at the process &quot;ping&quot;. Recall that it was started by executing:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="3187789769-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="3187789769-1">)</span></code></pre><p>Looking at the function <code class="inline">ping/2</code>, the second clause of <code class="inline">ping/2</code> is executed
│ │ │ │ +another message.</p><p>Now let us look at the process &quot;ping&quot;. Recall that it was started by executing:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="6116097706-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="6116097706-1">)</span></code></pre><p>Looking at the function <code class="inline">ping/2</code>, the second clause of <code class="inline">ping/2</code> is executed
│ │ │ │  since the value of the first argument is 3 (not 0) (first clause head is
│ │ │ │ -<code class="inline">ping(0,Pong_PID)</code>, second clause head is <code class="inline">ping(N,Pong_PID)</code>, so <code class="inline">N</code> becomes 3).</p><p>The second clause sends a message to &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6264141986-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6264141986-2">(</span><span class="p" data-group-id="6264141986-2">)</span><span class="p" data-group-id="6264141986-1">}</span><span class="p">,</span></code></pre><p><a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the pid of the process that executes <a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a>, in this case the
│ │ │ │ +<code class="inline">ping(0,Pong_PID)</code>, second clause head is <code class="inline">ping(N,Pong_PID)</code>, so <code class="inline">N</code> becomes 3).</p><p>The second clause sends a message to &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9932595070-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9932595070-2">(</span><span class="p" data-group-id="9932595070-2">)</span><span class="p" data-group-id="9932595070-1">}</span><span class="p">,</span></code></pre><p><a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the pid of the process that executes <a href="../../../lib/../erts/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a>, in this case the
│ │ │ │  pid of &quot;ping&quot;. (Recall the code for &quot;pong&quot;, this lands up in the variable
│ │ │ │  <code class="inline">Ping_PID</code> in the <code class="inline">receive</code> previously explained.)</p><p>&quot;Ping&quot; now waits for a reply from &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ │      </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0223000584-1">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0223000584-2">[</span><span class="p" data-group-id="0223000584-2">]</span><span class="p" data-group-id="0223000584-1">)</span><span class="w">
│ │ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0685063368-1">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0685063368-2">[</span><span class="p" data-group-id="0685063368-2">]</span><span class="p" data-group-id="0685063368-1">)</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre><p>It writes &quot;Ping received pong&quot; when this reply arrives, after which &quot;ping&quot; calls
│ │ │ │ -the <code class="inline">ping</code> function again.</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="0107561382-1">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0107561382-1">)</span></code></pre><p><code class="inline">N-1</code> causes the first argument to be decremented until it becomes 0. When this
│ │ │ │ -occurs, the first clause of <code class="inline">ping/2</code> is executed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="7073564280-1">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="7073564280-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +the <code class="inline">ping</code> function again.</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="6889029218-1">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="6889029218-1">)</span></code></pre><p><code class="inline">N-1</code> causes the first argument to be decremented until it becomes 0. When this
│ │ │ │ +occurs, the first clause of <code class="inline">ping/2</code> is executed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="5383929530-1">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="5383929530-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7073564280-2">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7073564280-3">[</span><span class="p" data-group-id="7073564280-3">]</span><span class="p" data-group-id="7073564280-2">)</span><span class="p">;</span></code></pre><p>The atom <code class="inline">finished</code> is sent to &quot;pong&quot; (causing it to terminate as described
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5383929530-2">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5383929530-3">[</span><span class="p" data-group-id="5383929530-3">]</span><span class="p" data-group-id="5383929530-2">)</span><span class="p">;</span></code></pre><p>The atom <code class="inline">finished</code> is sent to &quot;pong&quot; (causing it to terminate as described
│ │ │ │  above) and &quot;ping finished&quot; is written to the output. &quot;Ping&quot; then terminates as
│ │ │ │  it has nothing left to do.</p><h2 id="registered-process-names" class="section-heading">
│ │ │ │    <a href="#registered-process-names" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Registered Process Names</span>
│ │ │ │  </h2>
│ │ │ │  <p>In the above example, &quot;pong&quot; was first created to be able to give the identity
│ │ │ │  of &quot;pong&quot; when &quot;ping&quot; was started. That is, in some way &quot;ping&quot; must be able to
│ │ │ │  know the identity of &quot;pong&quot; to be able to send a message to it. Sometimes
│ │ │ │  processes which need to know each other's identities are started independently
│ │ │ │  of each other. Erlang thus provides a mechanism for processes to be given names
│ │ │ │  so that these names can be used as identities instead of pids. This is done by
│ │ │ │ -using the <code class="inline">register</code> BIF:</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="4364317884-1">(</span><span class="ss">some_atom</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="4364317884-1">)</span></code></pre><p>Let us now rewrite the ping pong example using this and give the name <code class="inline">pong</code> to
│ │ │ │ -the &quot;pong&quot; process:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6184499425-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="6184499425-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +using the <code class="inline">register</code> BIF:</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="8836266044-1">(</span><span class="ss">some_atom</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="8836266044-1">)</span></code></pre><p>Let us now rewrite the ping pong example using this and give the name <code class="inline">pong</code> to
│ │ │ │ +the &quot;pong&quot; process:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0684864528-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="0684864528-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6184499425-2">(</span><span class="p" data-group-id="6184499425-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6184499425-3">]</span><span class="p" data-group-id="6184499425-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0684864528-2">(</span><span class="p" data-group-id="0684864528-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0684864528-3">]</span><span class="p" data-group-id="0684864528-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="6184499425-4">(</span><span class="mi">0</span><span class="p" data-group-id="6184499425-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="0684864528-4">(</span><span class="mi">0</span><span class="p" data-group-id="0684864528-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6184499425-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6184499425-6">[</span><span class="p" data-group-id="6184499425-6">]</span><span class="p" data-group-id="6184499425-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0684864528-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0684864528-6">[</span><span class="p" data-group-id="0684864528-6">]</span><span class="p" data-group-id="0684864528-5">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="6184499425-7">(</span><span class="n">N</span><span class="p" data-group-id="6184499425-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6184499425-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6184499425-9">(</span><span class="p" data-group-id="6184499425-9">)</span><span class="p" data-group-id="6184499425-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="0684864528-7">(</span><span class="n">N</span><span class="p" data-group-id="0684864528-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0684864528-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0684864528-9">(</span><span class="p" data-group-id="0684864528-9">)</span><span class="p" data-group-id="0684864528-8">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6184499425-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6184499425-11">[</span><span class="p" data-group-id="6184499425-11">]</span><span class="p" data-group-id="6184499425-10">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0684864528-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0684864528-11">[</span><span class="p" data-group-id="0684864528-11">]</span><span class="p" data-group-id="0684864528-10">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="6184499425-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6184499425-12">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="0684864528-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0684864528-12">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="6184499425-13">(</span><span class="p" data-group-id="6184499425-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="0684864528-13">(</span><span class="p" data-group-id="0684864528-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6184499425-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6184499425-15">[</span><span class="p" data-group-id="6184499425-15">]</span><span class="p" data-group-id="6184499425-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6184499425-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="6184499425-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6184499425-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6184499425-18">[</span><span class="p" data-group-id="6184499425-18">]</span><span class="p" data-group-id="6184499425-17">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0684864528-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0684864528-15">[</span><span class="p" data-group-id="0684864528-15">]</span><span class="p" data-group-id="0684864528-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0684864528-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="0684864528-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0684864528-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0684864528-18">[</span><span class="p" data-group-id="0684864528-18">]</span><span class="p" data-group-id="0684864528-17">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="6184499425-19">(</span><span class="p" data-group-id="6184499425-19">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="0684864528-19">(</span><span class="p" data-group-id="0684864528-19">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="6184499425-20">(</span><span class="p" data-group-id="6184499425-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="6184499425-21">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="6184499425-22">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6184499425-23">[</span><span class="p" data-group-id="6184499425-23">]</span><span class="p" data-group-id="6184499425-22">)</span><span class="p" data-group-id="6184499425-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="6184499425-24">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6184499425-25">[</span><span class="mi">3</span><span class="p" data-group-id="6184499425-25">]</span><span class="p" data-group-id="6184499425-24">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nf">c</span><span class="p" data-group-id="5005634157-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="5005634157-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5005634157-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut16</span><span class="p" data-group-id="5005634157-2">}</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">tut16</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5005634157-3">(</span><span class="p" data-group-id="5005634157-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="0684864528-20">(</span><span class="p" data-group-id="0684864528-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="0684864528-21">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0684864528-22">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0684864528-23">[</span><span class="p" data-group-id="0684864528-23">]</span><span class="p" data-group-id="0684864528-22">)</span><span class="p" data-group-id="0684864528-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="0684864528-24">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0684864528-25">[</span><span class="mi">3</span><span class="p" data-group-id="0684864528-25">]</span><span class="p" data-group-id="0684864528-24">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nf">c</span><span class="p" data-group-id="4451978317-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="4451978317-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4451978317-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut16</span><span class="p" data-group-id="4451978317-2">}</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">tut16</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4451978317-3">(</span><span class="p" data-group-id="4451978317-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.38</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span><span class="w">
│ │ │ │ -</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>Here the <code class="inline">start/0</code> function,</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="9179858919-1">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9179858919-2">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9179858919-3">[</span><span class="p" data-group-id="9179858919-3">]</span><span class="p" data-group-id="9179858919-2">)</span><span class="p" data-group-id="9179858919-1">)</span><span class="p">,</span></code></pre><p>both spawns the &quot;pong&quot; process and gives it the name <code class="inline">pong</code>. In the &quot;ping&quot;
│ │ │ │ -process, messages can be sent to <code class="inline">pong</code> by:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5820206930-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5820206930-2">(</span><span class="p" data-group-id="5820206930-2">)</span><span class="p" data-group-id="5820206930-1">}</span><span class="p">,</span></code></pre><p><code class="inline">ping/2</code> now becomes <code class="inline">ping/1</code> as the argument <code class="inline">Pong_PID</code> is not needed.</p><h2 id="distributed-programming" class="section-heading">
│ │ │ │ +</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>Here the <code class="inline">start/0</code> function,</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="5382193293-1">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5382193293-2">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5382193293-3">[</span><span class="p" data-group-id="5382193293-3">]</span><span class="p" data-group-id="5382193293-2">)</span><span class="p" data-group-id="5382193293-1">)</span><span class="p">,</span></code></pre><p>both spawns the &quot;pong&quot; process and gives it the name <code class="inline">pong</code>. In the &quot;ping&quot;
│ │ │ │ +process, messages can be sent to <code class="inline">pong</code> by:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3283176708-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3283176708-2">(</span><span class="p" data-group-id="3283176708-2">)</span><span class="p" data-group-id="3283176708-1">}</span><span class="p">,</span></code></pre><p><code class="inline">ping/2</code> now becomes <code class="inline">ping/1</code> as the argument <code class="inline">Pong_PID</code> is not needed.</p><h2 id="distributed-programming" class="section-heading">
│ │ │ │    <a href="#distributed-programming" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Distributed Programming</span>
│ │ │ │  </h2>
│ │ │ │  <p>Let us rewrite the ping pong program with &quot;ping&quot; and &quot;pong&quot; on different
│ │ │ │  computers. First a few things are needed to set up to get this to work. The
│ │ │ │ @@ -255,106 +255,106 @@
│ │ │ │  of the file. This is a requirement.</p><p>When you start an Erlang system that is going to talk to other Erlang systems,
│ │ │ │  you must give it a name, for example:</p><pre><code class="text">$ erl -sname my_name</code></pre><p>We will see more details of this later. If you want to experiment with
│ │ │ │  distributed Erlang, but you only have one computer to work on, you can start two
│ │ │ │  separate Erlang systems on the same computer but give them different names. Each
│ │ │ │  Erlang system running on a computer is called an <em>Erlang node</em>.</p><p>(Note: <code class="inline">erl -sname</code> assumes that all nodes are in the same IP domain and we can
│ │ │ │  use only the first component of the IP address, if we want to use nodes in
│ │ │ │  different domains we use <code class="inline">-name</code> instead, but then all IP address must be given
│ │ │ │ -in full.)</p><p>Here is the ping pong example modified to run on two separate nodes:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9343118620-1">(</span><span class="ss">tut17</span><span class="p" data-group-id="9343118620-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +in full.)</p><p>Here is the ping pong example modified to run on two separate nodes:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5243377903-1">(</span><span class="ss">tut17</span><span class="p" data-group-id="5243377903-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9343118620-2">(</span><span class="p" data-group-id="9343118620-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9343118620-3">]</span><span class="p" data-group-id="9343118620-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5243377903-2">(</span><span class="p" data-group-id="5243377903-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5243377903-3">]</span><span class="p" data-group-id="5243377903-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9343118620-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9343118620-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9343118620-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9343118620-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9343118620-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9343118620-7">[</span><span class="p" data-group-id="9343118620-7">]</span><span class="p" data-group-id="9343118620-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="5243377903-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5243377903-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5243377903-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5243377903-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5243377903-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5243377903-7">[</span><span class="p" data-group-id="5243377903-7">]</span><span class="p" data-group-id="5243377903-6">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9343118620-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9343118620-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9343118620-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9343118620-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9343118620-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9343118620-11">(</span><span class="p" data-group-id="9343118620-11">)</span><span class="p" data-group-id="9343118620-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="5243377903-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5243377903-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5243377903-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5243377903-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5243377903-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5243377903-11">(</span><span class="p" data-group-id="5243377903-11">)</span><span class="p" data-group-id="5243377903-10">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9343118620-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9343118620-13">[</span><span class="p" data-group-id="9343118620-13">]</span><span class="p" data-group-id="9343118620-12">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5243377903-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5243377903-13">[</span><span class="p" data-group-id="5243377903-13">]</span><span class="p" data-group-id="5243377903-12">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="9343118620-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9343118620-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="5243377903-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5243377903-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="9343118620-15">(</span><span class="p" data-group-id="9343118620-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="5243377903-15">(</span><span class="p" data-group-id="5243377903-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9343118620-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9343118620-17">[</span><span class="p" data-group-id="9343118620-17">]</span><span class="p" data-group-id="9343118620-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9343118620-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9343118620-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9343118620-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9343118620-20">[</span><span class="p" data-group-id="9343118620-20">]</span><span class="p" data-group-id="9343118620-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5243377903-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5243377903-17">[</span><span class="p" data-group-id="5243377903-17">]</span><span class="p" data-group-id="5243377903-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="5243377903-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="5243377903-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5243377903-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5243377903-20">[</span><span class="p" data-group-id="5243377903-20">]</span><span class="p" data-group-id="5243377903-19">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="9343118620-21">(</span><span class="p" data-group-id="9343118620-21">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="5243377903-21">(</span><span class="p" data-group-id="5243377903-21">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_pong</span><span class="p" data-group-id="9343118620-22">(</span><span class="p" data-group-id="9343118620-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9343118620-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9343118620-24">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9343118620-25">[</span><span class="p" data-group-id="9343118620-25">]</span><span class="p" data-group-id="9343118620-24">)</span><span class="p" data-group-id="9343118620-23">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_pong</span><span class="p" data-group-id="5243377903-22">(</span><span class="p" data-group-id="5243377903-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="5243377903-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5243377903-24">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5243377903-25">[</span><span class="p" data-group-id="5243377903-25">]</span><span class="p" data-group-id="5243377903-24">)</span><span class="p" data-group-id="5243377903-23">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start_ping</span><span class="p" data-group-id="9343118620-26">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="9343118620-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9343118620-27">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9343118620-28">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9343118620-28">]</span><span class="p" data-group-id="9343118620-27">)</span><span class="p">.</span></code></pre><p>Let us assume there are two computers called gollum and kosken. First a node is
│ │ │ │ +</span><span class="nf">start_ping</span><span class="p" data-group-id="5243377903-26">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="5243377903-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5243377903-27">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5243377903-28">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5243377903-28">]</span><span class="p" data-group-id="5243377903-27">)</span><span class="p">.</span></code></pre><p>Let us assume there are two computers called gollum and kosken. First a node is
│ │ │ │  started on kosken, called ping, and then a node on gollum, called pong.</p><p>On kosken (on a Linux/UNIX system):</p><pre><code class="text">kosken&gt; erl -sname ping
│ │ │ │  Erlang (BEAM) emulator version 5.2.3.7 [hipe] [threads:0]
│ │ │ │  
│ │ │ │  Eshell V5.2.3.7  (abort with ^G)
│ │ │ │  (ping@kosken)1&gt;</code></pre><p>On gollum:</p><pre><code class="text">gollum&gt; erl -sname pong
│ │ │ │  Erlang (BEAM) emulator version 5.2.3.7 [hipe] [threads:0]
│ │ │ │  
│ │ │ │  Eshell V5.2.3.7  (abort with ^G)
│ │ │ │ -(pong@gollum)1&gt;</code></pre><p>Now the &quot;pong&quot; process on gollum is started:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_pong</span><span class="p" data-group-id="6071611543-1">(</span><span class="p" data-group-id="6071611543-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +(pong@gollum)1&gt;</code></pre><p>Now the &quot;pong&quot; process on gollum is started:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_pong</span><span class="p" data-group-id="5937204108-1">(</span><span class="p" data-group-id="5937204108-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span></code></pre><p>And the &quot;ping&quot; process on kosken is started (from the code above you can see
│ │ │ │  that a parameter of the <code class="inline">start_ping</code> function is the node name of the Erlang
│ │ │ │ -system where &quot;pong&quot; is running):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(ping@kosken)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_ping</span><span class="p" data-group-id="6759436637-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="6759436637-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +system where &quot;pong&quot; is running):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(ping@kosken)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_ping</span><span class="p" data-group-id="5946490394-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="5946490394-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.37</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>As shown, the ping pong program has run. On the &quot;pong&quot; side:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)2&gt; </span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="nf">finished</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6053581292-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="6053581292-1">)</span><span class="mi">2</span><span class="o">&gt;</span><span class="w"> </span></code></pre><p>Looking at the <code class="inline">tut17</code> code, you see that the <code class="inline">pong</code> function itself is
│ │ │ │ +</span><span class="p" data-group-id="8714508289-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="8714508289-1">)</span><span class="mi">2</span><span class="o">&gt;</span><span class="w"> </span></code></pre><p>Looking at the <code class="inline">tut17</code> code, you see that the <code class="inline">pong</code> function itself is
│ │ │ │  unchanged, the following lines work in the same way irrespective of on which
│ │ │ │ -node the &quot;ping&quot; process is executes:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8849446113-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8849446113-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8849446113-2">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8849446113-3">[</span><span class="p" data-group-id="8849446113-3">]</span><span class="p" data-group-id="8849446113-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +node the &quot;ping&quot; process is executes:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8043622706-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="8043622706-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8043622706-2">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8043622706-3">[</span><span class="p" data-group-id="8043622706-3">]</span><span class="p" data-group-id="8043622706-2">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span></code></pre><p>Thus, Erlang pids contain information about where the process executes. So if
│ │ │ │  you know the pid of a process, the <code class="inline">!</code> operator can be used to send it a
│ │ │ │ -message disregarding if the process is on the same node or on a different node.</p><p>A difference is how messages are sent to a registered process on another node:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2231568783-1">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2231568783-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2231568783-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2231568783-3">(</span><span class="p" data-group-id="2231568783-3">)</span><span class="p" data-group-id="2231568783-2">}</span><span class="p">,</span></code></pre><p>A tuple <code class="inline">{registered_name,node_name}</code> is used instead of just the
│ │ │ │ +message disregarding if the process is on the same node or on a different node.</p><p>A difference is how messages are sent to a registered process on another node:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2248368712-1">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="2248368712-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2248368712-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2248368712-3">(</span><span class="p" data-group-id="2248368712-3">)</span><span class="p" data-group-id="2248368712-2">}</span><span class="p">,</span></code></pre><p>A tuple <code class="inline">{registered_name,node_name}</code> is used instead of just the
│ │ │ │  <code class="inline">registered_name</code>.</p><p>In the previous example, &quot;ping&quot; and &quot;pong&quot; were started from the shells of two
│ │ │ │  separate Erlang nodes. <code class="inline">spawn</code> can also be used to start processes in other
│ │ │ │  nodes.</p><p>The next example is the ping pong program, yet again, but this time &quot;ping&quot; is
│ │ │ │ -started in another node:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9846399521-1">(</span><span class="ss">tut18</span><span class="p" data-group-id="9846399521-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +started in another node:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1384925854-1">(</span><span class="ss">tut18</span><span class="p" data-group-id="1384925854-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9846399521-2">(</span><span class="p" data-group-id="9846399521-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9846399521-3">]</span><span class="p" data-group-id="9846399521-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1384925854-2">(</span><span class="p" data-group-id="1384925854-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1384925854-3">]</span><span class="p" data-group-id="1384925854-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9846399521-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9846399521-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9846399521-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9846399521-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9846399521-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9846399521-7">[</span><span class="p" data-group-id="9846399521-7">]</span><span class="p" data-group-id="9846399521-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="1384925854-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1384925854-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1384925854-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1384925854-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1384925854-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1384925854-7">[</span><span class="p" data-group-id="1384925854-7">]</span><span class="p" data-group-id="1384925854-6">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="9846399521-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9846399521-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9846399521-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9846399521-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9846399521-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9846399521-11">(</span><span class="p" data-group-id="9846399521-11">)</span><span class="p" data-group-id="9846399521-10">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="1384925854-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1384925854-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1384925854-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1384925854-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1384925854-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1384925854-11">(</span><span class="p" data-group-id="1384925854-11">)</span><span class="p" data-group-id="1384925854-10">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9846399521-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9846399521-13">[</span><span class="p" data-group-id="9846399521-13">]</span><span class="p" data-group-id="9846399521-12">)</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1384925854-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1384925854-13">[</span><span class="p" data-group-id="1384925854-13">]</span><span class="p" data-group-id="1384925854-12">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="9846399521-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9846399521-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="1384925854-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1384925854-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="9846399521-15">(</span><span class="p" data-group-id="9846399521-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="1384925854-15">(</span><span class="p" data-group-id="1384925854-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9846399521-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9846399521-17">[</span><span class="p" data-group-id="9846399521-17">]</span><span class="p" data-group-id="9846399521-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9846399521-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9846399521-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9846399521-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9846399521-20">[</span><span class="p" data-group-id="9846399521-20">]</span><span class="p" data-group-id="9846399521-19">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1384925854-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1384925854-17">[</span><span class="p" data-group-id="1384925854-17">]</span><span class="p" data-group-id="1384925854-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="1384925854-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="1384925854-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1384925854-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1384925854-20">[</span><span class="p" data-group-id="1384925854-20">]</span><span class="p" data-group-id="1384925854-19">)</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="9846399521-21">(</span><span class="p" data-group-id="9846399521-21">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="1384925854-21">(</span><span class="p" data-group-id="1384925854-21">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9846399521-22">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="9846399521-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9846399521-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9846399521-24">(</span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9846399521-25">[</span><span class="p" data-group-id="9846399521-25">]</span><span class="p" data-group-id="9846399521-24">)</span><span class="p" data-group-id="9846399521-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9846399521-26">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9846399521-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="9846399521-28">(</span><span class="p" data-group-id="9846399521-28">)</span><span class="p" data-group-id="9846399521-27">]</span><span class="p" data-group-id="9846399521-26">)</span><span class="p">.</span></code></pre><p>Assuming an Erlang system called ping (but not the &quot;ping&quot; process) has already
│ │ │ │ -been started on kosken, then on gollum this is done:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut18</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1687943835-1">(</span><span class="ss">ping@kosken</span><span class="p" data-group-id="1687943835-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="1384925854-22">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="1384925854-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="1384925854-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1384925854-24">(</span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1384925854-25">[</span><span class="p" data-group-id="1384925854-25">]</span><span class="p" data-group-id="1384925854-24">)</span><span class="p" data-group-id="1384925854-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="1384925854-26">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1384925854-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="1384925854-28">(</span><span class="p" data-group-id="1384925854-28">)</span><span class="p" data-group-id="1384925854-27">]</span><span class="p" data-group-id="1384925854-26">)</span><span class="p">.</span></code></pre><p>Assuming an Erlang system called ping (but not the &quot;ping&quot; process) has already
│ │ │ │ +been started on kosken, then on gollum this is done:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut18</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8936675710-1">(</span><span class="ss">ping@kosken</span><span class="p" data-group-id="8936675710-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">3934.39</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ │ @@ -421,184 +421,184 @@
│ │ │ │  </span><span class="c1">%%% Started: messenger:client(Server_Node, Name)</span><span class="w">
│ │ │ │  </span><span class="c1">%%% To client: logoff</span><span class="w">
│ │ │ │  </span><span class="c1">%%% To client: {message_to, ToName, Message}</span><span class="w">
│ │ │ │  </span><span class="c1">%%%</span><span class="w">
│ │ │ │  </span><span class="c1">%%% Configuration: change the server_node() function to return the</span><span class="w">
│ │ │ │  </span><span class="c1">%%% name of the node where the messenger server runs</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8322463518-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="8322463518-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8322463518-2">(</span><span class="p" data-group-id="8322463518-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8322463518-3">]</span><span class="p" data-group-id="8322463518-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6711776005-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="6711776005-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6711776005-2">(</span><span class="p" data-group-id="6711776005-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6711776005-3">]</span><span class="p" data-group-id="6711776005-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Change the function below to return the name of the node where the</span><span class="w">
│ │ │ │  </span><span class="c1">%%% messenger server runs</span><span class="w">
│ │ │ │ -</span><span class="nf">server_node</span><span class="p" data-group-id="8322463518-4">(</span><span class="p" data-group-id="8322463518-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_node</span><span class="p" data-group-id="6711776005-4">(</span><span class="p" data-group-id="6711776005-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">messenger@super</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% This is the server process for the &quot;messenger&quot;</span><span class="w">
│ │ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="8322463518-5">(</span><span class="n">User_List</span><span class="p" data-group-id="8322463518-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="6711776005-5">(</span><span class="n">User_List</span><span class="p" data-group-id="6711776005-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8322463518-6">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8322463518-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="8322463518-7">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="8322463518-8">(</span><span class="n">New_User_List</span><span class="p" data-group-id="8322463518-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8322463518-9">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="8322463518-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="8322463518-10">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="8322463518-11">(</span><span class="n">New_User_List</span><span class="p" data-group-id="8322463518-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8322463518-12">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8322463518-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="8322463518-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8322463518-14">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8322463518-15">[</span><span class="n">User_List</span><span class="p" data-group-id="8322463518-15">]</span><span class="p" data-group-id="8322463518-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="8322463518-16">(</span><span class="n">User_List</span><span class="p" data-group-id="8322463518-16">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6711776005-6">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6711776005-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="6711776005-7">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-7">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="6711776005-8">(</span><span class="n">New_User_List</span><span class="p" data-group-id="6711776005-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6711776005-9">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="6711776005-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="6711776005-10">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="6711776005-11">(</span><span class="n">New_User_List</span><span class="p" data-group-id="6711776005-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6711776005-12">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6711776005-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="6711776005-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-13">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6711776005-14">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6711776005-15">[</span><span class="n">User_List</span><span class="p" data-group-id="6711776005-15">]</span><span class="p" data-group-id="6711776005-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="6711776005-16">(</span><span class="n">User_List</span><span class="p" data-group-id="6711776005-16">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="8322463518-17">(</span><span class="p" data-group-id="8322463518-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="8322463518-18">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="8322463518-19">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8322463518-20">[</span><span class="p" data-group-id="8322463518-21">[</span><span class="p" data-group-id="8322463518-21">]</span><span class="p" data-group-id="8322463518-20">]</span><span class="p" data-group-id="8322463518-19">)</span><span class="p" data-group-id="8322463518-18">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="6711776005-17">(</span><span class="p" data-group-id="6711776005-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="6711776005-18">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="6711776005-19">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6711776005-20">[</span><span class="p" data-group-id="6711776005-21">[</span><span class="p" data-group-id="6711776005-21">]</span><span class="p" data-group-id="6711776005-20">]</span><span class="p" data-group-id="6711776005-19">)</span><span class="p" data-group-id="6711776005-18">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="8322463518-22">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="6711776005-22">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="8322463518-23">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-23">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="6711776005-23">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-23">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-24">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="8322463518-24">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-24">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="6711776005-24">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-25">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="8322463518-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="8322463518-26">[</span><span class="p" data-group-id="8322463518-27">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8322463518-27">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-26">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-25">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="6711776005-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6711776005-26">[</span><span class="p" data-group-id="6711776005-27">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6711776005-27">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-26">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="8322463518-28">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="8322463518-29">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-29">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="6711776005-28">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="6711776005-29">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-29">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="8322463518-30">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="6711776005-30">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="8322463518-31">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-31">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6711776005-31">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-31">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-32">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="8322463518-32">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8322463518-33">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8322463518-34">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8322463518-34">}</span><span class="p" data-group-id="8322463518-33">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="8322463518-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-35">)</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-32">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="6711776005-32">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6711776005-33">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6711776005-34">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6711776005-34">}</span><span class="p" data-group-id="6711776005-33">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="6711776005-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-35">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="8322463518-36">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="6711776005-36">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="8322463518-37">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8322463518-37">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="6711776005-37">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6711776005-37">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-38">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="8322463518-38">}</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8322463518-39">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8322463518-40">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="8322463518-40">}</span><span class="p" data-group-id="8322463518-39">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-41">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8322463518-41">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="8322463518-42">}</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-38">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="6711776005-38">}</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6711776005-39">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6711776005-40">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6711776005-40">}</span><span class="p" data-group-id="6711776005-39">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-41">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6711776005-41">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="6711776005-42">}</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% User Commands</span><span class="w">
│ │ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="8322463518-43">(</span><span class="n">Name</span><span class="p" data-group-id="8322463518-43">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="8322463518-44">(</span><span class="ss">mess_client</span><span class="p" data-group-id="8322463518-44">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="6711776005-43">(</span><span class="n">Name</span><span class="p" data-group-id="6711776005-43">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="6711776005-44">(</span><span class="ss">mess_client</span><span class="p" data-group-id="6711776005-44">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="8322463518-45">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="8322463518-46">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8322463518-47">[</span><span class="nf">server_node</span><span class="p" data-group-id="8322463518-48">(</span><span class="p" data-group-id="8322463518-48">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8322463518-47">]</span><span class="p" data-group-id="8322463518-46">)</span><span class="p" data-group-id="8322463518-45">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="6711776005-45">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="6711776005-46">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6711776005-47">[</span><span class="nf">server_node</span><span class="p" data-group-id="6711776005-48">(</span><span class="p" data-group-id="6711776005-48">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6711776005-47">]</span><span class="p" data-group-id="6711776005-46">)</span><span class="p" data-group-id="6711776005-45">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="8322463518-49">(</span><span class="p" data-group-id="8322463518-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="6711776005-49">(</span><span class="p" data-group-id="6711776005-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="8322463518-50">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8322463518-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="8322463518-51">(</span><span class="ss">mess_client</span><span class="p" data-group-id="8322463518-51">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="6711776005-50">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6711776005-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="6711776005-51">(</span><span class="ss">mess_client</span><span class="p" data-group-id="6711776005-51">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-52">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8322463518-52">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-52">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6711776005-52">}</span><span class="p">,</span><span class="w">
│ │ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% The client process which runs on each server node</span><span class="w">
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="8322463518-53">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8322463518-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8322463518-54">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="8322463518-54">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-55">{</span><span class="nf">self</span><span class="p" data-group-id="8322463518-56">(</span><span class="p" data-group-id="8322463518-56">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8322463518-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="8322463518-57">(</span><span class="p" data-group-id="8322463518-57">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="8322463518-58">(</span><span class="n">Server_Node</span><span class="p" data-group-id="8322463518-58">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="6711776005-53">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6711776005-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6711776005-54">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6711776005-54">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-55">{</span><span class="nf">self</span><span class="p" data-group-id="6711776005-56">(</span><span class="p" data-group-id="6711776005-56">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="6711776005-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="6711776005-57">(</span><span class="p" data-group-id="6711776005-57">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="6711776005-58">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6711776005-58">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="8322463518-59">(</span><span class="n">Server_Node</span><span class="p" data-group-id="8322463518-59">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="6711776005-59">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6711776005-59">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="8322463518-60">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="8322463518-60">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-61">{</span><span class="nf">self</span><span class="p" data-group-id="8322463518-62">(</span><span class="p" data-group-id="8322463518-62">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="8322463518-61">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="8322463518-63">(</span><span class="ss">normal</span><span class="p" data-group-id="8322463518-63">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8322463518-64">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8322463518-64">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="p" data-group-id="8322463518-65">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="8322463518-65">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8322463518-66">{</span><span class="nf">self</span><span class="p" data-group-id="8322463518-67">(</span><span class="p" data-group-id="8322463518-67">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8322463518-66">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="8322463518-68">(</span><span class="p" data-group-id="8322463518-68">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8322463518-69">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8322463518-69">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8322463518-70">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8322463518-71">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="8322463518-71">]</span><span class="p" data-group-id="8322463518-70">)</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6711776005-60">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6711776005-60">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-61">{</span><span class="nf">self</span><span class="p" data-group-id="6711776005-62">(</span><span class="p" data-group-id="6711776005-62">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="6711776005-61">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="6711776005-63">(</span><span class="ss">normal</span><span class="p" data-group-id="6711776005-63">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6711776005-64">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6711776005-64">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="p" data-group-id="6711776005-65">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="6711776005-65">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6711776005-66">{</span><span class="nf">self</span><span class="p" data-group-id="6711776005-67">(</span><span class="p" data-group-id="6711776005-67">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6711776005-66">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="6711776005-68">(</span><span class="p" data-group-id="6711776005-68">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6711776005-69">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6711776005-69">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6711776005-70">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6711776005-71">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="6711776005-71">]</span><span class="p" data-group-id="6711776005-70">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="8322463518-72">(</span><span class="n">Server_Node</span><span class="p" data-group-id="8322463518-72">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="6711776005-72">(</span><span class="n">Server_Node</span><span class="p" data-group-id="6711776005-72">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="8322463518-73">(</span><span class="p" data-group-id="8322463518-73">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="6711776005-73">(</span><span class="p" data-group-id="6711776005-73">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8322463518-74">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="8322463518-74">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8322463518-75">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8322463518-76">[</span><span class="n">Why</span><span class="p" data-group-id="8322463518-76">]</span><span class="p" data-group-id="8322463518-75">)</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="8322463518-77">(</span><span class="ss">normal</span><span class="p" data-group-id="8322463518-77">)</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8322463518-78">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="8322463518-78">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8322463518-79">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8322463518-80">[</span><span class="n">What</span><span class="p" data-group-id="8322463518-80">]</span><span class="p" data-group-id="8322463518-79">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6711776005-74">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="6711776005-74">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6711776005-75">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6711776005-76">[</span><span class="n">Why</span><span class="p" data-group-id="6711776005-76">]</span><span class="p" data-group-id="6711776005-75">)</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="6711776005-77">(</span><span class="ss">normal</span><span class="p" data-group-id="6711776005-77">)</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="6711776005-78">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="6711776005-78">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6711776005-79">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6711776005-80">[</span><span class="n">What</span><span class="p" data-group-id="6711776005-80">]</span><span class="p" data-group-id="6711776005-79">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>To use this program, you need to:</p><ul><li>Configure the <code class="inline">server_node()</code> function.</li><li>Copy the compiled code (<code class="inline">messenger.beam</code>) to the directory on each computer
│ │ │ │  where you start Erlang.</li></ul><p>In the following example using this program, nodes are started on four different
│ │ │ │  computers. If you do not have that many machines available on your network, you
│ │ │ │  can start several nodes on the same machine.</p><p>Four Erlang nodes are started up: messenger@super, c1@bilbo, c2@kosken,
│ │ │ │ -c3@gollum.</p><p>First the server at messenger@super is started up:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(messenger@super)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">start_server</span><span class="p" data-group-id="8527061795-1">(</span><span class="p" data-group-id="8527061795-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">true</span></code></pre><p>Now Peter logs on at c1@bilbo:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="8895058140-1">(</span><span class="ss">peter</span><span class="p" data-group-id="8895058140-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +c3@gollum.</p><p>First the server at messenger@super is started up:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(messenger@super)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">start_server</span><span class="p" data-group-id="1457578710-1">(</span><span class="p" data-group-id="1457578710-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">true</span></code></pre><p>Now Peter logs on at c1@bilbo:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="7371759799-1">(</span><span class="ss">peter</span><span class="p" data-group-id="7371759799-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="ss">logged_on</span></code></pre><p>James logs on at c2@kosken:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="0940957943-1">(</span><span class="ss">james</span><span class="p" data-group-id="0940957943-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">logged_on</span></code></pre><p>James logs on at c2@kosken:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="8910358070-1">(</span><span class="ss">james</span><span class="p" data-group-id="8910358070-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="ss">logged_on</span></code></pre><p>And Fred logs on at c3@gollum:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c3@gollum)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="0268328941-1">(</span><span class="ss">fred</span><span class="p" data-group-id="0268328941-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">logged_on</span></code></pre><p>And Fred logs on at c3@gollum:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c3@gollum)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="4846677372-1">(</span><span class="ss">fred</span><span class="p" data-group-id="4846677372-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="ss">logged_on</span></code></pre><p>Now Peter sends Fred a message:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="9180339700-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="9180339700-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">logged_on</span></code></pre><p>Now Peter sends Fred a message:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="9874833380-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="9874833380-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="ss">sent</span></code></pre><p>Fred receives the message and sends a message to Peter and logs off:</p><pre><code class="makeup erlang" translate="no"><span class="n">Message</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="nc">peter</span><span class="p">:</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">(c3@gollum)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="8100266632-1">(</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;go away, I&#39;m busy&quot;</span><span class="p" data-group-id="8100266632-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">(c3@gollum)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="2954725795-1">(</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;go away, I&#39;m busy&quot;</span><span class="p" data-group-id="2954725795-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="nf">sent</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="8100266632-2">(</span><span class="ss">c3@gollum</span><span class="p" data-group-id="8100266632-2">)</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logoff</span><span class="p" data-group-id="8100266632-3">(</span><span class="p" data-group-id="8100266632-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="ss">logoff</span></code></pre><p>James now tries to send a message to Fred:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="3411466402-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;peter doesn&#39;t like you&quot;</span><span class="p" data-group-id="3411466402-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2954725795-2">(</span><span class="ss">c3@gollum</span><span class="p" data-group-id="2954725795-2">)</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logoff</span><span class="p" data-group-id="2954725795-3">(</span><span class="p" data-group-id="2954725795-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="ss">logoff</span></code></pre><p>James now tries to send a message to Fred:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="6049262392-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;peter doesn&#39;t like you&quot;</span><span class="p" data-group-id="6049262392-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │  </span><span class="ss">receiver_not_found</span></code></pre><p>But this fails as Fred has already logged off.</p><p>First let us look at some of the new concepts that have been introduced.</p><p>There are two versions of the <code class="inline">server_transfer</code> function: one with four
│ │ │ │  arguments (<code class="inline">server_transfer/4</code>) and one with five (<code class="inline">server_transfer/5</code>). These
│ │ │ │  are regarded by Erlang as two separate functions.</p><p>Notice how to write the <code class="inline">server</code> function so that it calls itself, through
│ │ │ │  <code class="inline">server(User_List)</code>, and thus creates a loop. The Erlang compiler is &quot;clever&quot;
│ │ │ │  and optimizes the code so that this really is a sort of loop and not a proper
│ │ │ │  function call. But this only works if there is no code after the call.
│ │ │ │  Otherwise, the compiler expects the call to return and make a proper function
│ │ │ │  call. This would result in the process getting bigger and bigger for every loop.</p><p>Functions in the <code class="inline">lists</code> module are used. This is a very useful module and a
│ │ │ │  study of the manual page is recommended (<code class="inline">erl -man lists</code>).
│ │ │ │  <code class="inline">lists:keymember(Key,Position,Lists)</code> looks through a list of tuples and looks
│ │ │ │  at <code class="inline">Position</code> in each tuple to see if it is the same as <code class="inline">Key</code>. The first element
│ │ │ │  is position 1. If it finds a tuple where the element at <code class="inline">Position</code> is the same
│ │ │ │ -as <code class="inline">Key</code>, it returns <code class="inline">true</code>, otherwise <code class="inline">false</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="8198975077-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8198975077-2">[</span><span class="p" data-group-id="8198975077-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="8198975077-3">}</span><span class="p">,</span><span class="p" data-group-id="8198975077-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8198975077-4">}</span><span class="p">,</span><span class="p" data-group-id="8198975077-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8198975077-5">}</span><span class="p">,</span><span class="p" data-group-id="8198975077-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="8198975077-6">}</span><span class="p" data-group-id="8198975077-2">]</span><span class="p" data-group-id="8198975077-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +as <code class="inline">Key</code>, it returns <code class="inline">true</code>, otherwise <code class="inline">false</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="9812493628-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9812493628-2">[</span><span class="p" data-group-id="9812493628-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="9812493628-3">}</span><span class="p">,</span><span class="p" data-group-id="9812493628-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9812493628-4">}</span><span class="p">,</span><span class="p" data-group-id="9812493628-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9812493628-5">}</span><span class="p">,</span><span class="p" data-group-id="9812493628-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="9812493628-6">}</span><span class="p" data-group-id="9812493628-2">]</span><span class="p" data-group-id="9812493628-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="8198975077-7">(</span><span class="ss">p</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8198975077-8">[</span><span class="p" data-group-id="8198975077-9">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="8198975077-9">}</span><span class="p">,</span><span class="p" data-group-id="8198975077-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="8198975077-10">}</span><span class="p">,</span><span class="p" data-group-id="8198975077-11">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8198975077-11">}</span><span class="p">,</span><span class="p" data-group-id="8198975077-12">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="8198975077-12">}</span><span class="p" data-group-id="8198975077-8">]</span><span class="p" data-group-id="8198975077-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="9812493628-7">(</span><span class="ss">p</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9812493628-8">[</span><span class="p" data-group-id="9812493628-9">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="9812493628-9">}</span><span class="p">,</span><span class="p" data-group-id="9812493628-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9812493628-10">}</span><span class="p">,</span><span class="p" data-group-id="9812493628-11">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9812493628-11">}</span><span class="p">,</span><span class="p" data-group-id="9812493628-12">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="9812493628-12">}</span><span class="p" data-group-id="9812493628-8">]</span><span class="p" data-group-id="9812493628-7">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">false</span></code></pre><p><code class="inline">lists:keydelete</code> works in the same way but deletes the first tuple found (if
│ │ │ │ -any) and returns the remaining list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="5165477561-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5165477561-2">[</span><span class="p" data-group-id="5165477561-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="5165477561-3">}</span><span class="p">,</span><span class="p" data-group-id="5165477561-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5165477561-4">}</span><span class="p">,</span><span class="p" data-group-id="5165477561-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5165477561-5">}</span><span class="p">,</span><span class="p" data-group-id="5165477561-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="5165477561-6">}</span><span class="p" data-group-id="5165477561-2">]</span><span class="p" data-group-id="5165477561-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5165477561-7">[</span><span class="p" data-group-id="5165477561-8">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="5165477561-8">}</span><span class="p">,</span><span class="p" data-group-id="5165477561-9">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5165477561-9">}</span><span class="p">,</span><span class="p" data-group-id="5165477561-10">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="5165477561-10">}</span><span class="p" data-group-id="5165477561-7">]</span></code></pre><p><code class="inline">lists:keysearch</code> is like <code class="inline">lists:keymember</code>, but it returns
│ │ │ │ +any) and returns the remaining list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="1928623814-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1928623814-2">[</span><span class="p" data-group-id="1928623814-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="1928623814-3">}</span><span class="p">,</span><span class="p" data-group-id="1928623814-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1928623814-4">}</span><span class="p">,</span><span class="p" data-group-id="1928623814-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1928623814-5">}</span><span class="p">,</span><span class="p" data-group-id="1928623814-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="1928623814-6">}</span><span class="p" data-group-id="1928623814-2">]</span><span class="p" data-group-id="1928623814-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1928623814-7">[</span><span class="p" data-group-id="1928623814-8">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="1928623814-8">}</span><span class="p">,</span><span class="p" data-group-id="1928623814-9">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1928623814-9">}</span><span class="p">,</span><span class="p" data-group-id="1928623814-10">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="1928623814-10">}</span><span class="p" data-group-id="1928623814-7">]</span></code></pre><p><code class="inline">lists:keysearch</code> is like <code class="inline">lists:keymember</code>, but it returns
│ │ │ │  <code class="inline">{value,Tuple_Found}</code> or the atom <code class="inline">false</code>.</p><p>There are many very useful functions in the <code class="inline">lists</code> module.</p><p>An Erlang process (conceptually) runs until it does a <code class="inline">receive</code> and there is no
│ │ │ │  message which it wants to receive in the message queue. &quot;conceptually&quot; is used
│ │ │ │  here because the Erlang system shares the CPU time between the active processes
│ │ │ │  in the system.</p><p>A process terminates when there is nothing more for it to do, that is, the last
│ │ │ │  function it calls simply returns and does not call another function. Another way
│ │ │ │  for a process to terminate is for it to call <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a>. The argument
│ │ │ │  to <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a> has a special meaning, which is discussed later. In this
│ │ │ │  example, <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a> is done, which has the same effect as a
│ │ │ │  process running out of functions to call.</p><p>The BIF <a href="../../../lib/../erts/doc/html/erlang.html#whereis/1"><code class="inline">whereis(RegisteredName)</code></a> checks if a registered process
│ │ │ │  of name <code class="inline">RegisteredName</code> exists. If it exists, the pid of that process is
│ │ │ │  returned. If it does not exist, the atom <code class="inline">undefined</code> is returned.</p><p>You should by now be able to understand most of the code in the
│ │ │ │  messenger-module. Let us study one case in detail: a message is sent from one
│ │ │ │ -user to another.</p><p>The first user &quot;sends&quot; the message in the example above by:</p><pre><code class="makeup erlang" translate="no"><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="8570925878-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8570925878-1">)</span></code></pre><p>After testing that the client process exists:</p><pre><code class="makeup erlang" translate="no"><span class="nf">whereis</span><span class="p" data-group-id="8470796879-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="8470796879-1">)</span></code></pre><p>And a message is sent to <code class="inline">mess_client</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1774558212-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="1774558212-1">}</span></code></pre><p>The client sends the message to the server by:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8593311848-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="8593311848-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8593311848-2">{</span><span class="nf">self</span><span class="p" data-group-id="8593311848-3">(</span><span class="p" data-group-id="8593311848-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8593311848-2">}</span><span class="p">,</span></code></pre><p>And waits for a reply from the server.</p><p>The server receives this message and calls:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="1873279053-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="1873279053-1">)</span><span class="p">,</span></code></pre><p>This checks that the pid <code class="inline">From</code> is in the <code class="inline">User_List</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3543967889-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3543967889-1">)</span></code></pre><p>If <code class="inline">keysearch</code> returns the atom <code class="inline">false</code>, some error has occurred and the server
│ │ │ │ -sends back the message:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9794614401-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="9794614401-1">}</span></code></pre><p>This is received by the client, which in turn does <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a>
│ │ │ │ +user to another.</p><p>The first user &quot;sends&quot; the message in the example above by:</p><pre><code class="makeup erlang" translate="no"><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="4273091760-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4273091760-1">)</span></code></pre><p>After testing that the client process exists:</p><pre><code class="makeup erlang" translate="no"><span class="nf">whereis</span><span class="p" data-group-id="5471764194-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="5471764194-1">)</span></code></pre><p>And a message is sent to <code class="inline">mess_client</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6017579149-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6017579149-1">}</span></code></pre><p>The client sends the message to the server by:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5576084500-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="5576084500-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5576084500-2">{</span><span class="nf">self</span><span class="p" data-group-id="5576084500-3">(</span><span class="p" data-group-id="5576084500-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5576084500-2">}</span><span class="p">,</span></code></pre><p>And waits for a reply from the server.</p><p>The server receives this message and calls:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="6645025759-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="6645025759-1">)</span><span class="p">,</span></code></pre><p>This checks that the pid <code class="inline">From</code> is in the <code class="inline">User_List</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="1301317559-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="1301317559-1">)</span></code></pre><p>If <code class="inline">keysearch</code> returns the atom <code class="inline">false</code>, some error has occurred and the server
│ │ │ │ +sends back the message:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7198142043-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="7198142043-1">}</span></code></pre><p>This is received by the client, which in turn does <a href="../../../lib/../erts/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a>
│ │ │ │  and terminates. If <code class="inline">keysearch</code> returns <code class="inline">{value,{From,Name}}</code> it is certain that
│ │ │ │ -the user is logged on and that his name (peter) is in variable <code class="inline">Name</code>.</p><p>Let us now call:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="9093605928-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9093605928-1">)</span></code></pre><p>Notice that as this is <code class="inline">server_transfer/5</code>, it is not the same as the previous
│ │ │ │ +the user is logged on and that his name (peter) is in variable <code class="inline">Name</code>.</p><p>Let us now call:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="5594189820-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5594189820-1">)</span></code></pre><p>Notice that as this is <code class="inline">server_transfer/5</code>, it is not the same as the previous
│ │ │ │  function <code class="inline">server_transfer/4</code>. Another <code class="inline">keysearch</code> is done on <code class="inline">User_List</code> to find
│ │ │ │ -the pid of the client corresponding to fred:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3688955429-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3688955429-1">)</span></code></pre><p>This time argument 2 is used, which is the second element in the tuple. If this
│ │ │ │ +the pid of the client corresponding to fred:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="8790254208-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="8790254208-1">)</span></code></pre><p>This time argument 2 is used, which is the second element in the tuple. If this
│ │ │ │  returns the atom <code class="inline">false</code>, fred is not logged on and the following message is
│ │ │ │ -sent:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0882904975-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="0882904975-1">}</span><span class="p">;</span></code></pre><p>This is received by the client.</p><p>If <code class="inline">keysearch</code> returns:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3777906647-1">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3777906647-2">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p" data-group-id="3777906647-2">}</span><span class="p" data-group-id="3777906647-1">}</span></code></pre><p>The following message is sent to fred's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8883025282-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8883025282-1">}</span><span class="p">,</span></code></pre><p>The following message is sent to peter's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8792462866-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="8792462866-1">}</span></code></pre><p>Fred's client receives the message and prints it:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7735629997-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7735629997-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7735629997-2">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7735629997-3">[</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7735629997-3">]</span><span class="p" data-group-id="7735629997-2">)</span></code></pre><p>Peter's client receives the message in the <code class="inline">await_result</code> function.</p>
│ │ │ │ +sent:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4773545282-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="4773545282-1">}</span><span class="p">;</span></code></pre><p>This is received by the client.</p><p>If <code class="inline">keysearch</code> returns:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1260996212-1">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1260996212-2">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p" data-group-id="1260996212-2">}</span><span class="p" data-group-id="1260996212-1">}</span></code></pre><p>The following message is sent to fred's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4382334634-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4382334634-1">}</span><span class="p">,</span></code></pre><p>The following message is sent to peter's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6350952910-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="6350952910-1">}</span></code></pre><p>Fred's client receives the message and prints it:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5090292011-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5090292011-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5090292011-2">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5090292011-3">[</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5090292011-3">]</span><span class="p" data-group-id="5090292011-2">)</span></code></pre><p>Peter's client receives the message in the <code class="inline">await_result</code> function.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/commoncaveats.xhtml
│ │ │ │ @@ -23,31 +23,31 @@
│ │ │ │  <p>This section lists a few constructs to watch out for.</p><h2 id="operator" class="section-heading">
│ │ │ │    <a href="#operator" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Operator <code class="inline">++</code></span>
│ │ │ │  </h2>
│ │ │ │  <p>The <code class="inline">++</code> operator copies its left-hand side operand. That is clearly
│ │ │ │ -seen if we do our own implementation in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_plus_plus</span><span class="p" data-group-id="4704575110-1">(</span><span class="p" data-group-id="4704575110-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4704575110-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="4704575110-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4704575110-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="4704575110-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="4704575110-4">)</span><span class="p" data-group-id="4704575110-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="4704575110-5">(</span><span class="p" data-group-id="4704575110-6">[</span><span class="p" data-group-id="4704575110-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="4704575110-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>We must be careful how we use <code class="inline">++</code> in a loop. First is how not to use it:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_reverse</span><span class="p" data-group-id="3216464205-1">(</span><span class="p" data-group-id="3216464205-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3216464205-2">]</span><span class="p" data-group-id="3216464205-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">naive_reverse</span><span class="p" data-group-id="3216464205-3">(</span><span class="n">T</span><span class="p" data-group-id="3216464205-3">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3216464205-4">[</span><span class="n">H</span><span class="p" data-group-id="3216464205-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">naive_reverse</span><span class="p" data-group-id="3216464205-5">(</span><span class="p" data-group-id="3216464205-6">[</span><span class="p" data-group-id="3216464205-6">]</span><span class="p" data-group-id="3216464205-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3216464205-7">[</span><span class="p" data-group-id="3216464205-7">]</span><span class="p">.</span></code></pre><p>As the <code class="inline">++</code> operator copies its left-hand side operand, the growing
│ │ │ │ -result is copied repeatedly, leading to quadratic complexity.</p><p>On the other hand, using <code class="inline">++</code> in loop like this is perfectly fine:</p><p><strong>OK</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8044646048-1">(</span><span class="n">List</span><span class="p" data-group-id="8044646048-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8044646048-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8044646048-3">[</span><span class="p" data-group-id="8044646048-3">]</span><span class="p" data-group-id="8044646048-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +seen if we do our own implementation in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_plus_plus</span><span class="p" data-group-id="8146313117-1">(</span><span class="p" data-group-id="8146313117-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8146313117-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8146313117-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="8146313117-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="8146313117-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8146313117-4">)</span><span class="p" data-group-id="8146313117-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="8146313117-5">(</span><span class="p" data-group-id="8146313117-6">[</span><span class="p" data-group-id="8146313117-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8146313117-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>We must be careful how we use <code class="inline">++</code> in a loop. First is how not to use it:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_reverse</span><span class="p" data-group-id="3165127189-1">(</span><span class="p" data-group-id="3165127189-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3165127189-2">]</span><span class="p" data-group-id="3165127189-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">naive_reverse</span><span class="p" data-group-id="3165127189-3">(</span><span class="n">T</span><span class="p" data-group-id="3165127189-3">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3165127189-4">[</span><span class="n">H</span><span class="p" data-group-id="3165127189-4">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">naive_reverse</span><span class="p" data-group-id="3165127189-5">(</span><span class="p" data-group-id="3165127189-6">[</span><span class="p" data-group-id="3165127189-6">]</span><span class="p" data-group-id="3165127189-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3165127189-7">[</span><span class="p" data-group-id="3165127189-7">]</span><span class="p">.</span></code></pre><p>As the <code class="inline">++</code> operator copies its left-hand side operand, the growing
│ │ │ │ +result is copied repeatedly, leading to quadratic complexity.</p><p>On the other hand, using <code class="inline">++</code> in loop like this is perfectly fine:</p><p><strong>OK</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7652717550-1">(</span><span class="n">List</span><span class="p" data-group-id="7652717550-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7652717550-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7652717550-3">[</span><span class="p" data-group-id="7652717550-3">]</span><span class="p" data-group-id="7652717550-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8044646048-4">(</span><span class="p" data-group-id="8044646048-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8044646048-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8044646048-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8044646048-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8044646048-7">[</span><span class="n">H</span><span class="p" data-group-id="8044646048-7">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8044646048-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8044646048-8">(</span><span class="p" data-group-id="8044646048-9">[</span><span class="p" data-group-id="8044646048-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8044646048-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7652717550-4">(</span><span class="p" data-group-id="7652717550-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7652717550-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7652717550-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7652717550-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7652717550-7">[</span><span class="n">H</span><span class="p" data-group-id="7652717550-7">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7652717550-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7652717550-8">(</span><span class="p" data-group-id="7652717550-9">[</span><span class="p" data-group-id="7652717550-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7652717550-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Each list element is copied only once. The growing result <code class="inline">Acc</code> is the right-hand
│ │ │ │ -side operand, which it is <em>not</em> copied.</p><p>Experienced Erlang programmers would probably write as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">vanilla_reverse</span><span class="p" data-group-id="9396145709-1">(</span><span class="p" data-group-id="9396145709-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9396145709-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9396145709-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="9396145709-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9396145709-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="9396145709-4">]</span><span class="p" data-group-id="9396145709-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="9396145709-5">(</span><span class="p" data-group-id="9396145709-6">[</span><span class="p" data-group-id="9396145709-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9396145709-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +side operand, which it is <em>not</em> copied.</p><p>Experienced Erlang programmers would probably write as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">vanilla_reverse</span><span class="p" data-group-id="5409598139-1">(</span><span class="p" data-group-id="5409598139-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5409598139-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5409598139-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="5409598139-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5409598139-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="5409598139-4">]</span><span class="p" data-group-id="5409598139-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="5409598139-5">(</span><span class="p" data-group-id="5409598139-6">[</span><span class="p" data-group-id="5409598139-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5409598139-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>In principle, this is slightly more efficient because the list element <code class="inline">[H]</code>
│ │ │ │  is not built before being copied and discarded. In practice, the compiler
│ │ │ │  rewrites <code class="inline">[H] ++ Acc</code> to <code class="inline">[H|Acc]</code>.</p><h2 id="timer-module" class="section-heading">
│ │ │ │    <a href="#timer-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Timer Module</span>
│ │ │ │ @@ -65,77 +65,77 @@
│ │ │ │  therefore harmless.</p><h2 id="accidental-copying-and-loss-of-sharing" class="section-heading">
│ │ │ │    <a href="#accidental-copying-and-loss-of-sharing" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Accidental Copying and Loss of Sharing</span>
│ │ │ │  </h2>
│ │ │ │  <p>When spawning a new process using a fun, one can accidentally copy more data to
│ │ │ │ -the process than intended. For example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental1</span><span class="p" data-group-id="6163291921-1">(</span><span class="n">State</span><span class="p" data-group-id="6163291921-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="6163291921-2">(</span><span class="nf">fun</span><span class="p" data-group-id="6163291921-3">(</span><span class="p" data-group-id="6163291921-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6163291921-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6163291921-5">[</span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p" data-group-id="6163291921-5">]</span><span class="p" data-group-id="6163291921-4">)</span><span class="w">
│ │ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="6163291921-2">)</span><span class="p">.</span></code></pre><p>The code in the fun will extract one element from the record and print it. The
│ │ │ │ +the process than intended. For example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental1</span><span class="p" data-group-id="8753292309-1">(</span><span class="n">State</span><span class="p" data-group-id="8753292309-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="8753292309-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8753292309-3">(</span><span class="p" data-group-id="8753292309-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8753292309-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8753292309-5">[</span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p" data-group-id="8753292309-5">]</span><span class="p" data-group-id="8753292309-4">)</span><span class="w">
│ │ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="8753292309-2">)</span><span class="p">.</span></code></pre><p>The code in the fun will extract one element from the record and print it. The
│ │ │ │  rest of the <code class="inline">state</code> record is not used. However, when the <a href="../../../lib/../erts/doc/html/erlang.html#spawn/1"><code class="inline">spawn/1</code></a>
│ │ │ │ -function is executed, the entire record is copied to the newly created process.</p><p>The same kind of problem can happen with a map:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental2</span><span class="p" data-group-id="1898361180-1">(</span><span class="n">State</span><span class="p" data-group-id="1898361180-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1898361180-2">(</span><span class="nf">fun</span><span class="p" data-group-id="1898361180-3">(</span><span class="p" data-group-id="1898361180-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1898361180-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1898361180-5">[</span><span class="nf">map_get</span><span class="p" data-group-id="1898361180-6">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1898361180-6">)</span><span class="p" data-group-id="1898361180-5">]</span><span class="p" data-group-id="1898361180-4">)</span><span class="w">
│ │ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="1898361180-2">)</span><span class="p">.</span></code></pre><p>In the following example (part of a module implementing the <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ │ -behavior) the created fun is sent to another process:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="9348490030-1">(</span><span class="ss">give_me_a_fun</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9348490030-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9348490030-2">(</span><span class="p" data-group-id="9348490030-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="nb">size</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9348490030-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9348490030-3">}</span><span class="p">.</span></code></pre><p>How bad that unnecessary copy is depends on the contents of the record or the
│ │ │ │ -map.</p><p>For example, if the <code class="inline">state</code> record is initialized like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init1</span><span class="p" data-group-id="4991458249-1">(</span><span class="p" data-group-id="4991458249-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="4991458249-2">{</span><span class="ss">data</span><span class="o">=</span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="4991458249-3">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">10000</span><span class="p" data-group-id="4991458249-3">)</span><span class="p" data-group-id="4991458249-2">}</span><span class="p">.</span></code></pre><p>a list with 10000 elements (or about 20000 heap words) will be copied to the
│ │ │ │ +function is executed, the entire record is copied to the newly created process.</p><p>The same kind of problem can happen with a map:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental2</span><span class="p" data-group-id="0005302926-1">(</span><span class="n">State</span><span class="p" data-group-id="0005302926-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="0005302926-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0005302926-3">(</span><span class="p" data-group-id="0005302926-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0005302926-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0005302926-5">[</span><span class="nf">map_get</span><span class="p" data-group-id="0005302926-6">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0005302926-6">)</span><span class="p" data-group-id="0005302926-5">]</span><span class="p" data-group-id="0005302926-4">)</span><span class="w">
│ │ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="0005302926-2">)</span><span class="p">.</span></code></pre><p>In the following example (part of a module implementing the <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ │ +behavior) the created fun is sent to another process:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="1171016453-1">(</span><span class="ss">give_me_a_fun</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1171016453-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1171016453-2">(</span><span class="p" data-group-id="1171016453-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="nb">size</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1171016453-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1171016453-3">}</span><span class="p">.</span></code></pre><p>How bad that unnecessary copy is depends on the contents of the record or the
│ │ │ │ +map.</p><p>For example, if the <code class="inline">state</code> record is initialized like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init1</span><span class="p" data-group-id="2636949354-1">(</span><span class="p" data-group-id="2636949354-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="2636949354-2">{</span><span class="ss">data</span><span class="o">=</span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2636949354-3">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">10000</span><span class="p" data-group-id="2636949354-3">)</span><span class="p" data-group-id="2636949354-2">}</span><span class="p">.</span></code></pre><p>a list with 10000 elements (or about 20000 heap words) will be copied to the
│ │ │ │  newly created process.</p><p>An unnecessary copy of 10000 element list can be bad enough, but it can get even
│ │ │ │  worse if the <code class="inline">state</code> record contains <em>shared subterms</em>. Here is a simple example
│ │ │ │ -of a term with a shared subterm:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0322170571-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="0322170571-1">}</span></code></pre><p>When a term is copied to another process, sharing of subterms will be lost and
│ │ │ │ -the copied term can be many times larger than the original term. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init2</span><span class="p" data-group-id="0856910695-1">(</span><span class="p" data-group-id="0856910695-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">SharedSubTerms</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="0856910695-2">(</span><span class="nf">fun</span><span class="p" data-group-id="0856910695-3">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="0856910695-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0856910695-4">[</span><span class="n">A</span><span class="p">|</span><span class="n">A</span><span class="p" data-group-id="0856910695-4">]</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0856910695-5">[</span><span class="mi">0</span><span class="p" data-group-id="0856910695-5">]</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="0856910695-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p" data-group-id="0856910695-6">)</span><span class="p" data-group-id="0856910695-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="0856910695-7">{</span><span class="ss">data</span><span class="o">=</span><span class="n">Shared</span><span class="p" data-group-id="0856910695-7">}</span><span class="p">.</span></code></pre><p>In the process that calls <code class="inline">init2/0</code>, the size of the <code class="inline">data</code> field in the <code class="inline">state</code>
│ │ │ │ +of a term with a shared subterm:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6051084378-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="6051084378-1">}</span></code></pre><p>When a term is copied to another process, sharing of subterms will be lost and
│ │ │ │ +the copied term can be many times larger than the original term. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init2</span><span class="p" data-group-id="2006219212-1">(</span><span class="p" data-group-id="2006219212-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">SharedSubTerms</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="2006219212-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2006219212-3">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2006219212-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2006219212-4">[</span><span class="n">A</span><span class="p">|</span><span class="n">A</span><span class="p" data-group-id="2006219212-4">]</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2006219212-5">[</span><span class="mi">0</span><span class="p" data-group-id="2006219212-5">]</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2006219212-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p" data-group-id="2006219212-6">)</span><span class="p" data-group-id="2006219212-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="2006219212-7">{</span><span class="ss">data</span><span class="o">=</span><span class="n">Shared</span><span class="p" data-group-id="2006219212-7">}</span><span class="p">.</span></code></pre><p>In the process that calls <code class="inline">init2/0</code>, the size of the <code class="inline">data</code> field in the <code class="inline">state</code>
│ │ │ │  record will be 32 heap words. When the record is copied to the newly created
│ │ │ │  process, sharing will be lost and the size of the copied <code class="inline">data</code> field will be
│ │ │ │  131070 heap words. More details about
│ │ │ │  <a href="eff_guide_processes.xhtml#loss-of-sharing">loss off sharing</a> are found in a later
│ │ │ │  section.</p><p>To avoid the problem, outside of the fun extract only the fields of the record
│ │ │ │ -that are actually used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental1</span><span class="p" data-group-id="2240080788-1">(</span><span class="n">State</span><span class="p" data-group-id="2240080788-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +that are actually used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental1</span><span class="p" data-group-id="6632702831-1">(</span><span class="n">State</span><span class="p" data-group-id="6632702831-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2240080788-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2240080788-3">(</span><span class="p" data-group-id="2240080788-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2240080788-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2240080788-5">[</span><span class="n">Info</span><span class="p" data-group-id="2240080788-5">]</span><span class="p" data-group-id="2240080788-4">)</span><span class="w">
│ │ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="2240080788-2">)</span><span class="p">.</span></code></pre><p>Similarly, outside of the fun extract only the map elements that are actually
│ │ │ │ -used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental2</span><span class="p" data-group-id="9365432164-1">(</span><span class="n">State</span><span class="p" data-group-id="9365432164-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">map_get</span><span class="p" data-group-id="9365432164-2">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9365432164-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9365432164-3">(</span><span class="nf">fun</span><span class="p" data-group-id="9365432164-4">(</span><span class="p" data-group-id="9365432164-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9365432164-5">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9365432164-6">[</span><span class="n">Info</span><span class="p" data-group-id="9365432164-6">]</span><span class="p" data-group-id="9365432164-5">)</span><span class="w">
│ │ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="9365432164-3">)</span><span class="p">.</span></code></pre><h2 id="list_to_atom-1" class="section-heading">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="6632702831-2">(</span><span class="nf">fun</span><span class="p" data-group-id="6632702831-3">(</span><span class="p" data-group-id="6632702831-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6632702831-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6632702831-5">[</span><span class="n">Info</span><span class="p" data-group-id="6632702831-5">]</span><span class="p" data-group-id="6632702831-4">)</span><span class="w">
│ │ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="6632702831-2">)</span><span class="p">.</span></code></pre><p>Similarly, outside of the fun extract only the map elements that are actually
│ │ │ │ +used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental2</span><span class="p" data-group-id="9139743911-1">(</span><span class="n">State</span><span class="p" data-group-id="9139743911-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">map_get</span><span class="p" data-group-id="9139743911-2">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9139743911-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9139743911-3">(</span><span class="nf">fun</span><span class="p" data-group-id="9139743911-4">(</span><span class="p" data-group-id="9139743911-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9139743911-5">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9139743911-6">[</span><span class="n">Info</span><span class="p" data-group-id="9139743911-6">]</span><span class="p" data-group-id="9139743911-5">)</span><span class="w">
│ │ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="9139743911-3">)</span><span class="p">.</span></code></pre><h2 id="list_to_atom-1" class="section-heading">
│ │ │ │    <a href="#list_to_atom-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">list_to_atom/1</span>
│ │ │ │  </h2>
│ │ │ │  <p>Atoms are not garbage-collected. Once an atom is created, it is never removed.
│ │ │ │  The emulator terminates if the limit for the number of atoms (1,048,576 by
│ │ │ │  default) is reached.</p><p>Therefore, converting arbitrary input strings to atoms can be dangerous in a
│ │ │ │  system that runs continuously. If only certain well-defined atoms are allowed as
│ │ │ │  input, <a href="../../../lib/../erts/doc/html/erlang.html#list_to_existing_atom/1"><code class="inline">list_to_existing_atom/1</code></a> or
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#binary_to_existing_atom/1"><code class="inline">binary_to_existing_atom/1</code></a> can be used
│ │ │ │  to guard against a denial-of-service attack. (All atoms that are allowed must
│ │ │ │  have been created earlier, for example, by using all of them in a module
│ │ │ │  and loading that module.)</p><p>Using <a href="../../../lib/../erts/doc/html/erlang.html#list_to_atom/1"><code class="inline">list_to_atom/1</code></a> to construct an atom that
│ │ │ │ -is passed to <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply/3</code></a> is quite expensive.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">apply</span><span class="p" data-group-id="5732819333-1">(</span><span class="nf">list_to_atom</span><span class="p" data-group-id="5732819333-2">(</span><span class="s">&quot;some_prefix&quot;</span><span class="o">++</span><span class="n">Var</span><span class="p" data-group-id="5732819333-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="5732819333-1">)</span></code></pre><h2 id="length-1" class="section-heading">
│ │ │ │ +is passed to <a href="../../../lib/../erts/doc/html/erlang.html#apply/3"><code class="inline">apply/3</code></a> is quite expensive.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">apply</span><span class="p" data-group-id="5117328847-1">(</span><span class="nf">list_to_atom</span><span class="p" data-group-id="5117328847-2">(</span><span class="s">&quot;some_prefix&quot;</span><span class="o">++</span><span class="n">Var</span><span class="p" data-group-id="5117328847-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="5117328847-1">)</span></code></pre><h2 id="length-1" class="section-heading">
│ │ │ │    <a href="#length-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">length/1</span>
│ │ │ │  </h2>
│ │ │ │  <p>The time for calculating the length of a list is proportional to the length of
│ │ │ │  the list, as opposed to <a href="../../../lib/../erts/doc/html/erlang.html#tuple_size/1"><code class="inline">tuple_size/1</code></a>,
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#byte_size/1"><code class="inline">byte_size/1</code></a>, and <a href="../../../lib/../erts/doc/html/erlang.html#bit_size/1"><code class="inline">bit_size/1</code></a>, which all
│ │ │ │  execute in constant time.</p><p>Normally, there is no need to worry about the speed of <a href="../../../lib/../erts/doc/html/erlang.html#length/1"><code class="inline">length/1</code></a>,
│ │ │ │  because it is efficiently implemented in C. In time-critical code, you might
│ │ │ │  want to avoid it if the input list could potentially be very long.</p><p>Some uses of <a href="../../../lib/../erts/doc/html/erlang.html#length/1"><code class="inline">length/1</code></a> can be replaced by matching. For example,
│ │ │ │ -the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="8597535151-1">(</span><span class="n">L</span><span class="p" data-group-id="8597535151-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8597535151-2">(</span><span class="n">L</span><span class="p" data-group-id="8597535151-2">)</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="8804360511-1">(</span><span class="p" data-group-id="8804360511-2">[</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="8804360511-2">]</span><span class="o">=</span><span class="n">L</span><span class="p" data-group-id="8804360511-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="6159883846-1">(</span><span class="n">L</span><span class="p" data-group-id="6159883846-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="6159883846-2">(</span><span class="n">L</span><span class="p" data-group-id="6159883846-2">)</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="3002381595-1">(</span><span class="p" data-group-id="3002381595-2">[</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="3002381595-2">]</span><span class="o">=</span><span class="n">L</span><span class="p" data-group-id="3002381595-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>One slight difference is that <a href="../../../lib/../erts/doc/html/erlang.html#length/1"><code class="inline">length(L)</code></a> fails if <code class="inline">L</code> is an
│ │ │ │  improper list, while the pattern in the second code fragment accepts an improper
│ │ │ │  list.</p><h2 id="setelement-3" class="section-heading">
│ │ │ │    <a href="#setelement-3" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">setelement/3</span>
│ │ │ │ @@ -143,18 +143,18 @@
│ │ │ │  <p><a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> copies the tuple it modifies. Therefore,
│ │ │ │  updating a tuple in a loop using <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> creates a new
│ │ │ │  copy of the tuple every time.</p><p>There is one exception to the rule that the tuple is copied. If the compiler
│ │ │ │  clearly can see that destructively updating the tuple would give the same result
│ │ │ │  as if the tuple was copied, the call to <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> is
│ │ │ │  replaced with a special destructive <code class="inline">setelement</code> instruction. In the following
│ │ │ │  code sequence, the first <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> call copies the tuple
│ │ │ │ -and modifies the ninth element:</p><pre><code class="makeup erlang" translate="no"><span class="nf">multiple_setelement</span><span class="p" data-group-id="1286293725-1">(</span><span class="n">T0</span><span class="p" data-group-id="1286293725-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="1286293725-2">(</span><span class="n">T0</span><span class="p" data-group-id="1286293725-2">)</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">T1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="1286293725-3">(</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p" data-group-id="1286293725-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">T2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="1286293725-4">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="ss">foobar</span><span class="p" data-group-id="1286293725-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">setelement</span><span class="p" data-group-id="1286293725-5">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p">,</span><span class="w"> </span><span class="ss">new_value</span><span class="p" data-group-id="1286293725-5">)</span><span class="p">.</span></code></pre><p>The two following <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> calls modify the tuple in
│ │ │ │ +and modifies the ninth element:</p><pre><code class="makeup erlang" translate="no"><span class="nf">multiple_setelement</span><span class="p" data-group-id="8462267993-1">(</span><span class="n">T0</span><span class="p" data-group-id="8462267993-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="8462267993-2">(</span><span class="n">T0</span><span class="p" data-group-id="8462267993-2">)</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">T1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="8462267993-3">(</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p" data-group-id="8462267993-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">T2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="8462267993-4">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="ss">foobar</span><span class="p" data-group-id="8462267993-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">setelement</span><span class="p" data-group-id="8462267993-5">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p">,</span><span class="w"> </span><span class="ss">new_value</span><span class="p" data-group-id="8462267993-5">)</span><span class="p">.</span></code></pre><p>The two following <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> calls modify the tuple in
│ │ │ │  place.</p><p>For the optimization to be applied, <em>all</em> the following conditions must be true:</p><ul><li>The tuple argument must be known to be a tuple of a known size.</li><li>The indices must be integer literals, not variables or expressions.</li><li>The indices must be given in descending order.</li><li>There must be no calls to another function in between the calls to
│ │ │ │  <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a>.</li><li>The tuple returned from one <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> call must only be
│ │ │ │  used in the subsequent call to <a href="../../../lib/../erts/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a>.</li></ul><p>If the code cannot be structured as in the <code class="inline">multiple_setelement/1</code> example, the
│ │ │ │  best way to modify multiple elements in a large tuple is to convert the tuple to
│ │ │ │  a list, modify the list, and convert it back to a tuple.</p><h2 id="size-1" class="section-heading">
│ │ │ │    <a href="#size-1" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ ├── OEBPS/code_loading.xhtml
│ │ │ │ @@ -27,16 +27,16 @@
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Compilation</span>
│ │ │ │  </h2>
│ │ │ │  <p>Erlang programs must be <em>compiled</em> to object code. The compiler can generate a
│ │ │ │  new file that contains the object code. The current abstract machine, which runs
│ │ │ │  the object code, is called BEAM, therefore the object files get the suffix
│ │ │ │ -<code class="inline">.beam</code>. The compiler can also generate a binary which can be loaded directly.</p><p>The compiler is located in the module <a href="../../../lib/compiler/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><pre><code class="makeup erlang" translate="no"><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="0957049244-1">(</span><span class="n">Module</span><span class="p" data-group-id="0957049244-1">)</span><span class="w">
│ │ │ │ -</span><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="0957049244-2">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="0957049244-2">)</span></code></pre><p>The Erlang shell understands the command <code class="inline">c(Module)</code>, which both compiles and
│ │ │ │ +<code class="inline">.beam</code>. The compiler can also generate a binary which can be loaded directly.</p><p>The compiler is located in the module <a href="../../../lib/compiler/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><pre><code class="makeup erlang" translate="no"><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="6211392932-1">(</span><span class="n">Module</span><span class="p" data-group-id="6211392932-1">)</span><span class="w">
│ │ │ │ +</span><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="6211392932-2">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="6211392932-2">)</span></code></pre><p>The Erlang shell understands the command <code class="inline">c(Module)</code>, which both compiles and
│ │ │ │  loads <code class="inline">Module</code>.</p><p>There is also a module <code class="inline">make</code>, which provides a set of functions similar to the
│ │ │ │  UNIX type Make functions, see module <a href="../../../lib/tools/doc/html/make.html"><code class="inline">make</code></a> in Tools.</p><p>The compiler can also be accessed from the OS prompt using the
│ │ │ │  <a href="../../../lib/../erts/doc/html/erl_cmd.xhtml">erl</a> executable in ERTS.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -compile Module1...ModuleN</span><span class="w">
│ │ │ │  </span><span class="c1">% erl -make</span></code></pre><p>The <code class="inline">erlc</code> program provides way to compile modules from the OS
│ │ │ │  shell, see the <a href="../../../lib/../erts/doc/html/erlc_cmd.xhtml">erlc</a> executable in ERTS. It
│ │ │ │  understands a number of flags that can be used to define macros, add search
│ │ │ │  paths for include files, and more.</p><pre><code class="text">% erlc &lt;flags&gt; File1.erl...FileN.erl</code></pre><p><a href="" id="loading"></a></p><h2 id="code-loading" class="section-heading">
│ │ │ │ @@ -61,51 +61,51 @@
│ │ │ │  When a module is loaded into the system for the first time, the code becomes
│ │ │ │  'current'. If then a new instance of the module is loaded, the code of the
│ │ │ │  previous instance becomes 'old' and the new instance becomes 'current'.</p><p>Both old and current code is valid, and can be evaluated concurrently. Fully
│ │ │ │  qualified function calls always refer to current code. Old code can still be
│ │ │ │  evaluated because of processes lingering in the old code.</p><p>If a third instance of the module is loaded, the code server removes (purges)
│ │ │ │  the old code and any processes lingering in it is terminated. Then the third
│ │ │ │  instance becomes 'current' and the previously current code becomes 'old'.</p><p>To change from old code to current code, a process must make a fully qualified
│ │ │ │ -function call.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6386989704-1">(</span><span class="ss">m</span><span class="p" data-group-id="6386989704-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6386989704-2">(</span><span class="p" data-group-id="6386989704-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6386989704-3">]</span><span class="p" data-group-id="6386989704-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +function call.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4902507940-1">(</span><span class="ss">m</span><span class="p" data-group-id="4902507940-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4902507940-2">(</span><span class="p" data-group-id="4902507940-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4902507940-3">]</span><span class="p" data-group-id="4902507940-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="6386989704-4">(</span><span class="p" data-group-id="6386989704-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="4902507940-4">(</span><span class="p" data-group-id="4902507940-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │          </span><span class="ss">code_switch</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="nc">m</span><span class="p">:</span><span class="nf">loop</span><span class="p" data-group-id="6386989704-5">(</span><span class="p" data-group-id="6386989704-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +            </span><span class="nc">m</span><span class="p">:</span><span class="nf">loop</span><span class="p" data-group-id="4902507940-5">(</span><span class="p" data-group-id="4902507940-5">)</span><span class="p">;</span><span class="w">
│ │ │ │          </span><span class="n">Msg</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="6386989704-6">(</span><span class="p" data-group-id="6386989704-6">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="4902507940-6">(</span><span class="p" data-group-id="4902507940-6">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>To make the process change code, send the message <code class="inline">code_switch</code> to it. The
│ │ │ │  process then makes a fully qualified call to <code class="inline">m:loop()</code> and changes to current
│ │ │ │  code. Notice that <code class="inline">m:loop/0</code> must be exported.</p><p>For code replacement of funs to work, use the syntax
│ │ │ │  <code class="inline">fun Module:FunctionName/Arity</code>.</p><p><a href="" id="on_load"></a></p><h2 id="running-a-function-when-a-module-is-loaded" class="section-heading">
│ │ │ │    <a href="#running-a-function-when-a-module-is-loaded" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Running a Function When a Module is Loaded</span>
│ │ │ │  </h2>
│ │ │ │  <p>The <code class="inline">-on_load()</code> directive names a function that is to be run automatically when
│ │ │ │ -a module is loaded.</p><p>Its syntax is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="7667718398-1">(</span><span class="n">Name</span><span class="o">/</span><span class="mi">0</span><span class="p" data-group-id="7667718398-1">)</span><span class="p">.</span></code></pre><p>It is not necessary to export the function. It is called in a freshly spawned
│ │ │ │ +a module is loaded.</p><p>Its syntax is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="3503154688-1">(</span><span class="n">Name</span><span class="o">/</span><span class="mi">0</span><span class="p" data-group-id="3503154688-1">)</span><span class="p">.</span></code></pre><p>It is not necessary to export the function. It is called in a freshly spawned
│ │ │ │  process (which terminates as soon as the function returns).</p><p>The function must return <code class="inline">ok</code> if the module is to become the new current code
│ │ │ │  for the module and become callable.</p><p>Returning any other value or generating an exception causes the new code to be
│ │ │ │  unloaded. If the return value is not an atom, a warning error report is sent to
│ │ │ │  the error logger.</p><p>If there already is current code for the module, that code will remain current
│ │ │ │  and can be called until the <code class="inline">on_load</code> function has returned. If the <code class="inline">on_load</code>
│ │ │ │  function fails, the current code (if any) will remain current. If there is no
│ │ │ │  current code for a module, any process that makes an external call to the module
│ │ │ │  before the <code class="inline">on_load</code> function has finished will be suspended until the <code class="inline">on_load</code>
│ │ │ │  function have finished.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 19, if the <code class="inline">on_load</code> function failed, any previously current
│ │ │ │  code would become old, essentially leaving the system without any working and
│ │ │ │  reachable instance of the module.</p></section><p>In embedded mode, first all modules are loaded. Then all <code class="inline">on_load</code> functions are
│ │ │ │  called. The system is terminated unless all of the <code class="inline">on_load</code> functions return
│ │ │ │ -<code class="inline">ok</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2258823510-1">(</span><span class="ss">m</span><span class="p" data-group-id="2258823510-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="2258823510-2">(</span><span class="ss">load_my_nifs</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2258823510-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<code class="inline">ok</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5124032360-1">(</span><span class="ss">m</span><span class="p" data-group-id="5124032360-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="5124032360-2">(</span><span class="ss">load_my_nifs</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5124032360-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">load_my_nifs</span><span class="p" data-group-id="2258823510-3">(</span><span class="p" data-group-id="2258823510-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">load_my_nifs</span><span class="p" data-group-id="5124032360-3">(</span><span class="p" data-group-id="5124032360-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">NifPath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">    </span><span class="c1">%Set up the path to the NIF library.</span><span class="w">
│ │ │ │      </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">       </span><span class="c1">%Initialize the Info term</span><span class="w">
│ │ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="2258823510-4">(</span><span class="n">NifPath</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="2258823510-4">)</span><span class="p">.</span></code></pre><p>If the call to <a href="../../../lib/../erts/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a> fails, the module is unloaded and a warning
│ │ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="5124032360-4">(</span><span class="n">NifPath</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="5124032360-4">)</span><span class="p">.</span></code></pre><p>If the call to <a href="../../../lib/../erts/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a> fails, the module is unloaded and a warning
│ │ │ │  report is sent to the error loader.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/c_portdriver.xhtml
│ │ │ │ @@ -56,112 +56,112 @@
│ │ │ │  <p>Like a port program, the port communicates with an Erlang process. All
│ │ │ │  communication goes through one Erlang process that is the <em>connected process</em> of
│ │ │ │  the port driver. Terminating this process closes the port driver.</p><p>Before the port is created, the driver must be loaded. This is done with the
│ │ │ │  function <a href="../../../lib/kernel/doc/html/erl_ddll.html#load_driver/2"><code class="inline">erl_ddll:load_driver/2</code></a>, with the name of the shared library as
│ │ │ │  argument.</p><p>The port is then created using the BIF <a href="../../../lib/../erts/doc/html/erlang.html#open_port/2"><code class="inline">open_port/2</code></a>, with the
│ │ │ │  tuple <code class="inline">{spawn, DriverName}</code> as the first argument. The string <code class="inline">SharedLib</code> is the
│ │ │ │  name of the port driver. The second argument is a list of options, none in this
│ │ │ │ -case:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2972096468-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="2972096468-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2972096468-2">(</span><span class="p" data-group-id="2972096468-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2972096468-3">]</span><span class="p" data-group-id="2972096468-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +case:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2652740622-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="2652740622-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2652740622-2">(</span><span class="p" data-group-id="2652740622-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2652740622-3">]</span><span class="p" data-group-id="2652740622-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2972096468-4">(</span><span class="n">SharedLib</span><span class="p" data-group-id="2972096468-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="2972096468-5">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="2972096468-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="2652740622-4">(</span><span class="n">SharedLib</span><span class="p" data-group-id="2652740622-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="2652740622-5">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="2652740622-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │          </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2972096468-6">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="2972096468-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="2972096468-7">(</span><span class="p" data-group-id="2972096468-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="2972096468-8">}</span><span class="p" data-group-id="2972096468-7">)</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2652740622-6">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="2652740622-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="2652740622-7">(</span><span class="p" data-group-id="2652740622-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="2652740622-8">}</span><span class="p" data-group-id="2652740622-7">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2972096468-9">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2972096468-10">[</span><span class="n">SharedLib</span><span class="p" data-group-id="2972096468-10">]</span><span class="p" data-group-id="2972096468-9">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="2652740622-9">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2652740622-10">[</span><span class="n">SharedLib</span><span class="p" data-group-id="2652740622-10">]</span><span class="p" data-group-id="2652740622-9">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="2972096468-11">(</span><span class="n">SharedLib</span><span class="p" data-group-id="2972096468-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">register</span><span class="p" data-group-id="2972096468-12">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2972096468-13">(</span><span class="p" data-group-id="2972096468-13">)</span><span class="p" data-group-id="2972096468-12">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="2972096468-14">(</span><span class="p" data-group-id="2972096468-15">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="2972096468-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2972096468-16">[</span><span class="p" data-group-id="2972096468-16">]</span><span class="p" data-group-id="2972096468-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="nf">loop</span><span class="p" data-group-id="2972096468-17">(</span><span class="n">Port</span><span class="p" data-group-id="2972096468-17">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex5:foo/1</code> and <code class="inline">complex5:bar/1</code> can be implemented. Both send a
│ │ │ │ -message to the <code class="inline">complex</code> process and receive the following reply:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="6783493833-1">(</span><span class="n">X</span><span class="p" data-group-id="6783493833-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="6783493833-2">(</span><span class="p" data-group-id="6783493833-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6783493833-3">}</span><span class="p" data-group-id="6783493833-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="6783493833-4">(</span><span class="n">Y</span><span class="p" data-group-id="6783493833-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="6783493833-5">(</span><span class="p" data-group-id="6783493833-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6783493833-6">}</span><span class="p" data-group-id="6783493833-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2652740622-11">(</span><span class="n">SharedLib</span><span class="p" data-group-id="2652740622-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">register</span><span class="p" data-group-id="2652740622-12">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2652740622-13">(</span><span class="p" data-group-id="2652740622-13">)</span><span class="p" data-group-id="2652740622-12">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="2652740622-14">(</span><span class="p" data-group-id="2652740622-15">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="2652740622-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2652740622-16">[</span><span class="p" data-group-id="2652740622-16">]</span><span class="p" data-group-id="2652740622-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="nf">loop</span><span class="p" data-group-id="2652740622-17">(</span><span class="n">Port</span><span class="p" data-group-id="2652740622-17">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex5:foo/1</code> and <code class="inline">complex5:bar/1</code> can be implemented. Both send a
│ │ │ │ +message to the <code class="inline">complex</code> process and receive the following reply:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="0206228386-1">(</span><span class="n">X</span><span class="p" data-group-id="0206228386-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="0206228386-2">(</span><span class="p" data-group-id="0206228386-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0206228386-3">}</span><span class="p" data-group-id="0206228386-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="0206228386-4">(</span><span class="n">Y</span><span class="p" data-group-id="0206228386-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="0206228386-5">(</span><span class="p" data-group-id="0206228386-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0206228386-6">}</span><span class="p" data-group-id="0206228386-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="6783493833-7">(</span><span class="n">Msg</span><span class="p" data-group-id="6783493833-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6783493833-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6783493833-9">(</span><span class="p" data-group-id="6783493833-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6783493833-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="0206228386-7">(</span><span class="n">Msg</span><span class="p" data-group-id="0206228386-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0206228386-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0206228386-9">(</span><span class="p" data-group-id="0206228386-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="0206228386-8">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="6783493833-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6783493833-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0206228386-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="0206228386-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="n">Result</span><span class="w">
│ │ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process performs the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="9770348113-1">(</span><span class="n">Port</span><span class="p" data-group-id="9770348113-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process performs the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="4805644509-1">(</span><span class="n">Port</span><span class="p" data-group-id="4805644509-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="9770348113-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9770348113-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -            </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9770348113-3">{</span><span class="nf">self</span><span class="p" data-group-id="9770348113-4">(</span><span class="p" data-group-id="9770348113-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9770348113-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9770348113-6">(</span><span class="n">Msg</span><span class="p" data-group-id="9770348113-6">)</span><span class="p" data-group-id="9770348113-5">}</span><span class="p" data-group-id="9770348113-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="4805644509-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4805644509-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +            </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4805644509-3">{</span><span class="nf">self</span><span class="p" data-group-id="4805644509-4">(</span><span class="p" data-group-id="4805644509-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4805644509-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="4805644509-6">(</span><span class="n">Msg</span><span class="p" data-group-id="4805644509-6">)</span><span class="p" data-group-id="4805644509-5">}</span><span class="p" data-group-id="4805644509-3">}</span><span class="p">,</span><span class="w">
│ │ │ │              </span><span class="k">receive</span><span class="w">
│ │ │ │ -                </span><span class="p" data-group-id="9770348113-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9770348113-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9770348113-8">}</span><span class="p" data-group-id="9770348113-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -                    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9770348113-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9770348113-10">(</span><span class="n">Data</span><span class="p" data-group-id="9770348113-10">)</span><span class="p" data-group-id="9770348113-9">}</span><span class="w">
│ │ │ │ +                </span><span class="p" data-group-id="4805644509-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4805644509-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4805644509-8">}</span><span class="p" data-group-id="4805644509-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +                    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4805644509-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="4805644509-10">(</span><span class="n">Data</span><span class="p" data-group-id="4805644509-10">)</span><span class="p" data-group-id="4805644509-9">}</span><span class="w">
│ │ │ │              </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="9770348113-11">(</span><span class="n">Port</span><span class="p" data-group-id="9770348113-11">)</span><span class="w">
│ │ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="4805644509-11">(</span><span class="n">Port</span><span class="p" data-group-id="4805644509-11">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Assuming that both the arguments and the results from the C functions are less
│ │ │ │  than 256, a simple encoding/decoding scheme is employed. In this scheme, <code class="inline">foo</code>
│ │ │ │  is represented by byte 1, <code class="inline">bar</code> is represented by 2, and the argument/result is
│ │ │ │ -represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="6934172297-1">(</span><span class="p" data-group-id="6934172297-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6934172297-2">}</span><span class="p" data-group-id="6934172297-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6934172297-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6934172297-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="6934172297-4">(</span><span class="p" data-group-id="6934172297-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6934172297-5">}</span><span class="p" data-group-id="6934172297-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6934172297-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6934172297-6">]</span><span class="p">.</span><span class="w">
│ │ │ │ +represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="7580564881-1">(</span><span class="p" data-group-id="7580564881-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7580564881-2">}</span><span class="p" data-group-id="7580564881-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7580564881-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7580564881-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="7580564881-4">(</span><span class="p" data-group-id="7580564881-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7580564881-5">}</span><span class="p" data-group-id="7580564881-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7580564881-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7580564881-6">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="6934172297-7">(</span><span class="p" data-group-id="6934172297-8">[</span><span class="n">Int</span><span class="p" data-group-id="6934172297-8">]</span><span class="p" data-group-id="6934172297-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functions for stopping the port and
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="7580564881-7">(</span><span class="p" data-group-id="7580564881-8">[</span><span class="n">Int</span><span class="p" data-group-id="7580564881-8">]</span><span class="p" data-group-id="7580564881-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functions for stopping the port and
│ │ │ │  detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1595157393-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="1595157393-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1595157393-2">(</span><span class="p" data-group-id="1595157393-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1595157393-3">]</span><span class="p" data-group-id="1595157393-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1595157393-4">(</span><span class="p" data-group-id="1595157393-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1595157393-5">]</span><span class="p" data-group-id="1595157393-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9714517586-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="9714517586-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9714517586-2">(</span><span class="p" data-group-id="9714517586-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9714517586-3">]</span><span class="p" data-group-id="9714517586-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9714517586-4">(</span><span class="p" data-group-id="9714517586-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9714517586-5">]</span><span class="p" data-group-id="9714517586-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="1595157393-6">(</span><span class="n">SharedLib</span><span class="p" data-group-id="1595157393-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="1595157393-7">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="1595157393-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="9714517586-6">(</span><span class="n">SharedLib</span><span class="p" data-group-id="9714517586-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="9714517586-7">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="9714517586-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │  	</span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1595157393-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="1595157393-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="1595157393-9">(</span><span class="p" data-group-id="1595157393-10">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="1595157393-10">}</span><span class="p" data-group-id="1595157393-9">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="9714517586-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="9714517586-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ │ +	</span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="9714517586-9">(</span><span class="p" data-group-id="9714517586-10">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="9714517586-10">}</span><span class="p" data-group-id="9714517586-9">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1595157393-11">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1595157393-12">[</span><span class="n">SharedLib</span><span class="p" data-group-id="1595157393-12">]</span><span class="p" data-group-id="1595157393-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9714517586-11">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9714517586-12">[</span><span class="n">SharedLib</span><span class="p" data-group-id="9714517586-12">]</span><span class="p" data-group-id="9714517586-11">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1595157393-13">(</span><span class="n">SharedLib</span><span class="p" data-group-id="1595157393-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="1595157393-14">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1595157393-15">(</span><span class="p" data-group-id="1595157393-15">)</span><span class="p" data-group-id="1595157393-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="1595157393-16">(</span><span class="p" data-group-id="1595157393-17">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="1595157393-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1595157393-18">[</span><span class="p" data-group-id="1595157393-18">]</span><span class="p" data-group-id="1595157393-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="1595157393-19">(</span><span class="n">Port</span><span class="p" data-group-id="1595157393-19">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="9714517586-13">(</span><span class="n">SharedLib</span><span class="p" data-group-id="9714517586-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="9714517586-14">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9714517586-15">(</span><span class="p" data-group-id="9714517586-15">)</span><span class="p" data-group-id="9714517586-14">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="9714517586-16">(</span><span class="p" data-group-id="9714517586-17">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="9714517586-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9714517586-18">[</span><span class="p" data-group-id="9714517586-18">]</span><span class="p" data-group-id="9714517586-16">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="9714517586-19">(</span><span class="n">Port</span><span class="p" data-group-id="9714517586-19">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="1595157393-20">(</span><span class="p" data-group-id="1595157393-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="9714517586-20">(</span><span class="p" data-group-id="9714517586-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="1595157393-21">(</span><span class="n">X</span><span class="p" data-group-id="1595157393-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="1595157393-22">(</span><span class="p" data-group-id="1595157393-23">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1595157393-23">}</span><span class="p" data-group-id="1595157393-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="1595157393-24">(</span><span class="n">Y</span><span class="p" data-group-id="1595157393-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="1595157393-25">(</span><span class="p" data-group-id="1595157393-26">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1595157393-26">}</span><span class="p" data-group-id="1595157393-25">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="9714517586-21">(</span><span class="n">X</span><span class="p" data-group-id="9714517586-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="9714517586-22">(</span><span class="p" data-group-id="9714517586-23">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9714517586-23">}</span><span class="p" data-group-id="9714517586-22">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="9714517586-24">(</span><span class="n">Y</span><span class="p" data-group-id="9714517586-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="9714517586-25">(</span><span class="p" data-group-id="9714517586-26">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9714517586-26">}</span><span class="p" data-group-id="9714517586-25">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="1595157393-27">(</span><span class="n">Msg</span><span class="p" data-group-id="1595157393-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1595157393-28">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1595157393-29">(</span><span class="p" data-group-id="1595157393-29">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1595157393-28">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="9714517586-27">(</span><span class="n">Msg</span><span class="p" data-group-id="9714517586-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9714517586-28">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9714517586-29">(</span><span class="p" data-group-id="9714517586-29">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9714517586-28">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1595157393-30">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1595157393-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="9714517586-30">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9714517586-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="1595157393-31">(</span><span class="n">Port</span><span class="p" data-group-id="1595157393-31">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="9714517586-31">(</span><span class="n">Port</span><span class="p" data-group-id="9714517586-31">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1595157393-32">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1595157393-32">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1595157393-33">{</span><span class="nf">self</span><span class="p" data-group-id="1595157393-34">(</span><span class="p" data-group-id="1595157393-34">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1595157393-35">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="1595157393-36">(</span><span class="n">Msg</span><span class="p" data-group-id="1595157393-36">)</span><span class="p" data-group-id="1595157393-35">}</span><span class="p" data-group-id="1595157393-33">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="9714517586-32">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9714517586-32">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9714517586-33">{</span><span class="nf">self</span><span class="p" data-group-id="9714517586-34">(</span><span class="p" data-group-id="9714517586-34">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9714517586-35">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9714517586-36">(</span><span class="n">Msg</span><span class="p" data-group-id="9714517586-36">)</span><span class="p" data-group-id="9714517586-35">}</span><span class="p" data-group-id="9714517586-33">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="1595157393-37">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1595157393-38">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1595157393-38">}</span><span class="p" data-group-id="1595157393-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1595157393-39">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="1595157393-40">(</span><span class="n">Data</span><span class="p" data-group-id="1595157393-40">)</span><span class="p" data-group-id="1595157393-39">}</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="9714517586-37">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9714517586-38">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9714517586-38">}</span><span class="p" data-group-id="9714517586-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9714517586-39">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9714517586-40">(</span><span class="n">Data</span><span class="p" data-group-id="9714517586-40">)</span><span class="p" data-group-id="9714517586-39">}</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="1595157393-41">(</span><span class="n">Port</span><span class="p" data-group-id="1595157393-41">)</span><span class="p">;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="9714517586-41">(</span><span class="n">Port</span><span class="p" data-group-id="9714517586-41">)</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1595157393-42">{</span><span class="nf">self</span><span class="p" data-group-id="1595157393-43">(</span><span class="p" data-group-id="1595157393-43">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="1595157393-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9714517586-42">{</span><span class="nf">self</span><span class="p" data-group-id="9714517586-43">(</span><span class="p" data-group-id="9714517586-43">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="9714517586-42">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="1595157393-44">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="1595157393-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="1595157393-45">(</span><span class="ss">normal</span><span class="p" data-group-id="1595157393-45">)</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="9714517586-44">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="9714517586-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="9714517586-45">(</span><span class="ss">normal</span><span class="p" data-group-id="9714517586-45">)</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="1595157393-46">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1595157393-46">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1595157393-47">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1595157393-48">[</span><span class="n">Reason</span><span class="p" data-group-id="1595157393-48">]</span><span class="p" data-group-id="1595157393-47">)</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="1595157393-49">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="1595157393-49">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="9714517586-46">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9714517586-46">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9714517586-47">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9714517586-48">[</span><span class="n">Reason</span><span class="p" data-group-id="9714517586-48">]</span><span class="p" data-group-id="9714517586-47">)</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="9714517586-49">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="9714517586-49">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="1595157393-50">(</span><span class="p" data-group-id="1595157393-51">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1595157393-51">}</span><span class="p" data-group-id="1595157393-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1595157393-52">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1595157393-52">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="1595157393-53">(</span><span class="p" data-group-id="1595157393-54">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1595157393-54">}</span><span class="p" data-group-id="1595157393-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1595157393-55">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1595157393-55">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="9714517586-50">(</span><span class="p" data-group-id="9714517586-51">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9714517586-51">}</span><span class="p" data-group-id="9714517586-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9714517586-52">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9714517586-52">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="9714517586-53">(</span><span class="p" data-group-id="9714517586-54">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9714517586-54">}</span><span class="p" data-group-id="9714517586-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9714517586-55">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9714517586-55">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="1595157393-56">(</span><span class="p" data-group-id="1595157393-57">[</span><span class="n">Int</span><span class="p" data-group-id="1595157393-57">]</span><span class="p" data-group-id="1595157393-56">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-driver" class="section-heading">
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="9714517586-56">(</span><span class="p" data-group-id="9714517586-57">[</span><span class="n">Int</span><span class="p" data-group-id="9714517586-57">]</span><span class="p" data-group-id="9714517586-56">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-driver" class="section-heading">
│ │ │ │    <a href="#c-driver" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">C Driver</span>
│ │ │ │  </h2>
│ │ │ │  <p>The C driver is a module that is compiled and linked into a shared library. It
│ │ │ │  uses a driver structure and includes the header file <code class="inline">erl_driver.h</code>.</p><p>The driver structure is filled with the driver name and function pointers. It is
│ │ │ │ @@ -178,44 +178,44 @@
│ │ │ │  reference.</p><p>It is not a good idea to use a global variable as the port driver can be spawned
│ │ │ │  by multiple Erlang processes. This driver-structure is to be instantiated
│ │ │ │  multiple times:</p><pre><code class="makeup c" translate="no"><span class="cm">/* port_driver.c */</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdio</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="s">&quot;erl_driver.h&quot;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="p" data-group-id="3741884016-1">{</span><span class="w">
│ │ │ │ +</span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="p" data-group-id="2518234770-1">{</span><span class="w">
│ │ │ │      </span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-1">}</span><span class="w"> </span><span class="n">example_data</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-1">}</span><span class="w"> </span><span class="n">example_data</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">example_drv_start</span><span class="p" data-group-id="3741884016-2">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="3741884016-2">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-3">{</span><span class="w">
│ │ │ │ -    </span><span class="n">example_data</span><span class="o">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3741884016-4">(</span><span class="n">example_data</span><span class="o">*</span><span class="p" data-group-id="3741884016-4">)</span><span class="nf">driver_alloc</span><span class="p" data-group-id="3741884016-5">(</span><span class="nf">sizeof</span><span class="p" data-group-id="3741884016-6">(</span><span class="n">example_data</span><span class="p" data-group-id="3741884016-6">)</span><span class="p" data-group-id="3741884016-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">example_drv_start</span><span class="p" data-group-id="2518234770-2">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="2518234770-2">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-3">{</span><span class="w">
│ │ │ │ +    </span><span class="n">example_data</span><span class="o">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2518234770-4">(</span><span class="n">example_data</span><span class="o">*</span><span class="p" data-group-id="2518234770-4">)</span><span class="nf">driver_alloc</span><span class="p" data-group-id="2518234770-5">(</span><span class="nf">sizeof</span><span class="p" data-group-id="2518234770-6">(</span><span class="n">example_data</span><span class="p" data-group-id="2518234770-6">)</span><span class="p" data-group-id="2518234770-5">)</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">d</span><span class="o">-&gt;</span><span class="n">port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">port</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="3741884016-7">(</span><span class="no">ErlDrvData</span><span class="p" data-group-id="3741884016-7">)</span><span class="n">d</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-3">}</span><span class="w">
│ │ │ │ +    </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="2518234770-7">(</span><span class="no">ErlDrvData</span><span class="p" data-group-id="2518234770-7">)</span><span class="n">d</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-3">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">example_drv_stop</span><span class="p" data-group-id="3741884016-8">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p" data-group-id="3741884016-8">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-9">{</span><span class="w">
│ │ │ │ -    </span><span class="nf">driver_free</span><span class="p" data-group-id="3741884016-10">(</span><span class="p" data-group-id="3741884016-11">(</span><span class="kt">char</span><span class="o">*</span><span class="p" data-group-id="3741884016-11">)</span><span class="n">handle</span><span class="p" data-group-id="3741884016-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-9">}</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">example_drv_output</span><span class="p" data-group-id="3741884016-12">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="w">       </span><span class="no">ErlDrvSizeT</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="3741884016-12">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-13">{</span><span class="w">
│ │ │ │ -    </span><span class="n">example_data</span><span class="o">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3741884016-14">(</span><span class="n">example_data</span><span class="o">*</span><span class="p" data-group-id="3741884016-14">)</span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="kt">char</span><span class="w"> </span><span class="n">fn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p" data-group-id="3741884016-15">[</span><span class="mi">0</span><span class="p" data-group-id="3741884016-15">]</span><span class="p">,</span><span class="w"> </span><span class="n">arg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p" data-group-id="3741884016-16">[</span><span class="mi">1</span><span class="p" data-group-id="3741884016-16">]</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3741884016-17">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3741884016-17">)</span><span class="w"> </span><span class="p" data-group-id="3741884016-18">{</span><span class="w">
│ │ │ │ -      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="3741884016-19">(</span><span class="n">arg</span><span class="p" data-group-id="3741884016-19">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3741884016-18">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3741884016-20">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3741884016-20">)</span><span class="w"> </span><span class="p" data-group-id="3741884016-21">{</span><span class="w">
│ │ │ │ -      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="3741884016-22">(</span><span class="n">arg</span><span class="p" data-group-id="3741884016-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="3741884016-21">}</span><span class="w">
│ │ │ │ -    </span><span class="nf">driver_output</span><span class="p" data-group-id="3741884016-23">(</span><span class="n">d</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3741884016-23">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-13">}</span><span class="w">
│ │ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">example_drv_stop</span><span class="p" data-group-id="2518234770-8">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p" data-group-id="2518234770-8">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-9">{</span><span class="w">
│ │ │ │ +    </span><span class="nf">driver_free</span><span class="p" data-group-id="2518234770-10">(</span><span class="p" data-group-id="2518234770-11">(</span><span class="kt">char</span><span class="o">*</span><span class="p" data-group-id="2518234770-11">)</span><span class="n">handle</span><span class="p" data-group-id="2518234770-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-9">}</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">example_drv_output</span><span class="p" data-group-id="2518234770-12">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="w">       </span><span class="no">ErlDrvSizeT</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="2518234770-12">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-13">{</span><span class="w">
│ │ │ │ +    </span><span class="n">example_data</span><span class="o">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2518234770-14">(</span><span class="n">example_data</span><span class="o">*</span><span class="p" data-group-id="2518234770-14">)</span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="kt">char</span><span class="w"> </span><span class="n">fn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p" data-group-id="2518234770-15">[</span><span class="mi">0</span><span class="p" data-group-id="2518234770-15">]</span><span class="p">,</span><span class="w"> </span><span class="n">arg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p" data-group-id="2518234770-16">[</span><span class="mi">1</span><span class="p" data-group-id="2518234770-16">]</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2518234770-17">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2518234770-17">)</span><span class="w"> </span><span class="p" data-group-id="2518234770-18">{</span><span class="w">
│ │ │ │ +      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="2518234770-19">(</span><span class="n">arg</span><span class="p" data-group-id="2518234770-19">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2518234770-18">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2518234770-20">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2518234770-20">)</span><span class="w"> </span><span class="p" data-group-id="2518234770-21">{</span><span class="w">
│ │ │ │ +      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="2518234770-22">(</span><span class="n">arg</span><span class="p" data-group-id="2518234770-22">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2518234770-21">}</span><span class="w">
│ │ │ │ +    </span><span class="nf">driver_output</span><span class="p" data-group-id="2518234770-23">(</span><span class="n">d</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2518234770-23">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-13">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="no">ErlDrvEntry</span><span class="w"> </span><span class="n">example_driver_entry</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3741884016-24">{</span><span class="w">
│ │ │ │ +</span><span class="no">ErlDrvEntry</span><span class="w"> </span><span class="n">example_driver_entry</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2518234770-24">{</span><span class="w">
│ │ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR init, called when driver is loaded */</span><span class="w">
│ │ │ │      </span><span class="n">example_drv_start</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="cm">/* L_PTR start, called when port is opened */</span><span class="w">
│ │ │ │      </span><span class="n">example_drv_stop</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR stop, called when port is closed */</span><span class="w">
│ │ │ │      </span><span class="n">example_drv_output</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR output, called when erlang has sent */</span><span class="w">
│ │ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR ready_input, called when input descriptor ready */</span><span class="w">
│ │ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR ready_output, called when output descriptor ready */</span><span class="w">
│ │ │ │      </span><span class="s">&quot;example_drv&quot;</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="cm">/* char *driver_name, the argument to open_port */</span><span class="w">
│ │ │ │ @@ -239,35 +239,35 @@
│ │ │ │  				       set to this value */</span><span class="w">
│ │ │ │      </span><span class="mi">0</span><span class="p">,</span><span class="w">                          </span><span class="cm">/* int driver_flags, see documentation */</span><span class="w">
│ │ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* void *handle2, reserved for VM use */</span><span class="w">
│ │ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* F_PTR process_exit, called when a
│ │ │ │  				   monitored process dies */</span><span class="w">
│ │ │ │      </span><span class="no">NULL</span><span class="w">                        </span><span class="cm">/* F_PTR stop_select, called to close an
│ │ │ │  				   event object */</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-24">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-24">}</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="no">DRIVER_INIT</span><span class="p" data-group-id="3741884016-25">(</span><span class="n">example_drv</span><span class="p" data-group-id="3741884016-25">)</span><span class="w"> </span><span class="cm">/* must match name in driver_entry */</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-26">{</span><span class="w">
│ │ │ │ +</span><span class="no">DRIVER_INIT</span><span class="p" data-group-id="2518234770-25">(</span><span class="n">example_drv</span><span class="p" data-group-id="2518234770-25">)</span><span class="w"> </span><span class="cm">/* must match name in driver_entry */</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-26">{</span><span class="w">
│ │ │ │      </span><span class="k">return</span><span class="w"> </span><span class="o">&amp;</span><span class="n">example_driver_entry</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3741884016-26">}</span></code></pre><h2 id="running-the-example" class="section-heading">
│ │ │ │ +</span><span class="p" data-group-id="2518234770-26">}</span></code></pre><h2 id="running-the-example" class="section-heading">
│ │ │ │    <a href="#running-the-example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Running the Example</span>
│ │ │ │  </h2>
│ │ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">unix&gt; gcc -o example_drv.so -fpic -shared complex.c port_driver.c
│ │ │ │  windows&gt; cl -LD -MD -Fe example_drv.dll complex.c port_driver.c</code></pre><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="ss">erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="3786078871-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="3786078871-1">]</span><span class="w"> </span><span class="p" data-group-id="3786078871-2">[</span><span class="ss">source</span><span class="p" data-group-id="3786078871-2">]</span><span class="w"> </span><span class="p" data-group-id="3786078871-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="3786078871-3">]</span><span class="w"> </span><span class="p" data-group-id="3786078871-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="3786078871-4">]</span><span class="w"> </span><span class="p" data-group-id="3786078871-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="3786078871-5">]</span><span class="w"> </span><span class="p" data-group-id="3786078871-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="3786078871-6">]</span><span class="w"> </span><span class="p" data-group-id="3786078871-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="3786078871-7">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="3850581687-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="3850581687-1">]</span><span class="w"> </span><span class="p" data-group-id="3850581687-2">[</span><span class="ss">source</span><span class="p" data-group-id="3850581687-2">]</span><span class="w"> </span><span class="p" data-group-id="3850581687-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="3850581687-3">]</span><span class="w"> </span><span class="p" data-group-id="3850581687-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="3850581687-4">]</span><span class="w"> </span><span class="p" data-group-id="3850581687-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="3850581687-5">]</span><span class="w"> </span><span class="p" data-group-id="3850581687-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="3850581687-6">]</span><span class="w"> </span><span class="p" data-group-id="3850581687-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="3850581687-7">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="3786078871-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="3786078871-9">(</span><span class="p" data-group-id="3786078871-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="3786078871-8">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="3786078871-10">(</span><span class="ss">complex5</span><span class="p" data-group-id="3786078871-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3786078871-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex5</span><span class="p" data-group-id="3786078871-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7953895223-1">(</span><span class="s">&quot;example_drv&quot;</span><span class="p" data-group-id="7953895223-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="3850581687-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="3850581687-9">(</span><span class="p" data-group-id="3850581687-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="3850581687-8">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="3850581687-10">(</span><span class="ss">complex5</span><span class="p" data-group-id="3850581687-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3850581687-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex5</span><span class="p" data-group-id="3850581687-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2446081034-1">(</span><span class="s">&quot;example_drv&quot;</span><span class="p" data-group-id="2446081034-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="7953895223-2">(</span><span class="mi">3</span><span class="p" data-group-id="7953895223-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="2446081034-2">(</span><span class="mi">3</span><span class="p" data-group-id="2446081034-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="7953895223-3">(</span><span class="mi">5</span><span class="p" data-group-id="7953895223-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="2446081034-3">(</span><span class="mi">5</span><span class="p" data-group-id="2446081034-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7953895223-4">(</span><span class="p" data-group-id="7953895223-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="2446081034-4">(</span><span class="p" data-group-id="2446081034-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/c_port.xhtml
│ │ │ │ @@ -53,101 +53,101 @@
│ │ │ │  external program, if it is written properly).</p><p>The port is created using the BIF <a href="../../../lib/../erts/doc/html/erlang.html#open_port/2"><code class="inline">open_port/2</code></a> with
│ │ │ │  <code class="inline">{spawn,ExtPrg}</code> as the first argument. The string <code class="inline">ExtPrg</code> is the name of the
│ │ │ │  external program, including any command line arguments. The second argument is a
│ │ │ │  list of options, in this case only <code class="inline">{packet,2}</code>. This option says that a 2 byte
│ │ │ │  length indicator is to be used to simplify the communication between C and
│ │ │ │  Erlang. The Erlang port automatically adds the length indicator, but this must
│ │ │ │  be done explicitly in the external C program.</p><p>The process is also set to trap exits, which enables detection of failure of the
│ │ │ │ -external program:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6084077173-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="6084077173-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6084077173-2">(</span><span class="p" data-group-id="6084077173-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6084077173-3">]</span><span class="p" data-group-id="6084077173-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +external program:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8726005046-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="8726005046-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8726005046-2">(</span><span class="p" data-group-id="8726005046-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8726005046-3">]</span><span class="p" data-group-id="8726005046-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="6084077173-4">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="6084077173-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">spawn</span><span class="p" data-group-id="6084077173-5">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6084077173-6">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="6084077173-6">]</span><span class="p" data-group-id="6084077173-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8726005046-4">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="8726005046-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">spawn</span><span class="p" data-group-id="8726005046-5">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8726005046-6">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="8726005046-6">]</span><span class="p" data-group-id="8726005046-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6084077173-7">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="6084077173-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">register</span><span class="p" data-group-id="6084077173-8">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6084077173-9">(</span><span class="p" data-group-id="6084077173-9">)</span><span class="p" data-group-id="6084077173-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="nf">process_flag</span><span class="p" data-group-id="6084077173-10">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6084077173-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6084077173-11">(</span><span class="p" data-group-id="6084077173-12">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="6084077173-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6084077173-13">[</span><span class="p" data-group-id="6084077173-14">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6084077173-14">}</span><span class="p" data-group-id="6084077173-13">]</span><span class="p" data-group-id="6084077173-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="nf">loop</span><span class="p" data-group-id="6084077173-15">(</span><span class="n">Port</span><span class="p" data-group-id="6084077173-15">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex1:foo/1</code> and <code class="inline">complex1:bar/1</code> can be implemented. Both send a
│ │ │ │ -message to the <code class="inline">complex</code> process and receive the following replies:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="6889978111-1">(</span><span class="n">X</span><span class="p" data-group-id="6889978111-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">call_port</span><span class="p" data-group-id="6889978111-2">(</span><span class="p" data-group-id="6889978111-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6889978111-3">}</span><span class="p" data-group-id="6889978111-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="6889978111-4">(</span><span class="n">Y</span><span class="p" data-group-id="6889978111-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="nf">call_port</span><span class="p" data-group-id="6889978111-5">(</span><span class="p" data-group-id="6889978111-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6889978111-6">}</span><span class="p" data-group-id="6889978111-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8726005046-7">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="8726005046-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">register</span><span class="p" data-group-id="8726005046-8">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8726005046-9">(</span><span class="p" data-group-id="8726005046-9">)</span><span class="p" data-group-id="8726005046-8">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="nf">process_flag</span><span class="p" data-group-id="8726005046-10">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8726005046-10">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8726005046-11">(</span><span class="p" data-group-id="8726005046-12">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="8726005046-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8726005046-13">[</span><span class="p" data-group-id="8726005046-14">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8726005046-14">}</span><span class="p" data-group-id="8726005046-13">]</span><span class="p" data-group-id="8726005046-11">)</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="nf">loop</span><span class="p" data-group-id="8726005046-15">(</span><span class="n">Port</span><span class="p" data-group-id="8726005046-15">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex1:foo/1</code> and <code class="inline">complex1:bar/1</code> can be implemented. Both send a
│ │ │ │ +message to the <code class="inline">complex</code> process and receive the following replies:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="6378133018-1">(</span><span class="n">X</span><span class="p" data-group-id="6378133018-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">call_port</span><span class="p" data-group-id="6378133018-2">(</span><span class="p" data-group-id="6378133018-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6378133018-3">}</span><span class="p" data-group-id="6378133018-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="6378133018-4">(</span><span class="n">Y</span><span class="p" data-group-id="6378133018-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="nf">call_port</span><span class="p" data-group-id="6378133018-5">(</span><span class="p" data-group-id="6378133018-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="6378133018-6">}</span><span class="p" data-group-id="6378133018-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="6889978111-7">(</span><span class="n">Msg</span><span class="p" data-group-id="6889978111-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -  </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6889978111-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6889978111-9">(</span><span class="p" data-group-id="6889978111-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6889978111-8">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="6378133018-7">(</span><span class="n">Msg</span><span class="p" data-group-id="6378133018-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6378133018-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6378133018-9">(</span><span class="p" data-group-id="6378133018-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6378133018-8">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="6889978111-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6889978111-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6378133018-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="6378133018-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │        </span><span class="n">Result</span><span class="w">
│ │ │ │ -  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process does the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="2037901371-1">(</span><span class="n">Port</span><span class="p" data-group-id="2037901371-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process does the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="0525783338-1">(</span><span class="n">Port</span><span class="p" data-group-id="0525783338-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2037901371-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="2037901371-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -      </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2037901371-3">{</span><span class="nf">self</span><span class="p" data-group-id="2037901371-4">(</span><span class="p" data-group-id="2037901371-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2037901371-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="2037901371-6">(</span><span class="n">Msg</span><span class="p" data-group-id="2037901371-6">)</span><span class="p" data-group-id="2037901371-5">}</span><span class="p" data-group-id="2037901371-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0525783338-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="0525783338-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +      </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0525783338-3">{</span><span class="nf">self</span><span class="p" data-group-id="0525783338-4">(</span><span class="p" data-group-id="0525783338-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0525783338-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="0525783338-6">(</span><span class="n">Msg</span><span class="p" data-group-id="0525783338-6">)</span><span class="p" data-group-id="0525783338-5">}</span><span class="p" data-group-id="0525783338-3">}</span><span class="p">,</span><span class="w">
│ │ │ │        </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="2037901371-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2037901371-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2037901371-8">}</span><span class="p" data-group-id="2037901371-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -          </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2037901371-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="2037901371-10">(</span><span class="n">Data</span><span class="p" data-group-id="2037901371-10">)</span><span class="p" data-group-id="2037901371-9">}</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="0525783338-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0525783338-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0525783338-8">}</span><span class="p" data-group-id="0525783338-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +          </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0525783338-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="0525783338-10">(</span><span class="n">Data</span><span class="p" data-group-id="0525783338-10">)</span><span class="p" data-group-id="0525783338-9">}</span><span class="w">
│ │ │ │        </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -      </span><span class="nf">loop</span><span class="p" data-group-id="2037901371-11">(</span><span class="n">Port</span><span class="p" data-group-id="2037901371-11">)</span><span class="w">
│ │ │ │ +      </span><span class="nf">loop</span><span class="p" data-group-id="0525783338-11">(</span><span class="n">Port</span><span class="p" data-group-id="0525783338-11">)</span><span class="w">
│ │ │ │    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Assuming that both the arguments and the results from the C functions are less
│ │ │ │  than 256, a simple encoding/decoding scheme is employed. In this scheme, <code class="inline">foo</code>
│ │ │ │  is represented by byte 1, <code class="inline">bar</code> is represented by 2, and the argument/result is
│ │ │ │ -represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="8368301940-1">(</span><span class="p" data-group-id="8368301940-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8368301940-2">}</span><span class="p" data-group-id="8368301940-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8368301940-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8368301940-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="8368301940-4">(</span><span class="p" data-group-id="8368301940-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8368301940-5">}</span><span class="p" data-group-id="8368301940-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8368301940-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8368301940-6">]</span><span class="p">.</span><span class="w">
│ │ │ │ +represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="2794700044-1">(</span><span class="p" data-group-id="2794700044-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2794700044-2">}</span><span class="p" data-group-id="2794700044-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2794700044-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2794700044-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="2794700044-4">(</span><span class="p" data-group-id="2794700044-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2794700044-5">}</span><span class="p" data-group-id="2794700044-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2794700044-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2794700044-6">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="8368301940-7">(</span><span class="p" data-group-id="8368301940-8">[</span><span class="n">Int</span><span class="p" data-group-id="8368301940-8">]</span><span class="p" data-group-id="8368301940-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functionality for stopping the port and
│ │ │ │ -detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2858926599-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="2858926599-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2858926599-2">(</span><span class="p" data-group-id="2858926599-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2858926599-3">]</span><span class="p" data-group-id="2858926599-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2858926599-4">(</span><span class="p" data-group-id="2858926599-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2858926599-5">]</span><span class="p" data-group-id="2858926599-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ -
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2858926599-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="2858926599-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2858926599-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2858926599-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="2858926599-8">]</span><span class="p" data-group-id="2858926599-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="2858926599-9">(</span><span class="p" data-group-id="2858926599-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="2794700044-7">(</span><span class="p" data-group-id="2794700044-8">[</span><span class="n">Int</span><span class="p" data-group-id="2794700044-8">]</span><span class="p" data-group-id="2794700044-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functionality for stopping the port and
│ │ │ │ +detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4539851343-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="4539851343-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4539851343-2">(</span><span class="p" data-group-id="4539851343-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4539851343-3">]</span><span class="p" data-group-id="4539851343-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4539851343-4">(</span><span class="p" data-group-id="4539851343-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4539851343-5">]</span><span class="p" data-group-id="4539851343-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="4539851343-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="4539851343-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="4539851343-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4539851343-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="4539851343-8">]</span><span class="p" data-group-id="4539851343-7">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="4539851343-9">(</span><span class="p" data-group-id="4539851343-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="2858926599-10">(</span><span class="n">X</span><span class="p" data-group-id="2858926599-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="2858926599-11">(</span><span class="p" data-group-id="2858926599-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2858926599-12">}</span><span class="p" data-group-id="2858926599-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="2858926599-13">(</span><span class="n">Y</span><span class="p" data-group-id="2858926599-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="2858926599-14">(</span><span class="p" data-group-id="2858926599-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2858926599-15">}</span><span class="p" data-group-id="2858926599-14">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="4539851343-10">(</span><span class="n">X</span><span class="p" data-group-id="4539851343-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="4539851343-11">(</span><span class="p" data-group-id="4539851343-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4539851343-12">}</span><span class="p" data-group-id="4539851343-11">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="4539851343-13">(</span><span class="n">Y</span><span class="p" data-group-id="4539851343-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="4539851343-14">(</span><span class="p" data-group-id="4539851343-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4539851343-15">}</span><span class="p" data-group-id="4539851343-14">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="2858926599-16">(</span><span class="n">Msg</span><span class="p" data-group-id="2858926599-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2858926599-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2858926599-18">(</span><span class="p" data-group-id="2858926599-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="2858926599-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="4539851343-16">(</span><span class="n">Msg</span><span class="p" data-group-id="4539851343-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4539851343-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4539851343-18">(</span><span class="p" data-group-id="4539851343-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4539851343-17">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="2858926599-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2858926599-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="4539851343-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="4539851343-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="2858926599-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="2858926599-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="2858926599-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2858926599-22">(</span><span class="p" data-group-id="2858926599-22">)</span><span class="p" data-group-id="2858926599-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="2858926599-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2858926599-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="2858926599-24">(</span><span class="p" data-group-id="2858926599-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="2858926599-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2858926599-26">[</span><span class="p" data-group-id="2858926599-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2858926599-27">}</span><span class="p" data-group-id="2858926599-26">]</span><span class="p" data-group-id="2858926599-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="2858926599-28">(</span><span class="n">Port</span><span class="p" data-group-id="2858926599-28">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4539851343-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="4539851343-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="4539851343-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4539851343-22">(</span><span class="p" data-group-id="4539851343-22">)</span><span class="p" data-group-id="4539851343-21">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="4539851343-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4539851343-23">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="4539851343-24">(</span><span class="p" data-group-id="4539851343-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="4539851343-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4539851343-26">[</span><span class="p" data-group-id="4539851343-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4539851343-27">}</span><span class="p" data-group-id="4539851343-26">]</span><span class="p" data-group-id="4539851343-24">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="4539851343-28">(</span><span class="n">Port</span><span class="p" data-group-id="4539851343-28">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="2858926599-29">(</span><span class="n">Port</span><span class="p" data-group-id="2858926599-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="4539851343-29">(</span><span class="n">Port</span><span class="p" data-group-id="4539851343-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="2858926599-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="2858926599-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2858926599-31">{</span><span class="nf">self</span><span class="p" data-group-id="2858926599-32">(</span><span class="p" data-group-id="2858926599-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2858926599-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="2858926599-34">(</span><span class="n">Msg</span><span class="p" data-group-id="2858926599-34">)</span><span class="p" data-group-id="2858926599-33">}</span><span class="p" data-group-id="2858926599-31">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="4539851343-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4539851343-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4539851343-31">{</span><span class="nf">self</span><span class="p" data-group-id="4539851343-32">(</span><span class="p" data-group-id="4539851343-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4539851343-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="4539851343-34">(</span><span class="n">Msg</span><span class="p" data-group-id="4539851343-34">)</span><span class="p" data-group-id="4539851343-33">}</span><span class="p" data-group-id="4539851343-31">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="2858926599-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2858926599-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2858926599-36">}</span><span class="p" data-group-id="2858926599-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2858926599-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="2858926599-38">(</span><span class="n">Data</span><span class="p" data-group-id="2858926599-38">)</span><span class="p" data-group-id="2858926599-37">}</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="4539851343-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4539851343-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4539851343-36">}</span><span class="p" data-group-id="4539851343-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4539851343-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="4539851343-38">(</span><span class="n">Data</span><span class="p" data-group-id="4539851343-38">)</span><span class="p" data-group-id="4539851343-37">}</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="2858926599-39">(</span><span class="n">Port</span><span class="p" data-group-id="2858926599-39">)</span><span class="p">;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="4539851343-39">(</span><span class="n">Port</span><span class="p" data-group-id="4539851343-39">)</span><span class="p">;</span><span class="w">
│ │ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2858926599-40">{</span><span class="nf">self</span><span class="p" data-group-id="2858926599-41">(</span><span class="p" data-group-id="2858926599-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="2858926599-40">}</span><span class="p">,</span><span class="w">
│ │ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4539851343-40">{</span><span class="nf">self</span><span class="p" data-group-id="4539851343-41">(</span><span class="p" data-group-id="4539851343-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="4539851343-40">}</span><span class="p">,</span><span class="w">
│ │ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ │ -		</span><span class="p" data-group-id="2858926599-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="2858926599-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="2858926599-43">(</span><span class="ss">normal</span><span class="p" data-group-id="2858926599-43">)</span><span class="w">
│ │ │ │ +		</span><span class="p" data-group-id="4539851343-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="4539851343-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="4539851343-43">(</span><span class="ss">normal</span><span class="p" data-group-id="4539851343-43">)</span><span class="w">
│ │ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ │ -	</span><span class="p" data-group-id="2858926599-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="2858926599-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="2858926599-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="2858926599-45">)</span><span class="w">
│ │ │ │ +	</span><span class="p" data-group-id="4539851343-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="4539851343-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="4539851343-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="4539851343-45">)</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="2858926599-46">(</span><span class="p" data-group-id="2858926599-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2858926599-47">}</span><span class="p" data-group-id="2858926599-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2858926599-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2858926599-48">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="2858926599-49">(</span><span class="p" data-group-id="2858926599-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2858926599-50">}</span><span class="p" data-group-id="2858926599-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2858926599-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2858926599-51">]</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="4539851343-46">(</span><span class="p" data-group-id="4539851343-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4539851343-47">}</span><span class="p" data-group-id="4539851343-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4539851343-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4539851343-48">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="4539851343-49">(</span><span class="p" data-group-id="4539851343-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4539851343-50">}</span><span class="p" data-group-id="4539851343-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4539851343-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4539851343-51">]</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="2858926599-52">(</span><span class="p" data-group-id="2858926599-53">[</span><span class="n">Int</span><span class="p" data-group-id="2858926599-53">]</span><span class="p" data-group-id="2858926599-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-program" class="section-heading">
│ │ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="4539851343-52">(</span><span class="p" data-group-id="4539851343-53">[</span><span class="n">Int</span><span class="p" data-group-id="4539851343-53">]</span><span class="p" data-group-id="4539851343-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-program" class="section-heading">
│ │ │ │    <a href="#c-program" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">C Program</span>
│ │ │ │  </h2>
│ │ │ │  <p>On the C side, it is necessary to write functions for receiving and sending data
│ │ │ │  with 2 byte length indicators from/to Erlang. By default, the C program is to
│ │ │ │ @@ -156,104 +156,104 @@
│ │ │ │  follows:</p><pre><code class="makeup c" translate="no"><span class="cm">/* erl_comm.c */</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdio</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">unistd</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="kt">byte</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="2051177382-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="2051177382-1">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2051177382-2">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="5705818222-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="5705818222-1">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5705818222-2">{</span><span class="w">
│ │ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">got</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="2051177382-3">{</span><span class="w">
│ │ │ │ -      </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2051177382-4">(</span><span class="p" data-group-id="2051177382-5">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read</span><span class="p" data-group-id="2051177382-6">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">got</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">got</span><span class="p" data-group-id="2051177382-6">)</span><span class="p" data-group-id="2051177382-5">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2051177382-4">)</span><span class="p" data-group-id="2051177382-7">{</span><span class="w">
│ │ │ │ -          </span><span class="nf">return</span><span class="p" data-group-id="2051177382-8">(</span><span class="n">i</span><span class="p" data-group-id="2051177382-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ -      </span><span class="p" data-group-id="2051177382-7">}</span><span class="w">
│ │ │ │ +  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="5705818222-3">{</span><span class="w">
│ │ │ │ +      </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5705818222-4">(</span><span class="p" data-group-id="5705818222-5">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read</span><span class="p" data-group-id="5705818222-6">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">got</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">got</span><span class="p" data-group-id="5705818222-6">)</span><span class="p" data-group-id="5705818222-5">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5705818222-4">)</span><span class="p" data-group-id="5705818222-7">{</span><span class="w">
│ │ │ │ +          </span><span class="nf">return</span><span class="p" data-group-id="5705818222-8">(</span><span class="n">i</span><span class="p" data-group-id="5705818222-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +      </span><span class="p" data-group-id="5705818222-7">}</span><span class="w">
│ │ │ │      </span><span class="n">got</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2051177382-3">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="2051177382-9">(</span><span class="n">got</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="2051177382-9">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5705818222-3">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="5705818222-9">(</span><span class="n">got</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="5705818222-9">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="nf">return</span><span class="p" data-group-id="2051177382-10">(</span><span class="n">len</span><span class="p" data-group-id="2051177382-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2051177382-2">}</span><span class="w">
│ │ │ │ +  </span><span class="nf">return</span><span class="p" data-group-id="5705818222-10">(</span><span class="n">len</span><span class="p" data-group-id="5705818222-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5705818222-2">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="2051177382-11">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="2051177382-11">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2051177382-12">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="5705818222-11">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="5705818222-11">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5705818222-12">{</span><span class="w">
│ │ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">wrote</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="2051177382-13">{</span><span class="w">
│ │ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2051177382-14">(</span><span class="p" data-group-id="2051177382-15">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">write</span><span class="p" data-group-id="2051177382-16">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">wrote</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">wrote</span><span class="p" data-group-id="2051177382-16">)</span><span class="p" data-group-id="2051177382-15">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2051177382-14">)</span><span class="w">
│ │ │ │ -      </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="2051177382-17">(</span><span class="n">i</span><span class="p" data-group-id="2051177382-17">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="5705818222-13">{</span><span class="w">
│ │ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5705818222-14">(</span><span class="p" data-group-id="5705818222-15">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">write</span><span class="p" data-group-id="5705818222-16">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">wrote</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">wrote</span><span class="p" data-group-id="5705818222-16">)</span><span class="p" data-group-id="5705818222-15">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5705818222-14">)</span><span class="w">
│ │ │ │ +      </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="5705818222-17">(</span><span class="n">i</span><span class="p" data-group-id="5705818222-17">)</span><span class="p">;</span><span class="w">
│ │ │ │      </span><span class="n">wrote</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2051177382-13">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="2051177382-18">(</span><span class="n">wrote</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="2051177382-18">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5705818222-13">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="5705818222-18">(</span><span class="n">wrote</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="5705818222-18">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="2051177382-19">(</span><span class="n">len</span><span class="p" data-group-id="2051177382-19">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2051177382-12">}</span><span class="w">
│ │ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="5705818222-19">(</span><span class="n">len</span><span class="p" data-group-id="5705818222-19">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5705818222-12">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="2051177382-20">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="2051177382-20">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2051177382-21">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="5705818222-20">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="5705818222-20">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5705818222-21">{</span><span class="w">
│ │ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2051177382-22">(</span><span class="nf">read_exact</span><span class="p" data-group-id="2051177382-23">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2051177382-23">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2051177382-22">)</span><span class="w">
│ │ │ │ -    </span><span class="nf">return</span><span class="p" data-group-id="2051177382-24">(</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="2051177382-24">)</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="n">len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2051177382-25">(</span><span class="n">buf</span><span class="p" data-group-id="2051177382-26">[</span><span class="mi">0</span><span class="p" data-group-id="2051177382-26">]</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="2051177382-25">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="2051177382-27">[</span><span class="mi">1</span><span class="p" data-group-id="2051177382-27">]</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="2051177382-28">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="2051177382-28">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2051177382-21">}</span><span class="w">
│ │ │ │ +  </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5705818222-22">(</span><span class="nf">read_exact</span><span class="p" data-group-id="5705818222-23">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5705818222-23">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5705818222-22">)</span><span class="w">
│ │ │ │ +    </span><span class="nf">return</span><span class="p" data-group-id="5705818222-24">(</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5705818222-24">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="n">len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5705818222-25">(</span><span class="n">buf</span><span class="p" data-group-id="5705818222-26">[</span><span class="mi">0</span><span class="p" data-group-id="5705818222-26">]</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="5705818222-25">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="5705818222-27">[</span><span class="mi">1</span><span class="p" data-group-id="5705818222-27">]</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="5705818222-28">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="5705818222-28">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5705818222-21">}</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="2051177382-29">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="2051177382-29">)</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2051177382-30">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="5705818222-29">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="5705818222-29">)</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5705818222-30">{</span><span class="w">
│ │ │ │    </span><span class="kt">byte</span><span class="w"> </span><span class="n">li</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2051177382-31">(</span><span class="n">len</span><span class="w"> </span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="2051177382-31">)</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="nf">write_exact</span><span class="p" data-group-id="2051177382-32">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2051177382-32">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5705818222-31">(</span><span class="n">len</span><span class="w"> </span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="5705818222-31">)</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="nf">write_exact</span><span class="p" data-group-id="5705818222-32">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5705818222-32">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │    </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">len</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="nf">write_exact</span><span class="p" data-group-id="2051177382-33">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2051177382-33">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="nf">write_exact</span><span class="p" data-group-id="5705818222-33">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5705818222-33">)</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="2051177382-34">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="2051177382-34">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2051177382-30">}</span></code></pre><p>Notice that <code class="inline">stdin</code> and <code class="inline">stdout</code> are for buffered input/output and must <em>not</em> be
│ │ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="5705818222-34">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="5705818222-34">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5705818222-30">}</span></code></pre><p>Notice that <code class="inline">stdin</code> and <code class="inline">stdout</code> are for buffered input/output and must <em>not</em> be
│ │ │ │  used for the communication with Erlang.</p><p>In the <code class="inline">main</code> function, the C program is to listen for a message from Erlang
│ │ │ │  and, according to the selected encoding/decoding scheme, use the first byte to
│ │ │ │  determine which function to call and the second byte as argument to the
│ │ │ │  function. The result of calling the function is then to be sent back to Erlang:</p><pre><code class="makeup c" translate="no"><span class="cm">/* port.c */</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="kt">byte</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p" data-group-id="2785450579-1">(</span><span class="p" data-group-id="2785450579-1">)</span><span class="w"> </span><span class="p" data-group-id="2785450579-2">{</span><span class="w">
│ │ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p" data-group-id="5226035602-1">(</span><span class="p" data-group-id="5226035602-1">)</span><span class="w"> </span><span class="p" data-group-id="5226035602-2">{</span><span class="w">
│ │ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">fn</span><span class="p">,</span><span class="w"> </span><span class="n">arg</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="kt">byte</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="2785450579-3">[</span><span class="mi">100</span><span class="p" data-group-id="2785450579-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="kt">byte</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="5226035602-3">[</span><span class="mi">100</span><span class="p" data-group-id="5226035602-3">]</span><span class="p">;</span><span class="w">
│ │ │ │  
│ │ │ │ -  </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="2785450579-4">(</span><span class="nf">read_cmd</span><span class="p" data-group-id="2785450579-5">(</span><span class="n">buf</span><span class="p" data-group-id="2785450579-5">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2785450579-4">)</span><span class="w"> </span><span class="p" data-group-id="2785450579-6">{</span><span class="w">
│ │ │ │ -    </span><span class="n">fn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="2785450579-7">[</span><span class="mi">0</span><span class="p" data-group-id="2785450579-7">]</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="n">arg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="2785450579-8">[</span><span class="mi">1</span><span class="p" data-group-id="2785450579-8">]</span><span class="p">;</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2785450579-9">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2785450579-9">)</span><span class="w"> </span><span class="p" data-group-id="2785450579-10">{</span><span class="w">
│ │ │ │ -      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="2785450579-11">(</span><span class="n">arg</span><span class="p" data-group-id="2785450579-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2785450579-10">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2785450579-12">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2785450579-12">)</span><span class="w"> </span><span class="p" data-group-id="2785450579-13">{</span><span class="w">
│ │ │ │ -      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="2785450579-14">(</span><span class="n">arg</span><span class="p" data-group-id="2785450579-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2785450579-13">}</span><span class="w">
│ │ │ │ -
│ │ │ │ -    </span><span class="n">buf</span><span class="p" data-group-id="2785450579-15">[</span><span class="mi">0</span><span class="p" data-group-id="2785450579-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ │ -    </span><span class="nf">write_cmd</span><span class="p" data-group-id="2785450579-16">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2785450579-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2785450579-6">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2785450579-2">}</span></code></pre><p>Notice that the C program is in a <code class="inline">while</code>-loop, checking for the return value
│ │ │ │ +  </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="5226035602-4">(</span><span class="nf">read_cmd</span><span class="p" data-group-id="5226035602-5">(</span><span class="n">buf</span><span class="p" data-group-id="5226035602-5">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5226035602-4">)</span><span class="w"> </span><span class="p" data-group-id="5226035602-6">{</span><span class="w">
│ │ │ │ +    </span><span class="n">fn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="5226035602-7">[</span><span class="mi">0</span><span class="p" data-group-id="5226035602-7">]</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="n">arg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="5226035602-8">[</span><span class="mi">1</span><span class="p" data-group-id="5226035602-8">]</span><span class="p">;</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5226035602-9">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5226035602-9">)</span><span class="w"> </span><span class="p" data-group-id="5226035602-10">{</span><span class="w">
│ │ │ │ +      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="5226035602-11">(</span><span class="n">arg</span><span class="p" data-group-id="5226035602-11">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5226035602-10">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5226035602-12">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5226035602-12">)</span><span class="w"> </span><span class="p" data-group-id="5226035602-13">{</span><span class="w">
│ │ │ │ +      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="5226035602-14">(</span><span class="n">arg</span><span class="p" data-group-id="5226035602-14">)</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5226035602-13">}</span><span class="w">
│ │ │ │ +
│ │ │ │ +    </span><span class="n">buf</span><span class="p" data-group-id="5226035602-15">[</span><span class="mi">0</span><span class="p" data-group-id="5226035602-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ │ +    </span><span class="nf">write_cmd</span><span class="p" data-group-id="5226035602-16">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5226035602-16">)</span><span class="p">;</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="5226035602-6">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5226035602-2">}</span></code></pre><p>Notice that the C program is in a <code class="inline">while</code>-loop, checking for the return value
│ │ │ │  of <code class="inline">read_cmd/1</code>. This is because the C program must detect when the port closes
│ │ │ │  and terminates.</p><h2 id="running-the-example" class="section-heading">
│ │ │ │    <a href="#running-the-example" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Running the Example</span>
│ │ │ │  </h2>
│ │ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">$ gcc -o extprg complex.c erl_comm.c port.c</code></pre><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$ </span><span class="ss">erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="2089608378-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="2089608378-1">]</span><span class="w"> </span><span class="p" data-group-id="2089608378-2">[</span><span class="ss">source</span><span class="p" data-group-id="2089608378-2">]</span><span class="w"> </span><span class="p" data-group-id="2089608378-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="2089608378-3">]</span><span class="w"> </span><span class="p" data-group-id="2089608378-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="2089608378-4">]</span><span class="w"> </span><span class="p" data-group-id="2089608378-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="2089608378-5">]</span><span class="w"> </span><span class="p" data-group-id="2089608378-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2089608378-6">]</span><span class="w"> </span><span class="p" data-group-id="2089608378-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="2089608378-7">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="4780372330-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="4780372330-1">]</span><span class="w"> </span><span class="p" data-group-id="4780372330-2">[</span><span class="ss">source</span><span class="p" data-group-id="4780372330-2">]</span><span class="w"> </span><span class="p" data-group-id="4780372330-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4780372330-3">]</span><span class="w"> </span><span class="p" data-group-id="4780372330-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4780372330-4">]</span><span class="w"> </span><span class="p" data-group-id="4780372330-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4780372330-5">]</span><span class="w"> </span><span class="p" data-group-id="4780372330-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4780372330-6">]</span><span class="w"> </span><span class="p" data-group-id="4780372330-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="4780372330-7">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="2089608378-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="2089608378-9">(</span><span class="p" data-group-id="2089608378-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="2089608378-8">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="2089608378-10">(</span><span class="ss">complex1</span><span class="p" data-group-id="2089608378-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2089608378-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex1</span><span class="p" data-group-id="2089608378-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4004859301-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="4004859301-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="4780372330-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4780372330-9">(</span><span class="p" data-group-id="4780372330-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4780372330-8">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="4780372330-10">(</span><span class="ss">complex1</span><span class="p" data-group-id="4780372330-10">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4780372330-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex1</span><span class="p" data-group-id="4780372330-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8701903357-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="8701903357-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="4004859301-2">(</span><span class="mi">3</span><span class="p" data-group-id="4004859301-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="8701903357-2">(</span><span class="mi">3</span><span class="p" data-group-id="8701903357-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="4004859301-3">(</span><span class="mi">5</span><span class="p" data-group-id="4004859301-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="8701903357-3">(</span><span class="mi">5</span><span class="p" data-group-id="8701903357-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="mi">10</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="4004859301-4">(</span><span class="p" data-group-id="4004859301-4">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="8701903357-4">(</span><span class="p" data-group-id="8701903357-4">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/bit_syntax.xhtml
│ │ │ │ @@ -24,48 +24,48 @@
│ │ │ │    <a href="#introduction" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Introduction</span>
│ │ │ │  </h2>
│ │ │ │  <p>The complete specification for the bit syntax appears in the
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml#bit-syntax-expressions">Reference Manual</a>.</p><p>In Erlang, a Bin is used for constructing binaries and matching binary patterns.
│ │ │ │ -A Bin is written with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4750957405-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="4750957405-1">&gt;&gt;</span></code></pre><p>A Bin is a low-level sequence of bits or bytes. The purpose of a Bin is to
│ │ │ │ -enable construction of binaries:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8586007199-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="8586007199-1">&gt;&gt;</span></code></pre><p>All elements must be bound. Or match a binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9285548901-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="9285548901-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span></code></pre><p>Here, <code class="inline">Bin</code> is bound and the elements are bound or unbound, as in any match.</p><p>A Bin does not need to consist of a whole number of bytes.</p><p>A <em>bitstring</em> is a sequence of zero or more bits, where the number of bits does
│ │ │ │ +A Bin is written with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1820297904-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="1820297904-1">&gt;&gt;</span></code></pre><p>A Bin is a low-level sequence of bits or bytes. The purpose of a Bin is to
│ │ │ │ +enable construction of binaries:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3736080189-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="3736080189-1">&gt;&gt;</span></code></pre><p>All elements must be bound. Or match a binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3404813881-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="3404813881-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span></code></pre><p>Here, <code class="inline">Bin</code> is bound and the elements are bound or unbound, as in any match.</p><p>A Bin does not need to consist of a whole number of bytes.</p><p>A <em>bitstring</em> is a sequence of zero or more bits, where the number of bits does
│ │ │ │  not need to be divisible by 8. If the number of bits is divisible by 8, the
│ │ │ │  bitstring is also a binary.</p><p>Each element specifies a certain <em>segment</em> of the bitstring. A segment is a set
│ │ │ │  of contiguous bits of the binary (not necessarily on a byte boundary). The first
│ │ │ │  element specifies the initial segment, the second element specifies the
│ │ │ │  following segment, and so on.</p><p>The following examples illustrate how binaries are constructed, or matched, and
│ │ │ │  how elements and tails are specified.</p><h3 id="examples" class="section-heading">
│ │ │ │    <a href="#examples" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Examples</span>
│ │ │ │  </h3>
│ │ │ │  <p><em>Example 1:</em> A binary can be constructed from a set of constants or a string
│ │ │ │ -literal:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin11</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2215147810-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="2215147810-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Bin12</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2215147810-2">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="2215147810-2">&gt;&gt;</span></code></pre><p>This gives two binaries of size 3, with the following evaluations:</p><ul><li><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin11)</code></a> evaluates to <code class="inline">[1, 17, 42]</code>.</li><li><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin12)</code></a> evaluates to <code class="inline">[97, 98, 99]</code>.</li></ul><p><em>Example 2:</em>Similarly, a binary can be constructed from a set of bound
│ │ │ │ +literal:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin11</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6031859438-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="6031859438-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Bin12</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6031859438-2">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6031859438-2">&gt;&gt;</span></code></pre><p>This gives two binaries of size 3, with the following evaluations:</p><ul><li><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin11)</code></a> evaluates to <code class="inline">[1, 17, 42]</code>.</li><li><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin12)</code></a> evaluates to <code class="inline">[97, 98, 99]</code>.</li></ul><p><em>Example 2:</em>Similarly, a binary can be constructed from a set of bound
│ │ │ │  variables:</p><pre><code class="makeup erlang" translate="no"><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4034707666-1">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="4034707666-1">&gt;&gt;</span></code></pre><p>This gives a binary of size 4. Here, a <em>size expression</em> is used for the
│ │ │ │ +</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6864894005-1">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6864894005-1">&gt;&gt;</span></code></pre><p>This gives a binary of size 4. Here, a <em>size expression</em> is used for the
│ │ │ │  variable <code class="inline">C</code> to specify a 16-bits segment of <code class="inline">Bin2</code>.</p><p><a href="../../../lib/../erts/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin2)</code></a> evaluates to <code class="inline">[1, 17, 00, 42]</code>.</p><p><em>Example 3:</em> A Bin can also be used for matching. <code class="inline">D</code>, <code class="inline">E</code>, and <code class="inline">F</code> are unbound
│ │ │ │ -variables, and <code class="inline">Bin2</code> is bound, as in Example 2:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5822973045-1">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5822973045-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin2</span></code></pre><p>This gives <code class="inline">D = 273</code>, <code class="inline">E = 00</code>, and F binds to a binary of size 1:
│ │ │ │ +variables, and <code class="inline">Bin2</code> is bound, as in Example 2:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3454186481-1">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3454186481-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin2</span></code></pre><p>This gives <code class="inline">D = 273</code>, <code class="inline">E = 00</code>, and F binds to a binary of size 1:
│ │ │ │  <code class="inline">binary_to_list(F) = [42]</code>.</p><p><em>Example 4:</em> The following is a more elaborate example of matching. Here,
│ │ │ │  <code class="inline">Dgram</code> is bound to the consecutive bytes of an IP datagram of IP protocol
│ │ │ │ -version 4. The ambition is to extract the header and the data of the datagram:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1925299699-1">(</span><span class="n">IP_VERSION</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1925299699-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1925299699-2">(</span><span class="n">IP_MIN_HDR_LEN</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="1925299699-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +version 4. The ambition is to extract the header and the data of the datagram:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2438244814-1">(</span><span class="n">IP_VERSION</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="2438244814-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2438244814-2">(</span><span class="n">IP_MIN_HDR_LEN</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="2438244814-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">DgramSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="1925299699-3">(</span><span class="n">Dgram</span><span class="p" data-group-id="1925299699-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">DgramSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="2438244814-3">(</span><span class="n">Dgram</span><span class="p" data-group-id="2438244814-3">)</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="k">case</span><span class="w"> </span><span class="n">Dgram</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1925299699-4">&lt;&lt;</span><span class="o">?</span><span class="n">IP_VERSION</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">HLen</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">SrvcType</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">TotLen</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2438244814-4">&lt;&lt;</span><span class="o">?</span><span class="n">IP_VERSION</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">HLen</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">SrvcType</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">TotLen</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │ │        </span><span class="n">ID</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">Flgs</span><span class="p">:</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">FragOff</span><span class="p">:</span><span class="mi">13</span><span class="p">,</span><span class="w">
│ │ │ │        </span><span class="n">TTL</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">Proto</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">HdrChkSum</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │ │        </span><span class="n">SrcIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w">
│ │ │ │ -      </span><span class="n">DestIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w"> </span><span class="n">RestDgram</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1925299699-4">&gt;&gt;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">HLen</span><span class="o">&gt;=</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="n">HLen</span><span class="o">=&lt;</span><span class="n">DgramSize</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -        </span><span class="n">OptsLen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="p" data-group-id="1925299699-5">(</span><span class="n">HLen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">?</span><span class="n">IP_MIN_HDR_LEN</span><span class="p" data-group-id="1925299699-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="1925299699-6">&lt;&lt;</span><span class="n">Opts</span><span class="p">:</span><span class="n">OptsLen</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Data</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1925299699-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RestDgram</span><span class="p">,</span><span class="w">
│ │ │ │ +      </span><span class="n">DestIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w"> </span><span class="n">RestDgram</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2438244814-4">&gt;&gt;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">HLen</span><span class="o">&gt;=</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="n">HLen</span><span class="o">=&lt;</span><span class="n">DgramSize</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="n">OptsLen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="p" data-group-id="2438244814-5">(</span><span class="n">HLen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">?</span><span class="n">IP_MIN_HDR_LEN</span><span class="p" data-group-id="2438244814-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="2438244814-6">&lt;&lt;</span><span class="n">Opts</span><span class="p">:</span><span class="n">OptsLen</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Data</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2438244814-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RestDgram</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>Here, the segment corresponding to the <code class="inline">Opts</code> variable has a <em>type modifier</em>,
│ │ │ │  specifying that <code class="inline">Opts</code> is to bind to a binary. All other variables have the
│ │ │ │  default type equal to unsigned integer.</p><p>An IP datagram header is of variable length. This length is measured in the
│ │ │ │  number of 32-bit words and is given in the segment corresponding to <code class="inline">HLen</code>. The
│ │ │ │  minimum value of <code class="inline">HLen</code> is 5. It is the segment corresponding to <code class="inline">Opts</code> that is
│ │ │ │  variable, so if <code class="inline">HLen</code> is equal to 5, <code class="inline">Opts</code> becomes an empty binary.</p><p>The tail variables <code class="inline">RestDgram</code> and <code class="inline">Data</code> bind to binaries, as all tail
│ │ │ │ @@ -123,77 +123,77 @@
│ │ │ │  <p>This section describes the rules for constructing binaries using the bit syntax.
│ │ │ │  Unlike when constructing lists or tuples, the construction of a binary can fail
│ │ │ │  with a <code class="inline">badarg</code> exception.</p><p>There can be zero or more segments in a binary to be constructed. The expression
│ │ │ │  <code class="inline">&lt;&lt;&gt;&gt;</code> constructs a zero length binary.</p><p>Each segment in a binary can consist of zero or more bits. There are no
│ │ │ │  alignment rules for individual segments of type <code class="inline">integer</code> and <code class="inline">float</code>. For
│ │ │ │  binaries and bitstrings without size, the unit specifies the alignment. Since
│ │ │ │  the default alignment for the <code class="inline">binary</code> type is 8, the size of a binary segment
│ │ │ │ -must be a multiple of 8 bits, that is, only whole bytes.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9917889013-1">&lt;&lt;</span><span class="n">Bin</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Bitstring</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="9917889013-1">&gt;&gt;</span></code></pre><p>The variable <code class="inline">Bin</code> must contain a whole number of bytes, because the <code class="inline">binary</code>
│ │ │ │ +must be a multiple of 8 bits, that is, only whole bytes.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3547313259-1">&lt;&lt;</span><span class="n">Bin</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Bitstring</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="3547313259-1">&gt;&gt;</span></code></pre><p>The variable <code class="inline">Bin</code> must contain a whole number of bytes, because the <code class="inline">binary</code>
│ │ │ │  type defaults to <code class="inline">unit:8</code>. A <code class="inline">badarg</code> exception is generated if <code class="inline">Bin</code> consist
│ │ │ │  of, for example, 17 bits.</p><p>The <code class="inline">Bitstring</code> variable can consist of any number of bits, for example, 0, 1,
│ │ │ │  8, 11, 17, 42, and so on. This is because the default <code class="inline">unit</code> for bitstrings
│ │ │ │  is 1.</p><p>For clarity, it is recommended not to change the unit size for binaries.
│ │ │ │  Instead, use <code class="inline">binary</code> when you need byte alignment and <code class="inline">bitstring</code> when you need
│ │ │ │  bit alignment.</p><p>The following example successfully constructs a bitstring of 7 bits, provided
│ │ │ │ -that all of X and Y are integers:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9421789342-1">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">6</span><span class="p" data-group-id="9421789342-1">&gt;&gt;</span></code></pre><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When constructing binaries, <code class="inline">Value</code> and <code class="inline">Size</code> can be any Erlang expression.
│ │ │ │ +that all of X and Y are integers:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9745463476-1">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">6</span><span class="p" data-group-id="9745463476-1">&gt;&gt;</span></code></pre><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When constructing binaries, <code class="inline">Value</code> and <code class="inline">Size</code> can be any Erlang expression.
│ │ │ │  However, for syntactical reasons, both <code class="inline">Value</code> and <code class="inline">Size</code> must be enclosed in
│ │ │ │  parenthesis if the expression consists of anything more than a single literal or
│ │ │ │ -a variable. The following gives a compiler syntax error:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4334255994-1">&lt;&lt;</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4334255994-1">&gt;&gt;</span></code></pre><p>This expression must be rewritten into the following, to be accepted by the
│ │ │ │ -compiler:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8605793511-1">&lt;&lt;</span><span class="p" data-group-id="8605793511-2">(</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="8605793511-2">)</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="8605793511-1">&gt;&gt;</span></code></pre><h3 id="including-literal-strings" class="section-heading">
│ │ │ │ +a variable. The following gives a compiler syntax error:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7345589140-1">&lt;&lt;</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="7345589140-1">&gt;&gt;</span></code></pre><p>This expression must be rewritten into the following, to be accepted by the
│ │ │ │ +compiler:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2081972278-1">&lt;&lt;</span><span class="p" data-group-id="2081972278-2">(</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="2081972278-2">)</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="2081972278-1">&gt;&gt;</span></code></pre><h3 id="including-literal-strings" class="section-heading">
│ │ │ │    <a href="#including-literal-strings" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Including Literal Strings</span>
│ │ │ │  </h3>
│ │ │ │ -<p>A literal string can be written instead of an element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8935872789-1">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8935872789-1">&gt;&gt;</span></code></pre><p>This is syntactic sugar for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3908661368-1">&lt;&lt;</span><span class="sc">$h</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$o</span><span class="p" data-group-id="3908661368-1">&gt;&gt;</span></code></pre><h2 id="matching-binaries" class="section-heading">
│ │ │ │ +<p>A literal string can be written instead of an element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0125293377-1">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0125293377-1">&gt;&gt;</span></code></pre><p>This is syntactic sugar for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1641929894-1">&lt;&lt;</span><span class="sc">$h</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$o</span><span class="p" data-group-id="1641929894-1">&gt;&gt;</span></code></pre><h2 id="matching-binaries" class="section-heading">
│ │ │ │    <a href="#matching-binaries" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Matching Binaries</span>
│ │ │ │  </h2>
│ │ │ │  <p>This section describes the rules for matching binaries, using the bit syntax.</p><p>There can be zero or more segments in a binary pattern. A binary pattern can
│ │ │ │  occur wherever patterns are allowed, including inside other patterns. Binary
│ │ │ │  patterns cannot be nested. The pattern <code class="inline">&lt;&lt;&gt;&gt;</code> matches a zero length binary.</p><p>Each segment in a binary can consist of zero or more bits. A segment of type
│ │ │ │  <code class="inline">binary</code> must have a size evenly divisible by 8 (or divisible by the unit size,
│ │ │ │  if the unit size has been changed). A segment of type <code class="inline">bitstring</code> has no
│ │ │ │  restrictions on the size. A segment of type <code class="inline">float</code> must have size 64 or 32.</p><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When matching <code class="inline">Value</code>, value must be either a variable or an integer, or a
│ │ │ │  floating point literal. Expressions are not allowed.</p><p><code class="inline">Size</code> must be a
│ │ │ │  <a href="../../../lib/../system/doc/html/expressions.xhtml#guard-expressions">guard expression</a>, which can use
│ │ │ │ -literals and previously bound variables. The following is not allowed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="0534422141-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0534422141-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0534422141-2">&gt;&gt;</span><span class="p" data-group-id="0534422141-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0534422141-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="0534422141-3">}</span><span class="p">.</span></code></pre><p>The two occurrences of <code class="inline">N</code> are not related. The compiler will complain that the
│ │ │ │ -<code class="inline">N</code> in the size field is unbound.</p><p>The correct way to write this example is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="2330088492-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="2330088492-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="2330088492-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2330088492-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="2330088492-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="2330088492-3">}</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Before OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable bound to
│ │ │ │ +literals and previously bound variables. The following is not allowed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="5838419428-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5838419428-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5838419428-2">&gt;&gt;</span><span class="p" data-group-id="5838419428-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="5838419428-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="5838419428-3">}</span><span class="p">.</span></code></pre><p>The two occurrences of <code class="inline">N</code> are not related. The compiler will complain that the
│ │ │ │ +<code class="inline">N</code> in the size field is unbound.</p><p>The correct way to write this example is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="6340505190-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="6340505190-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="6340505190-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6340505190-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="6340505190-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="6340505190-3">}</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Before OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable bound to
│ │ │ │  an integer.</p></section><h3 id="binding-and-using-a-size-variable" class="section-heading">
│ │ │ │    <a href="#binding-and-using-a-size-variable" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Binding and Using a Size Variable</span>
│ │ │ │  </h3>
│ │ │ │  <p>There is one exception to the rule that a variable that is used as size must be
│ │ │ │  previously bound. It is possible to match and bind a variable, and use it as a
│ │ │ │ -size within the same binary pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="1337650039-1">(</span><span class="p" data-group-id="1337650039-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="n">Sz</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1337650039-2">&gt;&gt;</span><span class="p" data-group-id="1337650039-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="1337650039-3">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="1337650039-3">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is bound to the value in the first byte of the binary. <code class="inline">Sz</code> is then
│ │ │ │ -used at the number of bytes to match out as a binary.</p><p>Starting in OTP 23, the size can be a guard expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="8415064834-1">(</span><span class="p" data-group-id="8415064834-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="p" data-group-id="8415064834-3">(</span><span class="p" data-group-id="8415064834-4">(</span><span class="n">Sz</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="8415064834-4">)</span><span class="o">*</span><span class="mi">8</span><span class="p" data-group-id="8415064834-3">)</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8415064834-2">&gt;&gt;</span><span class="p" data-group-id="8415064834-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="8415064834-5">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="8415064834-5">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is the combined size of the header and the payload, so we will need to
│ │ │ │ +size within the same binary pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="8215672773-1">(</span><span class="p" data-group-id="8215672773-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="n">Sz</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8215672773-2">&gt;&gt;</span><span class="p" data-group-id="8215672773-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="8215672773-3">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="8215672773-3">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is bound to the value in the first byte of the binary. <code class="inline">Sz</code> is then
│ │ │ │ +used at the number of bytes to match out as a binary.</p><p>Starting in OTP 23, the size can be a guard expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="0643738657-1">(</span><span class="p" data-group-id="0643738657-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="p" data-group-id="0643738657-3">(</span><span class="p" data-group-id="0643738657-4">(</span><span class="n">Sz</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0643738657-4">)</span><span class="o">*</span><span class="mi">8</span><span class="p" data-group-id="0643738657-3">)</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0643738657-2">&gt;&gt;</span><span class="p" data-group-id="0643738657-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="0643738657-5">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="0643738657-5">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is the combined size of the header and the payload, so we will need to
│ │ │ │  subtract one byte to get the size of the payload.</p><h3 id="getting-the-rest-of-the-binary-or-bitstring" class="section-heading">
│ │ │ │    <a href="#getting-the-rest-of-the-binary-or-bitstring" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Getting the Rest of the Binary or Bitstring</span>
│ │ │ │  </h3>
│ │ │ │ -<p>To match out the rest of a binary, specify a binary field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="7725311496-1">(</span><span class="p" data-group-id="7725311496-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7725311496-2">&gt;&gt;</span><span class="p" data-group-id="7725311496-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>The size of the tail must be evenly divisible by 8.</p><p>To match out the rest of a bitstring, specify a field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="7160092314-1">(</span><span class="p" data-group-id="7160092314-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="7160092314-2">&gt;&gt;</span><span class="p" data-group-id="7160092314-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>There are no restrictions on the number of bits in the tail.</p><h2 id="appending-to-a-binary" class="section-heading">
│ │ │ │ +<p>To match out the rest of a binary, specify a binary field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="3829365796-1">(</span><span class="p" data-group-id="3829365796-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3829365796-2">&gt;&gt;</span><span class="p" data-group-id="3829365796-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>The size of the tail must be evenly divisible by 8.</p><p>To match out the rest of a bitstring, specify a field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="2260525868-1">(</span><span class="p" data-group-id="2260525868-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="2260525868-2">&gt;&gt;</span><span class="p" data-group-id="2260525868-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>There are no restrictions on the number of bits in the tail.</p><h2 id="appending-to-a-binary" class="section-heading">
│ │ │ │    <a href="#appending-to-a-binary" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Appending to a Binary</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Appending to a binary in an efficient way can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">triples_to_bin</span><span class="p" data-group-id="5681797821-1">(</span><span class="n">T</span><span class="p" data-group-id="5681797821-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="5681797821-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5681797821-3">&lt;&lt;</span><span class="p" data-group-id="5681797821-3">&gt;&gt;</span><span class="p" data-group-id="5681797821-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>Appending to a binary in an efficient way can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">triples_to_bin</span><span class="p" data-group-id="9350122581-1">(</span><span class="n">T</span><span class="p" data-group-id="9350122581-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="9350122581-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9350122581-3">&lt;&lt;</span><span class="p" data-group-id="9350122581-3">&gt;&gt;</span><span class="p" data-group-id="9350122581-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="5681797821-4">(</span><span class="p" data-group-id="5681797821-5">[</span><span class="p" data-group-id="5681797821-6">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p" data-group-id="5681797821-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5681797821-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5681797821-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="5681797821-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5681797821-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">X</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Z</span><span class="p">:</span><span class="mi">32</span><span class="p" data-group-id="5681797821-8">&gt;&gt;</span><span class="p" data-group-id="5681797821-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="5681797821-9">(</span><span class="p" data-group-id="5681797821-10">[</span><span class="p" data-group-id="5681797821-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5681797821-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="9350122581-4">(</span><span class="p" data-group-id="9350122581-5">[</span><span class="p" data-group-id="9350122581-6">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p" data-group-id="9350122581-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9350122581-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9350122581-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="9350122581-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9350122581-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">X</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Z</span><span class="p">:</span><span class="mi">32</span><span class="p" data-group-id="9350122581-8">&gt;&gt;</span><span class="p" data-group-id="9350122581-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="9350122581-9">(</span><span class="p" data-group-id="9350122581-10">[</span><span class="p" data-group-id="9350122581-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9350122581-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/binaryhandling.xhtml
│ │ │ │ @@ -19,43 +19,43 @@
│ │ │ │  
│ │ │ │      <h1 id="content">
│ │ │ │  Constructing and Matching Binaries
│ │ │ │      </h1>
│ │ │ │  <p>This section gives a few examples on how to handle binaries in an efficient way.
│ │ │ │  The sections that follow take an in-depth look at how binaries are implemented
│ │ │ │  and how to best take advantages of the optimizations done by the compiler and
│ │ │ │ -runtime system.</p><p>Binaries can be efficiently <em>built</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8957109516-1">(</span><span class="n">List</span><span class="p" data-group-id="8957109516-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8957109516-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8957109516-3">&lt;&lt;</span><span class="p" data-group-id="8957109516-3">&gt;&gt;</span><span class="p" data-group-id="8957109516-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +runtime system.</p><p>Binaries can be efficiently <em>built</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6458407328-1">(</span><span class="n">List</span><span class="p" data-group-id="6458407328-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6458407328-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6458407328-3">&lt;&lt;</span><span class="p" data-group-id="6458407328-3">&gt;&gt;</span><span class="p" data-group-id="6458407328-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8957109516-4">(</span><span class="p" data-group-id="8957109516-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8957109516-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8957109516-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8957109516-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8957109516-7">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="8957109516-7">&gt;&gt;</span><span class="p" data-group-id="8957109516-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="8957109516-8">(</span><span class="p" data-group-id="8957109516-9">[</span><span class="p" data-group-id="8957109516-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8957109516-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6458407328-4">(</span><span class="p" data-group-id="6458407328-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6458407328-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6458407328-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6458407328-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6458407328-7">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="6458407328-7">&gt;&gt;</span><span class="p" data-group-id="6458407328-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="6458407328-8">(</span><span class="p" data-group-id="6458407328-9">[</span><span class="p" data-group-id="6458407328-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6458407328-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Appending data to a binary as in the example is efficient because it is
│ │ │ │  specially optimized by the runtime system to avoid copying the <code class="inline">Acc</code> binary
│ │ │ │ -every time.</p><p>Prepending data to a binary in a loop is not efficient:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8405935024-1">(</span><span class="n">List</span><span class="p" data-group-id="8405935024-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8405935024-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8405935024-3">&lt;&lt;</span><span class="p" data-group-id="8405935024-3">&gt;&gt;</span><span class="p" data-group-id="8405935024-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +every time.</p><p>Prepending data to a binary in a loop is not efficient:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9178912635-1">(</span><span class="n">List</span><span class="p" data-group-id="9178912635-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9178912635-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9178912635-3">&lt;&lt;</span><span class="p" data-group-id="9178912635-3">&gt;&gt;</span><span class="p" data-group-id="9178912635-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8405935024-4">(</span><span class="p" data-group-id="8405935024-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8405935024-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8405935024-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8405935024-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8405935024-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8405935024-7">&gt;&gt;</span><span class="p" data-group-id="8405935024-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8405935024-8">(</span><span class="p" data-group-id="8405935024-9">[</span><span class="p" data-group-id="8405935024-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8405935024-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9178912635-4">(</span><span class="p" data-group-id="9178912635-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9178912635-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9178912635-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9178912635-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9178912635-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9178912635-7">&gt;&gt;</span><span class="p" data-group-id="9178912635-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9178912635-8">(</span><span class="p" data-group-id="9178912635-9">[</span><span class="p" data-group-id="9178912635-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9178912635-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>This is not efficient for long lists because the <code class="inline">Acc</code> binary is copied every
│ │ │ │ -time. One way to make the function more efficient is like this:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1876936924-1">(</span><span class="n">List</span><span class="p" data-group-id="1876936924-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1876936924-2">(</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="1876936924-3">(</span><span class="n">List</span><span class="p" data-group-id="1876936924-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1876936924-4">&lt;&lt;</span><span class="p" data-group-id="1876936924-4">&gt;&gt;</span><span class="p" data-group-id="1876936924-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +time. One way to make the function more efficient is like this:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9748590225-1">(</span><span class="n">List</span><span class="p" data-group-id="9748590225-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9748590225-2">(</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9748590225-3">(</span><span class="n">List</span><span class="p" data-group-id="9748590225-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9748590225-4">&lt;&lt;</span><span class="p" data-group-id="9748590225-4">&gt;&gt;</span><span class="p" data-group-id="9748590225-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1876936924-5">(</span><span class="p" data-group-id="1876936924-6">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1876936924-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1876936924-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1876936924-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1876936924-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="1876936924-8">&gt;&gt;</span><span class="p" data-group-id="1876936924-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1876936924-9">(</span><span class="p" data-group-id="1876936924-10">[</span><span class="p" data-group-id="1876936924-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1876936924-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Another way to avoid copying the binary each time is like this:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4004871776-1">(</span><span class="p" data-group-id="4004871776-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4004871776-2">]</span><span class="p" data-group-id="4004871776-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="n">RevTail</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4004871776-3">(</span><span class="n">T</span><span class="p" data-group-id="4004871776-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4004871776-4">&lt;&lt;</span><span class="n">RevTail</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="4004871776-4">&gt;&gt;</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4004871776-5">(</span><span class="p" data-group-id="4004871776-6">[</span><span class="p" data-group-id="4004871776-6">]</span><span class="p" data-group-id="4004871776-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4004871776-7">&lt;&lt;</span><span class="p" data-group-id="4004871776-7">&gt;&gt;</span><span class="p">.</span></code></pre><p>Note that in each of the <strong>DO</strong> examples, the binary to be appended to is always
│ │ │ │ -given as the first segment.</p><p>Binaries can be efficiently <em>matched</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="2524411830-1">(</span><span class="p" data-group-id="2524411830-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2524411830-2">&gt;&gt;</span><span class="p" data-group-id="2524411830-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="2524411830-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="2524411830-4">(</span><span class="n">T</span><span class="p" data-group-id="2524411830-4">)</span><span class="p" data-group-id="2524411830-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="2524411830-5">(</span><span class="p" data-group-id="2524411830-6">&lt;&lt;</span><span class="p" data-group-id="2524411830-6">&gt;&gt;</span><span class="p" data-group-id="2524411830-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2524411830-7">[</span><span class="p" data-group-id="2524411830-7">]</span><span class="p">.</span></code></pre><h2 id="how-binaries-are-implemented" class="section-heading">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9748590225-5">(</span><span class="p" data-group-id="9748590225-6">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9748590225-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9748590225-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9748590225-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9748590225-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="9748590225-8">&gt;&gt;</span><span class="p" data-group-id="9748590225-7">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9748590225-9">(</span><span class="p" data-group-id="9748590225-10">[</span><span class="p" data-group-id="9748590225-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9748590225-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Another way to avoid copying the binary each time is like this:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4379894004-1">(</span><span class="p" data-group-id="4379894004-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4379894004-2">]</span><span class="p" data-group-id="4379894004-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="n">RevTail</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4379894004-3">(</span><span class="n">T</span><span class="p" data-group-id="4379894004-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4379894004-4">&lt;&lt;</span><span class="n">RevTail</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="4379894004-4">&gt;&gt;</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="4379894004-5">(</span><span class="p" data-group-id="4379894004-6">[</span><span class="p" data-group-id="4379894004-6">]</span><span class="p" data-group-id="4379894004-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4379894004-7">&lt;&lt;</span><span class="p" data-group-id="4379894004-7">&gt;&gt;</span><span class="p">.</span></code></pre><p>Note that in each of the <strong>DO</strong> examples, the binary to be appended to is always
│ │ │ │ +given as the first segment.</p><p>Binaries can be efficiently <em>matched</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="1114832945-1">(</span><span class="p" data-group-id="1114832945-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1114832945-2">&gt;&gt;</span><span class="p" data-group-id="1114832945-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1114832945-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="1114832945-4">(</span><span class="n">T</span><span class="p" data-group-id="1114832945-4">)</span><span class="p" data-group-id="1114832945-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="1114832945-5">(</span><span class="p" data-group-id="1114832945-6">&lt;&lt;</span><span class="p" data-group-id="1114832945-6">&gt;&gt;</span><span class="p" data-group-id="1114832945-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1114832945-7">[</span><span class="p" data-group-id="1114832945-7">]</span><span class="p">.</span></code></pre><h2 id="how-binaries-are-implemented" class="section-heading">
│ │ │ │    <a href="#how-binaries-are-implemented" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">How Binaries are Implemented</span>
│ │ │ │  </h2>
│ │ │ │  <p>Internally, binaries and bitstrings are implemented in the same way. In this
│ │ │ │  section, they are called <em>binaries</em> because that is what they are called in the
│ │ │ │ @@ -110,29 +110,29 @@
│ │ │ │  called referential transparency) of Erlang would break.</p><h2 id="constructing-binaries" class="section-heading">
│ │ │ │    <a href="#constructing-binaries" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Constructing Binaries</span>
│ │ │ │  </h2>
│ │ │ │  <p>Appending to a binary or bitstring in the following way is specially optimized
│ │ │ │ -to avoid copying the binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6585186626-1">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6585186626-1">&gt;&gt;</span><span class="w">
│ │ │ │ +to avoid copying the binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2825248377-1">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2825248377-1">&gt;&gt;</span><span class="w">
│ │ │ │  </span><span class="c1">%% - OR -</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6585186626-2">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">bitstring</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6585186626-2">&gt;&gt;</span></code></pre><p>This optimization is applied by the runtime system in a way that makes it
│ │ │ │ +</span><span class="p" data-group-id="2825248377-2">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">bitstring</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2825248377-2">&gt;&gt;</span></code></pre><p>This optimization is applied by the runtime system in a way that makes it
│ │ │ │  effective in most circumstances (for exceptions, see
│ │ │ │  <a href="binaryhandling.xhtml#forced_copying">Circumstances That Force Copying</a>). The
│ │ │ │  optimization in its basic form does not need any help from the compiler.
│ │ │ │  However, the compiler add hints to the runtime system when it is safe to apply
│ │ │ │  the optimization in a more efficient way.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>The compiler support for making the optimization more efficient was added in
│ │ │ │  Erlang/OTP 26.</p></section><p>To explain how the basic optimization works, let us examine the following code
│ │ │ │ -line by line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6948027098-1">&lt;&lt;</span><span class="mi">0</span><span class="p" data-group-id="6948027098-1">&gt;&gt;</span><span class="p">,</span><span class="w">                    </span><span class="c1">%% 1</span><span class="w">
│ │ │ │ -</span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6948027098-2">&lt;&lt;</span><span class="n">Bin0</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6948027098-2">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 2</span><span class="w">
│ │ │ │ -</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6948027098-3">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6948027098-3">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 3</span><span class="w">
│ │ │ │ -</span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6948027098-4">&lt;&lt;</span><span class="n">Bin2</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="6948027098-4">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 4</span><span class="w">
│ │ │ │ -</span><span class="n">Bin4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6948027098-5">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="6948027098-5">&gt;&gt;</span><span class="p">,</span><span class="w">       </span><span class="c1">%% 5 !!!</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6948027098-6">{</span><span class="n">Bin4</span><span class="p">,</span><span class="n">Bin3</span><span class="p" data-group-id="6948027098-6">}</span><span class="w">                      </span><span class="c1">%% 6</span></code></pre><ul><li><p>Line 1 (marked with the <code class="inline">%% 1</code> comment), assigns a
│ │ │ │ +line by line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9409446522-1">&lt;&lt;</span><span class="mi">0</span><span class="p" data-group-id="9409446522-1">&gt;&gt;</span><span class="p">,</span><span class="w">                    </span><span class="c1">%% 1</span><span class="w">
│ │ │ │ +</span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9409446522-2">&lt;&lt;</span><span class="n">Bin0</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9409446522-2">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 2</span><span class="w">
│ │ │ │ +</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9409446522-3">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9409446522-3">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 3</span><span class="w">
│ │ │ │ +</span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9409446522-4">&lt;&lt;</span><span class="n">Bin2</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="9409446522-4">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 4</span><span class="w">
│ │ │ │ +</span><span class="n">Bin4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9409446522-5">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="9409446522-5">&gt;&gt;</span><span class="p">,</span><span class="w">       </span><span class="c1">%% 5 !!!</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9409446522-6">{</span><span class="n">Bin4</span><span class="p">,</span><span class="n">Bin3</span><span class="p" data-group-id="9409446522-6">}</span><span class="w">                      </span><span class="c1">%% 6</span></code></pre><ul><li><p>Line 1 (marked with the <code class="inline">%% 1</code> comment), assigns a
│ │ │ │  <a href="binaryhandling.xhtml#heap_binary">heap binary</a> to the <code class="inline">Bin0</code> variable.</p></li><li><p>Line 2 is an append operation. As <code class="inline">Bin0</code> has not been involved in an append
│ │ │ │  operation, a new <a href="binaryhandling.xhtml#refc_binary">refc binary</a> is created and
│ │ │ │  the contents of <code class="inline">Bin0</code> is copied into it. The <em>ProcBin</em> part of the refc
│ │ │ │  binary has its size set to the size of the data stored in the binary, while
│ │ │ │  the binary object has extra space allocated. The size of the binary object is
│ │ │ │  either twice the size of <code class="inline">Bin1</code> or 256, whichever is larger. In this case it
│ │ │ │  is 256.</p></li><li><p>Line 3 is more interesting. <code class="inline">Bin1</code> <em>has</em> been used in an append operation, and
│ │ │ │ @@ -158,23 +158,23 @@
│ │ │ │  handle an append operation to a heap binary by copying it to a refc binary (line
│ │ │ │  2), and also handle an append operation to a previous version of the binary by
│ │ │ │  copying it (line 5). The support for doing that does not come for free. For
│ │ │ │  example, to make it possible to know when it is necessary to copy the binary,
│ │ │ │  for every append operation, the runtime system must create a sub binary.</p><p>When the compiler can determine that none of those situations need to be handled
│ │ │ │  and that the append operation cannot possibly fail, the compiler generates code
│ │ │ │  that causes the runtime system to apply a more efficient variant of the
│ │ │ │ -optimization.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8173745593-1">(</span><span class="ss">repack</span><span class="p" data-group-id="8173745593-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8173745593-2">(</span><span class="p" data-group-id="8173745593-3">[</span><span class="ss">repack</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8173745593-3">]</span><span class="p" data-group-id="8173745593-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +optimization.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7428801651-1">(</span><span class="ss">repack</span><span class="p" data-group-id="7428801651-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7428801651-2">(</span><span class="p" data-group-id="7428801651-3">[</span><span class="ss">repack</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7428801651-3">]</span><span class="p" data-group-id="7428801651-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="8173745593-4">(</span><span class="n">Bin</span><span class="p" data-group-id="8173745593-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_binary</span><span class="p" data-group-id="8173745593-5">(</span><span class="n">Bin</span><span class="p" data-group-id="8173745593-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">repack</span><span class="p" data-group-id="8173745593-6">(</span><span class="n">Bin</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8173745593-7">&lt;&lt;</span><span class="p" data-group-id="8173745593-7">&gt;&gt;</span><span class="p" data-group-id="8173745593-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="7428801651-4">(</span><span class="n">Bin</span><span class="p" data-group-id="7428801651-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_binary</span><span class="p" data-group-id="7428801651-5">(</span><span class="n">Bin</span><span class="p" data-group-id="7428801651-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">repack</span><span class="p" data-group-id="7428801651-6">(</span><span class="n">Bin</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7428801651-7">&lt;&lt;</span><span class="p" data-group-id="7428801651-7">&gt;&gt;</span><span class="p" data-group-id="7428801651-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="8173745593-8">(</span><span class="p" data-group-id="8173745593-9">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8173745593-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8173745593-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">repack</span><span class="p" data-group-id="8173745593-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8173745593-11">&lt;&lt;</span><span class="n">Result</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="8173745593-11">&gt;&gt;</span><span class="p" data-group-id="8173745593-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="8173745593-12">(</span><span class="p" data-group-id="8173745593-13">&lt;&lt;</span><span class="p" data-group-id="8173745593-13">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8173745593-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="7428801651-8">(</span><span class="p" data-group-id="7428801651-9">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7428801651-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7428801651-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">repack</span><span class="p" data-group-id="7428801651-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7428801651-11">&lt;&lt;</span><span class="n">Result</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="7428801651-11">&gt;&gt;</span><span class="p" data-group-id="7428801651-10">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="7428801651-12">(</span><span class="p" data-group-id="7428801651-13">&lt;&lt;</span><span class="p" data-group-id="7428801651-13">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7428801651-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">Result</span><span class="p">.</span></code></pre><p>The <code class="inline">repack/2</code> function only keeps a single version of the binary, so there is
│ │ │ │  never any need to copy the binary. The compiler rewrites the creation of the
│ │ │ │  empty binary in <code class="inline">repack/1</code> to instead create a refc binary with 256 bytes
│ │ │ │  already reserved; thus, the append operation in <code class="inline">repack/2</code> never needs to handle
│ │ │ │  a binary not prepared for appending.</p><p><a href="" id="forced_copying"></a></p><h3 id="circumstances-that-force-copying" class="section-heading">
│ │ │ │    <a href="#circumstances-that-force-copying" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -186,72 +186,72 @@
│ │ │ │  reason is that the binary object can be moved (reallocated) during an append
│ │ │ │  operation, and when that happens, the pointer in the ProcBin must be updated. If
│ │ │ │  there would be more than one ProcBin pointing to the binary object, it would not
│ │ │ │  be possible to find and update all of them.</p><p>Therefore, certain operations on a binary mark it so that any future append
│ │ │ │  operation will be forced to copy the binary. In most cases, the binary object
│ │ │ │  will be shrunk at the same time to reclaim the extra space allocated for
│ │ │ │  growing.</p><p>When appending to a binary as follows, only the binary returned from the latest
│ │ │ │ -append operation will support further cheap append operations:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6368998112-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6368998112-1">&gt;&gt;</span></code></pre><p>In the code fragment in the beginning of this section, appending to <code class="inline">Bin</code> will
│ │ │ │ +append operation will support further cheap append operations:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3494974099-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3494974099-1">&gt;&gt;</span></code></pre><p>In the code fragment in the beginning of this section, appending to <code class="inline">Bin</code> will
│ │ │ │  be cheap, while appending to <code class="inline">Bin0</code> will force the creation of a new binary and
│ │ │ │  copying of the contents of <code class="inline">Bin0</code>.</p><p>If a binary is sent as a message to a process or port, the binary will be shrunk
│ │ │ │  and any further append operation will copy the binary data into a new binary.
│ │ │ │  For example, in the following code fragment <code class="inline">Bin1</code> will be copied in the third
│ │ │ │ -line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0753663994-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0753663994-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6096143421-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6096143421-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │  </span><span class="n">PortOrPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0753663994-2">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0753663994-2">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The same happens if you insert a binary into an Ets table, send it to a port
│ │ │ │ +</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6096143421-2">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6096143421-2">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The same happens if you insert a binary into an Ets table, send it to a port
│ │ │ │  using <a href="../../../lib/../erts/doc/html/erlang.html#port_command/2"><code class="inline">erlang:port_command/2</code></a>, or pass it to
│ │ │ │  <a href="../../../lib/../erts/doc/html/erl_nif.xhtml#enif_inspect_binary">enif_inspect_binary</a> in a NIF.</p><p>Matching a binary will also cause it to shrink and the next append operation
│ │ │ │ -will copy the binary data:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0919705686-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0919705686-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0919705686-2">&lt;&lt;</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0919705686-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ │ -</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0919705686-3">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0919705686-3">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The reason is that a <a href="binaryhandling.xhtml#match_context">match context</a> contains a
│ │ │ │ +will copy the binary data:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4983822123-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4983822123-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4983822123-2">&lt;&lt;</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4983822123-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ │ +</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4983822123-3">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4983822123-3">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The reason is that a <a href="binaryhandling.xhtml#match_context">match context</a> contains a
│ │ │ │  direct pointer to the binary data.</p><p>If a process simply keeps binaries (either in &quot;loop data&quot; or in the process
│ │ │ │  dictionary), the garbage collector can eventually shrink the binaries. If only
│ │ │ │  one such binary is kept, it will not be shrunk. If the process later appends to
│ │ │ │  a binary that has been shrunk, the binary object will be reallocated to make
│ │ │ │  place for the data to be appended.</p><h2 id="matching-binaries" class="section-heading">
│ │ │ │    <a href="#matching-binaries" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Matching Binaries</span>
│ │ │ │  </h2>
│ │ │ │ -<p>Let us revisit the example in the beginning of the previous section:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="8811091499-1">(</span><span class="p" data-group-id="8811091499-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8811091499-2">&gt;&gt;</span><span class="p" data-group-id="8811091499-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8811091499-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="8811091499-4">(</span><span class="n">T</span><span class="p" data-group-id="8811091499-4">)</span><span class="p" data-group-id="8811091499-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="8811091499-5">(</span><span class="p" data-group-id="8811091499-6">&lt;&lt;</span><span class="p" data-group-id="8811091499-6">&gt;&gt;</span><span class="p" data-group-id="8811091499-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8811091499-7">[</span><span class="p" data-group-id="8811091499-7">]</span><span class="p">.</span></code></pre><p>The first time <code class="inline">my_binary_to_list/1</code> is called, a
│ │ │ │ +<p>Let us revisit the example in the beginning of the previous section:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="2210789674-1">(</span><span class="p" data-group-id="2210789674-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2210789674-2">&gt;&gt;</span><span class="p" data-group-id="2210789674-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="2210789674-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="2210789674-4">(</span><span class="n">T</span><span class="p" data-group-id="2210789674-4">)</span><span class="p" data-group-id="2210789674-3">]</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="2210789674-5">(</span><span class="p" data-group-id="2210789674-6">&lt;&lt;</span><span class="p" data-group-id="2210789674-6">&gt;&gt;</span><span class="p" data-group-id="2210789674-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2210789674-7">[</span><span class="p" data-group-id="2210789674-7">]</span><span class="p">.</span></code></pre><p>The first time <code class="inline">my_binary_to_list/1</code> is called, a
│ │ │ │  <a href="binaryhandling.xhtml#match_context">match context</a> is created. The match context
│ │ │ │  points to the first byte of the binary. 1 byte is matched out and the match
│ │ │ │  context is updated to point to the second byte in the binary.</p><p>At this point it would make sense to create a
│ │ │ │  <a href="binaryhandling.xhtml#sub_binary">sub binary</a>, but in this particular example the
│ │ │ │  compiler sees that there will soon be a call to a function (in this case, to
│ │ │ │  <code class="inline">my_binary_to_list/1</code> itself) that immediately will create a new match context
│ │ │ │  and discard the sub binary.</p><p>Therefore <code class="inline">my_binary_to_list/1</code> calls itself with the match context instead of
│ │ │ │  with a sub binary. The instruction that initializes the matching operation
│ │ │ │  basically does nothing when it sees that it was passed a match context instead
│ │ │ │  of a binary.</p><p>When the end of the binary is reached and the second clause matches, the match
│ │ │ │  context will simply be discarded (removed in the next garbage collection, as
│ │ │ │  there is no longer any reference to it).</p><p>To summarize, <code class="inline">my_binary_to_list/1</code> only needs to create <em>one</em> match context and
│ │ │ │  no sub binaries.</p><p>Notice that the match context in <code class="inline">my_binary_to_list/1</code> was discarded when the
│ │ │ │  entire binary had been traversed. What happens if the iteration stops before it
│ │ │ │ -has reached the end of the binary? Will the optimization still work?</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="7354822083-1">(</span><span class="p" data-group-id="7354822083-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7354822083-2">&gt;&gt;</span><span class="p" data-group-id="7354822083-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +has reached the end of the binary? Will the optimization still work?</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="4120594477-1">(</span><span class="p" data-group-id="4120594477-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4120594477-2">&gt;&gt;</span><span class="p" data-group-id="4120594477-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="7354822083-3">(</span><span class="p" data-group-id="7354822083-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7354822083-4">&gt;&gt;</span><span class="p" data-group-id="7354822083-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="7354822083-5">(</span><span class="n">T</span><span class="p" data-group-id="7354822083-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="7354822083-6">(</span><span class="p" data-group-id="7354822083-7">&lt;&lt;</span><span class="p" data-group-id="7354822083-7">&gt;&gt;</span><span class="p" data-group-id="7354822083-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7354822083-8">&lt;&lt;</span><span class="p" data-group-id="7354822083-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>Yes, it will. The compiler will remove the building of the sub binary in the
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="4120594477-3">(</span><span class="p" data-group-id="4120594477-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4120594477-4">&gt;&gt;</span><span class="p" data-group-id="4120594477-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="4120594477-5">(</span><span class="n">T</span><span class="p" data-group-id="4120594477-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="4120594477-6">(</span><span class="p" data-group-id="4120594477-7">&lt;&lt;</span><span class="p" data-group-id="4120594477-7">&gt;&gt;</span><span class="p" data-group-id="4120594477-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4120594477-8">&lt;&lt;</span><span class="p" data-group-id="4120594477-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>Yes, it will. The compiler will remove the building of the sub binary in the
│ │ │ │  second clause:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="7099337865-1">(</span><span class="p" data-group-id="7099337865-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7099337865-2">&gt;&gt;</span><span class="p" data-group-id="7099337865-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="7099337865-3">(</span><span class="n">T</span><span class="p" data-group-id="7099337865-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>But it will generate code that builds a sub binary in the first clause:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="0243262900-1">(</span><span class="p" data-group-id="0243262900-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0243262900-2">&gt;&gt;</span><span class="p" data-group-id="0243262900-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="9414958779-1">(</span><span class="p" data-group-id="9414958779-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9414958779-2">&gt;&gt;</span><span class="p" data-group-id="9414958779-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="9414958779-3">(</span><span class="n">T</span><span class="p" data-group-id="9414958779-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>But it will generate code that builds a sub binary in the first clause:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="1886470699-1">(</span><span class="p" data-group-id="1886470699-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1886470699-2">&gt;&gt;</span><span class="p" data-group-id="1886470699-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Therefore, <code class="inline">after_zero/1</code> builds one match context and one sub binary (assuming
│ │ │ │ -it is passed a binary that contains a zero byte).</p><p>Code like the following will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="1878661225-1">(</span><span class="n">Buffer</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1878661225-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1878661225-2">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="1878661225-3">(</span><span class="n">Acc</span><span class="p" data-group-id="1878661225-3">)</span><span class="p">,</span><span class="n">Buffer</span><span class="p" data-group-id="1878661225-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="1878661225-4">(</span><span class="p" data-group-id="1878661225-5">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1878661225-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="1878661225-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="1878661225-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="1878661225-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="1878661225-7">(</span><span class="p" data-group-id="1878661225-8">&lt;&lt;</span><span class="n">Byte</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1878661225-8">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="1878661225-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="1878661225-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1878661225-10">[</span><span class="n">Byte</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="1878661225-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="1878661225-9">)</span><span class="p">.</span></code></pre><p>The compiler removes building of sub binaries in the second and third clauses,
│ │ │ │ +it is passed a binary that contains a zero byte).</p><p>Code like the following will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9757389837-1">(</span><span class="n">Buffer</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="9757389837-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9757389837-2">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9757389837-3">(</span><span class="n">Acc</span><span class="p" data-group-id="9757389837-3">)</span><span class="p">,</span><span class="n">Buffer</span><span class="p" data-group-id="9757389837-2">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9757389837-4">(</span><span class="p" data-group-id="9757389837-5">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9757389837-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="9757389837-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9757389837-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="9757389837-6">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9757389837-7">(</span><span class="p" data-group-id="9757389837-8">&lt;&lt;</span><span class="n">Byte</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9757389837-8">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="9757389837-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9757389837-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9757389837-10">[</span><span class="n">Byte</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="9757389837-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="9757389837-9">)</span><span class="p">.</span></code></pre><p>The compiler removes building of sub binaries in the second and third clauses,
│ │ │ │  and it adds an instruction to the first clause that converts <code class="inline">Buffer</code> from a
│ │ │ │  match context to a sub binary (or do nothing if <code class="inline">Buffer</code> is a binary already).</p><p>But in more complicated code, how can one know whether the optimization is
│ │ │ │  applied or not?</p><p><a href="" id="bin_opt_info"></a></p><h3 id="option-bin_opt_info" class="section-heading">
│ │ │ │    <a href="#option-bin_opt_info" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Option bin_opt_info</span>
│ │ │ │ @@ -259,35 +259,35 @@
│ │ │ │  <p>Use the <code class="inline">bin_opt_info</code> option to have the compiler print a lot of information
│ │ │ │  about binary optimizations. It can be given either to the compiler or <code class="inline">erlc</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">erlc</span><span class="w"> </span><span class="o">+</span><span class="ss">bin_opt_info</span><span class="w"> </span><span class="n">Mod</span><span class="p">.</span><span class="ss">erl</span></code></pre><p>or passed through an environment variable:</p><pre><code class="makeup erlang" translate="no"><span class="ss">export</span><span class="w"> </span><span class="n">ERL_COMPILER_OPTIONS</span><span class="o">=</span><span class="ss">bin_opt_info</span></code></pre><p>Notice that the <code class="inline">bin_opt_info</code> is not meant to be a permanent option added to
│ │ │ │  your <code class="inline">Makefile</code>s, because all messages that it generates cannot be eliminated.
│ │ │ │  Therefore, passing the option through the environment is in most cases the most
│ │ │ │  practical approach.</p><p>The warnings look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="o">/</span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">60</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">NOT</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">binary</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">returned</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">function</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="o">/</span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">62</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">context</span><span class="w"> </span><span class="ss">reused</span></code></pre><p>To make it clearer exactly what code the warnings refer to, the warnings in the
│ │ │ │  following examples are inserted as comments after the clause they refer to, for
│ │ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="9852376938-1">(</span><span class="p" data-group-id="9852376938-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9852376938-2">&gt;&gt;</span><span class="p" data-group-id="9852376938-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="3019853383-1">(</span><span class="p" data-group-id="3019853383-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3019853383-2">&gt;&gt;</span><span class="p" data-group-id="3019853383-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │           </span><span class="c1">%% BINARY CREATED: binary is returned from the function</span><span class="w">
│ │ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="9852376938-3">(</span><span class="p" data-group-id="9852376938-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9852376938-4">&gt;&gt;</span><span class="p" data-group-id="9852376938-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="3019853383-3">(</span><span class="p" data-group-id="3019853383-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3019853383-4">&gt;&gt;</span><span class="p" data-group-id="3019853383-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │           </span><span class="c1">%% OPTIMIZED: match context reused</span><span class="w">
│ │ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="9852376938-5">(</span><span class="n">T</span><span class="p" data-group-id="9852376938-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="9852376938-6">(</span><span class="p" data-group-id="9852376938-7">&lt;&lt;</span><span class="p" data-group-id="9852376938-7">&gt;&gt;</span><span class="p" data-group-id="9852376938-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="9852376938-8">&lt;&lt;</span><span class="p" data-group-id="9852376938-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>The warning for the first clause says that the creation of a sub binary cannot
│ │ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="3019853383-5">(</span><span class="n">T</span><span class="p" data-group-id="3019853383-5">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="3019853383-6">(</span><span class="p" data-group-id="3019853383-7">&lt;&lt;</span><span class="p" data-group-id="3019853383-7">&gt;&gt;</span><span class="p" data-group-id="3019853383-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="3019853383-8">&lt;&lt;</span><span class="p" data-group-id="3019853383-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>The warning for the first clause says that the creation of a sub binary cannot
│ │ │ │  be delayed, because it will be returned. The warning for the second clause says
│ │ │ │  that a sub binary will not be created (yet).</p><h3 id="unused-variables" class="section-heading">
│ │ │ │    <a href="#unused-variables" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Unused Variables</span>
│ │ │ │  </h3>
│ │ │ │  <p>The compiler figures out if a variable is unused. The same code is generated for
│ │ │ │ -each of the following functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">count1</span><span class="p" data-group-id="2637862291-1">(</span><span class="p" data-group-id="2637862291-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2637862291-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2637862291-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count1</span><span class="p" data-group-id="2637862291-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="2637862291-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">count1</span><span class="p" data-group-id="2637862291-4">(</span><span class="p" data-group-id="2637862291-5">&lt;&lt;</span><span class="p" data-group-id="2637862291-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2637862291-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ │ +each of the following functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">count1</span><span class="p" data-group-id="2941567675-1">(</span><span class="p" data-group-id="2941567675-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2941567675-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2941567675-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count1</span><span class="p" data-group-id="2941567675-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="2941567675-3">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">count1</span><span class="p" data-group-id="2941567675-4">(</span><span class="p" data-group-id="2941567675-5">&lt;&lt;</span><span class="p" data-group-id="2941567675-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2941567675-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">count2</span><span class="p" data-group-id="2637862291-6">(</span><span class="p" data-group-id="2637862291-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2637862291-7">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2637862291-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count2</span><span class="p" data-group-id="2637862291-8">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="2637862291-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">count2</span><span class="p" data-group-id="2637862291-9">(</span><span class="p" data-group-id="2637862291-10">&lt;&lt;</span><span class="p" data-group-id="2637862291-10">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2637862291-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">count2</span><span class="p" data-group-id="2941567675-6">(</span><span class="p" data-group-id="2941567675-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2941567675-7">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2941567675-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count2</span><span class="p" data-group-id="2941567675-8">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="2941567675-8">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">count2</span><span class="p" data-group-id="2941567675-9">(</span><span class="p" data-group-id="2941567675-10">&lt;&lt;</span><span class="p" data-group-id="2941567675-10">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2941567675-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">count3</span><span class="p" data-group-id="2637862291-11">(</span><span class="p" data-group-id="2637862291-12">&lt;&lt;</span><span class="p">_</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2637862291-12">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2637862291-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count3</span><span class="p" data-group-id="2637862291-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="2637862291-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">count3</span><span class="p" data-group-id="2637862291-14">(</span><span class="p" data-group-id="2637862291-15">&lt;&lt;</span><span class="p" data-group-id="2637862291-15">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2637862291-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span></code></pre><p>In each iteration, the first 8 bits in the binary will be skipped, not matched
│ │ │ │ +</span><span class="nf">count3</span><span class="p" data-group-id="2941567675-11">(</span><span class="p" data-group-id="2941567675-12">&lt;&lt;</span><span class="p">_</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2941567675-12">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2941567675-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count3</span><span class="p" data-group-id="2941567675-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="2941567675-13">)</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">count3</span><span class="p" data-group-id="2941567675-14">(</span><span class="p" data-group-id="2941567675-15">&lt;&lt;</span><span class="p" data-group-id="2941567675-15">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="2941567675-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span></code></pre><p>In each iteration, the first 8 bits in the binary will be skipped, not matched
│ │ │ │  out.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/benchmarking.xhtml
│ │ │ │ @@ -49,16 +49,16 @@
│ │ │ │  fast as possible, what can we do? One way could be to generate more
│ │ │ │  than two bytes at the time.</p><pre><code class="text">% erlperf 'rand:bytes(100).' 'crypto:strong_rand_bytes(100).'
│ │ │ │  Code                                   ||        QPS       Time   Rel
│ │ │ │  rand:bytes(100).                        1    2124 Ki     470 ns  100%
│ │ │ │  crypto:strong_rand_bytes(100).          1    1915 Ki     522 ns   90%</code></pre><p><a href="../../../lib/stdlib/doc/html/rand.html#bytes/1"><code class="inline">rand:bytes/1</code></a> is still faster when we generate 100 bytes at the time,
│ │ │ │  but the relative difference is smaller.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erlperf &#39;rand:bytes(1000).&#39; &#39;crypto:strong_rand_bytes(1000).&#39;</span><span class="w">
│ │ │ │  </span><span class="n">Code</span><span class="w">                                    </span><span class="p">||</span><span class="w">        </span><span class="n">QPS</span><span class="w">       </span><span class="n">Time</span><span class="w">   </span><span class="n">Rel</span><span class="w">
│ │ │ │ -</span><span class="nc">crypto</span><span class="p">:</span><span class="nf">strong_rand_bytes</span><span class="p" data-group-id="6239493998-1">(</span><span class="mi">1000</span><span class="p" data-group-id="6239493998-1">)</span><span class="p">.</span><span class="w">          </span><span class="mi">1</span><span class="w">    </span><span class="mi">1518</span><span class="w"> </span><span class="n">Ki</span><span class="w">     </span><span class="mi">658</span><span class="w"> </span><span class="ss">ns</span><span class="w">  </span><span class="mi">100</span><span class="c1">%</span><span class="w">
│ │ │ │ -</span><span class="nc">rand</span><span class="p">:</span><span class="nf">bytes</span><span class="p" data-group-id="6239493998-2">(</span><span class="mi">1000</span><span class="p" data-group-id="6239493998-2">)</span><span class="p">.</span><span class="w">                        </span><span class="mi">1</span><span class="w">     </span><span class="mi">284</span><span class="w"> </span><span class="n">Ki</span><span class="w">    </span><span class="mi">3521</span><span class="w"> </span><span class="ss">ns</span><span class="w">   </span><span class="mi">19</span><span class="c1">%</span></code></pre><p>When we generate 1000 bytes at the time, <a href="../../../lib/crypto/doc/html/crypto.html#strong_rand_bytes/1"><code class="inline">crypto:strong_rand_bytes/1</code></a> is
│ │ │ │ +</span><span class="nc">crypto</span><span class="p">:</span><span class="nf">strong_rand_bytes</span><span class="p" data-group-id="5416114784-1">(</span><span class="mi">1000</span><span class="p" data-group-id="5416114784-1">)</span><span class="p">.</span><span class="w">          </span><span class="mi">1</span><span class="w">    </span><span class="mi">1518</span><span class="w"> </span><span class="n">Ki</span><span class="w">     </span><span class="mi">658</span><span class="w"> </span><span class="ss">ns</span><span class="w">  </span><span class="mi">100</span><span class="c1">%</span><span class="w">
│ │ │ │ +</span><span class="nc">rand</span><span class="p">:</span><span class="nf">bytes</span><span class="p" data-group-id="5416114784-2">(</span><span class="mi">1000</span><span class="p" data-group-id="5416114784-2">)</span><span class="p">.</span><span class="w">                        </span><span class="mi">1</span><span class="w">     </span><span class="mi">284</span><span class="w"> </span><span class="n">Ki</span><span class="w">    </span><span class="mi">3521</span><span class="w"> </span><span class="ss">ns</span><span class="w">   </span><span class="mi">19</span><span class="c1">%</span></code></pre><p>When we generate 1000 bytes at the time, <a href="../../../lib/crypto/doc/html/crypto.html#strong_rand_bytes/1"><code class="inline">crypto:strong_rand_bytes/1</code></a> is
│ │ │ │  now the fastest.</p><h2 id="benchmarking-using-erlang-otp-functionality" class="section-heading">
│ │ │ │    <a href="#benchmarking-using-erlang-otp-functionality" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Benchmarking using Erlang/OTP functionality</span>
│ │ │ │  </h2>
│ │ │ │  <p>Benchmarks can measure wall-clock time or CPU time.</p><ul><li><p><a href="../../../lib/stdlib/doc/html/timer.html#tc/3"><code class="inline">timer:tc/3</code></a> measures wall-clock time. The advantage with wall-clock time is
│ │ │ ├── OEBPS/appup_cookbook.xhtml
│ │ │ │ @@ -25,18 +25,18 @@
│ │ │ │    <a href="#changing-a-functional-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing a Functional Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>When a functional module has been changed, for example, if a new function has
│ │ │ │  been added or a bug has been corrected, simple code replacement is sufficient,
│ │ │ │ -for example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1638324347-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="1638324347-2">[</span><span class="p" data-group-id="1638324347-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1638324347-4">[</span><span class="p" data-group-id="1638324347-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="1638324347-5">}</span><span class="p" data-group-id="1638324347-4">]</span><span class="p" data-group-id="1638324347-3">}</span><span class="p" data-group-id="1638324347-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="1638324347-6">[</span><span class="p" data-group-id="1638324347-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1638324347-8">[</span><span class="p" data-group-id="1638324347-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="1638324347-9">}</span><span class="p" data-group-id="1638324347-8">]</span><span class="p" data-group-id="1638324347-7">}</span><span class="p" data-group-id="1638324347-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="1638324347-1">}</span><span class="p">.</span></code></pre><h2 id="changing-a-residence-module" class="section-heading">
│ │ │ │ +for example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5704903185-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5704903185-2">[</span><span class="p" data-group-id="5704903185-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5704903185-4">[</span><span class="p" data-group-id="5704903185-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="5704903185-5">}</span><span class="p" data-group-id="5704903185-4">]</span><span class="p" data-group-id="5704903185-3">}</span><span class="p" data-group-id="5704903185-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5704903185-6">[</span><span class="p" data-group-id="5704903185-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5704903185-8">[</span><span class="p" data-group-id="5704903185-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="5704903185-9">}</span><span class="p" data-group-id="5704903185-8">]</span><span class="p" data-group-id="5704903185-7">}</span><span class="p" data-group-id="5704903185-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5704903185-1">}</span><span class="p">.</span></code></pre><h2 id="changing-a-residence-module" class="section-heading">
│ │ │ │    <a href="#changing-a-residence-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing a Residence Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>In a system implemented according to the OTP design principles, all processes,
│ │ │ │  except system processes and special processes, reside in one of the behaviours
│ │ │ │ @@ -47,46 +47,46 @@
│ │ │ │    <a href="#changing-a-callback-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing a Callback Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>A callback module is a functional module, and for code extensions simple code
│ │ │ │  replacement is sufficient.</p><p><em>Example</em></p><p>When adding a function to <code class="inline">ch3</code>, as described in the example in
│ │ │ │ -<a href="release_handling.xhtml#appup">Release Handling</a>, <code class="inline">ch_app.appup</code> looks as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0957194062-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0957194062-2">[</span><span class="p" data-group-id="0957194062-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0957194062-4">[</span><span class="p" data-group-id="0957194062-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0957194062-5">}</span><span class="p" data-group-id="0957194062-4">]</span><span class="p" data-group-id="0957194062-3">}</span><span class="p" data-group-id="0957194062-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0957194062-6">[</span><span class="p" data-group-id="0957194062-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0957194062-8">[</span><span class="p" data-group-id="0957194062-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0957194062-9">}</span><span class="p" data-group-id="0957194062-8">]</span><span class="p" data-group-id="0957194062-7">}</span><span class="p" data-group-id="0957194062-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0957194062-1">}</span><span class="p">.</span></code></pre><p>OTP also supports changing the internal state of behaviour processes; see
│ │ │ │ +<a href="release_handling.xhtml#appup">Release Handling</a>, <code class="inline">ch_app.appup</code> looks as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3557030151-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3557030151-2">[</span><span class="p" data-group-id="3557030151-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3557030151-4">[</span><span class="p" data-group-id="3557030151-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3557030151-5">}</span><span class="p" data-group-id="3557030151-4">]</span><span class="p" data-group-id="3557030151-3">}</span><span class="p" data-group-id="3557030151-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3557030151-6">[</span><span class="p" data-group-id="3557030151-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3557030151-8">[</span><span class="p" data-group-id="3557030151-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3557030151-9">}</span><span class="p" data-group-id="3557030151-8">]</span><span class="p" data-group-id="3557030151-7">}</span><span class="p" data-group-id="3557030151-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3557030151-1">}</span><span class="p">.</span></code></pre><p>OTP also supports changing the internal state of behaviour processes; see
│ │ │ │  <a href="appup_cookbook.xhtml#int_state">Changing Internal State</a>.</p><p><a href="" id="int_state"></a></p><h2 id="changing-internal-state" class="section-heading">
│ │ │ │    <a href="#changing-internal-state" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Internal State</span>
│ │ │ │  </h2>
│ │ │ │  <p>In this case, simple code replacement is not sufficient. The process must
│ │ │ │  explicitly transform its state using the callback function <code class="inline">code_change/3</code> before
│ │ │ │  switching to the new version of the callback module. Thus, synchronized code
│ │ │ │  replacement is used.</p><p><em>Example</em></p><p>Consider the <code class="inline">ch3</code> module from
│ │ │ │  <a href="gen_server_concepts.xhtml#ex">gen_server Behaviour</a>. The internal state is a term
│ │ │ │  <code class="inline">Chs</code> representing the available channels. Assume you want to add a counter <code class="inline">N</code>,
│ │ │ │  which keeps track of the number of <code class="inline">alloc</code> requests so far. This means that the
│ │ │ │ -format must be changed to <code class="inline">{Chs,N}</code>.</p><p>The <code class="inline">.appup</code> file can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9284743389-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9284743389-2">[</span><span class="p" data-group-id="9284743389-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9284743389-4">[</span><span class="p" data-group-id="9284743389-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9284743389-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9284743389-7">[</span><span class="p" data-group-id="9284743389-7">]</span><span class="p" data-group-id="9284743389-6">}</span><span class="p" data-group-id="9284743389-5">}</span><span class="p" data-group-id="9284743389-4">]</span><span class="p" data-group-id="9284743389-3">}</span><span class="p" data-group-id="9284743389-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="9284743389-8">[</span><span class="p" data-group-id="9284743389-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9284743389-10">[</span><span class="p" data-group-id="9284743389-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9284743389-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9284743389-13">[</span><span class="p" data-group-id="9284743389-13">]</span><span class="p" data-group-id="9284743389-12">}</span><span class="p" data-group-id="9284743389-11">}</span><span class="p" data-group-id="9284743389-10">]</span><span class="p" data-group-id="9284743389-9">}</span><span class="p" data-group-id="9284743389-8">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="9284743389-1">}</span><span class="p">.</span></code></pre><p>The third element of the <code class="inline">update</code> instruction is a tuple <code class="inline">{advanced,Extra}</code>,
│ │ │ │ +format must be changed to <code class="inline">{Chs,N}</code>.</p><p>The <code class="inline">.appup</code> file can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4509946505-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4509946505-2">[</span><span class="p" data-group-id="4509946505-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4509946505-4">[</span><span class="p" data-group-id="4509946505-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4509946505-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4509946505-7">[</span><span class="p" data-group-id="4509946505-7">]</span><span class="p" data-group-id="4509946505-6">}</span><span class="p" data-group-id="4509946505-5">}</span><span class="p" data-group-id="4509946505-4">]</span><span class="p" data-group-id="4509946505-3">}</span><span class="p" data-group-id="4509946505-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4509946505-8">[</span><span class="p" data-group-id="4509946505-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4509946505-10">[</span><span class="p" data-group-id="4509946505-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4509946505-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4509946505-13">[</span><span class="p" data-group-id="4509946505-13">]</span><span class="p" data-group-id="4509946505-12">}</span><span class="p" data-group-id="4509946505-11">}</span><span class="p" data-group-id="4509946505-10">]</span><span class="p" data-group-id="4509946505-9">}</span><span class="p" data-group-id="4509946505-8">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4509946505-1">}</span><span class="p">.</span></code></pre><p>The third element of the <code class="inline">update</code> instruction is a tuple <code class="inline">{advanced,Extra}</code>,
│ │ │ │  which says that the affected processes are to do a state transformation before
│ │ │ │  loading the new version of the module. This is done by the processes calling the
│ │ │ │  callback function <code class="inline">code_change/3</code> (see <a href="../../../lib/stdlib/doc/html/gen_server.html"><code class="inline">gen_server</code></a> in STDLIB).
│ │ │ │ -The term <code class="inline">Extra</code>, in this case <code class="inline">[]</code>, is passed as is to the function:</p><p><a href="" id="code_change"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4694589693-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="4694589693-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +The term <code class="inline">Extra</code>, in this case <code class="inline">[]</code>, is passed as is to the function:</p><p><a href="" id="code_change"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0445246968-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="0445246968-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4694589693-2">(</span><span class="p" data-group-id="4694589693-3">[</span><span class="ss">code_change</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4694589693-3">]</span><span class="p" data-group-id="4694589693-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0445246968-2">(</span><span class="p" data-group-id="0445246968-3">[</span><span class="ss">code_change</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="0445246968-3">]</span><span class="p" data-group-id="0445246968-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="nf">code_change</span><span class="p" data-group-id="4694589693-4">(</span><span class="p" data-group-id="4694589693-5">{</span><span class="ss">down</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vsn</span><span class="p" data-group-id="4694589693-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4694589693-6">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="4694589693-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="4694589693-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4694589693-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4694589693-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ -</span><span class="nf">code_change</span><span class="p" data-group-id="4694589693-8">(</span><span class="p">_</span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="4694589693-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4694589693-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4694589693-10">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4694589693-10">}</span><span class="p" data-group-id="4694589693-9">}</span><span class="p">.</span></code></pre><p>The first argument is <code class="inline">{down,Vsn}</code> if there is a downgrade, or <code class="inline">Vsn</code> if there is
│ │ │ │ +</span><span class="nf">code_change</span><span class="p" data-group-id="0445246968-4">(</span><span class="p" data-group-id="0445246968-5">{</span><span class="ss">down</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vsn</span><span class="p" data-group-id="0445246968-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0445246968-6">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="0445246968-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="0445246968-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0445246968-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0445246968-7">}</span><span class="p">;</span><span class="w">
│ │ │ │ +</span><span class="nf">code_change</span><span class="p" data-group-id="0445246968-8">(</span><span class="p">_</span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="0445246968-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="0445246968-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0445246968-10">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0445246968-10">}</span><span class="p" data-group-id="0445246968-9">}</span><span class="p">.</span></code></pre><p>The first argument is <code class="inline">{down,Vsn}</code> if there is a downgrade, or <code class="inline">Vsn</code> if there is
│ │ │ │  a upgrade. The term <code class="inline">Vsn</code> is fetched from the 'original' version of the module,
│ │ │ │  that is, the version you are upgrading from, or downgrading to.</p><p>The version is defined by the module attribute <code class="inline">vsn</code>, if any. There is no such
│ │ │ │  attribute in <code class="inline">ch3</code>, so in this case the version is the checksum (a huge integer)
│ │ │ │  of the beam file, an uninteresting value, which is ignored.</p><p>The other callback functions of <code class="inline">ch3</code> must also be modified and perhaps a new
│ │ │ │  interface function must be added, but this is not shown here.</p><h2 id="module-dependencies" class="section-heading">
│ │ │ │    <a href="#module-dependencies" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -95,67 +95,67 @@
│ │ │ │  </h2>
│ │ │ │  <p>Assume that a module is extended by adding an interface function, as in the
│ │ │ │  example in <a href="release_handling.xhtml#appup">Release Handling</a>, where a function
│ │ │ │  <code class="inline">available/0</code> is added to <code class="inline">ch3</code>.</p><p>If a call is added to this function, say in module <code class="inline">m1</code>, a runtime error could
│ │ │ │  can occur during release upgrade if the new version of <code class="inline">m1</code> is loaded first and
│ │ │ │  calls <code class="inline">ch3:available/0</code> before the new version of <code class="inline">ch3</code> is loaded.</p><p>Thus, <code class="inline">ch3</code> must be loaded before <code class="inline">m1</code>, in the upgrade case, and conversely in
│ │ │ │  the downgrade case. <code class="inline">m1</code> is said to be <em>dependent on</em> <code class="inline">ch3</code>. In a release
│ │ │ │ -handling instruction, this is expressed by the <code class="inline">DepMods</code> element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3192841434-1">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="3192841434-1">}</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3192841434-2">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3192841434-3">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="3192841434-3">}</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="3192841434-2">}</span></code></pre><p><code class="inline">DepMods</code> is a list of modules, on which <code class="inline">Module</code> is dependent.</p><p><em>Example</em></p><p>The module <code class="inline">m1</code> in application <code class="inline">myapp</code> is dependent on <code class="inline">ch3</code> when
│ │ │ │ +handling instruction, this is expressed by the <code class="inline">DepMods</code> element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7447380110-1">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="7447380110-1">}</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="7447380110-2">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7447380110-3">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="7447380110-3">}</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="7447380110-2">}</span></code></pre><p><code class="inline">DepMods</code> is a list of modules, on which <code class="inline">Module</code> is dependent.</p><p><em>Example</em></p><p>The module <code class="inline">m1</code> in application <code class="inline">myapp</code> is dependent on <code class="inline">ch3</code> when
│ │ │ │  upgrading from &quot;1&quot; to &quot;2&quot;, or downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="ss">myapp</span><span class="p">.</span><span class="nc">appup</span><span class="p">:</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="3877620859-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3877620859-2">[</span><span class="p" data-group-id="3877620859-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3877620859-4">[</span><span class="p" data-group-id="3877620859-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3877620859-6">[</span><span class="ss">ch3</span><span class="p" data-group-id="3877620859-6">]</span><span class="p" data-group-id="3877620859-5">}</span><span class="p" data-group-id="3877620859-4">]</span><span class="p" data-group-id="3877620859-3">}</span><span class="p" data-group-id="3877620859-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3877620859-7">[</span><span class="p" data-group-id="3877620859-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3877620859-9">[</span><span class="p" data-group-id="3877620859-10">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3877620859-11">[</span><span class="ss">ch3</span><span class="p" data-group-id="3877620859-11">]</span><span class="p" data-group-id="3877620859-10">}</span><span class="p" data-group-id="3877620859-9">]</span><span class="p" data-group-id="3877620859-8">}</span><span class="p" data-group-id="3877620859-7">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3877620859-1">}</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8786561658-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8786561658-2">[</span><span class="p" data-group-id="8786561658-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8786561658-4">[</span><span class="p" data-group-id="8786561658-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8786561658-6">[</span><span class="ss">ch3</span><span class="p" data-group-id="8786561658-6">]</span><span class="p" data-group-id="8786561658-5">}</span><span class="p" data-group-id="8786561658-4">]</span><span class="p" data-group-id="8786561658-3">}</span><span class="p" data-group-id="8786561658-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8786561658-7">[</span><span class="p" data-group-id="8786561658-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8786561658-9">[</span><span class="p" data-group-id="8786561658-10">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8786561658-11">[</span><span class="ss">ch3</span><span class="p" data-group-id="8786561658-11">]</span><span class="p" data-group-id="8786561658-10">}</span><span class="p" data-group-id="8786561658-9">]</span><span class="p" data-group-id="8786561658-8">}</span><span class="p" data-group-id="8786561658-7">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8786561658-1">}</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │  </span><span class="ss">ch_app</span><span class="p">.</span><span class="nc">appup</span><span class="p">:</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="p" data-group-id="3877620859-12">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3877620859-13">[</span><span class="p" data-group-id="3877620859-14">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3877620859-15">[</span><span class="p" data-group-id="3877620859-16">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3877620859-16">}</span><span class="p" data-group-id="3877620859-15">]</span><span class="p" data-group-id="3877620859-14">}</span><span class="p" data-group-id="3877620859-13">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3877620859-17">[</span><span class="p" data-group-id="3877620859-18">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3877620859-19">[</span><span class="p" data-group-id="3877620859-20">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3877620859-20">}</span><span class="p" data-group-id="3877620859-19">]</span><span class="p" data-group-id="3877620859-18">}</span><span class="p" data-group-id="3877620859-17">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="3877620859-12">}</span><span class="p">.</span></code></pre><p>If instead <code class="inline">m1</code> and <code class="inline">ch3</code> belong to the same application, the <code class="inline">.appup</code> file can
│ │ │ │ -look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0261417986-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0261417986-2">[</span><span class="p" data-group-id="0261417986-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0261417986-4">[</span><span class="p" data-group-id="0261417986-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0261417986-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0261417986-6">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0261417986-7">[</span><span class="ss">ch3</span><span class="p" data-group-id="0261417986-7">]</span><span class="p" data-group-id="0261417986-6">}</span><span class="p" data-group-id="0261417986-4">]</span><span class="p" data-group-id="0261417986-3">}</span><span class="p" data-group-id="0261417986-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0261417986-8">[</span><span class="p" data-group-id="0261417986-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0261417986-10">[</span><span class="p" data-group-id="0261417986-11">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0261417986-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0261417986-12">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0261417986-13">[</span><span class="ss">ch3</span><span class="p" data-group-id="0261417986-13">]</span><span class="p" data-group-id="0261417986-12">}</span><span class="p" data-group-id="0261417986-10">]</span><span class="p" data-group-id="0261417986-9">}</span><span class="p" data-group-id="0261417986-8">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0261417986-1">}</span><span class="p">.</span></code></pre><p><code class="inline">m1</code> is dependent on <code class="inline">ch3</code> also when downgrading. <code class="inline">systools</code> knows the
│ │ │ │ +</span><span class="p" data-group-id="8786561658-12">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8786561658-13">[</span><span class="p" data-group-id="8786561658-14">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8786561658-15">[</span><span class="p" data-group-id="8786561658-16">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8786561658-16">}</span><span class="p" data-group-id="8786561658-15">]</span><span class="p" data-group-id="8786561658-14">}</span><span class="p" data-group-id="8786561658-13">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8786561658-17">[</span><span class="p" data-group-id="8786561658-18">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8786561658-19">[</span><span class="p" data-group-id="8786561658-20">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="8786561658-20">}</span><span class="p" data-group-id="8786561658-19">]</span><span class="p" data-group-id="8786561658-18">}</span><span class="p" data-group-id="8786561658-17">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8786561658-12">}</span><span class="p">.</span></code></pre><p>If instead <code class="inline">m1</code> and <code class="inline">ch3</code> belong to the same application, the <code class="inline">.appup</code> file can
│ │ │ │ +look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4517540225-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4517540225-2">[</span><span class="p" data-group-id="4517540225-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4517540225-4">[</span><span class="p" data-group-id="4517540225-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="4517540225-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4517540225-6">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4517540225-7">[</span><span class="ss">ch3</span><span class="p" data-group-id="4517540225-7">]</span><span class="p" data-group-id="4517540225-6">}</span><span class="p" data-group-id="4517540225-4">]</span><span class="p" data-group-id="4517540225-3">}</span><span class="p" data-group-id="4517540225-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4517540225-8">[</span><span class="p" data-group-id="4517540225-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4517540225-10">[</span><span class="p" data-group-id="4517540225-11">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="4517540225-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4517540225-12">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4517540225-13">[</span><span class="ss">ch3</span><span class="p" data-group-id="4517540225-13">]</span><span class="p" data-group-id="4517540225-12">}</span><span class="p" data-group-id="4517540225-10">]</span><span class="p" data-group-id="4517540225-9">}</span><span class="p" data-group-id="4517540225-8">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4517540225-1">}</span><span class="p">.</span></code></pre><p><code class="inline">m1</code> is dependent on <code class="inline">ch3</code> also when downgrading. <code class="inline">systools</code> knows the
│ │ │ │  difference between up- and downgrading and generates a correct <code class="inline">relup</code>, where
│ │ │ │  <code class="inline">ch3</code> is loaded before <code class="inline">m1</code> when upgrading, but <code class="inline">m1</code> is loaded before <code class="inline">ch3</code> when
│ │ │ │  downgrading.</p><p><a href="" id="spec"></a></p><h2 id="changing-code-for-a-special-process" class="section-heading">
│ │ │ │    <a href="#changing-code-for-a-special-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Code for a Special Process</span>
│ │ │ │  </h2>
│ │ │ │  <p>In this case, simple code replacement is not sufficient. When a new version of a
│ │ │ │  residence module for a special process is loaded, the process must make a fully
│ │ │ │  qualified call to its loop function to switch to the new code. Thus,
│ │ │ │  synchronized code replacement must be used.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The name(s) of the user-defined residence module(s) must be listed in the
│ │ │ │  <code class="inline">Modules</code> part of the child specification for the special process. Otherwise
│ │ │ │  the release handler cannot find the process.</p></section><p><em>Example</em></p><p>Consider the example <code class="inline">ch4</code> in <a href="spec_proc.xhtml#ex">sys and proc_lib</a>.
│ │ │ │ -When started by a supervisor, the child specification can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8176965435-1">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8176965435-2">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8176965435-3">[</span><span class="p" data-group-id="8176965435-3">]</span><span class="p" data-group-id="8176965435-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="ss">permanent</span><span class="p">,</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8176965435-4">[</span><span class="ss">ch4</span><span class="p" data-group-id="8176965435-4">]</span><span class="p" data-group-id="8176965435-1">}</span></code></pre><p>If <code class="inline">ch4</code> is part of the application <code class="inline">sp_app</code> and a new version of the module is
│ │ │ │ +When started by a supervisor, the child specification can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8312234254-1">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8312234254-2">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8312234254-3">[</span><span class="p" data-group-id="8312234254-3">]</span><span class="p" data-group-id="8312234254-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="ss">permanent</span><span class="p">,</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8312234254-4">[</span><span class="ss">ch4</span><span class="p" data-group-id="8312234254-4">]</span><span class="p" data-group-id="8312234254-1">}</span></code></pre><p>If <code class="inline">ch4</code> is part of the application <code class="inline">sp_app</code> and a new version of the module is
│ │ │ │  to be loaded when upgrading from version &quot;1&quot; to &quot;2&quot; of this application,
│ │ │ │ -<code class="inline">sp_app.appup</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7569454001-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7569454001-2">[</span><span class="p" data-group-id="7569454001-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7569454001-4">[</span><span class="p" data-group-id="7569454001-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7569454001-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7569454001-7">[</span><span class="p" data-group-id="7569454001-7">]</span><span class="p" data-group-id="7569454001-6">}</span><span class="p" data-group-id="7569454001-5">}</span><span class="p" data-group-id="7569454001-4">]</span><span class="p" data-group-id="7569454001-3">}</span><span class="p" data-group-id="7569454001-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7569454001-8">[</span><span class="p" data-group-id="7569454001-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7569454001-10">[</span><span class="p" data-group-id="7569454001-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7569454001-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7569454001-13">[</span><span class="p" data-group-id="7569454001-13">]</span><span class="p" data-group-id="7569454001-12">}</span><span class="p" data-group-id="7569454001-11">}</span><span class="p" data-group-id="7569454001-10">]</span><span class="p" data-group-id="7569454001-9">}</span><span class="p" data-group-id="7569454001-8">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7569454001-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">update</code> instruction must contain the tuple <code class="inline">{advanced,Extra}</code>. The
│ │ │ │ +<code class="inline">sp_app.appup</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1591413074-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1591413074-2">[</span><span class="p" data-group-id="1591413074-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1591413074-4">[</span><span class="p" data-group-id="1591413074-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1591413074-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1591413074-7">[</span><span class="p" data-group-id="1591413074-7">]</span><span class="p" data-group-id="1591413074-6">}</span><span class="p" data-group-id="1591413074-5">}</span><span class="p" data-group-id="1591413074-4">]</span><span class="p" data-group-id="1591413074-3">}</span><span class="p" data-group-id="1591413074-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1591413074-8">[</span><span class="p" data-group-id="1591413074-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1591413074-10">[</span><span class="p" data-group-id="1591413074-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1591413074-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1591413074-13">[</span><span class="p" data-group-id="1591413074-13">]</span><span class="p" data-group-id="1591413074-12">}</span><span class="p" data-group-id="1591413074-11">}</span><span class="p" data-group-id="1591413074-10">]</span><span class="p" data-group-id="1591413074-9">}</span><span class="p" data-group-id="1591413074-8">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1591413074-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">update</code> instruction must contain the tuple <code class="inline">{advanced,Extra}</code>. The
│ │ │ │  instruction makes the special process call the callback function
│ │ │ │  <code class="inline">system_code_change/4</code>, a function the user must implement. The term <code class="inline">Extra</code>, in
│ │ │ │ -this case <code class="inline">[]</code>, is passed as is to <code class="inline">system_code_change/4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7486729600-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="7486729600-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +this case <code class="inline">[]</code>, is passed as is to <code class="inline">system_code_change/4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1946952637-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="1946952637-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7486729600-2">(</span><span class="p" data-group-id="7486729600-3">[</span><span class="ss">system_code_change</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="7486729600-3">]</span><span class="p" data-group-id="7486729600-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1946952637-2">(</span><span class="p" data-group-id="1946952637-3">[</span><span class="ss">system_code_change</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="1946952637-3">]</span><span class="p" data-group-id="1946952637-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">system_code_change</span><span class="p" data-group-id="7486729600-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="7486729600-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7486729600-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7486729600-5">}</span><span class="p">.</span></code></pre><ul><li>The first argument is the internal state <code class="inline">State</code>, passed from
│ │ │ │ +</span><span class="nf">system_code_change</span><span class="p" data-group-id="1946952637-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="1946952637-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1946952637-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1946952637-5">}</span><span class="p">.</span></code></pre><ul><li>The first argument is the internal state <code class="inline">State</code>, passed from
│ │ │ │  function <a href="../../../lib/stdlib/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg(Request, From, Parent, Module, Deb, State)</code></a>, and called by the special
│ │ │ │  process when a system message is received. In <code class="inline">ch4</code>, the internal
│ │ │ │  state is the set of available channels <code class="inline">Chs</code>.</li><li>The second argument is the name of the module (<code class="inline">ch4</code>).</li><li>The third argument is <code class="inline">Vsn</code> or <code class="inline">{down,Vsn}</code>, as described for
│ │ │ │  <a href="../../../lib/stdlib/doc/html/gen_server.html#c:code_change/3"><code class="inline">gen_server:code_change/3</code></a> in
│ │ │ │  <a href="appup_cookbook.xhtml#code_change">Changing Internal State</a>.</li></ul><p>In this case, all arguments but the first are ignored and the function simply
│ │ │ │  returns the internal state again. This is enough if the code only has been
│ │ │ │  extended. If instead the internal state is changed (similar to the example in
│ │ │ │ @@ -176,85 +176,85 @@
│ │ │ │    <span class="text">Changing Properties</span>
│ │ │ │  </h3>
│ │ │ │  <p>Since the supervisor is to change its internal state, synchronized code
│ │ │ │  replacement is required. However, a special <code class="inline">update</code> instruction must be used.</p><p>First, the new version of the callback module must be loaded, both in the case
│ │ │ │  of upgrade and downgrade. Then the new return value of <code class="inline">init/1</code> can be checked
│ │ │ │  and the internal state be changed accordingly.</p><p>The following <code class="inline">upgrade</code> instruction is used for supervisors:</p><pre><code class="text">{update, Module, supervisor}</code></pre><p><em>Example</em></p><p>To change the restart strategy of <code class="inline">ch_sup</code> (from
│ │ │ │  <a href="sup_princ.xhtml#ex">Supervisor Behaviour</a>) from <code class="inline">one_for_one</code> to <code class="inline">one_for_all</code>,
│ │ │ │ -change the callback function <code class="inline">init/1</code> in <code class="inline">ch_sup.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1854520379-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="1854520379-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +change the callback function <code class="inline">init/1</code> in <code class="inline">ch_sup.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4661997792-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="4661997792-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1854520379-2">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="1854520379-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1854520379-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1854520379-4">{</span><span class="p" data-group-id="1854520379-5">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_all</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1854520379-5">}</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1854520379-4">}</span><span class="p" data-group-id="1854520379-3">}</span><span class="p">.</span></code></pre><p>The file <code class="inline">ch_app.appup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5797527737-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5797527737-2">[</span><span class="p" data-group-id="5797527737-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5797527737-4">[</span><span class="p" data-group-id="5797527737-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="5797527737-5">}</span><span class="p" data-group-id="5797527737-4">]</span><span class="p" data-group-id="5797527737-3">}</span><span class="p" data-group-id="5797527737-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="5797527737-6">[</span><span class="p" data-group-id="5797527737-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5797527737-8">[</span><span class="p" data-group-id="5797527737-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="5797527737-9">}</span><span class="p" data-group-id="5797527737-8">]</span><span class="p" data-group-id="5797527737-7">}</span><span class="p" data-group-id="5797527737-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5797527737-1">}</span><span class="p">.</span></code></pre><h3 id="changing-child-specifications" class="section-heading">
│ │ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4661997792-2">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="4661997792-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4661997792-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4661997792-4">{</span><span class="p" data-group-id="4661997792-5">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_all</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4661997792-5">}</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4661997792-4">}</span><span class="p" data-group-id="4661997792-3">}</span><span class="p">.</span></code></pre><p>The file <code class="inline">ch_app.appup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2411687282-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2411687282-2">[</span><span class="p" data-group-id="2411687282-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2411687282-4">[</span><span class="p" data-group-id="2411687282-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="2411687282-5">}</span><span class="p" data-group-id="2411687282-4">]</span><span class="p" data-group-id="2411687282-3">}</span><span class="p" data-group-id="2411687282-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="2411687282-6">[</span><span class="p" data-group-id="2411687282-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2411687282-8">[</span><span class="p" data-group-id="2411687282-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="2411687282-9">}</span><span class="p" data-group-id="2411687282-8">]</span><span class="p" data-group-id="2411687282-7">}</span><span class="p" data-group-id="2411687282-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="2411687282-1">}</span><span class="p">.</span></code></pre><h3 id="changing-child-specifications" class="section-heading">
│ │ │ │    <a href="#changing-child-specifications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Child Specifications</span>
│ │ │ │  </h3>
│ │ │ │  <p>The instruction, and thus the <code class="inline">.appup</code> file, when changing an existing child
│ │ │ │ -specification, is the same as when changing properties as described earlier:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0800789694-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0800789694-2">[</span><span class="p" data-group-id="0800789694-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0800789694-4">[</span><span class="p" data-group-id="0800789694-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0800789694-5">}</span><span class="p" data-group-id="0800789694-4">]</span><span class="p" data-group-id="0800789694-3">}</span><span class="p" data-group-id="0800789694-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0800789694-6">[</span><span class="p" data-group-id="0800789694-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0800789694-8">[</span><span class="p" data-group-id="0800789694-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0800789694-9">}</span><span class="p" data-group-id="0800789694-8">]</span><span class="p" data-group-id="0800789694-7">}</span><span class="p" data-group-id="0800789694-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0800789694-1">}</span><span class="p">.</span></code></pre><p>The changes do not affect existing child processes. For example, changing the
│ │ │ │ +specification, is the same as when changing properties as described earlier:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1745912423-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1745912423-2">[</span><span class="p" data-group-id="1745912423-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1745912423-4">[</span><span class="p" data-group-id="1745912423-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="1745912423-5">}</span><span class="p" data-group-id="1745912423-4">]</span><span class="p" data-group-id="1745912423-3">}</span><span class="p" data-group-id="1745912423-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1745912423-6">[</span><span class="p" data-group-id="1745912423-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1745912423-8">[</span><span class="p" data-group-id="1745912423-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="1745912423-9">}</span><span class="p" data-group-id="1745912423-8">]</span><span class="p" data-group-id="1745912423-7">}</span><span class="p" data-group-id="1745912423-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1745912423-1">}</span><span class="p">.</span></code></pre><p>The changes do not affect existing child processes. For example, changing the
│ │ │ │  start function only specifies how the child process is to be restarted, if
│ │ │ │  needed later on.</p><p>The id of the child specification cannot be changed.</p><p>Changing the <code class="inline">Modules</code> field of the child specification can affect the release
│ │ │ │  handling process itself, as this field is used to identify which processes are
│ │ │ │  affected when doing a synchronized code replacement.</p><p><a href="" id="sup_add"></a></p><h3 id="adding-and-deleting-child-processes" class="section-heading">
│ │ │ │    <a href="#adding-and-deleting-child-processes" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Adding and Deleting Child Processes</span>
│ │ │ │  </h3>
│ │ │ │  <p>As stated earlier, changing child specifications does not affect existing child
│ │ │ │  processes. New child specifications are automatically added, but not deleted.
│ │ │ │  Child processes are not automatically started or terminated, this must be done
│ │ │ │  using <code class="inline">apply</code> instructions.</p><p><em>Example</em></p><p>Assume a new child process <code class="inline">m1</code> is to be added to <code class="inline">ch_sup</code> when
│ │ │ │  upgrading <code class="inline">ch_app</code> from &quot;1&quot; to &quot;2&quot;. This means <code class="inline">m1</code> is to be deleted when
│ │ │ │ -downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0808313801-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0808313801-2">[</span><span class="p" data-group-id="0808313801-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0808313801-4">[</span><span class="p" data-group-id="0808313801-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0808313801-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0808313801-6">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808313801-7">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808313801-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="0808313801-8">]</span><span class="p" data-group-id="0808313801-7">}</span><span class="p" data-group-id="0808313801-6">}</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0808313801-4">]</span><span class="p" data-group-id="0808313801-3">}</span><span class="p" data-group-id="0808313801-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0808313801-9">[</span><span class="p" data-group-id="0808313801-10">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0808313801-11">[</span><span class="p" data-group-id="0808313801-12">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808313801-13">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808313801-14">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="0808313801-14">]</span><span class="p" data-group-id="0808313801-13">}</span><span class="p" data-group-id="0808313801-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0808313801-15">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808313801-16">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0808313801-17">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="0808313801-17">]</span><span class="p" data-group-id="0808313801-16">}</span><span class="p" data-group-id="0808313801-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0808313801-18">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0808313801-18">}</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0808313801-11">]</span><span class="p" data-group-id="0808313801-10">}</span><span class="p" data-group-id="0808313801-9">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0808313801-1">}</span><span class="p">.</span></code></pre><p>The order of the instructions is important.</p><p>The supervisor must be registered as <code class="inline">ch_sup</code> for the script to work. If the
│ │ │ │ +downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4189591035-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4189591035-2">[</span><span class="p" data-group-id="4189591035-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4189591035-4">[</span><span class="p" data-group-id="4189591035-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="4189591035-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4189591035-6">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4189591035-7">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4189591035-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="4189591035-8">]</span><span class="p" data-group-id="4189591035-7">}</span><span class="p" data-group-id="4189591035-6">}</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4189591035-4">]</span><span class="p" data-group-id="4189591035-3">}</span><span class="p" data-group-id="4189591035-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4189591035-9">[</span><span class="p" data-group-id="4189591035-10">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4189591035-11">[</span><span class="p" data-group-id="4189591035-12">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4189591035-13">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4189591035-14">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="4189591035-14">]</span><span class="p" data-group-id="4189591035-13">}</span><span class="p" data-group-id="4189591035-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4189591035-15">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4189591035-16">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4189591035-17">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="4189591035-17">]</span><span class="p" data-group-id="4189591035-16">}</span><span class="p" data-group-id="4189591035-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="4189591035-18">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="4189591035-18">}</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4189591035-11">]</span><span class="p" data-group-id="4189591035-10">}</span><span class="p" data-group-id="4189591035-9">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4189591035-1">}</span><span class="p">.</span></code></pre><p>The order of the instructions is important.</p><p>The supervisor must be registered as <code class="inline">ch_sup</code> for the script to work. If the
│ │ │ │  supervisor is not registered, it cannot be accessed directly from the script.
│ │ │ │  Instead a help function that finds the pid of the supervisor and calls
│ │ │ │  <code class="inline">supervisor:restart_child</code>, and so on, must be written. This function is then to
│ │ │ │  be called from the script using the <code class="inline">apply</code> instruction.</p><p>If the module <code class="inline">m1</code> is introduced in version &quot;2&quot; of <code class="inline">ch_app</code>, it must also be
│ │ │ │ -loaded when upgrading and deleted when downgrading:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7499638701-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7499638701-2">[</span><span class="p" data-group-id="7499638701-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7499638701-4">[</span><span class="p" data-group-id="7499638701-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7499638701-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7499638701-6">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7499638701-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7499638701-7">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7499638701-8">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7499638701-9">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7499638701-9">]</span><span class="p" data-group-id="7499638701-8">}</span><span class="p" data-group-id="7499638701-7">}</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7499638701-4">]</span><span class="p" data-group-id="7499638701-3">}</span><span class="p" data-group-id="7499638701-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7499638701-10">[</span><span class="p" data-group-id="7499638701-11">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7499638701-12">[</span><span class="p" data-group-id="7499638701-13">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7499638701-14">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7499638701-15">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7499638701-15">]</span><span class="p" data-group-id="7499638701-14">}</span><span class="p" data-group-id="7499638701-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7499638701-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7499638701-17">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7499638701-18">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7499638701-18">]</span><span class="p" data-group-id="7499638701-17">}</span><span class="p" data-group-id="7499638701-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7499638701-19">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7499638701-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="7499638701-20">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7499638701-20">}</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="7499638701-12">]</span><span class="p" data-group-id="7499638701-11">}</span><span class="p" data-group-id="7499638701-10">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7499638701-1">}</span><span class="p">.</span></code></pre><p>As stated earlier, the order of the instructions is important. When upgrading,
│ │ │ │ +loaded when upgrading and deleted when downgrading:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5528639704-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5528639704-2">[</span><span class="p" data-group-id="5528639704-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="5528639704-4">[</span><span class="p" data-group-id="5528639704-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="5528639704-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5528639704-6">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="5528639704-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5528639704-7">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5528639704-8">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5528639704-9">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="5528639704-9">]</span><span class="p" data-group-id="5528639704-8">}</span><span class="p" data-group-id="5528639704-7">}</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="5528639704-4">]</span><span class="p" data-group-id="5528639704-3">}</span><span class="p" data-group-id="5528639704-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="5528639704-10">[</span><span class="p" data-group-id="5528639704-11">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="5528639704-12">[</span><span class="p" data-group-id="5528639704-13">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5528639704-14">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5528639704-15">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="5528639704-15">]</span><span class="p" data-group-id="5528639704-14">}</span><span class="p" data-group-id="5528639704-13">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5528639704-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5528639704-17">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5528639704-18">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="5528639704-18">]</span><span class="p" data-group-id="5528639704-17">}</span><span class="p" data-group-id="5528639704-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5528639704-19">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="5528639704-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="5528639704-20">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="5528639704-20">}</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="5528639704-12">]</span><span class="p" data-group-id="5528639704-11">}</span><span class="p" data-group-id="5528639704-10">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="5528639704-1">}</span><span class="p">.</span></code></pre><p>As stated earlier, the order of the instructions is important. When upgrading,
│ │ │ │  <code class="inline">m1</code> must be loaded, and the supervisor child specification changed, before the
│ │ │ │  new child process can be started. When downgrading, the child process must be
│ │ │ │  terminated before the child specification is changed and the module is deleted.</p><h2 id="adding-or-deleting-a-module" class="section-heading">
│ │ │ │    <a href="#adding-or-deleting-a-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Adding or Deleting a Module</span>
│ │ │ │  </h2>
│ │ │ │ -<p>_Example</p><p>_ A new functional module <code class="inline">m</code> is added to <code class="inline">ch_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3234957593-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3234957593-2">[</span><span class="p" data-group-id="3234957593-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3234957593-4">[</span><span class="p" data-group-id="3234957593-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="3234957593-5">}</span><span class="p" data-group-id="3234957593-4">]</span><span class="p" data-group-id="3234957593-3">}</span><span class="p" data-group-id="3234957593-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="3234957593-6">[</span><span class="p" data-group-id="3234957593-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3234957593-8">[</span><span class="p" data-group-id="3234957593-9">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="3234957593-9">}</span><span class="p" data-group-id="3234957593-8">]</span><span class="p" data-group-id="3234957593-7">}</span><span class="p" data-group-id="3234957593-6">]</span></code></pre><h2 id="starting-or-terminating-a-process" class="section-heading">
│ │ │ │ +<p>_Example</p><p>_ A new functional module <code class="inline">m</code> is added to <code class="inline">ch_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8328629216-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8328629216-2">[</span><span class="p" data-group-id="8328629216-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8328629216-4">[</span><span class="p" data-group-id="8328629216-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="8328629216-5">}</span><span class="p" data-group-id="8328629216-4">]</span><span class="p" data-group-id="8328629216-3">}</span><span class="p" data-group-id="8328629216-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8328629216-6">[</span><span class="p" data-group-id="8328629216-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8328629216-8">[</span><span class="p" data-group-id="8328629216-9">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="8328629216-9">}</span><span class="p" data-group-id="8328629216-8">]</span><span class="p" data-group-id="8328629216-7">}</span><span class="p" data-group-id="8328629216-6">]</span></code></pre><h2 id="starting-or-terminating-a-process" class="section-heading">
│ │ │ │    <a href="#starting-or-terminating-a-process" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting or Terminating a Process</span>
│ │ │ │  </h2>
│ │ │ │  <p>In a system structured according to the OTP design principles, any process would
│ │ │ │  be a child process belonging to a supervisor, see
│ │ │ │ @@ -274,29 +274,29 @@
│ │ │ │    <span class="text">Restarting an Application</span>
│ │ │ │  </h2>
│ │ │ │  <p>Restarting an application is useful when a change is too complicated to be made
│ │ │ │  without restarting the processes, for example, if the supervisor hierarchy has
│ │ │ │  been restructured.</p><p><em>Example</em></p><p>When adding a child <code class="inline">m1</code> to <code class="inline">ch_sup</code>, as in
│ │ │ │  <a href="appup_cookbook.xhtml#sup_add">Adding and Deleting Child Processes</a> in Changing a
│ │ │ │  Supervisor, an alternative to updating the supervisor is to restart the entire
│ │ │ │ -application:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7487883745-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7487883745-2">[</span><span class="p" data-group-id="7487883745-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7487883745-4">[</span><span class="p" data-group-id="7487883745-5">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="7487883745-5">}</span><span class="p" data-group-id="7487883745-4">]</span><span class="p" data-group-id="7487883745-3">}</span><span class="p" data-group-id="7487883745-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7487883745-6">[</span><span class="p" data-group-id="7487883745-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7487883745-8">[</span><span class="p" data-group-id="7487883745-9">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="7487883745-9">}</span><span class="p" data-group-id="7487883745-8">]</span><span class="p" data-group-id="7487883745-7">}</span><span class="p" data-group-id="7487883745-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7487883745-1">}</span><span class="p">.</span></code></pre><p><a href="" id="app_spec"></a></p><h2 id="changing-an-application-specification" class="section-heading">
│ │ │ │ +application:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0333500992-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0333500992-2">[</span><span class="p" data-group-id="0333500992-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0333500992-4">[</span><span class="p" data-group-id="0333500992-5">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="0333500992-5">}</span><span class="p" data-group-id="0333500992-4">]</span><span class="p" data-group-id="0333500992-3">}</span><span class="p" data-group-id="0333500992-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0333500992-6">[</span><span class="p" data-group-id="0333500992-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0333500992-8">[</span><span class="p" data-group-id="0333500992-9">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="0333500992-9">}</span><span class="p" data-group-id="0333500992-8">]</span><span class="p" data-group-id="0333500992-7">}</span><span class="p" data-group-id="0333500992-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0333500992-1">}</span><span class="p">.</span></code></pre><p><a href="" id="app_spec"></a></p><h2 id="changing-an-application-specification" class="section-heading">
│ │ │ │    <a href="#changing-an-application-specification" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing an Application Specification</span>
│ │ │ │  </h2>
│ │ │ │  <p>When installing a release, the application specifications are automatically
│ │ │ │  updated before evaluating the <code class="inline">relup</code> script. Thus, no instructions are needed
│ │ │ │ -in the <code class="inline">.appup</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7136328899-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7136328899-2">[</span><span class="p" data-group-id="7136328899-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7136328899-4">[</span><span class="p" data-group-id="7136328899-4">]</span><span class="p" data-group-id="7136328899-3">}</span><span class="p" data-group-id="7136328899-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7136328899-5">[</span><span class="p" data-group-id="7136328899-6">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7136328899-7">[</span><span class="p" data-group-id="7136328899-7">]</span><span class="p" data-group-id="7136328899-6">}</span><span class="p" data-group-id="7136328899-5">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7136328899-1">}</span><span class="p">.</span></code></pre><h2 id="changing-application-configuration" class="section-heading">
│ │ │ │ +in the <code class="inline">.appup</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3865375257-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3865375257-2">[</span><span class="p" data-group-id="3865375257-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3865375257-4">[</span><span class="p" data-group-id="3865375257-4">]</span><span class="p" data-group-id="3865375257-3">}</span><span class="p" data-group-id="3865375257-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3865375257-5">[</span><span class="p" data-group-id="3865375257-6">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3865375257-7">[</span><span class="p" data-group-id="3865375257-7">]</span><span class="p" data-group-id="3865375257-6">}</span><span class="p" data-group-id="3865375257-5">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3865375257-1">}</span><span class="p">.</span></code></pre><h2 id="changing-application-configuration" class="section-heading">
│ │ │ │    <a href="#changing-application-configuration" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Application Configuration</span>
│ │ │ │  </h2>
│ │ │ │  <p>Changing an application configuration by updating the <code class="inline">env</code> key in the <code class="inline">.app</code>
│ │ │ │  file is an instance of changing an application specification, see the previous
│ │ │ │ @@ -311,26 +311,26 @@
│ │ │ │  applications apply to primary applications only. There are no corresponding
│ │ │ │  instructions for included applications. However, since an included application
│ │ │ │  is really a supervision tree with a topmost supervisor, started as a child
│ │ │ │  process to a supervisor in the including application, a <code class="inline">.relup</code> file can be
│ │ │ │  manually created.</p><p><em>Example</em></p><p>Assume there is a release containing an application <code class="inline">prim_app</code>, which
│ │ │ │  have a supervisor <code class="inline">prim_sup</code> in its supervision tree.</p><p>In a new version of the release, the application <code class="inline">ch_app</code> is to be included in
│ │ │ │  <code class="inline">prim_app</code>. That is, its topmost supervisor <code class="inline">ch_sup</code> is to be started as a child
│ │ │ │ -process to <code class="inline">prim_sup</code>.</p><p>The workflow is as follows:</p><p><em>Step 1)</em> Edit the code for <code class="inline">prim_sup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5345939523-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5345939523-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="5345939523-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5345939523-3">{</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="ss">supervisor</span><span class="w"> </span><span class="ss">flags</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -          </span><span class="p" data-group-id="5345939523-4">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -           </span><span class="p" data-group-id="5345939523-5">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5345939523-6">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="5345939523-7">[</span><span class="p" data-group-id="5345939523-7">]</span><span class="p" data-group-id="5345939523-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -            </span><span class="ss">permanent</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="ss">supervisor</span><span class="p">,</span><span class="p" data-group-id="5345939523-8">[</span><span class="ss">ch_sup</span><span class="p" data-group-id="5345939523-8">]</span><span class="p" data-group-id="5345939523-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -           </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5345939523-4">]</span><span class="p" data-group-id="5345939523-3">}</span><span class="p" data-group-id="5345939523-2">}</span><span class="p">.</span></code></pre><p><em>Step 2)</em> Edit the <code class="inline">.app</code> file for <code class="inline">prim_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4151101737-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4151101737-2">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4151101737-3">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="4151101737-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +process to <code class="inline">prim_sup</code>.</p><p>The workflow is as follows:</p><p><em>Step 1)</em> Edit the code for <code class="inline">prim_sup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6099918812-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6099918812-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="6099918812-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6099918812-3">{</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="ss">supervisor</span><span class="w"> </span><span class="ss">flags</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ +          </span><span class="p" data-group-id="6099918812-4">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ +           </span><span class="p" data-group-id="6099918812-5">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6099918812-6">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="6099918812-7">[</span><span class="p" data-group-id="6099918812-7">]</span><span class="p" data-group-id="6099918812-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +            </span><span class="ss">permanent</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="ss">supervisor</span><span class="p">,</span><span class="p" data-group-id="6099918812-8">[</span><span class="ss">ch_sup</span><span class="p" data-group-id="6099918812-8">]</span><span class="p" data-group-id="6099918812-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +           </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6099918812-4">]</span><span class="p" data-group-id="6099918812-3">}</span><span class="p" data-group-id="6099918812-2">}</span><span class="p">.</span></code></pre><p><em>Step 2)</em> Edit the <code class="inline">.app</code> file for <code class="inline">prim_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0113988050-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="0113988050-2">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0113988050-3">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="0113988050-3">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="4151101737-4">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4151101737-5">[</span><span class="ss">ch_app</span><span class="p" data-group-id="4151101737-5">]</span><span class="p" data-group-id="4151101737-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="0113988050-4">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0113988050-5">[</span><span class="ss">ch_app</span><span class="p" data-group-id="0113988050-5">]</span><span class="p" data-group-id="0113988050-4">}</span><span class="p">,</span><span class="w">
│ │ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4151101737-2">]</span><span class="p" data-group-id="4151101737-1">}</span><span class="p">.</span></code></pre><p><em>Step 3)</em> Create a new <code class="inline">.rel</code> file, including <code class="inline">ch_app</code>:</p><pre><code class="text">{release,
│ │ │ │ + </span><span class="p" data-group-id="0113988050-2">]</span><span class="p" data-group-id="0113988050-1">}</span><span class="p">.</span></code></pre><p><em>Step 3)</em> Create a new <code class="inline">.rel</code> file, including <code class="inline">ch_app</code>:</p><pre><code class="text">{release,
│ │ │ │   ...,
│ │ │ │   [...,
│ │ │ │    {prim_app, &quot;2&quot;},
│ │ │ │    {ch_app, &quot;1&quot;}]}.</code></pre><p>The included application can be started in two ways. This is described in the
│ │ │ │  next two sections.</p><h3 id="application-restart" class="section-heading">
│ │ │ │    <a href="#application-restart" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │ @@ -341,118 +341,118 @@
│ │ │ │  <code class="inline">prim_app</code> application. Normally, the <code class="inline">restart_application</code> instruction in the
│ │ │ │  <code class="inline">.appup</code> file for <code class="inline">prim_app</code> would be used.</p><p>However, if this is done and a <code class="inline">.relup</code> file is generated, not only would it
│ │ │ │  contain instructions for restarting (that is, removing and adding) <code class="inline">prim_app</code>,
│ │ │ │  it would also contain instructions for starting <code class="inline">ch_app</code> (and stopping it, in
│ │ │ │  the case of downgrade). This is because <code class="inline">ch_app</code> is included in the new <code class="inline">.rel</code>
│ │ │ │  file, but not in the old one.</p><p>Instead, a correct <code class="inline">relup</code> file can be created manually, either from scratch or
│ │ │ │  by editing the generated version. The instructions for starting/stopping
│ │ │ │ -<code class="inline">ch_app</code> are replaced by instructions for loading/unloading the application:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="4201512121-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4201512121-2">[</span><span class="p" data-group-id="4201512121-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4201512121-4">[</span><span class="p" data-group-id="4201512121-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4201512121-5">[</span><span class="p" data-group-id="4201512121-6">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="4201512121-7">{</span><span class="n">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="4201512121-8">[</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">ch3</span><span class="p" data-group-id="4201512121-8">]</span><span class="p" data-group-id="4201512121-7">}</span><span class="p" data-group-id="4201512121-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-9">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="4201512121-10">{</span><span class="n">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="4201512121-11">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="4201512121-11">]</span><span class="p" data-group-id="4201512121-10">}</span><span class="p" data-group-id="4201512121-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +<code class="inline">ch_app</code> are replaced by instructions for loading/unloading the application:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="1411889590-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1411889590-2">[</span><span class="p" data-group-id="1411889590-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1411889590-4">[</span><span class="p" data-group-id="1411889590-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1411889590-5">[</span><span class="p" data-group-id="1411889590-6">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="1411889590-7">{</span><span class="n">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="1411889590-8">[</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">ch3</span><span class="p" data-group-id="1411889590-8">]</span><span class="p" data-group-id="1411889590-7">}</span><span class="p" data-group-id="1411889590-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-9">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="1411889590-10">{</span><span class="n">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="1411889590-11">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="1411889590-11">]</span><span class="p" data-group-id="1411889590-10">}</span><span class="p" data-group-id="1411889590-9">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-12">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="4201512121-13">{</span><span class="n">application</span><span class="p">,</span><span class="n">stop</span><span class="p">,</span><span class="p" data-group-id="4201512121-14">[</span><span class="n">prim_app</span><span class="p" data-group-id="4201512121-14">]</span><span class="p" data-group-id="4201512121-13">}</span><span class="p" data-group-id="4201512121-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-15">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="4201512121-16">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-16">}</span><span class="p" data-group-id="4201512121-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-17">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="4201512121-18">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-18">}</span><span class="p" data-group-id="4201512121-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-19">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="4201512121-20">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="4201512121-20">]</span><span class="p" data-group-id="4201512121-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-21">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="4201512121-22">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-22">}</span><span class="p" data-group-id="4201512121-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-23">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="4201512121-24">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-24">}</span><span class="p" data-group-id="4201512121-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-25">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="4201512121-26">{</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-26">}</span><span class="p" data-group-id="4201512121-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-27">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="4201512121-28">{</span><span class="n">ch3</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-28">}</span><span class="p" data-group-id="4201512121-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-29">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="4201512121-30">{</span><span class="n">application</span><span class="p">,</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="4201512121-31">[</span><span class="n">ch_app</span><span class="p" data-group-id="4201512121-31">]</span><span class="p" data-group-id="4201512121-30">}</span><span class="p" data-group-id="4201512121-29">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-32">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="4201512121-33">{</span><span class="n">application</span><span class="p">,</span><span class="n">start</span><span class="p">,</span><span class="p" data-group-id="4201512121-34">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">permanent</span><span class="p" data-group-id="4201512121-34">]</span><span class="p" data-group-id="4201512121-33">}</span><span class="p" data-group-id="4201512121-32">}</span><span class="p" data-group-id="4201512121-5">]</span><span class="p" data-group-id="4201512121-3">}</span><span class="p" data-group-id="4201512121-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4201512121-35">[</span><span class="p" data-group-id="4201512121-36">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4201512121-37">[</span><span class="p" data-group-id="4201512121-37">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4201512121-38">[</span><span class="p" data-group-id="4201512121-39">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="4201512121-40">{</span><span class="n">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="4201512121-41">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="4201512121-41">]</span><span class="p" data-group-id="4201512121-40">}</span><span class="p" data-group-id="4201512121-39">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-12">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1411889590-13">{</span><span class="n">application</span><span class="p">,</span><span class="n">stop</span><span class="p">,</span><span class="p" data-group-id="1411889590-14">[</span><span class="n">prim_app</span><span class="p" data-group-id="1411889590-14">]</span><span class="p" data-group-id="1411889590-13">}</span><span class="p" data-group-id="1411889590-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-15">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1411889590-16">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-16">}</span><span class="p" data-group-id="1411889590-15">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-17">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1411889590-18">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-18">}</span><span class="p" data-group-id="1411889590-17">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-19">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="1411889590-20">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="1411889590-20">]</span><span class="p" data-group-id="1411889590-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-21">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1411889590-22">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-22">}</span><span class="p" data-group-id="1411889590-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-23">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1411889590-24">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-24">}</span><span class="p" data-group-id="1411889590-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-25">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1411889590-26">{</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-26">}</span><span class="p" data-group-id="1411889590-25">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-27">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1411889590-28">{</span><span class="n">ch3</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-28">}</span><span class="p" data-group-id="1411889590-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-29">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1411889590-30">{</span><span class="n">application</span><span class="p">,</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1411889590-31">[</span><span class="n">ch_app</span><span class="p" data-group-id="1411889590-31">]</span><span class="p" data-group-id="1411889590-30">}</span><span class="p" data-group-id="1411889590-29">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-32">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1411889590-33">{</span><span class="n">application</span><span class="p">,</span><span class="n">start</span><span class="p">,</span><span class="p" data-group-id="1411889590-34">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">permanent</span><span class="p" data-group-id="1411889590-34">]</span><span class="p" data-group-id="1411889590-33">}</span><span class="p" data-group-id="1411889590-32">}</span><span class="p" data-group-id="1411889590-5">]</span><span class="p" data-group-id="1411889590-3">}</span><span class="p" data-group-id="1411889590-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1411889590-35">[</span><span class="p" data-group-id="1411889590-36">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1411889590-37">[</span><span class="p" data-group-id="1411889590-37">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1411889590-38">[</span><span class="p" data-group-id="1411889590-39">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="1411889590-40">{</span><span class="n">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="1411889590-41">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="1411889590-41">]</span><span class="p" data-group-id="1411889590-40">}</span><span class="p" data-group-id="1411889590-39">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="n">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-42">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="4201512121-43">{</span><span class="n">application</span><span class="p">,</span><span class="n">stop</span><span class="p">,</span><span class="p" data-group-id="4201512121-44">[</span><span class="n">prim_app</span><span class="p" data-group-id="4201512121-44">]</span><span class="p" data-group-id="4201512121-43">}</span><span class="p" data-group-id="4201512121-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-45">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="4201512121-46">{</span><span class="n">application</span><span class="p">,</span><span class="n">unload</span><span class="p">,</span><span class="p" data-group-id="4201512121-47">[</span><span class="n">ch_app</span><span class="p" data-group-id="4201512121-47">]</span><span class="p" data-group-id="4201512121-46">}</span><span class="p" data-group-id="4201512121-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-48">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="4201512121-49">{</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-49">}</span><span class="p" data-group-id="4201512121-48">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-50">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="4201512121-51">{</span><span class="n">ch3</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-51">}</span><span class="p" data-group-id="4201512121-50">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-52">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="4201512121-53">[</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">ch3</span><span class="p" data-group-id="4201512121-53">]</span><span class="p" data-group-id="4201512121-52">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-54">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="4201512121-55">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-55">}</span><span class="p" data-group-id="4201512121-54">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-56">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="4201512121-57">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-57">}</span><span class="p" data-group-id="4201512121-56">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-58">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="4201512121-59">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="4201512121-59">]</span><span class="p" data-group-id="4201512121-58">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-60">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="4201512121-61">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-61">}</span><span class="p" data-group-id="4201512121-60">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-62">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="4201512121-63">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="4201512121-63">}</span><span class="p" data-group-id="4201512121-62">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="4201512121-64">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="4201512121-65">{</span><span class="n">application</span><span class="p">,</span><span class="n">start</span><span class="p">,</span><span class="p" data-group-id="4201512121-66">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">permanent</span><span class="p" data-group-id="4201512121-66">]</span><span class="p" data-group-id="4201512121-65">}</span><span class="p" data-group-id="4201512121-64">}</span><span class="p" data-group-id="4201512121-38">]</span><span class="p" data-group-id="4201512121-36">}</span><span class="p" data-group-id="4201512121-35">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4201512121-1">}</span><span class="p">.</span></code></pre><h3 id="supervisor-change" class="section-heading">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-42">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1411889590-43">{</span><span class="n">application</span><span class="p">,</span><span class="n">stop</span><span class="p">,</span><span class="p" data-group-id="1411889590-44">[</span><span class="n">prim_app</span><span class="p" data-group-id="1411889590-44">]</span><span class="p" data-group-id="1411889590-43">}</span><span class="p" data-group-id="1411889590-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-45">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1411889590-46">{</span><span class="n">application</span><span class="p">,</span><span class="n">unload</span><span class="p">,</span><span class="p" data-group-id="1411889590-47">[</span><span class="n">ch_app</span><span class="p" data-group-id="1411889590-47">]</span><span class="p" data-group-id="1411889590-46">}</span><span class="p" data-group-id="1411889590-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-48">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1411889590-49">{</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-49">}</span><span class="p" data-group-id="1411889590-48">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-50">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1411889590-51">{</span><span class="n">ch3</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-51">}</span><span class="p" data-group-id="1411889590-50">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-52">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="1411889590-53">[</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">ch3</span><span class="p" data-group-id="1411889590-53">]</span><span class="p" data-group-id="1411889590-52">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-54">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1411889590-55">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-55">}</span><span class="p" data-group-id="1411889590-54">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-56">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1411889590-57">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-57">}</span><span class="p" data-group-id="1411889590-56">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-58">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="1411889590-59">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="1411889590-59">]</span><span class="p" data-group-id="1411889590-58">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-60">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1411889590-61">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-61">}</span><span class="p" data-group-id="1411889590-60">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-62">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1411889590-63">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1411889590-63">}</span><span class="p" data-group-id="1411889590-62">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1411889590-64">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1411889590-65">{</span><span class="n">application</span><span class="p">,</span><span class="n">start</span><span class="p">,</span><span class="p" data-group-id="1411889590-66">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">permanent</span><span class="p" data-group-id="1411889590-66">]</span><span class="p" data-group-id="1411889590-65">}</span><span class="p" data-group-id="1411889590-64">}</span><span class="p" data-group-id="1411889590-38">]</span><span class="p" data-group-id="1411889590-36">}</span><span class="p" data-group-id="1411889590-35">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1411889590-1">}</span><span class="p">.</span></code></pre><h3 id="supervisor-change" class="section-heading">
│ │ │ │    <a href="#supervisor-change" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Supervisor Change</span>
│ │ │ │  </h3>
│ │ │ │  <p><em>Step 4b)</em> Another way to start the included application (or stop it in the case
│ │ │ │  of downgrade) is by combining instructions for adding and removing child
│ │ │ │  processes to/from <code class="inline">prim_sup</code> with instructions for loading/unloading all
│ │ │ │  <code class="inline">ch_app</code> code and its application specification.</p><p>Again, the <code class="inline">.relup</code> file is created manually, either from scratch or by editing a
│ │ │ │  generated version. Load all code for <code class="inline">ch_app</code> first, and also load the
│ │ │ │  application specification, before <code class="inline">prim_sup</code> is updated. When downgrading,
│ │ │ │  <code class="inline">prim_sup</code> is to updated first, before the code for <code class="inline">ch_app</code> and its application
│ │ │ │ -specification are unloaded.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0342075105-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0342075105-2">[</span><span class="p" data-group-id="0342075105-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0342075105-4">[</span><span class="p" data-group-id="0342075105-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0342075105-5">[</span><span class="p" data-group-id="0342075105-6">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="0342075105-7">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="0342075105-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="0342075105-8">]</span><span class="p" data-group-id="0342075105-7">}</span><span class="p" data-group-id="0342075105-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-9">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="0342075105-10">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="0342075105-11">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="0342075105-11">]</span><span class="p" data-group-id="0342075105-10">}</span><span class="p" data-group-id="0342075105-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +specification are unloaded.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1943400348-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1943400348-2">[</span><span class="p" data-group-id="1943400348-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1943400348-4">[</span><span class="p" data-group-id="1943400348-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1943400348-5">[</span><span class="p" data-group-id="1943400348-6">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="1943400348-7">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="1943400348-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="1943400348-8">]</span><span class="p" data-group-id="1943400348-7">}</span><span class="p" data-group-id="1943400348-6">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-9">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="1943400348-10">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="1943400348-11">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="1943400348-11">]</span><span class="p" data-group-id="1943400348-10">}</span><span class="p" data-group-id="1943400348-9">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-12">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="0342075105-13">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="0342075105-13">}</span><span class="p" data-group-id="0342075105-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-14">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="0342075105-15">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="0342075105-15">}</span><span class="p" data-group-id="0342075105-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="0342075105-17">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="0342075105-18">[</span><span class="ss">ch_app</span><span class="p" data-group-id="0342075105-18">]</span><span class="p" data-group-id="0342075105-17">}</span><span class="p" data-group-id="0342075105-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-19">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="0342075105-20">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="0342075105-20">]</span><span class="p" data-group-id="0342075105-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-21">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="0342075105-22">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="0342075105-22">}</span><span class="p" data-group-id="0342075105-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-23">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">up</span><span class="p">,</span><span class="p" data-group-id="0342075105-24">[</span><span class="p" data-group-id="0342075105-25">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="0342075105-26">[</span><span class="p" data-group-id="0342075105-26">]</span><span class="p" data-group-id="0342075105-25">}</span><span class="p" data-group-id="0342075105-24">]</span><span class="p" data-group-id="0342075105-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-27">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="0342075105-28">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="0342075105-28">]</span><span class="p" data-group-id="0342075105-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-29">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="0342075105-30">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">restart_child</span><span class="p">,</span><span class="p" data-group-id="0342075105-31">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="0342075105-31">]</span><span class="p" data-group-id="0342075105-30">}</span><span class="p" data-group-id="0342075105-29">}</span><span class="p" data-group-id="0342075105-5">]</span><span class="p" data-group-id="0342075105-3">}</span><span class="p" data-group-id="0342075105-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0342075105-32">[</span><span class="p" data-group-id="0342075105-33">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0342075105-34">[</span><span class="p" data-group-id="0342075105-34">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="0342075105-35">[</span><span class="p" data-group-id="0342075105-36">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="0342075105-37">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="0342075105-38">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="0342075105-38">]</span><span class="p" data-group-id="0342075105-37">}</span><span class="p" data-group-id="0342075105-36">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-12">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="1943400348-13">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="1943400348-13">}</span><span class="p" data-group-id="1943400348-12">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-14">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="1943400348-15">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="1943400348-15">}</span><span class="p" data-group-id="1943400348-14">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="1943400348-17">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="1943400348-18">[</span><span class="ss">ch_app</span><span class="p" data-group-id="1943400348-18">]</span><span class="p" data-group-id="1943400348-17">}</span><span class="p" data-group-id="1943400348-16">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-19">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="1943400348-20">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="1943400348-20">]</span><span class="p" data-group-id="1943400348-19">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-21">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="1943400348-22">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="1943400348-22">}</span><span class="p" data-group-id="1943400348-21">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-23">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">up</span><span class="p">,</span><span class="p" data-group-id="1943400348-24">[</span><span class="p" data-group-id="1943400348-25">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="1943400348-26">[</span><span class="p" data-group-id="1943400348-26">]</span><span class="p" data-group-id="1943400348-25">}</span><span class="p" data-group-id="1943400348-24">]</span><span class="p" data-group-id="1943400348-23">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-27">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="1943400348-28">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="1943400348-28">]</span><span class="p" data-group-id="1943400348-27">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-29">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="1943400348-30">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">restart_child</span><span class="p">,</span><span class="p" data-group-id="1943400348-31">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="1943400348-31">]</span><span class="p" data-group-id="1943400348-30">}</span><span class="p" data-group-id="1943400348-29">}</span><span class="p" data-group-id="1943400348-5">]</span><span class="p" data-group-id="1943400348-3">}</span><span class="p" data-group-id="1943400348-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1943400348-32">[</span><span class="p" data-group-id="1943400348-33">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1943400348-34">[</span><span class="p" data-group-id="1943400348-34">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="1943400348-35">[</span><span class="p" data-group-id="1943400348-36">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="1943400348-37">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="1943400348-38">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="1943400348-38">]</span><span class="p" data-group-id="1943400348-37">}</span><span class="p" data-group-id="1943400348-36">}</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="ss">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-39">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="0342075105-40">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">terminate_child</span><span class="p">,</span><span class="p" data-group-id="0342075105-41">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="0342075105-41">]</span><span class="p" data-group-id="0342075105-40">}</span><span class="p" data-group-id="0342075105-39">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-42">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="0342075105-43">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">delete_child</span><span class="p">,</span><span class="p" data-group-id="0342075105-44">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="0342075105-44">]</span><span class="p" data-group-id="0342075105-43">}</span><span class="p" data-group-id="0342075105-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-45">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="0342075105-46">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="0342075105-46">]</span><span class="p" data-group-id="0342075105-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-47">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="0342075105-48">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="0342075105-48">}</span><span class="p" data-group-id="0342075105-47">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-49">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">down</span><span class="p">,</span><span class="p" data-group-id="0342075105-50">[</span><span class="p" data-group-id="0342075105-51">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="0342075105-52">[</span><span class="p" data-group-id="0342075105-52">]</span><span class="p" data-group-id="0342075105-51">}</span><span class="p" data-group-id="0342075105-50">]</span><span class="p" data-group-id="0342075105-49">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-53">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="0342075105-54">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="0342075105-54">]</span><span class="p" data-group-id="0342075105-53">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-55">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="0342075105-56">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="0342075105-56">}</span><span class="p" data-group-id="0342075105-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-57">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="0342075105-58">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="0342075105-58">}</span><span class="p" data-group-id="0342075105-57">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-59">{</span><span class="ss">purge</span><span class="p">,</span><span class="p" data-group-id="0342075105-60">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="0342075105-60">]</span><span class="p" data-group-id="0342075105-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="0342075105-61">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="0342075105-62">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">unload</span><span class="p">,</span><span class="p" data-group-id="0342075105-63">[</span><span class="ss">ch_app</span><span class="p" data-group-id="0342075105-63">]</span><span class="p" data-group-id="0342075105-62">}</span><span class="p" data-group-id="0342075105-61">}</span><span class="p" data-group-id="0342075105-35">]</span><span class="p" data-group-id="0342075105-33">}</span><span class="p" data-group-id="0342075105-32">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="0342075105-1">}</span><span class="p">.</span></code></pre><h2 id="changing-non-erlang-code" class="section-heading">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-39">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="1943400348-40">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">terminate_child</span><span class="p">,</span><span class="p" data-group-id="1943400348-41">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="1943400348-41">]</span><span class="p" data-group-id="1943400348-40">}</span><span class="p" data-group-id="1943400348-39">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-42">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="1943400348-43">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">delete_child</span><span class="p">,</span><span class="p" data-group-id="1943400348-44">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="1943400348-44">]</span><span class="p" data-group-id="1943400348-43">}</span><span class="p" data-group-id="1943400348-42">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-45">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="1943400348-46">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="1943400348-46">]</span><span class="p" data-group-id="1943400348-45">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-47">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="1943400348-48">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="1943400348-48">}</span><span class="p" data-group-id="1943400348-47">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-49">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">down</span><span class="p">,</span><span class="p" data-group-id="1943400348-50">[</span><span class="p" data-group-id="1943400348-51">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="1943400348-52">[</span><span class="p" data-group-id="1943400348-52">]</span><span class="p" data-group-id="1943400348-51">}</span><span class="p" data-group-id="1943400348-50">]</span><span class="p" data-group-id="1943400348-49">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-53">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="1943400348-54">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="1943400348-54">]</span><span class="p" data-group-id="1943400348-53">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-55">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="1943400348-56">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="1943400348-56">}</span><span class="p" data-group-id="1943400348-55">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-57">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="1943400348-58">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="1943400348-58">}</span><span class="p" data-group-id="1943400348-57">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-59">{</span><span class="ss">purge</span><span class="p">,</span><span class="p" data-group-id="1943400348-60">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="1943400348-60">]</span><span class="p" data-group-id="1943400348-59">}</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="1943400348-61">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="1943400348-62">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">unload</span><span class="p">,</span><span class="p" data-group-id="1943400348-63">[</span><span class="ss">ch_app</span><span class="p" data-group-id="1943400348-63">]</span><span class="p" data-group-id="1943400348-62">}</span><span class="p" data-group-id="1943400348-61">}</span><span class="p" data-group-id="1943400348-35">]</span><span class="p" data-group-id="1943400348-33">}</span><span class="p" data-group-id="1943400348-32">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1943400348-1">}</span><span class="p">.</span></code></pre><h2 id="changing-non-erlang-code" class="section-heading">
│ │ │ │    <a href="#changing-non-erlang-code" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Changing Non-Erlang Code</span>
│ │ │ │  </h2>
│ │ │ │  <p>Changing code for a program written in another programming language than Erlang,
│ │ │ │  for example, a port program, is application-dependent and OTP provides no
│ │ │ │  special support.</p><p><em>Example</em></p><p>When changing code for a port program, assume that the Erlang process
│ │ │ │  controlling the port is a <code class="inline">gen_server</code> <code class="inline">portc</code> and that the port is opened in
│ │ │ │ -the callback function <code class="inline">init/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1686461627-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1686461627-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +the callback function <code class="inline">init/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8513589298-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8513589298-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="1686461627-2">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="1686461627-3">(</span><span class="n">App</span><span class="p" data-group-id="1686461627-3">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="1686461627-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="1686461627-4">(</span><span class="p" data-group-id="1686461627-5">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="1686461627-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1686461627-6">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1686461627-6">]</span><span class="p" data-group-id="1686461627-4">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="8513589298-2">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="8513589298-3">(</span><span class="n">App</span><span class="p" data-group-id="8513589298-3">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="8513589298-2">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8513589298-4">(</span><span class="p" data-group-id="8513589298-5">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="8513589298-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8513589298-6">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8513589298-6">]</span><span class="p" data-group-id="8513589298-4">)</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="1686461627-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="1686461627-8">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1686461627-8">}</span><span class="p" data-group-id="1686461627-7">}</span><span class="p">.</span></code></pre><p>If the port program is to be updated, the code for the <code class="inline">gen_server</code> can be
│ │ │ │ +    </span><span class="p" data-group-id="8513589298-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="8513589298-8">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8513589298-8">}</span><span class="p" data-group-id="8513589298-7">}</span><span class="p">.</span></code></pre><p>If the port program is to be updated, the code for the <code class="inline">gen_server</code> can be
│ │ │ │  extended with a <code class="inline">code_change/3</code> function, which closes the old port and opens a
│ │ │ │  new port. (If necessary, the <code class="inline">gen_server</code> can first request data that must be
│ │ │ │ -saved from the port program and pass this data to the new port):</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="8739342491-1">(</span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="ss">port</span><span class="p" data-group-id="8739342491-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +saved from the port program and pass this data to the new port):</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="9840242905-1">(</span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="ss">port</span><span class="p" data-group-id="9840242905-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">close</span><span class="p">,</span><span class="w">
│ │ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ │ -        </span><span class="p" data-group-id="8739342491-2">{</span><span class="n">Port</span><span class="p">,</span><span class="ss">close</span><span class="p" data-group-id="8739342491-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +        </span><span class="p" data-group-id="9840242905-2">{</span><span class="n">Port</span><span class="p">,</span><span class="ss">close</span><span class="p" data-group-id="9840242905-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │              </span><span class="ss">true</span><span class="w">
│ │ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="8739342491-3">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="8739342491-4">(</span><span class="n">App</span><span class="p" data-group-id="8739342491-4">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="8739342491-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8739342491-5">(</span><span class="p" data-group-id="8739342491-6">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="8739342491-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8739342491-7">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8739342491-7">]</span><span class="p" data-group-id="8739342491-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ -    </span><span class="p" data-group-id="8739342491-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="8739342491-9">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8739342491-9">}</span><span class="p" data-group-id="8739342491-8">}</span><span class="p">.</span></code></pre><p>Update the application version number in the <code class="inline">.app</code> file and write an <code class="inline">.appup</code>
│ │ │ │ -file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4878347310-1">[</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4878347310-2">[</span><span class="p" data-group-id="4878347310-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4878347310-4">[</span><span class="p" data-group-id="4878347310-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4878347310-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="4878347310-6">}</span><span class="p" data-group-id="4878347310-5">}</span><span class="p" data-group-id="4878347310-4">]</span><span class="p" data-group-id="4878347310-3">}</span><span class="p" data-group-id="4878347310-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4878347310-7">[</span><span class="p" data-group-id="4878347310-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4878347310-9">[</span><span class="p" data-group-id="4878347310-10">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4878347310-11">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="4878347310-11">}</span><span class="p" data-group-id="4878347310-10">}</span><span class="p" data-group-id="4878347310-9">]</span><span class="p" data-group-id="4878347310-8">}</span><span class="p" data-group-id="4878347310-7">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4878347310-1">]</span><span class="p">.</span></code></pre><p>Ensure that the <code class="inline">priv</code> directory, where the C program is located, is included in
│ │ │ │ -the new release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="2596611682-1">(</span><span class="s">&quot;my_release&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2596611682-2">[</span><span class="p" data-group-id="2596611682-3">{</span><span class="ss">dirs</span><span class="p">,</span><span class="p" data-group-id="2596611682-4">[</span><span class="ss">priv</span><span class="p" data-group-id="2596611682-4">]</span><span class="p" data-group-id="2596611682-3">}</span><span class="p" data-group-id="2596611682-2">]</span><span class="p" data-group-id="2596611682-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="9840242905-3">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="9840242905-4">(</span><span class="n">App</span><span class="p" data-group-id="9840242905-4">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="9840242905-3">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="9840242905-5">(</span><span class="p" data-group-id="9840242905-6">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="9840242905-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9840242905-7">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9840242905-7">]</span><span class="p" data-group-id="9840242905-5">)</span><span class="p">,</span><span class="w">
│ │ │ │ +    </span><span class="p" data-group-id="9840242905-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="9840242905-9">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9840242905-9">}</span><span class="p" data-group-id="9840242905-8">}</span><span class="p">.</span></code></pre><p>Update the application version number in the <code class="inline">.app</code> file and write an <code class="inline">.appup</code>
│ │ │ │ +file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8306380743-1">[</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8306380743-2">[</span><span class="p" data-group-id="8306380743-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8306380743-4">[</span><span class="p" data-group-id="8306380743-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8306380743-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="8306380743-6">}</span><span class="p" data-group-id="8306380743-5">}</span><span class="p" data-group-id="8306380743-4">]</span><span class="p" data-group-id="8306380743-3">}</span><span class="p" data-group-id="8306380743-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8306380743-7">[</span><span class="p" data-group-id="8306380743-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8306380743-9">[</span><span class="p" data-group-id="8306380743-10">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8306380743-11">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="8306380743-11">}</span><span class="p" data-group-id="8306380743-10">}</span><span class="p" data-group-id="8306380743-9">]</span><span class="p" data-group-id="8306380743-8">}</span><span class="p" data-group-id="8306380743-7">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8306380743-1">]</span><span class="p">.</span></code></pre><p>Ensure that the <code class="inline">priv</code> directory, where the C program is located, is included in
│ │ │ │ +the new release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="8775387296-1">(</span><span class="s">&quot;my_release&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8775387296-2">[</span><span class="p" data-group-id="8775387296-3">{</span><span class="ss">dirs</span><span class="p">,</span><span class="p" data-group-id="8775387296-4">[</span><span class="ss">priv</span><span class="p" data-group-id="8775387296-4">]</span><span class="p" data-group-id="8775387296-3">}</span><span class="p" data-group-id="8775387296-2">]</span><span class="p" data-group-id="8775387296-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="runtime-system-restart-and-upgrade" class="section-heading">
│ │ │ │    <a href="#runtime-system-restart-and-upgrade" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Runtime System Restart and Upgrade</span>
│ │ │ │  </h2>
│ │ │ │  <p>Two upgrade instructions restart the runtime system:</p><ul><li><p><code class="inline">restart_new_emulator</code></p><p>Intended when ERTS, Kernel, STDLIB, or SASL is upgraded. It is automatically
│ │ │ │ @@ -460,20 +460,20 @@
│ │ │ │  executed before all other upgrade instructions. For more information about
│ │ │ │  this instruction, see restart_new_emulator (Low-Level) in
│ │ │ │  <a href="release_handling.xhtml#restart_new_emulator_instr">Release Handling Instructions</a>.</p></li><li><p><code class="inline">restart_emulator</code></p><p>Used when a restart of the runtime system is required after all other upgrade
│ │ │ │  instructions are executed. For more information about this instruction, see
│ │ │ │  restart_emulator (Low-Level) in
│ │ │ │  <a href="release_handling.xhtml#restart_emulator_instr">Release Handling Instructions</a>.</p></li></ul><p>If a runtime system restart is necessary and no upgrade instructions are needed,
│ │ │ │  that is, if the restart itself is enough for the upgraded applications to start
│ │ │ │ -running the new versions, a simple <code class="inline">.relup</code> file can be created manually:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4383614303-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4383614303-2">[</span><span class="p" data-group-id="4383614303-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4383614303-4">[</span><span class="p" data-group-id="4383614303-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4383614303-5">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="4383614303-5">]</span><span class="p" data-group-id="4383614303-3">}</span><span class="p" data-group-id="4383614303-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="4383614303-6">[</span><span class="p" data-group-id="4383614303-7">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4383614303-8">[</span><span class="p" data-group-id="4383614303-8">]</span><span class="p">,</span><span class="w">
│ │ │ │ -   </span><span class="p" data-group-id="4383614303-9">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="4383614303-9">]</span><span class="p" data-group-id="4383614303-7">}</span><span class="p" data-group-id="4383614303-6">]</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4383614303-1">}</span><span class="p">.</span></code></pre><p>In this case, the release handler framework with automatic packing and unpacking
│ │ │ │ +running the new versions, a simple <code class="inline">.relup</code> file can be created manually:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4568867762-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4568867762-2">[</span><span class="p" data-group-id="4568867762-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4568867762-4">[</span><span class="p" data-group-id="4568867762-4">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4568867762-5">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="4568867762-5">]</span><span class="p" data-group-id="4568867762-3">}</span><span class="p" data-group-id="4568867762-2">]</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="4568867762-6">[</span><span class="p" data-group-id="4568867762-7">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4568867762-8">[</span><span class="p" data-group-id="4568867762-8">]</span><span class="p">,</span><span class="w">
│ │ │ │ +   </span><span class="p" data-group-id="4568867762-9">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="4568867762-9">]</span><span class="p" data-group-id="4568867762-7">}</span><span class="p" data-group-id="4568867762-6">]</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4568867762-1">}</span><span class="p">.</span></code></pre><p>In this case, the release handler framework with automatic packing and unpacking
│ │ │ │  of release packages, automatic path updates, and so on, can be used without
│ │ │ │  having to specify <code class="inline">.appup</code> files.</p>
│ │ │ │  
│ │ │ │    </body>
│ │ │ │  </html>
│ │ │ ├── OEBPS/applications.xhtml
│ │ │ │ @@ -40,34 +40,34 @@
│ │ │ │  <a href="applications.xhtml#app_dir">directory structure</a>.</p><p><a href="" id="callback_module"></a></p><h2 id="application-callback-module" class="section-heading">
│ │ │ │    <a href="#application-callback-module" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Application Callback Module</span>
│ │ │ │  </h2>
│ │ │ │  <p>How to start and stop the code for the application, including its supervision
│ │ │ │ -tree, is described by two callback functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start</span><span class="p" data-group-id="6746157988-1">(</span><span class="n">StartType</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="6746157988-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6746157988-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="6746157988-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="6746157988-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6746157988-3">}</span><span class="w">
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="6746157988-4">(</span><span class="n">State</span><span class="p" data-group-id="6746157988-4">)</span></code></pre><ul><li><code class="inline">start/2</code> is called when starting the application and is to create the
│ │ │ │ +tree, is described by two callback functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start</span><span class="p" data-group-id="7079380021-1">(</span><span class="n">StartType</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="7079380021-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7079380021-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="7079380021-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="7079380021-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7079380021-3">}</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="7079380021-4">(</span><span class="n">State</span><span class="p" data-group-id="7079380021-4">)</span></code></pre><ul><li><code class="inline">start/2</code> is called when starting the application and is to create the
│ │ │ │  supervision tree by starting the top supervisor. It is expected to return the
│ │ │ │  pid of the top supervisor and an optional term, <code class="inline">State</code>, which defaults to
│ │ │ │  <code class="inline">[]</code>. This term is passed as is to <code class="inline">stop/1</code>.</li><li><code class="inline">StartType</code> is usually the atom <code class="inline">normal</code>. It has other values only in the case
│ │ │ │  of a takeover or failover; see
│ │ │ │  <a href="distributed_applications.xhtml">Distributed Applications</a>.</li><li><code class="inline">StartArgs</code> is defined by the key <code class="inline">mod</code> in the
│ │ │ │  <a href="applications.xhtml#appl_res_file">application resource file</a>.</li><li><code class="inline">stop/1</code> is called <em>after</em> the application has been stopped and is to do any
│ │ │ │  necessary cleaning up. The actual stopping of the application, that is,
│ │ │ │  shutting down the supervision tree, is handled automatically as described in
│ │ │ │  <a href="applications.xhtml#stopping">Starting and Stopping Applications</a>.</li></ul><p><a href="" id="ch_app"></a></p><p>Example of an application callback module for packaging the supervision tree
│ │ │ │ -from <a href="sup_princ.xhtml#ex">Supervisor Behaviour</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9983812543-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="9983812543-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="9983812543-2">(</span><span class="ss">application</span><span class="p" data-group-id="9983812543-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +from <a href="sup_princ.xhtml#ex">Supervisor Behaviour</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4586556818-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="4586556818-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4586556818-2">(</span><span class="ss">application</span><span class="p" data-group-id="4586556818-2">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="w">
│ │ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9983812543-3">(</span><span class="p" data-group-id="9983812543-4">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9983812543-4">]</span><span class="p" data-group-id="9983812543-3">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4586556818-3">(</span><span class="p" data-group-id="4586556818-4">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4586556818-4">]</span><span class="p" data-group-id="4586556818-3">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9983812543-5">(</span><span class="p">_</span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="9983812543-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ -    </span><span class="nc">ch_sup</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9983812543-6">(</span><span class="p" data-group-id="9983812543-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="4586556818-5">(</span><span class="p">_</span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="4586556818-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +    </span><span class="nc">ch_sup</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4586556818-6">(</span><span class="p" data-group-id="4586556818-6">)</span><span class="p">.</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="9983812543-7">(</span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="9983812543-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="4586556818-7">(</span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="4586556818-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>A library application that cannot be started or stopped does not need any
│ │ │ │  application callback module.</p><p><a href="" id="appl_res_file"></a></p><h2 id="application-resource-file" class="section-heading">
│ │ │ │    <a href="#application-resource-file" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Application Resource File</span>
│ │ │ │  </h2>
│ │ │ │ @@ -78,22 +78,22 @@
│ │ │ │  keys.</li></ul><p>The contents of a minimal <code class="inline">.app</code> file for a library application <code class="inline">libapp</code> looks
│ │ │ │  as follows:</p><pre><code class="text">{application, libapp, []}.</code></pre><p>The contents of a minimal <code class="inline">.app</code> file <code class="inline">ch_app.app</code> for a supervision tree
│ │ │ │  application like <code class="inline">ch_app</code> looks as follows:</p><pre><code class="text">{application, ch_app,
│ │ │ │   [{mod, {ch_app,[]}}]}.</code></pre><p>The key <code class="inline">mod</code> defines the callback module and start argument of the application,
│ │ │ │  in this case <code class="inline">ch_app</code> and <code class="inline">[]</code>, respectively. This means that the following is
│ │ │ │  called when the application is to be started:</p><pre><code class="text">ch_app:start(normal, [])</code></pre><p>The following is called when the application is stopped:</p><pre><code class="text">ch_app:stop([])</code></pre><p>When using <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a>, the Erlang/OTP tools for packaging code (see Section
│ │ │ │  <a href="release_structure.xhtml">Releases</a>), the keys <code class="inline">description</code>, <code class="inline">vsn</code>, <code class="inline">modules</code>,
│ │ │ │ -<code class="inline">registered</code>, and <code class="inline">applications</code> are also to be specified:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0719560348-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0719560348-2">[</span><span class="p" data-group-id="0719560348-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="0719560348-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0719560348-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0719560348-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0719560348-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0719560348-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0719560348-6">]</span><span class="p" data-group-id="0719560348-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0719560348-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0719560348-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="0719560348-8">]</span><span class="p" data-group-id="0719560348-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0719560348-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0719560348-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="0719560348-10">]</span><span class="p" data-group-id="0719560348-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="0719560348-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0719560348-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="0719560348-13">[</span><span class="p" data-group-id="0719560348-13">]</span><span class="p" data-group-id="0719560348-12">}</span><span class="p" data-group-id="0719560348-11">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0719560348-2">]</span><span class="p" data-group-id="0719560348-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">description</code> - A short description, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">vsn</code> - Version number, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">modules</code> - All modules <em>introduced</em> by this application. <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> uses
│ │ │ │ +<code class="inline">registered</code>, and <code class="inline">applications</code> are also to be specified:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6308613066-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6308613066-2">[</span><span class="p" data-group-id="6308613066-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="6308613066-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6308613066-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6308613066-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6308613066-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6308613066-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6308613066-6">]</span><span class="p" data-group-id="6308613066-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6308613066-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6308613066-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="6308613066-8">]</span><span class="p" data-group-id="6308613066-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6308613066-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6308613066-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="6308613066-10">]</span><span class="p" data-group-id="6308613066-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="6308613066-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6308613066-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="6308613066-13">[</span><span class="p" data-group-id="6308613066-13">]</span><span class="p" data-group-id="6308613066-12">}</span><span class="p" data-group-id="6308613066-11">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="6308613066-2">]</span><span class="p" data-group-id="6308613066-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">description</code> - A short description, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">vsn</code> - Version number, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">modules</code> - All modules <em>introduced</em> by this application. <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> uses
│ │ │ │  this list when generating boot scripts and tar files. A module must only
│ │ │ │  be included in one application. Defaults to <code class="inline">[]</code>.</li><li><code class="inline">registered</code> - All names of registered processes in the application.
│ │ │ │  <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> uses this list to detect name clashes between applications.
│ │ │ │  Defaults to <code class="inline">[]</code>.</li><li><code class="inline">applications</code> - All applications that must be started before this
│ │ │ │  application is started. <a href="../../../lib/sasl/doc/html/systools.html"><code class="inline">systools</code></a> uses this list to generate correct boot
│ │ │ │  scripts. Defaults to <code class="inline">[]</code>. Notice that all applications have dependencies to
│ │ │ │  at least Kernel and STDLIB.</li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>For details about the syntax and contents of the application resource file,
│ │ │ │ @@ -205,38 +205,38 @@
│ │ │ │  stop applications.</p><h2 id="loading-and-unloading-applications" class="section-heading">
│ │ │ │    <a href="#loading-and-unloading-applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Loading and Unloading Applications</span>
│ │ │ │  </h2>
│ │ │ │  <p>Before an application can be started, it must be <em>loaded</em>. The application
│ │ │ │ -controller reads and stores the information from the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="6185638951-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="6185638951-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +controller reads and stores the information from the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="3884005638-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3884005638-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="6185638951-2">(</span><span class="p" data-group-id="6185638951-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="6185638951-3">[</span><span class="p" data-group-id="6185638951-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="6185638951-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6185638951-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="6185638951-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="6185638951-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6185638951-6">}</span><span class="p" data-group-id="6185638951-3">]</span></code></pre><p>An application that has been stopped, or has never been started, can be
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="3884005638-2">(</span><span class="p" data-group-id="3884005638-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="3884005638-3">[</span><span class="p" data-group-id="3884005638-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="3884005638-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3884005638-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="3884005638-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3884005638-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="3884005638-6">}</span><span class="p" data-group-id="3884005638-3">]</span></code></pre><p>An application that has been stopped, or has never been started, can be
│ │ │ │  unloaded. The information about the application is erased from the internal
│ │ │ │ -database of the application controller.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">unload</span><span class="p" data-group-id="7449745061-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="7449745061-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +database of the application controller.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">unload</span><span class="p" data-group-id="1310411787-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="1310411787-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="7449745061-2">(</span><span class="p" data-group-id="7449745061-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7449745061-3">[</span><span class="p" data-group-id="7449745061-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="7449745061-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="7449745061-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="7449745061-5">}</span><span class="p" data-group-id="7449745061-3">]</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Loading/unloading an application does not load/unload the code used by the
│ │ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="1310411787-2">(</span><span class="p" data-group-id="1310411787-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="1310411787-3">[</span><span class="p" data-group-id="1310411787-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="1310411787-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="1310411787-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="1310411787-5">}</span><span class="p" data-group-id="1310411787-3">]</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Loading/unloading an application does not load/unload the code used by the
│ │ │ │  application. Code loading is handled in the usual way by the code server.</p></section><p><a href="" id="stopping"></a></p><h2 id="starting-and-stopping-applications" class="section-heading">
│ │ │ │    <a href="#starting-and-stopping-applications" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Starting and Stopping Applications</span>
│ │ │ │  </h2>
│ │ │ │ -<p>An application is started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2673180848-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="2673180848-1">)</span><span class="p">.</span><span class="w">
│ │ │ │ +<p>An application is started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8353157905-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="8353157905-1">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">which_applications</span><span class="p" data-group-id="2673180848-2">(</span><span class="p" data-group-id="2673180848-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="2673180848-3">[</span><span class="p" data-group-id="2673180848-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="2673180848-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2673180848-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="2673180848-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2673180848-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="2673180848-6">}</span><span class="p" data-group-id="2673180848-3">]</span></code></pre><p>If the application is not already loaded, the application controller first loads
│ │ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">which_applications</span><span class="p" data-group-id="8353157905-2">(</span><span class="p" data-group-id="8353157905-2">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="8353157905-3">[</span><span class="p" data-group-id="8353157905-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="8353157905-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8353157905-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="8353157905-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="8353157905-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="8353157905-6">}</span><span class="p" data-group-id="8353157905-3">]</span></code></pre><p>If the application is not already loaded, the application controller first loads
│ │ │ │  it using <a href="../../../lib/kernel/doc/html/application.html#load/1"><code class="inline">application:load/1</code></a>. It checks the value of the <code class="inline">applications</code> key to
│ │ │ │  ensure that all applications that are to be started before this application are
│ │ │ │  running.</p><p><a href="" id="application_master"></a></p><p>Following that, the application controller creates an <em>application master</em> for
│ │ │ │  the application.</p><p>The application master establishes itself as the <a href="../../../lib/../erts/doc/html/erlang.html#group_leader/0">group
│ │ │ │  leader</a> of all processes in the application
│ │ │ │  and will forward I/O to the previous group leader.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The purpose of the application master being the group leader is to easily
│ │ │ │  keep track of which processes that belong to the application. That is needed
│ │ │ │ @@ -252,55 +252,55 @@
│ │ │ │  defined by the <code class="inline">mod</code> key.</p><h2 id="configuring-an-application" class="section-heading">
│ │ │ │    <a href="#configuring-an-application" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Configuring an Application</span>
│ │ │ │  </h2>
│ │ │ │  <p>An application can be configured using <em>configuration parameters</em>. These are a
│ │ │ │ -list of <code class="inline">{Par,Val}</code> tuples specified by a key <code class="inline">env</code> in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2543575910-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2543575910-2">[</span><span class="p" data-group-id="2543575910-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="2543575910-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2543575910-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="2543575910-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2543575910-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2543575910-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2543575910-6">]</span><span class="p" data-group-id="2543575910-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2543575910-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2543575910-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="2543575910-8">]</span><span class="p" data-group-id="2543575910-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2543575910-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2543575910-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="2543575910-10">]</span><span class="p" data-group-id="2543575910-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2543575910-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2543575910-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="2543575910-13">[</span><span class="p" data-group-id="2543575910-13">]</span><span class="p" data-group-id="2543575910-12">}</span><span class="p" data-group-id="2543575910-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ -  </span><span class="p" data-group-id="2543575910-14">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2543575910-15">[</span><span class="p" data-group-id="2543575910-16">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="2543575910-16">}</span><span class="p" data-group-id="2543575910-15">]</span><span class="p" data-group-id="2543575910-14">}</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="2543575910-2">]</span><span class="p" data-group-id="2543575910-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Par</code> is to be an atom. <code class="inline">Val</code> is any term. The application can retrieve the
│ │ │ │ +list of <code class="inline">{Par,Val}</code> tuples specified by a key <code class="inline">env</code> in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3248493510-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3248493510-2">[</span><span class="p" data-group-id="3248493510-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="3248493510-3">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3248493510-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="3248493510-4">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3248493510-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3248493510-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="3248493510-6">]</span><span class="p" data-group-id="3248493510-5">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3248493510-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3248493510-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="3248493510-8">]</span><span class="p" data-group-id="3248493510-7">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3248493510-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3248493510-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="3248493510-10">]</span><span class="p" data-group-id="3248493510-9">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3248493510-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3248493510-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="3248493510-13">[</span><span class="p" data-group-id="3248493510-13">]</span><span class="p" data-group-id="3248493510-12">}</span><span class="p" data-group-id="3248493510-11">}</span><span class="p">,</span><span class="w">
│ │ │ │ +  </span><span class="p" data-group-id="3248493510-14">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3248493510-15">[</span><span class="p" data-group-id="3248493510-16">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="3248493510-16">}</span><span class="p" data-group-id="3248493510-15">]</span><span class="p" data-group-id="3248493510-14">}</span><span class="w">
│ │ │ │ + </span><span class="p" data-group-id="3248493510-2">]</span><span class="p" data-group-id="3248493510-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Par</code> is to be an atom. <code class="inline">Val</code> is any term. The application can retrieve the
│ │ │ │  value of a configuration parameter by calling <code class="inline">application:get_env(App, Par)</code> or
│ │ │ │  a number of similar functions. For more information, see module <a href="../../../lib/kernel/doc/html/application.html"><code class="inline">application</code></a>
│ │ │ │  in Kernel.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="4944079964-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="4944079964-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="4944079964-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="4944079964-2">]</span><span class="w"> </span><span class="p" data-group-id="4944079964-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="4944079964-3">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="9435715427-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="9435715427-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="9435715427-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="9435715427-2">]</span><span class="w"> </span><span class="p" data-group-id="9435715427-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="9435715427-3">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="4944079964-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="4944079964-4">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4944079964-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="4944079964-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="9435715427-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="9435715427-4">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9435715427-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="9435715427-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="4944079964-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="4944079964-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="4944079964-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="4944079964-7">}</span></code></pre><p>The values in the <code class="inline">.app</code> file can be overridden by values in a <em>system
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="9435715427-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="9435715427-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="9435715427-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="9435715427-7">}</span></code></pre><p>The values in the <code class="inline">.app</code> file can be overridden by values in a <em>system
│ │ │ │  configuration file</em>. This is a file that contains configuration parameters for
│ │ │ │ -relevant applications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0200709143-1">[</span><span class="p" data-group-id="0200709143-2">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0200709143-3">[</span><span class="p" data-group-id="0200709143-4">{</span><span class="n">Par11</span><span class="p">,</span><span class="n">Val11</span><span class="p" data-group-id="0200709143-4">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0200709143-3">]</span><span class="p" data-group-id="0200709143-2">}</span><span class="p">,</span><span class="w">
│ │ │ │ +relevant applications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0881020266-1">[</span><span class="p" data-group-id="0881020266-2">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0881020266-3">[</span><span class="p" data-group-id="0881020266-4">{</span><span class="n">Par11</span><span class="p">,</span><span class="n">Val11</span><span class="p" data-group-id="0881020266-4">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0881020266-3">]</span><span class="p" data-group-id="0881020266-2">}</span><span class="p">,</span><span class="w">
│ │ │ │   </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ │ - </span><span class="p" data-group-id="0200709143-5">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0200709143-6">[</span><span class="p" data-group-id="0200709143-7">{</span><span class="n">ParN1</span><span class="p">,</span><span class="n">ValN1</span><span class="p" data-group-id="0200709143-7">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0200709143-6">]</span><span class="p" data-group-id="0200709143-5">}</span><span class="p" data-group-id="0200709143-1">]</span><span class="p">.</span></code></pre><p>The system configuration is to be called <code class="inline">Name.config</code> and Erlang is to be
│ │ │ │ + </span><span class="p" data-group-id="0881020266-5">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0881020266-6">[</span><span class="p" data-group-id="0881020266-7">{</span><span class="n">ParN1</span><span class="p">,</span><span class="n">ValN1</span><span class="p" data-group-id="0881020266-7">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0881020266-6">]</span><span class="p" data-group-id="0881020266-5">}</span><span class="p" data-group-id="0881020266-1">]</span><span class="p">.</span></code></pre><p>The system configuration is to be called <code class="inline">Name.config</code> and Erlang is to be
│ │ │ │  started with the command-line argument <code class="inline">-config Name</code>. For details, see
│ │ │ │  <a href="../../../lib/kernel/doc/html/config.xhtml"><code class="inline">config</code></a> in Kernel.</p><p><em>Example:</em></p><p>A file <code class="inline">test.config</code> is created with the following contents:</p><pre><code class="text">[{ch_app, [{file, &quot;testlog&quot;}]}].</code></pre><p>The value of <code class="inline">file</code> overrides the value of <code class="inline">file</code> as defined in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -config test</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="7403626609-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="7403626609-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="7403626609-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="7403626609-2">]</span><span class="w"> </span><span class="p" data-group-id="7403626609-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="7403626609-3">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="4223507259-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="4223507259-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="4223507259-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="4223507259-2">]</span><span class="w"> </span><span class="p" data-group-id="4223507259-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="4223507259-3">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="7403626609-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="7403626609-4">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7403626609-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="7403626609-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="4223507259-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="4223507259-4">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4223507259-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="4223507259-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="7403626609-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="7403626609-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="7403626609-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="7403626609-7">}</span></code></pre><p>If <a href="release_handling.xhtml#sys">release handling</a> is used, exactly one system
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="4223507259-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="4223507259-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="4223507259-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="4223507259-7">}</span></code></pre><p>If <a href="release_handling.xhtml#sys">release handling</a> is used, exactly one system
│ │ │ │  configuration file is to be used and that file is to be called <code class="inline">sys.config</code>.</p><p>The values in the <code class="inline">.app</code> file and the values in a system configuration file can
│ │ │ │  be overridden directly from the command line:</p><pre><code class="text">% erl -ApplName Par1 Val1 ... ParN ValN</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -ch_app file &#39;&quot;testlog&quot;&#39;</span><span class="w">
│ │ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="5733474924-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="5733474924-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="5733474924-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="5733474924-2">]</span><span class="w"> </span><span class="p" data-group-id="5733474924-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="5733474924-3">]</span><span class="w">
│ │ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="0383371319-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="0383371319-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="0383371319-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="0383371319-2">]</span><span class="w"> </span><span class="p" data-group-id="0383371319-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="0383371319-3">]</span><span class="w">
│ │ │ │  
│ │ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="5733474924-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="5733474924-4">)</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5733474924-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="5733474924-5">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="0383371319-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0383371319-4">)</span><span class="w">
│ │ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="0383371319-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="0383371319-5">)</span><span class="p">.</span><span class="w">
│ │ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="5733474924-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="5733474924-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ -</span><span class="p" data-group-id="5733474924-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="5733474924-7">}</span></code></pre><h2 id="application-start-types" class="section-heading">
│ │ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="0383371319-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="0383371319-6">)</span><span class="p">.</span><span class="w">
│ │ │ │ +</span><span class="p" data-group-id="0383371319-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="0383371319-7">}</span></code></pre><h2 id="application-start-types" class="section-heading">
│ │ │ │    <a href="#application-start-types" class="hover-link">
│ │ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ │    </a>
│ │ │ │    <span class="text">Application Start Types</span>
│ │ │ │  </h2>
│ │ │ │  <p>A <em>start type</em> is defined when starting the application:</p><pre><code class="text">application:start(Application, Type)</code></pre><p><code class="inline">application:start(Application)</code> is the same as calling
│ │ │ │  <code class="inline">application:start(Application, temporary)</code>. The type can also be <code class="inline">permanent</code> or
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/applications.html
│ │ │ @@ -135,34 +135,34 @@
│ │ │  <a href="applications.html#app_dir">directory structure</a>.</p><p><a href="" id="callback_module"></a></p><h2 id="application-callback-module" class="section-heading">
│ │ │    <a href="#application-callback-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Application Callback Module</span>
│ │ │  </h2>
│ │ │  <p>How to start and stop the code for the application, including its supervision
│ │ │ -tree, is described by two callback functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start</span><span class="p" data-group-id="0512739880-1">(</span><span class="n">StartType</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="0512739880-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0512739880-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="0512739880-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="0512739880-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0512739880-3">}</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="0512739880-4">(</span><span class="n">State</span><span class="p" data-group-id="0512739880-4">)</span></code></pre><ul><li><code class="inline">start/2</code> is called when starting the application and is to create the
│ │ │ +tree, is described by two callback functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start</span><span class="p" data-group-id="5824138540-1">(</span><span class="n">StartType</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="5824138540-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5824138540-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="5824138540-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="5824138540-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5824138540-3">}</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="5824138540-4">(</span><span class="n">State</span><span class="p" data-group-id="5824138540-4">)</span></code></pre><ul><li><code class="inline">start/2</code> is called when starting the application and is to create the
│ │ │  supervision tree by starting the top supervisor. It is expected to return the
│ │ │  pid of the top supervisor and an optional term, <code class="inline">State</code>, which defaults to
│ │ │  <code class="inline">[]</code>. This term is passed as is to <code class="inline">stop/1</code>.</li><li><code class="inline">StartType</code> is usually the atom <code class="inline">normal</code>. It has other values only in the case
│ │ │  of a takeover or failover; see
│ │ │  <a href="distributed_applications.html">Distributed Applications</a>.</li><li><code class="inline">StartArgs</code> is defined by the key <code class="inline">mod</code> in the
│ │ │  <a href="applications.html#appl_res_file">application resource file</a>.</li><li><code class="inline">stop/1</code> is called <em>after</em> the application has been stopped and is to do any
│ │ │  necessary cleaning up. The actual stopping of the application, that is,
│ │ │  shutting down the supervision tree, is handled automatically as described in
│ │ │  <a href="applications.html#stopping">Starting and Stopping Applications</a>.</li></ul><p><a href="" id="ch_app"></a></p><p>Example of an application callback module for packaging the supervision tree
│ │ │ -from <a href="sup_princ.html#ex">Supervisor Behaviour</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7280117458-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="7280117458-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="7280117458-2">(</span><span class="ss">application</span><span class="p" data-group-id="7280117458-2">)</span><span class="p">.</span><span class="w">
│ │ │ +from <a href="sup_princ.html#ex">Supervisor Behaviour</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6890773212-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="6890773212-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6890773212-2">(</span><span class="ss">application</span><span class="p" data-group-id="6890773212-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7280117458-3">(</span><span class="p" data-group-id="7280117458-4">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7280117458-4">]</span><span class="p" data-group-id="7280117458-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6890773212-3">(</span><span class="p" data-group-id="6890773212-4">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6890773212-4">]</span><span class="p" data-group-id="6890773212-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="7280117458-5">(</span><span class="p">_</span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="7280117458-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">ch_sup</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="7280117458-6">(</span><span class="p" data-group-id="7280117458-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="6890773212-5">(</span><span class="p">_</span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6890773212-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">ch_sup</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6890773212-6">(</span><span class="p" data-group-id="6890773212-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="7280117458-7">(</span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="7280117458-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="6890773212-7">(</span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="6890773212-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>A library application that cannot be started or stopped does not need any
│ │ │  application callback module.</p><p><a href="" id="appl_res_file"></a></p><h2 id="application-resource-file" class="section-heading">
│ │ │    <a href="#application-resource-file" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Application Resource File</span>
│ │ │  </h2>
│ │ │ @@ -173,22 +173,22 @@
│ │ │  keys.</li></ul><p>The contents of a minimal <code class="inline">.app</code> file for a library application <code class="inline">libapp</code> looks
│ │ │  as follows:</p><pre><code class="text">{application, libapp, []}.</code></pre><p>The contents of a minimal <code class="inline">.app</code> file <code class="inline">ch_app.app</code> for a supervision tree
│ │ │  application like <code class="inline">ch_app</code> looks as follows:</p><pre><code class="text">{application, ch_app,
│ │ │   [{mod, {ch_app,[]}}]}.</code></pre><p>The key <code class="inline">mod</code> defines the callback module and start argument of the application,
│ │ │  in this case <code class="inline">ch_app</code> and <code class="inline">[]</code>, respectively. This means that the following is
│ │ │  called when the application is to be started:</p><pre><code class="text">ch_app:start(normal, [])</code></pre><p>The following is called when the application is stopped:</p><pre><code class="text">ch_app:stop([])</code></pre><p>When using <a href="../../lib/sasl-4.2.2.1/doc/html/systools.html"><code class="inline">systools</code></a>, the Erlang/OTP tools for packaging code (see Section
│ │ │  <a href="release_structure.html">Releases</a>), the keys <code class="inline">description</code>, <code class="inline">vsn</code>, <code class="inline">modules</code>,
│ │ │ -<code class="inline">registered</code>, and <code class="inline">applications</code> are also to be specified:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2861657072-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2861657072-2">[</span><span class="p" data-group-id="2861657072-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="2861657072-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="2861657072-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="2861657072-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="2861657072-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2861657072-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2861657072-6">]</span><span class="p" data-group-id="2861657072-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="2861657072-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2861657072-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="2861657072-8">]</span><span class="p" data-group-id="2861657072-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="2861657072-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2861657072-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="2861657072-10">]</span><span class="p" data-group-id="2861657072-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="2861657072-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2861657072-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="2861657072-13">[</span><span class="p" data-group-id="2861657072-13">]</span><span class="p" data-group-id="2861657072-12">}</span><span class="p" data-group-id="2861657072-11">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2861657072-2">]</span><span class="p" data-group-id="2861657072-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">description</code> - A short description, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">vsn</code> - Version number, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">modules</code> - All modules <em>introduced</em> by this application. <a href="../../lib/sasl-4.2.2.1/doc/html/systools.html"><code class="inline">systools</code></a> uses
│ │ │ +<code class="inline">registered</code>, and <code class="inline">applications</code> are also to be specified:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4101581748-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4101581748-2">[</span><span class="p" data-group-id="4101581748-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="4101581748-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4101581748-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="4101581748-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4101581748-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4101581748-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="4101581748-6">]</span><span class="p" data-group-id="4101581748-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4101581748-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4101581748-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="4101581748-8">]</span><span class="p" data-group-id="4101581748-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4101581748-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4101581748-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="4101581748-10">]</span><span class="p" data-group-id="4101581748-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4101581748-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4101581748-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="4101581748-13">[</span><span class="p" data-group-id="4101581748-13">]</span><span class="p" data-group-id="4101581748-12">}</span><span class="p" data-group-id="4101581748-11">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4101581748-2">]</span><span class="p" data-group-id="4101581748-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">description</code> - A short description, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">vsn</code> - Version number, a string. Defaults to <code class="inline">&quot;&quot;</code>.</li><li><code class="inline">modules</code> - All modules <em>introduced</em> by this application. <a href="../../lib/sasl-4.2.2.1/doc/html/systools.html"><code class="inline">systools</code></a> uses
│ │ │  this list when generating boot scripts and tar files. A module must only
│ │ │  be included in one application. Defaults to <code class="inline">[]</code>.</li><li><code class="inline">registered</code> - All names of registered processes in the application.
│ │ │  <a href="../../lib/sasl-4.2.2.1/doc/html/systools.html"><code class="inline">systools</code></a> uses this list to detect name clashes between applications.
│ │ │  Defaults to <code class="inline">[]</code>.</li><li><code class="inline">applications</code> - All applications that must be started before this
│ │ │  application is started. <a href="../../lib/sasl-4.2.2.1/doc/html/systools.html"><code class="inline">systools</code></a> uses this list to generate correct boot
│ │ │  scripts. Defaults to <code class="inline">[]</code>. Notice that all applications have dependencies to
│ │ │  at least Kernel and STDLIB.</li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>For details about the syntax and contents of the application resource file,
│ │ │ @@ -300,38 +300,38 @@
│ │ │  stop applications.</p><h2 id="loading-and-unloading-applications" class="section-heading">
│ │ │    <a href="#loading-and-unloading-applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Loading and Unloading Applications</span>
│ │ │  </h2>
│ │ │  <p>Before an application can be started, it must be <em>loaded</em>. The application
│ │ │ -controller reads and stores the information from the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="5584150289-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="5584150289-1">)</span><span class="p">.</span><span class="w">
│ │ │ +controller reads and stores the information from the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">load</span><span class="p" data-group-id="9699039668-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="9699039668-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="5584150289-2">(</span><span class="p" data-group-id="5584150289-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5584150289-3">[</span><span class="p" data-group-id="5584150289-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="5584150289-4">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5584150289-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="5584150289-5">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5584150289-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="5584150289-6">}</span><span class="p" data-group-id="5584150289-3">]</span></code></pre><p>An application that has been stopped, or has never been started, can be
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="9699039668-2">(</span><span class="p" data-group-id="9699039668-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9699039668-3">[</span><span class="p" data-group-id="9699039668-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="9699039668-4">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9699039668-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="9699039668-5">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9699039668-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9699039668-6">}</span><span class="p" data-group-id="9699039668-3">]</span></code></pre><p>An application that has been stopped, or has never been started, can be
│ │ │  unloaded. The information about the application is erased from the internal
│ │ │ -database of the application controller.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">unload</span><span class="p" data-group-id="3181746108-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3181746108-1">)</span><span class="p">.</span><span class="w">
│ │ │ +database of the application controller.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">unload</span><span class="p" data-group-id="0435101874-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="0435101874-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="3181746108-2">(</span><span class="p" data-group-id="3181746108-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3181746108-3">[</span><span class="p" data-group-id="3181746108-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="3181746108-4">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3181746108-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="3181746108-5">}</span><span class="p" data-group-id="3181746108-3">]</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Loading/unloading an application does not load/unload the code used by the
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">loaded_applications</span><span class="p" data-group-id="0435101874-2">(</span><span class="p" data-group-id="0435101874-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0435101874-3">[</span><span class="p" data-group-id="0435101874-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="0435101874-4">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0435101874-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="0435101874-5">}</span><span class="p" data-group-id="0435101874-3">]</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Loading/unloading an application does not load/unload the code used by the
│ │ │  application. Code loading is handled in the usual way by the code server.</p></section><p><a href="" id="stopping"></a></p><h2 id="starting-and-stopping-applications" class="section-heading">
│ │ │    <a href="#starting-and-stopping-applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting and Stopping Applications</span>
│ │ │  </h2>
│ │ │ -<p>An application is started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6286975043-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="6286975043-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>An application is started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3409140509-1">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3409140509-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">which_applications</span><span class="p" data-group-id="6286975043-2">(</span><span class="p" data-group-id="6286975043-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6286975043-3">[</span><span class="p" data-group-id="6286975043-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="6286975043-4">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6286975043-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="6286975043-5">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6286975043-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="6286975043-6">}</span><span class="p" data-group-id="6286975043-3">]</span></code></pre><p>If the application is not already loaded, the application controller first loads
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">which_applications</span><span class="p" data-group-id="3409140509-2">(</span><span class="p" data-group-id="3409140509-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3409140509-3">[</span><span class="p" data-group-id="3409140509-4">{</span><span class="ss">kernel</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;2.8.1.3&quot;</span><span class="p" data-group-id="3409140509-4">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3409140509-5">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="s">&quot;ERTS  CXC 138 10&quot;</span><span class="p">,</span><span class="s">&quot;1.11.4.3&quot;</span><span class="p" data-group-id="3409140509-5">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3409140509-6">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;Channel allocator&quot;</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="3409140509-6">}</span><span class="p" data-group-id="3409140509-3">]</span></code></pre><p>If the application is not already loaded, the application controller first loads
│ │ │  it using <a href="../../lib/kernel-10.2.7.4/doc/html/application.html#load/1"><code class="inline">application:load/1</code></a>. It checks the value of the <code class="inline">applications</code> key to
│ │ │  ensure that all applications that are to be started before this application are
│ │ │  running.</p><p><a href="" id="application_master"></a></p><p>Following that, the application controller creates an <em>application master</em> for
│ │ │  the application.</p><p>The application master establishes itself as the <a href="../../erts-15.2.7.8/doc/html/erlang.html#group_leader/0">group
│ │ │  leader</a> of all processes in the application
│ │ │  and will forward I/O to the previous group leader.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The purpose of the application master being the group leader is to easily
│ │ │  keep track of which processes that belong to the application. That is needed
│ │ │ @@ -347,55 +347,55 @@
│ │ │  defined by the <code class="inline">mod</code> key.</p><h2 id="configuring-an-application" class="section-heading">
│ │ │    <a href="#configuring-an-application" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Configuring an Application</span>
│ │ │  </h2>
│ │ │  <p>An application can be configured using <em>configuration parameters</em>. These are a
│ │ │ -list of <code class="inline">{Par,Val}</code> tuples specified by a key <code class="inline">env</code> in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0729453901-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0729453901-2">[</span><span class="p" data-group-id="0729453901-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="0729453901-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0729453901-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0729453901-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0729453901-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0729453901-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0729453901-6">]</span><span class="p" data-group-id="0729453901-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0729453901-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0729453901-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="0729453901-8">]</span><span class="p" data-group-id="0729453901-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0729453901-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0729453901-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="0729453901-10">]</span><span class="p" data-group-id="0729453901-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0729453901-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0729453901-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="0729453901-13">[</span><span class="p" data-group-id="0729453901-13">]</span><span class="p" data-group-id="0729453901-12">}</span><span class="p" data-group-id="0729453901-11">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0729453901-14">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0729453901-15">[</span><span class="p" data-group-id="0729453901-16">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="0729453901-16">}</span><span class="p" data-group-id="0729453901-15">]</span><span class="p" data-group-id="0729453901-14">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0729453901-2">]</span><span class="p" data-group-id="0729453901-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Par</code> is to be an atom. <code class="inline">Val</code> is any term. The application can retrieve the
│ │ │ +list of <code class="inline">{Par,Val}</code> tuples specified by a key <code class="inline">env</code> in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1194516767-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1194516767-2">[</span><span class="p" data-group-id="1194516767-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="1194516767-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1194516767-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="1194516767-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1194516767-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1194516767-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1194516767-6">]</span><span class="p" data-group-id="1194516767-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1194516767-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1194516767-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="1194516767-8">]</span><span class="p" data-group-id="1194516767-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1194516767-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1194516767-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="1194516767-10">]</span><span class="p" data-group-id="1194516767-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1194516767-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1194516767-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="1194516767-13">[</span><span class="p" data-group-id="1194516767-13">]</span><span class="p" data-group-id="1194516767-12">}</span><span class="p" data-group-id="1194516767-11">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1194516767-14">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1194516767-15">[</span><span class="p" data-group-id="1194516767-16">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="1194516767-16">}</span><span class="p" data-group-id="1194516767-15">]</span><span class="p" data-group-id="1194516767-14">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1194516767-2">]</span><span class="p" data-group-id="1194516767-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Par</code> is to be an atom. <code class="inline">Val</code> is any term. The application can retrieve the
│ │ │  value of a configuration parameter by calling <code class="inline">application:get_env(App, Par)</code> or
│ │ │  a number of similar functions. For more information, see module <a href="../../lib/kernel-10.2.7.4/doc/html/application.html"><code class="inline">application</code></a>
│ │ │  in Kernel.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="7831772946-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="7831772946-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="7831772946-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="7831772946-2">]</span><span class="w"> </span><span class="p" data-group-id="7831772946-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="7831772946-3">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="6437580448-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="6437580448-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="6437580448-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="6437580448-2">]</span><span class="w"> </span><span class="p" data-group-id="6437580448-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="6437580448-3">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="7831772946-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="7831772946-4">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7831772946-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="7831772946-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="6437580448-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="6437580448-4">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6437580448-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="6437580448-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="7831772946-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="7831772946-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7831772946-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="7831772946-7">}</span></code></pre><p>The values in the <code class="inline">.app</code> file can be overridden by values in a <em>system
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="6437580448-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="6437580448-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6437580448-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="6437580448-7">}</span></code></pre><p>The values in the <code class="inline">.app</code> file can be overridden by values in a <em>system
│ │ │  configuration file</em>. This is a file that contains configuration parameters for
│ │ │ -relevant applications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6721395351-1">[</span><span class="p" data-group-id="6721395351-2">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6721395351-3">[</span><span class="p" data-group-id="6721395351-4">{</span><span class="n">Par11</span><span class="p">,</span><span class="n">Val11</span><span class="p" data-group-id="6721395351-4">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6721395351-3">]</span><span class="p" data-group-id="6721395351-2">}</span><span class="p">,</span><span class="w">
│ │ │ +relevant applications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5282845414-1">[</span><span class="p" data-group-id="5282845414-2">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5282845414-3">[</span><span class="p" data-group-id="5282845414-4">{</span><span class="n">Par11</span><span class="p">,</span><span class="n">Val11</span><span class="p" data-group-id="5282845414-4">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5282845414-3">]</span><span class="p" data-group-id="5282845414-2">}</span><span class="p">,</span><span class="w">
│ │ │   </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6721395351-5">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6721395351-6">[</span><span class="p" data-group-id="6721395351-7">{</span><span class="n">ParN1</span><span class="p">,</span><span class="n">ValN1</span><span class="p" data-group-id="6721395351-7">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6721395351-6">]</span><span class="p" data-group-id="6721395351-5">}</span><span class="p" data-group-id="6721395351-1">]</span><span class="p">.</span></code></pre><p>The system configuration is to be called <code class="inline">Name.config</code> and Erlang is to be
│ │ │ + </span><span class="p" data-group-id="5282845414-5">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5282845414-6">[</span><span class="p" data-group-id="5282845414-7">{</span><span class="n">ParN1</span><span class="p">,</span><span class="n">ValN1</span><span class="p" data-group-id="5282845414-7">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5282845414-6">]</span><span class="p" data-group-id="5282845414-5">}</span><span class="p" data-group-id="5282845414-1">]</span><span class="p">.</span></code></pre><p>The system configuration is to be called <code class="inline">Name.config</code> and Erlang is to be
│ │ │  started with the command-line argument <code class="inline">-config Name</code>. For details, see
│ │ │  <a href="../../lib/kernel-10.2.7.4/doc/html/config.html"><code class="inline">config</code></a> in Kernel.</p><p><em>Example:</em></p><p>A file <code class="inline">test.config</code> is created with the following contents:</p><pre><code class="text">[{ch_app, [{file, &quot;testlog&quot;}]}].</code></pre><p>The value of <code class="inline">file</code> overrides the value of <code class="inline">file</code> as defined in the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -config test</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="6291673123-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="6291673123-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="6291673123-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="6291673123-2">]</span><span class="w"> </span><span class="p" data-group-id="6291673123-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="6291673123-3">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="3266346946-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="3266346946-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="3266346946-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="3266346946-2">]</span><span class="w"> </span><span class="p" data-group-id="3266346946-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="3266346946-3">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="6291673123-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="6291673123-4">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6291673123-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="6291673123-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="3266346946-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="3266346946-4">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3266346946-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="3266346946-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="6291673123-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="6291673123-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6291673123-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="6291673123-7">}</span></code></pre><p>If <a href="release_handling.html#sys">release handling</a> is used, exactly one system
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="3266346946-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="3266346946-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3266346946-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="3266346946-7">}</span></code></pre><p>If <a href="release_handling.html#sys">release handling</a> is used, exactly one system
│ │ │  configuration file is to be used and that file is to be called <code class="inline">sys.config</code>.</p><p>The values in the <code class="inline">.app</code> file and the values in a system configuration file can
│ │ │  be overridden directly from the command line:</p><pre><code class="text">% erl -ApplName Par1 Val1 ... ParN ValN</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -ch_app file &#39;&quot;testlog&quot;&#39;</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="5873051784-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="5873051784-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="5873051784-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="5873051784-2">]</span><span class="w"> </span><span class="p" data-group-id="5873051784-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="5873051784-3">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="p" data-group-id="5261161833-1">(</span><span class="n">BEAM</span><span class="p" data-group-id="5261161833-1">)</span><span class="w"> </span><span class="ss">emulator</span><span class="w"> </span><span class="ss">version</span><span class="w"> </span><span class="mf">5.2</span><span class="p">.</span><span class="mf">3.6</span><span class="w"> </span><span class="p" data-group-id="5261161833-2">[</span><span class="ss">hipe</span><span class="p" data-group-id="5261161833-2">]</span><span class="w"> </span><span class="p" data-group-id="5261161833-3">[</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="5261161833-3">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="5873051784-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="5873051784-4">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5873051784-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="5873051784-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">2.3</span><span class="p">.</span><span class="mi">6</span><span class="w">  </span><span class="p" data-group-id="5261161833-4">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="5261161833-4">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5261161833-5">(</span><span class="ss">ch_app</span><span class="p" data-group-id="5261161833-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="5873051784-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="5873051784-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5873051784-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="5873051784-7">}</span></code></pre><h2 id="application-start-types" class="section-heading">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">application</span><span class="p">:</span><span class="nf">get_env</span><span class="p" data-group-id="5261161833-6">(</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">file</span><span class="p" data-group-id="5261161833-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5261161833-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;testlog&quot;</span><span class="p" data-group-id="5261161833-7">}</span></code></pre><h2 id="application-start-types" class="section-heading">
│ │ │    <a href="#application-start-types" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Application Start Types</span>
│ │ │  </h2>
│ │ │  <p>A <em>start type</em> is defined when starting the application:</p><pre><code class="text">application:start(Application, Type)</code></pre><p><code class="inline">application:start(Application)</code> is the same as calling
│ │ │  <code class="inline">application:start(Application, temporary)</code>. The type can also be <code class="inline">permanent</code> or
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/appup_cookbook.html
│ │ │ @@ -120,18 +120,18 @@
│ │ │    <a href="#changing-a-functional-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing a Functional Module</span>
│ │ │  </h2>
│ │ │  <p>When a functional module has been changed, for example, if a new function has
│ │ │  been added or a bug has been corrected, simple code replacement is sufficient,
│ │ │ -for example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6696626486-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6696626486-2">[</span><span class="p" data-group-id="6696626486-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6696626486-4">[</span><span class="p" data-group-id="6696626486-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="6696626486-5">}</span><span class="p" data-group-id="6696626486-4">]</span><span class="p" data-group-id="6696626486-3">}</span><span class="p" data-group-id="6696626486-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6696626486-6">[</span><span class="p" data-group-id="6696626486-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6696626486-8">[</span><span class="p" data-group-id="6696626486-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="6696626486-9">}</span><span class="p" data-group-id="6696626486-8">]</span><span class="p" data-group-id="6696626486-7">}</span><span class="p" data-group-id="6696626486-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6696626486-1">}</span><span class="p">.</span></code></pre><h2 id="changing-a-residence-module" class="section-heading">
│ │ │ +for example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7063069378-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7063069378-2">[</span><span class="p" data-group-id="7063069378-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7063069378-4">[</span><span class="p" data-group-id="7063069378-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="7063069378-5">}</span><span class="p" data-group-id="7063069378-4">]</span><span class="p" data-group-id="7063069378-3">}</span><span class="p" data-group-id="7063069378-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7063069378-6">[</span><span class="p" data-group-id="7063069378-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7063069378-8">[</span><span class="p" data-group-id="7063069378-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="7063069378-9">}</span><span class="p" data-group-id="7063069378-8">]</span><span class="p" data-group-id="7063069378-7">}</span><span class="p" data-group-id="7063069378-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7063069378-1">}</span><span class="p">.</span></code></pre><h2 id="changing-a-residence-module" class="section-heading">
│ │ │    <a href="#changing-a-residence-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing a Residence Module</span>
│ │ │  </h2>
│ │ │  <p>In a system implemented according to the OTP design principles, all processes,
│ │ │  except system processes and special processes, reside in one of the behaviours
│ │ │ @@ -142,46 +142,46 @@
│ │ │    <a href="#changing-a-callback-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing a Callback Module</span>
│ │ │  </h2>
│ │ │  <p>A callback module is a functional module, and for code extensions simple code
│ │ │  replacement is sufficient.</p><p><em>Example</em></p><p>When adding a function to <code class="inline">ch3</code>, as described in the example in
│ │ │ -<a href="release_handling.html#appup">Release Handling</a>, <code class="inline">ch_app.appup</code> looks as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0480045943-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0480045943-2">[</span><span class="p" data-group-id="0480045943-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0480045943-4">[</span><span class="p" data-group-id="0480045943-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0480045943-5">}</span><span class="p" data-group-id="0480045943-4">]</span><span class="p" data-group-id="0480045943-3">}</span><span class="p" data-group-id="0480045943-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0480045943-6">[</span><span class="p" data-group-id="0480045943-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0480045943-8">[</span><span class="p" data-group-id="0480045943-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0480045943-9">}</span><span class="p" data-group-id="0480045943-8">]</span><span class="p" data-group-id="0480045943-7">}</span><span class="p" data-group-id="0480045943-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0480045943-1">}</span><span class="p">.</span></code></pre><p>OTP also supports changing the internal state of behaviour processes; see
│ │ │ +<a href="release_handling.html#appup">Release Handling</a>, <code class="inline">ch_app.appup</code> looks as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0214160704-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0214160704-2">[</span><span class="p" data-group-id="0214160704-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0214160704-4">[</span><span class="p" data-group-id="0214160704-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0214160704-5">}</span><span class="p" data-group-id="0214160704-4">]</span><span class="p" data-group-id="0214160704-3">}</span><span class="p" data-group-id="0214160704-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0214160704-6">[</span><span class="p" data-group-id="0214160704-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0214160704-8">[</span><span class="p" data-group-id="0214160704-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0214160704-9">}</span><span class="p" data-group-id="0214160704-8">]</span><span class="p" data-group-id="0214160704-7">}</span><span class="p" data-group-id="0214160704-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0214160704-1">}</span><span class="p">.</span></code></pre><p>OTP also supports changing the internal state of behaviour processes; see
│ │ │  <a href="appup_cookbook.html#int_state">Changing Internal State</a>.</p><p><a href="" id="int_state"></a></p><h2 id="changing-internal-state" class="section-heading">
│ │ │    <a href="#changing-internal-state" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Internal State</span>
│ │ │  </h2>
│ │ │  <p>In this case, simple code replacement is not sufficient. The process must
│ │ │  explicitly transform its state using the callback function <code class="inline">code_change/3</code> before
│ │ │  switching to the new version of the callback module. Thus, synchronized code
│ │ │  replacement is used.</p><p><em>Example</em></p><p>Consider the <code class="inline">ch3</code> module from
│ │ │  <a href="gen_server_concepts.html#ex">gen_server Behaviour</a>. The internal state is a term
│ │ │  <code class="inline">Chs</code> representing the available channels. Assume you want to add a counter <code class="inline">N</code>,
│ │ │  which keeps track of the number of <code class="inline">alloc</code> requests so far. This means that the
│ │ │ -format must be changed to <code class="inline">{Chs,N}</code>.</p><p>The <code class="inline">.appup</code> file can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9952875484-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9952875484-2">[</span><span class="p" data-group-id="9952875484-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9952875484-4">[</span><span class="p" data-group-id="9952875484-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9952875484-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9952875484-7">[</span><span class="p" data-group-id="9952875484-7">]</span><span class="p" data-group-id="9952875484-6">}</span><span class="p" data-group-id="9952875484-5">}</span><span class="p" data-group-id="9952875484-4">]</span><span class="p" data-group-id="9952875484-3">}</span><span class="p" data-group-id="9952875484-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9952875484-8">[</span><span class="p" data-group-id="9952875484-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9952875484-10">[</span><span class="p" data-group-id="9952875484-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9952875484-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9952875484-13">[</span><span class="p" data-group-id="9952875484-13">]</span><span class="p" data-group-id="9952875484-12">}</span><span class="p" data-group-id="9952875484-11">}</span><span class="p" data-group-id="9952875484-10">]</span><span class="p" data-group-id="9952875484-9">}</span><span class="p" data-group-id="9952875484-8">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9952875484-1">}</span><span class="p">.</span></code></pre><p>The third element of the <code class="inline">update</code> instruction is a tuple <code class="inline">{advanced,Extra}</code>,
│ │ │ +format must be changed to <code class="inline">{Chs,N}</code>.</p><p>The <code class="inline">.appup</code> file can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6895951739-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6895951739-2">[</span><span class="p" data-group-id="6895951739-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6895951739-4">[</span><span class="p" data-group-id="6895951739-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6895951739-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6895951739-7">[</span><span class="p" data-group-id="6895951739-7">]</span><span class="p" data-group-id="6895951739-6">}</span><span class="p" data-group-id="6895951739-5">}</span><span class="p" data-group-id="6895951739-4">]</span><span class="p" data-group-id="6895951739-3">}</span><span class="p" data-group-id="6895951739-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6895951739-8">[</span><span class="p" data-group-id="6895951739-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6895951739-10">[</span><span class="p" data-group-id="6895951739-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6895951739-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6895951739-13">[</span><span class="p" data-group-id="6895951739-13">]</span><span class="p" data-group-id="6895951739-12">}</span><span class="p" data-group-id="6895951739-11">}</span><span class="p" data-group-id="6895951739-10">]</span><span class="p" data-group-id="6895951739-9">}</span><span class="p" data-group-id="6895951739-8">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6895951739-1">}</span><span class="p">.</span></code></pre><p>The third element of the <code class="inline">update</code> instruction is a tuple <code class="inline">{advanced,Extra}</code>,
│ │ │  which says that the affected processes are to do a state transformation before
│ │ │  loading the new version of the module. This is done by the processes calling the
│ │ │  callback function <code class="inline">code_change/3</code> (see <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html"><code class="inline">gen_server</code></a> in STDLIB).
│ │ │ -The term <code class="inline">Extra</code>, in this case <code class="inline">[]</code>, is passed as is to the function:</p><p><a href="" id="code_change"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6005195777-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="6005195777-1">)</span><span class="p">.</span><span class="w">
│ │ │ +The term <code class="inline">Extra</code>, in this case <code class="inline">[]</code>, is passed as is to the function:</p><p><a href="" id="code_change"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7252043469-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="7252043469-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6005195777-2">(</span><span class="p" data-group-id="6005195777-3">[</span><span class="ss">code_change</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="6005195777-3">]</span><span class="p" data-group-id="6005195777-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7252043469-2">(</span><span class="p" data-group-id="7252043469-3">[</span><span class="ss">code_change</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="7252043469-3">]</span><span class="p" data-group-id="7252043469-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">code_change</span><span class="p" data-group-id="6005195777-4">(</span><span class="p" data-group-id="6005195777-5">{</span><span class="ss">down</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vsn</span><span class="p" data-group-id="6005195777-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6005195777-6">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="6005195777-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="6005195777-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6005195777-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6005195777-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">code_change</span><span class="p" data-group-id="6005195777-8">(</span><span class="p">_</span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="6005195777-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6005195777-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6005195777-10">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6005195777-10">}</span><span class="p" data-group-id="6005195777-9">}</span><span class="p">.</span></code></pre><p>The first argument is <code class="inline">{down,Vsn}</code> if there is a downgrade, or <code class="inline">Vsn</code> if there is
│ │ │ +</span><span class="nf">code_change</span><span class="p" data-group-id="7252043469-4">(</span><span class="p" data-group-id="7252043469-5">{</span><span class="ss">down</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vsn</span><span class="p" data-group-id="7252043469-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7252043469-6">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="7252043469-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="7252043469-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7252043469-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7252043469-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">code_change</span><span class="p" data-group-id="7252043469-8">(</span><span class="p">_</span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="7252043469-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7252043469-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7252043469-10">{</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7252043469-10">}</span><span class="p" data-group-id="7252043469-9">}</span><span class="p">.</span></code></pre><p>The first argument is <code class="inline">{down,Vsn}</code> if there is a downgrade, or <code class="inline">Vsn</code> if there is
│ │ │  a upgrade. The term <code class="inline">Vsn</code> is fetched from the 'original' version of the module,
│ │ │  that is, the version you are upgrading from, or downgrading to.</p><p>The version is defined by the module attribute <code class="inline">vsn</code>, if any. There is no such
│ │ │  attribute in <code class="inline">ch3</code>, so in this case the version is the checksum (a huge integer)
│ │ │  of the beam file, an uninteresting value, which is ignored.</p><p>The other callback functions of <code class="inline">ch3</code> must also be modified and perhaps a new
│ │ │  interface function must be added, but this is not shown here.</p><h2 id="module-dependencies" class="section-heading">
│ │ │    <a href="#module-dependencies" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -190,67 +190,67 @@
│ │ │  </h2>
│ │ │  <p>Assume that a module is extended by adding an interface function, as in the
│ │ │  example in <a href="release_handling.html#appup">Release Handling</a>, where a function
│ │ │  <code class="inline">available/0</code> is added to <code class="inline">ch3</code>.</p><p>If a call is added to this function, say in module <code class="inline">m1</code>, a runtime error could
│ │ │  can occur during release upgrade if the new version of <code class="inline">m1</code> is loaded first and
│ │ │  calls <code class="inline">ch3:available/0</code> before the new version of <code class="inline">ch3</code> is loaded.</p><p>Thus, <code class="inline">ch3</code> must be loaded before <code class="inline">m1</code>, in the upgrade case, and conversely in
│ │ │  the downgrade case. <code class="inline">m1</code> is said to be <em>dependent on</em> <code class="inline">ch3</code>. In a release
│ │ │ -handling instruction, this is expressed by the <code class="inline">DepMods</code> element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3588856224-1">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="3588856224-1">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3588856224-2">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3588856224-3">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="3588856224-3">}</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="3588856224-2">}</span></code></pre><p><code class="inline">DepMods</code> is a list of modules, on which <code class="inline">Module</code> is dependent.</p><p><em>Example</em></p><p>The module <code class="inline">m1</code> in application <code class="inline">myapp</code> is dependent on <code class="inline">ch3</code> when
│ │ │ +handling instruction, this is expressed by the <code class="inline">DepMods</code> element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4866221483-1">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="4866221483-1">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4866221483-2">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4866221483-3">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="4866221483-3">}</span><span class="p">,</span><span class="w"> </span><span class="n">DepMods</span><span class="p" data-group-id="4866221483-2">}</span></code></pre><p><code class="inline">DepMods</code> is a list of modules, on which <code class="inline">Module</code> is dependent.</p><p><em>Example</em></p><p>The module <code class="inline">m1</code> in application <code class="inline">myapp</code> is dependent on <code class="inline">ch3</code> when
│ │ │  upgrading from &quot;1&quot; to &quot;2&quot;, or downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="ss">myapp</span><span class="p">.</span><span class="nc">appup</span><span class="p">:</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="0875537596-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0875537596-2">[</span><span class="p" data-group-id="0875537596-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0875537596-4">[</span><span class="p" data-group-id="0875537596-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0875537596-6">[</span><span class="ss">ch3</span><span class="p" data-group-id="0875537596-6">]</span><span class="p" data-group-id="0875537596-5">}</span><span class="p" data-group-id="0875537596-4">]</span><span class="p" data-group-id="0875537596-3">}</span><span class="p" data-group-id="0875537596-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0875537596-7">[</span><span class="p" data-group-id="0875537596-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0875537596-9">[</span><span class="p" data-group-id="0875537596-10">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0875537596-11">[</span><span class="ss">ch3</span><span class="p" data-group-id="0875537596-11">]</span><span class="p" data-group-id="0875537596-10">}</span><span class="p" data-group-id="0875537596-9">]</span><span class="p" data-group-id="0875537596-8">}</span><span class="p" data-group-id="0875537596-7">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0875537596-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1492306236-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1492306236-2">[</span><span class="p" data-group-id="1492306236-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1492306236-4">[</span><span class="p" data-group-id="1492306236-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1492306236-6">[</span><span class="ss">ch3</span><span class="p" data-group-id="1492306236-6">]</span><span class="p" data-group-id="1492306236-5">}</span><span class="p" data-group-id="1492306236-4">]</span><span class="p" data-group-id="1492306236-3">}</span><span class="p" data-group-id="1492306236-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1492306236-7">[</span><span class="p" data-group-id="1492306236-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1492306236-9">[</span><span class="p" data-group-id="1492306236-10">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1492306236-11">[</span><span class="ss">ch3</span><span class="p" data-group-id="1492306236-11">]</span><span class="p" data-group-id="1492306236-10">}</span><span class="p" data-group-id="1492306236-9">]</span><span class="p" data-group-id="1492306236-8">}</span><span class="p" data-group-id="1492306236-7">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1492306236-1">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="ss">ch_app</span><span class="p">.</span><span class="nc">appup</span><span class="p">:</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="0875537596-12">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0875537596-13">[</span><span class="p" data-group-id="0875537596-14">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0875537596-15">[</span><span class="p" data-group-id="0875537596-16">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0875537596-16">}</span><span class="p" data-group-id="0875537596-15">]</span><span class="p" data-group-id="0875537596-14">}</span><span class="p" data-group-id="0875537596-13">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0875537596-17">[</span><span class="p" data-group-id="0875537596-18">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0875537596-19">[</span><span class="p" data-group-id="0875537596-20">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0875537596-20">}</span><span class="p" data-group-id="0875537596-19">]</span><span class="p" data-group-id="0875537596-18">}</span><span class="p" data-group-id="0875537596-17">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0875537596-12">}</span><span class="p">.</span></code></pre><p>If instead <code class="inline">m1</code> and <code class="inline">ch3</code> belong to the same application, the <code class="inline">.appup</code> file can
│ │ │ -look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6427287629-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6427287629-2">[</span><span class="p" data-group-id="6427287629-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6427287629-4">[</span><span class="p" data-group-id="6427287629-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6427287629-5">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6427287629-6">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6427287629-7">[</span><span class="ss">ch3</span><span class="p" data-group-id="6427287629-7">]</span><span class="p" data-group-id="6427287629-6">}</span><span class="p" data-group-id="6427287629-4">]</span><span class="p" data-group-id="6427287629-3">}</span><span class="p" data-group-id="6427287629-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6427287629-8">[</span><span class="p" data-group-id="6427287629-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6427287629-10">[</span><span class="p" data-group-id="6427287629-11">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="6427287629-11">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6427287629-12">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6427287629-13">[</span><span class="ss">ch3</span><span class="p" data-group-id="6427287629-13">]</span><span class="p" data-group-id="6427287629-12">}</span><span class="p" data-group-id="6427287629-10">]</span><span class="p" data-group-id="6427287629-9">}</span><span class="p" data-group-id="6427287629-8">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6427287629-1">}</span><span class="p">.</span></code></pre><p><code class="inline">m1</code> is dependent on <code class="inline">ch3</code> also when downgrading. <code class="inline">systools</code> knows the
│ │ │ +</span><span class="p" data-group-id="1492306236-12">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1492306236-13">[</span><span class="p" data-group-id="1492306236-14">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1492306236-15">[</span><span class="p" data-group-id="1492306236-16">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1492306236-16">}</span><span class="p" data-group-id="1492306236-15">]</span><span class="p" data-group-id="1492306236-14">}</span><span class="p" data-group-id="1492306236-13">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1492306236-17">[</span><span class="p" data-group-id="1492306236-18">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1492306236-19">[</span><span class="p" data-group-id="1492306236-20">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="1492306236-20">}</span><span class="p" data-group-id="1492306236-19">]</span><span class="p" data-group-id="1492306236-18">}</span><span class="p" data-group-id="1492306236-17">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1492306236-12">}</span><span class="p">.</span></code></pre><p>If instead <code class="inline">m1</code> and <code class="inline">ch3</code> belong to the same application, the <code class="inline">.appup</code> file can
│ │ │ +look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2104920960-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2104920960-2">[</span><span class="p" data-group-id="2104920960-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2104920960-4">[</span><span class="p" data-group-id="2104920960-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2104920960-5">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2104920960-6">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2104920960-7">[</span><span class="ss">ch3</span><span class="p" data-group-id="2104920960-7">]</span><span class="p" data-group-id="2104920960-6">}</span><span class="p" data-group-id="2104920960-4">]</span><span class="p" data-group-id="2104920960-3">}</span><span class="p" data-group-id="2104920960-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2104920960-8">[</span><span class="p" data-group-id="2104920960-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2104920960-10">[</span><span class="p" data-group-id="2104920960-11">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2104920960-11">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2104920960-12">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2104920960-13">[</span><span class="ss">ch3</span><span class="p" data-group-id="2104920960-13">]</span><span class="p" data-group-id="2104920960-12">}</span><span class="p" data-group-id="2104920960-10">]</span><span class="p" data-group-id="2104920960-9">}</span><span class="p" data-group-id="2104920960-8">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2104920960-1">}</span><span class="p">.</span></code></pre><p><code class="inline">m1</code> is dependent on <code class="inline">ch3</code> also when downgrading. <code class="inline">systools</code> knows the
│ │ │  difference between up- and downgrading and generates a correct <code class="inline">relup</code>, where
│ │ │  <code class="inline">ch3</code> is loaded before <code class="inline">m1</code> when upgrading, but <code class="inline">m1</code> is loaded before <code class="inline">ch3</code> when
│ │ │  downgrading.</p><p><a href="" id="spec"></a></p><h2 id="changing-code-for-a-special-process" class="section-heading">
│ │ │    <a href="#changing-code-for-a-special-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Code for a Special Process</span>
│ │ │  </h2>
│ │ │  <p>In this case, simple code replacement is not sufficient. When a new version of a
│ │ │  residence module for a special process is loaded, the process must make a fully
│ │ │  qualified call to its loop function to switch to the new code. Thus,
│ │ │  synchronized code replacement must be used.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The name(s) of the user-defined residence module(s) must be listed in the
│ │ │  <code class="inline">Modules</code> part of the child specification for the special process. Otherwise
│ │ │  the release handler cannot find the process.</p></section><p><em>Example</em></p><p>Consider the example <code class="inline">ch4</code> in <a href="spec_proc.html#ex">sys and proc_lib</a>.
│ │ │ -When started by a supervisor, the child specification can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6564626916-1">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6564626916-2">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6564626916-3">[</span><span class="p" data-group-id="6564626916-3">]</span><span class="p" data-group-id="6564626916-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="ss">permanent</span><span class="p">,</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6564626916-4">[</span><span class="ss">ch4</span><span class="p" data-group-id="6564626916-4">]</span><span class="p" data-group-id="6564626916-1">}</span></code></pre><p>If <code class="inline">ch4</code> is part of the application <code class="inline">sp_app</code> and a new version of the module is
│ │ │ +When started by a supervisor, the child specification can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9532855395-1">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9532855395-2">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9532855395-3">[</span><span class="p" data-group-id="9532855395-3">]</span><span class="p" data-group-id="9532855395-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="ss">permanent</span><span class="p">,</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9532855395-4">[</span><span class="ss">ch4</span><span class="p" data-group-id="9532855395-4">]</span><span class="p" data-group-id="9532855395-1">}</span></code></pre><p>If <code class="inline">ch4</code> is part of the application <code class="inline">sp_app</code> and a new version of the module is
│ │ │  to be loaded when upgrading from version &quot;1&quot; to &quot;2&quot; of this application,
│ │ │ -<code class="inline">sp_app.appup</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4682978253-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4682978253-2">[</span><span class="p" data-group-id="4682978253-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4682978253-4">[</span><span class="p" data-group-id="4682978253-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4682978253-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4682978253-7">[</span><span class="p" data-group-id="4682978253-7">]</span><span class="p" data-group-id="4682978253-6">}</span><span class="p" data-group-id="4682978253-5">}</span><span class="p" data-group-id="4682978253-4">]</span><span class="p" data-group-id="4682978253-3">}</span><span class="p" data-group-id="4682978253-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4682978253-8">[</span><span class="p" data-group-id="4682978253-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4682978253-10">[</span><span class="p" data-group-id="4682978253-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4682978253-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4682978253-13">[</span><span class="p" data-group-id="4682978253-13">]</span><span class="p" data-group-id="4682978253-12">}</span><span class="p" data-group-id="4682978253-11">}</span><span class="p" data-group-id="4682978253-10">]</span><span class="p" data-group-id="4682978253-9">}</span><span class="p" data-group-id="4682978253-8">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4682978253-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">update</code> instruction must contain the tuple <code class="inline">{advanced,Extra}</code>. The
│ │ │ +<code class="inline">sp_app.appup</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1468067880-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1468067880-2">[</span><span class="p" data-group-id="1468067880-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1468067880-4">[</span><span class="p" data-group-id="1468067880-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1468067880-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1468067880-7">[</span><span class="p" data-group-id="1468067880-7">]</span><span class="p" data-group-id="1468067880-6">}</span><span class="p" data-group-id="1468067880-5">}</span><span class="p" data-group-id="1468067880-4">]</span><span class="p" data-group-id="1468067880-3">}</span><span class="p" data-group-id="1468067880-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1468067880-8">[</span><span class="p" data-group-id="1468067880-9">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1468067880-10">[</span><span class="p" data-group-id="1468067880-11">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1468067880-12">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1468067880-13">[</span><span class="p" data-group-id="1468067880-13">]</span><span class="p" data-group-id="1468067880-12">}</span><span class="p" data-group-id="1468067880-11">}</span><span class="p" data-group-id="1468067880-10">]</span><span class="p" data-group-id="1468067880-9">}</span><span class="p" data-group-id="1468067880-8">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1468067880-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">update</code> instruction must contain the tuple <code class="inline">{advanced,Extra}</code>. The
│ │ │  instruction makes the special process call the callback function
│ │ │  <code class="inline">system_code_change/4</code>, a function the user must implement. The term <code class="inline">Extra</code>, in
│ │ │ -this case <code class="inline">[]</code>, is passed as is to <code class="inline">system_code_change/4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4214904616-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="4214904616-1">)</span><span class="p">.</span><span class="w">
│ │ │ +this case <code class="inline">[]</code>, is passed as is to <code class="inline">system_code_change/4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9922588272-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="9922588272-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4214904616-2">(</span><span class="p" data-group-id="4214904616-3">[</span><span class="ss">system_code_change</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="4214904616-3">]</span><span class="p" data-group-id="4214904616-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9922588272-2">(</span><span class="p" data-group-id="9922588272-3">[</span><span class="ss">system_code_change</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="9922588272-3">]</span><span class="p" data-group-id="9922588272-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_code_change</span><span class="p" data-group-id="4214904616-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="4214904616-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4214904616-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4214904616-5">}</span><span class="p">.</span></code></pre><ul><li>The first argument is the internal state <code class="inline">State</code>, passed from
│ │ │ +</span><span class="nf">system_code_change</span><span class="p" data-group-id="9922588272-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Extra</span><span class="p" data-group-id="9922588272-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9922588272-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9922588272-5">}</span><span class="p">.</span></code></pre><ul><li>The first argument is the internal state <code class="inline">State</code>, passed from
│ │ │  function <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg(Request, From, Parent, Module, Deb, State)</code></a>, and called by the special
│ │ │  process when a system message is received. In <code class="inline">ch4</code>, the internal
│ │ │  state is the set of available channels <code class="inline">Chs</code>.</li><li>The second argument is the name of the module (<code class="inline">ch4</code>).</li><li>The third argument is <code class="inline">Vsn</code> or <code class="inline">{down,Vsn}</code>, as described for
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#c:code_change/3"><code class="inline">gen_server:code_change/3</code></a> in
│ │ │  <a href="appup_cookbook.html#code_change">Changing Internal State</a>.</li></ul><p>In this case, all arguments but the first are ignored and the function simply
│ │ │  returns the internal state again. This is enough if the code only has been
│ │ │  extended. If instead the internal state is changed (similar to the example in
│ │ │ @@ -271,85 +271,85 @@
│ │ │    <span class="text">Changing Properties</span>
│ │ │  </h3>
│ │ │  <p>Since the supervisor is to change its internal state, synchronized code
│ │ │  replacement is required. However, a special <code class="inline">update</code> instruction must be used.</p><p>First, the new version of the callback module must be loaded, both in the case
│ │ │  of upgrade and downgrade. Then the new return value of <code class="inline">init/1</code> can be checked
│ │ │  and the internal state be changed accordingly.</p><p>The following <code class="inline">upgrade</code> instruction is used for supervisors:</p><pre><code class="text">{update, Module, supervisor}</code></pre><p><em>Example</em></p><p>To change the restart strategy of <code class="inline">ch_sup</code> (from
│ │ │  <a href="sup_princ.html#ex">Supervisor Behaviour</a>) from <code class="inline">one_for_one</code> to <code class="inline">one_for_all</code>,
│ │ │ -change the callback function <code class="inline">init/1</code> in <code class="inline">ch_sup.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7474629376-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="7474629376-1">)</span><span class="p">.</span><span class="w">
│ │ │ +change the callback function <code class="inline">init/1</code> in <code class="inline">ch_sup.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3604720894-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="3604720894-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="7474629376-2">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="7474629376-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7474629376-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7474629376-4">{</span><span class="p" data-group-id="7474629376-5">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_all</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7474629376-5">}</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7474629376-4">}</span><span class="p" data-group-id="7474629376-3">}</span><span class="p">.</span></code></pre><p>The file <code class="inline">ch_app.appup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6971186503-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6971186503-2">[</span><span class="p" data-group-id="6971186503-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6971186503-4">[</span><span class="p" data-group-id="6971186503-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="6971186503-5">}</span><span class="p" data-group-id="6971186503-4">]</span><span class="p" data-group-id="6971186503-3">}</span><span class="p" data-group-id="6971186503-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6971186503-6">[</span><span class="p" data-group-id="6971186503-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6971186503-8">[</span><span class="p" data-group-id="6971186503-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="6971186503-9">}</span><span class="p" data-group-id="6971186503-8">]</span><span class="p" data-group-id="6971186503-7">}</span><span class="p" data-group-id="6971186503-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6971186503-1">}</span><span class="p">.</span></code></pre><h3 id="changing-child-specifications" class="section-heading">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3604720894-2">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="3604720894-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3604720894-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3604720894-4">{</span><span class="p" data-group-id="3604720894-5">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_all</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3604720894-5">}</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3604720894-4">}</span><span class="p" data-group-id="3604720894-3">}</span><span class="p">.</span></code></pre><p>The file <code class="inline">ch_app.appup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0193456874-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0193456874-2">[</span><span class="p" data-group-id="0193456874-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0193456874-4">[</span><span class="p" data-group-id="0193456874-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0193456874-5">}</span><span class="p" data-group-id="0193456874-4">]</span><span class="p" data-group-id="0193456874-3">}</span><span class="p" data-group-id="0193456874-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0193456874-6">[</span><span class="p" data-group-id="0193456874-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0193456874-8">[</span><span class="p" data-group-id="0193456874-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0193456874-9">}</span><span class="p" data-group-id="0193456874-8">]</span><span class="p" data-group-id="0193456874-7">}</span><span class="p" data-group-id="0193456874-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0193456874-1">}</span><span class="p">.</span></code></pre><h3 id="changing-child-specifications" class="section-heading">
│ │ │    <a href="#changing-child-specifications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Child Specifications</span>
│ │ │  </h3>
│ │ │  <p>The instruction, and thus the <code class="inline">.appup</code> file, when changing an existing child
│ │ │ -specification, is the same as when changing properties as described earlier:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3349602196-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3349602196-2">[</span><span class="p" data-group-id="3349602196-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3349602196-4">[</span><span class="p" data-group-id="3349602196-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3349602196-5">}</span><span class="p" data-group-id="3349602196-4">]</span><span class="p" data-group-id="3349602196-3">}</span><span class="p" data-group-id="3349602196-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3349602196-6">[</span><span class="p" data-group-id="3349602196-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3349602196-8">[</span><span class="p" data-group-id="3349602196-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="3349602196-9">}</span><span class="p" data-group-id="3349602196-8">]</span><span class="p" data-group-id="3349602196-7">}</span><span class="p" data-group-id="3349602196-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3349602196-1">}</span><span class="p">.</span></code></pre><p>The changes do not affect existing child processes. For example, changing the
│ │ │ +specification, is the same as when changing properties as described earlier:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0088473602-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0088473602-2">[</span><span class="p" data-group-id="0088473602-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0088473602-4">[</span><span class="p" data-group-id="0088473602-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0088473602-5">}</span><span class="p" data-group-id="0088473602-4">]</span><span class="p" data-group-id="0088473602-3">}</span><span class="p" data-group-id="0088473602-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0088473602-6">[</span><span class="p" data-group-id="0088473602-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0088473602-8">[</span><span class="p" data-group-id="0088473602-9">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0088473602-9">}</span><span class="p" data-group-id="0088473602-8">]</span><span class="p" data-group-id="0088473602-7">}</span><span class="p" data-group-id="0088473602-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0088473602-1">}</span><span class="p">.</span></code></pre><p>The changes do not affect existing child processes. For example, changing the
│ │ │  start function only specifies how the child process is to be restarted, if
│ │ │  needed later on.</p><p>The id of the child specification cannot be changed.</p><p>Changing the <code class="inline">Modules</code> field of the child specification can affect the release
│ │ │  handling process itself, as this field is used to identify which processes are
│ │ │  affected when doing a synchronized code replacement.</p><p><a href="" id="sup_add"></a></p><h3 id="adding-and-deleting-child-processes" class="section-heading">
│ │ │    <a href="#adding-and-deleting-child-processes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Adding and Deleting Child Processes</span>
│ │ │  </h3>
│ │ │  <p>As stated earlier, changing child specifications does not affect existing child
│ │ │  processes. New child specifications are automatically added, but not deleted.
│ │ │  Child processes are not automatically started or terminated, this must be done
│ │ │  using <code class="inline">apply</code> instructions.</p><p><em>Example</em></p><p>Assume a new child process <code class="inline">m1</code> is to be added to <code class="inline">ch_sup</code> when
│ │ │  upgrading <code class="inline">ch_app</code> from &quot;1&quot; to &quot;2&quot;. This means <code class="inline">m1</code> is to be deleted when
│ │ │ -downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0006186321-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0006186321-2">[</span><span class="p" data-group-id="0006186321-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="0006186321-4">[</span><span class="p" data-group-id="0006186321-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0006186321-5">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0006186321-6">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0006186321-7">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0006186321-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="0006186321-8">]</span><span class="p" data-group-id="0006186321-7">}</span><span class="p" data-group-id="0006186321-6">}</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="0006186321-4">]</span><span class="p" data-group-id="0006186321-3">}</span><span class="p" data-group-id="0006186321-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0006186321-9">[</span><span class="p" data-group-id="0006186321-10">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="0006186321-11">[</span><span class="p" data-group-id="0006186321-12">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0006186321-13">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0006186321-14">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="0006186321-14">]</span><span class="p" data-group-id="0006186321-13">}</span><span class="p" data-group-id="0006186321-12">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0006186321-15">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0006186321-16">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0006186321-17">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="0006186321-17">]</span><span class="p" data-group-id="0006186321-16">}</span><span class="p" data-group-id="0006186321-15">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0006186321-18">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="0006186321-18">}</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="0006186321-11">]</span><span class="p" data-group-id="0006186321-10">}</span><span class="p" data-group-id="0006186321-9">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0006186321-1">}</span><span class="p">.</span></code></pre><p>The order of the instructions is important.</p><p>The supervisor must be registered as <code class="inline">ch_sup</code> for the script to work. If the
│ │ │ +downgrading from &quot;2&quot; to &quot;1&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7005112853-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7005112853-2">[</span><span class="p" data-group-id="7005112853-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="7005112853-4">[</span><span class="p" data-group-id="7005112853-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7005112853-5">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7005112853-6">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7005112853-7">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7005112853-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7005112853-8">]</span><span class="p" data-group-id="7005112853-7">}</span><span class="p" data-group-id="7005112853-6">}</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="7005112853-4">]</span><span class="p" data-group-id="7005112853-3">}</span><span class="p" data-group-id="7005112853-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7005112853-9">[</span><span class="p" data-group-id="7005112853-10">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="7005112853-11">[</span><span class="p" data-group-id="7005112853-12">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7005112853-13">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7005112853-14">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7005112853-14">]</span><span class="p" data-group-id="7005112853-13">}</span><span class="p" data-group-id="7005112853-12">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7005112853-15">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7005112853-16">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7005112853-17">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="7005112853-17">]</span><span class="p" data-group-id="7005112853-16">}</span><span class="p" data-group-id="7005112853-15">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7005112853-18">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="7005112853-18">}</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="7005112853-11">]</span><span class="p" data-group-id="7005112853-10">}</span><span class="p" data-group-id="7005112853-9">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7005112853-1">}</span><span class="p">.</span></code></pre><p>The order of the instructions is important.</p><p>The supervisor must be registered as <code class="inline">ch_sup</code> for the script to work. If the
│ │ │  supervisor is not registered, it cannot be accessed directly from the script.
│ │ │  Instead a help function that finds the pid of the supervisor and calls
│ │ │  <code class="inline">supervisor:restart_child</code>, and so on, must be written. This function is then to
│ │ │  be called from the script using the <code class="inline">apply</code> instruction.</p><p>If the module <code class="inline">m1</code> is introduced in version &quot;2&quot; of <code class="inline">ch_app</code>, it must also be
│ │ │ -loaded when upgrading and deleted when downgrading:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6423113678-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6423113678-2">[</span><span class="p" data-group-id="6423113678-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6423113678-4">[</span><span class="p" data-group-id="6423113678-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="6423113678-5">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6423113678-6">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="6423113678-6">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6423113678-7">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6423113678-8">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6423113678-9">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="6423113678-9">]</span><span class="p" data-group-id="6423113678-8">}</span><span class="p" data-group-id="6423113678-7">}</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6423113678-4">]</span><span class="p" data-group-id="6423113678-3">}</span><span class="p" data-group-id="6423113678-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6423113678-10">[</span><span class="p" data-group-id="6423113678-11">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6423113678-12">[</span><span class="p" data-group-id="6423113678-13">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6423113678-14">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6423113678-15">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="6423113678-15">]</span><span class="p" data-group-id="6423113678-14">}</span><span class="p" data-group-id="6423113678-13">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6423113678-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6423113678-17">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6423113678-18">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="6423113678-18">]</span><span class="p" data-group-id="6423113678-17">}</span><span class="p" data-group-id="6423113678-16">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6423113678-19">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="6423113678-19">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6423113678-20">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="6423113678-20">}</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6423113678-12">]</span><span class="p" data-group-id="6423113678-11">}</span><span class="p" data-group-id="6423113678-10">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6423113678-1">}</span><span class="p">.</span></code></pre><p>As stated earlier, the order of the instructions is important. When upgrading,
│ │ │ +loaded when upgrading and deleted when downgrading:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8451688822-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8451688822-2">[</span><span class="p" data-group-id="8451688822-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8451688822-4">[</span><span class="p" data-group-id="8451688822-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="8451688822-5">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8451688822-6">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="8451688822-6">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8451688822-7">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8451688822-8">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">restart_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8451688822-9">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="8451688822-9">]</span><span class="p" data-group-id="8451688822-8">}</span><span class="p" data-group-id="8451688822-7">}</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8451688822-4">]</span><span class="p" data-group-id="8451688822-3">}</span><span class="p" data-group-id="8451688822-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8451688822-10">[</span><span class="p" data-group-id="8451688822-11">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8451688822-12">[</span><span class="p" data-group-id="8451688822-13">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8451688822-14">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8451688822-15">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="8451688822-15">]</span><span class="p" data-group-id="8451688822-14">}</span><span class="p" data-group-id="8451688822-13">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8451688822-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8451688822-17">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="w"> </span><span class="ss">delete_child</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8451688822-18">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="8451688822-18">]</span><span class="p" data-group-id="8451688822-17">}</span><span class="p" data-group-id="8451688822-16">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8451688822-19">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="8451688822-19">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8451688822-20">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m1</span><span class="p" data-group-id="8451688822-20">}</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8451688822-12">]</span><span class="p" data-group-id="8451688822-11">}</span><span class="p" data-group-id="8451688822-10">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8451688822-1">}</span><span class="p">.</span></code></pre><p>As stated earlier, the order of the instructions is important. When upgrading,
│ │ │  <code class="inline">m1</code> must be loaded, and the supervisor child specification changed, before the
│ │ │  new child process can be started. When downgrading, the child process must be
│ │ │  terminated before the child specification is changed and the module is deleted.</p><h2 id="adding-or-deleting-a-module" class="section-heading">
│ │ │    <a href="#adding-or-deleting-a-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Adding or Deleting a Module</span>
│ │ │  </h2>
│ │ │ -<p>_Example</p><p>_ A new functional module <code class="inline">m</code> is added to <code class="inline">ch_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7185155441-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7185155441-2">[</span><span class="p" data-group-id="7185155441-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7185155441-4">[</span><span class="p" data-group-id="7185155441-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="7185155441-5">}</span><span class="p" data-group-id="7185155441-4">]</span><span class="p" data-group-id="7185155441-3">}</span><span class="p" data-group-id="7185155441-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7185155441-6">[</span><span class="p" data-group-id="7185155441-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7185155441-8">[</span><span class="p" data-group-id="7185155441-9">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="7185155441-9">}</span><span class="p" data-group-id="7185155441-8">]</span><span class="p" data-group-id="7185155441-7">}</span><span class="p" data-group-id="7185155441-6">]</span></code></pre><h2 id="starting-or-terminating-a-process" class="section-heading">
│ │ │ +<p>_Example</p><p>_ A new functional module <code class="inline">m</code> is added to <code class="inline">ch_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5444746093-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5444746093-2">[</span><span class="p" data-group-id="5444746093-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5444746093-4">[</span><span class="p" data-group-id="5444746093-5">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="5444746093-5">}</span><span class="p" data-group-id="5444746093-4">]</span><span class="p" data-group-id="5444746093-3">}</span><span class="p" data-group-id="5444746093-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5444746093-6">[</span><span class="p" data-group-id="5444746093-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5444746093-8">[</span><span class="p" data-group-id="5444746093-9">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="ss">m</span><span class="p" data-group-id="5444746093-9">}</span><span class="p" data-group-id="5444746093-8">]</span><span class="p" data-group-id="5444746093-7">}</span><span class="p" data-group-id="5444746093-6">]</span></code></pre><h2 id="starting-or-terminating-a-process" class="section-heading">
│ │ │    <a href="#starting-or-terminating-a-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting or Terminating a Process</span>
│ │ │  </h2>
│ │ │  <p>In a system structured according to the OTP design principles, any process would
│ │ │  be a child process belonging to a supervisor, see
│ │ │ @@ -369,29 +369,29 @@
│ │ │    <span class="text">Restarting an Application</span>
│ │ │  </h2>
│ │ │  <p>Restarting an application is useful when a change is too complicated to be made
│ │ │  without restarting the processes, for example, if the supervisor hierarchy has
│ │ │  been restructured.</p><p><em>Example</em></p><p>When adding a child <code class="inline">m1</code> to <code class="inline">ch_sup</code>, as in
│ │ │  <a href="appup_cookbook.html#sup_add">Adding and Deleting Child Processes</a> in Changing a
│ │ │  Supervisor, an alternative to updating the supervisor is to restart the entire
│ │ │ -application:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6083681978-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6083681978-2">[</span><span class="p" data-group-id="6083681978-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6083681978-4">[</span><span class="p" data-group-id="6083681978-5">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="6083681978-5">}</span><span class="p" data-group-id="6083681978-4">]</span><span class="p" data-group-id="6083681978-3">}</span><span class="p" data-group-id="6083681978-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6083681978-6">[</span><span class="p" data-group-id="6083681978-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6083681978-8">[</span><span class="p" data-group-id="6083681978-9">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="6083681978-9">}</span><span class="p" data-group-id="6083681978-8">]</span><span class="p" data-group-id="6083681978-7">}</span><span class="p" data-group-id="6083681978-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6083681978-1">}</span><span class="p">.</span></code></pre><p><a href="" id="app_spec"></a></p><h2 id="changing-an-application-specification" class="section-heading">
│ │ │ +application:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7491931389-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7491931389-2">[</span><span class="p" data-group-id="7491931389-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7491931389-4">[</span><span class="p" data-group-id="7491931389-5">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="7491931389-5">}</span><span class="p" data-group-id="7491931389-4">]</span><span class="p" data-group-id="7491931389-3">}</span><span class="p" data-group-id="7491931389-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7491931389-6">[</span><span class="p" data-group-id="7491931389-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7491931389-8">[</span><span class="p" data-group-id="7491931389-9">{</span><span class="ss">restart_application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p" data-group-id="7491931389-9">}</span><span class="p" data-group-id="7491931389-8">]</span><span class="p" data-group-id="7491931389-7">}</span><span class="p" data-group-id="7491931389-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7491931389-1">}</span><span class="p">.</span></code></pre><p><a href="" id="app_spec"></a></p><h2 id="changing-an-application-specification" class="section-heading">
│ │ │    <a href="#changing-an-application-specification" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing an Application Specification</span>
│ │ │  </h2>
│ │ │  <p>When installing a release, the application specifications are automatically
│ │ │  updated before evaluating the <code class="inline">relup</code> script. Thus, no instructions are needed
│ │ │ -in the <code class="inline">.appup</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6907189049-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6907189049-2">[</span><span class="p" data-group-id="6907189049-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6907189049-4">[</span><span class="p" data-group-id="6907189049-4">]</span><span class="p" data-group-id="6907189049-3">}</span><span class="p" data-group-id="6907189049-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6907189049-5">[</span><span class="p" data-group-id="6907189049-6">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6907189049-7">[</span><span class="p" data-group-id="6907189049-7">]</span><span class="p" data-group-id="6907189049-6">}</span><span class="p" data-group-id="6907189049-5">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6907189049-1">}</span><span class="p">.</span></code></pre><h2 id="changing-application-configuration" class="section-heading">
│ │ │ +in the <code class="inline">.appup</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0086953070-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0086953070-2">[</span><span class="p" data-group-id="0086953070-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0086953070-4">[</span><span class="p" data-group-id="0086953070-4">]</span><span class="p" data-group-id="0086953070-3">}</span><span class="p" data-group-id="0086953070-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0086953070-5">[</span><span class="p" data-group-id="0086953070-6">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0086953070-7">[</span><span class="p" data-group-id="0086953070-7">]</span><span class="p" data-group-id="0086953070-6">}</span><span class="p" data-group-id="0086953070-5">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0086953070-1">}</span><span class="p">.</span></code></pre><h2 id="changing-application-configuration" class="section-heading">
│ │ │    <a href="#changing-application-configuration" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Application Configuration</span>
│ │ │  </h2>
│ │ │  <p>Changing an application configuration by updating the <code class="inline">env</code> key in the <code class="inline">.app</code>
│ │ │  file is an instance of changing an application specification, see the previous
│ │ │ @@ -406,26 +406,26 @@
│ │ │  applications apply to primary applications only. There are no corresponding
│ │ │  instructions for included applications. However, since an included application
│ │ │  is really a supervision tree with a topmost supervisor, started as a child
│ │ │  process to a supervisor in the including application, a <code class="inline">.relup</code> file can be
│ │ │  manually created.</p><p><em>Example</em></p><p>Assume there is a release containing an application <code class="inline">prim_app</code>, which
│ │ │  have a supervisor <code class="inline">prim_sup</code> in its supervision tree.</p><p>In a new version of the release, the application <code class="inline">ch_app</code> is to be included in
│ │ │  <code class="inline">prim_app</code>. That is, its topmost supervisor <code class="inline">ch_sup</code> is to be started as a child
│ │ │ -process to <code class="inline">prim_sup</code>.</p><p>The workflow is as follows:</p><p><em>Step 1)</em> Edit the code for <code class="inline">prim_sup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8343019437-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8343019437-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8343019437-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8343019437-3">{</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="ss">supervisor</span><span class="w"> </span><span class="ss">flags</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="8343019437-4">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -           </span><span class="p" data-group-id="8343019437-5">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8343019437-6">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="8343019437-7">[</span><span class="p" data-group-id="8343019437-7">]</span><span class="p" data-group-id="8343019437-6">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="ss">permanent</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="ss">supervisor</span><span class="p">,</span><span class="p" data-group-id="8343019437-8">[</span><span class="ss">ch_sup</span><span class="p" data-group-id="8343019437-8">]</span><span class="p" data-group-id="8343019437-5">}</span><span class="p">,</span><span class="w">
│ │ │ -           </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8343019437-4">]</span><span class="p" data-group-id="8343019437-3">}</span><span class="p" data-group-id="8343019437-2">}</span><span class="p">.</span></code></pre><p><em>Step 2)</em> Edit the <code class="inline">.app</code> file for <code class="inline">prim_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3304031169-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3304031169-2">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="3304031169-3">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="3304031169-3">}</span><span class="p">,</span><span class="w">
│ │ │ +process to <code class="inline">prim_sup</code>.</p><p>The workflow is as follows:</p><p><em>Step 1)</em> Edit the code for <code class="inline">prim_sup</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="0582796038-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0582796038-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0582796038-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582796038-3">{</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="ss">supervisor</span><span class="w"> </span><span class="ss">flags</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="0582796038-4">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ +           </span><span class="p" data-group-id="0582796038-5">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0582796038-6">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="0582796038-7">[</span><span class="p" data-group-id="0582796038-7">]</span><span class="p" data-group-id="0582796038-6">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="ss">permanent</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="ss">supervisor</span><span class="p">,</span><span class="p" data-group-id="0582796038-8">[</span><span class="ss">ch_sup</span><span class="p" data-group-id="0582796038-8">]</span><span class="p" data-group-id="0582796038-5">}</span><span class="p">,</span><span class="w">
│ │ │ +           </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0582796038-4">]</span><span class="p" data-group-id="0582796038-3">}</span><span class="p" data-group-id="0582796038-2">}</span><span class="p">.</span></code></pre><p><em>Step 2)</em> Edit the <code class="inline">.app</code> file for <code class="inline">prim_app</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4554293627-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4554293627-2">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4554293627-3">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="4554293627-3">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="3304031169-4">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3304031169-5">[</span><span class="ss">ch_app</span><span class="p" data-group-id="3304031169-5">]</span><span class="p" data-group-id="3304031169-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4554293627-4">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4554293627-5">[</span><span class="ss">ch_app</span><span class="p" data-group-id="4554293627-5">]</span><span class="p" data-group-id="4554293627-4">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3304031169-2">]</span><span class="p" data-group-id="3304031169-1">}</span><span class="p">.</span></code></pre><p><em>Step 3)</em> Create a new <code class="inline">.rel</code> file, including <code class="inline">ch_app</code>:</p><pre><code class="text">{release,
│ │ │ + </span><span class="p" data-group-id="4554293627-2">]</span><span class="p" data-group-id="4554293627-1">}</span><span class="p">.</span></code></pre><p><em>Step 3)</em> Create a new <code class="inline">.rel</code> file, including <code class="inline">ch_app</code>:</p><pre><code class="text">{release,
│ │ │   ...,
│ │ │   [...,
│ │ │    {prim_app, &quot;2&quot;},
│ │ │    {ch_app, &quot;1&quot;}]}.</code></pre><p>The included application can be started in two ways. This is described in the
│ │ │  next two sections.</p><h3 id="application-restart" class="section-heading">
│ │ │    <a href="#application-restart" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -436,118 +436,118 @@
│ │ │  <code class="inline">prim_app</code> application. Normally, the <code class="inline">restart_application</code> instruction in the
│ │ │  <code class="inline">.appup</code> file for <code class="inline">prim_app</code> would be used.</p><p>However, if this is done and a <code class="inline">.relup</code> file is generated, not only would it
│ │ │  contain instructions for restarting (that is, removing and adding) <code class="inline">prim_app</code>,
│ │ │  it would also contain instructions for starting <code class="inline">ch_app</code> (and stopping it, in
│ │ │  the case of downgrade). This is because <code class="inline">ch_app</code> is included in the new <code class="inline">.rel</code>
│ │ │  file, but not in the old one.</p><p>Instead, a correct <code class="inline">relup</code> file can be created manually, either from scratch or
│ │ │  by editing the generated version. The instructions for starting/stopping
│ │ │ -<code class="inline">ch_app</code> are replaced by instructions for loading/unloading the application:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="8829653701-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8829653701-2">[</span><span class="p" data-group-id="8829653701-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8829653701-4">[</span><span class="p" data-group-id="8829653701-4">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8829653701-5">[</span><span class="p" data-group-id="8829653701-6">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="8829653701-7">{</span><span class="n">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="8829653701-8">[</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">ch3</span><span class="p" data-group-id="8829653701-8">]</span><span class="p" data-group-id="8829653701-7">}</span><span class="p" data-group-id="8829653701-6">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-9">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="8829653701-10">{</span><span class="n">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="8829653701-11">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="8829653701-11">]</span><span class="p" data-group-id="8829653701-10">}</span><span class="p" data-group-id="8829653701-9">}</span><span class="p">,</span><span class="w">
│ │ │ +<code class="inline">ch_app</code> are replaced by instructions for loading/unloading the application:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="1758852743-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1758852743-2">[</span><span class="p" data-group-id="1758852743-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1758852743-4">[</span><span class="p" data-group-id="1758852743-4">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1758852743-5">[</span><span class="p" data-group-id="1758852743-6">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="1758852743-7">{</span><span class="n">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="1758852743-8">[</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">ch3</span><span class="p" data-group-id="1758852743-8">]</span><span class="p" data-group-id="1758852743-7">}</span><span class="p" data-group-id="1758852743-6">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-9">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="1758852743-10">{</span><span class="n">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="1758852743-11">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="1758852743-11">]</span><span class="p" data-group-id="1758852743-10">}</span><span class="p" data-group-id="1758852743-9">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-12">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="8829653701-13">{</span><span class="n">application</span><span class="p">,</span><span class="n">stop</span><span class="p">,</span><span class="p" data-group-id="8829653701-14">[</span><span class="n">prim_app</span><span class="p" data-group-id="8829653701-14">]</span><span class="p" data-group-id="8829653701-13">}</span><span class="p" data-group-id="8829653701-12">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-15">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="8829653701-16">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-16">}</span><span class="p" data-group-id="8829653701-15">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-17">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="8829653701-18">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-18">}</span><span class="p" data-group-id="8829653701-17">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-19">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="8829653701-20">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="8829653701-20">]</span><span class="p" data-group-id="8829653701-19">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-21">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="8829653701-22">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-22">}</span><span class="p" data-group-id="8829653701-21">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-23">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="8829653701-24">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-24">}</span><span class="p" data-group-id="8829653701-23">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-25">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="8829653701-26">{</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-26">}</span><span class="p" data-group-id="8829653701-25">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-27">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="8829653701-28">{</span><span class="n">ch3</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-28">}</span><span class="p" data-group-id="8829653701-27">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-29">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="8829653701-30">{</span><span class="n">application</span><span class="p">,</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="8829653701-31">[</span><span class="n">ch_app</span><span class="p" data-group-id="8829653701-31">]</span><span class="p" data-group-id="8829653701-30">}</span><span class="p" data-group-id="8829653701-29">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-32">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="8829653701-33">{</span><span class="n">application</span><span class="p">,</span><span class="n">start</span><span class="p">,</span><span class="p" data-group-id="8829653701-34">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">permanent</span><span class="p" data-group-id="8829653701-34">]</span><span class="p" data-group-id="8829653701-33">}</span><span class="p" data-group-id="8829653701-32">}</span><span class="p" data-group-id="8829653701-5">]</span><span class="p" data-group-id="8829653701-3">}</span><span class="p" data-group-id="8829653701-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8829653701-35">[</span><span class="p" data-group-id="8829653701-36">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8829653701-37">[</span><span class="p" data-group-id="8829653701-37">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8829653701-38">[</span><span class="p" data-group-id="8829653701-39">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="8829653701-40">{</span><span class="n">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="8829653701-41">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="8829653701-41">]</span><span class="p" data-group-id="8829653701-40">}</span><span class="p" data-group-id="8829653701-39">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-12">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1758852743-13">{</span><span class="n">application</span><span class="p">,</span><span class="n">stop</span><span class="p">,</span><span class="p" data-group-id="1758852743-14">[</span><span class="n">prim_app</span><span class="p" data-group-id="1758852743-14">]</span><span class="p" data-group-id="1758852743-13">}</span><span class="p" data-group-id="1758852743-12">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-15">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1758852743-16">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-16">}</span><span class="p" data-group-id="1758852743-15">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-17">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1758852743-18">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-18">}</span><span class="p" data-group-id="1758852743-17">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-19">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="1758852743-20">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="1758852743-20">]</span><span class="p" data-group-id="1758852743-19">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-21">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1758852743-22">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-22">}</span><span class="p" data-group-id="1758852743-21">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-23">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1758852743-24">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-24">}</span><span class="p" data-group-id="1758852743-23">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-25">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1758852743-26">{</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-26">}</span><span class="p" data-group-id="1758852743-25">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-27">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1758852743-28">{</span><span class="n">ch3</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-28">}</span><span class="p" data-group-id="1758852743-27">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-29">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1758852743-30">{</span><span class="n">application</span><span class="p">,</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1758852743-31">[</span><span class="n">ch_app</span><span class="p" data-group-id="1758852743-31">]</span><span class="p" data-group-id="1758852743-30">}</span><span class="p" data-group-id="1758852743-29">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-32">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1758852743-33">{</span><span class="n">application</span><span class="p">,</span><span class="n">start</span><span class="p">,</span><span class="p" data-group-id="1758852743-34">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">permanent</span><span class="p" data-group-id="1758852743-34">]</span><span class="p" data-group-id="1758852743-33">}</span><span class="p" data-group-id="1758852743-32">}</span><span class="p" data-group-id="1758852743-5">]</span><span class="p" data-group-id="1758852743-3">}</span><span class="p" data-group-id="1758852743-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1758852743-35">[</span><span class="p" data-group-id="1758852743-36">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1758852743-37">[</span><span class="p" data-group-id="1758852743-37">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="1758852743-38">[</span><span class="p" data-group-id="1758852743-39">{</span><span class="n">load_object_code</span><span class="p">,</span><span class="p" data-group-id="1758852743-40">{</span><span class="n">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="1758852743-41">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="1758852743-41">]</span><span class="p" data-group-id="1758852743-40">}</span><span class="p" data-group-id="1758852743-39">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-42">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="8829653701-43">{</span><span class="n">application</span><span class="p">,</span><span class="n">stop</span><span class="p">,</span><span class="p" data-group-id="8829653701-44">[</span><span class="n">prim_app</span><span class="p" data-group-id="8829653701-44">]</span><span class="p" data-group-id="8829653701-43">}</span><span class="p" data-group-id="8829653701-42">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-45">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="8829653701-46">{</span><span class="n">application</span><span class="p">,</span><span class="n">unload</span><span class="p">,</span><span class="p" data-group-id="8829653701-47">[</span><span class="n">ch_app</span><span class="p" data-group-id="8829653701-47">]</span><span class="p" data-group-id="8829653701-46">}</span><span class="p" data-group-id="8829653701-45">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-48">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="8829653701-49">{</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-49">}</span><span class="p" data-group-id="8829653701-48">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-50">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="8829653701-51">{</span><span class="n">ch3</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-51">}</span><span class="p" data-group-id="8829653701-50">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-52">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="8829653701-53">[</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">ch3</span><span class="p" data-group-id="8829653701-53">]</span><span class="p" data-group-id="8829653701-52">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-54">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="8829653701-55">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-55">}</span><span class="p" data-group-id="8829653701-54">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-56">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="8829653701-57">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-57">}</span><span class="p" data-group-id="8829653701-56">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-58">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="8829653701-59">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="8829653701-59">]</span><span class="p" data-group-id="8829653701-58">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-60">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="8829653701-61">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-61">}</span><span class="p" data-group-id="8829653701-60">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-62">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="8829653701-63">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="8829653701-63">}</span><span class="p" data-group-id="8829653701-62">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8829653701-64">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="8829653701-65">{</span><span class="n">application</span><span class="p">,</span><span class="n">start</span><span class="p">,</span><span class="p" data-group-id="8829653701-66">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">permanent</span><span class="p" data-group-id="8829653701-66">]</span><span class="p" data-group-id="8829653701-65">}</span><span class="p" data-group-id="8829653701-64">}</span><span class="p" data-group-id="8829653701-38">]</span><span class="p" data-group-id="8829653701-36">}</span><span class="p" data-group-id="8829653701-35">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8829653701-1">}</span><span class="p">.</span></code></pre><h3 id="supervisor-change" class="section-heading">
│ │ │ +    </span><span class="p" data-group-id="1758852743-42">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1758852743-43">{</span><span class="n">application</span><span class="p">,</span><span class="n">stop</span><span class="p">,</span><span class="p" data-group-id="1758852743-44">[</span><span class="n">prim_app</span><span class="p" data-group-id="1758852743-44">]</span><span class="p" data-group-id="1758852743-43">}</span><span class="p" data-group-id="1758852743-42">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-45">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1758852743-46">{</span><span class="n">application</span><span class="p">,</span><span class="n">unload</span><span class="p">,</span><span class="p" data-group-id="1758852743-47">[</span><span class="n">ch_app</span><span class="p" data-group-id="1758852743-47">]</span><span class="p" data-group-id="1758852743-46">}</span><span class="p" data-group-id="1758852743-45">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-48">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1758852743-49">{</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-49">}</span><span class="p" data-group-id="1758852743-48">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-50">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1758852743-51">{</span><span class="n">ch3</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-51">}</span><span class="p" data-group-id="1758852743-50">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-52">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="1758852743-53">[</span><span class="n">ch_sup</span><span class="p">,</span><span class="n">ch3</span><span class="p" data-group-id="1758852743-53">]</span><span class="p" data-group-id="1758852743-52">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-54">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1758852743-55">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-55">}</span><span class="p" data-group-id="1758852743-54">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-56">{</span><span class="n">remove</span><span class="p">,</span><span class="p" data-group-id="1758852743-57">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-57">}</span><span class="p" data-group-id="1758852743-56">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-58">{</span><span class="n">purge</span><span class="p">,</span><span class="p" data-group-id="1758852743-59">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">prim_sup</span><span class="p" data-group-id="1758852743-59">]</span><span class="p" data-group-id="1758852743-58">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-60">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1758852743-61">{</span><span class="n">prim_app</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-61">}</span><span class="p" data-group-id="1758852743-60">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-62">{</span><span class="n">load</span><span class="p">,</span><span class="p" data-group-id="1758852743-63">{</span><span class="n">prim_sup</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p">,</span><span class="n">brutal_purge</span><span class="p" data-group-id="1758852743-63">}</span><span class="p" data-group-id="1758852743-62">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1758852743-64">{</span><span class="n">apply</span><span class="p">,</span><span class="p" data-group-id="1758852743-65">{</span><span class="n">application</span><span class="p">,</span><span class="n">start</span><span class="p">,</span><span class="p" data-group-id="1758852743-66">[</span><span class="n">prim_app</span><span class="p">,</span><span class="n">permanent</span><span class="p" data-group-id="1758852743-66">]</span><span class="p" data-group-id="1758852743-65">}</span><span class="p" data-group-id="1758852743-64">}</span><span class="p" data-group-id="1758852743-38">]</span><span class="p" data-group-id="1758852743-36">}</span><span class="p" data-group-id="1758852743-35">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1758852743-1">}</span><span class="p">.</span></code></pre><h3 id="supervisor-change" class="section-heading">
│ │ │    <a href="#supervisor-change" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Supervisor Change</span>
│ │ │  </h3>
│ │ │  <p><em>Step 4b)</em> Another way to start the included application (or stop it in the case
│ │ │  of downgrade) is by combining instructions for adding and removing child
│ │ │  processes to/from <code class="inline">prim_sup</code> with instructions for loading/unloading all
│ │ │  <code class="inline">ch_app</code> code and its application specification.</p><p>Again, the <code class="inline">.relup</code> file is created manually, either from scratch or by editing a
│ │ │  generated version. Load all code for <code class="inline">ch_app</code> first, and also load the
│ │ │  application specification, before <code class="inline">prim_sup</code> is updated. When downgrading,
│ │ │  <code class="inline">prim_sup</code> is to updated first, before the code for <code class="inline">ch_app</code> and its application
│ │ │ -specification are unloaded.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7635381186-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7635381186-2">[</span><span class="p" data-group-id="7635381186-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="7635381186-4">[</span><span class="p" data-group-id="7635381186-4">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="7635381186-5">[</span><span class="p" data-group-id="7635381186-6">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="7635381186-7">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="7635381186-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="7635381186-8">]</span><span class="p" data-group-id="7635381186-7">}</span><span class="p" data-group-id="7635381186-6">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-9">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="7635381186-10">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="7635381186-11">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="7635381186-11">]</span><span class="p" data-group-id="7635381186-10">}</span><span class="p" data-group-id="7635381186-9">}</span><span class="p">,</span><span class="w">
│ │ │ +specification are unloaded.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8121752377-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8121752377-2">[</span><span class="p" data-group-id="8121752377-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8121752377-4">[</span><span class="p" data-group-id="8121752377-4">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8121752377-5">[</span><span class="p" data-group-id="8121752377-6">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="8121752377-7">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="8121752377-8">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="8121752377-8">]</span><span class="p" data-group-id="8121752377-7">}</span><span class="p" data-group-id="8121752377-6">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-9">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="8121752377-10">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="p" data-group-id="8121752377-11">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8121752377-11">]</span><span class="p" data-group-id="8121752377-10">}</span><span class="p" data-group-id="8121752377-9">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-12">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="7635381186-13">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="7635381186-13">}</span><span class="p" data-group-id="7635381186-12">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-14">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="7635381186-15">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="7635381186-15">}</span><span class="p" data-group-id="7635381186-14">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="7635381186-17">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="7635381186-18">[</span><span class="ss">ch_app</span><span class="p" data-group-id="7635381186-18">]</span><span class="p" data-group-id="7635381186-17">}</span><span class="p" data-group-id="7635381186-16">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-19">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="7635381186-20">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="7635381186-20">]</span><span class="p" data-group-id="7635381186-19">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-21">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="7635381186-22">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="7635381186-22">}</span><span class="p" data-group-id="7635381186-21">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-23">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">up</span><span class="p">,</span><span class="p" data-group-id="7635381186-24">[</span><span class="p" data-group-id="7635381186-25">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="7635381186-26">[</span><span class="p" data-group-id="7635381186-26">]</span><span class="p" data-group-id="7635381186-25">}</span><span class="p" data-group-id="7635381186-24">]</span><span class="p" data-group-id="7635381186-23">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-27">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="7635381186-28">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="7635381186-28">]</span><span class="p" data-group-id="7635381186-27">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-29">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="7635381186-30">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">restart_child</span><span class="p">,</span><span class="p" data-group-id="7635381186-31">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="7635381186-31">]</span><span class="p" data-group-id="7635381186-30">}</span><span class="p" data-group-id="7635381186-29">}</span><span class="p" data-group-id="7635381186-5">]</span><span class="p" data-group-id="7635381186-3">}</span><span class="p" data-group-id="7635381186-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7635381186-32">[</span><span class="p" data-group-id="7635381186-33">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="7635381186-34">[</span><span class="p" data-group-id="7635381186-34">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="7635381186-35">[</span><span class="p" data-group-id="7635381186-36">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="7635381186-37">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="7635381186-38">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="7635381186-38">]</span><span class="p" data-group-id="7635381186-37">}</span><span class="p" data-group-id="7635381186-36">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-12">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8121752377-13">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8121752377-13">}</span><span class="p" data-group-id="8121752377-12">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-14">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8121752377-15">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8121752377-15">}</span><span class="p" data-group-id="8121752377-14">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-16">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8121752377-17">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8121752377-18">[</span><span class="ss">ch_app</span><span class="p" data-group-id="8121752377-18">]</span><span class="p" data-group-id="8121752377-17">}</span><span class="p" data-group-id="8121752377-16">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-19">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="8121752377-20">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8121752377-20">]</span><span class="p" data-group-id="8121752377-19">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-21">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8121752377-22">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8121752377-22">}</span><span class="p" data-group-id="8121752377-21">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-23">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">up</span><span class="p">,</span><span class="p" data-group-id="8121752377-24">[</span><span class="p" data-group-id="8121752377-25">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="8121752377-26">[</span><span class="p" data-group-id="8121752377-26">]</span><span class="p" data-group-id="8121752377-25">}</span><span class="p" data-group-id="8121752377-24">]</span><span class="p" data-group-id="8121752377-23">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-27">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="8121752377-28">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8121752377-28">]</span><span class="p" data-group-id="8121752377-27">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-29">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8121752377-30">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">restart_child</span><span class="p">,</span><span class="p" data-group-id="8121752377-31">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="8121752377-31">]</span><span class="p" data-group-id="8121752377-30">}</span><span class="p" data-group-id="8121752377-29">}</span><span class="p" data-group-id="8121752377-5">]</span><span class="p" data-group-id="8121752377-3">}</span><span class="p" data-group-id="8121752377-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8121752377-32">[</span><span class="p" data-group-id="8121752377-33">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8121752377-34">[</span><span class="p" data-group-id="8121752377-34">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8121752377-35">[</span><span class="p" data-group-id="8121752377-36">{</span><span class="ss">load_object_code</span><span class="p">,</span><span class="p" data-group-id="8121752377-37">{</span><span class="ss">prim_app</span><span class="p">,</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="p" data-group-id="8121752377-38">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8121752377-38">]</span><span class="p" data-group-id="8121752377-37">}</span><span class="p" data-group-id="8121752377-36">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">point_of_no_return</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-39">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="7635381186-40">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">terminate_child</span><span class="p">,</span><span class="p" data-group-id="7635381186-41">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="7635381186-41">]</span><span class="p" data-group-id="7635381186-40">}</span><span class="p" data-group-id="7635381186-39">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-42">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="7635381186-43">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">delete_child</span><span class="p">,</span><span class="p" data-group-id="7635381186-44">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="7635381186-44">]</span><span class="p" data-group-id="7635381186-43">}</span><span class="p" data-group-id="7635381186-42">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-45">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="7635381186-46">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="7635381186-46">]</span><span class="p" data-group-id="7635381186-45">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-47">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="7635381186-48">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="7635381186-48">}</span><span class="p" data-group-id="7635381186-47">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-49">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">down</span><span class="p">,</span><span class="p" data-group-id="7635381186-50">[</span><span class="p" data-group-id="7635381186-51">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="7635381186-52">[</span><span class="p" data-group-id="7635381186-52">]</span><span class="p" data-group-id="7635381186-51">}</span><span class="p" data-group-id="7635381186-50">]</span><span class="p" data-group-id="7635381186-49">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-53">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="7635381186-54">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="7635381186-54">]</span><span class="p" data-group-id="7635381186-53">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-55">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="7635381186-56">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="7635381186-56">}</span><span class="p" data-group-id="7635381186-55">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-57">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="7635381186-58">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="7635381186-58">}</span><span class="p" data-group-id="7635381186-57">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-59">{</span><span class="ss">purge</span><span class="p">,</span><span class="p" data-group-id="7635381186-60">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="7635381186-60">]</span><span class="p" data-group-id="7635381186-59">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7635381186-61">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="7635381186-62">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">unload</span><span class="p">,</span><span class="p" data-group-id="7635381186-63">[</span><span class="ss">ch_app</span><span class="p" data-group-id="7635381186-63">]</span><span class="p" data-group-id="7635381186-62">}</span><span class="p" data-group-id="7635381186-61">}</span><span class="p" data-group-id="7635381186-35">]</span><span class="p" data-group-id="7635381186-33">}</span><span class="p" data-group-id="7635381186-32">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7635381186-1">}</span><span class="p">.</span></code></pre><h2 id="changing-non-erlang-code" class="section-heading">
│ │ │ +    </span><span class="p" data-group-id="8121752377-39">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8121752377-40">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">terminate_child</span><span class="p">,</span><span class="p" data-group-id="8121752377-41">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="8121752377-41">]</span><span class="p" data-group-id="8121752377-40">}</span><span class="p" data-group-id="8121752377-39">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-42">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8121752377-43">{</span><span class="ss">supervisor</span><span class="p">,</span><span class="ss">delete_child</span><span class="p">,</span><span class="p" data-group-id="8121752377-44">[</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">ch_sup</span><span class="p" data-group-id="8121752377-44">]</span><span class="p" data-group-id="8121752377-43">}</span><span class="p" data-group-id="8121752377-42">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-45">{</span><span class="ss">suspend</span><span class="p">,</span><span class="p" data-group-id="8121752377-46">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8121752377-46">]</span><span class="p" data-group-id="8121752377-45">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-47">{</span><span class="ss">load</span><span class="p">,</span><span class="p" data-group-id="8121752377-48">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8121752377-48">}</span><span class="p" data-group-id="8121752377-47">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-49">{</span><span class="ss">code_change</span><span class="p">,</span><span class="ss">down</span><span class="p">,</span><span class="p" data-group-id="8121752377-50">[</span><span class="p" data-group-id="8121752377-51">{</span><span class="ss">prim_sup</span><span class="p">,</span><span class="p" data-group-id="8121752377-52">[</span><span class="p" data-group-id="8121752377-52">]</span><span class="p" data-group-id="8121752377-51">}</span><span class="p" data-group-id="8121752377-50">]</span><span class="p" data-group-id="8121752377-49">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-53">{</span><span class="ss">resume</span><span class="p">,</span><span class="p" data-group-id="8121752377-54">[</span><span class="ss">prim_sup</span><span class="p" data-group-id="8121752377-54">]</span><span class="p" data-group-id="8121752377-53">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-55">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="8121752377-56">{</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8121752377-56">}</span><span class="p" data-group-id="8121752377-55">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-57">{</span><span class="ss">remove</span><span class="p">,</span><span class="p" data-group-id="8121752377-58">{</span><span class="ss">ch3</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p">,</span><span class="ss">brutal_purge</span><span class="p" data-group-id="8121752377-58">}</span><span class="p" data-group-id="8121752377-57">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-59">{</span><span class="ss">purge</span><span class="p">,</span><span class="p" data-group-id="8121752377-60">[</span><span class="ss">ch_sup</span><span class="p">,</span><span class="ss">ch3</span><span class="p" data-group-id="8121752377-60">]</span><span class="p" data-group-id="8121752377-59">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8121752377-61">{</span><span class="nb">apply</span><span class="p">,</span><span class="p" data-group-id="8121752377-62">{</span><span class="ss">application</span><span class="p">,</span><span class="ss">unload</span><span class="p">,</span><span class="p" data-group-id="8121752377-63">[</span><span class="ss">ch_app</span><span class="p" data-group-id="8121752377-63">]</span><span class="p" data-group-id="8121752377-62">}</span><span class="p" data-group-id="8121752377-61">}</span><span class="p" data-group-id="8121752377-35">]</span><span class="p" data-group-id="8121752377-33">}</span><span class="p" data-group-id="8121752377-32">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8121752377-1">}</span><span class="p">.</span></code></pre><h2 id="changing-non-erlang-code" class="section-heading">
│ │ │    <a href="#changing-non-erlang-code" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Changing Non-Erlang Code</span>
│ │ │  </h2>
│ │ │  <p>Changing code for a program written in another programming language than Erlang,
│ │ │  for example, a port program, is application-dependent and OTP provides no
│ │ │  special support.</p><p><em>Example</em></p><p>When changing code for a port program, assume that the Erlang process
│ │ │  controlling the port is a <code class="inline">gen_server</code> <code class="inline">portc</code> and that the port is opened in
│ │ │ -the callback function <code class="inline">init/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6948410376-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6948410376-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +the callback function <code class="inline">init/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6557078327-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6557078327-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6948410376-2">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="6948410376-3">(</span><span class="n">App</span><span class="p" data-group-id="6948410376-3">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="6948410376-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6948410376-4">(</span><span class="p" data-group-id="6948410376-5">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="6948410376-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6948410376-6">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6948410376-6">]</span><span class="p" data-group-id="6948410376-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="6557078327-2">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="6557078327-3">(</span><span class="n">App</span><span class="p" data-group-id="6557078327-3">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="6557078327-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6557078327-4">(</span><span class="p" data-group-id="6557078327-5">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="6557078327-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6557078327-6">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6557078327-6">]</span><span class="p" data-group-id="6557078327-4">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6948410376-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="6948410376-8">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6948410376-8">}</span><span class="p" data-group-id="6948410376-7">}</span><span class="p">.</span></code></pre><p>If the port program is to be updated, the code for the <code class="inline">gen_server</code> can be
│ │ │ +    </span><span class="p" data-group-id="6557078327-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="6557078327-8">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6557078327-8">}</span><span class="p" data-group-id="6557078327-7">}</span><span class="p">.</span></code></pre><p>If the port program is to be updated, the code for the <code class="inline">gen_server</code> can be
│ │ │  extended with a <code class="inline">code_change/3</code> function, which closes the old port and opens a
│ │ │  new port. (If necessary, the <code class="inline">gen_server</code> can first request data that must be
│ │ │ -saved from the port program and pass this data to the new port):</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="7532021311-1">(</span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="ss">port</span><span class="p" data-group-id="7532021311-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +saved from the port program and pass this data to the new port):</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="4714038596-1">(</span><span class="p">_</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="ss">port</span><span class="p" data-group-id="4714038596-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">close</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7532021311-2">{</span><span class="n">Port</span><span class="p">,</span><span class="ss">close</span><span class="p" data-group-id="7532021311-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="4714038596-2">{</span><span class="n">Port</span><span class="p">,</span><span class="ss">close</span><span class="p" data-group-id="4714038596-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7532021311-3">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="7532021311-4">(</span><span class="n">App</span><span class="p" data-group-id="7532021311-4">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="7532021311-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="7532021311-5">(</span><span class="p" data-group-id="7532021311-6">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="7532021311-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7532021311-7">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7532021311-7">]</span><span class="p" data-group-id="7532021311-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7532021311-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="7532021311-9">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7532021311-9">}</span><span class="p" data-group-id="7532021311-8">}</span><span class="p">.</span></code></pre><p>Update the application version number in the <code class="inline">.app</code> file and write an <code class="inline">.appup</code>
│ │ │ -file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8568621700-1">[</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8568621700-2">[</span><span class="p" data-group-id="8568621700-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8568621700-4">[</span><span class="p" data-group-id="8568621700-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8568621700-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="8568621700-6">}</span><span class="p" data-group-id="8568621700-5">}</span><span class="p" data-group-id="8568621700-4">]</span><span class="p" data-group-id="8568621700-3">}</span><span class="p" data-group-id="8568621700-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8568621700-7">[</span><span class="p" data-group-id="8568621700-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8568621700-9">[</span><span class="p" data-group-id="8568621700-10">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8568621700-11">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="8568621700-11">}</span><span class="p" data-group-id="8568621700-10">}</span><span class="p" data-group-id="8568621700-9">]</span><span class="p" data-group-id="8568621700-8">}</span><span class="p" data-group-id="8568621700-7">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8568621700-1">]</span><span class="p">.</span></code></pre><p>Ensure that the <code class="inline">priv</code> directory, where the C program is located, is included in
│ │ │ -the new release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="5903362123-1">(</span><span class="s">&quot;my_release&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5903362123-2">[</span><span class="p" data-group-id="5903362123-3">{</span><span class="ss">dirs</span><span class="p">,</span><span class="p" data-group-id="5903362123-4">[</span><span class="ss">priv</span><span class="p" data-group-id="5903362123-4">]</span><span class="p" data-group-id="5903362123-3">}</span><span class="p" data-group-id="5903362123-2">]</span><span class="p" data-group-id="5903362123-1">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="n">PortPrg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="4714038596-3">(</span><span class="nc">code</span><span class="p">:</span><span class="nf">priv_dir</span><span class="p" data-group-id="4714038596-4">(</span><span class="n">App</span><span class="p" data-group-id="4714038596-4">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;portc&quot;</span><span class="p" data-group-id="4714038596-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="4714038596-5">(</span><span class="p" data-group-id="4714038596-6">{</span><span class="nb">spawn</span><span class="p">,</span><span class="n">PortPrg</span><span class="p" data-group-id="4714038596-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4714038596-7">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4714038596-7">]</span><span class="p" data-group-id="4714038596-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4714038596-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="4714038596-9">{</span><span class="ss">port</span><span class="o">=</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4714038596-9">}</span><span class="p" data-group-id="4714038596-8">}</span><span class="p">.</span></code></pre><p>Update the application version number in the <code class="inline">.app</code> file and write an <code class="inline">.appup</code>
│ │ │ +file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9838505824-1">[</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9838505824-2">[</span><span class="p" data-group-id="9838505824-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9838505824-4">[</span><span class="p" data-group-id="9838505824-5">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9838505824-6">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="9838505824-6">}</span><span class="p" data-group-id="9838505824-5">}</span><span class="p" data-group-id="9838505824-4">]</span><span class="p" data-group-id="9838505824-3">}</span><span class="p" data-group-id="9838505824-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9838505824-7">[</span><span class="p" data-group-id="9838505824-8">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9838505824-9">[</span><span class="p" data-group-id="9838505824-10">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="ss">portc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9838505824-11">{</span><span class="ss">advanced</span><span class="p">,</span><span class="ss">port</span><span class="p" data-group-id="9838505824-11">}</span><span class="p" data-group-id="9838505824-10">}</span><span class="p" data-group-id="9838505824-9">]</span><span class="p" data-group-id="9838505824-8">}</span><span class="p" data-group-id="9838505824-7">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9838505824-1">]</span><span class="p">.</span></code></pre><p>Ensure that the <code class="inline">priv</code> directory, where the C program is located, is included in
│ │ │ +the new release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="2958748146-1">(</span><span class="s">&quot;my_release&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2958748146-2">[</span><span class="p" data-group-id="2958748146-3">{</span><span class="ss">dirs</span><span class="p">,</span><span class="p" data-group-id="2958748146-4">[</span><span class="ss">priv</span><span class="p" data-group-id="2958748146-4">]</span><span class="p" data-group-id="2958748146-3">}</span><span class="p" data-group-id="2958748146-2">]</span><span class="p" data-group-id="2958748146-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="runtime-system-restart-and-upgrade" class="section-heading">
│ │ │    <a href="#runtime-system-restart-and-upgrade" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Runtime System Restart and Upgrade</span>
│ │ │  </h2>
│ │ │  <p>Two upgrade instructions restart the runtime system:</p><ul><li><p><code class="inline">restart_new_emulator</code></p><p>Intended when ERTS, Kernel, STDLIB, or SASL is upgraded. It is automatically
│ │ │ @@ -555,22 +555,22 @@
│ │ │  executed before all other upgrade instructions. For more information about
│ │ │  this instruction, see restart_new_emulator (Low-Level) in
│ │ │  <a href="release_handling.html#restart_new_emulator_instr">Release Handling Instructions</a>.</p></li><li><p><code class="inline">restart_emulator</code></p><p>Used when a restart of the runtime system is required after all other upgrade
│ │ │  instructions are executed. For more information about this instruction, see
│ │ │  restart_emulator (Low-Level) in
│ │ │  <a href="release_handling.html#restart_emulator_instr">Release Handling Instructions</a>.</p></li></ul><p>If a runtime system restart is necessary and no upgrade instructions are needed,
│ │ │  that is, if the restart itself is enough for the upgraded applications to start
│ │ │ -running the new versions, a simple <code class="inline">.relup</code> file can be created manually:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6764332665-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6764332665-2">[</span><span class="p" data-group-id="6764332665-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6764332665-4">[</span><span class="p" data-group-id="6764332665-4">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6764332665-5">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="6764332665-5">]</span><span class="p" data-group-id="6764332665-3">}</span><span class="p" data-group-id="6764332665-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6764332665-6">[</span><span class="p" data-group-id="6764332665-7">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6764332665-8">[</span><span class="p" data-group-id="6764332665-8">]</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="6764332665-9">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="6764332665-9">]</span><span class="p" data-group-id="6764332665-7">}</span><span class="p" data-group-id="6764332665-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6764332665-1">}</span><span class="p">.</span></code></pre><p>In this case, the release handler framework with automatic packing and unpacking
│ │ │ +running the new versions, a simple <code class="inline">.relup</code> file can be created manually:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7465370485-1">{</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7465370485-2">[</span><span class="p" data-group-id="7465370485-3">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="7465370485-4">[</span><span class="p" data-group-id="7465370485-4">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="7465370485-5">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="7465370485-5">]</span><span class="p" data-group-id="7465370485-3">}</span><span class="p" data-group-id="7465370485-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7465370485-6">[</span><span class="p" data-group-id="7465370485-7">{</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="7465370485-8">[</span><span class="p" data-group-id="7465370485-8">]</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="7465370485-9">[</span><span class="ss">restart_emulator</span><span class="p" data-group-id="7465370485-9">]</span><span class="p" data-group-id="7465370485-7">}</span><span class="p" data-group-id="7465370485-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7465370485-1">}</span><span class="p">.</span></code></pre><p>In this case, the release handler framework with automatic packing and unpacking
│ │ │  of release packages, automatic path updates, and so on, can be used without
│ │ │  having to specify <code class="inline">.appup</code> files.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/benchmarking.html
│ │ │ @@ -144,16 +144,16 @@
│ │ │  fast as possible, what can we do? One way could be to generate more
│ │ │  than two bytes at the time.</p><pre><code class="text">% erlperf 'rand:bytes(100).' 'crypto:strong_rand_bytes(100).'
│ │ │  Code                                   ||        QPS       Time   Rel
│ │ │  rand:bytes(100).                        1    2124 Ki     470 ns  100%
│ │ │  crypto:strong_rand_bytes(100).          1    1915 Ki     522 ns   90%</code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/rand.html#bytes/1"><code class="inline">rand:bytes/1</code></a> is still faster when we generate 100 bytes at the time,
│ │ │  but the relative difference is smaller.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erlperf &#39;rand:bytes(1000).&#39; &#39;crypto:strong_rand_bytes(1000).&#39;</span><span class="w">
│ │ │  </span><span class="n">Code</span><span class="w">                                    </span><span class="p">||</span><span class="w">        </span><span class="n">QPS</span><span class="w">       </span><span class="n">Time</span><span class="w">   </span><span class="n">Rel</span><span class="w">
│ │ │ -</span><span class="nc">crypto</span><span class="p">:</span><span class="nf">strong_rand_bytes</span><span class="p" data-group-id="6543399879-1">(</span><span class="mi">1000</span><span class="p" data-group-id="6543399879-1">)</span><span class="p">.</span><span class="w">          </span><span class="mi">1</span><span class="w">    </span><span class="mi">1518</span><span class="w"> </span><span class="n">Ki</span><span class="w">     </span><span class="mi">658</span><span class="w"> </span><span class="ss">ns</span><span class="w">  </span><span class="mi">100</span><span class="c1">%</span><span class="w">
│ │ │ -</span><span class="nc">rand</span><span class="p">:</span><span class="nf">bytes</span><span class="p" data-group-id="6543399879-2">(</span><span class="mi">1000</span><span class="p" data-group-id="6543399879-2">)</span><span class="p">.</span><span class="w">                        </span><span class="mi">1</span><span class="w">     </span><span class="mi">284</span><span class="w"> </span><span class="n">Ki</span><span class="w">    </span><span class="mi">3521</span><span class="w"> </span><span class="ss">ns</span><span class="w">   </span><span class="mi">19</span><span class="c1">%</span></code></pre><p>When we generate 1000 bytes at the time, <a href="../../lib/crypto-5.5.3.2/doc/html/crypto.html#strong_rand_bytes/1"><code class="inline">crypto:strong_rand_bytes/1</code></a> is
│ │ │ +</span><span class="nc">crypto</span><span class="p">:</span><span class="nf">strong_rand_bytes</span><span class="p" data-group-id="9480589351-1">(</span><span class="mi">1000</span><span class="p" data-group-id="9480589351-1">)</span><span class="p">.</span><span class="w">          </span><span class="mi">1</span><span class="w">    </span><span class="mi">1518</span><span class="w"> </span><span class="n">Ki</span><span class="w">     </span><span class="mi">658</span><span class="w"> </span><span class="ss">ns</span><span class="w">  </span><span class="mi">100</span><span class="c1">%</span><span class="w">
│ │ │ +</span><span class="nc">rand</span><span class="p">:</span><span class="nf">bytes</span><span class="p" data-group-id="9480589351-2">(</span><span class="mi">1000</span><span class="p" data-group-id="9480589351-2">)</span><span class="p">.</span><span class="w">                        </span><span class="mi">1</span><span class="w">     </span><span class="mi">284</span><span class="w"> </span><span class="n">Ki</span><span class="w">    </span><span class="mi">3521</span><span class="w"> </span><span class="ss">ns</span><span class="w">   </span><span class="mi">19</span><span class="c1">%</span></code></pre><p>When we generate 1000 bytes at the time, <a href="../../lib/crypto-5.5.3.2/doc/html/crypto.html#strong_rand_bytes/1"><code class="inline">crypto:strong_rand_bytes/1</code></a> is
│ │ │  now the fastest.</p><h2 id="benchmarking-using-erlang-otp-functionality" class="section-heading">
│ │ │    <a href="#benchmarking-using-erlang-otp-functionality" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Benchmarking using Erlang/OTP functionality</span>
│ │ │  </h2>
│ │ │  <p>Benchmarks can measure wall-clock time or CPU time.</p><ul><li><p><a href="../../lib/stdlib-6.2.2.3/doc/html/timer.html#tc/3"><code class="inline">timer:tc/3</code></a> measures wall-clock time. The advantage with wall-clock time is
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/binaryhandling.html
│ │ │ @@ -114,43 +114,43 @@
│ │ │  
│ │ │      <span>Constructing and Matching Binaries</span>
│ │ │    </h1>
│ │ │  
│ │ │  <p>This section gives a few examples on how to handle binaries in an efficient way.
│ │ │  The sections that follow take an in-depth look at how binaries are implemented
│ │ │  and how to best take advantages of the optimizations done by the compiler and
│ │ │ -runtime system.</p><p>Binaries can be efficiently <em>built</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_list_to_binary</span><span class="p" data-group-id="2891255025-1">(</span><span class="n">List</span><span class="p" data-group-id="2891255025-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="2891255025-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2891255025-3">&lt;&lt;</span><span class="p" data-group-id="2891255025-3">&gt;&gt;</span><span class="p" data-group-id="2891255025-2">)</span><span class="p">.</span><span class="w">
│ │ │ +runtime system.</p><p>Binaries can be efficiently <em>built</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_list_to_binary</span><span class="p" data-group-id="1105195151-1">(</span><span class="n">List</span><span class="p" data-group-id="1105195151-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="1105195151-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1105195151-3">&lt;&lt;</span><span class="p" data-group-id="1105195151-3">&gt;&gt;</span><span class="p" data-group-id="1105195151-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="2891255025-4">(</span><span class="p" data-group-id="2891255025-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2891255025-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2891255025-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="2891255025-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2891255025-7">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="2891255025-7">&gt;&gt;</span><span class="p" data-group-id="2891255025-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="2891255025-8">(</span><span class="p" data-group-id="2891255025-9">[</span><span class="p" data-group-id="2891255025-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2891255025-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="1105195151-4">(</span><span class="p" data-group-id="1105195151-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1105195151-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1105195151-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="1105195151-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1105195151-7">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="1105195151-7">&gt;&gt;</span><span class="p" data-group-id="1105195151-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">my_list_to_binary</span><span class="p" data-group-id="1105195151-8">(</span><span class="p" data-group-id="1105195151-9">[</span><span class="p" data-group-id="1105195151-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1105195151-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Appending data to a binary as in the example is efficient because it is
│ │ │  specially optimized by the runtime system to avoid copying the <code class="inline">Acc</code> binary
│ │ │ -every time.</p><p>Prepending data to a binary in a loop is not efficient:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="7251516678-1">(</span><span class="n">List</span><span class="p" data-group-id="7251516678-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="7251516678-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7251516678-3">&lt;&lt;</span><span class="p" data-group-id="7251516678-3">&gt;&gt;</span><span class="p" data-group-id="7251516678-2">)</span><span class="p">.</span><span class="w">
│ │ │ +every time.</p><p>Prepending data to a binary in a loop is not efficient:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8260801138-1">(</span><span class="n">List</span><span class="p" data-group-id="8260801138-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8260801138-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8260801138-3">&lt;&lt;</span><span class="p" data-group-id="8260801138-3">&gt;&gt;</span><span class="p" data-group-id="8260801138-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="7251516678-4">(</span><span class="p" data-group-id="7251516678-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7251516678-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7251516678-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="7251516678-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7251516678-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7251516678-7">&gt;&gt;</span><span class="p" data-group-id="7251516678-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="7251516678-8">(</span><span class="p" data-group-id="7251516678-9">[</span><span class="p" data-group-id="7251516678-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7251516678-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8260801138-4">(</span><span class="p" data-group-id="8260801138-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8260801138-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8260801138-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8260801138-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8260801138-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8260801138-7">&gt;&gt;</span><span class="p" data-group-id="8260801138-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="8260801138-8">(</span><span class="p" data-group-id="8260801138-9">[</span><span class="p" data-group-id="8260801138-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8260801138-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>This is not efficient for long lists because the <code class="inline">Acc</code> binary is copied every
│ │ │ -time. One way to make the function more efficient is like this:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5825680526-1">(</span><span class="n">List</span><span class="p" data-group-id="5825680526-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5825680526-2">(</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="5825680526-3">(</span><span class="n">List</span><span class="p" data-group-id="5825680526-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5825680526-4">&lt;&lt;</span><span class="p" data-group-id="5825680526-4">&gt;&gt;</span><span class="p" data-group-id="5825680526-2">)</span><span class="p">.</span><span class="w">
│ │ │ +time. One way to make the function more efficient is like this:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1673579594-1">(</span><span class="n">List</span><span class="p" data-group-id="1673579594-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1673579594-2">(</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="1673579594-3">(</span><span class="n">List</span><span class="p" data-group-id="1673579594-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1673579594-4">&lt;&lt;</span><span class="p" data-group-id="1673579594-4">&gt;&gt;</span><span class="p" data-group-id="1673579594-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5825680526-5">(</span><span class="p" data-group-id="5825680526-6">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5825680526-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5825680526-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5825680526-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5825680526-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="5825680526-8">&gt;&gt;</span><span class="p" data-group-id="5825680526-7">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5825680526-9">(</span><span class="p" data-group-id="5825680526-10">[</span><span class="p" data-group-id="5825680526-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5825680526-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Another way to avoid copying the binary each time is like this:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5874632255-1">(</span><span class="p" data-group-id="5874632255-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5874632255-2">]</span><span class="p" data-group-id="5874632255-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">RevTail</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5874632255-3">(</span><span class="n">T</span><span class="p" data-group-id="5874632255-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5874632255-4">&lt;&lt;</span><span class="n">RevTail</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="5874632255-4">&gt;&gt;</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="5874632255-5">(</span><span class="p" data-group-id="5874632255-6">[</span><span class="p" data-group-id="5874632255-6">]</span><span class="p" data-group-id="5874632255-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5874632255-7">&lt;&lt;</span><span class="p" data-group-id="5874632255-7">&gt;&gt;</span><span class="p">.</span></code></pre><p>Note that in each of the <strong>DO</strong> examples, the binary to be appended to is always
│ │ │ -given as the first segment.</p><p>Binaries can be efficiently <em>matched</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="6414861715-1">(</span><span class="p" data-group-id="6414861715-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6414861715-2">&gt;&gt;</span><span class="p" data-group-id="6414861715-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6414861715-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="6414861715-4">(</span><span class="n">T</span><span class="p" data-group-id="6414861715-4">)</span><span class="p" data-group-id="6414861715-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="6414861715-5">(</span><span class="p" data-group-id="6414861715-6">&lt;&lt;</span><span class="p" data-group-id="6414861715-6">&gt;&gt;</span><span class="p" data-group-id="6414861715-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6414861715-7">[</span><span class="p" data-group-id="6414861715-7">]</span><span class="p">.</span></code></pre><h2 id="how-binaries-are-implemented" class="section-heading">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1673579594-5">(</span><span class="p" data-group-id="1673579594-6">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1673579594-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1673579594-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1673579594-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1673579594-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="1673579594-8">&gt;&gt;</span><span class="p" data-group-id="1673579594-7">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="1673579594-9">(</span><span class="p" data-group-id="1673579594-10">[</span><span class="p" data-group-id="1673579594-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1673579594-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Another way to avoid copying the binary each time is like this:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9302509995-1">(</span><span class="p" data-group-id="9302509995-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9302509995-2">]</span><span class="p" data-group-id="9302509995-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">RevTail</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9302509995-3">(</span><span class="n">T</span><span class="p" data-group-id="9302509995-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9302509995-4">&lt;&lt;</span><span class="n">RevTail</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">H</span><span class="p" data-group-id="9302509995-4">&gt;&gt;</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">rev_list_to_binary</span><span class="p" data-group-id="9302509995-5">(</span><span class="p" data-group-id="9302509995-6">[</span><span class="p" data-group-id="9302509995-6">]</span><span class="p" data-group-id="9302509995-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9302509995-7">&lt;&lt;</span><span class="p" data-group-id="9302509995-7">&gt;&gt;</span><span class="p">.</span></code></pre><p>Note that in each of the <strong>DO</strong> examples, the binary to be appended to is always
│ │ │ +given as the first segment.</p><p>Binaries can be efficiently <em>matched</em> in the following way:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="3003393259-1">(</span><span class="p" data-group-id="3003393259-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3003393259-2">&gt;&gt;</span><span class="p" data-group-id="3003393259-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3003393259-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="3003393259-4">(</span><span class="n">T</span><span class="p" data-group-id="3003393259-4">)</span><span class="p" data-group-id="3003393259-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="3003393259-5">(</span><span class="p" data-group-id="3003393259-6">&lt;&lt;</span><span class="p" data-group-id="3003393259-6">&gt;&gt;</span><span class="p" data-group-id="3003393259-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3003393259-7">[</span><span class="p" data-group-id="3003393259-7">]</span><span class="p">.</span></code></pre><h2 id="how-binaries-are-implemented" class="section-heading">
│ │ │    <a href="#how-binaries-are-implemented" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">How Binaries are Implemented</span>
│ │ │  </h2>
│ │ │  <p>Internally, binaries and bitstrings are implemented in the same way. In this
│ │ │  section, they are called <em>binaries</em> because that is what they are called in the
│ │ │ @@ -205,29 +205,29 @@
│ │ │  called referential transparency) of Erlang would break.</p><h2 id="constructing-binaries" class="section-heading">
│ │ │    <a href="#constructing-binaries" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Constructing Binaries</span>
│ │ │  </h2>
│ │ │  <p>Appending to a binary or bitstring in the following way is specially optimized
│ │ │ -to avoid copying the binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2151394065-1">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2151394065-1">&gt;&gt;</span><span class="w">
│ │ │ +to avoid copying the binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3218975611-1">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3218975611-1">&gt;&gt;</span><span class="w">
│ │ │  </span><span class="c1">%% - OR -</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2151394065-2">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">bitstring</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2151394065-2">&gt;&gt;</span></code></pre><p>This optimization is applied by the runtime system in a way that makes it
│ │ │ +</span><span class="p" data-group-id="3218975611-2">&lt;&lt;</span><span class="n">Binary</span><span class="o">/</span><span class="ss">bitstring</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3218975611-2">&gt;&gt;</span></code></pre><p>This optimization is applied by the runtime system in a way that makes it
│ │ │  effective in most circumstances (for exceptions, see
│ │ │  <a href="binaryhandling.html#forced_copying">Circumstances That Force Copying</a>). The
│ │ │  optimization in its basic form does not need any help from the compiler.
│ │ │  However, the compiler add hints to the runtime system when it is safe to apply
│ │ │  the optimization in a more efficient way.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>The compiler support for making the optimization more efficient was added in
│ │ │  Erlang/OTP 26.</p></section><p>To explain how the basic optimization works, let us examine the following code
│ │ │ -line by line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3899457390-1">&lt;&lt;</span><span class="mi">0</span><span class="p" data-group-id="3899457390-1">&gt;&gt;</span><span class="p">,</span><span class="w">                    </span><span class="c1">%% 1</span><span class="w">
│ │ │ -</span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3899457390-2">&lt;&lt;</span><span class="n">Bin0</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3899457390-2">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 2</span><span class="w">
│ │ │ -</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3899457390-3">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3899457390-3">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 3</span><span class="w">
│ │ │ -</span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3899457390-4">&lt;&lt;</span><span class="n">Bin2</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="3899457390-4">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 4</span><span class="w">
│ │ │ -</span><span class="n">Bin4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3899457390-5">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="3899457390-5">&gt;&gt;</span><span class="p">,</span><span class="w">       </span><span class="c1">%% 5 !!!</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3899457390-6">{</span><span class="n">Bin4</span><span class="p">,</span><span class="n">Bin3</span><span class="p" data-group-id="3899457390-6">}</span><span class="w">                      </span><span class="c1">%% 6</span></code></pre><ul><li><p>Line 1 (marked with the <code class="inline">%% 1</code> comment), assigns a
│ │ │ +line by line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8929230419-1">&lt;&lt;</span><span class="mi">0</span><span class="p" data-group-id="8929230419-1">&gt;&gt;</span><span class="p">,</span><span class="w">                    </span><span class="c1">%% 1</span><span class="w">
│ │ │ +</span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8929230419-2">&lt;&lt;</span><span class="n">Bin0</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8929230419-2">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 2</span><span class="w">
│ │ │ +</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8929230419-3">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8929230419-3">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 3</span><span class="w">
│ │ │ +</span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8929230419-4">&lt;&lt;</span><span class="n">Bin2</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p" data-group-id="8929230419-4">&gt;&gt;</span><span class="p">,</span><span class="w">    </span><span class="c1">%% 4</span><span class="w">
│ │ │ +</span><span class="n">Bin4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8929230419-5">&lt;&lt;</span><span class="n">Bin1</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="8929230419-5">&gt;&gt;</span><span class="p">,</span><span class="w">       </span><span class="c1">%% 5 !!!</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8929230419-6">{</span><span class="n">Bin4</span><span class="p">,</span><span class="n">Bin3</span><span class="p" data-group-id="8929230419-6">}</span><span class="w">                      </span><span class="c1">%% 6</span></code></pre><ul><li><p>Line 1 (marked with the <code class="inline">%% 1</code> comment), assigns a
│ │ │  <a href="binaryhandling.html#heap_binary">heap binary</a> to the <code class="inline">Bin0</code> variable.</p></li><li><p>Line 2 is an append operation. As <code class="inline">Bin0</code> has not been involved in an append
│ │ │  operation, a new <a href="binaryhandling.html#refc_binary">refc binary</a> is created and
│ │ │  the contents of <code class="inline">Bin0</code> is copied into it. The <em>ProcBin</em> part of the refc
│ │ │  binary has its size set to the size of the data stored in the binary, while
│ │ │  the binary object has extra space allocated. The size of the binary object is
│ │ │  either twice the size of <code class="inline">Bin1</code> or 256, whichever is larger. In this case it
│ │ │  is 256.</p></li><li><p>Line 3 is more interesting. <code class="inline">Bin1</code> <em>has</em> been used in an append operation, and
│ │ │ @@ -253,23 +253,23 @@
│ │ │  handle an append operation to a heap binary by copying it to a refc binary (line
│ │ │  2), and also handle an append operation to a previous version of the binary by
│ │ │  copying it (line 5). The support for doing that does not come for free. For
│ │ │  example, to make it possible to know when it is necessary to copy the binary,
│ │ │  for every append operation, the runtime system must create a sub binary.</p><p>When the compiler can determine that none of those situations need to be handled
│ │ │  and that the append operation cannot possibly fail, the compiler generates code
│ │ │  that causes the runtime system to apply a more efficient variant of the
│ │ │ -optimization.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8612879782-1">(</span><span class="ss">repack</span><span class="p" data-group-id="8612879782-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8612879782-2">(</span><span class="p" data-group-id="8612879782-3">[</span><span class="ss">repack</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8612879782-3">]</span><span class="p" data-group-id="8612879782-2">)</span><span class="p">.</span><span class="w">
│ │ │ +optimization.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5653363711-1">(</span><span class="ss">repack</span><span class="p" data-group-id="5653363711-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5653363711-2">(</span><span class="p" data-group-id="5653363711-3">[</span><span class="ss">repack</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5653363711-3">]</span><span class="p" data-group-id="5653363711-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="8612879782-4">(</span><span class="n">Bin</span><span class="p" data-group-id="8612879782-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_binary</span><span class="p" data-group-id="8612879782-5">(</span><span class="n">Bin</span><span class="p" data-group-id="8612879782-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">repack</span><span class="p" data-group-id="8612879782-6">(</span><span class="n">Bin</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8612879782-7">&lt;&lt;</span><span class="p" data-group-id="8612879782-7">&gt;&gt;</span><span class="p" data-group-id="8612879782-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="5653363711-4">(</span><span class="n">Bin</span><span class="p" data-group-id="5653363711-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_binary</span><span class="p" data-group-id="5653363711-5">(</span><span class="n">Bin</span><span class="p" data-group-id="5653363711-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">repack</span><span class="p" data-group-id="5653363711-6">(</span><span class="n">Bin</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5653363711-7">&lt;&lt;</span><span class="p" data-group-id="5653363711-7">&gt;&gt;</span><span class="p" data-group-id="5653363711-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="8612879782-8">(</span><span class="p" data-group-id="8612879782-9">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8612879782-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8612879782-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">repack</span><span class="p" data-group-id="8612879782-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8612879782-11">&lt;&lt;</span><span class="n">Result</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="8612879782-11">&gt;&gt;</span><span class="p" data-group-id="8612879782-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">repack</span><span class="p" data-group-id="8612879782-12">(</span><span class="p" data-group-id="8612879782-13">&lt;&lt;</span><span class="p" data-group-id="8612879782-13">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8612879782-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="5653363711-8">(</span><span class="p" data-group-id="5653363711-9">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5653363711-9">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="5653363711-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">repack</span><span class="p" data-group-id="5653363711-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5653363711-11">&lt;&lt;</span><span class="n">Result</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5653363711-11">&gt;&gt;</span><span class="p" data-group-id="5653363711-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">repack</span><span class="p" data-group-id="5653363711-12">(</span><span class="p" data-group-id="5653363711-13">&lt;&lt;</span><span class="p" data-group-id="5653363711-13">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="5653363711-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Result</span><span class="p">.</span></code></pre><p>The <code class="inline">repack/2</code> function only keeps a single version of the binary, so there is
│ │ │  never any need to copy the binary. The compiler rewrites the creation of the
│ │ │  empty binary in <code class="inline">repack/1</code> to instead create a refc binary with 256 bytes
│ │ │  already reserved; thus, the append operation in <code class="inline">repack/2</code> never needs to handle
│ │ │  a binary not prepared for appending.</p><p><a href="" id="forced_copying"></a></p><h3 id="circumstances-that-force-copying" class="section-heading">
│ │ │    <a href="#circumstances-that-force-copying" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -281,72 +281,72 @@
│ │ │  reason is that the binary object can be moved (reallocated) during an append
│ │ │  operation, and when that happens, the pointer in the ProcBin must be updated. If
│ │ │  there would be more than one ProcBin pointing to the binary object, it would not
│ │ │  be possible to find and update all of them.</p><p>Therefore, certain operations on a binary mark it so that any future append
│ │ │  operation will be forced to copy the binary. In most cases, the binary object
│ │ │  will be shrunk at the same time to reclaim the extra space allocated for
│ │ │  growing.</p><p>When appending to a binary as follows, only the binary returned from the latest
│ │ │ -append operation will support further cheap append operations:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1022029533-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1022029533-1">&gt;&gt;</span></code></pre><p>In the code fragment in the beginning of this section, appending to <code class="inline">Bin</code> will
│ │ │ +append operation will support further cheap append operations:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0031134804-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0031134804-1">&gt;&gt;</span></code></pre><p>In the code fragment in the beginning of this section, appending to <code class="inline">Bin</code> will
│ │ │  be cheap, while appending to <code class="inline">Bin0</code> will force the creation of a new binary and
│ │ │  copying of the contents of <code class="inline">Bin0</code>.</p><p>If a binary is sent as a message to a process or port, the binary will be shrunk
│ │ │  and any further append operation will copy the binary data into a new binary.
│ │ │  For example, in the following code fragment <code class="inline">Bin1</code> will be copied in the third
│ │ │ -line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9426688845-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9426688845-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ +line:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8445155935-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8445155935-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">PortOrPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9426688845-2">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9426688845-2">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The same happens if you insert a binary into an Ets table, send it to a port
│ │ │ +</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8445155935-2">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8445155935-2">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The same happens if you insert a binary into an Ets table, send it to a port
│ │ │  using <a href="../../erts-15.2.7.8/doc/html/erlang.html#port_command/2"><code class="inline">erlang:port_command/2</code></a>, or pass it to
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erl_nif.html#enif_inspect_binary">enif_inspect_binary</a> in a NIF.</p><p>Matching a binary will also cause it to shrink and the next append operation
│ │ │ -will copy the binary data:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0466833890-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0466833890-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0466833890-2">&lt;&lt;</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0466833890-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0466833890-3">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0466833890-3">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The reason is that a <a href="binaryhandling.html#match_context">match context</a> contains a
│ │ │ +will copy the binary data:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7925508435-1">&lt;&lt;</span><span class="n">Bin0</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7925508435-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7925508435-2">&lt;&lt;</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7925508435-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin1</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7925508435-3">&lt;&lt;</span><span class="n">Bin1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="7925508435-3">&gt;&gt;</span><span class="w">  </span><span class="c1">%% Bin1 will be COPIED</span></code></pre><p>The reason is that a <a href="binaryhandling.html#match_context">match context</a> contains a
│ │ │  direct pointer to the binary data.</p><p>If a process simply keeps binaries (either in &quot;loop data&quot; or in the process
│ │ │  dictionary), the garbage collector can eventually shrink the binaries. If only
│ │ │  one such binary is kept, it will not be shrunk. If the process later appends to
│ │ │  a binary that has been shrunk, the binary object will be reallocated to make
│ │ │  place for the data to be appended.</p><h2 id="matching-binaries" class="section-heading">
│ │ │    <a href="#matching-binaries" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Matching Binaries</span>
│ │ │  </h2>
│ │ │ -<p>Let us revisit the example in the beginning of the previous section:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="5105510545-1">(</span><span class="p" data-group-id="5105510545-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5105510545-2">&gt;&gt;</span><span class="p" data-group-id="5105510545-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5105510545-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="5105510545-4">(</span><span class="n">T</span><span class="p" data-group-id="5105510545-4">)</span><span class="p" data-group-id="5105510545-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="5105510545-5">(</span><span class="p" data-group-id="5105510545-6">&lt;&lt;</span><span class="p" data-group-id="5105510545-6">&gt;&gt;</span><span class="p" data-group-id="5105510545-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5105510545-7">[</span><span class="p" data-group-id="5105510545-7">]</span><span class="p">.</span></code></pre><p>The first time <code class="inline">my_binary_to_list/1</code> is called, a
│ │ │ +<p>Let us revisit the example in the beginning of the previous section:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">my_binary_to_list</span><span class="p" data-group-id="6879916349-1">(</span><span class="p" data-group-id="6879916349-2">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6879916349-2">&gt;&gt;</span><span class="p" data-group-id="6879916349-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6879916349-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="6879916349-4">(</span><span class="n">T</span><span class="p" data-group-id="6879916349-4">)</span><span class="p" data-group-id="6879916349-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">my_binary_to_list</span><span class="p" data-group-id="6879916349-5">(</span><span class="p" data-group-id="6879916349-6">&lt;&lt;</span><span class="p" data-group-id="6879916349-6">&gt;&gt;</span><span class="p" data-group-id="6879916349-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6879916349-7">[</span><span class="p" data-group-id="6879916349-7">]</span><span class="p">.</span></code></pre><p>The first time <code class="inline">my_binary_to_list/1</code> is called, a
│ │ │  <a href="binaryhandling.html#match_context">match context</a> is created. The match context
│ │ │  points to the first byte of the binary. 1 byte is matched out and the match
│ │ │  context is updated to point to the second byte in the binary.</p><p>At this point it would make sense to create a
│ │ │  <a href="binaryhandling.html#sub_binary">sub binary</a>, but in this particular example the
│ │ │  compiler sees that there will soon be a call to a function (in this case, to
│ │ │  <code class="inline">my_binary_to_list/1</code> itself) that immediately will create a new match context
│ │ │  and discard the sub binary.</p><p>Therefore <code class="inline">my_binary_to_list/1</code> calls itself with the match context instead of
│ │ │  with a sub binary. The instruction that initializes the matching operation
│ │ │  basically does nothing when it sees that it was passed a match context instead
│ │ │  of a binary.</p><p>When the end of the binary is reached and the second clause matches, the match
│ │ │  context will simply be discarded (removed in the next garbage collection, as
│ │ │  there is no longer any reference to it).</p><p>To summarize, <code class="inline">my_binary_to_list/1</code> only needs to create <em>one</em> match context and
│ │ │  no sub binaries.</p><p>Notice that the match context in <code class="inline">my_binary_to_list/1</code> was discarded when the
│ │ │  entire binary had been traversed. What happens if the iteration stops before it
│ │ │ -has reached the end of the binary? Will the optimization still work?</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="2789097669-1">(</span><span class="p" data-group-id="2789097669-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2789097669-2">&gt;&gt;</span><span class="p" data-group-id="2789097669-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +has reached the end of the binary? Will the optimization still work?</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="0428214088-1">(</span><span class="p" data-group-id="0428214088-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0428214088-2">&gt;&gt;</span><span class="p" data-group-id="0428214088-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="2789097669-3">(</span><span class="p" data-group-id="2789097669-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2789097669-4">&gt;&gt;</span><span class="p" data-group-id="2789097669-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="2789097669-5">(</span><span class="n">T</span><span class="p" data-group-id="2789097669-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="2789097669-6">(</span><span class="p" data-group-id="2789097669-7">&lt;&lt;</span><span class="p" data-group-id="2789097669-7">&gt;&gt;</span><span class="p" data-group-id="2789097669-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2789097669-8">&lt;&lt;</span><span class="p" data-group-id="2789097669-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>Yes, it will. The compiler will remove the building of the sub binary in the
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="0428214088-3">(</span><span class="p" data-group-id="0428214088-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0428214088-4">&gt;&gt;</span><span class="p" data-group-id="0428214088-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="0428214088-5">(</span><span class="n">T</span><span class="p" data-group-id="0428214088-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="0428214088-6">(</span><span class="p" data-group-id="0428214088-7">&lt;&lt;</span><span class="p" data-group-id="0428214088-7">&gt;&gt;</span><span class="p" data-group-id="0428214088-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0428214088-8">&lt;&lt;</span><span class="p" data-group-id="0428214088-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>Yes, it will. The compiler will remove the building of the sub binary in the
│ │ │  second clause:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="5288471431-1">(</span><span class="p" data-group-id="5288471431-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5288471431-2">&gt;&gt;</span><span class="p" data-group-id="5288471431-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="5288471431-3">(</span><span class="n">T</span><span class="p" data-group-id="5288471431-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>But it will generate code that builds a sub binary in the first clause:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="1183583964-1">(</span><span class="p" data-group-id="1183583964-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1183583964-2">&gt;&gt;</span><span class="p" data-group-id="1183583964-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="4185310273-1">(</span><span class="p" data-group-id="4185310273-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4185310273-2">&gt;&gt;</span><span class="p" data-group-id="4185310273-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="4185310273-3">(</span><span class="n">T</span><span class="p" data-group-id="4185310273-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>But it will generate code that builds a sub binary in the first clause:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="9970178049-1">(</span><span class="p" data-group-id="9970178049-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9970178049-2">&gt;&gt;</span><span class="p" data-group-id="9970178049-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Therefore, <code class="inline">after_zero/1</code> builds one match context and one sub binary (assuming
│ │ │ -it is passed a binary that contains a zero byte).</p><p>Code like the following will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="4425483373-1">(</span><span class="n">Buffer</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4425483373-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4425483373-2">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="4425483373-3">(</span><span class="n">Acc</span><span class="p" data-group-id="4425483373-3">)</span><span class="p">,</span><span class="n">Buffer</span><span class="p" data-group-id="4425483373-2">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="4425483373-4">(</span><span class="p" data-group-id="4425483373-5">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4425483373-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="4425483373-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="4425483373-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="4425483373-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="4425483373-7">(</span><span class="p" data-group-id="4425483373-8">&lt;&lt;</span><span class="n">Byte</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4425483373-8">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="4425483373-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="4425483373-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4425483373-10">[</span><span class="n">Byte</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="4425483373-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="4425483373-9">)</span><span class="p">.</span></code></pre><p>The compiler removes building of sub binaries in the second and third clauses,
│ │ │ +it is passed a binary that contains a zero byte).</p><p>Code like the following will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9749771142-1">(</span><span class="n">Buffer</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="9749771142-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9749771142-2">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="9749771142-3">(</span><span class="n">Acc</span><span class="p" data-group-id="9749771142-3">)</span><span class="p">,</span><span class="n">Buffer</span><span class="p" data-group-id="9749771142-2">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9749771142-4">(</span><span class="p" data-group-id="9749771142-5">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9749771142-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="9749771142-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9749771142-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="9749771142-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9749771142-7">(</span><span class="p" data-group-id="9749771142-8">&lt;&lt;</span><span class="n">Byte</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9749771142-8">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="p" data-group-id="9749771142-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">all_but_zeroes_to_list</span><span class="p" data-group-id="9749771142-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9749771142-10">[</span><span class="n">Byte</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="9749771142-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Remaining</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="9749771142-9">)</span><span class="p">.</span></code></pre><p>The compiler removes building of sub binaries in the second and third clauses,
│ │ │  and it adds an instruction to the first clause that converts <code class="inline">Buffer</code> from a
│ │ │  match context to a sub binary (or do nothing if <code class="inline">Buffer</code> is a binary already).</p><p>But in more complicated code, how can one know whether the optimization is
│ │ │  applied or not?</p><p><a href="" id="bin_opt_info"></a></p><h3 id="option-bin_opt_info" class="section-heading">
│ │ │    <a href="#option-bin_opt_info" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Option bin_opt_info</span>
│ │ │ @@ -354,38 +354,38 @@
│ │ │  <p>Use the <code class="inline">bin_opt_info</code> option to have the compiler print a lot of information
│ │ │  about binary optimizations. It can be given either to the compiler or <code class="inline">erlc</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">erlc</span><span class="w"> </span><span class="o">+</span><span class="ss">bin_opt_info</span><span class="w"> </span><span class="n">Mod</span><span class="p">.</span><span class="ss">erl</span></code></pre><p>or passed through an environment variable:</p><pre><code class="makeup erlang" translate="no"><span class="ss">export</span><span class="w"> </span><span class="n">ERL_COMPILER_OPTIONS</span><span class="o">=</span><span class="ss">bin_opt_info</span></code></pre><p>Notice that the <code class="inline">bin_opt_info</code> is not meant to be a permanent option added to
│ │ │  your <code class="inline">Makefile</code>s, because all messages that it generates cannot be eliminated.
│ │ │  Therefore, passing the option through the environment is in most cases the most
│ │ │  practical approach.</p><p>The warnings look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="o">/</span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">60</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">NOT</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">binary</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">returned</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">function</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="o">/</span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">62</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">context</span><span class="w"> </span><span class="ss">reused</span></code></pre><p>To make it clearer exactly what code the warnings refer to, the warnings in the
│ │ │  following examples are inserted as comments after the clause they refer to, for
│ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="9905524859-1">(</span><span class="p" data-group-id="9905524859-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9905524859-2">&gt;&gt;</span><span class="p" data-group-id="9905524859-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">after_zero</span><span class="p" data-group-id="7035697857-1">(</span><span class="p" data-group-id="7035697857-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7035697857-2">&gt;&gt;</span><span class="p" data-group-id="7035697857-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │           </span><span class="c1">%% BINARY CREATED: binary is returned from the function</span><span class="w">
│ │ │      </span><span class="n">T</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="9905524859-3">(</span><span class="p" data-group-id="9905524859-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9905524859-4">&gt;&gt;</span><span class="p" data-group-id="9905524859-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="7035697857-3">(</span><span class="p" data-group-id="7035697857-4">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7035697857-4">&gt;&gt;</span><span class="p" data-group-id="7035697857-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │           </span><span class="c1">%% OPTIMIZED: match context reused</span><span class="w">
│ │ │ -    </span><span class="nf">after_zero</span><span class="p" data-group-id="9905524859-5">(</span><span class="n">T</span><span class="p" data-group-id="9905524859-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">after_zero</span><span class="p" data-group-id="9905524859-6">(</span><span class="p" data-group-id="9905524859-7">&lt;&lt;</span><span class="p" data-group-id="9905524859-7">&gt;&gt;</span><span class="p" data-group-id="9905524859-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9905524859-8">&lt;&lt;</span><span class="p" data-group-id="9905524859-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>The warning for the first clause says that the creation of a sub binary cannot
│ │ │ +    </span><span class="nf">after_zero</span><span class="p" data-group-id="7035697857-5">(</span><span class="n">T</span><span class="p" data-group-id="7035697857-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">after_zero</span><span class="p" data-group-id="7035697857-6">(</span><span class="p" data-group-id="7035697857-7">&lt;&lt;</span><span class="p" data-group-id="7035697857-7">&gt;&gt;</span><span class="p" data-group-id="7035697857-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7035697857-8">&lt;&lt;</span><span class="p" data-group-id="7035697857-8">&gt;&gt;</span><span class="p">.</span></code></pre><p>The warning for the first clause says that the creation of a sub binary cannot
│ │ │  be delayed, because it will be returned. The warning for the second clause says
│ │ │  that a sub binary will not be created (yet).</p><h3 id="unused-variables" class="section-heading">
│ │ │    <a href="#unused-variables" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Unused Variables</span>
│ │ │  </h3>
│ │ │  <p>The compiler figures out if a variable is unused. The same code is generated for
│ │ │ -each of the following functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">count1</span><span class="p" data-group-id="0766002529-1">(</span><span class="p" data-group-id="0766002529-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0766002529-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="0766002529-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count1</span><span class="p" data-group-id="0766002529-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0766002529-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">count1</span><span class="p" data-group-id="0766002529-4">(</span><span class="p" data-group-id="0766002529-5">&lt;&lt;</span><span class="p" data-group-id="0766002529-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="0766002529-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ +each of the following functions:</p><pre><code class="makeup erlang" translate="no"><span class="nf">count1</span><span class="p" data-group-id="6478584072-1">(</span><span class="p" data-group-id="6478584072-2">&lt;&lt;</span><span class="p">_</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6478584072-2">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="6478584072-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count1</span><span class="p" data-group-id="6478584072-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="6478584072-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">count1</span><span class="p" data-group-id="6478584072-4">(</span><span class="p" data-group-id="6478584072-5">&lt;&lt;</span><span class="p" data-group-id="6478584072-5">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="6478584072-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">count2</span><span class="p" data-group-id="0766002529-6">(</span><span class="p" data-group-id="0766002529-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0766002529-7">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="0766002529-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count2</span><span class="p" data-group-id="0766002529-8">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0766002529-8">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">count2</span><span class="p" data-group-id="0766002529-9">(</span><span class="p" data-group-id="0766002529-10">&lt;&lt;</span><span class="p" data-group-id="0766002529-10">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="0766002529-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">count2</span><span class="p" data-group-id="6478584072-6">(</span><span class="p" data-group-id="6478584072-7">&lt;&lt;</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6478584072-7">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="6478584072-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count2</span><span class="p" data-group-id="6478584072-8">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="6478584072-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">count2</span><span class="p" data-group-id="6478584072-9">(</span><span class="p" data-group-id="6478584072-10">&lt;&lt;</span><span class="p" data-group-id="6478584072-10">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="6478584072-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">count3</span><span class="p" data-group-id="0766002529-11">(</span><span class="p" data-group-id="0766002529-12">&lt;&lt;</span><span class="p">_</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0766002529-12">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="0766002529-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count3</span><span class="p" data-group-id="0766002529-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0766002529-13">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">count3</span><span class="p" data-group-id="0766002529-14">(</span><span class="p" data-group-id="0766002529-15">&lt;&lt;</span><span class="p" data-group-id="0766002529-15">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="0766002529-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span></code></pre><p>In each iteration, the first 8 bits in the binary will be skipped, not matched
│ │ │ +</span><span class="nf">count3</span><span class="p" data-group-id="6478584072-11">(</span><span class="p" data-group-id="6478584072-12">&lt;&lt;</span><span class="p">_</span><span class="n">H</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6478584072-12">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="6478584072-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">count3</span><span class="p" data-group-id="6478584072-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="6478584072-13">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">count3</span><span class="p" data-group-id="6478584072-14">(</span><span class="p" data-group-id="6478584072-15">&lt;&lt;</span><span class="p" data-group-id="6478584072-15">&gt;&gt;</span><span class="p">,</span><span class="w"> </span><span class="n">Count</span><span class="p" data-group-id="6478584072-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Count</span><span class="p">.</span></code></pre><p>In each iteration, the first 8 bits in the binary will be skipped, not matched
│ │ │  out.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="commoncaveats.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/bit_syntax.html
│ │ │ @@ -119,48 +119,48 @@
│ │ │    <a href="#introduction" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Introduction</span>
│ │ │  </h2>
│ │ │  <p>The complete specification for the bit syntax appears in the
│ │ │  <a href="../../doc/system/expressions.html#bit-syntax-expressions">Reference Manual</a>.</p><p>In Erlang, a Bin is used for constructing binaries and matching binary patterns.
│ │ │ -A Bin is written with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2500495304-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="2500495304-1">&gt;&gt;</span></code></pre><p>A Bin is a low-level sequence of bits or bytes. The purpose of a Bin is to
│ │ │ -enable construction of binaries:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3907833703-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="3907833703-1">&gt;&gt;</span></code></pre><p>All elements must be bound. Or match a binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9703934546-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="9703934546-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span></code></pre><p>Here, <code class="inline">Bin</code> is bound and the elements are bound or unbound, as in any match.</p><p>A Bin does not need to consist of a whole number of bytes.</p><p>A <em>bitstring</em> is a sequence of zero or more bits, where the number of bits does
│ │ │ +A Bin is written with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8797565495-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="8797565495-1">&gt;&gt;</span></code></pre><p>A Bin is a low-level sequence of bits or bytes. The purpose of a Bin is to
│ │ │ +enable construction of binaries:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8777708516-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="8777708516-1">&gt;&gt;</span></code></pre><p>All elements must be bound. Or match a binary:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9555339080-1">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">En</span><span class="p" data-group-id="9555339080-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span></code></pre><p>Here, <code class="inline">Bin</code> is bound and the elements are bound or unbound, as in any match.</p><p>A Bin does not need to consist of a whole number of bytes.</p><p>A <em>bitstring</em> is a sequence of zero or more bits, where the number of bits does
│ │ │  not need to be divisible by 8. If the number of bits is divisible by 8, the
│ │ │  bitstring is also a binary.</p><p>Each element specifies a certain <em>segment</em> of the bitstring. A segment is a set
│ │ │  of contiguous bits of the binary (not necessarily on a byte boundary). The first
│ │ │  element specifies the initial segment, the second element specifies the
│ │ │  following segment, and so on.</p><p>The following examples illustrate how binaries are constructed, or matched, and
│ │ │  how elements and tails are specified.</p><h3 id="examples" class="section-heading">
│ │ │    <a href="#examples" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Examples</span>
│ │ │  </h3>
│ │ │  <p><em>Example 1:</em> A binary can be constructed from a set of constants or a string
│ │ │ -literal:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin11</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4834733641-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="4834733641-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Bin12</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4834733641-2">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="4834733641-2">&gt;&gt;</span></code></pre><p>This gives two binaries of size 3, with the following evaluations:</p><ul><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin11)</code></a> evaluates to <code class="inline">[1, 17, 42]</code>.</li><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin12)</code></a> evaluates to <code class="inline">[97, 98, 99]</code>.</li></ul><p><em>Example 2:</em>Similarly, a binary can be constructed from a set of bound
│ │ │ +literal:</p><pre><code class="makeup erlang" translate="no"><span class="n">Bin11</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9210009077-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="9210009077-1">&gt;&gt;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Bin12</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9210009077-2">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9210009077-2">&gt;&gt;</span></code></pre><p>This gives two binaries of size 3, with the following evaluations:</p><ul><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin11)</code></a> evaluates to <code class="inline">[1, 17, 42]</code>.</li><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin12)</code></a> evaluates to <code class="inline">[97, 98, 99]</code>.</li></ul><p><em>Example 2:</em>Similarly, a binary can be constructed from a set of bound
│ │ │  variables:</p><pre><code class="makeup erlang" translate="no"><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6988222846-1">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6988222846-1">&gt;&gt;</span></code></pre><p>This gives a binary of size 4. Here, a <em>size expression</em> is used for the
│ │ │ +</span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0252571656-1">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0252571656-1">&gt;&gt;</span></code></pre><p>This gives a binary of size 4. Here, a <em>size expression</em> is used for the
│ │ │  variable <code class="inline">C</code> to specify a 16-bits segment of <code class="inline">Bin2</code>.</p><p><a href="../../erts-15.2.7.8/doc/html/erlang.html#binary_to_list/1"><code class="inline">binary_to_list(Bin2)</code></a> evaluates to <code class="inline">[1, 17, 00, 42]</code>.</p><p><em>Example 3:</em> A Bin can also be used for matching. <code class="inline">D</code>, <code class="inline">E</code>, and <code class="inline">F</code> are unbound
│ │ │ -variables, and <code class="inline">Bin2</code> is bound, as in Example 2:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5537707292-1">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5537707292-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin2</span></code></pre><p>This gives <code class="inline">D = 273</code>, <code class="inline">E = 00</code>, and F binds to a binary of size 1:
│ │ │ +variables, and <code class="inline">Bin2</code> is bound, as in Example 2:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3948714218-1">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3948714218-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin2</span></code></pre><p>This gives <code class="inline">D = 273</code>, <code class="inline">E = 00</code>, and F binds to a binary of size 1:
│ │ │  <code class="inline">binary_to_list(F) = [42]</code>.</p><p><em>Example 4:</em> The following is a more elaborate example of matching. Here,
│ │ │  <code class="inline">Dgram</code> is bound to the consecutive bytes of an IP datagram of IP protocol
│ │ │ -version 4. The ambition is to extract the header and the data of the datagram:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3457651986-1">(</span><span class="n">IP_VERSION</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="3457651986-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3457651986-2">(</span><span class="n">IP_MIN_HDR_LEN</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="3457651986-2">)</span><span class="p">.</span><span class="w">
│ │ │ +version 4. The ambition is to extract the header and the data of the datagram:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1164557517-1">(</span><span class="n">IP_VERSION</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1164557517-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1164557517-2">(</span><span class="n">IP_MIN_HDR_LEN</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="1164557517-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">DgramSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="3457651986-3">(</span><span class="n">Dgram</span><span class="p" data-group-id="3457651986-3">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">DgramSize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">byte_size</span><span class="p" data-group-id="1164557517-3">(</span><span class="n">Dgram</span><span class="p" data-group-id="1164557517-3">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">case</span><span class="w"> </span><span class="n">Dgram</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3457651986-4">&lt;&lt;</span><span class="o">?</span><span class="n">IP_VERSION</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">HLen</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">SrvcType</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">TotLen</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1164557517-4">&lt;&lt;</span><span class="o">?</span><span class="n">IP_VERSION</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">HLen</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="n">SrvcType</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">TotLen</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │        </span><span class="n">ID</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w"> </span><span class="n">Flgs</span><span class="p">:</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">FragOff</span><span class="p">:</span><span class="mi">13</span><span class="p">,</span><span class="w">
│ │ │        </span><span class="n">TTL</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">Proto</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="n">HdrChkSum</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="w">
│ │ │        </span><span class="n">SrcIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w">
│ │ │ -      </span><span class="n">DestIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w"> </span><span class="n">RestDgram</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3457651986-4">&gt;&gt;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">HLen</span><span class="o">&gt;=</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="n">HLen</span><span class="o">=&lt;</span><span class="n">DgramSize</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="n">OptsLen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="p" data-group-id="3457651986-5">(</span><span class="n">HLen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">?</span><span class="n">IP_MIN_HDR_LEN</span><span class="p" data-group-id="3457651986-5">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3457651986-6">&lt;&lt;</span><span class="n">Opts</span><span class="p">:</span><span class="n">OptsLen</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Data</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3457651986-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RestDgram</span><span class="p">,</span><span class="w">
│ │ │ +      </span><span class="n">DestIP</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="w"> </span><span class="n">RestDgram</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1164557517-4">&gt;&gt;</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">HLen</span><span class="o">&gt;=</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="n">HLen</span><span class="o">=&lt;</span><span class="n">DgramSize</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="n">OptsLen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="o">*</span><span class="p" data-group-id="1164557517-5">(</span><span class="n">HLen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="o">?</span><span class="n">IP_MIN_HDR_LEN</span><span class="p" data-group-id="1164557517-5">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="1164557517-6">&lt;&lt;</span><span class="n">Opts</span><span class="p">:</span><span class="n">OptsLen</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Data</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1164557517-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RestDgram</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>Here, the segment corresponding to the <code class="inline">Opts</code> variable has a <em>type modifier</em>,
│ │ │  specifying that <code class="inline">Opts</code> is to bind to a binary. All other variables have the
│ │ │  default type equal to unsigned integer.</p><p>An IP datagram header is of variable length. This length is measured in the
│ │ │  number of 32-bit words and is given in the segment corresponding to <code class="inline">HLen</code>. The
│ │ │  minimum value of <code class="inline">HLen</code> is 5. It is the segment corresponding to <code class="inline">Opts</code> that is
│ │ │  variable, so if <code class="inline">HLen</code> is equal to 5, <code class="inline">Opts</code> becomes an empty binary.</p><p>The tail variables <code class="inline">RestDgram</code> and <code class="inline">Data</code> bind to binaries, as all tail
│ │ │ @@ -218,80 +218,80 @@
│ │ │  <p>This section describes the rules for constructing binaries using the bit syntax.
│ │ │  Unlike when constructing lists or tuples, the construction of a binary can fail
│ │ │  with a <code class="inline">badarg</code> exception.</p><p>There can be zero or more segments in a binary to be constructed. The expression
│ │ │  <code class="inline">&lt;&lt;&gt;&gt;</code> constructs a zero length binary.</p><p>Each segment in a binary can consist of zero or more bits. There are no
│ │ │  alignment rules for individual segments of type <code class="inline">integer</code> and <code class="inline">float</code>. For
│ │ │  binaries and bitstrings without size, the unit specifies the alignment. Since
│ │ │  the default alignment for the <code class="inline">binary</code> type is 8, the size of a binary segment
│ │ │ -must be a multiple of 8 bits, that is, only whole bytes.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2992135770-1">&lt;&lt;</span><span class="n">Bin</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Bitstring</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="2992135770-1">&gt;&gt;</span></code></pre><p>The variable <code class="inline">Bin</code> must contain a whole number of bytes, because the <code class="inline">binary</code>
│ │ │ +must be a multiple of 8 bits, that is, only whole bytes.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2907307494-1">&lt;&lt;</span><span class="n">Bin</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Bitstring</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="2907307494-1">&gt;&gt;</span></code></pre><p>The variable <code class="inline">Bin</code> must contain a whole number of bytes, because the <code class="inline">binary</code>
│ │ │  type defaults to <code class="inline">unit:8</code>. A <code class="inline">badarg</code> exception is generated if <code class="inline">Bin</code> consist
│ │ │  of, for example, 17 bits.</p><p>The <code class="inline">Bitstring</code> variable can consist of any number of bits, for example, 0, 1,
│ │ │  8, 11, 17, 42, and so on. This is because the default <code class="inline">unit</code> for bitstrings
│ │ │  is 1.</p><p>For clarity, it is recommended not to change the unit size for binaries.
│ │ │  Instead, use <code class="inline">binary</code> when you need byte alignment and <code class="inline">bitstring</code> when you need
│ │ │  bit alignment.</p><p>The following example successfully constructs a bitstring of 7 bits, provided
│ │ │ -that all of X and Y are integers:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0744558621-1">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">6</span><span class="p" data-group-id="0744558621-1">&gt;&gt;</span></code></pre><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When constructing binaries, <code class="inline">Value</code> and <code class="inline">Size</code> can be any Erlang expression.
│ │ │ +that all of X and Y are integers:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5847776973-1">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">6</span><span class="p" data-group-id="5847776973-1">&gt;&gt;</span></code></pre><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When constructing binaries, <code class="inline">Value</code> and <code class="inline">Size</code> can be any Erlang expression.
│ │ │  However, for syntactical reasons, both <code class="inline">Value</code> and <code class="inline">Size</code> must be enclosed in
│ │ │  parenthesis if the expression consists of anything more than a single literal or
│ │ │ -a variable. The following gives a compiler syntax error:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6268458119-1">&lt;&lt;</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="6268458119-1">&gt;&gt;</span></code></pre><p>This expression must be rewritten into the following, to be accepted by the
│ │ │ -compiler:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9698246379-1">&lt;&lt;</span><span class="p" data-group-id="9698246379-2">(</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="9698246379-2">)</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="9698246379-1">&gt;&gt;</span></code></pre><h3 id="including-literal-strings" class="section-heading">
│ │ │ +a variable. The following gives a compiler syntax error:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5445133809-1">&lt;&lt;</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="5445133809-1">&gt;&gt;</span></code></pre><p>This expression must be rewritten into the following, to be accepted by the
│ │ │ +compiler:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0849301253-1">&lt;&lt;</span><span class="p" data-group-id="0849301253-2">(</span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0849301253-2">)</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0849301253-1">&gt;&gt;</span></code></pre><h3 id="including-literal-strings" class="section-heading">
│ │ │    <a href="#including-literal-strings" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Including Literal Strings</span>
│ │ │  </h3>
│ │ │ -<p>A literal string can be written instead of an element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8633519696-1">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="8633519696-1">&gt;&gt;</span></code></pre><p>This is syntactic sugar for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1194679962-1">&lt;&lt;</span><span class="sc">$h</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$o</span><span class="p" data-group-id="1194679962-1">&gt;&gt;</span></code></pre><h2 id="matching-binaries" class="section-heading">
│ │ │ +<p>A literal string can be written instead of an element:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3225508289-1">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="3225508289-1">&gt;&gt;</span></code></pre><p>This is syntactic sugar for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9674522688-1">&lt;&lt;</span><span class="sc">$h</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$l</span><span class="p">,</span><span class="sc">$o</span><span class="p" data-group-id="9674522688-1">&gt;&gt;</span></code></pre><h2 id="matching-binaries" class="section-heading">
│ │ │    <a href="#matching-binaries" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Matching Binaries</span>
│ │ │  </h2>
│ │ │  <p>This section describes the rules for matching binaries, using the bit syntax.</p><p>There can be zero or more segments in a binary pattern. A binary pattern can
│ │ │  occur wherever patterns are allowed, including inside other patterns. Binary
│ │ │  patterns cannot be nested. The pattern <code class="inline">&lt;&lt;&gt;&gt;</code> matches a zero length binary.</p><p>Each segment in a binary can consist of zero or more bits. A segment of type
│ │ │  <code class="inline">binary</code> must have a size evenly divisible by 8 (or divisible by the unit size,
│ │ │  if the unit size has been changed). A segment of type <code class="inline">bitstring</code> has no
│ │ │  restrictions on the size. A segment of type <code class="inline">float</code> must have size 64 or 32.</p><p>As mentioned earlier, segments have the following general syntax:</p><p><code class="inline">Value:Size/TypeSpecifierList</code></p><p>When matching <code class="inline">Value</code>, value must be either a variable or an integer, or a
│ │ │  floating point literal. Expressions are not allowed.</p><p><code class="inline">Size</code> must be a
│ │ │  <a href="../../doc/system/expressions.html#guard-expressions">guard expression</a>, which can use
│ │ │ -literals and previously bound variables. The following is not allowed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="9135797332-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9135797332-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9135797332-2">&gt;&gt;</span><span class="p" data-group-id="9135797332-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="9135797332-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="9135797332-3">}</span><span class="p">.</span></code></pre><p>The two occurrences of <code class="inline">N</code> are not related. The compiler will complain that the
│ │ │ -<code class="inline">N</code> in the size field is unbound.</p><p>The correct way to write this example is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="1441567076-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="1441567076-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="1441567076-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1441567076-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="1441567076-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="1441567076-3">}</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Before OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable bound to
│ │ │ +literals and previously bound variables. The following is not allowed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="2474285214-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2474285214-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="2474285214-2">&gt;&gt;</span><span class="p" data-group-id="2474285214-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2474285214-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="2474285214-3">}</span><span class="p">.</span></code></pre><p>The two occurrences of <code class="inline">N</code> are not related. The compiler will complain that the
│ │ │ +<code class="inline">N</code> in the size field is unbound.</p><p>The correct way to write this example is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="4365039931-1">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="4365039931-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="4365039931-2">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">N</span><span class="p">,</span><span class="n">T</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="4365039931-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Bin</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="4365039931-3">{</span><span class="n">X</span><span class="p">,</span><span class="n">T</span><span class="p" data-group-id="4365039931-3">}</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Before OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable bound to
│ │ │  an integer.</p></section><h3 id="binding-and-using-a-size-variable" class="section-heading">
│ │ │    <a href="#binding-and-using-a-size-variable" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Binding and Using a Size Variable</span>
│ │ │  </h3>
│ │ │  <p>There is one exception to the rule that a variable that is used as size must be
│ │ │  previously bound. It is possible to match and bind a variable, and use it as a
│ │ │ -size within the same binary pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="9339606294-1">(</span><span class="p" data-group-id="9339606294-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="n">Sz</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9339606294-2">&gt;&gt;</span><span class="p" data-group-id="9339606294-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="9339606294-3">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="9339606294-3">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is bound to the value in the first byte of the binary. <code class="inline">Sz</code> is then
│ │ │ -used at the number of bytes to match out as a binary.</p><p>Starting in OTP 23, the size can be a guard expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="0969665277-1">(</span><span class="p" data-group-id="0969665277-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="p" data-group-id="0969665277-3">(</span><span class="p" data-group-id="0969665277-4">(</span><span class="n">Sz</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0969665277-4">)</span><span class="o">*</span><span class="mi">8</span><span class="p" data-group-id="0969665277-3">)</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0969665277-2">&gt;&gt;</span><span class="p" data-group-id="0969665277-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="0969665277-5">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="0969665277-5">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is the combined size of the header and the payload, so we will need to
│ │ │ +size within the same binary pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="0412795829-1">(</span><span class="p" data-group-id="0412795829-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="n">Sz</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="0412795829-2">&gt;&gt;</span><span class="p" data-group-id="0412795829-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="0412795829-3">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="0412795829-3">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is bound to the value in the first byte of the binary. <code class="inline">Sz</code> is then
│ │ │ +used at the number of bytes to match out as a binary.</p><p>Starting in OTP 23, the size can be a guard expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="8591767288-1">(</span><span class="p" data-group-id="8591767288-2">&lt;&lt;</span><span class="n">Sz</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Payload</span><span class="p">:</span><span class="p" data-group-id="8591767288-3">(</span><span class="p" data-group-id="8591767288-4">(</span><span class="n">Sz</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="8591767288-4">)</span><span class="o">*</span><span class="mi">8</span><span class="p" data-group-id="8591767288-3">)</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8591767288-2">&gt;&gt;</span><span class="p" data-group-id="8591767288-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="8591767288-5">{</span><span class="n">Payload</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="8591767288-5">}</span><span class="p">.</span></code></pre><p>Here <code class="inline">Sz</code> is the combined size of the header and the payload, so we will need to
│ │ │  subtract one byte to get the size of the payload.</p><h3 id="getting-the-rest-of-the-binary-or-bitstring" class="section-heading">
│ │ │    <a href="#getting-the-rest-of-the-binary-or-bitstring" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Getting the Rest of the Binary or Bitstring</span>
│ │ │  </h3>
│ │ │ -<p>To match out the rest of a binary, specify a binary field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="6438160104-1">(</span><span class="p" data-group-id="6438160104-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6438160104-2">&gt;&gt;</span><span class="p" data-group-id="6438160104-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>The size of the tail must be evenly divisible by 8.</p><p>To match out the rest of a bitstring, specify a field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="0518903443-1">(</span><span class="p" data-group-id="0518903443-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="0518903443-2">&gt;&gt;</span><span class="p" data-group-id="0518903443-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>There are no restrictions on the number of bits in the tail.</p><h2 id="appending-to-a-binary" class="section-heading">
│ │ │ +<p>To match out the rest of a binary, specify a binary field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="8164826474-1">(</span><span class="p" data-group-id="8164826474-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8164826474-2">&gt;&gt;</span><span class="p" data-group-id="8164826474-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>The size of the tail must be evenly divisible by 8.</p><p>To match out the rest of a bitstring, specify a field without size:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="9905250546-1">(</span><span class="p" data-group-id="9905250546-2">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">Rest</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="9905250546-2">&gt;&gt;</span><span class="p" data-group-id="9905250546-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>There are no restrictions on the number of bits in the tail.</p><h2 id="appending-to-a-binary" class="section-heading">
│ │ │    <a href="#appending-to-a-binary" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Appending to a Binary</span>
│ │ │  </h2>
│ │ │ -<p>Appending to a binary in an efficient way can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">triples_to_bin</span><span class="p" data-group-id="0916610186-1">(</span><span class="n">T</span><span class="p" data-group-id="0916610186-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="0916610186-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0916610186-3">&lt;&lt;</span><span class="p" data-group-id="0916610186-3">&gt;&gt;</span><span class="p" data-group-id="0916610186-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Appending to a binary in an efficient way can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">triples_to_bin</span><span class="p" data-group-id="2775652153-1">(</span><span class="n">T</span><span class="p" data-group-id="2775652153-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="2775652153-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2775652153-3">&lt;&lt;</span><span class="p" data-group-id="2775652153-3">&gt;&gt;</span><span class="p" data-group-id="2775652153-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="0916610186-4">(</span><span class="p" data-group-id="0916610186-5">[</span><span class="p" data-group-id="0916610186-6">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p" data-group-id="0916610186-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="0916610186-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0916610186-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="0916610186-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0916610186-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">X</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Z</span><span class="p">:</span><span class="mi">32</span><span class="p" data-group-id="0916610186-8">&gt;&gt;</span><span class="p" data-group-id="0916610186-7">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="0916610186-9">(</span><span class="p" data-group-id="0916610186-10">[</span><span class="p" data-group-id="0916610186-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0916610186-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="2775652153-4">(</span><span class="p" data-group-id="2775652153-5">[</span><span class="p" data-group-id="2775652153-6">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p">,</span><span class="n">Z</span><span class="p" data-group-id="2775652153-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2775652153-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2775652153-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">triples_to_bin</span><span class="p" data-group-id="2775652153-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2775652153-8">&lt;&lt;</span><span class="n">Acc</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="n">X</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Y</span><span class="p">:</span><span class="mi">32</span><span class="p">,</span><span class="n">Z</span><span class="p">:</span><span class="mi">32</span><span class="p" data-group-id="2775652153-8">&gt;&gt;</span><span class="p" data-group-id="2775652153-7">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">triples_to_bin</span><span class="p" data-group-id="2775652153-9">(</span><span class="p" data-group-id="2775652153-10">[</span><span class="p" data-group-id="2775652153-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2775652153-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="list_comprehensions.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/c_port.html
│ │ │ @@ -148,101 +148,101 @@
│ │ │  external program, if it is written properly).</p><p>The port is created using the BIF <a href="../../erts-15.2.7.8/doc/html/erlang.html#open_port/2"><code class="inline">open_port/2</code></a> with
│ │ │  <code class="inline">{spawn,ExtPrg}</code> as the first argument. The string <code class="inline">ExtPrg</code> is the name of the
│ │ │  external program, including any command line arguments. The second argument is a
│ │ │  list of options, in this case only <code class="inline">{packet,2}</code>. This option says that a 2 byte
│ │ │  length indicator is to be used to simplify the communication between C and
│ │ │  Erlang. The Erlang port automatically adds the length indicator, but this must
│ │ │  be done explicitly in the external C program.</p><p>The process is also set to trap exits, which enables detection of failure of the
│ │ │ -external program:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1537415099-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="1537415099-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1537415099-2">(</span><span class="p" data-group-id="1537415099-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1537415099-3">]</span><span class="p" data-group-id="1537415099-2">)</span><span class="p">.</span><span class="w">
│ │ │ +external program:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8936039848-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="8936039848-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8936039848-2">(</span><span class="p" data-group-id="8936039848-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8936039848-3">]</span><span class="p" data-group-id="8936039848-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="1537415099-4">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1537415099-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">spawn</span><span class="p" data-group-id="1537415099-5">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1537415099-6">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="1537415099-6">]</span><span class="p" data-group-id="1537415099-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="8936039848-4">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="8936039848-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">spawn</span><span class="p" data-group-id="8936039848-5">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8936039848-6">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="8936039848-6">]</span><span class="p" data-group-id="8936039848-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1537415099-7">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1537415099-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">register</span><span class="p" data-group-id="1537415099-8">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1537415099-9">(</span><span class="p" data-group-id="1537415099-9">)</span><span class="p" data-group-id="1537415099-8">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="nf">process_flag</span><span class="p" data-group-id="1537415099-10">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1537415099-10">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="1537415099-11">(</span><span class="p" data-group-id="1537415099-12">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="1537415099-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1537415099-13">[</span><span class="p" data-group-id="1537415099-14">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1537415099-14">}</span><span class="p" data-group-id="1537415099-13">]</span><span class="p" data-group-id="1537415099-11">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="nf">loop</span><span class="p" data-group-id="1537415099-15">(</span><span class="n">Port</span><span class="p" data-group-id="1537415099-15">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex1:foo/1</code> and <code class="inline">complex1:bar/1</code> can be implemented. Both send a
│ │ │ -message to the <code class="inline">complex</code> process and receive the following replies:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="7846925161-1">(</span><span class="n">X</span><span class="p" data-group-id="7846925161-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">call_port</span><span class="p" data-group-id="7846925161-2">(</span><span class="p" data-group-id="7846925161-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7846925161-3">}</span><span class="p" data-group-id="7846925161-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="7846925161-4">(</span><span class="n">Y</span><span class="p" data-group-id="7846925161-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">call_port</span><span class="p" data-group-id="7846925161-5">(</span><span class="p" data-group-id="7846925161-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7846925161-6">}</span><span class="p" data-group-id="7846925161-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8936039848-7">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="8936039848-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">register</span><span class="p" data-group-id="8936039848-8">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8936039848-9">(</span><span class="p" data-group-id="8936039848-9">)</span><span class="p" data-group-id="8936039848-8">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="nf">process_flag</span><span class="p" data-group-id="8936039848-10">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8936039848-10">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8936039848-11">(</span><span class="p" data-group-id="8936039848-12">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="8936039848-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8936039848-13">[</span><span class="p" data-group-id="8936039848-14">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8936039848-14">}</span><span class="p" data-group-id="8936039848-13">]</span><span class="p" data-group-id="8936039848-11">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="nf">loop</span><span class="p" data-group-id="8936039848-15">(</span><span class="n">Port</span><span class="p" data-group-id="8936039848-15">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex1:foo/1</code> and <code class="inline">complex1:bar/1</code> can be implemented. Both send a
│ │ │ +message to the <code class="inline">complex</code> process and receive the following replies:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="4120438031-1">(</span><span class="n">X</span><span class="p" data-group-id="4120438031-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">call_port</span><span class="p" data-group-id="4120438031-2">(</span><span class="p" data-group-id="4120438031-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4120438031-3">}</span><span class="p" data-group-id="4120438031-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="4120438031-4">(</span><span class="n">Y</span><span class="p" data-group-id="4120438031-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">call_port</span><span class="p" data-group-id="4120438031-5">(</span><span class="p" data-group-id="4120438031-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4120438031-6">}</span><span class="p" data-group-id="4120438031-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="7846925161-7">(</span><span class="n">Msg</span><span class="p" data-group-id="7846925161-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7846925161-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7846925161-9">(</span><span class="p" data-group-id="7846925161-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="7846925161-8">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="4120438031-7">(</span><span class="n">Msg</span><span class="p" data-group-id="4120438031-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4120438031-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4120438031-9">(</span><span class="p" data-group-id="4120438031-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4120438031-8">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7846925161-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7846925161-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4120438031-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="4120438031-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │        </span><span class="n">Result</span><span class="w">
│ │ │ -  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process does the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="9574975683-1">(</span><span class="n">Port</span><span class="p" data-group-id="9574975683-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process does the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="5251482957-1">(</span><span class="n">Port</span><span class="p" data-group-id="5251482957-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9574975683-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9574975683-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -      </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9574975683-3">{</span><span class="nf">self</span><span class="p" data-group-id="9574975683-4">(</span><span class="p" data-group-id="9574975683-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9574975683-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9574975683-6">(</span><span class="n">Msg</span><span class="p" data-group-id="9574975683-6">)</span><span class="p" data-group-id="9574975683-5">}</span><span class="p" data-group-id="9574975683-3">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5251482957-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5251482957-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +      </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5251482957-3">{</span><span class="nf">self</span><span class="p" data-group-id="5251482957-4">(</span><span class="p" data-group-id="5251482957-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5251482957-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="5251482957-6">(</span><span class="n">Msg</span><span class="p" data-group-id="5251482957-6">)</span><span class="p" data-group-id="5251482957-5">}</span><span class="p" data-group-id="5251482957-3">}</span><span class="p">,</span><span class="w">
│ │ │        </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9574975683-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9574975683-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9574975683-8">}</span><span class="p" data-group-id="9574975683-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -          </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9574975683-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9574975683-10">(</span><span class="n">Data</span><span class="p" data-group-id="9574975683-10">)</span><span class="p" data-group-id="9574975683-9">}</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5251482957-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5251482957-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5251482957-8">}</span><span class="p" data-group-id="5251482957-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +          </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5251482957-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="5251482957-10">(</span><span class="n">Data</span><span class="p" data-group-id="5251482957-10">)</span><span class="p" data-group-id="5251482957-9">}</span><span class="w">
│ │ │        </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -      </span><span class="nf">loop</span><span class="p" data-group-id="9574975683-11">(</span><span class="n">Port</span><span class="p" data-group-id="9574975683-11">)</span><span class="w">
│ │ │ +      </span><span class="nf">loop</span><span class="p" data-group-id="5251482957-11">(</span><span class="n">Port</span><span class="p" data-group-id="5251482957-11">)</span><span class="w">
│ │ │    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Assuming that both the arguments and the results from the C functions are less
│ │ │  than 256, a simple encoding/decoding scheme is employed. In this scheme, <code class="inline">foo</code>
│ │ │  is represented by byte 1, <code class="inline">bar</code> is represented by 2, and the argument/result is
│ │ │ -represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="2859577098-1">(</span><span class="p" data-group-id="2859577098-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2859577098-2">}</span><span class="p" data-group-id="2859577098-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2859577098-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2859577098-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="2859577098-4">(</span><span class="p" data-group-id="2859577098-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2859577098-5">}</span><span class="p" data-group-id="2859577098-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2859577098-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2859577098-6">]</span><span class="p">.</span><span class="w">
│ │ │ +represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="7026271545-1">(</span><span class="p" data-group-id="7026271545-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7026271545-2">}</span><span class="p" data-group-id="7026271545-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7026271545-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7026271545-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="7026271545-4">(</span><span class="p" data-group-id="7026271545-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7026271545-5">}</span><span class="p" data-group-id="7026271545-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7026271545-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7026271545-6">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="2859577098-7">(</span><span class="p" data-group-id="2859577098-8">[</span><span class="n">Int</span><span class="p" data-group-id="2859577098-8">]</span><span class="p" data-group-id="2859577098-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functionality for stopping the port and
│ │ │ -detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9166434597-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="9166434597-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9166434597-2">(</span><span class="p" data-group-id="9166434597-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9166434597-3">]</span><span class="p" data-group-id="9166434597-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9166434597-4">(</span><span class="p" data-group-id="9166434597-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9166434597-5">]</span><span class="p" data-group-id="9166434597-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="9166434597-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9166434597-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="9166434597-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9166434597-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="9166434597-8">]</span><span class="p" data-group-id="9166434597-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="9166434597-9">(</span><span class="p" data-group-id="9166434597-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="7026271545-7">(</span><span class="p" data-group-id="7026271545-8">[</span><span class="n">Int</span><span class="p" data-group-id="7026271545-8">]</span><span class="p" data-group-id="7026271545-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functionality for stopping the port and
│ │ │ +detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2366846204-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="2366846204-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2366846204-2">(</span><span class="p" data-group-id="2366846204-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2366846204-3">]</span><span class="p" data-group-id="2366846204-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2366846204-4">(</span><span class="p" data-group-id="2366846204-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2366846204-5">]</span><span class="p" data-group-id="2366846204-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="2366846204-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="2366846204-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="2366846204-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2366846204-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="2366846204-8">]</span><span class="p" data-group-id="2366846204-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="2366846204-9">(</span><span class="p" data-group-id="2366846204-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="9166434597-10">(</span><span class="n">X</span><span class="p" data-group-id="9166434597-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="9166434597-11">(</span><span class="p" data-group-id="9166434597-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9166434597-12">}</span><span class="p" data-group-id="9166434597-11">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="9166434597-13">(</span><span class="n">Y</span><span class="p" data-group-id="9166434597-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="9166434597-14">(</span><span class="p" data-group-id="9166434597-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9166434597-15">}</span><span class="p" data-group-id="9166434597-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="2366846204-10">(</span><span class="n">X</span><span class="p" data-group-id="2366846204-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="2366846204-11">(</span><span class="p" data-group-id="2366846204-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2366846204-12">}</span><span class="p" data-group-id="2366846204-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="2366846204-13">(</span><span class="n">Y</span><span class="p" data-group-id="2366846204-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="2366846204-14">(</span><span class="p" data-group-id="2366846204-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2366846204-15">}</span><span class="p" data-group-id="2366846204-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="9166434597-16">(</span><span class="n">Msg</span><span class="p" data-group-id="9166434597-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9166434597-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9166434597-18">(</span><span class="p" data-group-id="9166434597-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9166434597-17">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="2366846204-16">(</span><span class="n">Msg</span><span class="p" data-group-id="2366846204-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2366846204-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2366846204-18">(</span><span class="p" data-group-id="2366846204-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="2366846204-17">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9166434597-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9166434597-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="2366846204-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2366846204-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="9166434597-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9166434597-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9166434597-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9166434597-22">(</span><span class="p" data-group-id="9166434597-22">)</span><span class="p" data-group-id="9166434597-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9166434597-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9166434597-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="9166434597-24">(</span><span class="p" data-group-id="9166434597-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="9166434597-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9166434597-26">[</span><span class="p" data-group-id="9166434597-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9166434597-27">}</span><span class="p" data-group-id="9166434597-26">]</span><span class="p" data-group-id="9166434597-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="9166434597-28">(</span><span class="n">Port</span><span class="p" data-group-id="9166434597-28">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2366846204-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="2366846204-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="2366846204-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2366846204-22">(</span><span class="p" data-group-id="2366846204-22">)</span><span class="p" data-group-id="2366846204-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="2366846204-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2366846204-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="2366846204-24">(</span><span class="p" data-group-id="2366846204-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="2366846204-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2366846204-26">[</span><span class="p" data-group-id="2366846204-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2366846204-27">}</span><span class="p" data-group-id="2366846204-26">]</span><span class="p" data-group-id="2366846204-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="2366846204-28">(</span><span class="n">Port</span><span class="p" data-group-id="2366846204-28">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="9166434597-29">(</span><span class="n">Port</span><span class="p" data-group-id="9166434597-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="2366846204-29">(</span><span class="n">Port</span><span class="p" data-group-id="2366846204-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9166434597-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9166434597-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9166434597-31">{</span><span class="nf">self</span><span class="p" data-group-id="9166434597-32">(</span><span class="p" data-group-id="9166434597-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9166434597-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9166434597-34">(</span><span class="n">Msg</span><span class="p" data-group-id="9166434597-34">)</span><span class="p" data-group-id="9166434597-33">}</span><span class="p" data-group-id="9166434597-31">}</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="2366846204-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="2366846204-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2366846204-31">{</span><span class="nf">self</span><span class="p" data-group-id="2366846204-32">(</span><span class="p" data-group-id="2366846204-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2366846204-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="2366846204-34">(</span><span class="n">Msg</span><span class="p" data-group-id="2366846204-34">)</span><span class="p" data-group-id="2366846204-33">}</span><span class="p" data-group-id="2366846204-31">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="9166434597-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9166434597-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9166434597-36">}</span><span class="p" data-group-id="9166434597-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9166434597-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9166434597-38">(</span><span class="n">Data</span><span class="p" data-group-id="9166434597-38">)</span><span class="p" data-group-id="9166434597-37">}</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="2366846204-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2366846204-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2366846204-36">}</span><span class="p" data-group-id="2366846204-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2366846204-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="2366846204-38">(</span><span class="n">Data</span><span class="p" data-group-id="2366846204-38">)</span><span class="p" data-group-id="2366846204-37">}</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="9166434597-39">(</span><span class="n">Port</span><span class="p" data-group-id="9166434597-39">)</span><span class="p">;</span><span class="w">
│ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="2366846204-39">(</span><span class="n">Port</span><span class="p" data-group-id="2366846204-39">)</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9166434597-40">{</span><span class="nf">self</span><span class="p" data-group-id="9166434597-41">(</span><span class="p" data-group-id="9166434597-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="9166434597-40">}</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2366846204-40">{</span><span class="nf">self</span><span class="p" data-group-id="2366846204-41">(</span><span class="p" data-group-id="2366846204-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="2366846204-40">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="9166434597-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="9166434597-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="9166434597-43">(</span><span class="ss">normal</span><span class="p" data-group-id="9166434597-43">)</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="2366846204-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="2366846204-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="2366846204-43">(</span><span class="ss">normal</span><span class="p" data-group-id="2366846204-43">)</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="9166434597-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9166434597-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="9166434597-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="9166434597-45">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="2366846204-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="2366846204-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="2366846204-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="2366846204-45">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="9166434597-46">(</span><span class="p" data-group-id="9166434597-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9166434597-47">}</span><span class="p" data-group-id="9166434597-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9166434597-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9166434597-48">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="9166434597-49">(</span><span class="p" data-group-id="9166434597-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9166434597-50">}</span><span class="p" data-group-id="9166434597-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9166434597-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9166434597-51">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="2366846204-46">(</span><span class="p" data-group-id="2366846204-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2366846204-47">}</span><span class="p" data-group-id="2366846204-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2366846204-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2366846204-48">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="2366846204-49">(</span><span class="p" data-group-id="2366846204-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2366846204-50">}</span><span class="p" data-group-id="2366846204-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2366846204-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2366846204-51">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="9166434597-52">(</span><span class="p" data-group-id="9166434597-53">[</span><span class="n">Int</span><span class="p" data-group-id="9166434597-53">]</span><span class="p" data-group-id="9166434597-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-program" class="section-heading">
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="2366846204-52">(</span><span class="p" data-group-id="2366846204-53">[</span><span class="n">Int</span><span class="p" data-group-id="2366846204-53">]</span><span class="p" data-group-id="2366846204-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-program" class="section-heading">
│ │ │    <a href="#c-program" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">C Program</span>
│ │ │  </h2>
│ │ │  <p>On the C side, it is necessary to write functions for receiving and sending data
│ │ │  with 2 byte length indicators from/to Erlang. By default, the C program is to
│ │ │ @@ -251,107 +251,107 @@
│ │ │  follows:</p><pre><code class="makeup c" translate="no"><span class="cm">/* erl_comm.c */</span><span class="w">
│ │ │  
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdio</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">unistd</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  
│ │ │  </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="kt">byte</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="0948668503-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0948668503-1">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0948668503-2">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="6303420506-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="6303420506-1">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6303420506-2">{</span><span class="w">
│ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">got</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="0948668503-3">{</span><span class="w">
│ │ │ -      </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0948668503-4">(</span><span class="p" data-group-id="0948668503-5">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read</span><span class="p" data-group-id="0948668503-6">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">got</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">got</span><span class="p" data-group-id="0948668503-6">)</span><span class="p" data-group-id="0948668503-5">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0948668503-4">)</span><span class="p" data-group-id="0948668503-7">{</span><span class="w">
│ │ │ -          </span><span class="nf">return</span><span class="p" data-group-id="0948668503-8">(</span><span class="n">i</span><span class="p" data-group-id="0948668503-8">)</span><span class="p">;</span><span class="w">
│ │ │ -      </span><span class="p" data-group-id="0948668503-7">}</span><span class="w">
│ │ │ +  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="6303420506-3">{</span><span class="w">
│ │ │ +      </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6303420506-4">(</span><span class="p" data-group-id="6303420506-5">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read</span><span class="p" data-group-id="6303420506-6">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">got</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">got</span><span class="p" data-group-id="6303420506-6">)</span><span class="p" data-group-id="6303420506-5">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6303420506-4">)</span><span class="p" data-group-id="6303420506-7">{</span><span class="w">
│ │ │ +          </span><span class="nf">return</span><span class="p" data-group-id="6303420506-8">(</span><span class="n">i</span><span class="p" data-group-id="6303420506-8">)</span><span class="p">;</span><span class="w">
│ │ │ +      </span><span class="p" data-group-id="6303420506-7">}</span><span class="w">
│ │ │      </span><span class="n">got</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0948668503-3">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="0948668503-9">(</span><span class="n">got</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="0948668503-9">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6303420506-3">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="6303420506-9">(</span><span class="n">got</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="6303420506-9">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="nf">return</span><span class="p" data-group-id="0948668503-10">(</span><span class="n">len</span><span class="p" data-group-id="0948668503-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0948668503-2">}</span><span class="w">
│ │ │ +  </span><span class="nf">return</span><span class="p" data-group-id="6303420506-10">(</span><span class="n">len</span><span class="p" data-group-id="6303420506-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6303420506-2">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="0948668503-11">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0948668503-11">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0948668503-12">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="6303420506-11">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="6303420506-11">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6303420506-12">{</span><span class="w">
│ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">wrote</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="0948668503-13">{</span><span class="w">
│ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0948668503-14">(</span><span class="p" data-group-id="0948668503-15">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">write</span><span class="p" data-group-id="0948668503-16">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">wrote</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">wrote</span><span class="p" data-group-id="0948668503-16">)</span><span class="p" data-group-id="0948668503-15">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0948668503-14">)</span><span class="w">
│ │ │ -      </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="0948668503-17">(</span><span class="n">i</span><span class="p" data-group-id="0948668503-17">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="6303420506-13">{</span><span class="w">
│ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6303420506-14">(</span><span class="p" data-group-id="6303420506-15">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">write</span><span class="p" data-group-id="6303420506-16">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">wrote</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">wrote</span><span class="p" data-group-id="6303420506-16">)</span><span class="p" data-group-id="6303420506-15">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6303420506-14">)</span><span class="w">
│ │ │ +      </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="6303420506-17">(</span><span class="n">i</span><span class="p" data-group-id="6303420506-17">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">wrote</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0948668503-13">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="0948668503-18">(</span><span class="n">wrote</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="0948668503-18">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6303420506-13">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="6303420506-18">(</span><span class="n">wrote</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="6303420506-18">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="0948668503-19">(</span><span class="n">len</span><span class="p" data-group-id="0948668503-19">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0948668503-12">}</span><span class="w">
│ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="6303420506-19">(</span><span class="n">len</span><span class="p" data-group-id="6303420506-19">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6303420506-12">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="0948668503-20">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="0948668503-20">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0948668503-21">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="6303420506-20">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="6303420506-20">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6303420506-21">{</span><span class="w">
│ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0948668503-22">(</span><span class="nf">read_exact</span><span class="p" data-group-id="0948668503-23">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0948668503-23">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0948668503-22">)</span><span class="w">
│ │ │ -    </span><span class="nf">return</span><span class="p" data-group-id="0948668503-24">(</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="0948668503-24">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0948668503-25">(</span><span class="n">buf</span><span class="p" data-group-id="0948668503-26">[</span><span class="mi">0</span><span class="p" data-group-id="0948668503-26">]</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="0948668503-25">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="0948668503-27">[</span><span class="mi">1</span><span class="p" data-group-id="0948668503-27">]</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="0948668503-28">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0948668503-28">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0948668503-21">}</span><span class="w">
│ │ │ +  </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6303420506-22">(</span><span class="nf">read_exact</span><span class="p" data-group-id="6303420506-23">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6303420506-23">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6303420506-22">)</span><span class="w">
│ │ │ +    </span><span class="nf">return</span><span class="p" data-group-id="6303420506-24">(</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="6303420506-24">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6303420506-25">(</span><span class="n">buf</span><span class="p" data-group-id="6303420506-26">[</span><span class="mi">0</span><span class="p" data-group-id="6303420506-26">]</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="6303420506-25">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="6303420506-27">[</span><span class="mi">1</span><span class="p" data-group-id="6303420506-27">]</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="6303420506-28">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="6303420506-28">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6303420506-21">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="0948668503-29">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0948668503-29">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0948668503-30">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="6303420506-29">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="6303420506-29">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6303420506-30">{</span><span class="w">
│ │ │    </span><span class="kt">byte</span><span class="w"> </span><span class="n">li</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0948668503-31">(</span><span class="n">len</span><span class="w"> </span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="0948668503-31">)</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">write_exact</span><span class="p" data-group-id="0948668503-32">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0948668503-32">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6303420506-31">(</span><span class="n">len</span><span class="w"> </span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="6303420506-31">)</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">write_exact</span><span class="p" data-group-id="6303420506-32">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6303420506-32">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │    </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">len</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">write_exact</span><span class="p" data-group-id="0948668503-33">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0948668503-33">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">write_exact</span><span class="p" data-group-id="6303420506-33">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6303420506-33">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="0948668503-34">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="0948668503-34">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0948668503-30">}</span></code></pre><p>Notice that <code class="inline">stdin</code> and <code class="inline">stdout</code> are for buffered input/output and must <em>not</em> be
│ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="6303420506-34">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="6303420506-34">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6303420506-30">}</span></code></pre><p>Notice that <code class="inline">stdin</code> and <code class="inline">stdout</code> are for buffered input/output and must <em>not</em> be
│ │ │  used for the communication with Erlang.</p><p>In the <code class="inline">main</code> function, the C program is to listen for a message from Erlang
│ │ │  and, according to the selected encoding/decoding scheme, use the first byte to
│ │ │  determine which function to call and the second byte as argument to the
│ │ │  function. The result of calling the function is then to be sent back to Erlang:</p><pre><code class="makeup c" translate="no"><span class="cm">/* port.c */</span><span class="w">
│ │ │  
│ │ │  </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="kt">byte</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p" data-group-id="5131933487-1">(</span><span class="p" data-group-id="5131933487-1">)</span><span class="w"> </span><span class="p" data-group-id="5131933487-2">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p" data-group-id="8740063863-1">(</span><span class="p" data-group-id="8740063863-1">)</span><span class="w"> </span><span class="p" data-group-id="8740063863-2">{</span><span class="w">
│ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">fn</span><span class="p">,</span><span class="w"> </span><span class="n">arg</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="kt">byte</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="5131933487-3">[</span><span class="mi">100</span><span class="p" data-group-id="5131933487-3">]</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="kt">byte</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="8740063863-3">[</span><span class="mi">100</span><span class="p" data-group-id="8740063863-3">]</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="5131933487-4">(</span><span class="nf">read_cmd</span><span class="p" data-group-id="5131933487-5">(</span><span class="n">buf</span><span class="p" data-group-id="5131933487-5">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5131933487-4">)</span><span class="w"> </span><span class="p" data-group-id="5131933487-6">{</span><span class="w">
│ │ │ -    </span><span class="n">fn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="5131933487-7">[</span><span class="mi">0</span><span class="p" data-group-id="5131933487-7">]</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">arg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="5131933487-8">[</span><span class="mi">1</span><span class="p" data-group-id="5131933487-8">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5131933487-9">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5131933487-9">)</span><span class="w"> </span><span class="p" data-group-id="5131933487-10">{</span><span class="w">
│ │ │ -      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="5131933487-11">(</span><span class="n">arg</span><span class="p" data-group-id="5131933487-11">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5131933487-10">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5131933487-12">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5131933487-12">)</span><span class="w"> </span><span class="p" data-group-id="5131933487-13">{</span><span class="w">
│ │ │ -      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="5131933487-14">(</span><span class="n">arg</span><span class="p" data-group-id="5131933487-14">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5131933487-13">}</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="n">buf</span><span class="p" data-group-id="5131933487-15">[</span><span class="mi">0</span><span class="p" data-group-id="5131933487-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">write_cmd</span><span class="p" data-group-id="5131933487-16">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5131933487-16">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5131933487-6">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5131933487-2">}</span></code></pre><p>Notice that the C program is in a <code class="inline">while</code>-loop, checking for the return value
│ │ │ +  </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="8740063863-4">(</span><span class="nf">read_cmd</span><span class="p" data-group-id="8740063863-5">(</span><span class="n">buf</span><span class="p" data-group-id="8740063863-5">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8740063863-4">)</span><span class="w"> </span><span class="p" data-group-id="8740063863-6">{</span><span class="w">
│ │ │ +    </span><span class="n">fn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="8740063863-7">[</span><span class="mi">0</span><span class="p" data-group-id="8740063863-7">]</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">arg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="8740063863-8">[</span><span class="mi">1</span><span class="p" data-group-id="8740063863-8">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8740063863-9">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8740063863-9">)</span><span class="w"> </span><span class="p" data-group-id="8740063863-10">{</span><span class="w">
│ │ │ +      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="8740063863-11">(</span><span class="n">arg</span><span class="p" data-group-id="8740063863-11">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8740063863-10">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8740063863-12">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8740063863-12">)</span><span class="w"> </span><span class="p" data-group-id="8740063863-13">{</span><span class="w">
│ │ │ +      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="8740063863-14">(</span><span class="n">arg</span><span class="p" data-group-id="8740063863-14">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8740063863-13">}</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="n">buf</span><span class="p" data-group-id="8740063863-15">[</span><span class="mi">0</span><span class="p" data-group-id="8740063863-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">write_cmd</span><span class="p" data-group-id="8740063863-16">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8740063863-16">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8740063863-6">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8740063863-2">}</span></code></pre><p>Notice that the C program is in a <code class="inline">while</code>-loop, checking for the return value
│ │ │  of <code class="inline">read_cmd/1</code>. This is because the C program must detect when the port closes
│ │ │  and terminates.</p><h2 id="running-the-example" class="section-heading">
│ │ │    <a href="#running-the-example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running the Example</span>
│ │ │  </h2>
│ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">$ gcc -o extprg complex.c erl_comm.c port.c</code></pre><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$ </span><span class="ss">erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="3434132478-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="3434132478-1">]</span><span class="w"> </span><span class="p" data-group-id="3434132478-2">[</span><span class="ss">source</span><span class="p" data-group-id="3434132478-2">]</span><span class="w"> </span><span class="p" data-group-id="3434132478-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="3434132478-3">]</span><span class="w"> </span><span class="p" data-group-id="3434132478-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="3434132478-4">]</span><span class="w"> </span><span class="p" data-group-id="3434132478-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="3434132478-5">]</span><span class="w"> </span><span class="p" data-group-id="3434132478-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="3434132478-6">]</span><span class="w"> </span><span class="p" data-group-id="3434132478-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="3434132478-7">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="3484423596-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="3484423596-1">]</span><span class="w"> </span><span class="p" data-group-id="3484423596-2">[</span><span class="ss">source</span><span class="p" data-group-id="3484423596-2">]</span><span class="w"> </span><span class="p" data-group-id="3484423596-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="3484423596-3">]</span><span class="w"> </span><span class="p" data-group-id="3484423596-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="3484423596-4">]</span><span class="w"> </span><span class="p" data-group-id="3484423596-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="3484423596-5">]</span><span class="w"> </span><span class="p" data-group-id="3484423596-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="3484423596-6">]</span><span class="w"> </span><span class="p" data-group-id="3484423596-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="3484423596-7">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="3434132478-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="3434132478-9">(</span><span class="p" data-group-id="3434132478-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="3434132478-8">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="3434132478-10">(</span><span class="ss">complex1</span><span class="p" data-group-id="3434132478-10">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3434132478-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex1</span><span class="p" data-group-id="3434132478-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="6311786992-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="6311786992-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="3484423596-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="3484423596-9">(</span><span class="p" data-group-id="3484423596-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="3484423596-8">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="3484423596-10">(</span><span class="ss">complex1</span><span class="p" data-group-id="3484423596-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3484423596-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex1</span><span class="p" data-group-id="3484423596-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7107522813-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="7107522813-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="6311786992-2">(</span><span class="mi">3</span><span class="p" data-group-id="6311786992-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="7107522813-2">(</span><span class="mi">3</span><span class="p" data-group-id="7107522813-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="6311786992-3">(</span><span class="mi">5</span><span class="p" data-group-id="6311786992-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="7107522813-3">(</span><span class="mi">5</span><span class="p" data-group-id="7107522813-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="6311786992-4">(</span><span class="p" data-group-id="6311786992-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">complex1</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7107522813-4">(</span><span class="p" data-group-id="7107522813-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="example.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/c_portdriver.html
│ │ │ @@ -151,112 +151,112 @@
│ │ │  <p>Like a port program, the port communicates with an Erlang process. All
│ │ │  communication goes through one Erlang process that is the <em>connected process</em> of
│ │ │  the port driver. Terminating this process closes the port driver.</p><p>Before the port is created, the driver must be loaded. This is done with the
│ │ │  function <a href="../../lib/kernel-10.2.7.4/doc/html/erl_ddll.html#load_driver/2"><code class="inline">erl_ddll:load_driver/2</code></a>, with the name of the shared library as
│ │ │  argument.</p><p>The port is then created using the BIF <a href="../../erts-15.2.7.8/doc/html/erlang.html#open_port/2"><code class="inline">open_port/2</code></a>, with the
│ │ │  tuple <code class="inline">{spawn, DriverName}</code> as the first argument. The string <code class="inline">SharedLib</code> is the
│ │ │  name of the port driver. The second argument is a list of options, none in this
│ │ │ -case:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0241757512-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="0241757512-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0241757512-2">(</span><span class="p" data-group-id="0241757512-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0241757512-3">]</span><span class="p" data-group-id="0241757512-2">)</span><span class="p">.</span><span class="w">
│ │ │ +case:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6568229956-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="6568229956-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6568229956-2">(</span><span class="p" data-group-id="6568229956-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6568229956-3">]</span><span class="p" data-group-id="6568229956-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="0241757512-4">(</span><span class="n">SharedLib</span><span class="p" data-group-id="0241757512-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="0241757512-5">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="0241757512-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="6568229956-4">(</span><span class="n">SharedLib</span><span class="p" data-group-id="6568229956-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="6568229956-5">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="6568229956-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0241757512-6">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="0241757512-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="0241757512-7">(</span><span class="p" data-group-id="0241757512-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="0241757512-8">}</span><span class="p" data-group-id="0241757512-7">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="6568229956-6">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="6568229956-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="6568229956-7">(</span><span class="p" data-group-id="6568229956-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="6568229956-8">}</span><span class="p" data-group-id="6568229956-7">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="0241757512-9">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0241757512-10">[</span><span class="n">SharedLib</span><span class="p" data-group-id="0241757512-10">]</span><span class="p" data-group-id="0241757512-9">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="6568229956-9">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6568229956-10">[</span><span class="n">SharedLib</span><span class="p" data-group-id="6568229956-10">]</span><span class="p" data-group-id="6568229956-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="0241757512-11">(</span><span class="n">SharedLib</span><span class="p" data-group-id="0241757512-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nf">register</span><span class="p" data-group-id="0241757512-12">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0241757512-13">(</span><span class="p" data-group-id="0241757512-13">)</span><span class="p" data-group-id="0241757512-12">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="0241757512-14">(</span><span class="p" data-group-id="0241757512-15">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="0241757512-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0241757512-16">[</span><span class="p" data-group-id="0241757512-16">]</span><span class="p" data-group-id="0241757512-14">)</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="nf">loop</span><span class="p" data-group-id="0241757512-17">(</span><span class="n">Port</span><span class="p" data-group-id="0241757512-17">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex5:foo/1</code> and <code class="inline">complex5:bar/1</code> can be implemented. Both send a
│ │ │ -message to the <code class="inline">complex</code> process and receive the following reply:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="4118714608-1">(</span><span class="n">X</span><span class="p" data-group-id="4118714608-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="4118714608-2">(</span><span class="p" data-group-id="4118714608-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4118714608-3">}</span><span class="p" data-group-id="4118714608-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="4118714608-4">(</span><span class="n">Y</span><span class="p" data-group-id="4118714608-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="4118714608-5">(</span><span class="p" data-group-id="4118714608-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4118714608-6">}</span><span class="p" data-group-id="4118714608-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="6568229956-11">(</span><span class="n">SharedLib</span><span class="p" data-group-id="6568229956-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nf">register</span><span class="p" data-group-id="6568229956-12">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6568229956-13">(</span><span class="p" data-group-id="6568229956-13">)</span><span class="p" data-group-id="6568229956-12">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="6568229956-14">(</span><span class="p" data-group-id="6568229956-15">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="6568229956-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6568229956-16">[</span><span class="p" data-group-id="6568229956-16">]</span><span class="p" data-group-id="6568229956-14">)</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="nf">loop</span><span class="p" data-group-id="6568229956-17">(</span><span class="n">Port</span><span class="p" data-group-id="6568229956-17">)</span><span class="p">.</span></code></pre><p>Now <code class="inline">complex5:foo/1</code> and <code class="inline">complex5:bar/1</code> can be implemented. Both send a
│ │ │ +message to the <code class="inline">complex</code> process and receive the following reply:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="3415264125-1">(</span><span class="n">X</span><span class="p" data-group-id="3415264125-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="3415264125-2">(</span><span class="p" data-group-id="3415264125-3">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3415264125-3">}</span><span class="p" data-group-id="3415264125-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="3415264125-4">(</span><span class="n">Y</span><span class="p" data-group-id="3415264125-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="3415264125-5">(</span><span class="p" data-group-id="3415264125-6">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3415264125-6">}</span><span class="p" data-group-id="3415264125-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="4118714608-7">(</span><span class="n">Msg</span><span class="p" data-group-id="4118714608-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4118714608-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4118714608-9">(</span><span class="p" data-group-id="4118714608-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="4118714608-8">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="3415264125-7">(</span><span class="n">Msg</span><span class="p" data-group-id="3415264125-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3415264125-8">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3415264125-9">(</span><span class="p" data-group-id="3415264125-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3415264125-8">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4118714608-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="4118714608-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3415264125-10">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="3415264125-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Result</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process performs the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="5583347545-1">(</span><span class="n">Port</span><span class="p" data-group-id="5583347545-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">complex</code> process performs the following:</p><ul><li>Encodes the message into a sequence of bytes.</li><li>Sends it to the port.</li><li>Waits for a reply.</li><li>Decodes the reply.</li><li>Sends it back to the caller:</li></ul><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="1437871880-1">(</span><span class="n">Port</span><span class="p" data-group-id="1437871880-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5583347545-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="5583347545-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5583347545-3">{</span><span class="nf">self</span><span class="p" data-group-id="5583347545-4">(</span><span class="p" data-group-id="5583347545-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5583347545-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="5583347545-6">(</span><span class="n">Msg</span><span class="p" data-group-id="5583347545-6">)</span><span class="p" data-group-id="5583347545-5">}</span><span class="p" data-group-id="5583347545-3">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="1437871880-2">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1437871880-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1437871880-3">{</span><span class="nf">self</span><span class="p" data-group-id="1437871880-4">(</span><span class="p" data-group-id="1437871880-4">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1437871880-5">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="1437871880-6">(</span><span class="n">Msg</span><span class="p" data-group-id="1437871880-6">)</span><span class="p" data-group-id="1437871880-5">}</span><span class="p" data-group-id="1437871880-3">}</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="k">receive</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="5583347545-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5583347545-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5583347545-8">}</span><span class="p" data-group-id="5583347545-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5583347545-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="5583347545-10">(</span><span class="n">Data</span><span class="p" data-group-id="5583347545-10">)</span><span class="p" data-group-id="5583347545-9">}</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="1437871880-7">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1437871880-8">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1437871880-8">}</span><span class="p" data-group-id="1437871880-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1437871880-9">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="1437871880-10">(</span><span class="n">Data</span><span class="p" data-group-id="1437871880-10">)</span><span class="p" data-group-id="1437871880-9">}</span><span class="w">
│ │ │              </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="5583347545-11">(</span><span class="n">Port</span><span class="p" data-group-id="5583347545-11">)</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="1437871880-11">(</span><span class="n">Port</span><span class="p" data-group-id="1437871880-11">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Assuming that both the arguments and the results from the C functions are less
│ │ │  than 256, a simple encoding/decoding scheme is employed. In this scheme, <code class="inline">foo</code>
│ │ │  is represented by byte 1, <code class="inline">bar</code> is represented by 2, and the argument/result is
│ │ │ -represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="0167280693-1">(</span><span class="p" data-group-id="0167280693-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0167280693-2">}</span><span class="p" data-group-id="0167280693-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0167280693-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="0167280693-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="0167280693-4">(</span><span class="p" data-group-id="0167280693-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0167280693-5">}</span><span class="p" data-group-id="0167280693-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0167280693-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0167280693-6">]</span><span class="p">.</span><span class="w">
│ │ │ +represented by a single byte as well:</p><pre><code class="makeup erlang" translate="no"><span class="nf">encode</span><span class="p" data-group-id="7244307486-1">(</span><span class="p" data-group-id="7244307486-2">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7244307486-2">}</span><span class="p" data-group-id="7244307486-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7244307486-3">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7244307486-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="7244307486-4">(</span><span class="p" data-group-id="7244307486-5">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7244307486-5">}</span><span class="p" data-group-id="7244307486-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7244307486-6">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7244307486-6">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="0167280693-7">(</span><span class="p" data-group-id="0167280693-8">[</span><span class="n">Int</span><span class="p" data-group-id="0167280693-8">]</span><span class="p" data-group-id="0167280693-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functions for stopping the port and
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="7244307486-7">(</span><span class="p" data-group-id="7244307486-8">[</span><span class="n">Int</span><span class="p" data-group-id="7244307486-8">]</span><span class="p" data-group-id="7244307486-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>The resulting Erlang program, including functions for stopping the port and
│ │ │  detecting port failures, is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8986633249-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="8986633249-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8986633249-2">(</span><span class="p" data-group-id="8986633249-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8986633249-3">]</span><span class="p" data-group-id="8986633249-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8986633249-4">(</span><span class="p" data-group-id="8986633249-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8986633249-5">]</span><span class="p" data-group-id="8986633249-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3315916386-1">(</span><span class="ss">complex5</span><span class="p" data-group-id="3315916386-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3315916386-2">(</span><span class="p" data-group-id="3315916386-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3315916386-3">]</span><span class="p" data-group-id="3315916386-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3315916386-4">(</span><span class="p" data-group-id="3315916386-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3315916386-5">]</span><span class="p" data-group-id="3315916386-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="8986633249-6">(</span><span class="n">SharedLib</span><span class="p" data-group-id="8986633249-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="8986633249-7">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="8986633249-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="3315916386-6">(</span><span class="n">SharedLib</span><span class="p" data-group-id="3315916386-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">erl_ddll</span><span class="p">:</span><span class="nf">load_driver</span><span class="p" data-group-id="3315916386-7">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="3315916386-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │  	</span><span class="ss">ok</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="8986633249-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="8986633249-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="8986633249-9">(</span><span class="p" data-group-id="8986633249-10">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="8986633249-10">}</span><span class="p" data-group-id="8986633249-9">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="3315916386-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">already_loaded</span><span class="p" data-group-id="3315916386-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ +	</span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">exit</span><span class="p" data-group-id="3315916386-9">(</span><span class="p" data-group-id="3315916386-10">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="ss">could_not_load_driver</span><span class="p" data-group-id="3315916386-10">}</span><span class="p" data-group-id="3315916386-9">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="8986633249-11">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8986633249-12">[</span><span class="n">SharedLib</span><span class="p" data-group-id="8986633249-12">]</span><span class="p" data-group-id="8986633249-11">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="3315916386-11">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3315916386-12">[</span><span class="n">SharedLib</span><span class="p" data-group-id="3315916386-12">]</span><span class="p" data-group-id="3315916386-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8986633249-13">(</span><span class="n">SharedLib</span><span class="p" data-group-id="8986633249-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="8986633249-14">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8986633249-15">(</span><span class="p" data-group-id="8986633249-15">)</span><span class="p" data-group-id="8986633249-14">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="8986633249-16">(</span><span class="p" data-group-id="8986633249-17">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="8986633249-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8986633249-18">[</span><span class="p" data-group-id="8986633249-18">]</span><span class="p" data-group-id="8986633249-16">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="8986633249-19">(</span><span class="n">Port</span><span class="p" data-group-id="8986633249-19">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3315916386-13">(</span><span class="n">SharedLib</span><span class="p" data-group-id="3315916386-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="3315916386-14">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3315916386-15">(</span><span class="p" data-group-id="3315916386-15">)</span><span class="p" data-group-id="3315916386-14">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="3315916386-16">(</span><span class="p" data-group-id="3315916386-17">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">SharedLib</span><span class="p" data-group-id="3315916386-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3315916386-18">[</span><span class="p" data-group-id="3315916386-18">]</span><span class="p" data-group-id="3315916386-16">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="3315916386-19">(</span><span class="n">Port</span><span class="p" data-group-id="3315916386-19">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="8986633249-20">(</span><span class="p" data-group-id="8986633249-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="3315916386-20">(</span><span class="p" data-group-id="3315916386-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="8986633249-21">(</span><span class="n">X</span><span class="p" data-group-id="8986633249-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="8986633249-22">(</span><span class="p" data-group-id="8986633249-23">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8986633249-23">}</span><span class="p" data-group-id="8986633249-22">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="8986633249-24">(</span><span class="n">Y</span><span class="p" data-group-id="8986633249-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="8986633249-25">(</span><span class="p" data-group-id="8986633249-26">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8986633249-26">}</span><span class="p" data-group-id="8986633249-25">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="3315916386-21">(</span><span class="n">X</span><span class="p" data-group-id="3315916386-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="3315916386-22">(</span><span class="p" data-group-id="3315916386-23">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3315916386-23">}</span><span class="p" data-group-id="3315916386-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="3315916386-24">(</span><span class="n">Y</span><span class="p" data-group-id="3315916386-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="3315916386-25">(</span><span class="p" data-group-id="3315916386-26">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3315916386-26">}</span><span class="p" data-group-id="3315916386-25">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="8986633249-27">(</span><span class="n">Msg</span><span class="p" data-group-id="8986633249-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8986633249-28">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8986633249-29">(</span><span class="p" data-group-id="8986633249-29">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8986633249-28">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="3315916386-27">(</span><span class="n">Msg</span><span class="p" data-group-id="3315916386-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3315916386-28">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3315916386-29">(</span><span class="p" data-group-id="3315916386-29">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3315916386-28">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="8986633249-30">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8986633249-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="3315916386-30">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="3315916386-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="8986633249-31">(</span><span class="n">Port</span><span class="p" data-group-id="8986633249-31">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="3315916386-31">(</span><span class="n">Port</span><span class="p" data-group-id="3315916386-31">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="8986633249-32">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8986633249-32">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8986633249-33">{</span><span class="nf">self</span><span class="p" data-group-id="8986633249-34">(</span><span class="p" data-group-id="8986633249-34">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8986633249-35">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="8986633249-36">(</span><span class="n">Msg</span><span class="p" data-group-id="8986633249-36">)</span><span class="p" data-group-id="8986633249-35">}</span><span class="p" data-group-id="8986633249-33">}</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="3315916386-32">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3315916386-32">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3315916386-33">{</span><span class="nf">self</span><span class="p" data-group-id="3315916386-34">(</span><span class="p" data-group-id="3315916386-34">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3315916386-35">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="3315916386-36">(</span><span class="n">Msg</span><span class="p" data-group-id="3315916386-36">)</span><span class="p" data-group-id="3315916386-35">}</span><span class="p" data-group-id="3315916386-33">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="8986633249-37">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8986633249-38">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8986633249-38">}</span><span class="p" data-group-id="8986633249-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8986633249-39">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="8986633249-40">(</span><span class="n">Data</span><span class="p" data-group-id="8986633249-40">)</span><span class="p" data-group-id="8986633249-39">}</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="3315916386-37">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3315916386-38">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3315916386-38">}</span><span class="p" data-group-id="3315916386-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3315916386-39">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="3315916386-40">(</span><span class="n">Data</span><span class="p" data-group-id="3315916386-40">)</span><span class="p" data-group-id="3315916386-39">}</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="8986633249-41">(</span><span class="n">Port</span><span class="p" data-group-id="8986633249-41">)</span><span class="p">;</span><span class="w">
│ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="3315916386-41">(</span><span class="n">Port</span><span class="p" data-group-id="3315916386-41">)</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8986633249-42">{</span><span class="nf">self</span><span class="p" data-group-id="8986633249-43">(</span><span class="p" data-group-id="8986633249-43">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="8986633249-42">}</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3315916386-42">{</span><span class="nf">self</span><span class="p" data-group-id="3315916386-43">(</span><span class="p" data-group-id="3315916386-43">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="3315916386-42">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="8986633249-44">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="8986633249-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="8986633249-45">(</span><span class="ss">normal</span><span class="p" data-group-id="8986633249-45">)</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="3315916386-44">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="3315916386-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="3315916386-45">(</span><span class="ss">normal</span><span class="p" data-group-id="3315916386-45">)</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="8986633249-46">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="8986633249-46">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8986633249-47">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8986633249-48">[</span><span class="n">Reason</span><span class="p" data-group-id="8986633249-48">]</span><span class="p" data-group-id="8986633249-47">)</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="8986633249-49">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="8986633249-49">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="3315916386-46">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="3315916386-46">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3315916386-47">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3315916386-48">[</span><span class="n">Reason</span><span class="p" data-group-id="3315916386-48">]</span><span class="p" data-group-id="3315916386-47">)</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="3315916386-49">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="3315916386-49">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="8986633249-50">(</span><span class="p" data-group-id="8986633249-51">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8986633249-51">}</span><span class="p" data-group-id="8986633249-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8986633249-52">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8986633249-52">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="8986633249-53">(</span><span class="p" data-group-id="8986633249-54">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8986633249-54">}</span><span class="p" data-group-id="8986633249-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8986633249-55">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8986633249-55">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="3315916386-50">(</span><span class="p" data-group-id="3315916386-51">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3315916386-51">}</span><span class="p" data-group-id="3315916386-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3315916386-52">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3315916386-52">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="3315916386-53">(</span><span class="p" data-group-id="3315916386-54">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3315916386-54">}</span><span class="p" data-group-id="3315916386-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3315916386-55">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3315916386-55">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="8986633249-56">(</span><span class="p" data-group-id="8986633249-57">[</span><span class="n">Int</span><span class="p" data-group-id="8986633249-57">]</span><span class="p" data-group-id="8986633249-56">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-driver" class="section-heading">
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="3315916386-56">(</span><span class="p" data-group-id="3315916386-57">[</span><span class="n">Int</span><span class="p" data-group-id="3315916386-57">]</span><span class="p" data-group-id="3315916386-56">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><h2 id="c-driver" class="section-heading">
│ │ │    <a href="#c-driver" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">C Driver</span>
│ │ │  </h2>
│ │ │  <p>The C driver is a module that is compiled and linked into a shared library. It
│ │ │  uses a driver structure and includes the header file <code class="inline">erl_driver.h</code>.</p><p>The driver structure is filled with the driver name and function pointers. It is
│ │ │ @@ -273,44 +273,44 @@
│ │ │  reference.</p><p>It is not a good idea to use a global variable as the port driver can be spawned
│ │ │  by multiple Erlang processes. This driver-structure is to be instantiated
│ │ │  multiple times:</p><pre><code class="makeup c" translate="no"><span class="cm">/* port_driver.c */</span><span class="w">
│ │ │  
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdio</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="s">&quot;erl_driver.h&quot;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="p" data-group-id="4874977332-1">{</span><span class="w">
│ │ │ +</span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="p" data-group-id="4950852749-1">{</span><span class="w">
│ │ │      </span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-1">}</span><span class="w"> </span><span class="n">example_data</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4950852749-1">}</span><span class="w"> </span><span class="n">example_data</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">example_drv_start</span><span class="p" data-group-id="4874977332-2">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="4874977332-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-3">{</span><span class="w">
│ │ │ -    </span><span class="n">example_data</span><span class="o">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4874977332-4">(</span><span class="n">example_data</span><span class="o">*</span><span class="p" data-group-id="4874977332-4">)</span><span class="nf">driver_alloc</span><span class="p" data-group-id="4874977332-5">(</span><span class="nf">sizeof</span><span class="p" data-group-id="4874977332-6">(</span><span class="n">example_data</span><span class="p" data-group-id="4874977332-6">)</span><span class="p" data-group-id="4874977332-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">example_drv_start</span><span class="p" data-group-id="4950852749-2">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="4950852749-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4950852749-3">{</span><span class="w">
│ │ │ +    </span><span class="n">example_data</span><span class="o">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4950852749-4">(</span><span class="n">example_data</span><span class="o">*</span><span class="p" data-group-id="4950852749-4">)</span><span class="nf">driver_alloc</span><span class="p" data-group-id="4950852749-5">(</span><span class="nf">sizeof</span><span class="p" data-group-id="4950852749-6">(</span><span class="n">example_data</span><span class="p" data-group-id="4950852749-6">)</span><span class="p" data-group-id="4950852749-5">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">d</span><span class="o">-&gt;</span><span class="n">port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">port</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="4874977332-7">(</span><span class="no">ErlDrvData</span><span class="p" data-group-id="4874977332-7">)</span><span class="n">d</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-3">}</span><span class="w">
│ │ │ +    </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="4950852749-7">(</span><span class="no">ErlDrvData</span><span class="p" data-group-id="4950852749-7">)</span><span class="n">d</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4950852749-3">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">example_drv_stop</span><span class="p" data-group-id="4874977332-8">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p" data-group-id="4874977332-8">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-9">{</span><span class="w">
│ │ │ -    </span><span class="nf">driver_free</span><span class="p" data-group-id="4874977332-10">(</span><span class="p" data-group-id="4874977332-11">(</span><span class="kt">char</span><span class="o">*</span><span class="p" data-group-id="4874977332-11">)</span><span class="n">handle</span><span class="p" data-group-id="4874977332-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-9">}</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">example_drv_output</span><span class="p" data-group-id="4874977332-12">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="w">       </span><span class="no">ErlDrvSizeT</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="4874977332-12">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-13">{</span><span class="w">
│ │ │ -    </span><span class="n">example_data</span><span class="o">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4874977332-14">(</span><span class="n">example_data</span><span class="o">*</span><span class="p" data-group-id="4874977332-14">)</span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="kt">char</span><span class="w"> </span><span class="n">fn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p" data-group-id="4874977332-15">[</span><span class="mi">0</span><span class="p" data-group-id="4874977332-15">]</span><span class="p">,</span><span class="w"> </span><span class="n">arg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p" data-group-id="4874977332-16">[</span><span class="mi">1</span><span class="p" data-group-id="4874977332-16">]</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4874977332-17">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4874977332-17">)</span><span class="w"> </span><span class="p" data-group-id="4874977332-18">{</span><span class="w">
│ │ │ -      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="4874977332-19">(</span><span class="n">arg</span><span class="p" data-group-id="4874977332-19">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4874977332-18">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4874977332-20">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4874977332-20">)</span><span class="w"> </span><span class="p" data-group-id="4874977332-21">{</span><span class="w">
│ │ │ -      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="4874977332-22">(</span><span class="n">arg</span><span class="p" data-group-id="4874977332-22">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4874977332-21">}</span><span class="w">
│ │ │ -    </span><span class="nf">driver_output</span><span class="p" data-group-id="4874977332-23">(</span><span class="n">d</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4874977332-23">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-13">}</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">example_drv_stop</span><span class="p" data-group-id="4950852749-8">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p" data-group-id="4950852749-8">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4950852749-9">{</span><span class="w">
│ │ │ +    </span><span class="nf">driver_free</span><span class="p" data-group-id="4950852749-10">(</span><span class="p" data-group-id="4950852749-11">(</span><span class="kt">char</span><span class="o">*</span><span class="p" data-group-id="4950852749-11">)</span><span class="n">handle</span><span class="p" data-group-id="4950852749-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4950852749-9">}</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">example_drv_output</span><span class="p" data-group-id="4950852749-12">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="w">       </span><span class="no">ErlDrvSizeT</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="4950852749-12">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4950852749-13">{</span><span class="w">
│ │ │ +    </span><span class="n">example_data</span><span class="o">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4950852749-14">(</span><span class="n">example_data</span><span class="o">*</span><span class="p" data-group-id="4950852749-14">)</span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="kt">char</span><span class="w"> </span><span class="n">fn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p" data-group-id="4950852749-15">[</span><span class="mi">0</span><span class="p" data-group-id="4950852749-15">]</span><span class="p">,</span><span class="w"> </span><span class="n">arg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p" data-group-id="4950852749-16">[</span><span class="mi">1</span><span class="p" data-group-id="4950852749-16">]</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4950852749-17">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4950852749-17">)</span><span class="w"> </span><span class="p" data-group-id="4950852749-18">{</span><span class="w">
│ │ │ +      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="4950852749-19">(</span><span class="n">arg</span><span class="p" data-group-id="4950852749-19">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4950852749-18">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4950852749-20">(</span><span class="n">fn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4950852749-20">)</span><span class="w"> </span><span class="p" data-group-id="4950852749-21">{</span><span class="w">
│ │ │ +      </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="4950852749-22">(</span><span class="n">arg</span><span class="p" data-group-id="4950852749-22">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4950852749-21">}</span><span class="w">
│ │ │ +    </span><span class="nf">driver_output</span><span class="p" data-group-id="4950852749-23">(</span><span class="n">d</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4950852749-23">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4950852749-13">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="no">ErlDrvEntry</span><span class="w"> </span><span class="n">example_driver_entry</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4874977332-24">{</span><span class="w">
│ │ │ +</span><span class="no">ErlDrvEntry</span><span class="w"> </span><span class="n">example_driver_entry</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4950852749-24">{</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR init, called when driver is loaded */</span><span class="w">
│ │ │      </span><span class="n">example_drv_start</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="cm">/* L_PTR start, called when port is opened */</span><span class="w">
│ │ │      </span><span class="n">example_drv_stop</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR stop, called when port is closed */</span><span class="w">
│ │ │      </span><span class="n">example_drv_output</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR output, called when erlang has sent */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR ready_input, called when input descriptor ready */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="err">	</span><span class="cm">/* F_PTR ready_output, called when output descriptor ready */</span><span class="w">
│ │ │      </span><span class="s">&quot;example_drv&quot;</span><span class="p">,</span><span class="err">	</span><span class="err">	</span><span class="cm">/* char *driver_name, the argument to open_port */</span><span class="w">
│ │ │ @@ -334,38 +334,38 @@
│ │ │  				       set to this value */</span><span class="w">
│ │ │      </span><span class="mi">0</span><span class="p">,</span><span class="w">                          </span><span class="cm">/* int driver_flags, see documentation */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* void *handle2, reserved for VM use */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* F_PTR process_exit, called when a
│ │ │  				   monitored process dies */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="w">                        </span><span class="cm">/* F_PTR stop_select, called to close an
│ │ │  				   event object */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-24">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4950852749-24">}</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="no">DRIVER_INIT</span><span class="p" data-group-id="4874977332-25">(</span><span class="n">example_drv</span><span class="p" data-group-id="4874977332-25">)</span><span class="w"> </span><span class="cm">/* must match name in driver_entry */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-26">{</span><span class="w">
│ │ │ +</span><span class="no">DRIVER_INIT</span><span class="p" data-group-id="4950852749-25">(</span><span class="n">example_drv</span><span class="p" data-group-id="4950852749-25">)</span><span class="w"> </span><span class="cm">/* must match name in driver_entry */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4950852749-26">{</span><span class="w">
│ │ │      </span><span class="k">return</span><span class="w"> </span><span class="o">&amp;</span><span class="n">example_driver_entry</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4874977332-26">}</span></code></pre><h2 id="running-the-example" class="section-heading">
│ │ │ +</span><span class="p" data-group-id="4950852749-26">}</span></code></pre><h2 id="running-the-example" class="section-heading">
│ │ │    <a href="#running-the-example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running the Example</span>
│ │ │  </h2>
│ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">unix&gt; gcc -o example_drv.so -fpic -shared complex.c port_driver.c
│ │ │  windows&gt; cl -LD -MD -Fe example_drv.dll complex.c port_driver.c</code></pre><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="ss">erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="9281912509-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="9281912509-1">]</span><span class="w"> </span><span class="p" data-group-id="9281912509-2">[</span><span class="ss">source</span><span class="p" data-group-id="9281912509-2">]</span><span class="w"> </span><span class="p" data-group-id="9281912509-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="9281912509-3">]</span><span class="w"> </span><span class="p" data-group-id="9281912509-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="9281912509-4">]</span><span class="w"> </span><span class="p" data-group-id="9281912509-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="9281912509-5">]</span><span class="w"> </span><span class="p" data-group-id="9281912509-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="9281912509-6">]</span><span class="w"> </span><span class="p" data-group-id="9281912509-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="9281912509-7">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="4539670913-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="4539670913-1">]</span><span class="w"> </span><span class="p" data-group-id="4539670913-2">[</span><span class="ss">source</span><span class="p" data-group-id="4539670913-2">]</span><span class="w"> </span><span class="p" data-group-id="4539670913-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4539670913-3">]</span><span class="w"> </span><span class="p" data-group-id="4539670913-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4539670913-4">]</span><span class="w"> </span><span class="p" data-group-id="4539670913-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4539670913-5">]</span><span class="w"> </span><span class="p" data-group-id="4539670913-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4539670913-6">]</span><span class="w"> </span><span class="p" data-group-id="4539670913-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="4539670913-7">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="9281912509-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="9281912509-9">(</span><span class="p" data-group-id="9281912509-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="9281912509-8">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="9281912509-10">(</span><span class="ss">complex5</span><span class="p" data-group-id="9281912509-10">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9281912509-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex5</span><span class="p" data-group-id="9281912509-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7674772688-1">(</span><span class="s">&quot;example_drv&quot;</span><span class="p" data-group-id="7674772688-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="4539670913-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="4539670913-9">(</span><span class="p" data-group-id="4539670913-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="4539670913-8">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="4539670913-10">(</span><span class="ss">complex5</span><span class="p" data-group-id="4539670913-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4539670913-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex5</span><span class="p" data-group-id="4539670913-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7541580315-1">(</span><span class="s">&quot;example_drv&quot;</span><span class="p" data-group-id="7541580315-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="7674772688-2">(</span><span class="mi">3</span><span class="p" data-group-id="7674772688-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="7541580315-2">(</span><span class="mi">3</span><span class="p" data-group-id="7541580315-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="7674772688-3">(</span><span class="mi">5</span><span class="p" data-group-id="7674772688-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="7541580315-3">(</span><span class="mi">5</span><span class="p" data-group-id="7541580315-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7674772688-4">(</span><span class="p" data-group-id="7674772688-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">complex5</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7541580315-4">(</span><span class="p" data-group-id="7541580315-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="erl_interface.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/code_loading.html
│ │ │ @@ -122,16 +122,16 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Compilation</span>
│ │ │  </h2>
│ │ │  <p>Erlang programs must be <em>compiled</em> to object code. The compiler can generate a
│ │ │  new file that contains the object code. The current abstract machine, which runs
│ │ │  the object code, is called BEAM, therefore the object files get the suffix
│ │ │ -<code class="inline">.beam</code>. The compiler can also generate a binary which can be loaded directly.</p><p>The compiler is located in the module <a href="../../lib/compiler-8.6.1.4/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><pre><code class="makeup erlang" translate="no"><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="3038893334-1">(</span><span class="n">Module</span><span class="p" data-group-id="3038893334-1">)</span><span class="w">
│ │ │ -</span><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="3038893334-2">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="3038893334-2">)</span></code></pre><p>The Erlang shell understands the command <code class="inline">c(Module)</code>, which both compiles and
│ │ │ +<code class="inline">.beam</code>. The compiler can also generate a binary which can be loaded directly.</p><p>The compiler is located in the module <a href="../../lib/compiler-8.6.1.4/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><pre><code class="makeup erlang" translate="no"><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="7501799939-1">(</span><span class="n">Module</span><span class="p" data-group-id="7501799939-1">)</span><span class="w">
│ │ │ +</span><span class="nc">compile</span><span class="p">:</span><span class="nf">file</span><span class="p" data-group-id="7501799939-2">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="7501799939-2">)</span></code></pre><p>The Erlang shell understands the command <code class="inline">c(Module)</code>, which both compiles and
│ │ │  loads <code class="inline">Module</code>.</p><p>There is also a module <code class="inline">make</code>, which provides a set of functions similar to the
│ │ │  UNIX type Make functions, see module <a href="../../lib/tools-4.1.1/doc/html/make.html"><code class="inline">make</code></a> in Tools.</p><p>The compiler can also be accessed from the OS prompt using the
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erl_cmd.html">erl</a> executable in ERTS.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -compile Module1...ModuleN</span><span class="w">
│ │ │  </span><span class="c1">% erl -make</span></code></pre><p>The <code class="inline">erlc</code> program provides way to compile modules from the OS
│ │ │  shell, see the <a href="../../erts-15.2.7.8/doc/html/erlc_cmd.html">erlc</a> executable in ERTS. It
│ │ │  understands a number of flags that can be used to define macros, add search
│ │ │  paths for include files, and more.</p><pre><code class="text">% erlc &lt;flags&gt; File1.erl...FileN.erl</code></pre><p><a href="" id="loading"></a></p><h2 id="code-loading" class="section-heading">
│ │ │ @@ -156,54 +156,54 @@
│ │ │  When a module is loaded into the system for the first time, the code becomes
│ │ │  'current'. If then a new instance of the module is loaded, the code of the
│ │ │  previous instance becomes 'old' and the new instance becomes 'current'.</p><p>Both old and current code is valid, and can be evaluated concurrently. Fully
│ │ │  qualified function calls always refer to current code. Old code can still be
│ │ │  evaluated because of processes lingering in the old code.</p><p>If a third instance of the module is loaded, the code server removes (purges)
│ │ │  the old code and any processes lingering in it is terminated. Then the third
│ │ │  instance becomes 'current' and the previously current code becomes 'old'.</p><p>To change from old code to current code, a process must make a fully qualified
│ │ │ -function call.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9540480221-1">(</span><span class="ss">m</span><span class="p" data-group-id="9540480221-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9540480221-2">(</span><span class="p" data-group-id="9540480221-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9540480221-3">]</span><span class="p" data-group-id="9540480221-2">)</span><span class="p">.</span><span class="w">
│ │ │ +function call.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1042535706-1">(</span><span class="ss">m</span><span class="p" data-group-id="1042535706-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1042535706-2">(</span><span class="p" data-group-id="1042535706-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1042535706-3">]</span><span class="p" data-group-id="1042535706-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="9540480221-4">(</span><span class="p" data-group-id="9540480221-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="1042535706-4">(</span><span class="p" data-group-id="1042535706-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">code_switch</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">m</span><span class="p">:</span><span class="nf">loop</span><span class="p" data-group-id="9540480221-5">(</span><span class="p" data-group-id="9540480221-5">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nc">m</span><span class="p">:</span><span class="nf">loop</span><span class="p" data-group-id="1042535706-5">(</span><span class="p" data-group-id="1042535706-5">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">Msg</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="9540480221-6">(</span><span class="p" data-group-id="9540480221-6">)</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="1042535706-6">(</span><span class="p" data-group-id="1042535706-6">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>To make the process change code, send the message <code class="inline">code_switch</code> to it. The
│ │ │  process then makes a fully qualified call to <code class="inline">m:loop()</code> and changes to current
│ │ │  code. Notice that <code class="inline">m:loop/0</code> must be exported.</p><p>For code replacement of funs to work, use the syntax
│ │ │  <code class="inline">fun Module:FunctionName/Arity</code>.</p><p><a href="" id="on_load"></a></p><h2 id="running-a-function-when-a-module-is-loaded" class="section-heading">
│ │ │    <a href="#running-a-function-when-a-module-is-loaded" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running a Function When a Module is Loaded</span>
│ │ │  </h2>
│ │ │  <p>The <code class="inline">-on_load()</code> directive names a function that is to be run automatically when
│ │ │ -a module is loaded.</p><p>Its syntax is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="3859219683-1">(</span><span class="n">Name</span><span class="o">/</span><span class="mi">0</span><span class="p" data-group-id="3859219683-1">)</span><span class="p">.</span></code></pre><p>It is not necessary to export the function. It is called in a freshly spawned
│ │ │ +a module is loaded.</p><p>Its syntax is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="4976483524-1">(</span><span class="n">Name</span><span class="o">/</span><span class="mi">0</span><span class="p" data-group-id="4976483524-1">)</span><span class="p">.</span></code></pre><p>It is not necessary to export the function. It is called in a freshly spawned
│ │ │  process (which terminates as soon as the function returns).</p><p>The function must return <code class="inline">ok</code> if the module is to become the new current code
│ │ │  for the module and become callable.</p><p>Returning any other value or generating an exception causes the new code to be
│ │ │  unloaded. If the return value is not an atom, a warning error report is sent to
│ │ │  the error logger.</p><p>If there already is current code for the module, that code will remain current
│ │ │  and can be called until the <code class="inline">on_load</code> function has returned. If the <code class="inline">on_load</code>
│ │ │  function fails, the current code (if any) will remain current. If there is no
│ │ │  current code for a module, any process that makes an external call to the module
│ │ │  before the <code class="inline">on_load</code> function has finished will be suspended until the <code class="inline">on_load</code>
│ │ │  function have finished.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 19, if the <code class="inline">on_load</code> function failed, any previously current
│ │ │  code would become old, essentially leaving the system without any working and
│ │ │  reachable instance of the module.</p></section><p>In embedded mode, first all modules are loaded. Then all <code class="inline">on_load</code> functions are
│ │ │  called. The system is terminated unless all of the <code class="inline">on_load</code> functions return
│ │ │ -<code class="inline">ok</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5061132355-1">(</span><span class="ss">m</span><span class="p" data-group-id="5061132355-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="5061132355-2">(</span><span class="ss">load_my_nifs</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5061132355-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">ok</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6058629192-1">(</span><span class="ss">m</span><span class="p" data-group-id="6058629192-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="6058629192-2">(</span><span class="ss">load_my_nifs</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6058629192-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">load_my_nifs</span><span class="p" data-group-id="5061132355-3">(</span><span class="p" data-group-id="5061132355-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">load_my_nifs</span><span class="p" data-group-id="6058629192-3">(</span><span class="p" data-group-id="6058629192-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NifPath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">    </span><span class="c1">%Set up the path to the NIF library.</span><span class="w">
│ │ │      </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">       </span><span class="c1">%Initialize the Info term</span><span class="w">
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="5061132355-4">(</span><span class="n">NifPath</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="5061132355-4">)</span><span class="p">.</span></code></pre><p>If the call to <a href="../../erts-15.2.7.8/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a> fails, the module is unloaded and a warning
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="6058629192-4">(</span><span class="n">NifPath</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p" data-group-id="6058629192-4">)</span><span class="p">.</span></code></pre><p>If the call to <a href="../../erts-15.2.7.8/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a> fails, the module is unloaded and a warning
│ │ │  report is sent to the error loader.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="distributed.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/commoncaveats.html
│ │ │ @@ -118,31 +118,31 @@
│ │ │  <p>This section lists a few constructs to watch out for.</p><h2 id="operator" class="section-heading">
│ │ │    <a href="#operator" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Operator <code class="inline">++</code></span>
│ │ │  </h2>
│ │ │  <p>The <code class="inline">++</code> operator copies its left-hand side operand. That is clearly
│ │ │ -seen if we do our own implementation in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_plus_plus</span><span class="p" data-group-id="8134457358-1">(</span><span class="p" data-group-id="8134457358-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8134457358-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8134457358-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8134457358-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="8134457358-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8134457358-4">)</span><span class="p" data-group-id="8134457358-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="8134457358-5">(</span><span class="p" data-group-id="8134457358-6">[</span><span class="p" data-group-id="8134457358-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="8134457358-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>We must be careful how we use <code class="inline">++</code> in a loop. First is how not to use it:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_reverse</span><span class="p" data-group-id="0249686334-1">(</span><span class="p" data-group-id="0249686334-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0249686334-2">]</span><span class="p" data-group-id="0249686334-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">naive_reverse</span><span class="p" data-group-id="0249686334-3">(</span><span class="n">T</span><span class="p" data-group-id="0249686334-3">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0249686334-4">[</span><span class="n">H</span><span class="p" data-group-id="0249686334-4">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">naive_reverse</span><span class="p" data-group-id="0249686334-5">(</span><span class="p" data-group-id="0249686334-6">[</span><span class="p" data-group-id="0249686334-6">]</span><span class="p" data-group-id="0249686334-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0249686334-7">[</span><span class="p" data-group-id="0249686334-7">]</span><span class="p">.</span></code></pre><p>As the <code class="inline">++</code> operator copies its left-hand side operand, the growing
│ │ │ -result is copied repeatedly, leading to quadratic complexity.</p><p>On the other hand, using <code class="inline">++</code> in loop like this is perfectly fine:</p><p><strong>OK</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8060143501-1">(</span><span class="n">List</span><span class="p" data-group-id="8060143501-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8060143501-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8060143501-3">[</span><span class="p" data-group-id="8060143501-3">]</span><span class="p" data-group-id="8060143501-2">)</span><span class="p">.</span><span class="w">
│ │ │ +seen if we do our own implementation in Erlang:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_plus_plus</span><span class="p" data-group-id="0047171107-1">(</span><span class="p" data-group-id="0047171107-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0047171107-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0047171107-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0047171107-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="0047171107-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0047171107-4">)</span><span class="p" data-group-id="0047171107-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">my_plus_plus</span><span class="p" data-group-id="0047171107-5">(</span><span class="p" data-group-id="0047171107-6">[</span><span class="p" data-group-id="0047171107-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0047171107-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>We must be careful how we use <code class="inline">++</code> in a loop. First is how not to use it:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_reverse</span><span class="p" data-group-id="0893084498-1">(</span><span class="p" data-group-id="0893084498-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0893084498-2">]</span><span class="p" data-group-id="0893084498-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">naive_reverse</span><span class="p" data-group-id="0893084498-3">(</span><span class="n">T</span><span class="p" data-group-id="0893084498-3">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0893084498-4">[</span><span class="n">H</span><span class="p" data-group-id="0893084498-4">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">naive_reverse</span><span class="p" data-group-id="0893084498-5">(</span><span class="p" data-group-id="0893084498-6">[</span><span class="p" data-group-id="0893084498-6">]</span><span class="p" data-group-id="0893084498-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0893084498-7">[</span><span class="p" data-group-id="0893084498-7">]</span><span class="p">.</span></code></pre><p>As the <code class="inline">++</code> operator copies its left-hand side operand, the growing
│ │ │ +result is copied repeatedly, leading to quadratic complexity.</p><p>On the other hand, using <code class="inline">++</code> in loop like this is perfectly fine:</p><p><strong>OK</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7605923332-1">(</span><span class="n">List</span><span class="p" data-group-id="7605923332-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7605923332-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7605923332-3">[</span><span class="p" data-group-id="7605923332-3">]</span><span class="p" data-group-id="7605923332-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8060143501-4">(</span><span class="p" data-group-id="8060143501-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8060143501-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8060143501-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8060143501-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8060143501-7">[</span><span class="n">H</span><span class="p" data-group-id="8060143501-7">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8060143501-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="8060143501-8">(</span><span class="p" data-group-id="8060143501-9">[</span><span class="p" data-group-id="8060143501-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="8060143501-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7605923332-4">(</span><span class="p" data-group-id="7605923332-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7605923332-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7605923332-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7605923332-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7605923332-7">[</span><span class="n">H</span><span class="p" data-group-id="7605923332-7">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7605923332-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">naive_but_ok_reverse</span><span class="p" data-group-id="7605923332-8">(</span><span class="p" data-group-id="7605923332-9">[</span><span class="p" data-group-id="7605923332-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="7605923332-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>Each list element is copied only once. The growing result <code class="inline">Acc</code> is the right-hand
│ │ │ -side operand, which it is <em>not</em> copied.</p><p>Experienced Erlang programmers would probably write as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">vanilla_reverse</span><span class="p" data-group-id="9919350799-1">(</span><span class="p" data-group-id="9919350799-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9919350799-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9919350799-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="9919350799-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9919350799-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="9919350799-4">]</span><span class="p" data-group-id="9919350799-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="9919350799-5">(</span><span class="p" data-group-id="9919350799-6">[</span><span class="p" data-group-id="9919350799-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9919350799-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +side operand, which it is <em>not</em> copied.</p><p>Experienced Erlang programmers would probably write as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">vanilla_reverse</span><span class="p" data-group-id="2470383409-1">(</span><span class="p" data-group-id="2470383409-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2470383409-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2470383409-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="2470383409-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2470383409-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="2470383409-4">]</span><span class="p" data-group-id="2470383409-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">vanilla_reverse</span><span class="p" data-group-id="2470383409-5">(</span><span class="p" data-group-id="2470383409-6">[</span><span class="p" data-group-id="2470383409-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2470383409-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">.</span></code></pre><p>In principle, this is slightly more efficient because the list element <code class="inline">[H]</code>
│ │ │  is not built before being copied and discarded. In practice, the compiler
│ │ │  rewrites <code class="inline">[H] ++ Acc</code> to <code class="inline">[H|Acc]</code>.</p><h2 id="timer-module" class="section-heading">
│ │ │    <a href="#timer-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Timer Module</span>
│ │ │ @@ -160,77 +160,77 @@
│ │ │  therefore harmless.</p><h2 id="accidental-copying-and-loss-of-sharing" class="section-heading">
│ │ │    <a href="#accidental-copying-and-loss-of-sharing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Accidental Copying and Loss of Sharing</span>
│ │ │  </h2>
│ │ │  <p>When spawning a new process using a fun, one can accidentally copy more data to
│ │ │ -the process than intended. For example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental1</span><span class="p" data-group-id="8374230438-1">(</span><span class="n">State</span><span class="p" data-group-id="8374230438-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="8374230438-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8374230438-3">(</span><span class="p" data-group-id="8374230438-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8374230438-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8374230438-5">[</span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p" data-group-id="8374230438-5">]</span><span class="p" data-group-id="8374230438-4">)</span><span class="w">
│ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="8374230438-2">)</span><span class="p">.</span></code></pre><p>The code in the fun will extract one element from the record and print it. The
│ │ │ +the process than intended. For example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental1</span><span class="p" data-group-id="2883024613-1">(</span><span class="n">State</span><span class="p" data-group-id="2883024613-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="2883024613-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2883024613-3">(</span><span class="p" data-group-id="2883024613-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2883024613-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2883024613-5">[</span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p" data-group-id="2883024613-5">]</span><span class="p" data-group-id="2883024613-4">)</span><span class="w">
│ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="2883024613-2">)</span><span class="p">.</span></code></pre><p>The code in the fun will extract one element from the record and print it. The
│ │ │  rest of the <code class="inline">state</code> record is not used. However, when the <a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn/1"><code class="inline">spawn/1</code></a>
│ │ │ -function is executed, the entire record is copied to the newly created process.</p><p>The same kind of problem can happen with a map:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental2</span><span class="p" data-group-id="4230131302-1">(</span><span class="n">State</span><span class="p" data-group-id="4230131302-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="4230131302-2">(</span><span class="nf">fun</span><span class="p" data-group-id="4230131302-3">(</span><span class="p" data-group-id="4230131302-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4230131302-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4230131302-5">[</span><span class="nf">map_get</span><span class="p" data-group-id="4230131302-6">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4230131302-6">)</span><span class="p" data-group-id="4230131302-5">]</span><span class="p" data-group-id="4230131302-4">)</span><span class="w">
│ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="4230131302-2">)</span><span class="p">.</span></code></pre><p>In the following example (part of a module implementing the <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ -behavior) the created fun is sent to another process:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="8736523109-1">(</span><span class="ss">give_me_a_fun</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8736523109-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8736523109-2">(</span><span class="p" data-group-id="8736523109-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="nb">size</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8736523109-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8736523109-3">}</span><span class="p">.</span></code></pre><p>How bad that unnecessary copy is depends on the contents of the record or the
│ │ │ -map.</p><p>For example, if the <code class="inline">state</code> record is initialized like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init1</span><span class="p" data-group-id="1508320835-1">(</span><span class="p" data-group-id="1508320835-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="1508320835-2">{</span><span class="ss">data</span><span class="o">=</span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1508320835-3">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">10000</span><span class="p" data-group-id="1508320835-3">)</span><span class="p" data-group-id="1508320835-2">}</span><span class="p">.</span></code></pre><p>a list with 10000 elements (or about 20000 heap words) will be copied to the
│ │ │ +function is executed, the entire record is copied to the newly created process.</p><p>The same kind of problem can happen with a map:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">accidental2</span><span class="p" data-group-id="1932176279-1">(</span><span class="n">State</span><span class="p" data-group-id="1932176279-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="1932176279-2">(</span><span class="nf">fun</span><span class="p" data-group-id="1932176279-3">(</span><span class="p" data-group-id="1932176279-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1932176279-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1932176279-5">[</span><span class="nf">map_get</span><span class="p" data-group-id="1932176279-6">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1932176279-6">)</span><span class="p" data-group-id="1932176279-5">]</span><span class="p" data-group-id="1932176279-4">)</span><span class="w">
│ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="1932176279-2">)</span><span class="p">.</span></code></pre><p>In the following example (part of a module implementing the <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │ +behavior) the created fun is sent to another process:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="9384153326-1">(</span><span class="ss">give_me_a_fun</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9384153326-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9384153326-2">(</span><span class="p" data-group-id="9384153326-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="nb">size</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9384153326-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="9384153326-3">}</span><span class="p">.</span></code></pre><p>How bad that unnecessary copy is depends on the contents of the record or the
│ │ │ +map.</p><p>For example, if the <code class="inline">state</code> record is initialized like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init1</span><span class="p" data-group-id="9473629869-1">(</span><span class="p" data-group-id="9473629869-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="9473629869-2">{</span><span class="ss">data</span><span class="o">=</span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="9473629869-3">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">10000</span><span class="p" data-group-id="9473629869-3">)</span><span class="p" data-group-id="9473629869-2">}</span><span class="p">.</span></code></pre><p>a list with 10000 elements (or about 20000 heap words) will be copied to the
│ │ │  newly created process.</p><p>An unnecessary copy of 10000 element list can be bad enough, but it can get even
│ │ │  worse if the <code class="inline">state</code> record contains <em>shared subterms</em>. Here is a simple example
│ │ │ -of a term with a shared subterm:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4651361352-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="4651361352-1">}</span></code></pre><p>When a term is copied to another process, sharing of subterms will be lost and
│ │ │ -the copied term can be many times larger than the original term. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init2</span><span class="p" data-group-id="7037460584-1">(</span><span class="p" data-group-id="7037460584-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SharedSubTerms</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="7037460584-2">(</span><span class="nf">fun</span><span class="p" data-group-id="7037460584-3">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="7037460584-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7037460584-4">[</span><span class="n">A</span><span class="p">|</span><span class="n">A</span><span class="p" data-group-id="7037460584-4">]</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7037460584-5">[</span><span class="mi">0</span><span class="p" data-group-id="7037460584-5">]</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="7037460584-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p" data-group-id="7037460584-6">)</span><span class="p" data-group-id="7037460584-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="7037460584-7">{</span><span class="ss">data</span><span class="o">=</span><span class="n">Shared</span><span class="p" data-group-id="7037460584-7">}</span><span class="p">.</span></code></pre><p>In the process that calls <code class="inline">init2/0</code>, the size of the <code class="inline">data</code> field in the <code class="inline">state</code>
│ │ │ +of a term with a shared subterm:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5416646788-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="5416646788-1">}</span></code></pre><p>When a term is copied to another process, sharing of subterms will be lost and
│ │ │ +the copied term can be many times larger than the original term. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init2</span><span class="p" data-group-id="3960510609-1">(</span><span class="p" data-group-id="3960510609-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SharedSubTerms</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="3960510609-2">(</span><span class="nf">fun</span><span class="p" data-group-id="3960510609-3">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="3960510609-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3960510609-4">[</span><span class="n">A</span><span class="p">|</span><span class="n">A</span><span class="p" data-group-id="3960510609-4">]</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3960510609-5">[</span><span class="mi">0</span><span class="p" data-group-id="3960510609-5">]</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="3960510609-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">15</span><span class="p" data-group-id="3960510609-6">)</span><span class="p" data-group-id="3960510609-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="3960510609-7">{</span><span class="ss">data</span><span class="o">=</span><span class="n">Shared</span><span class="p" data-group-id="3960510609-7">}</span><span class="p">.</span></code></pre><p>In the process that calls <code class="inline">init2/0</code>, the size of the <code class="inline">data</code> field in the <code class="inline">state</code>
│ │ │  record will be 32 heap words. When the record is copied to the newly created
│ │ │  process, sharing will be lost and the size of the copied <code class="inline">data</code> field will be
│ │ │  131070 heap words. More details about
│ │ │  <a href="eff_guide_processes.html#loss-of-sharing">loss off sharing</a> are found in a later
│ │ │  section.</p><p>To avoid the problem, outside of the fun extract only the fields of the record
│ │ │ -that are actually used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental1</span><span class="p" data-group-id="3190286482-1">(</span><span class="n">State</span><span class="p" data-group-id="3190286482-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +that are actually used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental1</span><span class="p" data-group-id="3814114905-1">(</span><span class="n">State</span><span class="p" data-group-id="3814114905-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">info</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="3190286482-2">(</span><span class="nf">fun</span><span class="p" data-group-id="3190286482-3">(</span><span class="p" data-group-id="3190286482-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3190286482-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3190286482-5">[</span><span class="n">Info</span><span class="p" data-group-id="3190286482-5">]</span><span class="p" data-group-id="3190286482-4">)</span><span class="w">
│ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="3190286482-2">)</span><span class="p">.</span></code></pre><p>Similarly, outside of the fun extract only the map elements that are actually
│ │ │ -used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental2</span><span class="p" data-group-id="7899868410-1">(</span><span class="n">State</span><span class="p" data-group-id="7899868410-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">map_get</span><span class="p" data-group-id="7899868410-2">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7899868410-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="7899868410-3">(</span><span class="nf">fun</span><span class="p" data-group-id="7899868410-4">(</span><span class="p" data-group-id="7899868410-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7899868410-5">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7899868410-6">[</span><span class="n">Info</span><span class="p" data-group-id="7899868410-6">]</span><span class="p" data-group-id="7899868410-5">)</span><span class="w">
│ │ │ -          </span><span class="k">end</span><span class="p" data-group-id="7899868410-3">)</span><span class="p">.</span></code></pre><h2 id="list_to_atom-1" class="section-heading">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="3814114905-2">(</span><span class="nf">fun</span><span class="p" data-group-id="3814114905-3">(</span><span class="p" data-group-id="3814114905-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3814114905-4">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3814114905-5">[</span><span class="n">Info</span><span class="p" data-group-id="3814114905-5">]</span><span class="p" data-group-id="3814114905-4">)</span><span class="w">
│ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="3814114905-2">)</span><span class="p">.</span></code></pre><p>Similarly, outside of the fun extract only the map elements that are actually
│ │ │ +used:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">fixed_accidental2</span><span class="p" data-group-id="0751161521-1">(</span><span class="n">State</span><span class="p" data-group-id="0751161521-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Info</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">map_get</span><span class="p" data-group-id="0751161521-2">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0751161521-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="0751161521-3">(</span><span class="nf">fun</span><span class="p" data-group-id="0751161521-4">(</span><span class="p" data-group-id="0751161521-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0751161521-5">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="s">\n&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0751161521-6">[</span><span class="n">Info</span><span class="p" data-group-id="0751161521-6">]</span><span class="p" data-group-id="0751161521-5">)</span><span class="w">
│ │ │ +          </span><span class="k">end</span><span class="p" data-group-id="0751161521-3">)</span><span class="p">.</span></code></pre><h2 id="list_to_atom-1" class="section-heading">
│ │ │    <a href="#list_to_atom-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">list_to_atom/1</span>
│ │ │  </h2>
│ │ │  <p>Atoms are not garbage-collected. Once an atom is created, it is never removed.
│ │ │  The emulator terminates if the limit for the number of atoms (1,048,576 by
│ │ │  default) is reached.</p><p>Therefore, converting arbitrary input strings to atoms can be dangerous in a
│ │ │  system that runs continuously. If only certain well-defined atoms are allowed as
│ │ │  input, <a href="../../erts-15.2.7.8/doc/html/erlang.html#list_to_existing_atom/1"><code class="inline">list_to_existing_atom/1</code></a> or
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#binary_to_existing_atom/1"><code class="inline">binary_to_existing_atom/1</code></a> can be used
│ │ │  to guard against a denial-of-service attack. (All atoms that are allowed must
│ │ │  have been created earlier, for example, by using all of them in a module
│ │ │  and loading that module.)</p><p>Using <a href="../../erts-15.2.7.8/doc/html/erlang.html#list_to_atom/1"><code class="inline">list_to_atom/1</code></a> to construct an atom that
│ │ │ -is passed to <a href="../../erts-15.2.7.8/doc/html/erlang.html#apply/3"><code class="inline">apply/3</code></a> is quite expensive.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">apply</span><span class="p" data-group-id="8336369129-1">(</span><span class="nf">list_to_atom</span><span class="p" data-group-id="8336369129-2">(</span><span class="s">&quot;some_prefix&quot;</span><span class="o">++</span><span class="n">Var</span><span class="p" data-group-id="8336369129-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="8336369129-1">)</span></code></pre><h2 id="length-1" class="section-heading">
│ │ │ +is passed to <a href="../../erts-15.2.7.8/doc/html/erlang.html#apply/3"><code class="inline">apply/3</code></a> is quite expensive.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">apply</span><span class="p" data-group-id="7807663417-1">(</span><span class="nf">list_to_atom</span><span class="p" data-group-id="7807663417-2">(</span><span class="s">&quot;some_prefix&quot;</span><span class="o">++</span><span class="n">Var</span><span class="p" data-group-id="7807663417-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="7807663417-1">)</span></code></pre><h2 id="length-1" class="section-heading">
│ │ │    <a href="#length-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">length/1</span>
│ │ │  </h2>
│ │ │  <p>The time for calculating the length of a list is proportional to the length of
│ │ │  the list, as opposed to <a href="../../erts-15.2.7.8/doc/html/erlang.html#tuple_size/1"><code class="inline">tuple_size/1</code></a>,
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#byte_size/1"><code class="inline">byte_size/1</code></a>, and <a href="../../erts-15.2.7.8/doc/html/erlang.html#bit_size/1"><code class="inline">bit_size/1</code></a>, which all
│ │ │  execute in constant time.</p><p>Normally, there is no need to worry about the speed of <a href="../../erts-15.2.7.8/doc/html/erlang.html#length/1"><code class="inline">length/1</code></a>,
│ │ │  because it is efficiently implemented in C. In time-critical code, you might
│ │ │  want to avoid it if the input list could potentially be very long.</p><p>Some uses of <a href="../../erts-15.2.7.8/doc/html/erlang.html#length/1"><code class="inline">length/1</code></a> can be replaced by matching. For example,
│ │ │ -the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="9572692470-1">(</span><span class="n">L</span><span class="p" data-group-id="9572692470-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9572692470-2">(</span><span class="n">L</span><span class="p" data-group-id="9572692470-2">)</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="5525914587-1">(</span><span class="p" data-group-id="5525914587-2">[</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="5525914587-2">]</span><span class="o">=</span><span class="n">L</span><span class="p" data-group-id="5525914587-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="2292948947-1">(</span><span class="n">L</span><span class="p" data-group-id="2292948947-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="2292948947-2">(</span><span class="n">L</span><span class="p" data-group-id="2292948947-2">)</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="0334788560-1">(</span><span class="p" data-group-id="0334788560-2">[</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="0334788560-2">]</span><span class="o">=</span><span class="n">L</span><span class="p" data-group-id="0334788560-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>One slight difference is that <a href="../../erts-15.2.7.8/doc/html/erlang.html#length/1"><code class="inline">length(L)</code></a> fails if <code class="inline">L</code> is an
│ │ │  improper list, while the pattern in the second code fragment accepts an improper
│ │ │  list.</p><h2 id="setelement-3" class="section-heading">
│ │ │    <a href="#setelement-3" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">setelement/3</span>
│ │ │ @@ -238,18 +238,18 @@
│ │ │  <p><a href="../../erts-15.2.7.8/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> copies the tuple it modifies. Therefore,
│ │ │  updating a tuple in a loop using <a href="../../erts-15.2.7.8/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> creates a new
│ │ │  copy of the tuple every time.</p><p>There is one exception to the rule that the tuple is copied. If the compiler
│ │ │  clearly can see that destructively updating the tuple would give the same result
│ │ │  as if the tuple was copied, the call to <a href="../../erts-15.2.7.8/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> is
│ │ │  replaced with a special destructive <code class="inline">setelement</code> instruction. In the following
│ │ │  code sequence, the first <a href="../../erts-15.2.7.8/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> call copies the tuple
│ │ │ -and modifies the ninth element:</p><pre><code class="makeup erlang" translate="no"><span class="nf">multiple_setelement</span><span class="p" data-group-id="7763064647-1">(</span><span class="n">T0</span><span class="p" data-group-id="7763064647-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="7763064647-2">(</span><span class="n">T0</span><span class="p" data-group-id="7763064647-2">)</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">T1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="7763064647-3">(</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p" data-group-id="7763064647-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">T2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="7763064647-4">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="ss">foobar</span><span class="p" data-group-id="7763064647-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">setelement</span><span class="p" data-group-id="7763064647-5">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p">,</span><span class="w"> </span><span class="ss">new_value</span><span class="p" data-group-id="7763064647-5">)</span><span class="p">.</span></code></pre><p>The two following <a href="../../erts-15.2.7.8/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> calls modify the tuple in
│ │ │ +and modifies the ninth element:</p><pre><code class="makeup erlang" translate="no"><span class="nf">multiple_setelement</span><span class="p" data-group-id="9844940613-1">(</span><span class="n">T0</span><span class="p" data-group-id="9844940613-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="9844940613-2">(</span><span class="n">T0</span><span class="p" data-group-id="9844940613-2">)</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">9</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">T1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="9844940613-3">(</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="n">T0</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p" data-group-id="9844940613-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">T2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="9844940613-4">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="ss">foobar</span><span class="p" data-group-id="9844940613-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">setelement</span><span class="p" data-group-id="9844940613-5">(</span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p">,</span><span class="w"> </span><span class="ss">new_value</span><span class="p" data-group-id="9844940613-5">)</span><span class="p">.</span></code></pre><p>The two following <a href="../../erts-15.2.7.8/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> calls modify the tuple in
│ │ │  place.</p><p>For the optimization to be applied, <em>all</em> the following conditions must be true:</p><ul><li>The tuple argument must be known to be a tuple of a known size.</li><li>The indices must be integer literals, not variables or expressions.</li><li>The indices must be given in descending order.</li><li>There must be no calls to another function in between the calls to
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a>.</li><li>The tuple returned from one <a href="../../erts-15.2.7.8/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a> call must only be
│ │ │  used in the subsequent call to <a href="../../erts-15.2.7.8/doc/html/erlang.html#setelement/3"><code class="inline">setelement/3</code></a>.</li></ul><p>If the code cannot be structured as in the <code class="inline">multiple_setelement/1</code> example, the
│ │ │  best way to modify multiple elements in a large tuple is to convert the tuple to
│ │ │  a list, modify the list, and convert it back to a tuple.</p><h2 id="size-1" class="section-heading">
│ │ │    <a href="#size-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/conc_prog.html
│ │ │ @@ -132,107 +132,107 @@
│ │ │  threads of execution in an Erlang program and to allow these threads to
│ │ │  communicate with each other. In Erlang, each thread of execution is called a
│ │ │  <em>process</em>.</p><p>(Aside: the term &quot;process&quot; is usually used when the threads of execution share
│ │ │  no data with each other and the term &quot;thread&quot; when they share data in some way.
│ │ │  Threads of execution in Erlang share no data, that is why they are called
│ │ │  processes).</p><p>The Erlang BIF <code class="inline">spawn</code> is used to create a new process:
│ │ │  <code class="inline">spawn(Module, Exported_Function, List of Arguments)</code>. Consider the following
│ │ │ -module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5478117019-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="5478117019-1">)</span><span class="p">.</span><span class="w">
│ │ │ +module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4797179019-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="4797179019-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5478117019-2">(</span><span class="p" data-group-id="5478117019-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5478117019-3">]</span><span class="p" data-group-id="5478117019-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4797179019-2">(</span><span class="p" data-group-id="4797179019-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4797179019-3">]</span><span class="p" data-group-id="4797179019-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">say_something</span><span class="p" data-group-id="5478117019-4">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5478117019-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">say_something</span><span class="p" data-group-id="4797179019-4">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4797179019-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">done</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">say_something</span><span class="p" data-group-id="5478117019-5">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="p" data-group-id="5478117019-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5478117019-6">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5478117019-7">[</span><span class="n">What</span><span class="p" data-group-id="5478117019-7">]</span><span class="p" data-group-id="5478117019-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">say_something</span><span class="p" data-group-id="5478117019-8">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5478117019-8">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="5478117019-9">(</span><span class="p" data-group-id="5478117019-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5478117019-10">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5478117019-11">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5478117019-11">]</span><span class="p" data-group-id="5478117019-10">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5478117019-12">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5478117019-13">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5478117019-13">]</span><span class="p" data-group-id="5478117019-12">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="9871283134-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="9871283134-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9871283134-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut14</span><span class="p" data-group-id="9871283134-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">say_something</span><span class="p" data-group-id="9871283134-3">(</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9871283134-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">say_something</span><span class="p" data-group-id="4797179019-5">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="p" data-group-id="4797179019-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4797179019-6">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4797179019-7">[</span><span class="n">What</span><span class="p" data-group-id="4797179019-7">]</span><span class="p" data-group-id="4797179019-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">say_something</span><span class="p" data-group-id="4797179019-8">(</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="n">Times</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4797179019-8">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="4797179019-9">(</span><span class="p" data-group-id="4797179019-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="4797179019-10">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4797179019-11">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4797179019-11">]</span><span class="p" data-group-id="4797179019-10">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="4797179019-12">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4797179019-13">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4797179019-13">]</span><span class="p" data-group-id="4797179019-12">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="7564836624-1">(</span><span class="ss">tut14</span><span class="p" data-group-id="7564836624-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7564836624-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut14</span><span class="p" data-group-id="7564836624-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">say_something</span><span class="p" data-group-id="7564836624-3">(</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7564836624-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">done</span></code></pre><p>As shown, the function <code class="inline">say_something</code> writes its first argument the number of
│ │ │  times specified by second argument. The function <code class="inline">start</code> starts two Erlang
│ │ │  processes, one that writes &quot;hello&quot; three times and one that writes &quot;goodbye&quot;
│ │ │  three times. Both processes use the function <code class="inline">say_something</code>. Notice that a
│ │ │  function used in this way by <code class="inline">spawn</code>, to start a process, must be exported from
│ │ │ -the module (that is, in the <code class="inline">-export</code> at the start of the module).</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9934760536-1">(</span><span class="p" data-group-id="9934760536-1">)</span><span class="p">.</span><span class="w">
│ │ │ +the module (that is, in the <code class="inline">-export</code> at the start of the module).</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nc">tut14</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3935344885-1">(</span><span class="p" data-group-id="3935344885-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.63</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">goodbye</span></code></pre><p>Notice that it did not write &quot;hello&quot; three times and then &quot;goodbye&quot; three times.
│ │ │  Instead, the first process wrote a &quot;hello&quot;, the second a &quot;goodbye&quot;, the first
│ │ │  another &quot;hello&quot; and so forth. But where did the <code class="inline">&lt;0.63.0&gt;</code> come from? The return
│ │ │  value of a function is the return value of the last &quot;thing&quot; in the function. The
│ │ │ -last thing in the function <code class="inline">start</code> is</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="7055095217-1">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7055095217-2">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7055095217-2">]</span><span class="p" data-group-id="7055095217-1">)</span><span class="p">.</span></code></pre><p><code class="inline">spawn</code> returns a <em>process identifier</em>, or <em>pid</em>, which uniquely identifies the
│ │ │ +last thing in the function <code class="inline">start</code> is</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="8206485967-1">(</span><span class="ss">tut14</span><span class="p">,</span><span class="w"> </span><span class="ss">say_something</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8206485967-2">[</span><span class="ss">goodbye</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8206485967-2">]</span><span class="p" data-group-id="8206485967-1">)</span><span class="p">.</span></code></pre><p><code class="inline">spawn</code> returns a <em>process identifier</em>, or <em>pid</em>, which uniquely identifies the
│ │ │  process. So <code class="inline">&lt;0.63.0&gt;</code> is the pid of the <code class="inline">spawn</code> function call above. The next
│ │ │  example shows how to use pids.</p><p>Notice also that ~p is used instead of ~w in <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a>. To quote <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#tilde_p">the manual</a>:</p><blockquote><p>~p Writes the data with standard syntax in the same way as ~w, but breaks terms
│ │ │  whose printed representation is longer than one line into many lines and indents
│ │ │  each line sensibly. It also tries to detect flat lists of printable characters and
│ │ │  to output these as strings</p></blockquote><h2 id="message-passing" class="section-heading">
│ │ │    <a href="#message-passing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Message Passing</span>
│ │ │  </h2>
│ │ │  <p>In the following example two processes are created and they send messages to
│ │ │ -each other a number of times.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4915356626-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="4915356626-1">)</span><span class="p">.</span><span class="w">
│ │ │ +each other a number of times.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7457988035-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="7457988035-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4915356626-2">(</span><span class="p" data-group-id="4915356626-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4915356626-3">]</span><span class="p" data-group-id="4915356626-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7457988035-2">(</span><span class="p" data-group-id="7457988035-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7457988035-3">]</span><span class="p" data-group-id="7457988035-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="4915356626-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="4915356626-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="7457988035-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="7457988035-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4915356626-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4915356626-6">[</span><span class="p" data-group-id="4915356626-6">]</span><span class="p" data-group-id="4915356626-5">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7457988035-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7457988035-6">[</span><span class="p" data-group-id="7457988035-6">]</span><span class="p" data-group-id="7457988035-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="4915356626-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="4915356626-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4915356626-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4915356626-9">(</span><span class="p" data-group-id="4915356626-9">)</span><span class="p" data-group-id="4915356626-8">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="7457988035-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="7457988035-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7457988035-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7457988035-9">(</span><span class="p" data-group-id="7457988035-9">)</span><span class="p" data-group-id="7457988035-8">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4915356626-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4915356626-11">[</span><span class="p" data-group-id="4915356626-11">]</span><span class="p" data-group-id="4915356626-10">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7457988035-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7457988035-11">[</span><span class="p" data-group-id="7457988035-11">]</span><span class="p" data-group-id="7457988035-10">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="4915356626-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="4915356626-12">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="7457988035-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="7457988035-12">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="4915356626-13">(</span><span class="p" data-group-id="4915356626-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="7457988035-13">(</span><span class="p" data-group-id="7457988035-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4915356626-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4915356626-15">[</span><span class="p" data-group-id="4915356626-15">]</span><span class="p" data-group-id="4915356626-14">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4915356626-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="4915356626-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4915356626-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4915356626-18">[</span><span class="p" data-group-id="4915356626-18">]</span><span class="p" data-group-id="4915356626-17">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7457988035-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7457988035-15">[</span><span class="p" data-group-id="7457988035-15">]</span><span class="p" data-group-id="7457988035-14">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7457988035-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="7457988035-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7457988035-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7457988035-18">[</span><span class="p" data-group-id="7457988035-18">]</span><span class="p" data-group-id="7457988035-17">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="4915356626-19">(</span><span class="p" data-group-id="4915356626-19">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="7457988035-19">(</span><span class="p" data-group-id="7457988035-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="4915356626-20">(</span><span class="p" data-group-id="4915356626-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="4915356626-21">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4915356626-22">[</span><span class="p" data-group-id="4915356626-22">]</span><span class="p" data-group-id="4915356626-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="4915356626-23">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4915356626-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="4915356626-24">]</span><span class="p" data-group-id="4915356626-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="6496141981-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="6496141981-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6496141981-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut15</span><span class="p" data-group-id="6496141981-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">tut15</span><span class="p">:</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="6496141981-3">(</span><span class="p" data-group-id="6496141981-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="7457988035-20">(</span><span class="p" data-group-id="7457988035-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7457988035-21">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7457988035-22">[</span><span class="p" data-group-id="7457988035-22">]</span><span class="p" data-group-id="7457988035-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="7457988035-23">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7457988035-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="7457988035-24">]</span><span class="p" data-group-id="7457988035-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="4675673562-1">(</span><span class="ss">tut15</span><span class="p" data-group-id="4675673562-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4675673562-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut15</span><span class="p" data-group-id="4675673562-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">tut15</span><span class="p">:</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="4675673562-3">(</span><span class="p" data-group-id="4675673562-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.36</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span><span class="w">
│ │ │ -</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>The function <code class="inline">start</code> first creates a process, let us call it &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7958087999-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7958087999-2">[</span><span class="p" data-group-id="7958087999-2">]</span><span class="p" data-group-id="7958087999-1">)</span></code></pre><p>This process executes <code class="inline">tut15:pong()</code>. <code class="inline">Pong_PID</code> is the process identity of the
│ │ │ -&quot;pong&quot; process. The function <code class="inline">start</code> now creates another process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="8129901460-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8129901460-2">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="8129901460-2">]</span><span class="p" data-group-id="8129901460-1">)</span><span class="p">,</span></code></pre><p>This process executes:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="0424110031-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="0424110031-1">)</span></code></pre><p><code class="inline">&lt;0.36.0&gt;</code> is the return value from the <code class="inline">start</code> function.</p><p>The process &quot;pong&quot; now does:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ +</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>The function <code class="inline">start</code> first creates a process, let us call it &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="4914115727-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4914115727-2">[</span><span class="p" data-group-id="4914115727-2">]</span><span class="p" data-group-id="4914115727-1">)</span></code></pre><p>This process executes <code class="inline">tut15:pong()</code>. <code class="inline">Pong_PID</code> is the process identity of the
│ │ │ +&quot;pong&quot; process. The function <code class="inline">start</code> now creates another process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="5725276317-1">(</span><span class="ss">tut15</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5725276317-2">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="5725276317-2">]</span><span class="p" data-group-id="5725276317-1">)</span><span class="p">,</span></code></pre><p>This process executes:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="4366661248-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="4366661248-1">)</span></code></pre><p><code class="inline">&lt;0.36.0&gt;</code> is the return value from the <code class="inline">start</code> function.</p><p>The process &quot;pong&quot; now does:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │      </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9909689402-1">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9909689402-2">[</span><span class="p" data-group-id="9909689402-2">]</span><span class="p" data-group-id="9909689402-1">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9909689402-3">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9909689402-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9909689402-4">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9909689402-5">[</span><span class="p" data-group-id="9909689402-5">]</span><span class="p" data-group-id="9909689402-4">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4689753217-1">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4689753217-2">[</span><span class="p" data-group-id="4689753217-2">]</span><span class="p" data-group-id="4689753217-1">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4689753217-3">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="4689753217-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4689753217-4">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4689753217-5">[</span><span class="p" data-group-id="4689753217-5">]</span><span class="p" data-group-id="4689753217-4">)</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="nf">pong</span><span class="p" data-group-id="9909689402-6">(</span><span class="p" data-group-id="9909689402-6">)</span><span class="w">
│ │ │ +        </span><span class="nf">pong</span><span class="p" data-group-id="4689753217-6">(</span><span class="p" data-group-id="4689753217-6">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">receive</code> construct is used to allow processes to wait for messages from
│ │ │  other processes. It has the following format:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │     </span><span class="ss">pattern1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │         </span><span class="ss">actions1</span><span class="p">;</span><span class="w">
│ │ │     </span><span class="ss">pattern2</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │         </span><span class="ss">actions2</span><span class="p">;</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ @@ -253,84 +253,84 @@
│ │ │  queue (keeping the first message and any other messages in the queue). If the
│ │ │  second message does not match, the third message is tried, and so on, until the
│ │ │  end of the queue is reached. If the end of the queue is reached, the process
│ │ │  blocks (stops execution) and waits until a new message is received and this
│ │ │  procedure is repeated.</p><p>The Erlang implementation is &quot;clever&quot; and minimizes the number of times each
│ │ │  message is tested against the patterns in each <code class="inline">receive</code>.</p><p>Now back to the ping pong example.</p><p>&quot;Pong&quot; is waiting for messages. If the atom <code class="inline">finished</code> is received, &quot;pong&quot;
│ │ │  writes &quot;Pong finished&quot; to the output and, as it has nothing more to do,
│ │ │ -terminates. If it receives a message with the format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9000610428-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9000610428-1">}</span></code></pre><p>it writes &quot;Pong received ping&quot; to the output and sends the atom <code class="inline">pong</code> to the
│ │ │ +terminates. If it receives a message with the format:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2456667782-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2456667782-1">}</span></code></pre><p>it writes &quot;Pong received ping&quot; to the output and sends the atom <code class="inline">pong</code> to the
│ │ │  process &quot;ping&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span></code></pre><p>Notice how the operator &quot;!&quot; is used to send messages. The syntax of &quot;!&quot; is:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Message</span></code></pre><p>That is, <code class="inline">Message</code> (any Erlang term) is sent to the process with identity <code class="inline">Pid</code>.</p><p>After sending the message <code class="inline">pong</code> to the process &quot;ping&quot;, &quot;pong&quot; calls the <code class="inline">pong</code>
│ │ │  function again, which causes it to get back to the <code class="inline">receive</code> again and wait for
│ │ │ -another message.</p><p>Now let us look at the process &quot;ping&quot;. Recall that it was started by executing:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="3978743075-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="3978743075-1">)</span></code></pre><p>Looking at the function <code class="inline">ping/2</code>, the second clause of <code class="inline">ping/2</code> is executed
│ │ │ +another message.</p><p>Now let us look at the process &quot;ping&quot;. Recall that it was started by executing:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut15</span><span class="p">:</span><span class="nf">ping</span><span class="p" data-group-id="8127583841-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="8127583841-1">)</span></code></pre><p>Looking at the function <code class="inline">ping/2</code>, the second clause of <code class="inline">ping/2</code> is executed
│ │ │  since the value of the first argument is 3 (not 0) (first clause head is
│ │ │ -<code class="inline">ping(0,Pong_PID)</code>, second clause head is <code class="inline">ping(N,Pong_PID)</code>, so <code class="inline">N</code> becomes 3).</p><p>The second clause sends a message to &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4912626860-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4912626860-2">(</span><span class="p" data-group-id="4912626860-2">)</span><span class="p" data-group-id="4912626860-1">}</span><span class="p">,</span></code></pre><p><a href="../../erts-15.2.7.8/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the pid of the process that executes <a href="../../erts-15.2.7.8/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a>, in this case the
│ │ │ +<code class="inline">ping(0,Pong_PID)</code>, second clause head is <code class="inline">ping(N,Pong_PID)</code>, so <code class="inline">N</code> becomes 3).</p><p>The second clause sends a message to &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7250621210-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7250621210-2">(</span><span class="p" data-group-id="7250621210-2">)</span><span class="p" data-group-id="7250621210-1">}</span><span class="p">,</span></code></pre><p><a href="../../erts-15.2.7.8/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the pid of the process that executes <a href="../../erts-15.2.7.8/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a>, in this case the
│ │ │  pid of &quot;ping&quot;. (Recall the code for &quot;pong&quot;, this lands up in the variable
│ │ │  <code class="inline">Ping_PID</code> in the <code class="inline">receive</code> previously explained.)</p><p>&quot;Ping&quot; now waits for a reply from &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │      </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7004220457-1">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7004220457-2">[</span><span class="p" data-group-id="7004220457-2">]</span><span class="p" data-group-id="7004220457-1">)</span><span class="w">
│ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0467475781-1">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0467475781-2">[</span><span class="p" data-group-id="0467475781-2">]</span><span class="p" data-group-id="0467475781-1">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre><p>It writes &quot;Ping received pong&quot; when this reply arrives, after which &quot;ping&quot; calls
│ │ │ -the <code class="inline">ping</code> function again.</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="8397355194-1">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="8397355194-1">)</span></code></pre><p><code class="inline">N-1</code> causes the first argument to be decremented until it becomes 0. When this
│ │ │ -occurs, the first clause of <code class="inline">ping/2</code> is executed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="2952281769-1">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="2952281769-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +the <code class="inline">ping</code> function again.</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="6905731554-1">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="6905731554-1">)</span></code></pre><p><code class="inline">N-1</code> causes the first argument to be decremented until it becomes 0. When this
│ │ │ +occurs, the first clause of <code class="inline">ping/2</code> is executed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">ping</span><span class="p" data-group-id="8792171439-1">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_PID</span><span class="p" data-group-id="8792171439-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Pong_PID</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2952281769-2">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2952281769-3">[</span><span class="p" data-group-id="2952281769-3">]</span><span class="p" data-group-id="2952281769-2">)</span><span class="p">;</span></code></pre><p>The atom <code class="inline">finished</code> is sent to &quot;pong&quot; (causing it to terminate as described
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8792171439-2">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8792171439-3">[</span><span class="p" data-group-id="8792171439-3">]</span><span class="p" data-group-id="8792171439-2">)</span><span class="p">;</span></code></pre><p>The atom <code class="inline">finished</code> is sent to &quot;pong&quot; (causing it to terminate as described
│ │ │  above) and &quot;ping finished&quot; is written to the output. &quot;Ping&quot; then terminates as
│ │ │  it has nothing left to do.</p><h2 id="registered-process-names" class="section-heading">
│ │ │    <a href="#registered-process-names" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Registered Process Names</span>
│ │ │  </h2>
│ │ │  <p>In the above example, &quot;pong&quot; was first created to be able to give the identity
│ │ │  of &quot;pong&quot; when &quot;ping&quot; was started. That is, in some way &quot;ping&quot; must be able to
│ │ │  know the identity of &quot;pong&quot; to be able to send a message to it. Sometimes
│ │ │  processes which need to know each other's identities are started independently
│ │ │  of each other. Erlang thus provides a mechanism for processes to be given names
│ │ │  so that these names can be used as identities instead of pids. This is done by
│ │ │ -using the <code class="inline">register</code> BIF:</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="9951800690-1">(</span><span class="ss">some_atom</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="9951800690-1">)</span></code></pre><p>Let us now rewrite the ping pong example using this and give the name <code class="inline">pong</code> to
│ │ │ -the &quot;pong&quot; process:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2568010551-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="2568010551-1">)</span><span class="p">.</span><span class="w">
│ │ │ +using the <code class="inline">register</code> BIF:</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="8258106719-1">(</span><span class="ss">some_atom</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="8258106719-1">)</span></code></pre><p>Let us now rewrite the ping pong example using this and give the name <code class="inline">pong</code> to
│ │ │ +the &quot;pong&quot; process:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5898173166-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="5898173166-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2568010551-2">(</span><span class="p" data-group-id="2568010551-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2568010551-3">]</span><span class="p" data-group-id="2568010551-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5898173166-2">(</span><span class="p" data-group-id="5898173166-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5898173166-3">]</span><span class="p" data-group-id="5898173166-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2568010551-4">(</span><span class="mi">0</span><span class="p" data-group-id="2568010551-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="5898173166-4">(</span><span class="mi">0</span><span class="p" data-group-id="5898173166-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2568010551-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2568010551-6">[</span><span class="p" data-group-id="2568010551-6">]</span><span class="p" data-group-id="2568010551-5">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5898173166-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5898173166-6">[</span><span class="p" data-group-id="5898173166-6">]</span><span class="p" data-group-id="5898173166-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2568010551-7">(</span><span class="n">N</span><span class="p" data-group-id="2568010551-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2568010551-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2568010551-9">(</span><span class="p" data-group-id="2568010551-9">)</span><span class="p" data-group-id="2568010551-8">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="5898173166-7">(</span><span class="n">N</span><span class="p" data-group-id="5898173166-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5898173166-8">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5898173166-9">(</span><span class="p" data-group-id="5898173166-9">)</span><span class="p" data-group-id="5898173166-8">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2568010551-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2568010551-11">[</span><span class="p" data-group-id="2568010551-11">]</span><span class="p" data-group-id="2568010551-10">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5898173166-10">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5898173166-11">[</span><span class="p" data-group-id="5898173166-11">]</span><span class="p" data-group-id="5898173166-10">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="2568010551-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2568010551-12">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="5898173166-12">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5898173166-12">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="2568010551-13">(</span><span class="p" data-group-id="2568010551-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="5898173166-13">(</span><span class="p" data-group-id="5898173166-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2568010551-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2568010551-15">[</span><span class="p" data-group-id="2568010551-15">]</span><span class="p" data-group-id="2568010551-14">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2568010551-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2568010551-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2568010551-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2568010551-18">[</span><span class="p" data-group-id="2568010551-18">]</span><span class="p" data-group-id="2568010551-17">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5898173166-14">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5898173166-15">[</span><span class="p" data-group-id="5898173166-15">]</span><span class="p" data-group-id="5898173166-14">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5898173166-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="5898173166-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5898173166-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5898173166-18">[</span><span class="p" data-group-id="5898173166-18">]</span><span class="p" data-group-id="5898173166-17">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="2568010551-19">(</span><span class="p" data-group-id="2568010551-19">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="5898173166-19">(</span><span class="p" data-group-id="5898173166-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2568010551-20">(</span><span class="p" data-group-id="2568010551-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="2568010551-21">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2568010551-22">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2568010551-23">[</span><span class="p" data-group-id="2568010551-23">]</span><span class="p" data-group-id="2568010551-22">)</span><span class="p" data-group-id="2568010551-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2568010551-24">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2568010551-25">[</span><span class="mi">3</span><span class="p" data-group-id="2568010551-25">]</span><span class="p" data-group-id="2568010551-24">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nf">c</span><span class="p" data-group-id="1603917982-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="1603917982-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1603917982-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut16</span><span class="p" data-group-id="1603917982-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">tut16</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1603917982-3">(</span><span class="p" data-group-id="1603917982-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="5898173166-20">(</span><span class="p" data-group-id="5898173166-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="5898173166-21">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5898173166-22">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5898173166-23">[</span><span class="p" data-group-id="5898173166-23">]</span><span class="p" data-group-id="5898173166-22">)</span><span class="p" data-group-id="5898173166-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5898173166-24">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5898173166-25">[</span><span class="mi">3</span><span class="p" data-group-id="5898173166-25">]</span><span class="p" data-group-id="5898173166-24">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nf">c</span><span class="p" data-group-id="1136342718-1">(</span><span class="ss">tut16</span><span class="p" data-group-id="1136342718-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1136342718-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut16</span><span class="p" data-group-id="1136342718-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">tut16</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1136342718-3">(</span><span class="p" data-group-id="1136342718-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.38</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span><span class="w">
│ │ │ -</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>Here the <code class="inline">start/0</code> function,</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="9326586265-1">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9326586265-2">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9326586265-3">[</span><span class="p" data-group-id="9326586265-3">]</span><span class="p" data-group-id="9326586265-2">)</span><span class="p" data-group-id="9326586265-1">)</span><span class="p">,</span></code></pre><p>both spawns the &quot;pong&quot; process and gives it the name <code class="inline">pong</code>. In the &quot;ping&quot;
│ │ │ -process, messages can be sent to <code class="inline">pong</code> by:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6461805513-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6461805513-2">(</span><span class="p" data-group-id="6461805513-2">)</span><span class="p" data-group-id="6461805513-1">}</span><span class="p">,</span></code></pre><p><code class="inline">ping/2</code> now becomes <code class="inline">ping/1</code> as the argument <code class="inline">Pong_PID</code> is not needed.</p><h2 id="distributed-programming" class="section-heading">
│ │ │ +</span><span class="n">Pong</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>Here the <code class="inline">start/0</code> function,</p><pre><code class="makeup erlang" translate="no"><span class="nf">register</span><span class="p" data-group-id="0293051573-1">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0293051573-2">(</span><span class="ss">tut16</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0293051573-3">[</span><span class="p" data-group-id="0293051573-3">]</span><span class="p" data-group-id="0293051573-2">)</span><span class="p" data-group-id="0293051573-1">)</span><span class="p">,</span></code></pre><p>both spawns the &quot;pong&quot; process and gives it the name <code class="inline">pong</code>. In the &quot;ping&quot;
│ │ │ +process, messages can be sent to <code class="inline">pong</code> by:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pong</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5449408006-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5449408006-2">(</span><span class="p" data-group-id="5449408006-2">)</span><span class="p" data-group-id="5449408006-1">}</span><span class="p">,</span></code></pre><p><code class="inline">ping/2</code> now becomes <code class="inline">ping/1</code> as the argument <code class="inline">Pong_PID</code> is not needed.</p><h2 id="distributed-programming" class="section-heading">
│ │ │    <a href="#distributed-programming" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Distributed Programming</span>
│ │ │  </h2>
│ │ │  <p>Let us rewrite the ping pong program with &quot;ping&quot; and &quot;pong&quot; on different
│ │ │  computers. First a few things are needed to set up to get this to work. The
│ │ │ @@ -350,106 +350,106 @@
│ │ │  of the file. This is a requirement.</p><p>When you start an Erlang system that is going to talk to other Erlang systems,
│ │ │  you must give it a name, for example:</p><pre><code class="text">$ erl -sname my_name</code></pre><p>We will see more details of this later. If you want to experiment with
│ │ │  distributed Erlang, but you only have one computer to work on, you can start two
│ │ │  separate Erlang systems on the same computer but give them different names. Each
│ │ │  Erlang system running on a computer is called an <em>Erlang node</em>.</p><p>(Note: <code class="inline">erl -sname</code> assumes that all nodes are in the same IP domain and we can
│ │ │  use only the first component of the IP address, if we want to use nodes in
│ │ │  different domains we use <code class="inline">-name</code> instead, but then all IP address must be given
│ │ │ -in full.)</p><p>Here is the ping pong example modified to run on two separate nodes:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1285879134-1">(</span><span class="ss">tut17</span><span class="p" data-group-id="1285879134-1">)</span><span class="p">.</span><span class="w">
│ │ │ +in full.)</p><p>Here is the ping pong example modified to run on two separate nodes:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5180414136-1">(</span><span class="ss">tut17</span><span class="p" data-group-id="5180414136-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1285879134-2">(</span><span class="p" data-group-id="1285879134-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1285879134-3">]</span><span class="p" data-group-id="1285879134-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5180414136-2">(</span><span class="p" data-group-id="5180414136-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5180414136-3">]</span><span class="p" data-group-id="5180414136-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="1285879134-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1285879134-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1285879134-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1285879134-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1285879134-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1285879134-7">[</span><span class="p" data-group-id="1285879134-7">]</span><span class="p" data-group-id="1285879134-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="5180414136-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5180414136-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5180414136-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5180414136-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5180414136-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5180414136-7">[</span><span class="p" data-group-id="5180414136-7">]</span><span class="p" data-group-id="5180414136-6">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="1285879134-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1285879134-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1285879134-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1285879134-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1285879134-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1285879134-11">(</span><span class="p" data-group-id="1285879134-11">)</span><span class="p" data-group-id="1285879134-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="5180414136-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5180414136-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5180414136-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5180414136-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5180414136-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5180414136-11">(</span><span class="p" data-group-id="5180414136-11">)</span><span class="p" data-group-id="5180414136-10">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1285879134-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1285879134-13">[</span><span class="p" data-group-id="1285879134-13">]</span><span class="p" data-group-id="1285879134-12">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5180414136-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5180414136-13">[</span><span class="p" data-group-id="5180414136-13">]</span><span class="p" data-group-id="5180414136-12">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="1285879134-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1285879134-14">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="5180414136-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5180414136-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="1285879134-15">(</span><span class="p" data-group-id="1285879134-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="5180414136-15">(</span><span class="p" data-group-id="5180414136-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1285879134-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1285879134-17">[</span><span class="p" data-group-id="1285879134-17">]</span><span class="p" data-group-id="1285879134-16">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="1285879134-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="1285879134-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1285879134-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1285879134-20">[</span><span class="p" data-group-id="1285879134-20">]</span><span class="p" data-group-id="1285879134-19">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5180414136-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5180414136-17">[</span><span class="p" data-group-id="5180414136-17">]</span><span class="p" data-group-id="5180414136-16">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5180414136-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="5180414136-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5180414136-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5180414136-20">[</span><span class="p" data-group-id="5180414136-20">]</span><span class="p" data-group-id="5180414136-19">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="1285879134-21">(</span><span class="p" data-group-id="1285879134-21">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="5180414136-21">(</span><span class="p" data-group-id="5180414136-21">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_pong</span><span class="p" data-group-id="1285879134-22">(</span><span class="p" data-group-id="1285879134-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="1285879134-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="1285879134-24">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1285879134-25">[</span><span class="p" data-group-id="1285879134-25">]</span><span class="p" data-group-id="1285879134-24">)</span><span class="p" data-group-id="1285879134-23">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_pong</span><span class="p" data-group-id="5180414136-22">(</span><span class="p" data-group-id="5180414136-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="5180414136-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5180414136-24">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5180414136-25">[</span><span class="p" data-group-id="5180414136-25">]</span><span class="p" data-group-id="5180414136-24">)</span><span class="p" data-group-id="5180414136-23">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_ping</span><span class="p" data-group-id="1285879134-26">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="1285879134-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1285879134-27">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1285879134-28">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="1285879134-28">]</span><span class="p" data-group-id="1285879134-27">)</span><span class="p">.</span></code></pre><p>Let us assume there are two computers called gollum and kosken. First a node is
│ │ │ +</span><span class="nf">start_ping</span><span class="p" data-group-id="5180414136-26">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="5180414136-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5180414136-27">(</span><span class="ss">tut17</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5180414136-28">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="5180414136-28">]</span><span class="p" data-group-id="5180414136-27">)</span><span class="p">.</span></code></pre><p>Let us assume there are two computers called gollum and kosken. First a node is
│ │ │  started on kosken, called ping, and then a node on gollum, called pong.</p><p>On kosken (on a Linux/UNIX system):</p><pre><code class="text">kosken&gt; erl -sname ping
│ │ │  Erlang (BEAM) emulator version 5.2.3.7 [hipe] [threads:0]
│ │ │  
│ │ │  Eshell V5.2.3.7  (abort with ^G)
│ │ │  (ping@kosken)1&gt;</code></pre><p>On gollum:</p><pre><code class="text">gollum&gt; erl -sname pong
│ │ │  Erlang (BEAM) emulator version 5.2.3.7 [hipe] [threads:0]
│ │ │  
│ │ │  Eshell V5.2.3.7  (abort with ^G)
│ │ │ -(pong@gollum)1&gt;</code></pre><p>Now the &quot;pong&quot; process on gollum is started:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_pong</span><span class="p" data-group-id="6134647489-1">(</span><span class="p" data-group-id="6134647489-1">)</span><span class="p">.</span><span class="w">
│ │ │ +(pong@gollum)1&gt;</code></pre><p>Now the &quot;pong&quot; process on gollum is started:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_pong</span><span class="p" data-group-id="6537658846-1">(</span><span class="p" data-group-id="6537658846-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><p>And the &quot;ping&quot; process on kosken is started (from the code above you can see
│ │ │  that a parameter of the <code class="inline">start_ping</code> function is the node name of the Erlang
│ │ │ -system where &quot;pong&quot; is running):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(ping@kosken)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_ping</span><span class="p" data-group-id="8601073787-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="8601073787-1">)</span><span class="p">.</span><span class="w">
│ │ │ +system where &quot;pong&quot; is running):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(ping@kosken)1&gt; </span><span class="nc">tut17</span><span class="p">:</span><span class="nf">start_ping</span><span class="p" data-group-id="1158156644-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="1158156644-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.37</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="ss">ping</span><span class="w"> </span><span class="ss">finished</span></code></pre><p>As shown, the ping pong program has run. On the &quot;pong&quot; side:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)2&gt; </span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="nf">finished</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7853535351-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="7853535351-1">)</span><span class="mi">2</span><span class="o">&gt;</span><span class="w"> </span></code></pre><p>Looking at the <code class="inline">tut17</code> code, you see that the <code class="inline">pong</code> function itself is
│ │ │ +</span><span class="p" data-group-id="5775950460-1">(</span><span class="ss">pong@gollum</span><span class="p" data-group-id="5775950460-1">)</span><span class="mi">2</span><span class="o">&gt;</span><span class="w"> </span></code></pre><p>Looking at the <code class="inline">tut17</code> code, you see that the <code class="inline">pong</code> function itself is
│ │ │  unchanged, the following lines work in the same way irrespective of on which
│ │ │ -node the &quot;ping&quot; process is executes:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5249997262-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="5249997262-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5249997262-2">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5249997262-3">[</span><span class="p" data-group-id="5249997262-3">]</span><span class="p" data-group-id="5249997262-2">)</span><span class="p">,</span><span class="w">
│ │ │ +node the &quot;ping&quot; process is executes:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2385972291-1">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2385972291-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2385972291-2">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2385972291-3">[</span><span class="p" data-group-id="2385972291-3">]</span><span class="p" data-group-id="2385972291-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span></code></pre><p>Thus, Erlang pids contain information about where the process executes. So if
│ │ │  you know the pid of a process, the <code class="inline">!</code> operator can be used to send it a
│ │ │ -message disregarding if the process is on the same node or on a different node.</p><p>A difference is how messages are sent to a registered process on another node:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0128539311-1">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0128539311-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0128539311-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0128539311-3">(</span><span class="p" data-group-id="0128539311-3">)</span><span class="p" data-group-id="0128539311-2">}</span><span class="p">,</span></code></pre><p>A tuple <code class="inline">{registered_name,node_name}</code> is used instead of just the
│ │ │ +message disregarding if the process is on the same node or on a different node.</p><p>A difference is how messages are sent to a registered process on another node:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4924598709-1">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="4924598709-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4924598709-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4924598709-3">(</span><span class="p" data-group-id="4924598709-3">)</span><span class="p" data-group-id="4924598709-2">}</span><span class="p">,</span></code></pre><p>A tuple <code class="inline">{registered_name,node_name}</code> is used instead of just the
│ │ │  <code class="inline">registered_name</code>.</p><p>In the previous example, &quot;ping&quot; and &quot;pong&quot; were started from the shells of two
│ │ │  separate Erlang nodes. <code class="inline">spawn</code> can also be used to start processes in other
│ │ │  nodes.</p><p>The next example is the ping pong program, yet again, but this time &quot;ping&quot; is
│ │ │ -started in another node:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7511817486-1">(</span><span class="ss">tut18</span><span class="p" data-group-id="7511817486-1">)</span><span class="p">.</span><span class="w">
│ │ │ +started in another node:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9036121941-1">(</span><span class="ss">tut18</span><span class="p" data-group-id="9036121941-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7511817486-2">(</span><span class="p" data-group-id="7511817486-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7511817486-3">]</span><span class="p" data-group-id="7511817486-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9036121941-2">(</span><span class="p" data-group-id="9036121941-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9036121941-3">]</span><span class="p" data-group-id="9036121941-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="7511817486-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7511817486-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7511817486-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7511817486-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7511817486-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7511817486-7">[</span><span class="p" data-group-id="7511817486-7">]</span><span class="p" data-group-id="7511817486-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="9036121941-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9036121941-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9036121941-5">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9036121941-5">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">finished</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9036121941-6">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9036121941-7">[</span><span class="p" data-group-id="9036121941-7">]</span><span class="p" data-group-id="9036121941-6">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="7511817486-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7511817486-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7511817486-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7511817486-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7511817486-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7511817486-11">(</span><span class="p" data-group-id="7511817486-11">)</span><span class="p" data-group-id="7511817486-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="9036121941-8">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9036121941-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9036121941-9">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9036121941-9">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9036121941-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9036121941-11">(</span><span class="p" data-group-id="9036121941-11">)</span><span class="p" data-group-id="9036121941-10">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7511817486-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7511817486-13">[</span><span class="p" data-group-id="7511817486-13">]</span><span class="p" data-group-id="7511817486-12">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9036121941-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9036121941-13">[</span><span class="p" data-group-id="9036121941-13">]</span><span class="p" data-group-id="9036121941-12">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="7511817486-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="7511817486-14">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="9036121941-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="9036121941-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="7511817486-15">(</span><span class="p" data-group-id="7511817486-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="9036121941-15">(</span><span class="p" data-group-id="9036121941-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">finished</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7511817486-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7511817486-17">[</span><span class="p" data-group-id="7511817486-17">]</span><span class="p" data-group-id="7511817486-16">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7511817486-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="7511817486-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7511817486-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7511817486-20">[</span><span class="p" data-group-id="7511817486-20">]</span><span class="p" data-group-id="7511817486-19">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9036121941-16">(</span><span class="s">&quot;Pong finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9036121941-17">[</span><span class="p" data-group-id="9036121941-17">]</span><span class="p" data-group-id="9036121941-16">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="9036121941-18">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="9036121941-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9036121941-19">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9036121941-20">[</span><span class="p" data-group-id="9036121941-20">]</span><span class="p" data-group-id="9036121941-19">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="7511817486-21">(</span><span class="p" data-group-id="7511817486-21">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="9036121941-21">(</span><span class="p" data-group-id="9036121941-21">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="7511817486-22">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="7511817486-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="7511817486-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7511817486-24">(</span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7511817486-25">[</span><span class="p" data-group-id="7511817486-25">]</span><span class="p" data-group-id="7511817486-24">)</span><span class="p" data-group-id="7511817486-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="7511817486-26">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7511817486-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="7511817486-28">(</span><span class="p" data-group-id="7511817486-28">)</span><span class="p" data-group-id="7511817486-27">]</span><span class="p" data-group-id="7511817486-26">)</span><span class="p">.</span></code></pre><p>Assuming an Erlang system called ping (but not the &quot;ping&quot; process) has already
│ │ │ -been started on kosken, then on gollum this is done:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut18</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="1873305220-1">(</span><span class="ss">ping@kosken</span><span class="p" data-group-id="1873305220-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="9036121941-22">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="9036121941-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="9036121941-23">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9036121941-24">(</span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9036121941-25">[</span><span class="p" data-group-id="9036121941-25">]</span><span class="p" data-group-id="9036121941-24">)</span><span class="p" data-group-id="9036121941-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9036121941-26">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut18</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9036121941-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="9036121941-28">(</span><span class="p" data-group-id="9036121941-28">)</span><span class="p" data-group-id="9036121941-27">]</span><span class="p" data-group-id="9036121941-26">)</span><span class="p">.</span></code></pre><p>Assuming an Erlang system called ping (but not the &quot;ping&quot; process) has already
│ │ │ +been started on kosken, then on gollum this is done:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(pong@gollum)1&gt; </span><span class="nc">tut18</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8216590909-1">(</span><span class="ss">ping@kosken</span><span class="p" data-group-id="8216590909-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">3934.39</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │  </span><span class="n">Pong</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">ping</span><span class="w">
│ │ │  </span><span class="n">Ping</span><span class="w"> </span><span class="ss">received</span><span class="w"> </span><span class="ss">pong</span><span class="w">
│ │ │ @@ -516,188 +516,188 @@
│ │ │  </span><span class="c1">%%% Started: messenger:client(Server_Node, Name)</span><span class="w">
│ │ │  </span><span class="c1">%%% To client: logoff</span><span class="w">
│ │ │  </span><span class="c1">%%% To client: {message_to, ToName, Message}</span><span class="w">
│ │ │  </span><span class="c1">%%%</span><span class="w">
│ │ │  </span><span class="c1">%%% Configuration: change the server_node() function to return the</span><span class="w">
│ │ │  </span><span class="c1">%%% name of the node where the messenger server runs</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0724895694-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="0724895694-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0724895694-2">(</span><span class="p" data-group-id="0724895694-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0724895694-3">]</span><span class="p" data-group-id="0724895694-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5815058239-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="5815058239-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5815058239-2">(</span><span class="p" data-group-id="5815058239-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5815058239-3">]</span><span class="p" data-group-id="5815058239-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Change the function below to return the name of the node where the</span><span class="w">
│ │ │  </span><span class="c1">%%% messenger server runs</span><span class="w">
│ │ │ -</span><span class="nf">server_node</span><span class="p" data-group-id="0724895694-4">(</span><span class="p" data-group-id="0724895694-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_node</span><span class="p" data-group-id="5815058239-4">(</span><span class="p" data-group-id="5815058239-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">messenger@super</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% This is the server process for the &quot;messenger&quot;</span><span class="w">
│ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="0724895694-5">(</span><span class="n">User_List</span><span class="p" data-group-id="0724895694-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="5815058239-5">(</span><span class="n">User_List</span><span class="p" data-group-id="5815058239-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0724895694-6">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0724895694-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="0724895694-7">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-7">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="0724895694-8">(</span><span class="n">New_User_List</span><span class="p" data-group-id="0724895694-8">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0724895694-9">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="0724895694-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="0724895694-10">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-10">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="0724895694-11">(</span><span class="n">New_User_List</span><span class="p" data-group-id="0724895694-11">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0724895694-12">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0724895694-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="0724895694-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-13">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0724895694-14">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0724895694-15">[</span><span class="n">User_List</span><span class="p" data-group-id="0724895694-15">]</span><span class="p" data-group-id="0724895694-14">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="0724895694-16">(</span><span class="n">User_List</span><span class="p" data-group-id="0724895694-16">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5815058239-6">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5815058239-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="5815058239-7">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-7">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="5815058239-8">(</span><span class="n">New_User_List</span><span class="p" data-group-id="5815058239-8">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5815058239-9">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="5815058239-9">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="5815058239-10">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-10">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="5815058239-11">(</span><span class="n">New_User_List</span><span class="p" data-group-id="5815058239-11">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5815058239-12">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5815058239-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="5815058239-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-13">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5815058239-14">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5815058239-15">[</span><span class="n">User_List</span><span class="p" data-group-id="5815058239-15">]</span><span class="p" data-group-id="5815058239-14">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="5815058239-16">(</span><span class="n">User_List</span><span class="p" data-group-id="5815058239-16">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="0724895694-17">(</span><span class="p" data-group-id="0724895694-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="0724895694-18">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0724895694-19">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0724895694-20">[</span><span class="p" data-group-id="0724895694-21">[</span><span class="p" data-group-id="0724895694-21">]</span><span class="p" data-group-id="0724895694-20">]</span><span class="p" data-group-id="0724895694-19">)</span><span class="p" data-group-id="0724895694-18">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="5815058239-17">(</span><span class="p" data-group-id="5815058239-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="5815058239-18">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="5815058239-19">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5815058239-20">[</span><span class="p" data-group-id="5815058239-21">[</span><span class="p" data-group-id="5815058239-21">]</span><span class="p" data-group-id="5815058239-20">]</span><span class="p" data-group-id="5815058239-19">)</span><span class="p" data-group-id="5815058239-18">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="0724895694-22">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="5815058239-22">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="0724895694-23">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-23">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="5815058239-23">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-23">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-24">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="0724895694-24">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-24">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="5815058239-24">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-25">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="0724895694-25">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="0724895694-26">[</span><span class="p" data-group-id="0724895694-27">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0724895694-27">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-26">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-25">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="5815058239-25">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="5815058239-26">[</span><span class="p" data-group-id="5815058239-27">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5815058239-27">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-26">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="0724895694-28">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="0724895694-29">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-29">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="5815058239-28">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="5815058239-29">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-29">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="0724895694-30">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="5815058239-30">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0724895694-31">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-31">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="5815058239-31">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-31">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-32">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="0724895694-32">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0724895694-33">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0724895694-34">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0724895694-34">}</span><span class="p" data-group-id="0724895694-33">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="0724895694-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-35">)</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-32">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="5815058239-32">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5815058239-33">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5815058239-34">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5815058239-34">}</span><span class="p" data-group-id="5815058239-33">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="5815058239-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-35">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="0724895694-36">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="5815058239-36">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0724895694-37">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0724895694-37">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="5815058239-37">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="5815058239-37">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-38">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="0724895694-38">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0724895694-39">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0724895694-40">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="0724895694-40">}</span><span class="p" data-group-id="0724895694-39">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-41">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0724895694-41">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="0724895694-42">}</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-38">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="5815058239-38">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5815058239-39">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5815058239-40">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="5815058239-40">}</span><span class="p" data-group-id="5815058239-39">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-41">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5815058239-41">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="5815058239-42">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% User Commands</span><span class="w">
│ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="0724895694-43">(</span><span class="n">Name</span><span class="p" data-group-id="0724895694-43">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="0724895694-44">(</span><span class="ss">mess_client</span><span class="p" data-group-id="0724895694-44">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="5815058239-43">(</span><span class="n">Name</span><span class="p" data-group-id="5815058239-43">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="5815058239-44">(</span><span class="ss">mess_client</span><span class="p" data-group-id="5815058239-44">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="0724895694-45">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="0724895694-46">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0724895694-47">[</span><span class="nf">server_node</span><span class="p" data-group-id="0724895694-48">(</span><span class="p" data-group-id="0724895694-48">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0724895694-47">]</span><span class="p" data-group-id="0724895694-46">)</span><span class="p" data-group-id="0724895694-45">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="5815058239-45">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="5815058239-46">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5815058239-47">[</span><span class="nf">server_node</span><span class="p" data-group-id="5815058239-48">(</span><span class="p" data-group-id="5815058239-48">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5815058239-47">]</span><span class="p" data-group-id="5815058239-46">)</span><span class="p" data-group-id="5815058239-45">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="0724895694-49">(</span><span class="p" data-group-id="0724895694-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="5815058239-49">(</span><span class="p" data-group-id="5815058239-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="0724895694-50">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0724895694-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="0724895694-51">(</span><span class="ss">mess_client</span><span class="p" data-group-id="0724895694-51">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="5815058239-50">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5815058239-50">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="5815058239-51">(</span><span class="ss">mess_client</span><span class="p" data-group-id="5815058239-51">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-52">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0724895694-52">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-52">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5815058239-52">}</span><span class="p">,</span><span class="w">
│ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% The client process which runs on each server node</span><span class="w">
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="0724895694-53">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0724895694-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0724895694-54">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0724895694-54">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-55">{</span><span class="nf">self</span><span class="p" data-group-id="0724895694-56">(</span><span class="p" data-group-id="0724895694-56">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0724895694-55">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="0724895694-57">(</span><span class="p" data-group-id="0724895694-57">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="0724895694-58">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0724895694-58">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="5815058239-53">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5815058239-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5815058239-54">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="5815058239-54">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-55">{</span><span class="nf">self</span><span class="p" data-group-id="5815058239-56">(</span><span class="p" data-group-id="5815058239-56">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5815058239-55">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="5815058239-57">(</span><span class="p" data-group-id="5815058239-57">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="5815058239-58">(</span><span class="n">Server_Node</span><span class="p" data-group-id="5815058239-58">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="0724895694-59">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0724895694-59">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="5815058239-59">(</span><span class="n">Server_Node</span><span class="p" data-group-id="5815058239-59">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="0724895694-60">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0724895694-60">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-61">{</span><span class="nf">self</span><span class="p" data-group-id="0724895694-62">(</span><span class="p" data-group-id="0724895694-62">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="0724895694-61">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="0724895694-63">(</span><span class="ss">normal</span><span class="p" data-group-id="0724895694-63">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0724895694-64">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0724895694-64">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="0724895694-65">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="0724895694-65">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0724895694-66">{</span><span class="nf">self</span><span class="p" data-group-id="0724895694-67">(</span><span class="p" data-group-id="0724895694-67">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0724895694-66">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="0724895694-68">(</span><span class="p" data-group-id="0724895694-68">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0724895694-69">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0724895694-69">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0724895694-70">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0724895694-71">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="0724895694-71">]</span><span class="p" data-group-id="0724895694-70">)</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="5815058239-60">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="5815058239-60">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-61">{</span><span class="nf">self</span><span class="p" data-group-id="5815058239-62">(</span><span class="p" data-group-id="5815058239-62">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p" data-group-id="5815058239-61">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="5815058239-63">(</span><span class="ss">normal</span><span class="p" data-group-id="5815058239-63">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5815058239-64">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5815058239-64">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="5815058239-65">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="5815058239-65">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5815058239-66">{</span><span class="nf">self</span><span class="p" data-group-id="5815058239-67">(</span><span class="p" data-group-id="5815058239-67">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5815058239-66">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="5815058239-68">(</span><span class="p" data-group-id="5815058239-68">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5815058239-69">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5815058239-69">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5815058239-70">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5815058239-71">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5815058239-71">]</span><span class="p" data-group-id="5815058239-70">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="0724895694-72">(</span><span class="n">Server_Node</span><span class="p" data-group-id="0724895694-72">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="5815058239-72">(</span><span class="n">Server_Node</span><span class="p" data-group-id="5815058239-72">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="0724895694-73">(</span><span class="p" data-group-id="0724895694-73">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="5815058239-73">(</span><span class="p" data-group-id="5815058239-73">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0724895694-74">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="0724895694-74">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0724895694-75">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0724895694-76">[</span><span class="n">Why</span><span class="p" data-group-id="0724895694-76">]</span><span class="p" data-group-id="0724895694-75">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="0724895694-77">(</span><span class="ss">normal</span><span class="p" data-group-id="0724895694-77">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0724895694-78">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="0724895694-78">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0724895694-79">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0724895694-80">[</span><span class="n">What</span><span class="p" data-group-id="0724895694-80">]</span><span class="p" data-group-id="0724895694-79">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5815058239-74">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="5815058239-74">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5815058239-75">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5815058239-76">[</span><span class="n">Why</span><span class="p" data-group-id="5815058239-76">]</span><span class="p" data-group-id="5815058239-75">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="5815058239-77">(</span><span class="ss">normal</span><span class="p" data-group-id="5815058239-77">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5815058239-78">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="5815058239-78">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5815058239-79">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5815058239-80">[</span><span class="n">What</span><span class="p" data-group-id="5815058239-80">]</span><span class="p" data-group-id="5815058239-79">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>To use this program, you need to:</p><ul><li>Configure the <code class="inline">server_node()</code> function.</li><li>Copy the compiled code (<code class="inline">messenger.beam</code>) to the directory on each computer
│ │ │  where you start Erlang.</li></ul><p>In the following example using this program, nodes are started on four different
│ │ │  computers. If you do not have that many machines available on your network, you
│ │ │  can start several nodes on the same machine.</p><p>Four Erlang nodes are started up: messenger@super, c1@bilbo, c2@kosken,
│ │ │ -c3@gollum.</p><p>First the server at messenger@super is started up:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(messenger@super)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">start_server</span><span class="p" data-group-id="2011911959-1">(</span><span class="p" data-group-id="2011911959-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">true</span></code></pre><p>Now Peter logs on at c1@bilbo:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="9553930223-1">(</span><span class="ss">peter</span><span class="p" data-group-id="9553930223-1">)</span><span class="p">.</span><span class="w">
│ │ │ +c3@gollum.</p><p>First the server at messenger@super is started up:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(messenger@super)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">start_server</span><span class="p" data-group-id="2272044504-1">(</span><span class="p" data-group-id="2272044504-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">true</span></code></pre><p>Now Peter logs on at c1@bilbo:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="7120187760-1">(</span><span class="ss">peter</span><span class="p" data-group-id="7120187760-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="ss">logged_on</span></code></pre><p>James logs on at c2@kosken:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="3090367480-1">(</span><span class="ss">james</span><span class="p" data-group-id="3090367480-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">logged_on</span></code></pre><p>James logs on at c2@kosken:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="3086848869-1">(</span><span class="ss">james</span><span class="p" data-group-id="3086848869-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="ss">logged_on</span></code></pre><p>And Fred logs on at c3@gollum:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c3@gollum)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="7679392986-1">(</span><span class="ss">fred</span><span class="p" data-group-id="7679392986-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">logged_on</span></code></pre><p>And Fred logs on at c3@gollum:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c3@gollum)1&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logon</span><span class="p" data-group-id="9658172967-1">(</span><span class="ss">fred</span><span class="p" data-group-id="9658172967-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="ss">logged_on</span></code></pre><p>Now Peter sends Fred a message:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="1573568766-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="1573568766-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">logged_on</span></code></pre><p>Now Peter sends Fred a message:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c1@bilbo)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="1732653120-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="1732653120-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="ss">sent</span></code></pre><p>Fred receives the message and sends a message to Peter and logs off:</p><pre><code class="makeup erlang" translate="no"><span class="n">Message</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="nc">peter</span><span class="p">:</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">(c3@gollum)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="6783306185-1">(</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;go away, I&#39;m busy&quot;</span><span class="p" data-group-id="6783306185-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">(c3@gollum)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="7659506506-1">(</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;go away, I&#39;m busy&quot;</span><span class="p" data-group-id="7659506506-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="nf">sent</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6783306185-2">(</span><span class="ss">c3@gollum</span><span class="p" data-group-id="6783306185-2">)</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logoff</span><span class="p" data-group-id="6783306185-3">(</span><span class="p" data-group-id="6783306185-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">logoff</span></code></pre><p>James now tries to send a message to Fred:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="0876488926-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;peter doesn&#39;t like you&quot;</span><span class="p" data-group-id="0876488926-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7659506506-2">(</span><span class="ss">c3@gollum</span><span class="p" data-group-id="7659506506-2">)</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">logoff</span><span class="p" data-group-id="7659506506-3">(</span><span class="p" data-group-id="7659506506-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">logoff</span></code></pre><p>James now tries to send a message to Fred:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">(c2@kosken)2&gt; </span><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="2934859516-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;peter doesn&#39;t like you&quot;</span><span class="p" data-group-id="2934859516-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="ss">receiver_not_found</span></code></pre><p>But this fails as Fred has already logged off.</p><p>First let us look at some of the new concepts that have been introduced.</p><p>There are two versions of the <code class="inline">server_transfer</code> function: one with four
│ │ │  arguments (<code class="inline">server_transfer/4</code>) and one with five (<code class="inline">server_transfer/5</code>). These
│ │ │  are regarded by Erlang as two separate functions.</p><p>Notice how to write the <code class="inline">server</code> function so that it calls itself, through
│ │ │  <code class="inline">server(User_List)</code>, and thus creates a loop. The Erlang compiler is &quot;clever&quot;
│ │ │  and optimizes the code so that this really is a sort of loop and not a proper
│ │ │  function call. But this only works if there is no code after the call.
│ │ │  Otherwise, the compiler expects the call to return and make a proper function
│ │ │  call. This would result in the process getting bigger and bigger for every loop.</p><p>Functions in the <code class="inline">lists</code> module are used. This is a very useful module and a
│ │ │  study of the manual page is recommended (<code class="inline">erl -man lists</code>).
│ │ │  <code class="inline">lists:keymember(Key,Position,Lists)</code> looks through a list of tuples and looks
│ │ │  at <code class="inline">Position</code> in each tuple to see if it is the same as <code class="inline">Key</code>. The first element
│ │ │  is position 1. If it finds a tuple where the element at <code class="inline">Position</code> is the same
│ │ │ -as <code class="inline">Key</code>, it returns <code class="inline">true</code>, otherwise <code class="inline">false</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="5178636276-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5178636276-2">[</span><span class="p" data-group-id="5178636276-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="5178636276-3">}</span><span class="p">,</span><span class="p" data-group-id="5178636276-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5178636276-4">}</span><span class="p">,</span><span class="p" data-group-id="5178636276-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5178636276-5">}</span><span class="p">,</span><span class="p" data-group-id="5178636276-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="5178636276-6">}</span><span class="p" data-group-id="5178636276-2">]</span><span class="p" data-group-id="5178636276-1">)</span><span class="p">.</span><span class="w">
│ │ │ +as <code class="inline">Key</code>, it returns <code class="inline">true</code>, otherwise <code class="inline">false</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="3233022771-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3233022771-2">[</span><span class="p" data-group-id="3233022771-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="3233022771-3">}</span><span class="p">,</span><span class="p" data-group-id="3233022771-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3233022771-4">}</span><span class="p">,</span><span class="p" data-group-id="3233022771-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3233022771-5">}</span><span class="p">,</span><span class="p" data-group-id="3233022771-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="3233022771-6">}</span><span class="p" data-group-id="3233022771-2">]</span><span class="p" data-group-id="3233022771-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="5178636276-7">(</span><span class="ss">p</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5178636276-8">[</span><span class="p" data-group-id="5178636276-9">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="5178636276-9">}</span><span class="p">,</span><span class="p" data-group-id="5178636276-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="5178636276-10">}</span><span class="p">,</span><span class="p" data-group-id="5178636276-11">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5178636276-11">}</span><span class="p">,</span><span class="p" data-group-id="5178636276-12">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="5178636276-12">}</span><span class="p" data-group-id="5178636276-8">]</span><span class="p" data-group-id="5178636276-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="3233022771-7">(</span><span class="ss">p</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3233022771-8">[</span><span class="p" data-group-id="3233022771-9">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="3233022771-9">}</span><span class="p">,</span><span class="p" data-group-id="3233022771-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3233022771-10">}</span><span class="p">,</span><span class="p" data-group-id="3233022771-11">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="3233022771-11">}</span><span class="p">,</span><span class="p" data-group-id="3233022771-12">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="3233022771-12">}</span><span class="p" data-group-id="3233022771-8">]</span><span class="p" data-group-id="3233022771-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><p><code class="inline">lists:keydelete</code> works in the same way but deletes the first tuple found (if
│ │ │ -any) and returns the remaining list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="1337259762-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1337259762-2">[</span><span class="p" data-group-id="1337259762-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="1337259762-3">}</span><span class="p">,</span><span class="p" data-group-id="1337259762-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1337259762-4">}</span><span class="p">,</span><span class="p" data-group-id="1337259762-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1337259762-5">}</span><span class="p">,</span><span class="p" data-group-id="1337259762-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="1337259762-6">}</span><span class="p" data-group-id="1337259762-2">]</span><span class="p" data-group-id="1337259762-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1337259762-7">[</span><span class="p" data-group-id="1337259762-8">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="1337259762-8">}</span><span class="p">,</span><span class="p" data-group-id="1337259762-9">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1337259762-9">}</span><span class="p">,</span><span class="p" data-group-id="1337259762-10">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="1337259762-10">}</span><span class="p" data-group-id="1337259762-7">]</span></code></pre><p><code class="inline">lists:keysearch</code> is like <code class="inline">lists:keymember</code>, but it returns
│ │ │ +any) and returns the remaining list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="4389682484-1">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4389682484-2">[</span><span class="p" data-group-id="4389682484-3">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="4389682484-3">}</span><span class="p">,</span><span class="p" data-group-id="4389682484-4">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4389682484-4">}</span><span class="p">,</span><span class="p" data-group-id="4389682484-5">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4389682484-5">}</span><span class="p">,</span><span class="p" data-group-id="4389682484-6">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="4389682484-6">}</span><span class="p" data-group-id="4389682484-2">]</span><span class="p" data-group-id="4389682484-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4389682484-7">[</span><span class="p" data-group-id="4389682484-8">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="4389682484-8">}</span><span class="p">,</span><span class="p" data-group-id="4389682484-9">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4389682484-9">}</span><span class="p">,</span><span class="p" data-group-id="4389682484-10">{</span><span class="ss">q</span><span class="p">,</span><span class="ss">r</span><span class="p">,</span><span class="ss">s</span><span class="p" data-group-id="4389682484-10">}</span><span class="p" data-group-id="4389682484-7">]</span></code></pre><p><code class="inline">lists:keysearch</code> is like <code class="inline">lists:keymember</code>, but it returns
│ │ │  <code class="inline">{value,Tuple_Found}</code> or the atom <code class="inline">false</code>.</p><p>There are many very useful functions in the <code class="inline">lists</code> module.</p><p>An Erlang process (conceptually) runs until it does a <code class="inline">receive</code> and there is no
│ │ │  message which it wants to receive in the message queue. &quot;conceptually&quot; is used
│ │ │  here because the Erlang system shares the CPU time between the active processes
│ │ │  in the system.</p><p>A process terminates when there is nothing more for it to do, that is, the last
│ │ │  function it calls simply returns and does not call another function. Another way
│ │ │  for a process to terminate is for it to call <a href="../../erts-15.2.7.8/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a>. The argument
│ │ │  to <a href="../../erts-15.2.7.8/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a> has a special meaning, which is discussed later. In this
│ │ │  example, <a href="../../erts-15.2.7.8/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a> is done, which has the same effect as a
│ │ │  process running out of functions to call.</p><p>The BIF <a href="../../erts-15.2.7.8/doc/html/erlang.html#whereis/1"><code class="inline">whereis(RegisteredName)</code></a> checks if a registered process
│ │ │  of name <code class="inline">RegisteredName</code> exists. If it exists, the pid of that process is
│ │ │  returned. If it does not exist, the atom <code class="inline">undefined</code> is returned.</p><p>You should by now be able to understand most of the code in the
│ │ │  messenger-module. Let us study one case in detail: a message is sent from one
│ │ │ -user to another.</p><p>The first user &quot;sends&quot; the message in the example above by:</p><pre><code class="makeup erlang" translate="no"><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="3259170469-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="3259170469-1">)</span></code></pre><p>After testing that the client process exists:</p><pre><code class="makeup erlang" translate="no"><span class="nf">whereis</span><span class="p" data-group-id="4638315477-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="4638315477-1">)</span></code></pre><p>And a message is sent to <code class="inline">mess_client</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5736700901-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="5736700901-1">}</span></code></pre><p>The client sends the message to the server by:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3201265329-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="3201265329-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3201265329-2">{</span><span class="nf">self</span><span class="p" data-group-id="3201265329-3">(</span><span class="p" data-group-id="3201265329-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="3201265329-2">}</span><span class="p">,</span></code></pre><p>And waits for a reply from the server.</p><p>The server receives this message and calls:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="9769772891-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9769772891-1">)</span><span class="p">,</span></code></pre><p>This checks that the pid <code class="inline">From</code> is in the <code class="inline">User_List</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="3397066727-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3397066727-1">)</span></code></pre><p>If <code class="inline">keysearch</code> returns the atom <code class="inline">false</code>, some error has occurred and the server
│ │ │ -sends back the message:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8570347505-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="8570347505-1">}</span></code></pre><p>This is received by the client, which in turn does <a href="../../erts-15.2.7.8/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a>
│ │ │ +user to another.</p><p>The first user &quot;sends&quot; the message in the example above by:</p><pre><code class="makeup erlang" translate="no"><span class="nc">messenger</span><span class="p">:</span><span class="nf">message</span><span class="p" data-group-id="9385986692-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="9385986692-1">)</span></code></pre><p>After testing that the client process exists:</p><pre><code class="makeup erlang" translate="no"><span class="nf">whereis</span><span class="p" data-group-id="5021738366-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="5021738366-1">)</span></code></pre><p>And a message is sent to <code class="inline">mess_client</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7187735463-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7187735463-1">}</span></code></pre><p>The client sends the message to the server by:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2049322818-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="2049322818-1">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2049322818-2">{</span><span class="nf">self</span><span class="p" data-group-id="2049322818-3">(</span><span class="p" data-group-id="2049322818-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="2049322818-2">}</span><span class="p">,</span></code></pre><p>And waits for a reply from the server.</p><p>The server receives this message and calls:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="1121186224-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="1121186224-1">)</span><span class="p">,</span></code></pre><p>This checks that the pid <code class="inline">From</code> is in the <code class="inline">User_List</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0862159554-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0862159554-1">)</span></code></pre><p>If <code class="inline">keysearch</code> returns the atom <code class="inline">false</code>, some error has occurred and the server
│ │ │ +sends back the message:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7572460002-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="7572460002-1">}</span></code></pre><p>This is received by the client, which in turn does <a href="../../erts-15.2.7.8/doc/html/erlang.html#exit/1"><code class="inline">exit(normal)</code></a>
│ │ │  and terminates. If <code class="inline">keysearch</code> returns <code class="inline">{value,{From,Name}}</code> it is certain that
│ │ │ -the user is logged on and that his name (peter) is in variable <code class="inline">Name</code>.</p><p>Let us now call:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="7305701897-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7305701897-1">)</span></code></pre><p>Notice that as this is <code class="inline">server_transfer/5</code>, it is not the same as the previous
│ │ │ +the user is logged on and that his name (peter) is in variable <code class="inline">Name</code>.</p><p>Let us now call:</p><pre><code class="makeup erlang" translate="no"><span class="nf">server_transfer</span><span class="p" data-group-id="3838746422-1">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="3838746422-1">)</span></code></pre><p>Notice that as this is <code class="inline">server_transfer/5</code>, it is not the same as the previous
│ │ │  function <code class="inline">server_transfer/4</code>. Another <code class="inline">keysearch</code> is done on <code class="inline">User_List</code> to find
│ │ │ -the pid of the client corresponding to fred:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="0666177603-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="0666177603-1">)</span></code></pre><p>This time argument 2 is used, which is the second element in the tuple. If this
│ │ │ +the pid of the client corresponding to fred:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="7265089650-1">(</span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="7265089650-1">)</span></code></pre><p>This time argument 2 is used, which is the second element in the tuple. If this
│ │ │  returns the atom <code class="inline">false</code>, fred is not logged on and the following message is
│ │ │ -sent:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5482770136-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="5482770136-1">}</span><span class="p">;</span></code></pre><p>This is received by the client.</p><p>If <code class="inline">keysearch</code> returns:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2765976541-1">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2765976541-2">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p" data-group-id="2765976541-2">}</span><span class="p" data-group-id="2765976541-1">}</span></code></pre><p>The following message is sent to fred's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9586869817-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="9586869817-1">}</span><span class="p">,</span></code></pre><p>The following message is sent to peter's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6399780137-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="6399780137-1">}</span></code></pre><p>Fred's client receives the message and prints it:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3107626283-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="3107626283-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3107626283-2">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3107626283-3">[</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="3107626283-3">]</span><span class="p" data-group-id="3107626283-2">)</span></code></pre><p>Peter's client receives the message in the <code class="inline">await_result</code> function.</p>
│ │ │ +sent:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9450622056-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="9450622056-1">}</span><span class="p">;</span></code></pre><p>This is received by the client.</p><p>If <code class="inline">keysearch</code> returns:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9099996596-1">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9099996596-2">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p" data-group-id="9099996596-2">}</span><span class="p" data-group-id="9099996596-1">}</span></code></pre><p>The following message is sent to fred's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="6612977118-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="6612977118-1">}</span><span class="p">,</span></code></pre><p>The following message is sent to peter's client:</p><pre><code class="makeup erlang" translate="no"><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9339646031-1">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="9339646031-1">}</span></code></pre><p>Fred's client receives the message and prints it:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0215545985-1">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0215545985-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0215545985-2">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0215545985-3">[</span><span class="ss">peter</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0215545985-3">]</span><span class="p" data-group-id="0215545985-2">)</span></code></pre><p>Peter's client receives the message in the <code class="inline">await_result</code> function.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="seq_prog.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/create_target.html
│ │ │ @@ -138,21 +138,21 @@
│ │ │    <span class="text">Creating a Target System</span>
│ │ │  </h2>
│ │ │  <p>It is assumed that you have a working Erlang/OTP system structured according to
│ │ │  the OTP design principles.</p><p><em>Step 1.</em> Create a <code class="inline">.rel</code> file (see the <a href="../../lib/sasl-4.2.2.1/doc/html/rel.html">rel(4)</a> manual page in
│ │ │  SASL), which specifies the ERTS version and lists all applications that are to
│ │ │  be included in the new basic target system. An example is the following
│ │ │  <code class="inline">mysystem.rel</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% mysystem.rel</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5866006194-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5866006194-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;FIRST&quot;</span><span class="p" data-group-id="5866006194-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5866006194-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.10.4&quot;</span><span class="p" data-group-id="5866006194-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5866006194-4">[</span><span class="p" data-group-id="5866006194-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.16.4&quot;</span><span class="p" data-group-id="5866006194-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5866006194-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.19.4&quot;</span><span class="p" data-group-id="5866006194-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5866006194-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.3.4&quot;</span><span class="p" data-group-id="5866006194-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5866006194-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="5866006194-8">}</span><span class="p" data-group-id="5866006194-4">]</span><span class="p" data-group-id="5866006194-1">}</span><span class="p">.</span></code></pre><p>The listed applications are not only original Erlang/OTP applications but
│ │ │ +</span><span class="p" data-group-id="6075915378-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6075915378-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;FIRST&quot;</span><span class="p" data-group-id="6075915378-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6075915378-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.10.4&quot;</span><span class="p" data-group-id="6075915378-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="6075915378-4">[</span><span class="p" data-group-id="6075915378-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.16.4&quot;</span><span class="p" data-group-id="6075915378-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6075915378-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.19.4&quot;</span><span class="p" data-group-id="6075915378-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6075915378-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.3.4&quot;</span><span class="p" data-group-id="6075915378-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6075915378-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="6075915378-8">}</span><span class="p" data-group-id="6075915378-4">]</span><span class="p" data-group-id="6075915378-1">}</span><span class="p">.</span></code></pre><p>The listed applications are not only original Erlang/OTP applications but
│ │ │  possibly also new applications that you have written (here exemplified by the
│ │ │  application Pea (<code class="inline">pea</code>)).</p><p><em>Step 2.</em> Start Erlang/OTP from the directory where the <code class="inline">mysystem.rel</code> file
│ │ │  resides:</p><pre><code class="text">% erl -pa /home/user/target_system/myapps/pea-1.0/ebin</code></pre><p>The <code class="inline">-pa</code> argument prepends the path to the <code class="inline">ebin</code> directory for
│ │ │  the Pea application to the code path.</p><p><em>Step 3.</em> Create the target system:</p><pre><code class="text">1&gt; target_system:create(&quot;mysystem&quot;).</code></pre><p>The function <code class="inline">target_system:create/1</code> performs the following:</p><ol><li><p>Reads the file <code class="inline">mysystem.rel</code> and creates a new file <code class="inline">plain.rel</code>.
│ │ │  The new file is identical to the original, except that it only
│ │ │  lists the Kernel and STDLIB applications.</p></li><li><p>From the files <code class="inline">mysystem.rel</code> and <code class="inline">plain.rel</code> creates the files
│ │ │  <code class="inline">mysystem.script</code>, <code class="inline">mysystem.boot</code>, <code class="inline">plain.script</code>, and <code class="inline">plain.boot</code>
│ │ │ @@ -242,25 +242,25 @@
│ │ │    <a href="#creating-the-next-version" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating the Next Version</span>
│ │ │  </h2>
│ │ │  <p>In this example the Pea application has been changed, and so are the
│ │ │  applications ERTS, Kernel, STDLIB and SASL.</p><p><em>Step 1.</em> Create the file <code class="inline">.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% mysystem2.rel</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5229601087-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5229601087-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;SECOND&quot;</span><span class="p" data-group-id="5229601087-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5229601087-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;6.0&quot;</span><span class="p" data-group-id="5229601087-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5229601087-4">[</span><span class="p" data-group-id="5229601087-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;3.0&quot;</span><span class="p" data-group-id="5229601087-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5229601087-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="5229601087-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5229601087-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.4&quot;</span><span class="p" data-group-id="5229601087-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5229601087-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="5229601087-8">}</span><span class="p" data-group-id="5229601087-4">]</span><span class="p" data-group-id="5229601087-1">}</span><span class="p">.</span></code></pre><p><em>Step 2.</em> Create the application upgrade file (see
│ │ │ +</span><span class="p" data-group-id="5152133292-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5152133292-2">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;SECOND&quot;</span><span class="p" data-group-id="5152133292-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5152133292-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;6.0&quot;</span><span class="p" data-group-id="5152133292-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5152133292-4">[</span><span class="p" data-group-id="5152133292-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;3.0&quot;</span><span class="p" data-group-id="5152133292-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5152133292-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="5152133292-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5152133292-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.4&quot;</span><span class="p" data-group-id="5152133292-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5152133292-8">{</span><span class="ss">pea</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="5152133292-8">}</span><span class="p" data-group-id="5152133292-4">]</span><span class="p" data-group-id="5152133292-1">}</span><span class="p">.</span></code></pre><p><em>Step 2.</em> Create the application upgrade file (see
│ │ │  <a href="../../lib/sasl-4.2.2.1/doc/html/appup.html">appup</a> in SASL) for Pea, for example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% pea.appup</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9338499590-1">{</span><span class="s">&quot;2.0&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9338499590-2">[</span><span class="p" data-group-id="9338499590-3">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="9338499590-4">[</span><span class="p" data-group-id="9338499590-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="9338499590-5">}</span><span class="p" data-group-id="9338499590-4">]</span><span class="p" data-group-id="9338499590-3">}</span><span class="p" data-group-id="9338499590-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9338499590-6">[</span><span class="p" data-group-id="9338499590-7">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="9338499590-8">[</span><span class="p" data-group-id="9338499590-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="9338499590-9">}</span><span class="p" data-group-id="9338499590-8">]</span><span class="p" data-group-id="9338499590-7">}</span><span class="p" data-group-id="9338499590-6">]</span><span class="p" data-group-id="9338499590-1">}</span><span class="p">.</span></code></pre><p><em>Step 3.</em> From the directory where the file <code class="inline">mysystem2.rel</code> resides, start the
│ │ │ +</span><span class="p" data-group-id="4569587134-1">{</span><span class="s">&quot;2.0&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4569587134-2">[</span><span class="p" data-group-id="4569587134-3">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="4569587134-4">[</span><span class="p" data-group-id="4569587134-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="4569587134-5">}</span><span class="p" data-group-id="4569587134-4">]</span><span class="p" data-group-id="4569587134-3">}</span><span class="p" data-group-id="4569587134-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4569587134-6">[</span><span class="p" data-group-id="4569587134-7">{</span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="p" data-group-id="4569587134-8">[</span><span class="p" data-group-id="4569587134-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="ss">pea_lib</span><span class="p" data-group-id="4569587134-9">}</span><span class="p" data-group-id="4569587134-8">]</span><span class="p" data-group-id="4569587134-7">}</span><span class="p" data-group-id="4569587134-6">]</span><span class="p" data-group-id="4569587134-1">}</span><span class="p">.</span></code></pre><p><em>Step 3.</em> From the directory where the file <code class="inline">mysystem2.rel</code> resides, start the
│ │ │  Erlang/OTP system, giving the path to the new version of Pea:</p><pre><code class="text">% erl -pa /home/user/target_system/myapps/pea-2.0/ebin</code></pre><p><em>Step 4.</em> Create the release upgrade file (see <a href="../../lib/sasl-4.2.2.1/doc/html/relup.html">relup</a>
│ │ │  in SASL):</p><pre><code class="text">1&gt; systools:make_relup(&quot;mysystem2&quot;,[&quot;mysystem&quot;],[&quot;mysystem&quot;],
│ │ │      [{path,[&quot;/home/user/target_system/myapps/pea-1.0/ebin&quot;,
│ │ │      &quot;/my/old/erlang/lib/*/ebin&quot;]}]).</code></pre><p>Here <code class="inline">&quot;mysystem&quot;</code> is the base release and <code class="inline">&quot;mysystem2&quot;</code> is the release to
│ │ │  upgrade to.</p><p>The <code class="inline">path</code> option is used for pointing out the old version of all applications.
│ │ │  (The new versions are already in the code path - assuming of course that the
│ │ │  Erlang node on which this is executed is running the correct version of
│ │ │ @@ -292,291 +292,291 @@
│ │ │  {continue_after_restart,&quot;FIRST&quot;,[]}
│ │ │  heart: Tue Apr  1 12:15:10 2014: Erlang has closed.
│ │ │  heart: Tue Apr  1 12:15:11 2014: Executed &quot;/usr/local/erl-target/bin/start /usr/local/erl-target/releases/new_start_erl.data&quot; -&gt; 0. Terminating.
│ │ │  [End]</code></pre><p>The above return value and output after the call to
│ │ │  <a href="../../lib/sasl-4.2.2.1/doc/html/release_handler.html#install_release/1"><code class="inline">release_handler:install_release/1</code></a> means that the <code class="inline">release_handler</code> has
│ │ │  restarted the node by using <code class="inline">heart</code>. This is always done when the upgrade
│ │ │  involves a change of the applications ERTS, Kernel, STDLIB, or SASL. For more
│ │ │ -information, see <a href="upgrade.html">Upgrade when Erlang/OTP has Changed</a>.</p><p>The node is accessible through a new pipe:</p><pre><code class="text">% /usr/local/erl-target/bin/to_erl /tmp/erlang.pipe.2</code></pre><p>List the available releases in the system:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">which_releases</span><span class="p" data-group-id="1213768091-1">(</span><span class="p" data-group-id="1213768091-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1213768091-2">[</span><span class="p" data-group-id="1213768091-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1213768091-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="1213768091-4">]</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">current</span><span class="p" data-group-id="1213768091-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1213768091-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1213768091-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="1213768091-6">]</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">permanent</span><span class="p" data-group-id="1213768091-5">}</span><span class="p" data-group-id="1213768091-2">]</span></code></pre><p>Our new release, &quot;SECOND&quot;, is now the current release, but we can also see that
│ │ │ +information, see <a href="upgrade.html">Upgrade when Erlang/OTP has Changed</a>.</p><p>The node is accessible through a new pipe:</p><pre><code class="text">% /usr/local/erl-target/bin/to_erl /tmp/erlang.pipe.2</code></pre><p>List the available releases in the system:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">which_releases</span><span class="p" data-group-id="1008725274-1">(</span><span class="p" data-group-id="1008725274-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1008725274-2">[</span><span class="p" data-group-id="1008725274-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1008725274-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="1008725274-4">]</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">current</span><span class="p" data-group-id="1008725274-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1008725274-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1008725274-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="1008725274-6">]</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">permanent</span><span class="p" data-group-id="1008725274-5">}</span><span class="p" data-group-id="1008725274-2">]</span></code></pre><p>Our new release, &quot;SECOND&quot;, is now the current release, but we can also see that
│ │ │  our &quot;FIRST&quot; release is still permanent. This means that if the node would be
│ │ │ -restarted now, it would come up running the &quot;FIRST&quot; release again.</p><p><em>Step 3.</em> Make the new release permanent:</p><pre><code class="text">2&gt; release_handler:make_permanent(&quot;SECOND&quot;).</code></pre><p>Check the releases again:</p><pre><code class="makeup c" translate="no"><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">release_handler</span><span class="o">:</span><span class="nf">which_releases</span><span class="p" data-group-id="2588102003-1">(</span><span class="p" data-group-id="2588102003-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2588102003-2">[</span><span class="p" data-group-id="2588102003-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="2588102003-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="2588102003-4">]</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="n">permanent</span><span class="p" data-group-id="2588102003-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2588102003-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="2588102003-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="2588102003-6">]</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="n">old</span><span class="p" data-group-id="2588102003-5">}</span><span class="p" data-group-id="2588102003-2">]</span></code></pre><p>We see that the new release version is <code class="inline">permanent</code>, so it would be safe to
│ │ │ +restarted now, it would come up running the &quot;FIRST&quot; release again.</p><p><em>Step 3.</em> Make the new release permanent:</p><pre><code class="text">2&gt; release_handler:make_permanent(&quot;SECOND&quot;).</code></pre><p>Check the releases again:</p><pre><code class="makeup c" translate="no"><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">release_handler</span><span class="o">:</span><span class="nf">which_releases</span><span class="p" data-group-id="0314553606-1">(</span><span class="p" data-group-id="0314553606-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0314553606-2">[</span><span class="p" data-group-id="0314553606-3">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;SECOND&quot;</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="0314553606-4">[</span><span class="s">&quot;kernel-3.0&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-2.0&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-2.0&quot;</span><span class="p" data-group-id="0314553606-4">]</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="n">permanent</span><span class="p" data-group-id="0314553606-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0314553606-5">{</span><span class="s">&quot;MYSYSTEM&quot;</span><span class="p">,</span><span class="s">&quot;FIRST&quot;</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="0314553606-6">[</span><span class="s">&quot;kernel-2.16.4&quot;</span><span class="p">,</span><span class="s">&quot;stdlib-1.19.4&quot;</span><span class="p">,</span><span class="s">&quot;sasl-2.3.4&quot;</span><span class="p">,</span><span class="s">&quot;pea-1.0&quot;</span><span class="p" data-group-id="0314553606-6">]</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="n">old</span><span class="p" data-group-id="0314553606-5">}</span><span class="p" data-group-id="0314553606-2">]</span></code></pre><p>We see that the new release version is <code class="inline">permanent</code>, so it would be safe to
│ │ │  restart the node.</p><p><a href="" id="listing-of-target-system"></a></p><h2 id="listing-of-target_system-erl" class="section-heading">
│ │ │    <a href="#listing-of-target_system-erl" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Listing of target_system.erl</span>
│ │ │  </h2>
│ │ │  <p>This module can also be found in the <code class="inline">examples</code> directory of the SASL
│ │ │  application.</p><pre><code class="makeup erlang" translate="no"><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7926741327-1">(</span><span class="ss">target_system</span><span class="p" data-group-id="7926741327-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7926741327-2">(</span><span class="p" data-group-id="7926741327-3">[</span><span class="ss">create</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">create</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">install</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7926741327-3">]</span><span class="p" data-group-id="7926741327-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2290236864-1">(</span><span class="ss">target_system</span><span class="p" data-group-id="2290236864-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2290236864-2">(</span><span class="p" data-group-id="2290236864-3">[</span><span class="ss">create</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">create</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">install</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2290236864-3">]</span><span class="p" data-group-id="2290236864-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Note: RelFileName below is the *stem* without trailing .rel,</span><span class="w">
│ │ │  </span><span class="c1">%% .script etc.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% create(RelFileName)</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">create</span><span class="p" data-group-id="7926741327-4">(</span><span class="n">RelFileName</span><span class="p" data-group-id="7926741327-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">create</span><span class="p" data-group-id="7926741327-5">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="p" data-group-id="7926741327-6">[</span><span class="p" data-group-id="7926741327-6">]</span><span class="p" data-group-id="7926741327-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">create</span><span class="p" data-group-id="2290236864-4">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2290236864-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">create</span><span class="p" data-group-id="2290236864-5">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="p" data-group-id="2290236864-6">[</span><span class="p" data-group-id="2290236864-6">]</span><span class="p" data-group-id="2290236864-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">create</span><span class="p" data-group-id="7926741327-7">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="7926741327-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">create</span><span class="p" data-group-id="2290236864-7">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2290236864-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">RelFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="7926741327-8">(</span><span class="n">RelFileName</span><span class="p" data-group-id="7926741327-8">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-9">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;plain&quot;</span><span class="p" data-group-id="7926741327-9">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="2290236864-8">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2290236864-8">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-9">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;plain&quot;</span><span class="p" data-group-id="2290236864-9">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">PlainRelFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PlainRelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-10">(</span><span class="s">&quot;Reading file: ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-11">[</span><span class="n">RelFile</span><span class="p" data-group-id="7926741327-11">]</span><span class="p" data-group-id="7926741327-10">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-13">[</span><span class="n">RelSpec</span><span class="p" data-group-id="7926741327-13">]</span><span class="p" data-group-id="7926741327-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">consult</span><span class="p" data-group-id="7926741327-14">(</span><span class="n">RelFile</span><span class="p" data-group-id="7926741327-14">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-15">(</span><span class="s">&quot;Creating file: ~ts from ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="7926741327-16">[</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="n">RelFile</span><span class="p" data-group-id="7926741327-16">]</span><span class="p" data-group-id="7926741327-15">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-17">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="7926741327-18">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="7926741327-18">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="7926741327-19">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="7926741327-19">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="n">AppVsns</span><span class="p" data-group-id="7926741327-17">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelSpec</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">PlainRelSpec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7926741327-20">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="7926741327-21">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="7926741327-21">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="7926741327-22">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="7926741327-22">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="7926741327-23">(</span><span class="nf">fun</span><span class="p" data-group-id="7926741327-24">(</span><span class="p" data-group-id="7926741327-25">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7926741327-25">}</span><span class="p" data-group-id="7926741327-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-10">(</span><span class="s">&quot;Reading file: ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-11">[</span><span class="n">RelFile</span><span class="p" data-group-id="2290236864-11">]</span><span class="p" data-group-id="2290236864-10">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-13">[</span><span class="n">RelSpec</span><span class="p" data-group-id="2290236864-13">]</span><span class="p" data-group-id="2290236864-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">consult</span><span class="p" data-group-id="2290236864-14">(</span><span class="n">RelFile</span><span class="p" data-group-id="2290236864-14">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-15">(</span><span class="s">&quot;Creating file: ~ts from ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2290236864-16">[</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="n">RelFile</span><span class="p" data-group-id="2290236864-16">]</span><span class="p" data-group-id="2290236864-15">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-17">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="2290236864-18">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="2290236864-18">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="2290236864-19">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="2290236864-19">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="n">AppVsns</span><span class="p" data-group-id="2290236864-17">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelSpec</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">PlainRelSpec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2290236864-20">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="2290236864-21">{</span><span class="n">RelName</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="2290236864-21">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="2290236864-22">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p" data-group-id="2290236864-22">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="2290236864-23">(</span><span class="nf">fun</span><span class="p" data-group-id="2290236864-24">(</span><span class="p" data-group-id="2290236864-25">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2290236864-25">}</span><span class="p" data-group-id="2290236864-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                                           </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -                                    </span><span class="p" data-group-id="7926741327-26">(</span><span class="p" data-group-id="7926741327-27">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7926741327-27">}</span><span class="p" data-group-id="7926741327-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                                    </span><span class="p" data-group-id="2290236864-26">(</span><span class="p" data-group-id="2290236864-27">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2290236864-27">}</span><span class="p" data-group-id="2290236864-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                                           </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -                                    </span><span class="p" data-group-id="7926741327-28">(</span><span class="p">_</span><span class="p" data-group-id="7926741327-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                                    </span><span class="p" data-group-id="2290236864-28">(</span><span class="p">_</span><span class="p" data-group-id="2290236864-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                                           </span><span class="ss">false</span><span class="w">
│ │ │ -                                 </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsns</span><span class="p" data-group-id="7926741327-23">)</span><span class="w">
│ │ │ -                   </span><span class="p" data-group-id="7926741327-20">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="7926741327-29">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="7926741327-30">(</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-31">[</span><span class="ss">write</span><span class="p" data-group-id="7926741327-31">]</span><span class="p" data-group-id="7926741327-30">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-32">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-33">[</span><span class="n">PlainRelSpec</span><span class="p" data-group-id="7926741327-33">]</span><span class="p" data-group-id="7926741327-32">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="7926741327-34">(</span><span class="n">Fd</span><span class="p" data-group-id="7926741327-34">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-35">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -	      </span><span class="p" data-group-id="7926741327-36">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">PlainRelFileName</span><span class="p" data-group-id="7926741327-36">]</span><span class="p" data-group-id="7926741327-35">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">make_script</span><span class="p" data-group-id="7926741327-37">(</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="7926741327-37">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-38">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="7926741327-39">[</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="7926741327-39">]</span><span class="p" data-group-id="7926741327-38">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">make_script</span><span class="p" data-group-id="7926741327-40">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="7926741327-40">)</span><span class="p">,</span><span class="w">
│ │ │ +                                 </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsns</span><span class="p" data-group-id="2290236864-23">)</span><span class="w">
│ │ │ +                   </span><span class="p" data-group-id="2290236864-20">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2290236864-29">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2290236864-30">(</span><span class="n">PlainRelFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-31">[</span><span class="ss">write</span><span class="p" data-group-id="2290236864-31">]</span><span class="p" data-group-id="2290236864-30">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-32">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-33">[</span><span class="n">PlainRelSpec</span><span class="p" data-group-id="2290236864-33">]</span><span class="p" data-group-id="2290236864-32">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2290236864-34">(</span><span class="n">Fd</span><span class="p" data-group-id="2290236864-34">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-35">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +	      </span><span class="p" data-group-id="2290236864-36">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">PlainRelFileName</span><span class="p" data-group-id="2290236864-36">]</span><span class="p" data-group-id="2290236864-35">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">make_script</span><span class="p" data-group-id="2290236864-37">(</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2290236864-37">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-38">(</span><span class="s">&quot;Making \&quot;~ts.script\&quot; and \&quot;~ts.boot\&quot; files ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2290236864-39">[</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="2290236864-39">]</span><span class="p" data-group-id="2290236864-38">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">make_script</span><span class="p" data-group-id="2290236864-40">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2290236864-40">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │      </span><span class="n">TarFileName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.tar.gz&quot;</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-41">(</span><span class="s">&quot;Creating tar file ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-42">[</span><span class="n">TarFileName</span><span class="p" data-group-id="7926741327-42">]</span><span class="p" data-group-id="7926741327-41">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">make_tar</span><span class="p" data-group-id="7926741327-43">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="7926741327-43">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-41">(</span><span class="s">&quot;Creating tar file ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-42">[</span><span class="n">TarFileName</span><span class="p" data-group-id="2290236864-42">]</span><span class="p" data-group-id="2290236864-41">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">make_tar</span><span class="p" data-group-id="2290236864-43">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">SystoolsOpts</span><span class="p" data-group-id="2290236864-43">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="n">TmpDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-44">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;tmp&quot;</span><span class="p" data-group-id="7926741327-44">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-45">(</span><span class="s">&quot;Creating directory ~tp ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="7926741327-46">[</span><span class="n">TmpDir</span><span class="p" data-group-id="7926741327-46">]</span><span class="p" data-group-id="7926741327-45">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="7926741327-47">(</span><span class="n">TmpDir</span><span class="p" data-group-id="7926741327-47">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-48">(</span><span class="s">&quot;Extracting ~ts into directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-49">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="7926741327-49">]</span><span class="p" data-group-id="7926741327-48">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">extract_tar</span><span class="p" data-group-id="7926741327-50">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="n">TmpDir</span><span class="p" data-group-id="7926741327-50">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="n">TmpBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-51">(</span><span class="p" data-group-id="7926741327-52">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="7926741327-52">]</span><span class="p" data-group-id="7926741327-51">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-53">(</span><span class="p" data-group-id="7926741327-54">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="7926741327-54">]</span><span class="p" data-group-id="7926741327-53">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-55">(</span><span class="s">&quot;Deleting \&quot;erl\&quot; and \&quot;start\&quot; in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="7926741327-56">[</span><span class="n">ErtsBinDir</span><span class="p" data-group-id="7926741327-56">]</span><span class="p" data-group-id="7926741327-55">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="7926741327-57">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-58">(</span><span class="p" data-group-id="7926741327-59">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erl&quot;</span><span class="p" data-group-id="7926741327-59">]</span><span class="p" data-group-id="7926741327-58">)</span><span class="p" data-group-id="7926741327-57">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="7926741327-60">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-61">(</span><span class="p" data-group-id="7926741327-62">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="7926741327-62">]</span><span class="p" data-group-id="7926741327-61">)</span><span class="p" data-group-id="7926741327-60">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-63">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-64">[</span><span class="n">TmpBinDir</span><span class="p" data-group-id="7926741327-64">]</span><span class="p" data-group-id="7926741327-63">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="7926741327-65">(</span><span class="n">TmpBinDir</span><span class="p" data-group-id="7926741327-65">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-66">(</span><span class="s">&quot;Copying file \&quot;~ts.boot\&quot; to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="7926741327-67">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-68">(</span><span class="p" data-group-id="7926741327-69">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="7926741327-69">]</span><span class="p" data-group-id="7926741327-68">)</span><span class="p" data-group-id="7926741327-67">]</span><span class="p" data-group-id="7926741327-66">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="7926741327-70">(</span><span class="n">PlainRelFileName</span><span class="o">++</span><span class="s">&quot;.boot&quot;</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-71">(</span><span class="p" data-group-id="7926741327-72">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="7926741327-72">]</span><span class="p" data-group-id="7926741327-71">)</span><span class="p" data-group-id="7926741327-70">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">TmpDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-44">(</span><span class="n">Dir</span><span class="p">,</span><span class="s">&quot;tmp&quot;</span><span class="p" data-group-id="2290236864-44">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-45">(</span><span class="s">&quot;Creating directory ~tp ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2290236864-46">[</span><span class="n">TmpDir</span><span class="p" data-group-id="2290236864-46">]</span><span class="p" data-group-id="2290236864-45">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="2290236864-47">(</span><span class="n">TmpDir</span><span class="p" data-group-id="2290236864-47">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-48">(</span><span class="s">&quot;Extracting ~ts into directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-49">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="2290236864-49">]</span><span class="p" data-group-id="2290236864-48">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">extract_tar</span><span class="p" data-group-id="2290236864-50">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="n">TmpDir</span><span class="p" data-group-id="2290236864-50">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="n">TmpBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-51">(</span><span class="p" data-group-id="2290236864-52">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2290236864-52">]</span><span class="p" data-group-id="2290236864-51">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-53">(</span><span class="p" data-group-id="2290236864-54">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2290236864-54">]</span><span class="p" data-group-id="2290236864-53">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-55">(</span><span class="s">&quot;Deleting \&quot;erl\&quot; and \&quot;start\&quot; in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2290236864-56">[</span><span class="n">ErtsBinDir</span><span class="p" data-group-id="2290236864-56">]</span><span class="p" data-group-id="2290236864-55">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2290236864-57">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-58">(</span><span class="p" data-group-id="2290236864-59">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erl&quot;</span><span class="p" data-group-id="2290236864-59">]</span><span class="p" data-group-id="2290236864-58">)</span><span class="p" data-group-id="2290236864-57">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2290236864-60">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-61">(</span><span class="p" data-group-id="2290236864-62">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="2290236864-62">]</span><span class="p" data-group-id="2290236864-61">)</span><span class="p" data-group-id="2290236864-60">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-63">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-64">[</span><span class="n">TmpBinDir</span><span class="p" data-group-id="2290236864-64">]</span><span class="p" data-group-id="2290236864-63">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="2290236864-65">(</span><span class="n">TmpBinDir</span><span class="p" data-group-id="2290236864-65">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-66">(</span><span class="s">&quot;Copying file \&quot;~ts.boot\&quot; to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2290236864-67">[</span><span class="n">PlainRelFileName</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-68">(</span><span class="p" data-group-id="2290236864-69">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="2290236864-69">]</span><span class="p" data-group-id="2290236864-68">)</span><span class="p" data-group-id="2290236864-67">]</span><span class="p" data-group-id="2290236864-66">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2290236864-70">(</span><span class="n">PlainRelFileName</span><span class="o">++</span><span class="s">&quot;.boot&quot;</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-71">(</span><span class="p" data-group-id="2290236864-72">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start.boot&quot;</span><span class="p" data-group-id="2290236864-72">]</span><span class="p" data-group-id="2290236864-71">)</span><span class="p" data-group-id="2290236864-70">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-73">(</span><span class="s">&quot;Copying files \&quot;epmd\&quot;, \&quot;run_erl\&quot; and \&quot;to_erl\&quot; from \n&quot;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-73">(</span><span class="s">&quot;Copying files \&quot;epmd\&quot;, \&quot;run_erl\&quot; and \&quot;to_erl\&quot; from \n&quot;</span><span class="w">
│ │ │                </span><span class="s">&quot;~ts to ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="7926741327-74">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">TmpBinDir</span><span class="p" data-group-id="7926741327-74">]</span><span class="p" data-group-id="7926741327-73">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="7926741327-75">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-76">(</span><span class="p" data-group-id="7926741327-77">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="7926741327-77">]</span><span class="p" data-group-id="7926741327-76">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-78">(</span><span class="p" data-group-id="7926741327-79">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="7926741327-79">]</span><span class="p" data-group-id="7926741327-78">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-80">[</span><span class="ss">preserve</span><span class="p" data-group-id="7926741327-80">]</span><span class="p" data-group-id="7926741327-75">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="7926741327-81">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-82">(</span><span class="p" data-group-id="7926741327-83">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="7926741327-83">]</span><span class="p" data-group-id="7926741327-82">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-84">(</span><span class="p" data-group-id="7926741327-85">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="7926741327-85">]</span><span class="p" data-group-id="7926741327-84">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-86">[</span><span class="ss">preserve</span><span class="p" data-group-id="7926741327-86">]</span><span class="p" data-group-id="7926741327-81">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="7926741327-87">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-88">(</span><span class="p" data-group-id="7926741327-89">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="7926741327-89">]</span><span class="p" data-group-id="7926741327-88">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-90">(</span><span class="p" data-group-id="7926741327-91">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="7926741327-91">]</span><span class="p" data-group-id="7926741327-90">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-92">[</span><span class="ss">preserve</span><span class="p" data-group-id="7926741327-92">]</span><span class="p" data-group-id="7926741327-87">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2290236864-74">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">TmpBinDir</span><span class="p" data-group-id="2290236864-74">]</span><span class="p" data-group-id="2290236864-73">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2290236864-75">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-76">(</span><span class="p" data-group-id="2290236864-77">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="2290236864-77">]</span><span class="p" data-group-id="2290236864-76">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-78">(</span><span class="p" data-group-id="2290236864-79">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;epmd&quot;</span><span class="p" data-group-id="2290236864-79">]</span><span class="p" data-group-id="2290236864-78">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-80">[</span><span class="ss">preserve</span><span class="p" data-group-id="2290236864-80">]</span><span class="p" data-group-id="2290236864-75">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2290236864-81">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-82">(</span><span class="p" data-group-id="2290236864-83">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="2290236864-83">]</span><span class="p" data-group-id="2290236864-82">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-84">(</span><span class="p" data-group-id="2290236864-85">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;run_erl&quot;</span><span class="p" data-group-id="2290236864-85">]</span><span class="p" data-group-id="2290236864-84">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-86">[</span><span class="ss">preserve</span><span class="p" data-group-id="2290236864-86">]</span><span class="p" data-group-id="2290236864-81">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2290236864-87">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-88">(</span><span class="p" data-group-id="2290236864-89">[</span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="2290236864-89">]</span><span class="p" data-group-id="2290236864-88">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-90">(</span><span class="p" data-group-id="2290236864-91">[</span><span class="n">TmpBinDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;to_erl&quot;</span><span class="p" data-group-id="2290236864-91">]</span><span class="p" data-group-id="2290236864-90">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-92">[</span><span class="ss">preserve</span><span class="p" data-group-id="2290236864-92">]</span><span class="p" data-group-id="2290236864-87">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │      </span><span class="c1">%% This is needed if &#39;start&#39; script created from &#39;start.src&#39; shall</span><span class="w">
│ │ │      </span><span class="c1">%% be used as it points out this directory as log dir for &#39;run_erl&#39;</span><span class="w">
│ │ │ -    </span><span class="n">TmpLogDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-93">(</span><span class="p" data-group-id="7926741327-94">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="7926741327-94">]</span><span class="p" data-group-id="7926741327-93">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-95">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-96">[</span><span class="n">TmpLogDir</span><span class="p" data-group-id="7926741327-96">]</span><span class="p" data-group-id="7926741327-95">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="7926741327-97">(</span><span class="n">TmpLogDir</span><span class="p" data-group-id="7926741327-97">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-98">(</span><span class="p" data-group-id="7926741327-99">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="7926741327-99">]</span><span class="p" data-group-id="7926741327-98">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-100">(</span><span class="s">&quot;Creating ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-101">[</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="7926741327-101">]</span><span class="p" data-group-id="7926741327-100">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">StartErlData</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">io_lib</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-102">(</span><span class="s">&quot;</span><span class="si">~s</span><span class="s"> </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-103">[</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="7926741327-103">]</span><span class="p" data-group-id="7926741327-102">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">write_file</span><span class="p" data-group-id="7926741327-104">(</span><span class="n">StartErlDataFile</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="7926741327-104">)</span><span class="p">,</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-105">(</span><span class="s">&quot;Recreating tar file ~ts from contents in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -	      </span><span class="p" data-group-id="7926741327-106">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="7926741327-106">]</span><span class="p" data-group-id="7926741327-105">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-107">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tar</span><span class="p" data-group-id="7926741327-107">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="7926741327-108">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-109">[</span><span class="ss">write</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="7926741327-109">]</span><span class="p" data-group-id="7926741327-108">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">TmpLogDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-93">(</span><span class="p" data-group-id="2290236864-94">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="2290236864-94">]</span><span class="p" data-group-id="2290236864-93">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-95">(</span><span class="s">&quot;Creating temporary directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-96">[</span><span class="n">TmpLogDir</span><span class="p" data-group-id="2290236864-96">]</span><span class="p" data-group-id="2290236864-95">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">make_dir</span><span class="p" data-group-id="2290236864-97">(</span><span class="n">TmpLogDir</span><span class="p" data-group-id="2290236864-97">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-98">(</span><span class="p" data-group-id="2290236864-99">[</span><span class="n">TmpDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="2290236864-99">]</span><span class="p" data-group-id="2290236864-98">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-100">(</span><span class="s">&quot;Creating ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-101">[</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="2290236864-101">]</span><span class="p" data-group-id="2290236864-100">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">StartErlData</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">io_lib</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-102">(</span><span class="s">&quot;</span><span class="si">~s</span><span class="s"> </span><span class="si">~s</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-103">[</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w"> </span><span class="n">RelVsn</span><span class="p" data-group-id="2290236864-103">]</span><span class="p" data-group-id="2290236864-102">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">write_file</span><span class="p" data-group-id="2290236864-104">(</span><span class="n">StartErlDataFile</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="2290236864-104">)</span><span class="p">,</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-105">(</span><span class="s">&quot;Recreating tar file ~ts from contents in directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +	      </span><span class="p" data-group-id="2290236864-106">[</span><span class="n">TarFileName</span><span class="p">,</span><span class="n">TmpDir</span><span class="p" data-group-id="2290236864-106">]</span><span class="p" data-group-id="2290236864-105">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-107">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tar</span><span class="p" data-group-id="2290236864-107">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2290236864-108">(</span><span class="n">TarFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-109">[</span><span class="ss">write</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="2290236864-109">]</span><span class="p" data-group-id="2290236864-108">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% {ok, Cwd} = file:get_cwd(),</span><span class="w">
│ │ │      </span><span class="c1">%% file:set_cwd(&quot;tmp&quot;),</span><span class="w">
│ │ │      </span><span class="n">ErtsDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="o">++</span><span class="n">ErtsVsn</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="7926741327-110">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-111">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="7926741327-111">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-112">[</span><span class="p" data-group-id="7926741327-112">]</span><span class="p" data-group-id="7926741327-110">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="7926741327-113">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-114">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="n">ErtsDir</span><span class="p" data-group-id="7926741327-114">)</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsDir</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-115">[</span><span class="p" data-group-id="7926741327-115">]</span><span class="p" data-group-id="7926741327-113">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="7926741327-116">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-117">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;releases&quot;</span><span class="p" data-group-id="7926741327-117">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-118">[</span><span class="p" data-group-id="7926741327-118">]</span><span class="p" data-group-id="7926741327-116">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="7926741327-119">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-120">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;lib&quot;</span><span class="p" data-group-id="7926741327-120">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;lib&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-121">[</span><span class="p" data-group-id="7926741327-121">]</span><span class="p" data-group-id="7926741327-119">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="7926741327-122">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-123">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="7926741327-123">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-124">[</span><span class="p" data-group-id="7926741327-124">]</span><span class="p" data-group-id="7926741327-122">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="7926741327-125">(</span><span class="n">Tar</span><span class="p" data-group-id="7926741327-125">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2290236864-110">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-111">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2290236864-111">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-112">[</span><span class="p" data-group-id="2290236864-112">]</span><span class="p" data-group-id="2290236864-110">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2290236864-113">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-114">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="n">ErtsDir</span><span class="p" data-group-id="2290236864-114">)</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsDir</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-115">[</span><span class="p" data-group-id="2290236864-115">]</span><span class="p" data-group-id="2290236864-113">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2290236864-116">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-117">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;releases&quot;</span><span class="p" data-group-id="2290236864-117">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-118">[</span><span class="p" data-group-id="2290236864-118">]</span><span class="p" data-group-id="2290236864-116">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2290236864-119">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-120">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;lib&quot;</span><span class="p" data-group-id="2290236864-120">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;lib&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-121">[</span><span class="p" data-group-id="2290236864-121">]</span><span class="p" data-group-id="2290236864-119">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">add</span><span class="p" data-group-id="2290236864-122">(</span><span class="n">Tar</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-123">(</span><span class="n">TmpDir</span><span class="p">,</span><span class="s">&quot;log&quot;</span><span class="p" data-group-id="2290236864-123">)</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;log&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-124">[</span><span class="p" data-group-id="2290236864-124">]</span><span class="p" data-group-id="2290236864-122">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2290236864-125">(</span><span class="n">Tar</span><span class="p" data-group-id="2290236864-125">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% file:set_cwd(Cwd),</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-126">(</span><span class="s">&quot;Removing directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="7926741327-127">[</span><span class="n">TmpDir</span><span class="p" data-group-id="7926741327-127">]</span><span class="p" data-group-id="7926741327-126">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="7926741327-128">(</span><span class="n">TmpDir</span><span class="p" data-group-id="7926741327-128">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-126">(</span><span class="s">&quot;Removing directory ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2290236864-127">[</span><span class="n">TmpDir</span><span class="p" data-group-id="2290236864-127">]</span><span class="p" data-group-id="2290236864-126">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="2290236864-128">(</span><span class="n">TmpDir</span><span class="p" data-group-id="2290236864-128">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │ -</span><span class="nf">install</span><span class="p" data-group-id="7926741327-129">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="7926741327-129">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">install</span><span class="p" data-group-id="2290236864-129">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2290236864-129">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">TarFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.tar.gz&quot;</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-130">(</span><span class="s">&quot;Extracting ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-131">[</span><span class="n">TarFile</span><span class="p" data-group-id="7926741327-131">]</span><span class="p" data-group-id="7926741327-130">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">extract_tar</span><span class="p" data-group-id="7926741327-132">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="7926741327-132">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-133">(</span><span class="p" data-group-id="7926741327-134">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="7926741327-134">]</span><span class="p" data-group-id="7926741327-133">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-135">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="7926741327-135">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="7926741327-136">(</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="7926741327-136">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-137">[</span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">RelVsn</span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7926741327-137">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">string</span><span class="p">:</span><span class="nf">tokens</span><span class="p" data-group-id="7926741327-138">(</span><span class="n">StartErlData</span><span class="p">,</span><span class="w"> </span><span class="s">&quot; \n&quot;</span><span class="p" data-group-id="7926741327-138">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-139">(</span><span class="p" data-group-id="7926741327-140">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="7926741327-140">]</span><span class="p" data-group-id="7926741327-139">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">BinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-141">(</span><span class="p" data-group-id="7926741327-142">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="7926741327-142">]</span><span class="p" data-group-id="7926741327-141">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-143">(</span><span class="s">&quot;Substituting in erl.src, start.src and start_erl.src to &quot;</span><span class="w">
│ │ │ -              </span><span class="s">&quot;form erl, start and start_erl ...\n&quot;</span><span class="p" data-group-id="7926741327-143">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="7926741327-144">(</span><span class="p" data-group-id="7926741327-145">[</span><span class="s">&quot;erl&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="7926741327-145">]</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">BinDir</span><span class="p">,</span><span class="w">
│ │ │ -                      </span><span class="p" data-group-id="7926741327-146">[</span><span class="p" data-group-id="7926741327-147">{</span><span class="s">&quot;FINAL_ROOTDIR&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="7926741327-147">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-148">{</span><span class="s">&quot;EMU&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;beam&quot;</span><span class="p" data-group-id="7926741327-148">}</span><span class="p" data-group-id="7926741327-146">]</span><span class="p">,</span><span class="w">
│ │ │ -                      </span><span class="p" data-group-id="7926741327-149">[</span><span class="ss">preserve</span><span class="p" data-group-id="7926741327-149">]</span><span class="p" data-group-id="7926741327-144">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-130">(</span><span class="s">&quot;Extracting ~ts ...</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-131">[</span><span class="n">TarFile</span><span class="p" data-group-id="2290236864-131">]</span><span class="p" data-group-id="2290236864-130">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">extract_tar</span><span class="p" data-group-id="2290236864-132">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2290236864-132">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">StartErlDataFile</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-133">(</span><span class="p" data-group-id="2290236864-134">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl.data&quot;</span><span class="p" data-group-id="2290236864-134">]</span><span class="p" data-group-id="2290236864-133">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-135">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">StartErlData</span><span class="p" data-group-id="2290236864-135">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="2290236864-136">(</span><span class="n">StartErlDataFile</span><span class="p" data-group-id="2290236864-136">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-137">[</span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">RelVsn</span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2290236864-137">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">string</span><span class="p">:</span><span class="nf">tokens</span><span class="p" data-group-id="2290236864-138">(</span><span class="n">StartErlData</span><span class="p">,</span><span class="w"> </span><span class="s">&quot; \n&quot;</span><span class="p" data-group-id="2290236864-138">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ErtsBinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-139">(</span><span class="p" data-group-id="2290236864-140">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;erts-&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">ErlVsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2290236864-140">]</span><span class="p" data-group-id="2290236864-139">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">BinDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-141">(</span><span class="p" data-group-id="2290236864-142">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bin&quot;</span><span class="p" data-group-id="2290236864-142">]</span><span class="p" data-group-id="2290236864-141">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-143">(</span><span class="s">&quot;Substituting in erl.src, start.src and start_erl.src to &quot;</span><span class="w">
│ │ │ +              </span><span class="s">&quot;form erl, start and start_erl ...\n&quot;</span><span class="p" data-group-id="2290236864-143">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="2290236864-144">(</span><span class="p" data-group-id="2290236864-145">[</span><span class="s">&quot;erl&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="2290236864-145">]</span><span class="p">,</span><span class="w"> </span><span class="n">ErtsBinDir</span><span class="p">,</span><span class="w"> </span><span class="n">BinDir</span><span class="p">,</span><span class="w">
│ │ │ +                      </span><span class="p" data-group-id="2290236864-146">[</span><span class="p" data-group-id="2290236864-147">{</span><span class="s">&quot;FINAL_ROOTDIR&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2290236864-147">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-148">{</span><span class="s">&quot;EMU&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;beam&quot;</span><span class="p" data-group-id="2290236864-148">}</span><span class="p" data-group-id="2290236864-146">]</span><span class="p">,</span><span class="w">
│ │ │ +                      </span><span class="p" data-group-id="2290236864-149">[</span><span class="ss">preserve</span><span class="p" data-group-id="2290236864-149">]</span><span class="p" data-group-id="2290236864-144">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%%! Workaround for pre OTP 17.0: start.src and start_erl.src did</span><span class="w">
│ │ │      </span><span class="c1">%%! not have correct permissions, so the above &#39;preserve&#39; option did not help</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="7926741327-150">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-151">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="7926741327-151">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="7926741327-150">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="7926741327-152">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-153">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="7926741327-153">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="7926741327-152">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="2290236864-150">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-151">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start&quot;</span><span class="p" data-group-id="2290236864-151">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="2290236864-150">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">change_mode</span><span class="p" data-group-id="2290236864-152">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-153">(</span><span class="n">BinDir</span><span class="p">,</span><span class="s">&quot;start_erl&quot;</span><span class="p" data-group-id="2290236864-153">)</span><span class="p">,</span><span class="mi">8#0755</span><span class="p" data-group-id="2290236864-152">)</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="7926741327-154">(</span><span class="s">&quot;Creating the RELEASES file ...\n&quot;</span><span class="p" data-group-id="7926741327-154">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">create_RELEASES</span><span class="p" data-group-id="7926741327-155">(</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-156">(</span><span class="p" data-group-id="7926741327-157">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w">
│ │ │ -					    </span><span class="nc">filename</span><span class="p">:</span><span class="nf">basename</span><span class="p" data-group-id="7926741327-158">(</span><span class="n">RelFileName</span><span class="p" data-group-id="7926741327-158">)</span><span class="p" data-group-id="7926741327-157">]</span><span class="p" data-group-id="7926741327-156">)</span><span class="p" data-group-id="7926741327-155">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">fwrite</span><span class="p" data-group-id="2290236864-154">(</span><span class="s">&quot;Creating the RELEASES file ...\n&quot;</span><span class="p" data-group-id="2290236864-154">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">create_RELEASES</span><span class="p" data-group-id="2290236864-155">(</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-156">(</span><span class="p" data-group-id="2290236864-157">[</span><span class="n">RootDir</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;releases&quot;</span><span class="p">,</span><span class="w">
│ │ │ +					    </span><span class="nc">filename</span><span class="p">:</span><span class="nf">basename</span><span class="p" data-group-id="2290236864-158">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2290236864-158">)</span><span class="p" data-group-id="2290236864-157">]</span><span class="p" data-group-id="2290236864-156">)</span><span class="p" data-group-id="2290236864-155">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% LOCALS</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% make_script(RelFileName,Opts)</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">make_script</span><span class="p" data-group-id="7926741327-159">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="7926741327-159">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="7926741327-160">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-161">[</span><span class="ss">no_module_tests</span><span class="p">,</span><span class="w">
│ │ │ -				       </span><span class="p" data-group-id="7926741327-162">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="7926741327-163">(</span><span class="n">RelFileName</span><span class="p" data-group-id="7926741327-163">)</span><span class="p" data-group-id="7926741327-162">}</span><span class="w">
│ │ │ -				       </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="7926741327-161">]</span><span class="p" data-group-id="7926741327-160">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">make_script</span><span class="p" data-group-id="2290236864-159">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="2290236864-159">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="2290236864-160">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-161">[</span><span class="ss">no_module_tests</span><span class="p">,</span><span class="w">
│ │ │ +				       </span><span class="p" data-group-id="2290236864-162">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="2290236864-163">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2290236864-163">)</span><span class="p" data-group-id="2290236864-162">}</span><span class="w">
│ │ │ +				       </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="2290236864-161">]</span><span class="p" data-group-id="2290236864-160">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% make_tar(RelFileName,Opts)</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">make_tar</span><span class="p" data-group-id="7926741327-164">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="7926741327-164">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">RootDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">code</span><span class="p">:</span><span class="nf">root_dir</span><span class="p" data-group-id="7926741327-165">(</span><span class="p" data-group-id="7926741327-165">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="7926741327-166">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-167">[</span><span class="p" data-group-id="7926741327-168">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="7926741327-168">}</span><span class="p">,</span><span class="w">
│ │ │ -				    </span><span class="p" data-group-id="7926741327-169">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="7926741327-170">(</span><span class="n">RelFileName</span><span class="p" data-group-id="7926741327-170">)</span><span class="p" data-group-id="7926741327-169">}</span><span class="w">
│ │ │ -				    </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="7926741327-167">]</span><span class="p" data-group-id="7926741327-166">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">make_tar</span><span class="p" data-group-id="2290236864-164">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="n">Opts</span><span class="p" data-group-id="2290236864-164">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">RootDir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">code</span><span class="p">:</span><span class="nf">root_dir</span><span class="p" data-group-id="2290236864-165">(</span><span class="p" data-group-id="2290236864-165">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="2290236864-166">(</span><span class="n">RelFileName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-167">[</span><span class="p" data-group-id="2290236864-168">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">RootDir</span><span class="p" data-group-id="2290236864-168">}</span><span class="p">,</span><span class="w">
│ │ │ +				    </span><span class="p" data-group-id="2290236864-169">{</span><span class="ss">outdir</span><span class="p">,</span><span class="nc">filename</span><span class="p">:</span><span class="nf">dirname</span><span class="p" data-group-id="2290236864-170">(</span><span class="n">RelFileName</span><span class="p" data-group-id="2290236864-170">)</span><span class="p" data-group-id="2290236864-169">}</span><span class="w">
│ │ │ +				    </span><span class="p">|</span><span class="n">Opts</span><span class="p" data-group-id="2290236864-167">]</span><span class="p" data-group-id="2290236864-166">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% extract_tar(TarFile, DestDir)</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">extract_tar</span><span class="p" data-group-id="7926741327-171">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="7926741327-171">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">extract</span><span class="p" data-group-id="7926741327-172">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-173">[</span><span class="p" data-group-id="7926741327-174">{</span><span class="ss">cwd</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="7926741327-174">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="7926741327-173">]</span><span class="p" data-group-id="7926741327-172">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">extract_tar</span><span class="p" data-group-id="2290236864-171">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="2290236864-171">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">erl_tar</span><span class="p">:</span><span class="nf">extract</span><span class="p" data-group-id="2290236864-172">(</span><span class="n">TarFile</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-173">[</span><span class="p" data-group-id="2290236864-174">{</span><span class="ss">cwd</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p" data-group-id="2290236864-174">}</span><span class="p">,</span><span class="w"> </span><span class="ss">compressed</span><span class="p" data-group-id="2290236864-173">]</span><span class="p" data-group-id="2290236864-172">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="7926741327-175">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="7926741327-175">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="7926741327-176">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p" data-group-id="7926741327-176">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="2290236864-175">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="p" data-group-id="2290236864-175">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">create_RELEASES</span><span class="p" data-group-id="2290236864-176">(</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">RelFileName</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.rel&quot;</span><span class="p" data-group-id="2290236864-176">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="7926741327-177">(</span><span class="n">Scripts</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7926741327-177">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="7926741327-178">(</span><span class="nf">fun</span><span class="p" data-group-id="7926741327-179">(</span><span class="n">Script</span><span class="p" data-group-id="7926741327-179">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                          </span><span class="nf">subst_src_script</span><span class="p" data-group-id="7926741327-180">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w">
│ │ │ -                                           </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7926741327-180">)</span><span class="w">
│ │ │ -                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Scripts</span><span class="p" data-group-id="7926741327-178">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">subst_src_script</span><span class="p" data-group-id="7926741327-181">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7926741327-181">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_file</span><span class="p" data-group-id="7926741327-182">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-183">(</span><span class="p" data-group-id="7926741327-184">[</span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.src&quot;</span><span class="p" data-group-id="7926741327-184">]</span><span class="p" data-group-id="7926741327-183">)</span><span class="p">,</span><span class="w">
│ │ │ -               </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-185">(</span><span class="p" data-group-id="7926741327-186">[</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="p" data-group-id="7926741327-186">]</span><span class="p" data-group-id="7926741327-185">)</span><span class="p">,</span><span class="w">
│ │ │ -               </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7926741327-182">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">subst_file</span><span class="p" data-group-id="7926741327-187">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7926741327-187">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-188">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="7926741327-188">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="7926741327-189">(</span><span class="n">Src</span><span class="p" data-group-id="7926741327-189">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">NConts</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">subst</span><span class="p" data-group-id="7926741327-190">(</span><span class="n">Conts</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="7926741327-190">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">write_file</span><span class="p" data-group-id="7926741327-191">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">NConts</span><span class="p" data-group-id="7926741327-191">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="7926741327-192">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7926741327-192">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">subst_src_scripts</span><span class="p" data-group-id="2290236864-177">(</span><span class="n">Scripts</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2290236864-177">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="2290236864-178">(</span><span class="nf">fun</span><span class="p" data-group-id="2290236864-179">(</span><span class="n">Script</span><span class="p" data-group-id="2290236864-179">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                          </span><span class="nf">subst_src_script</span><span class="p" data-group-id="2290236864-180">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w">
│ │ │ +                                           </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2290236864-180">)</span><span class="w">
│ │ │ +                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Scripts</span><span class="p" data-group-id="2290236864-178">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">subst_src_script</span><span class="p" data-group-id="2290236864-181">(</span><span class="n">Script</span><span class="p">,</span><span class="w"> </span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2290236864-181">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_file</span><span class="p" data-group-id="2290236864-182">(</span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-183">(</span><span class="p" data-group-id="2290236864-184">[</span><span class="n">SrcDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;.src&quot;</span><span class="p" data-group-id="2290236864-184">]</span><span class="p" data-group-id="2290236864-183">)</span><span class="p">,</span><span class="w">
│ │ │ +               </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-185">(</span><span class="p" data-group-id="2290236864-186">[</span><span class="n">DestDir</span><span class="p">,</span><span class="w"> </span><span class="n">Script</span><span class="p" data-group-id="2290236864-186">]</span><span class="p" data-group-id="2290236864-185">)</span><span class="p">,</span><span class="w">
│ │ │ +               </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2290236864-182">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">subst_file</span><span class="p" data-group-id="2290236864-187">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2290236864-187">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-188">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="2290236864-188">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read_txt_file</span><span class="p" data-group-id="2290236864-189">(</span><span class="n">Src</span><span class="p" data-group-id="2290236864-189">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">NConts</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">subst</span><span class="p" data-group-id="2290236864-190">(</span><span class="n">Conts</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="2290236864-190">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">write_file</span><span class="p" data-group-id="2290236864-191">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">NConts</span><span class="p" data-group-id="2290236864-191">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="2290236864-192">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2290236864-192">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="7926741327-193">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="7926741327-193">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="7926741327-194">(</span><span class="n">Src</span><span class="p" data-group-id="7926741327-194">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="7926741327-195">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="7926741327-195">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2290236864-193">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2290236864-193">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="2290236864-194">(</span><span class="n">Src</span><span class="p" data-group-id="2290236864-194">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="2290236864-195">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2290236864-195">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">ok</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% subst(Str, Vars)</span><span class="w">
│ │ │  </span><span class="c1">%% Vars = [{Var, Val}]</span><span class="w">
│ │ │  </span><span class="c1">%% Var = Val = string()</span><span class="w">
│ │ │  </span><span class="c1">%% Substitute all occurrences of %Var% for Val in Str, using the list</span><span class="w">
│ │ │  </span><span class="c1">%% of variables in Vars.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="7926741327-196">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="7926741327-196">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="7926741327-197">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-198">[</span><span class="p" data-group-id="7926741327-198">]</span><span class="p" data-group-id="7926741327-197">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2290236864-196">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="2290236864-196">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="2290236864-197">(</span><span class="n">Str</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-198">[</span><span class="p" data-group-id="2290236864-198">]</span><span class="p" data-group-id="2290236864-197">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="7926741327-199">(</span><span class="p" data-group-id="7926741327-200">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7926741327-200">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7926741327-199">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$Z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="7926741327-201">(</span><span class="p" data-group-id="7926741327-202">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7926741327-202">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-203">[</span><span class="p" data-group-id="7926741327-203">]</span><span class="p" data-group-id="7926741327-201">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="7926741327-204">(</span><span class="p" data-group-id="7926741327-205">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7926741327-205">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7926741327-204">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="7926741327-206">(</span><span class="p" data-group-id="7926741327-207">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7926741327-207">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-208">[</span><span class="p" data-group-id="7926741327-208">]</span><span class="p" data-group-id="7926741327-206">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="7926741327-209">(</span><span class="p" data-group-id="7926741327-210">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7926741327-210">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7926741327-209">)</span><span class="w"> </span><span class="k">when</span><span class="w">  </span><span class="n">C</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">$_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="7926741327-211">(</span><span class="p" data-group-id="7926741327-212">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7926741327-212">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-213">[</span><span class="p" data-group-id="7926741327-213">]</span><span class="p" data-group-id="7926741327-211">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="7926741327-214">(</span><span class="p" data-group-id="7926741327-215">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7926741327-215">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7926741327-214">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="7926741327-216">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-217">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7926741327-217">]</span><span class="p" data-group-id="7926741327-216">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst</span><span class="p" data-group-id="7926741327-218">(</span><span class="p" data-group-id="7926741327-219">[</span><span class="p" data-group-id="7926741327-219">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7926741327-218">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="7926741327-220">(</span><span class="n">Result</span><span class="p" data-group-id="7926741327-220">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="7926741327-221">(</span><span class="p" data-group-id="7926741327-222">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7926741327-222">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="7926741327-221">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Key</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="7926741327-223">(</span><span class="n">VarAcc</span><span class="p" data-group-id="7926741327-223">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="7926741327-224">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="7926741327-224">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7926741327-225">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-226">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="7926741327-226">}</span><span class="p" data-group-id="7926741327-225">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">subst</span><span class="p" data-group-id="7926741327-227">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="7926741327-228">(</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7926741327-228">)</span><span class="p" data-group-id="7926741327-227">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2290236864-199">(</span><span class="p" data-group-id="2290236864-200">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2290236864-200">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2290236864-199">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$Z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="2290236864-201">(</span><span class="p" data-group-id="2290236864-202">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2290236864-202">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-203">[</span><span class="p" data-group-id="2290236864-203">]</span><span class="p" data-group-id="2290236864-201">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2290236864-204">(</span><span class="p" data-group-id="2290236864-205">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2290236864-205">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2290236864-204">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="2290236864-206">(</span><span class="p" data-group-id="2290236864-207">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2290236864-207">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-208">[</span><span class="p" data-group-id="2290236864-208">]</span><span class="p" data-group-id="2290236864-206">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2290236864-209">(</span><span class="p" data-group-id="2290236864-210">[</span><span class="sc">$%</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2290236864-210">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2290236864-209">)</span><span class="w"> </span><span class="k">when</span><span class="w">  </span><span class="n">C</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">$_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="2290236864-211">(</span><span class="p" data-group-id="2290236864-212">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2290236864-212">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-213">[</span><span class="p" data-group-id="2290236864-213">]</span><span class="p" data-group-id="2290236864-211">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2290236864-214">(</span><span class="p" data-group-id="2290236864-215">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2290236864-215">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2290236864-214">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="2290236864-216">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-217">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2290236864-217">]</span><span class="p" data-group-id="2290236864-216">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst</span><span class="p" data-group-id="2290236864-218">(</span><span class="p" data-group-id="2290236864-219">[</span><span class="p" data-group-id="2290236864-219">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2290236864-218">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2290236864-220">(</span><span class="n">Result</span><span class="p" data-group-id="2290236864-220">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="2290236864-221">(</span><span class="p" data-group-id="2290236864-222">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2290236864-222">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2290236864-221">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Key</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2290236864-223">(</span><span class="n">VarAcc</span><span class="p" data-group-id="2290236864-223">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="2290236864-224">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p" data-group-id="2290236864-224">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2290236864-225">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-226">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="2290236864-226">}</span><span class="p" data-group-id="2290236864-225">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">subst</span><span class="p" data-group-id="2290236864-227">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2290236864-228">(</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2290236864-228">)</span><span class="p" data-group-id="2290236864-227">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">subst</span><span class="p" data-group-id="7926741327-229">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-230">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="7926741327-231">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7926741327-231">]</span><span class="p" data-group-id="7926741327-230">]</span><span class="p" data-group-id="7926741327-229">)</span><span class="w">
│ │ │ +            </span><span class="nf">subst</span><span class="p" data-group-id="2290236864-229">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-230">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2290236864-231">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2290236864-231">]</span><span class="p" data-group-id="2290236864-230">]</span><span class="p" data-group-id="2290236864-229">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="7926741327-232">(</span><span class="p" data-group-id="7926741327-233">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7926741327-233">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="7926741327-232">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst_var</span><span class="p" data-group-id="7926741327-234">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-235">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="7926741327-235">]</span><span class="p" data-group-id="7926741327-234">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">subst_var</span><span class="p" data-group-id="7926741327-236">(</span><span class="p" data-group-id="7926741327-237">[</span><span class="p" data-group-id="7926741327-237">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="7926741327-236">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">subst</span><span class="p" data-group-id="7926741327-238">(</span><span class="p" data-group-id="7926741327-239">[</span><span class="p" data-group-id="7926741327-239">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-240">[</span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="7926741327-241">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7926741327-241">]</span><span class="p" data-group-id="7926741327-240">]</span><span class="p" data-group-id="7926741327-238">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">copy_file</span><span class="p" data-group-id="7926741327-242">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="7926741327-242">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">copy_file</span><span class="p" data-group-id="7926741327-243">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-244">[</span><span class="p" data-group-id="7926741327-244">]</span><span class="p" data-group-id="7926741327-243">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">copy_file</span><span class="p" data-group-id="7926741327-245">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7926741327-245">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-246">{</span><span class="ss">ok</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7926741327-246">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">copy</span><span class="p" data-group-id="7926741327-247">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="7926741327-247">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="7926741327-248">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7926741327-248">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="2290236864-232">(</span><span class="p" data-group-id="2290236864-233">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2290236864-233">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2290236864-232">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst_var</span><span class="p" data-group-id="2290236864-234">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-235">[</span><span class="n">C</span><span class="p">|</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2290236864-235">]</span><span class="p" data-group-id="2290236864-234">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">subst_var</span><span class="p" data-group-id="2290236864-236">(</span><span class="p" data-group-id="2290236864-237">[</span><span class="p" data-group-id="2290236864-237">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p">,</span><span class="w"> </span><span class="n">VarAcc</span><span class="p" data-group-id="2290236864-236">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">subst</span><span class="p" data-group-id="2290236864-238">(</span><span class="p" data-group-id="2290236864-239">[</span><span class="p" data-group-id="2290236864-239">]</span><span class="p">,</span><span class="w"> </span><span class="n">Vars</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-240">[</span><span class="n">VarAcc</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2290236864-241">[</span><span class="sc">$%</span><span class="p">|</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="2290236864-241">]</span><span class="p" data-group-id="2290236864-240">]</span><span class="p" data-group-id="2290236864-238">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">copy_file</span><span class="p" data-group-id="2290236864-242">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="2290236864-242">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">copy_file</span><span class="p" data-group-id="2290236864-243">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-244">[</span><span class="p" data-group-id="2290236864-244">]</span><span class="p" data-group-id="2290236864-243">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">copy_file</span><span class="p" data-group-id="2290236864-245">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2290236864-245">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-246">{</span><span class="ss">ok</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2290236864-246">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">copy</span><span class="p" data-group-id="2290236864-247">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dest</span><span class="p" data-group-id="2290236864-247">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="2290236864-248">(</span><span class="ss">preserve</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="2290236864-248">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="7926741327-249">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="7926741327-249">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="7926741327-250">(</span><span class="n">Src</span><span class="p" data-group-id="7926741327-250">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="7926741327-251">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="7926741327-251">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2290236864-249">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2290236864-249">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file_info</span><span class="p" data-group-id="2290236864-250">(</span><span class="n">Src</span><span class="p" data-group-id="2290236864-250">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">file</span><span class="p">:</span><span class="nf">write_file_info</span><span class="p" data-group-id="2290236864-251">(</span><span class="n">Dest</span><span class="p">,</span><span class="w"> </span><span class="n">FileInfo</span><span class="p" data-group-id="2290236864-251">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">ok</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">write_file</span><span class="p" data-group-id="7926741327-252">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="7926741327-252">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Enc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">native_name_encoding</span><span class="p" data-group-id="7926741327-253">(</span><span class="p" data-group-id="7926741327-253">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-254">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="7926741327-254">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="7926741327-255">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-256">[</span><span class="ss">write</span><span class="p" data-group-id="7926741327-256">]</span><span class="p" data-group-id="7926741327-255">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">write</span><span class="p" data-group-id="7926741327-257">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="nc">unicode</span><span class="p">:</span><span class="nf">characters_to_binary</span><span class="p" data-group-id="7926741327-258">(</span><span class="n">Conts</span><span class="p">,</span><span class="n">Enc</span><span class="p">,</span><span class="n">Enc</span><span class="p" data-group-id="7926741327-258">)</span><span class="p" data-group-id="7926741327-257">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="7926741327-259">(</span><span class="n">Fd</span><span class="p" data-group-id="7926741327-259">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">read_txt_file</span><span class="p" data-group-id="7926741327-260">(</span><span class="n">File</span><span class="p" data-group-id="7926741327-260">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-261">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="7926741327-261">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file</span><span class="p" data-group-id="7926741327-262">(</span><span class="n">File</span><span class="p" data-group-id="7926741327-262">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7926741327-263">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_list</span><span class="p" data-group-id="7926741327-264">(</span><span class="n">Bin</span><span class="p" data-group-id="7926741327-264">)</span><span class="p" data-group-id="7926741327-263">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="7926741327-265">(</span><span class="n">Dir</span><span class="p" data-group-id="7926741327-265">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">remove_all_files</span><span class="p" data-group-id="7926741327-266">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7926741327-267">[</span><span class="n">Dir</span><span class="p" data-group-id="7926741327-267">]</span><span class="p" data-group-id="7926741327-266">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">remove_all_files</span><span class="p" data-group-id="7926741327-268">(</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="7926741327-268">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="7926741327-269">(</span><span class="nf">fun</span><span class="p" data-group-id="7926741327-270">(</span><span class="n">File</span><span class="p" data-group-id="7926741327-270">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                          </span><span class="n">FilePath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="7926741327-271">(</span><span class="p" data-group-id="7926741327-272">[</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">File</span><span class="p" data-group-id="7926741327-272">]</span><span class="p" data-group-id="7926741327-271">)</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="k">case</span><span class="w"> </span><span class="nc">filelib</span><span class="p">:</span><span class="nf">is_dir</span><span class="p" data-group-id="7926741327-273">(</span><span class="n">FilePath</span><span class="p" data-group-id="7926741327-273">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">write_file</span><span class="p" data-group-id="2290236864-252">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="n">Conts</span><span class="p" data-group-id="2290236864-252">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Enc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">native_name_encoding</span><span class="p" data-group-id="2290236864-253">(</span><span class="p" data-group-id="2290236864-253">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-254">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="2290236864-254">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="2290236864-255">(</span><span class="n">FName</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-256">[</span><span class="ss">write</span><span class="p" data-group-id="2290236864-256">]</span><span class="p" data-group-id="2290236864-255">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">write</span><span class="p" data-group-id="2290236864-257">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="nc">unicode</span><span class="p">:</span><span class="nf">characters_to_binary</span><span class="p" data-group-id="2290236864-258">(</span><span class="n">Conts</span><span class="p">,</span><span class="n">Enc</span><span class="p">,</span><span class="n">Enc</span><span class="p" data-group-id="2290236864-258">)</span><span class="p" data-group-id="2290236864-257">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="2290236864-259">(</span><span class="n">Fd</span><span class="p" data-group-id="2290236864-259">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">read_txt_file</span><span class="p" data-group-id="2290236864-260">(</span><span class="n">File</span><span class="p" data-group-id="2290236864-260">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-261">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Bin</span><span class="p" data-group-id="2290236864-261">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read_file</span><span class="p" data-group-id="2290236864-262">(</span><span class="n">File</span><span class="p" data-group-id="2290236864-262">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2290236864-263">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_list</span><span class="p" data-group-id="2290236864-264">(</span><span class="n">Bin</span><span class="p" data-group-id="2290236864-264">)</span><span class="p" data-group-id="2290236864-263">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">remove_dir_tree</span><span class="p" data-group-id="2290236864-265">(</span><span class="n">Dir</span><span class="p" data-group-id="2290236864-265">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">remove_all_files</span><span class="p" data-group-id="2290236864-266">(</span><span class="s">&quot;.&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2290236864-267">[</span><span class="n">Dir</span><span class="p" data-group-id="2290236864-267">]</span><span class="p" data-group-id="2290236864-266">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">remove_all_files</span><span class="p" data-group-id="2290236864-268">(</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="2290236864-268">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="2290236864-269">(</span><span class="nf">fun</span><span class="p" data-group-id="2290236864-270">(</span><span class="n">File</span><span class="p" data-group-id="2290236864-270">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                          </span><span class="n">FilePath</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">filename</span><span class="p">:</span><span class="nf">join</span><span class="p" data-group-id="2290236864-271">(</span><span class="p" data-group-id="2290236864-272">[</span><span class="n">Dir</span><span class="p">,</span><span class="w"> </span><span class="n">File</span><span class="p" data-group-id="2290236864-272">]</span><span class="p" data-group-id="2290236864-271">)</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="k">case</span><span class="w"> </span><span class="nc">filelib</span><span class="p">:</span><span class="nf">is_dir</span><span class="p" data-group-id="2290236864-273">(</span><span class="n">FilePath</span><span class="p" data-group-id="2290236864-273">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │                                </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                                  </span><span class="p" data-group-id="7926741327-274">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="7926741327-274">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">list_dir</span><span class="p" data-group-id="7926741327-275">(</span><span class="n">FilePath</span><span class="p" data-group-id="7926741327-275">)</span><span class="p">,</span><span class="w">
│ │ │ -                                  </span><span class="nf">remove_all_files</span><span class="p" data-group-id="7926741327-276">(</span><span class="n">FilePath</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="7926741327-276">)</span><span class="p">,</span><span class="w">
│ │ │ -                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">del_dir</span><span class="p" data-group-id="7926741327-277">(</span><span class="n">FilePath</span><span class="p" data-group-id="7926741327-277">)</span><span class="p">;</span><span class="w">
│ │ │ +                                  </span><span class="p" data-group-id="2290236864-274">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="2290236864-274">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">list_dir</span><span class="p" data-group-id="2290236864-275">(</span><span class="n">FilePath</span><span class="p" data-group-id="2290236864-275">)</span><span class="p">,</span><span class="w">
│ │ │ +                                  </span><span class="nf">remove_all_files</span><span class="p" data-group-id="2290236864-276">(</span><span class="n">FilePath</span><span class="p">,</span><span class="w"> </span><span class="n">DirFiles</span><span class="p" data-group-id="2290236864-276">)</span><span class="p">,</span><span class="w">
│ │ │ +                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">del_dir</span><span class="p" data-group-id="2290236864-277">(</span><span class="n">FilePath</span><span class="p" data-group-id="2290236864-277">)</span><span class="p">;</span><span class="w">
│ │ │                                </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="7926741327-278">(</span><span class="n">FilePath</span><span class="p" data-group-id="7926741327-278">)</span><span class="w">
│ │ │ +                                  </span><span class="nc">file</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2290236864-278">(</span><span class="n">FilePath</span><span class="p" data-group-id="2290236864-278">)</span><span class="w">
│ │ │                            </span><span class="k">end</span><span class="w">
│ │ │ -                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="7926741327-269">)</span><span class="p">.</span></code></pre>
│ │ │ +                  </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">Files</span><span class="p" data-group-id="2290236864-269">)</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="error_logging.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/data_types.html
│ │ │ @@ -192,18 +192,18 @@
│ │ │    </a>
│ │ │    <span class="text">Representation of Floating Point Numbers</span>
│ │ │  </h3>
│ │ │  <p>When working with floats you may not see what you expect when printing or doing
│ │ │  arithmetic operations. This is because floats are represented by a fixed number
│ │ │  of bits in a base-2 system while printed floats are represented with a base-10
│ │ │  system. Erlang uses 64-bit floats. Here are examples of this phenomenon:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mf">0.1</span><span class="o">+</span><span class="mf">0.2</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mf">0.30000000000000004</span></code></pre><p>The real numbers <code class="inline">0.1</code> and <code class="inline">0.2</code> cannot be represented exactly as floats.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2186212854-1">{</span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963968</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="mf">36028797018963970.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963970</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963970.0</span><span class="p" data-group-id="2186212854-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2186212854-2">{</span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="2186212854-2">}</span><span class="p">.</span></code></pre><p>The value <code class="inline">36028797018963968</code> can be represented exactly as a float value but
│ │ │ +</span><span class="mf">0.30000000000000004</span></code></pre><p>The real numbers <code class="inline">0.1</code> and <code class="inline">0.2</code> cannot be represented exactly as floats.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0756648360-1">{</span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963968</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963968.0</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="mf">36028797018963970.0</span><span class="p">,</span><span class="w"> </span><span class="mi">36028797018963970</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mf">36028797018963970.0</span><span class="p" data-group-id="0756648360-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0756648360-2">{</span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="mf">3.602879701896397e16</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0756648360-2">}</span><span class="p">.</span></code></pre><p>The value <code class="inline">36028797018963968</code> can be represented exactly as a float value but
│ │ │  Erlang's pretty printer rounds <code class="inline">36028797018963968.0</code> to <code class="inline">3.602879701896397e16</code>
│ │ │  (<code class="inline">=36028797018963970.0</code>) as all values in the range
│ │ │  <code class="inline">[36028797018963966.0, 36028797018963972.0]</code> are represented by
│ │ │  <code class="inline">36028797018963968.0</code>.</p><p>For more information about floats and issues with them see:</p><ul><li><a href="https://floating-point-gui.de/">What Every Programmer Should Know About Floating-Point Arithmetic</a></li><li><a href="https://0.30000000000000004.com/">0.30000000000000004.com/</a></li><li><a href="https://docs.python.org/3/tutorial/floatingpoint.html">Floating Point Arithmetic: Issues and Limitations</a></li></ul><p>If you need to work with exact decimal fractions, for instance to represent
│ │ │  money, it is recommended to use a library that handles that, or work in
│ │ │  cents instead of dollars or euros so that decimal fractions are not needed.</p><p>Also note that Erlang's floats do not exactly match IEEE 754 floats,
│ │ │  in that neither <em>Inf</em> nor <em>NaN</em> are supported in Erlang. Any
│ │ │ @@ -237,52 +237,52 @@
│ │ │  by eight are called <em>binaries</em>.</p><p><em>Examples:</em></p><pre><code class="text">1&gt; &lt;&lt;10,20&gt;&gt;.
│ │ │  &lt;&lt;10,20&gt;&gt;
│ │ │  2&gt; &lt;&lt;&quot;ABC&quot;&gt;&gt;.
│ │ │  &lt;&lt;&quot;ABC&quot;&gt;&gt;
│ │ │  3&gt; &lt;&lt;1:1,0:1&gt;&gt;.
│ │ │  &lt;&lt;2:2&gt;&gt;</code></pre><p>The <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_bitstring/1"><code class="inline">is_bitstring/1</code></a> BIF tests whether a
│ │ │  term is a bit string, and the <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_binary/1"><code class="inline">is_binary/1</code></a>
│ │ │ -BIF tests whether a term is a binary.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">is_bitstring</span><span class="p" data-group-id="1439424295-1">(</span><span class="p" data-group-id="1439424295-2">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1439424295-2">&gt;&gt;</span><span class="p" data-group-id="1439424295-1">)</span><span class="p">.</span><span class="w">
│ │ │ +BIF tests whether a term is a binary.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">is_bitstring</span><span class="p" data-group-id="8383175860-1">(</span><span class="p" data-group-id="8383175860-2">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8383175860-2">&gt;&gt;</span><span class="p" data-group-id="8383175860-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="1439424295-3">(</span><span class="p" data-group-id="1439424295-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1439424295-4">&gt;&gt;</span><span class="p" data-group-id="1439424295-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="8383175860-3">(</span><span class="p" data-group-id="8383175860-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8383175860-4">&gt;&gt;</span><span class="p" data-group-id="8383175860-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="1439424295-5">(</span><span class="p" data-group-id="1439424295-6">&lt;&lt;</span><span class="mi">42</span><span class="p" data-group-id="1439424295-6">&gt;&gt;</span><span class="p" data-group-id="1439424295-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">is_binary</span><span class="p" data-group-id="8383175860-5">(</span><span class="p" data-group-id="8383175860-6">&lt;&lt;</span><span class="mi">42</span><span class="p" data-group-id="8383175860-6">&gt;&gt;</span><span class="p" data-group-id="8383175860-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │  </span></code></pre><p>For more examples, see <a href="../../doc/system/bit_syntax.html">Programming Examples</a>.</p><h2 id="reference" class="section-heading">
│ │ │    <a href="#reference" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Reference</span>
│ │ │  </h2>
│ │ │  <p>A term that is <a href="../../doc/system/system_limits.html#unique_references">unique</a>
│ │ │  among connected nodes. A reference is created by calling the
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#make_ref/0"><code class="inline">make_ref/0</code></a> BIF. The
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_reference/1"><code class="inline">is_reference/1</code></a> BIF tests whether a term
│ │ │ -is a reference.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="5607535482-1">(</span><span class="p" data-group-id="5607535482-1">)</span><span class="p">.</span><span class="w">
│ │ │ +is a reference.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="5461203380-1">(</span><span class="p" data-group-id="5461203380-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Ref</span><span class="o">&lt;</span><span class="mf">0.76482849</span><span class="p">.</span><span class="mf">3801088007.198204</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">is_reference</span><span class="p" data-group-id="5607535482-2">(</span><span class="n">Ref</span><span class="p" data-group-id="5607535482-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">is_reference</span><span class="p" data-group-id="5461203380-2">(</span><span class="n">Ref</span><span class="p" data-group-id="5461203380-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><h2 id="fun" class="section-heading">
│ │ │    <a href="#fun" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Fun</span>
│ │ │  </h2>
│ │ │  <p>A fun is a functional object. Funs make it possible to create an anonymous
│ │ │  function and pass the function itself — not its name — as argument to other
│ │ │ -functions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2084367751-1">(</span><span class="n">X</span><span class="p" data-group-id="2084367751-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +functions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4747418771-1">(</span><span class="n">X</span><span class="p" data-group-id="4747418771-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="2084367751-2">(</span><span class="mi">2</span><span class="p" data-group-id="2084367751-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="4747418771-2">(</span><span class="mi">2</span><span class="p" data-group-id="4747418771-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span></code></pre><p>The <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> and <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_function/2"><code class="inline">is_function/2</code></a>
│ │ │ -BIFs tests whether a term is a fun.</p><p><em>Examples</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3940338608-1">(</span><span class="p" data-group-id="3940338608-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +BIFs tests whether a term is a fun.</p><p><em>Examples</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8220433096-1">(</span><span class="p" data-group-id="8220433096-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">43.105768164</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="3940338608-2">(</span><span class="n">F</span><span class="p" data-group-id="3940338608-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="8220433096-2">(</span><span class="n">F</span><span class="p" data-group-id="8220433096-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="3940338608-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3940338608-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="8220433096-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8220433096-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="3940338608-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3940338608-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nf">is_function</span><span class="p" data-group-id="8220433096-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8220433096-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><p>Read more about funs in <a href="expressions.html#fun-expressions">Fun Expressions</a>. For more
│ │ │  examples, see <a href="../../doc/system/funs.html">Programming Examples</a>.</p><h2 id="port-identifier" class="section-heading">
│ │ │    <a href="#port-identifier" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Port Identifier</span>
│ │ │  </h2>
│ │ │ @@ -300,94 +300,94 @@
│ │ │  for a new process after a while.</p><p>The BIF <a href="../../erts-15.2.7.8/doc/html/erlang.html#self/0"><code class="inline">self/0</code></a> returns the Pid of the calling process. When
│ │ │  <a href="ref_man_processes.html#process-creation">creating a new process</a>, the parent
│ │ │  process will be able to get the Pid of the child process either via the return
│ │ │  value, as is the case when calling the <a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn/3"><code class="inline">spawn/3</code></a> BIF, or via
│ │ │  a message, which is the case when calling the
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn_request/5"><code class="inline">spawn_request/5</code></a> BIF. A Pid is typically used when
│ │ │  when sending a process a <a href="ref_man_processes.html#signals">signal</a>. The
│ │ │ -<a href="../../erts-15.2.7.8/doc/html/erlang.html#is_pid/1"><code class="inline">is_pid/1</code></a> BIF tests whether a term is a Pid.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4860307575-1">(</span><span class="ss">m</span><span class="p" data-group-id="4860307575-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4860307575-2">(</span><span class="p" data-group-id="4860307575-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4860307575-3">]</span><span class="p" data-group-id="4860307575-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="../../erts-15.2.7.8/doc/html/erlang.html#is_pid/1"><code class="inline">is_pid/1</code></a> BIF tests whether a term is a Pid.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6408475492-1">(</span><span class="ss">m</span><span class="p" data-group-id="6408475492-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6408475492-2">(</span><span class="p" data-group-id="6408475492-3">[</span><span class="ss">loop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6408475492-3">]</span><span class="p" data-group-id="6408475492-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="4860307575-4">(</span><span class="p" data-group-id="4860307575-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="6408475492-4">(</span><span class="p" data-group-id="6408475492-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">who_are_you</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4860307575-5">(</span><span class="s">&quot;I am </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4860307575-6">[</span><span class="nf">self</span><span class="p" data-group-id="4860307575-7">(</span><span class="p" data-group-id="4860307575-7">)</span><span class="p" data-group-id="4860307575-6">]</span><span class="p" data-group-id="4860307575-5">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="4860307575-8">(</span><span class="p" data-group-id="4860307575-8">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6408475492-5">(</span><span class="s">&quot;I am </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6408475492-6">[</span><span class="nf">self</span><span class="p" data-group-id="6408475492-7">(</span><span class="p" data-group-id="6408475492-7">)</span><span class="p" data-group-id="6408475492-6">]</span><span class="p" data-group-id="6408475492-5">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="6408475492-8">(</span><span class="p" data-group-id="6408475492-8">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="4860307575-9">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">loop</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4860307575-10">[</span><span class="p" data-group-id="4860307575-10">]</span><span class="p" data-group-id="4860307575-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="6408475492-9">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">loop</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6408475492-10">[</span><span class="p" data-group-id="6408475492-10">]</span><span class="p" data-group-id="6408475492-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.58</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">who_are_you</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">I</span><span class="w"> </span><span class="ss">am</span><span class="w"> </span><span class="o">&lt;</span><span class="mf">0.58</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="ss">who_are_you</span></code></pre><p>Read more about processes in <a href="ref_man_processes.html">Processes</a>.</p><h2 id="tuple" class="section-heading">
│ │ │    <a href="#tuple" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Tuple</span>
│ │ │  </h2>
│ │ │  <p>A tuple is a compound data type with a fixed number of terms:</p><pre><code class="text">{Term1,...,TermN}</code></pre><p>Each term <code class="inline">Term</code> in the tuple is called an <em>element</em>. The number of elements is
│ │ │ -said to be the <em>size</em> of the tuple.</p><p>There exists a number of BIFs to manipulate tuples.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0714610187-1">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="0714610187-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="0714610187-2">}</span><span class="p" data-group-id="0714610187-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0714610187-3">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="0714610187-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="0714610187-4">}</span><span class="p" data-group-id="0714610187-3">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">element</span><span class="p" data-group-id="0714610187-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="0714610187-5">)</span><span class="p">.</span><span class="w">
│ │ │ +said to be the <em>size</em> of the tuple.</p><p>There exists a number of BIFs to manipulate tuples.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2534942367-1">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="2534942367-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2534942367-2">}</span><span class="p" data-group-id="2534942367-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2534942367-3">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">24</span><span class="p">,</span><span class="p" data-group-id="2534942367-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2534942367-4">}</span><span class="p" data-group-id="2534942367-3">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">element</span><span class="p" data-group-id="2534942367-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="2534942367-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">adam</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">element</span><span class="p" data-group-id="0714610187-6">(</span><span class="mi">3</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="0714610187-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0714610187-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="0714610187-7">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="0714610187-8">(</span><span class="mi">2</span><span class="p">,</span><span class="n">P</span><span class="p">,</span><span class="mi">25</span><span class="p" data-group-id="0714610187-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0714610187-9">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">25</span><span class="p">,</span><span class="p" data-group-id="0714610187-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="0714610187-10">}</span><span class="p" data-group-id="0714610187-9">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="0714610187-11">(</span><span class="n">P</span><span class="p" data-group-id="0714610187-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">element</span><span class="p" data-group-id="2534942367-6">(</span><span class="mi">3</span><span class="p">,</span><span class="n">P</span><span class="p" data-group-id="2534942367-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2534942367-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2534942367-7">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">setelement</span><span class="p" data-group-id="2534942367-8">(</span><span class="mi">2</span><span class="p">,</span><span class="n">P</span><span class="p">,</span><span class="mi">25</span><span class="p" data-group-id="2534942367-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2534942367-9">{</span><span class="ss">adam</span><span class="p">,</span><span class="mi">25</span><span class="p">,</span><span class="p" data-group-id="2534942367-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="2534942367-10">}</span><span class="p" data-group-id="2534942367-9">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="2534942367-11">(</span><span class="n">P</span><span class="p" data-group-id="2534942367-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="0714610187-12">(</span><span class="p" data-group-id="0714610187-13">{</span><span class="p" data-group-id="0714610187-13">}</span><span class="p" data-group-id="0714610187-12">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="2534942367-12">(</span><span class="p" data-group-id="2534942367-13">{</span><span class="p" data-group-id="2534942367-13">}</span><span class="p" data-group-id="2534942367-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">0</span><span class="w">
│ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="0714610187-14">(</span><span class="p" data-group-id="0714610187-15">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0714610187-15">}</span><span class="p" data-group-id="0714610187-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="2534942367-14">(</span><span class="p" data-group-id="2534942367-15">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="2534942367-15">}</span><span class="p" data-group-id="2534942367-14">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><h2 id="map" class="section-heading">
│ │ │    <a href="#map" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Map</span>
│ │ │  </h2>
│ │ │  <p>A map is a compound data type with a variable number of key-value associations:</p><pre><code class="text">#{Key1 =&gt; Value1, ..., KeyN =&gt; ValueN}</code></pre><p>Each key-value association in the map is called an <em>association pair</em>. The key
│ │ │  and value parts of the pair are called <em>elements</em>. The number of association
│ │ │ -pairs is said to be the <em>size</em> of the map.</p><p>There exists a number of BIFs to manipulate maps.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3955292059-1">#{</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="w"> </span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3955292059-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="3955292059-2">}</span><span class="p" data-group-id="3955292059-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3955292059-3">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3955292059-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="3955292059-4">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="3955292059-3">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="3955292059-5">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="3955292059-5">)</span><span class="p">.</span><span class="w">
│ │ │ +pairs is said to be the <em>size</em> of the map.</p><p>There exists a number of BIFs to manipulate maps.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8629639991-1">#{</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="w"> </span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8629639991-2">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8629639991-2">}</span><span class="p" data-group-id="8629639991-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8629639991-3">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">24</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8629639991-4">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8629639991-4">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="8629639991-3">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="8629639991-5">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="8629639991-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">adam</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="3955292059-6">(</span><span class="ss">date</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="3955292059-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3955292059-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="3955292059-7">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="3955292059-8">(</span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="3955292059-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3955292059-9">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="3955292059-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="3955292059-10">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="3955292059-9">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="3955292059-11">(</span><span class="n">M</span><span class="p" data-group-id="3955292059-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">maps</span><span class="p">:</span><span class="nf">get</span><span class="p" data-group-id="8629639991-6">(</span><span class="ss">date</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="8629639991-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8629639991-7">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8629639991-7">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="8629639991-8">(</span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="8629639991-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8629639991-9">#{</span><span class="ss">age</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">25</span><span class="p">,</span><span class="ss">date</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8629639991-10">{</span><span class="ss">july</span><span class="p">,</span><span class="mi">29</span><span class="p" data-group-id="8629639991-10">}</span><span class="p">,</span><span class="ss">name</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">adam</span><span class="p" data-group-id="8629639991-9">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="8629639991-11">(</span><span class="n">M</span><span class="p" data-group-id="8629639991-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="3955292059-12">(</span><span class="p" data-group-id="3955292059-13">#{</span><span class="p" data-group-id="3955292059-13">}</span><span class="p" data-group-id="3955292059-12">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nf">map_size</span><span class="p" data-group-id="8629639991-12">(</span><span class="p" data-group-id="8629639991-13">#{</span><span class="p" data-group-id="8629639991-13">}</span><span class="p" data-group-id="8629639991-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">0</span></code></pre><p>A collection of maps processing functions are found in module <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html"><code class="inline">maps</code></a>
│ │ │  in STDLIB.</p><p>Read more about maps in <a href="expressions.html#map-expressions">Map Expressions</a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Maps were introduced as an experimental feature in Erlang/OTP R17. Their
│ │ │  functionality was extended and became fully supported in Erlang/OTP 18.</p></section><h2 id="list" class="section-heading">
│ │ │    <a href="#list" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">List</span>
│ │ │  </h2>
│ │ │  <p>A list is a compound data type with a variable number of terms.</p><pre><code class="text">[Term1,...,TermN]</code></pre><p>Each term <code class="inline">Term</code> in the list is called an <em>element</em>. The number of elements is
│ │ │  said to be the <em>length</em> of the list.</p><p>Formally, a list is either the empty list <code class="inline">[]</code> or consists of a <em>head</em> (first
│ │ │  element) and a <em>tail</em> (remainder of the list). The <em>tail</em> is also a list. The
│ │ │  latter can be expressed as <code class="inline">[H|T]</code>. The notation <code class="inline">[Term1,...,TermN]</code> above is
│ │ │  equivalent with the list <code class="inline">[Term1|[...|[TermN|[]]]]</code>.</p><p><em>Example:</em></p><p><code class="inline">[]</code> is a list, thus<br/><code class="inline">[c|[]]</code> is a list, thus<br/><code class="inline">[b|[c|[]]]</code> is a list, thus<br/><code class="inline">[a|[b|[c|[]]]]</code> is a list, or in short <code class="inline">[a,b,c]</code></p><p>A list where the tail is a list is sometimes called a <em>proper list</em>. It is
│ │ │  allowed to have a list where the tail is not a list, for example, <code class="inline">[a|b]</code>.
│ │ │ -However, this type of list is of little practical use.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4063462390-1">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="4063462390-2">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4063462390-2">}</span><span class="p" data-group-id="4063462390-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4063462390-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="4063462390-4">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4063462390-4">}</span><span class="p" data-group-id="4063462390-3">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4063462390-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4063462390-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4063462390-6">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="4063462390-7">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4063462390-7">}</span><span class="p" data-group-id="4063462390-6">]</span><span class="w">
│ │ │ +However, this type of list is of little practical use.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5952636559-1">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5952636559-2">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5952636559-2">}</span><span class="p" data-group-id="5952636559-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5952636559-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5952636559-4">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5952636559-4">}</span><span class="p" data-group-id="5952636559-3">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="5952636559-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5952636559-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5952636559-6">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5952636559-7">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5952636559-7">}</span><span class="p" data-group-id="5952636559-6">]</span><span class="w">
│ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">H</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">a</span><span class="w">
│ │ │  </span><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4063462390-8">[</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="4063462390-9">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4063462390-9">}</span><span class="p" data-group-id="4063462390-8">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="n">L2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4063462390-10">[</span><span class="ss">d</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4063462390-10">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4063462390-11">[</span><span class="ss">d</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="4063462390-12">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4063462390-12">}</span><span class="p" data-group-id="4063462390-11">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nf">length</span><span class="p" data-group-id="4063462390-13">(</span><span class="n">L1</span><span class="p" data-group-id="4063462390-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5952636559-8">[</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5952636559-9">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5952636559-9">}</span><span class="p" data-group-id="5952636559-8">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="n">L2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5952636559-10">[</span><span class="ss">d</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5952636559-10">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5952636559-11">[</span><span class="ss">d</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="5952636559-12">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="5952636559-12">}</span><span class="p" data-group-id="5952636559-11">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nf">length</span><span class="p" data-group-id="5952636559-13">(</span><span class="n">L1</span><span class="p" data-group-id="5952636559-13">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nf">length</span><span class="p" data-group-id="4063462390-14">(</span><span class="p" data-group-id="4063462390-15">[</span><span class="p" data-group-id="4063462390-15">]</span><span class="p" data-group-id="4063462390-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nf">length</span><span class="p" data-group-id="5952636559-14">(</span><span class="p" data-group-id="5952636559-15">[</span><span class="p" data-group-id="5952636559-15">]</span><span class="p" data-group-id="5952636559-14">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">0</span></code></pre><p>A collection of list processing functions are found in module
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html"><code class="inline">lists</code></a> in STDLIB.</p><h2 id="string" class="section-heading">
│ │ │    <a href="#string" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">String</span>
│ │ │  </h2>
│ │ │ @@ -507,41 +507,41 @@
│ │ │    <span class="text">Record</span>
│ │ │  </h2>
│ │ │  <p>A record is a data structure for storing a fixed number of elements. It has
│ │ │  named fields and is similar to a struct in C. However, a record is not a true
│ │ │  data type. Instead, record expressions are translated to tuple expressions
│ │ │  during compilation. Therefore, record expressions are not understood by the
│ │ │  shell unless special actions are taken. For details, see module <a href="../../lib/stdlib-6.2.2.3/doc/html/shell.html"><code class="inline">shell</code></a>
│ │ │ -in STDLIB.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0186603837-1">(</span><span class="ss">person</span><span class="p" data-group-id="0186603837-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0186603837-2">(</span><span class="p" data-group-id="0186603837-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0186603837-3">]</span><span class="p" data-group-id="0186603837-2">)</span><span class="p">.</span><span class="w">
│ │ │ +in STDLIB.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0827202953-1">(</span><span class="ss">person</span><span class="p" data-group-id="0827202953-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0827202953-2">(</span><span class="p" data-group-id="0827202953-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0827202953-3">]</span><span class="p" data-group-id="0827202953-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0186603837-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0186603837-5">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="0186603837-5">}</span><span class="p" data-group-id="0186603837-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0827202953-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0827202953-5">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="0827202953-5">}</span><span class="p" data-group-id="0827202953-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">new</span><span class="p" data-group-id="0186603837-6">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="0186603837-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0186603837-7">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="o">=</span><span class="n">Age</span><span class="p" data-group-id="0186603837-7">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">new</span><span class="p" data-group-id="0827202953-6">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="0827202953-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0827202953-7">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="o">=</span><span class="n">Age</span><span class="p" data-group-id="0827202953-7">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">person</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0186603837-8">(</span><span class="ss">ernie</span><span class="p">,</span><span class="w"> </span><span class="mi">44</span><span class="p" data-group-id="0186603837-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0186603837-9">{</span><span class="ss">person</span><span class="p">,</span><span class="ss">ernie</span><span class="p">,</span><span class="mi">44</span><span class="p" data-group-id="0186603837-9">}</span></code></pre><p>Read more about records in <a href="ref_man_records.html">Records</a>. More examples are
│ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nc">person</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0827202953-8">(</span><span class="ss">ernie</span><span class="p">,</span><span class="w"> </span><span class="mi">44</span><span class="p" data-group-id="0827202953-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0827202953-9">{</span><span class="ss">person</span><span class="p">,</span><span class="ss">ernie</span><span class="p">,</span><span class="mi">44</span><span class="p" data-group-id="0827202953-9">}</span></code></pre><p>Read more about records in <a href="ref_man_records.html">Records</a>. More examples are
│ │ │  found in <a href="../../doc/system/prog_ex_records.html">Programming Examples</a>.</p><h2 id="boolean" class="section-heading">
│ │ │    <a href="#boolean" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Boolean</span>
│ │ │  </h2>
│ │ │  <p>There is no Boolean data type in Erlang. Instead the atoms <code class="inline">true</code> and <code class="inline">false</code>
│ │ │  are used to denote Boolean values. The <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_boolean/1"><code class="inline">is_boolean/1</code></a>
│ │ │  BIF tests whether a term is a boolean.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mi">2</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │  </span><span class="gp unselectable">2&gt; </span><span class="ss">true</span><span class="w"> </span><span class="ow">or</span><span class="w"> </span><span class="ss">false</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1063526219-1">(</span><span class="ss">true</span><span class="p" data-group-id="1063526219-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1217470747-1">(</span><span class="ss">true</span><span class="p" data-group-id="1217470747-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1063526219-2">(</span><span class="ss">false</span><span class="p" data-group-id="1063526219-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1217470747-2">(</span><span class="ss">false</span><span class="p" data-group-id="1217470747-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1063526219-3">(</span><span class="ss">ok</span><span class="p" data-group-id="1063526219-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nf">is_boolean</span><span class="p" data-group-id="1217470747-3">(</span><span class="ss">ok</span><span class="p" data-group-id="1217470747-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><h2 id="escape-sequences" class="section-heading">
│ │ │    <a href="#escape-sequences" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Escape Sequences</span>
│ │ │  </h2>
│ │ │  <p>Within strings (<code class="inline">&quot;</code>-delimited), quoted atoms, and the content of
│ │ │ @@ -559,47 +559,47 @@
│ │ │  <a href="data_types.html#sigil"><code class="inline">~b</code> or <code class="inline">~s</code> sigils </a>the escape sequences for normal
│ │ │  strings, above, are used.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Triple-quoted strings and sigils were introduced in Erlang/OTP 27.</p></section><h2 id="type-conversions" class="section-heading">
│ │ │    <a href="#type-conversions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Type Conversions</span>
│ │ │  </h2>
│ │ │ -<p>There are a number of BIFs for type conversions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="0729299244-1">(</span><span class="ss">hello</span><span class="p" data-group-id="0729299244-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>There are a number of BIFs for type conversions.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="0043603138-1">(</span><span class="ss">hello</span><span class="p" data-group-id="0043603138-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="0729299244-2">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0729299244-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="0043603138-2">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0043603138-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="0729299244-3">(</span><span class="p" data-group-id="0729299244-4">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0729299244-4">&gt;&gt;</span><span class="p" data-group-id="0729299244-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="0043603138-3">(</span><span class="p" data-group-id="0043603138-4">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0043603138-4">&gt;&gt;</span><span class="p" data-group-id="0043603138-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="0729299244-5">(</span><span class="p" data-group-id="0729299244-6">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="0729299244-6">&gt;&gt;</span><span class="p" data-group-id="0729299244-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nf">binary_to_list</span><span class="p" data-group-id="0043603138-5">(</span><span class="p" data-group-id="0043603138-6">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="0043603138-6">&gt;&gt;</span><span class="p" data-group-id="0043603138-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="0729299244-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0729299244-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0729299244-8">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="0729299244-8">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="0729299244-9">(</span><span class="mf">7.0</span><span class="p" data-group-id="0729299244-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nf">list_to_binary</span><span class="p" data-group-id="0043603138-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0043603138-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0043603138-8">&lt;&lt;</span><span class="mi">104</span><span class="p">,</span><span class="mi">101</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">108</span><span class="p">,</span><span class="mi">111</span><span class="p" data-group-id="0043603138-8">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nf">float_to_list</span><span class="p" data-group-id="0043603138-9">(</span><span class="mf">7.0</span><span class="p" data-group-id="0043603138-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="0729299244-10">(</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="0729299244-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nf">list_to_float</span><span class="p" data-group-id="0043603138-10">(</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="0043603138-10">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">7.0</span><span class="w">
│ │ │ -</span><span class="gp unselectable">8&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="0729299244-11">(</span><span class="mi">77</span><span class="p" data-group-id="0729299244-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">8&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="0043603138-11">(</span><span class="mi">77</span><span class="p" data-group-id="0043603138-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;77&quot;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="0729299244-12">(</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="0729299244-12">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="nf">list_to_integer</span><span class="p" data-group-id="0043603138-12">(</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="0043603138-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">77</span><span class="w">
│ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="0729299244-13">(</span><span class="p" data-group-id="0729299244-14">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0729299244-14">}</span><span class="p" data-group-id="0729299244-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0729299244-15">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0729299244-15">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">11&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="0729299244-16">(</span><span class="p" data-group-id="0729299244-17">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0729299244-17">]</span><span class="p" data-group-id="0729299244-16">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0729299244-18">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0729299244-18">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">12&gt; </span><span class="nf">term_to_binary</span><span class="p" data-group-id="0729299244-19">(</span><span class="p" data-group-id="0729299244-20">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0729299244-20">}</span><span class="p" data-group-id="0729299244-19">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0729299244-21">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="0729299244-21">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">13&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="0729299244-22">(</span><span class="p" data-group-id="0729299244-23">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="0729299244-23">&gt;&gt;</span><span class="p" data-group-id="0729299244-22">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0729299244-24">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0729299244-24">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">14&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="0729299244-25">(</span><span class="p" data-group-id="0729299244-26">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="0729299244-26">&gt;&gt;</span><span class="p" data-group-id="0729299244-25">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="nf">tuple_to_list</span><span class="p" data-group-id="0043603138-13">(</span><span class="p" data-group-id="0043603138-14">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0043603138-14">}</span><span class="p" data-group-id="0043603138-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0043603138-15">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0043603138-15">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">11&gt; </span><span class="nf">list_to_tuple</span><span class="p" data-group-id="0043603138-16">(</span><span class="p" data-group-id="0043603138-17">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0043603138-17">]</span><span class="p" data-group-id="0043603138-16">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0043603138-18">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0043603138-18">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">12&gt; </span><span class="nf">term_to_binary</span><span class="p" data-group-id="0043603138-19">(</span><span class="p" data-group-id="0043603138-20">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0043603138-20">}</span><span class="p" data-group-id="0043603138-19">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0043603138-21">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="0043603138-21">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">13&gt; </span><span class="nf">binary_to_term</span><span class="p" data-group-id="0043603138-22">(</span><span class="p" data-group-id="0043603138-23">&lt;&lt;</span><span class="mi">131</span><span class="p">,</span><span class="mi">104</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">97</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">100</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="0043603138-23">&gt;&gt;</span><span class="p" data-group-id="0043603138-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0043603138-24">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="0043603138-24">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">14&gt; </span><span class="nf">binary_to_integer</span><span class="p" data-group-id="0043603138-25">(</span><span class="p" data-group-id="0043603138-26">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="0043603138-26">&gt;&gt;</span><span class="p" data-group-id="0043603138-25">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">77</span><span class="w">
│ │ │ -</span><span class="gp unselectable">15&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="0729299244-27">(</span><span class="mi">77</span><span class="p" data-group-id="0729299244-27">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0729299244-28">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="0729299244-28">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">16&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="0729299244-29">(</span><span class="mf">7.0</span><span class="p" data-group-id="0729299244-29">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0729299244-30">&lt;&lt;</span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="p" data-group-id="0729299244-30">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">17&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="0729299244-31">(</span><span class="p" data-group-id="0729299244-32">&lt;&lt;</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="0729299244-32">&gt;&gt;</span><span class="p" data-group-id="0729299244-31">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">15&gt; </span><span class="nf">integer_to_binary</span><span class="p" data-group-id="0043603138-27">(</span><span class="mi">77</span><span class="p" data-group-id="0043603138-27">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0043603138-28">&lt;&lt;</span><span class="s">&quot;77&quot;</span><span class="p" data-group-id="0043603138-28">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">16&gt; </span><span class="nf">float_to_binary</span><span class="p" data-group-id="0043603138-29">(</span><span class="mf">7.0</span><span class="p" data-group-id="0043603138-29">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0043603138-30">&lt;&lt;</span><span class="s">&quot;7.00000000000000000000e+00&quot;</span><span class="p" data-group-id="0043603138-30">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">17&gt; </span><span class="nf">binary_to_float</span><span class="p" data-group-id="0043603138-31">(</span><span class="p" data-group-id="0043603138-32">&lt;&lt;</span><span class="s">&quot;7.000e+00&quot;</span><span class="p" data-group-id="0043603138-32">&gt;&gt;</span><span class="p" data-group-id="0043603138-31">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">7.0</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="character_set.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/design_principles.html
│ │ │ @@ -152,135 +152,135 @@
│ │ │  the code for a process in a generic part (a behaviour module) and a specific
│ │ │  part (a <em>callback module</em>).</p><p>The behaviour module is part of Erlang/OTP. To implement a process such as a
│ │ │  supervisor, the user only needs to implement the callback module, which is to
│ │ │  export a pre-defined set of functions, the <em>callback functions</em>.</p><p>The following example illustrate how code can be divided into a generic and a
│ │ │  specific part. Consider the following code (written in plain Erlang) for a
│ │ │  simple server, which keeps track of a number of &quot;channels&quot;. Other processes can
│ │ │  allocate and free the channels by calling the functions <code class="inline">alloc/0</code> and <code class="inline">free/1</code>,
│ │ │ -respectively.</p><p><a href="" id="ch1"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5602808730-1">(</span><span class="ss">ch1</span><span class="p" data-group-id="5602808730-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5602808730-2">(</span><span class="p" data-group-id="5602808730-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5602808730-3">]</span><span class="p" data-group-id="5602808730-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5602808730-4">(</span><span class="p" data-group-id="5602808730-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5602808730-5">]</span><span class="p" data-group-id="5602808730-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5602808730-6">(</span><span class="p" data-group-id="5602808730-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5602808730-7">]</span><span class="p" data-group-id="5602808730-6">)</span><span class="p">.</span><span class="w">
│ │ │ +respectively.</p><p><a href="" id="ch1"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5959075008-1">(</span><span class="ss">ch1</span><span class="p" data-group-id="5959075008-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5959075008-2">(</span><span class="p" data-group-id="5959075008-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5959075008-3">]</span><span class="p" data-group-id="5959075008-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5959075008-4">(</span><span class="p" data-group-id="5959075008-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5959075008-5">]</span><span class="p" data-group-id="5959075008-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5959075008-6">(</span><span class="p" data-group-id="5959075008-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5959075008-7">]</span><span class="p" data-group-id="5959075008-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="5602808730-8">(</span><span class="p" data-group-id="5602808730-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="5602808730-9">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5602808730-10">[</span><span class="p" data-group-id="5602808730-10">]</span><span class="p" data-group-id="5602808730-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="5959075008-8">(</span><span class="p" data-group-id="5959075008-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="5959075008-9">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5959075008-10">[</span><span class="p" data-group-id="5959075008-10">]</span><span class="p" data-group-id="5959075008-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="5602808730-11">(</span><span class="p" data-group-id="5602808730-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5602808730-12">{</span><span class="nf">self</span><span class="p" data-group-id="5602808730-13">(</span><span class="p" data-group-id="5602808730-13">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="5602808730-12">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="5959075008-11">(</span><span class="p" data-group-id="5959075008-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5959075008-12">{</span><span class="nf">self</span><span class="p" data-group-id="5959075008-13">(</span><span class="p" data-group-id="5959075008-13">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="5959075008-12">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5602808730-14">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="5602808730-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5959075008-14">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="5959075008-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Res</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="5602808730-15">(</span><span class="n">Ch</span><span class="p" data-group-id="5602808730-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5602808730-16">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5602808730-16">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="5959075008-15">(</span><span class="n">Ch</span><span class="p" data-group-id="5959075008-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ch1</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5959075008-16">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5959075008-16">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="5602808730-17">(</span><span class="p" data-group-id="5602808730-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="5602808730-18">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5602808730-19">(</span><span class="p" data-group-id="5602808730-19">)</span><span class="p" data-group-id="5602808730-18">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="5602808730-20">(</span><span class="p" data-group-id="5602808730-20">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="5602808730-21">(</span><span class="n">Chs</span><span class="p" data-group-id="5602808730-21">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="5959075008-17">(</span><span class="p" data-group-id="5959075008-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="5959075008-18">(</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5959075008-19">(</span><span class="p" data-group-id="5959075008-19">)</span><span class="p" data-group-id="5959075008-18">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="5959075008-20">(</span><span class="p" data-group-id="5959075008-20">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="5959075008-21">(</span><span class="n">Chs</span><span class="p" data-group-id="5959075008-21">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="5602808730-22">(</span><span class="n">Chs</span><span class="p" data-group-id="5602808730-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="5959075008-22">(</span><span class="n">Chs</span><span class="p" data-group-id="5959075008-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5602808730-23">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="5602808730-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="5602808730-24">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="5602808730-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="5602808730-25">(</span><span class="n">Chs</span><span class="p" data-group-id="5602808730-25">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5602808730-26">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5602808730-26">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="5602808730-27">(</span><span class="n">Chs2</span><span class="p" data-group-id="5602808730-27">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5602808730-28">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5602808730-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="5602808730-29">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5602808730-29">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="5602808730-30">(</span><span class="n">Chs2</span><span class="p" data-group-id="5602808730-30">)</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The code for the server can be rewritten into a generic part <code class="inline">server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8565027233-1">(</span><span class="ss">server</span><span class="p" data-group-id="8565027233-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8565027233-2">(</span><span class="p" data-group-id="8565027233-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8565027233-3">]</span><span class="p" data-group-id="8565027233-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8565027233-4">(</span><span class="p" data-group-id="8565027233-5">[</span><span class="ss">call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8565027233-5">]</span><span class="p" data-group-id="8565027233-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8565027233-6">(</span><span class="p" data-group-id="8565027233-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8565027233-7">]</span><span class="p" data-group-id="8565027233-6">)</span><span class="p">.</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5959075008-23">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="5959075008-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="5959075008-24">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="5959075008-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="5959075008-25">(</span><span class="n">Chs</span><span class="p" data-group-id="5959075008-25">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5959075008-26">{</span><span class="ss">ch1</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5959075008-26">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="5959075008-27">(</span><span class="n">Chs2</span><span class="p" data-group-id="5959075008-27">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5959075008-28">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="5959075008-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="5959075008-29">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5959075008-29">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="5959075008-30">(</span><span class="n">Chs2</span><span class="p" data-group-id="5959075008-30">)</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>The code for the server can be rewritten into a generic part <code class="inline">server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3823581970-1">(</span><span class="ss">server</span><span class="p" data-group-id="3823581970-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3823581970-2">(</span><span class="p" data-group-id="3823581970-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3823581970-3">]</span><span class="p" data-group-id="3823581970-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3823581970-4">(</span><span class="p" data-group-id="3823581970-5">[</span><span class="ss">call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3823581970-5">]</span><span class="p" data-group-id="3823581970-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3823581970-6">(</span><span class="p" data-group-id="3823581970-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3823581970-7">]</span><span class="p" data-group-id="3823581970-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="8565027233-8">(</span><span class="n">Mod</span><span class="p" data-group-id="8565027233-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="8565027233-9">(</span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8565027233-10">[</span><span class="n">Mod</span><span class="p" data-group-id="8565027233-10">]</span><span class="p" data-group-id="8565027233-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="3823581970-8">(</span><span class="n">Mod</span><span class="p" data-group-id="3823581970-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="3823581970-9">(</span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3823581970-10">[</span><span class="n">Mod</span><span class="p" data-group-id="3823581970-10">]</span><span class="p" data-group-id="3823581970-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call</span><span class="p" data-group-id="8565027233-11">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="8565027233-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8565027233-12">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8565027233-13">(</span><span class="p" data-group-id="8565027233-13">)</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="8565027233-12">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call</span><span class="p" data-group-id="3823581970-11">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="3823581970-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3823581970-12">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3823581970-13">(</span><span class="p" data-group-id="3823581970-13">)</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="3823581970-12">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8565027233-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="8565027233-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3823581970-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="3823581970-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Res</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">cast</span><span class="p" data-group-id="8565027233-15">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="8565027233-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8565027233-16">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="8565027233-16">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">cast</span><span class="p" data-group-id="3823581970-15">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="3823581970-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Name</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3823581970-16">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="3823581970-16">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8565027233-17">(</span><span class="n">Mod</span><span class="p" data-group-id="8565027233-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="8565027233-18">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8565027233-19">(</span><span class="p" data-group-id="8565027233-19">)</span><span class="p" data-group-id="8565027233-18">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">init</span><span class="p" data-group-id="8565027233-20">(</span><span class="p" data-group-id="8565027233-20">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="8565027233-21">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8565027233-21">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3823581970-17">(</span><span class="n">Mod</span><span class="p" data-group-id="3823581970-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="3823581970-18">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3823581970-19">(</span><span class="p" data-group-id="3823581970-19">)</span><span class="p" data-group-id="3823581970-18">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">init</span><span class="p" data-group-id="3823581970-20">(</span><span class="p" data-group-id="3823581970-20">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="3823581970-21">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3823581970-21">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="8565027233-22">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8565027233-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="3823581970-22">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3823581970-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8565027233-23">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="8565027233-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="8565027233-24">{</span><span class="n">Res</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="8565027233-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_call</span><span class="p" data-group-id="8565027233-25">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8565027233-25">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8565027233-26">{</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="8565027233-26">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="8565027233-27">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="8565027233-27">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8565027233-28">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="8565027233-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">State2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_cast</span><span class="p" data-group-id="8565027233-29">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8565027233-29">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="8565027233-30">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="8565027233-30">)</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>And a callback module <code class="inline">ch2.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7774588513-1">(</span><span class="ss">ch2</span><span class="p" data-group-id="7774588513-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7774588513-2">(</span><span class="p" data-group-id="7774588513-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7774588513-3">]</span><span class="p" data-group-id="7774588513-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7774588513-4">(</span><span class="p" data-group-id="7774588513-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7774588513-5">]</span><span class="p" data-group-id="7774588513-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7774588513-6">(</span><span class="p" data-group-id="7774588513-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7774588513-7">]</span><span class="p" data-group-id="7774588513-6">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="7774588513-8">(</span><span class="p" data-group-id="7774588513-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7774588513-9">(</span><span class="ss">ch2</span><span class="p" data-group-id="7774588513-9">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="7774588513-10">(</span><span class="p" data-group-id="7774588513-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="7774588513-11">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="7774588513-11">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="7774588513-12">(</span><span class="n">Ch</span><span class="p" data-group-id="7774588513-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="7774588513-13">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7774588513-14">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7774588513-14">}</span><span class="p" data-group-id="7774588513-13">)</span><span class="p">.</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3823581970-23">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="3823581970-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="3823581970-24">{</span><span class="n">Res</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="3823581970-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_call</span><span class="p" data-group-id="3823581970-25">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3823581970-25">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3823581970-26">{</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="3823581970-26">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="3823581970-27">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="3823581970-27">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3823581970-28">{</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="n">Req</span><span class="p" data-group-id="3823581970-28">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">State2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Mod</span><span class="p">:</span><span class="nf">handle_cast</span><span class="p" data-group-id="3823581970-29">(</span><span class="n">Req</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="3823581970-29">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="3823581970-30">(</span><span class="n">Mod</span><span class="p">,</span><span class="w"> </span><span class="n">State2</span><span class="p" data-group-id="3823581970-30">)</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>And a callback module <code class="inline">ch2.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4823832465-1">(</span><span class="ss">ch2</span><span class="p" data-group-id="4823832465-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4823832465-2">(</span><span class="p" data-group-id="4823832465-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4823832465-3">]</span><span class="p" data-group-id="4823832465-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4823832465-4">(</span><span class="p" data-group-id="4823832465-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4823832465-5">]</span><span class="p" data-group-id="4823832465-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4823832465-6">(</span><span class="p" data-group-id="4823832465-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4823832465-7">]</span><span class="p" data-group-id="4823832465-6">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="4823832465-8">(</span><span class="p" data-group-id="4823832465-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4823832465-9">(</span><span class="ss">ch2</span><span class="p" data-group-id="4823832465-9">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="4823832465-10">(</span><span class="p" data-group-id="4823832465-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4823832465-11">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="4823832465-11">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="4823832465-12">(</span><span class="n">Ch</span><span class="p" data-group-id="4823832465-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4823832465-13">(</span><span class="ss">ch2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4823832465-14">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4823832465-14">}</span><span class="p" data-group-id="4823832465-13">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="7774588513-15">(</span><span class="p" data-group-id="7774588513-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">channels</span><span class="p" data-group-id="7774588513-16">(</span><span class="p" data-group-id="7774588513-16">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4823832465-15">(</span><span class="p" data-group-id="4823832465-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">channels</span><span class="p" data-group-id="4823832465-16">(</span><span class="p" data-group-id="4823832465-16">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="7774588513-17">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7774588513-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">alloc</span><span class="p" data-group-id="7774588513-18">(</span><span class="n">Chs</span><span class="p" data-group-id="7774588513-18">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; {Ch,Chs2}</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="4823832465-17">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4823832465-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">alloc</span><span class="p" data-group-id="4823832465-18">(</span><span class="n">Chs</span><span class="p" data-group-id="4823832465-18">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; {Ch,Chs2}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="7774588513-19">(</span><span class="p" data-group-id="7774588513-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7774588513-20">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7774588513-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">free</span><span class="p" data-group-id="7774588513-21">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7774588513-21">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; Chs2</span></code></pre><p>Notice the following:</p><ul><li>The code in <code class="inline">server</code> can be reused to build many different servers.</li><li>The server name, in this example the atom <code class="inline">ch2</code>, is hidden from the users of
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="4823832465-19">(</span><span class="p" data-group-id="4823832465-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4823832465-20">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4823832465-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">free</span><span class="p" data-group-id="4823832465-21">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4823832465-21">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% =&gt; Chs2</span></code></pre><p>Notice the following:</p><ul><li>The code in <code class="inline">server</code> can be reused to build many different servers.</li><li>The server name, in this example the atom <code class="inline">ch2</code>, is hidden from the users of
│ │ │  the client functions. This means that the name can be changed without
│ │ │  affecting them.</li><li>The protocol (messages sent to and received from the server) is also hidden.
│ │ │  This is good programming practice and allows one to change the protocol
│ │ │  without changing the code using the interface functions.</li><li>The functionality of <code class="inline">server</code> can be extended without having to change <code class="inline">ch2</code>
│ │ │  or any other callback module.</li></ul><p>In <code class="inline">ch1.erl</code> and <code class="inline">ch2.erl</code> above, the implementation of <code class="inline">channels/0</code>, <code class="inline">alloc/1</code>,
│ │ │  and <code class="inline">free/2</code> has been intentionally left out, as it is not relevant to the
│ │ │  example. For completeness, one way to write these functions is given below. This
│ │ │  is an example only, a realistic implementation must be able to handle situations
│ │ │ -like running out of channels to allocate, and so on.</p><p><a href="" id="channels-implementation"></a></p><pre><code class="makeup erlang" translate="no"><span class="nf">channels</span><span class="p" data-group-id="1512436431-1">(</span><span class="p" data-group-id="1512436431-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="1512436431-2">{</span><span class="p">_</span><span class="n">Allocated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1512436431-3">[</span><span class="p" data-group-id="1512436431-3">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="1512436431-4">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="1512436431-4">)</span><span class="p" data-group-id="1512436431-2">}</span><span class="p">.</span><span class="w">
│ │ │ +like running out of channels to allocate, and so on.</p><p><a href="" id="channels-implementation"></a></p><pre><code class="makeup erlang" translate="no"><span class="nf">channels</span><span class="p" data-group-id="2933897688-1">(</span><span class="p" data-group-id="2933897688-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2933897688-2">{</span><span class="p">_</span><span class="n">Allocated</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2933897688-3">[</span><span class="p" data-group-id="2933897688-3">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="2933897688-4">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="2933897688-4">)</span><span class="p" data-group-id="2933897688-2">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="1512436431-5">(</span><span class="p" data-group-id="1512436431-6">{</span><span class="n">Allocated</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1512436431-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1512436431-7">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="p" data-group-id="1512436431-6">}</span><span class="p" data-group-id="1512436431-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="1512436431-8">{</span><span class="n">H</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1512436431-9">{</span><span class="p" data-group-id="1512436431-10">[</span><span class="n">H</span><span class="p">|</span><span class="n">Allocated</span><span class="p" data-group-id="1512436431-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="1512436431-9">}</span><span class="p" data-group-id="1512436431-8">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="2933897688-5">(</span><span class="p" data-group-id="2933897688-6">{</span><span class="n">Allocated</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2933897688-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2933897688-7">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">_</span><span class="n">Free</span><span class="p" data-group-id="2933897688-6">}</span><span class="p" data-group-id="2933897688-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="2933897688-8">{</span><span class="n">H</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2933897688-9">{</span><span class="p" data-group-id="2933897688-10">[</span><span class="n">H</span><span class="p">|</span><span class="n">Allocated</span><span class="p" data-group-id="2933897688-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="2933897688-9">}</span><span class="p" data-group-id="2933897688-8">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="1512436431-11">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1512436431-12">{</span><span class="n">Alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Free</span><span class="p" data-group-id="1512436431-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Channels</span><span class="p" data-group-id="1512436431-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="1512436431-13">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="1512436431-13">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="2933897688-11">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2933897688-12">{</span><span class="n">Alloc</span><span class="p">,</span><span class="w"> </span><span class="n">Free</span><span class="p" data-group-id="2933897688-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Channels</span><span class="p" data-group-id="2933897688-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">member</span><span class="p" data-group-id="2933897688-13">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="2933897688-13">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │        </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="1512436431-14">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="1512436431-15">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="1512436431-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1512436431-16">[</span><span class="n">Ch</span><span class="p">|</span><span class="n">Free</span><span class="p" data-group-id="1512436431-16">]</span><span class="p" data-group-id="1512436431-14">}</span><span class="p">;</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="2933897688-14">{</span><span class="nc">lists</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="2933897688-15">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="2933897688-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2933897688-16">[</span><span class="n">Ch</span><span class="p">|</span><span class="n">Free</span><span class="p" data-group-id="2933897688-16">]</span><span class="p" data-group-id="2933897688-14">}</span><span class="p">;</span><span class="w">
│ │ │        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │           </span><span class="n">Channels</span><span class="w">
│ │ │     </span><span class="k">end</span><span class="p">.</span></code></pre><p>Code written without using behaviours can be more efficient, but the increased
│ │ │  efficiency is at the expense of generality. The ability to manage all
│ │ │  applications in the system in a consistent manner is important.</p><p>Using behaviours also makes it easier to read and understand code written by
│ │ │  other programmers. Improvised programming structures, while possibly more
│ │ │  efficient, are always more difficult to understand.</p><p>The <code class="inline">server</code> module corresponds, greatly simplified, to the Erlang/OTP behaviour
│ │ │  <code class="inline">gen_server</code>.</p><p>The standard Erlang/OTP behaviours are:</p><ul><li><p><a href="gen_server_concepts.html">gen_server</a></p><p>For implementing the server of a client-server relation</p></li><li><p><a href="statem.html">gen_statem</a></p><p>For implementing state machines</p></li><li><p><a href="events.html">gen_event</a></p><p>For implementing event handling functionality</p></li><li><p><a href="sup_princ.html">supervisor</a></p><p>For implementing a supervisor in a supervision tree</p></li></ul><p>The compiler understands the module attribute <code class="inline">-behaviour(Behaviour)</code> and issues
│ │ │ -warnings about missing callback functions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3065105276-1">(</span><span class="ss">chs3</span><span class="p" data-group-id="3065105276-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3065105276-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="3065105276-2">)</span><span class="p">.</span><span class="w">
│ │ │ +warnings about missing callback functions, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3479057710-1">(</span><span class="ss">chs3</span><span class="p" data-group-id="3479057710-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3479057710-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="3479057710-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="3065105276-3">(</span><span class="ss">chs3</span><span class="p" data-group-id="3065105276-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="3479057710-3">(</span><span class="ss">chs3</span><span class="p" data-group-id="3479057710-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="o">/</span><span class="ss">chs3</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">10</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="ss">undefined</span><span class="w"> </span><span class="ss">call</span><span class="o">-</span><span class="ss">back</span><span class="w"> </span><span class="ss">function</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3065105276-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">chs3</span><span class="p" data-group-id="3065105276-4">}</span></code></pre><h2 id="applications" class="section-heading">
│ │ │ +</span><span class="p" data-group-id="3479057710-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">chs3</span><span class="p" data-group-id="3479057710-4">}</span></code></pre><h2 id="applications" class="section-heading">
│ │ │    <a href="#applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Applications</span>
│ │ │  </h2>
│ │ │  <p>Erlang/OTP comes with a number of components, each implementing some specific
│ │ │  functionality. Components are with Erlang/OTP terminology called <em>applications</em>.
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/distributed.html
│ │ │ @@ -142,25 +142,25 @@
│ │ │  </h2>
│ │ │  <p>A <em>node</em> is an executing Erlang runtime system that has been given a name, using
│ │ │  the command-line flag <a href="../../erts-15.2.7.8/doc/html/erl_cmd.html#name"><code class="inline">-name</code></a> (long names) or
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erl_cmd.html#sname"><code class="inline">-sname</code></a> (short names).</p><p>The format of the node name is an atom <code class="inline">name@host</code>. <code class="inline">name</code> is the name given by
│ │ │  the user. <code class="inline">host</code> is the full host name if long names are used, or the first part
│ │ │  of the host name if short names are used. Function <a href="../../erts-15.2.7.8/doc/html/erlang.html#node/0"><code class="inline">node()</code></a>
│ │ │  returns the name of the node.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -name dilbert</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6612865865-1">(</span><span class="ss">dilbert@uab</span><span class="p">.</span><span class="ss">ericsson</span><span class="p">.</span><span class="ss">se</span><span class="p" data-group-id="6612865865-1">)</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="6612865865-2">(</span><span class="p" data-group-id="6612865865-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5179365610-1">(</span><span class="ss">dilbert@uab</span><span class="p">.</span><span class="ss">ericsson</span><span class="p">.</span><span class="ss">se</span><span class="p" data-group-id="5179365610-1">)</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">node</span><span class="p" data-group-id="5179365610-2">(</span><span class="p" data-group-id="5179365610-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">&#39;dilbert@uab.ericsson.se&#39;</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">% erl -sname dilbert</span><span class="w">
│ │ │ -</span><span class="gp unselectable">(dilbert@uab)1&gt; </span><span class="nf">node</span><span class="p" data-group-id="6612865865-3">(</span><span class="p" data-group-id="6612865865-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">(dilbert@uab)1&gt; </span><span class="nf">node</span><span class="p" data-group-id="5179365610-3">(</span><span class="p" data-group-id="5179365610-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">dilbert@uab</span></code></pre><p>The node name can also be given in runtime by calling <a href="../../lib/kernel-10.2.7.4/doc/html/net_kernel.html#start/1"><code class="inline">net_kernel:start/1</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">node</span><span class="p" data-group-id="9405695807-1">(</span><span class="p" data-group-id="9405695807-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">node</span><span class="p" data-group-id="7748464923-1">(</span><span class="p" data-group-id="7748464923-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">net_kernel</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9405695807-2">(</span><span class="p" data-group-id="9405695807-3">[</span><span class="ss">dilbert</span><span class="p">,</span><span class="ss">shortnames</span><span class="p" data-group-id="9405695807-3">]</span><span class="p" data-group-id="9405695807-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9405695807-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.102</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9405695807-4">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">(dilbert@uab)3&gt; </span><span class="nf">node</span><span class="p" data-group-id="9405695807-5">(</span><span class="p" data-group-id="9405695807-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">net_kernel</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7748464923-2">(</span><span class="p" data-group-id="7748464923-3">[</span><span class="ss">dilbert</span><span class="p">,</span><span class="ss">shortnames</span><span class="p" data-group-id="7748464923-3">]</span><span class="p" data-group-id="7748464923-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7748464923-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.102</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="7748464923-4">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">(dilbert@uab)3&gt; </span><span class="nf">node</span><span class="p" data-group-id="7748464923-5">(</span><span class="p" data-group-id="7748464923-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">dilbert@uab</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>A node with a long node name cannot communicate with a node with a short node
│ │ │  name.</p></section><h2 id="node-connections" class="section-heading">
│ │ │    <a href="#node-connections" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Node Connections</span>
│ │ │  </h2>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/distributed_applications.html
│ │ │ @@ -150,36 +150,36 @@
│ │ │  (within the time-out specified by <code class="inline">sync_nodes_timeout</code>).</li><li><p><code class="inline">sync_nodes_timeout = integer() | infinity</code> - Specifies how many milliseconds
│ │ │  to wait for the other nodes to start.</p></li></ul><p>When started, the node waits for all nodes specified by <code class="inline">sync_nodes_mandatory</code>
│ │ │  and <code class="inline">sync_nodes_optional</code> to come up. When all nodes are up, or when all
│ │ │  mandatory nodes are up and the time specified by <code class="inline">sync_nodes_timeout</code> has
│ │ │  elapsed, all applications start. If not all mandatory nodes are up, the node
│ │ │  terminates.</p><p><em>Example:</em></p><p>An application <code class="inline">myapp</code> is to run at the node <code class="inline">cp1@cave</code>. If this node goes down,
│ │ │  <code class="inline">myapp</code> is to be restarted at <code class="inline">cp2@cave</code> or <code class="inline">cp3@cave</code>. A system configuration
│ │ │ -file <code class="inline">cp1.config</code> for <code class="inline">cp1@cave</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7158760172-1">[</span><span class="p" data-group-id="7158760172-2">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="7158760172-3">[</span><span class="p" data-group-id="7158760172-4">{</span><span class="ss">distributed</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7158760172-5">[</span><span class="p" data-group-id="7158760172-6">{</span><span class="ss">myapp</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7158760172-7">[</span><span class="ss">cp1@cave</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7158760172-8">{</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="7158760172-8">}</span><span class="p" data-group-id="7158760172-7">]</span><span class="p" data-group-id="7158760172-6">}</span><span class="p" data-group-id="7158760172-5">]</span><span class="p" data-group-id="7158760172-4">}</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="7158760172-9">{</span><span class="ss">sync_nodes_mandatory</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7158760172-10">[</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="7158760172-10">]</span><span class="p" data-group-id="7158760172-9">}</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="7158760172-11">{</span><span class="ss">sync_nodes_timeout</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p" data-group-id="7158760172-11">}</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="7158760172-3">]</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7158760172-2">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7158760172-1">]</span><span class="p">.</span></code></pre><p>The system configuration files for <code class="inline">cp2@cave</code> and <code class="inline">cp3@cave</code> are identical,
│ │ │ +file <code class="inline">cp1.config</code> for <code class="inline">cp1@cave</code> can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9102066459-1">[</span><span class="p" data-group-id="9102066459-2">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9102066459-3">[</span><span class="p" data-group-id="9102066459-4">{</span><span class="ss">distributed</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9102066459-5">[</span><span class="p" data-group-id="9102066459-6">{</span><span class="ss">myapp</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9102066459-7">[</span><span class="ss">cp1@cave</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9102066459-8">{</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="9102066459-8">}</span><span class="p" data-group-id="9102066459-7">]</span><span class="p" data-group-id="9102066459-6">}</span><span class="p" data-group-id="9102066459-5">]</span><span class="p" data-group-id="9102066459-4">}</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="9102066459-9">{</span><span class="ss">sync_nodes_mandatory</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9102066459-10">[</span><span class="ss">cp2@cave</span><span class="p">,</span><span class="w"> </span><span class="ss">cp3@cave</span><span class="p" data-group-id="9102066459-10">]</span><span class="p" data-group-id="9102066459-9">}</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="9102066459-11">{</span><span class="ss">sync_nodes_timeout</span><span class="p">,</span><span class="w"> </span><span class="mi">5000</span><span class="p" data-group-id="9102066459-11">}</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9102066459-3">]</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9102066459-2">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9102066459-1">]</span><span class="p">.</span></code></pre><p>The system configuration files for <code class="inline">cp2@cave</code> and <code class="inline">cp3@cave</code> are identical,
│ │ │  except for the list of mandatory nodes, which is to be <code class="inline">[cp1@cave, cp3@cave]</code>
│ │ │  for <code class="inline">cp2@cave</code> and <code class="inline">[cp1@cave, cp2@cave]</code> for <code class="inline">cp3@cave</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>All involved nodes must have the same value for <code class="inline">distributed</code> and
│ │ │  <code class="inline">sync_nodes_timeout</code>. Otherwise the system behavior is undefined.</p></section><h2 id="starting-and-stopping-distributed-applications" class="section-heading">
│ │ │    <a href="#starting-and-stopping-distributed-applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting and Stopping Distributed Applications</span>
│ │ │  </h2>
│ │ │  <p>When all involved (mandatory) nodes have been started, the distributed
│ │ │  application can be started by calling <code class="inline">application:start(Application)</code> at <em>all
│ │ │  of these nodes.</em></p><p>A boot script (see <a href="release_structure.html">Releases</a>) can be used that
│ │ │  automatically starts the application.</p><p>The application is started at the first operational node that is listed in the
│ │ │  list of nodes in the <code class="inline">distributed</code> configuration parameter. The application is
│ │ │  started as usual. That is, an application master is created and calls the
│ │ │ -application callback function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9398457175-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="9398457175-1">)</span></code></pre><p>Example:</p><p>Continuing the example from the previous section, the three nodes are started,
│ │ │ +application callback function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4424952111-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="4424952111-1">)</span></code></pre><p>Example:</p><p>Continuing the example from the previous section, the three nodes are started,
│ │ │  specifying the system configuration file:</p><pre><code class="text">&gt; erl -sname cp1 -config cp1
│ │ │  &gt; erl -sname cp2 -config cp2
│ │ │  &gt; erl -sname cp3 -config cp3</code></pre><p>When all nodes are operational, <code class="inline">myapp</code> can be started. This is achieved by
│ │ │  calling <code class="inline">application:start(myapp)</code> at all three nodes. It is then started at
│ │ │  <code class="inline">cp1</code>, as shown in the following figure:</p><p><a href="" id="dist1"></a></p><p><img src="assets/dist1.gif" alt="Application myapp - Situation 1" title="Application myapp - Situation 1"/></p><p>Similarly, the application must be stopped by calling
│ │ │  <code class="inline">application:stop(Application)</code> at all involved nodes.</p><h2 id="failover" class="section-heading">
│ │ │    <a href="#failover" class="hover-link">
│ │ │ @@ -187,30 +187,30 @@
│ │ │    </a>
│ │ │    <span class="text">Failover</span>
│ │ │  </h2>
│ │ │  <p>If the node where the application is running goes down, the application is
│ │ │  restarted (after the specified time-out) at the first operational node that is
│ │ │  listed in the list of nodes in the <code class="inline">distributed</code> configuration parameter. This
│ │ │  is called a <em>failover</em>.</p><p>The application is started the normal way at the new node, that is, by the
│ │ │ -application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3792002159-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="3792002159-1">)</span></code></pre><p>An exception is if the application has the <code class="inline">start_phases</code> key defined (see
│ │ │ +application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="5115416618-1">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="5115416618-1">)</span></code></pre><p>An exception is if the application has the <code class="inline">start_phases</code> key defined (see
│ │ │  <a href="included_applications.html">Included Applications</a>). The application is then
│ │ │ -instead started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8100395545-1">(</span><span class="p" data-group-id="8100395545-2">{</span><span class="ss">failover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="8100395545-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="8100395545-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the terminated node.</p><p><em>Example:</em></p><p>If <code class="inline">cp1</code> goes down, the system checks which one of the other nodes, <code class="inline">cp2</code> or
│ │ │ +instead started by calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="7188982473-1">(</span><span class="p" data-group-id="7188982473-2">{</span><span class="ss">failover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="7188982473-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="7188982473-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the terminated node.</p><p><em>Example:</em></p><p>If <code class="inline">cp1</code> goes down, the system checks which one of the other nodes, <code class="inline">cp2</code> or
│ │ │  <code class="inline">cp3</code>, has the least number of running applications, but waits for 5 seconds for
│ │ │  <code class="inline">cp1</code> to restart. If <code class="inline">cp1</code> does not restart and <code class="inline">cp2</code> runs fewer applications
│ │ │  than <code class="inline">cp3</code>, <code class="inline">myapp</code> is restarted on <code class="inline">cp2</code>.</p><p><a href="" id="dist2"></a></p><p><img src="assets/dist2.gif" alt="Application myapp - Situation 2" title="Application myapp - Situation 2"/></p><p>Suppose now that <code class="inline">cp2</code> goes also down and does not restart within 5 seconds.
│ │ │  <code class="inline">myapp</code> is now restarted on <code class="inline">cp3</code>.</p><p><a href="" id="dist3"></a></p><p><img src="assets/dist3.gif" alt="Application myapp - Situation 3" title="Application myapp - Situation 3"/></p><h2 id="takeover" class="section-heading">
│ │ │    <a href="#takeover" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Takeover</span>
│ │ │  </h2>
│ │ │  <p>If a node is started, which has higher priority according to <code class="inline">distributed</code> than
│ │ │  the node where a distributed application is running, the application is
│ │ │  restarted at the new node and stopped at the old node. This is called a
│ │ │ -<em>takeover</em>.</p><p>The application is started by the application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="4577136877-1">(</span><span class="p" data-group-id="4577136877-2">{</span><span class="ss">takeover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="4577136877-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="4577136877-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the old node.</p><p><em>Example:</em></p><p>If <code class="inline">myapp</code> is running at <code class="inline">cp3</code>, and if <code class="inline">cp2</code> now restarts, it does not restart
│ │ │ +<em>takeover</em>.</p><p>The application is started by the application master calling:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8445936777-1">(</span><span class="p" data-group-id="8445936777-2">{</span><span class="ss">takeover</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="8445936777-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">StartArgs</span><span class="p" data-group-id="8445936777-1">)</span></code></pre><p>Here <code class="inline">Node</code> is the old node.</p><p><em>Example:</em></p><p>If <code class="inline">myapp</code> is running at <code class="inline">cp3</code>, and if <code class="inline">cp2</code> now restarts, it does not restart
│ │ │  <code class="inline">myapp</code>, as the order between the <code class="inline">cp2</code> and <code class="inline">cp3</code> nodes is undefined.</p><p><a href="" id="dist4"></a></p><p><img src="assets/dist4.gif" alt="Application myapp - Situation 4" title="Application myapp - Situation 4"/></p><p>However, if <code class="inline">cp1</code> also restarts, the function <a href="../../lib/kernel-10.2.7.4/doc/html/application.html#takeover/2"><code class="inline">application:takeover/2</code></a> moves
│ │ │  <code class="inline">myapp</code> to <code class="inline">cp1</code>, as <code class="inline">cp1</code> has a higher priority than <code class="inline">cp3</code> for this
│ │ │  application. In this case, <code class="inline">Module:start({takeover, cp3@cave}, StartArgs)</code> is
│ │ │  executed at <code class="inline">cp1</code> to start the application.</p><p><a href="" id="dist5"></a></p><p><img src="assets/dist5.gif" alt="Application myapp - Situation 5" title="Application myapp - Situation 5"/></p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/documentation.html
│ │ │ @@ -112,23 +112,23 @@
│ │ │        </a>
│ │ │  
│ │ │  
│ │ │      <span>Documentation</span>
│ │ │    </h1>
│ │ │  
│ │ │  <p>Documentation in Erlang is done through the <code class="inline">-moduledoc</code> and <code class="inline">-doc</code>
│ │ │ -<a href="modules.html#module-attributes">attributes</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9679648488-1">(</span><span class="ss">arith</span><span class="p" data-group-id="9679648488-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="modules.html#module-attributes">attributes</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4911946291-1">(</span><span class="ss">arith</span><span class="p" data-group-id="4911946291-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  A module for basic arithmetic.
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9679648488-2">(</span><span class="p" data-group-id="9679648488-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9679648488-3">]</span><span class="p" data-group-id="9679648488-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4911946291-2">(</span><span class="p" data-group-id="4911946291-3">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4911946291-3">]</span><span class="p" data-group-id="4911946291-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="9679648488-4">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="9679648488-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The <code class="inline">-moduledoc</code> attribute has to be located before the first <code class="inline">-doc</code> attribute
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="4911946291-4">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4911946291-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The <code class="inline">-moduledoc</code> attribute has to be located before the first <code class="inline">-doc</code> attribute
│ │ │  or function declaration. It documents the overall purpose of the module.</p><p>The <code class="inline">-doc</code> attribute always precedes the <a href="ref_man_functions.html">function</a> or
│ │ │  <a href="modules.html#module-attributes">attribute</a> it documents. The
│ │ │  attributes that can be documented are
│ │ │  <a href="typespec.html#type-declarations-of-user-defined-types">user-defined types</a>
│ │ │  (<code class="inline">-type</code> and <code class="inline">-opaque</code>) and
│ │ │  <a href="modules.html#behaviour-module-attribute">behaviour module attributes</a>
│ │ │  (<code class="inline">-callback</code>).</p><p>By default the format used for documentation attributes is
│ │ │ @@ -140,55 +140,55 @@
│ │ │  <a href="modules.html#documentation-attributes">Documentation Attributes</a>.</p><p><code class="inline">-doc</code> attributes have been available since Erlang/OTP 27.</p><h2 id="documentation-metadata" class="section-heading">
│ │ │    <a href="#documentation-metadata" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Documentation metadata</span>
│ │ │  </h2>
│ │ │  <p>It is possible to add metadata to the documentation entry. You do this by adding
│ │ │ -a <code class="inline">-moduledoc</code> or <code class="inline">-doc</code> attribute with a map as argument. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9830933690-1">(</span><span class="ss">arith</span><span class="p" data-group-id="9830933690-1">)</span><span class="p">.</span><span class="w">
│ │ │ +a <code class="inline">-moduledoc</code> or <code class="inline">-doc</code> attribute with a map as argument. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8918684481-1">(</span><span class="ss">arith</span><span class="p" data-group-id="8918684481-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  A module for basic arithmetic.
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="9830933690-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="9830933690-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="8918684481-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="8918684481-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9830933690-3">(</span><span class="p" data-group-id="9830933690-4">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9830933690-4">]</span><span class="p" data-group-id="9830933690-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8918684481-3">(</span><span class="p" data-group-id="8918684481-4">[</span><span class="ss">add</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8918684481-4">]</span><span class="p" data-group-id="8918684481-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="9830933690-5">(</span><span class="p" data-group-id="9830933690-6">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="9830933690-6">}</span><span class="p" data-group-id="9830933690-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="9830933690-7">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="9830933690-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The metadata is used by documentation tools to provide extra information to the
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="8918684481-5">(</span><span class="p" data-group-id="8918684481-6">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p" data-group-id="8918684481-6">}</span><span class="p" data-group-id="8918684481-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="8918684481-7">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="8918684481-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>The metadata is used by documentation tools to provide extra information to the
│ │ │  user. There can be multiple metadata documentation entries, in which case the
│ │ │  maps will be merged with the latest taking precedence if there are duplicate
│ │ │  keys. Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;Adds two numbers.&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="2964159758-1">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">author</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p" data-group-id="2964159758-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="2964159758-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="2964159758-2">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="2964159758-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="2964159758-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>This will result in a metadata entry of <code class="inline">#{since =&gt; &quot;2.0&quot;, author =&gt; &quot;Joe&quot;}</code>.</p><p>The keys and values in the metadata map can be any type, but it is recommended
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="5884147792-1">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;1.0&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">author</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p" data-group-id="5884147792-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="5884147792-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;2.0&quot;</span><span class="p" data-group-id="5884147792-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="5884147792-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="5884147792-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><p>This will result in a metadata entry of <code class="inline">#{since =&gt; &quot;2.0&quot;, author =&gt; &quot;Joe&quot;}</code>.</p><p>The keys and values in the metadata map can be any type, but it is recommended
│ │ │  that only <a href="data_types.html#atom">atoms</a> are used for keys and
│ │ │  <a href="data_types.html#string">strings</a> for the values.</p><h2 id="external-documentation-files" class="section-heading">
│ │ │    <a href="#external-documentation-files" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">External documentation files</span>
│ │ │  </h2>
│ │ │  <p>The <code class="inline">-moduledoc</code> and <code class="inline">-doc</code> can also be placed in external files. To do so use
│ │ │  <code class="inline">-doc {file, &quot;path/to/doc.md&quot;}</code> to point to the documentation. The path used is
│ │ │  relative to the file where the <code class="inline">-doc</code> attribute is located. For example:</p><pre><code class="markdown">%% doc/add.md
│ │ │  Adds two numbers.</code></pre><p>and</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% src/arith.erl</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="1384158763-1">(</span><span class="p" data-group-id="1384158763-2">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/add.md&quot;</span><span class="p" data-group-id="1384158763-2">}</span><span class="p" data-group-id="1384158763-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="1384158763-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="1384158763-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><h2 id="documenting-a-module" class="section-heading">
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="2665508648-1">(</span><span class="p" data-group-id="2665508648-2">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/add.md&quot;</span><span class="p" data-group-id="2665508648-2">}</span><span class="p" data-group-id="2665508648-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="2665508648-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="2665508648-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span></code></pre><h2 id="documenting-a-module" class="section-heading">
│ │ │    <a href="#documenting-a-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Documenting a module</span>
│ │ │  </h2>
│ │ │  <p>The module description should include details on how to use the API and examples
│ │ │  of the different functions working together. Here is a good place to use images
│ │ │  and other diagrams to better show the usage of the module. Instead of writing a
│ │ │  long text in the <code class="inline">moduledoc</code> attribute, it could be better to break it out into
│ │ │  an external page.</p><p>The <code class="inline">moduledoc</code> attribute should start with a short paragraph describing the
│ │ │ -module and then go into greater details. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4150257216-1">(</span><span class="ss">arith</span><span class="p" data-group-id="4150257216-1">)</span><span class="p">.</span><span class="w">
│ │ │ +module and then go into greater details. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6923536283-1">(</span><span class="ss">arith</span><span class="p" data-group-id="6923536283-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="s">&quot;
│ │ │     A module for basic arithmetic.
│ │ │  
│ │ │     This module can be used to add and subtract values. For example:
│ │ │  
│ │ │     ```erlang
│ │ │     1&gt; arith:substract(arith:add(2, 3), 1).
│ │ │ @@ -203,94 +203,94 @@
│ │ │  <p>There are three reserved metadata keys for <code class="inline">-moduledoc</code>:</p><ul><li><code class="inline">since</code> - Shows in which version of the application the module was added.
│ │ │  If this is added, all functions, types, and callbacks within will also receive
│ │ │  the same <code class="inline">since</code> value unless specified in the metadata of the function, type
│ │ │  or callback.</li><li><code class="inline">deprecated</code> - Shows a text in the documentation explaining that it is
│ │ │  deprecated and what to use instead.</li><li><code class="inline">format</code> - The format to use for all documentation in this module. The
│ │ │  default is <code class="inline">text/markdown</code>. It should be written using the
│ │ │  <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types">mime type</a>
│ │ │ -of the format.</li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="1236412252-1">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/arith.asciidoc&quot;</span><span class="p" data-group-id="1236412252-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="1236412252-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;0.1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">format</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;text/asciidoc&quot;</span><span class="p" data-group-id="1236412252-2">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="1236412252-3">#{</span><span class="ss">deprecated</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Use the Erlang arithmetic operators instead.&quot;</span><span class="p" data-group-id="1236412252-3">}</span><span class="p">.</span></code></pre><h2 id="documenting-functions-user-defined-types-and-callbacks" class="section-heading">
│ │ │ +of the format.</li></ul><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="9952058682-1">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;../doc/arith.asciidoc&quot;</span><span class="p" data-group-id="9952058682-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="9952058682-2">#{</span><span class="ss">since</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;0.1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">format</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;text/asciidoc&quot;</span><span class="p" data-group-id="9952058682-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">moduledoc</span><span class="w"> </span><span class="p" data-group-id="9952058682-3">#{</span><span class="ss">deprecated</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="s">&quot;Use the Erlang arithmetic operators instead.&quot;</span><span class="p" data-group-id="9952058682-3">}</span><span class="p">.</span></code></pre><h2 id="documenting-functions-user-defined-types-and-callbacks" class="section-heading">
│ │ │    <a href="#documenting-functions-user-defined-types-and-callbacks" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Documenting functions, user-defined types, and callbacks</span>
│ │ │  </h2>
│ │ │  <p>Functions, types, and callbacks can be documented using the <code class="inline">-doc</code> attribute.
│ │ │  Each entry should start with a short paragraph describing the purpose of entity,
│ │ │  and then go into greater detail in needed.</p><p>It is not recommended to include images or diagrams in this documentation as it
│ │ │  is used by IDEs and <a href="../../lib/stdlib-6.2.2.3/doc/html/c.html#h/1"><code class="inline">c:h/1</code></a> to show the documentation to the user.</p><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  A number that can be used by the arith module.
│ │ │  
│ │ │  We use a special number here so that we know
│ │ │  that this number comes from this module.
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4733506754-1">(</span><span class="p" data-group-id="4733506754-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4733506754-2">{</span><span class="ss">arith</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">number</span><span class="p" data-group-id="4733506754-3">(</span><span class="p" data-group-id="4733506754-3">)</span><span class="p" data-group-id="4733506754-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0645006415-1">(</span><span class="p" data-group-id="0645006415-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0645006415-2">{</span><span class="ss">arith</span><span class="p">,</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">number</span><span class="p" data-group-id="0645006415-3">(</span><span class="p" data-group-id="0645006415-3">)</span><span class="p" data-group-id="0645006415-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  Adds two numbers.
│ │ │  
│ │ │  ### Example:
│ │ │  
│ │ │  ```
│ │ │  1&gt; arith:add(arith:number(1), arith:number(2)). {number, 3}
│ │ │  ```
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="4733506754-4">(</span><span class="nf">number</span><span class="p" data-group-id="4733506754-5">(</span><span class="p" data-group-id="4733506754-5">)</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4733506754-6">(</span><span class="p" data-group-id="4733506754-6">)</span><span class="p" data-group-id="4733506754-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="4733506754-7">(</span><span class="p" data-group-id="4733506754-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="4733506754-8">(</span><span class="p" data-group-id="4733506754-9">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="p" data-group-id="4733506754-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4733506754-10">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4733506754-10">}</span><span class="p" data-group-id="4733506754-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4733506754-11">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="4733506754-11">}</span><span class="p">.</span></code></pre><h3 id="doc-metadata" class="section-heading">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="0645006415-4">(</span><span class="nf">number</span><span class="p" data-group-id="0645006415-5">(</span><span class="p" data-group-id="0645006415-5">)</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0645006415-6">(</span><span class="p" data-group-id="0645006415-6">)</span><span class="p" data-group-id="0645006415-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0645006415-7">(</span><span class="p" data-group-id="0645006415-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="0645006415-8">(</span><span class="p" data-group-id="0645006415-9">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="p" data-group-id="0645006415-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0645006415-10">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="0645006415-10">}</span><span class="p" data-group-id="0645006415-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0645006415-11">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="0645006415-11">}</span><span class="p">.</span></code></pre><h3 id="doc-metadata" class="section-heading">
│ │ │    <a href="#doc-metadata" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Doc metadata</span>
│ │ │  </h3>
│ │ │  <p>There are four reserved metadata keys for <code class="inline">-doc</code>:</p><ul><li><p><code class="inline">since =&gt; unicode:chardata()</code> - Shows which version of the application the
│ │ │  module was added.</p></li><li><p><code class="inline">deprecated =&gt; unicode:chardata()</code> - Shows a text in the documentation
│ │ │  explaining that it is deprecated and what to use instead. The compiler will
│ │ │  automatically insert this key if there is a <code class="inline">-deprecated</code> attribute marking a
│ │ │  function as deprecated.</p></li><li><p><code class="inline">equiv =&gt; unicode:chardata() | F/A | F(...)</code> - Notes that this function is equivalent to
│ │ │  another function in this module. The equivalence can be described using either
│ │ │ -<code class="inline">Func/Arity</code>, <code class="inline">Func(Args)</code> or a <a href="../../lib/stdlib-6.2.2.3/doc/html/unicode.html#t:chardata/0">unicode string</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="8676253302-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="8676253302-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="8676253302-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="8676253302-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="8676253302-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8676253302-4">[</span><span class="p" data-group-id="8676253302-4">]</span><span class="p" data-group-id="8676253302-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="8676253302-5">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="8676253302-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="3176235425-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="3176235425-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3176235425-3">[</span><span class="p" data-group-id="3176235425-3">]</span><span class="p" data-group-id="3176235425-2">)</span><span class="p" data-group-id="3176235425-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="3176235425-4">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3176235425-5">(</span><span class="p" data-group-id="3176235425-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3176235425-6">(</span><span class="p" data-group-id="3176235425-6">)</span><span class="p" data-group-id="3176235425-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="3176235425-7">(</span><span class="p" data-group-id="3176235425-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="3176235425-8">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="3176235425-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="3176235425-9">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3176235425-10">[</span><span class="p" data-group-id="3176235425-10">]</span><span class="p" data-group-id="3176235425-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="3176235425-11">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="3176235425-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The entry into the <a href="../../lib/kernel-10.2.7.4/doc/html/eep48_chapter.html">EEP-48</a> doc chunk metadata is
│ │ │ +<code class="inline">Func/Arity</code>, <code class="inline">Func(Args)</code> or a <a href="../../lib/stdlib-6.2.2.3/doc/html/unicode.html#t:chardata/0">unicode string</a>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="1774651736-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">add</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="1774651736-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="1774651736-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="1774651736-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="1774651736-3">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1774651736-4">[</span><span class="p" data-group-id="1774651736-4">]</span><span class="p" data-group-id="1774651736-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="1774651736-5">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="1774651736-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>or</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="p" data-group-id="0086791453-1">#{</span><span class="ss">equiv</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="0086791453-2">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0086791453-3">[</span><span class="p" data-group-id="0086791453-3">]</span><span class="p" data-group-id="0086791453-2">)</span><span class="p" data-group-id="0086791453-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="0086791453-4">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0086791453-5">(</span><span class="p" data-group-id="0086791453-5">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0086791453-6">(</span><span class="p" data-group-id="0086791453-6">)</span><span class="p" data-group-id="0086791453-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0086791453-7">(</span><span class="p" data-group-id="0086791453-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="0086791453-8">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="0086791453-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">add</span><span class="p" data-group-id="0086791453-9">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0086791453-10">[</span><span class="p" data-group-id="0086791453-10">]</span><span class="p" data-group-id="0086791453-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="0086791453-11">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p">,</span><span class="w"> </span><span class="n">Options</span><span class="p" data-group-id="0086791453-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The entry into the <a href="../../lib/kernel-10.2.7.4/doc/html/eep48_chapter.html">EEP-48</a> doc chunk metadata is
│ │ │  the value converted to a string.</p></li><li><p><code class="inline">exported =&gt; boolean()</code> - A <a href="../../erts-15.2.7.8/doc/html/erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a> signifying if the entry is <code class="inline">exported</code>
│ │ │  or not. This value is automatically set by the compiler and should not be set
│ │ │  by the user.</p></li></ul><h3 id="doc-signatures" class="section-heading">
│ │ │    <a href="#doc-signatures" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Doc signatures</span>
│ │ │  </h3>
│ │ │  <p>The doc signature is a short text shown to describe the function and its arguments.
│ │ │  By default it is determined by looking at the names of the arguments in the
│ │ │ -<code class="inline">-spec</code> or function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add</span><span class="p" data-group-id="8098986388-1">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="8098986388-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">-spec</code> or function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add</span><span class="p" data-group-id="0127690815-1">(</span><span class="n">One</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="p" data-group-id="0127690815-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Two</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">sub</span><span class="p" data-group-id="8098986388-2">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="8098986388-3">(</span><span class="p" data-group-id="8098986388-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="8098986388-4">(</span><span class="p" data-group-id="8098986388-4">)</span><span class="p" data-group-id="8098986388-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="8098986388-5">(</span><span class="p" data-group-id="8098986388-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">sub</span><span class="p" data-group-id="8098986388-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8098986388-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>will have a signature of <code class="inline">add(One, Two)</code> and <code class="inline">sub(One, Two)</code>.</p><p>For types or callbacks, the signature is derived from the type or callback
│ │ │ -specification. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="8158353127-1">(</span><span class="n">Value</span><span class="p" data-group-id="8158353127-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="8158353127-2">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="8158353127-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">sub</span><span class="p" data-group-id="0127690815-2">(</span><span class="n">One</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0127690815-3">(</span><span class="p" data-group-id="0127690815-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Two</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0127690815-4">(</span><span class="p" data-group-id="0127690815-4">)</span><span class="p" data-group-id="0127690815-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0127690815-5">(</span><span class="p" data-group-id="0127690815-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">sub</span><span class="p" data-group-id="0127690815-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0127690815-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>will have a signature of <code class="inline">add(One, Two)</code> and <code class="inline">sub(One, Two)</code>.</p><p>For types or callbacks, the signature is derived from the type or callback
│ │ │ +specification. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="9581148036-1">(</span><span class="n">Value</span><span class="p" data-group-id="9581148036-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="9581148036-2">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9581148036-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% signature will be `number(Value)`</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="8158353127-3">(</span><span class="p" data-group-id="8158353127-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="8158353127-4">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="8158353127-5">(</span><span class="p" data-group-id="8158353127-5">)</span><span class="p" data-group-id="8158353127-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="9581148036-3">(</span><span class="p" data-group-id="9581148036-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="9581148036-4">{</span><span class="ss">number</span><span class="p">,</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="9581148036-5">(</span><span class="p" data-group-id="9581148036-5">)</span><span class="p" data-group-id="9581148036-4">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% signature will be `number()`</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="8158353127-6">(</span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="8158353127-7">(</span><span class="p" data-group-id="8158353127-7">)</span><span class="p" data-group-id="8158353127-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="9581148036-6">(</span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="9581148036-7">(</span><span class="p" data-group-id="9581148036-7">)</span><span class="p" data-group-id="9581148036-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% signature will be `increment(In)`</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="8158353127-8">(</span><span class="n">In</span><span class="p" data-group-id="8158353127-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="8158353127-9">(</span><span class="p" data-group-id="8158353127-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">increment</span><span class="p" data-group-id="9581148036-8">(</span><span class="n">In</span><span class="p" data-group-id="9581148036-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Out</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="9581148036-9">(</span><span class="p" data-group-id="9581148036-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% signature will be `increment(In)`</span></code></pre><p>If it is not possible to &quot;easily&quot; figure out a nice signature from the code, the
│ │ │  MFA syntax is used instead. For example: <code class="inline">add/2</code>, <code class="inline">number/1</code>, <code class="inline">increment/1</code></p><p>It is possible to supply a custom signature by placing it as the first line of the
│ │ │  <code class="inline">-doc</code> attribute. The provided signature must be in the form of a function
│ │ │  declaration up until the <code class="inline">-&gt;</code>. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;&quot;
│ │ │  add(One, Two)
│ │ │  
│ │ │  Adds two numbers.
│ │ │  &quot;&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add</span><span class="p" data-group-id="7814495588-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="7814495588-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">.</span></code></pre><p>Will create the signature <code class="inline">add(One, Two)</code>. The signature will be removed from the
│ │ │ +</span><span class="nf">add</span><span class="p" data-group-id="0214697231-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="0214697231-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">.</span></code></pre><p>Will create the signature <code class="inline">add(One, Two)</code>. The signature will be removed from the
│ │ │  documentation string, so in the example above only the text <code class="inline">&quot;Adds two numbers&quot;</code>
│ │ │  will be part of the documentation. This works for functions, types, and
│ │ │  callbacks.</p><h2 id="links-in-markdown" class="section-heading">
│ │ │    <a href="#links-in-markdown" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Links in Markdown</span>
│ │ │ @@ -328,28 +328,28 @@
│ │ │  modules. That is, modules that should be used by other applications and modules
│ │ │  that should not. By default all modules in an application are visible, but by
│ │ │  setting <code class="inline">-moduledoc false.</code> specific modules can be hidden from being listed as
│ │ │  part of the available API.</p><p>An Erlang <a href="modules.html">module</a> consists of public and private functions and type
│ │ │  attributes. By default, all exported functions, exported types and callbacks are
│ │ │  considered visible and part of the modules public API. In addition, any
│ │ │  non-exported type that is referred to by any other visible type attribute is
│ │ │ -also visible, but not considered to be part of the public API. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2499219706-1">(</span><span class="p" data-group-id="2499219706-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2499219706-2">]</span><span class="p" data-group-id="2499219706-1">)</span><span class="p">.</span><span class="w">
│ │ │ +also visible, but not considered to be part of the public API. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2069771893-1">(</span><span class="p" data-group-id="2069771893-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2069771893-2">]</span><span class="p" data-group-id="2069771893-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="2499219706-3">(</span><span class="p" data-group-id="2499219706-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="2499219706-4">(</span><span class="p" data-group-id="2499219706-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="2499219706-5">(</span><span class="p" data-group-id="2499219706-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="2499219706-6">(</span><span class="p" data-group-id="2499219706-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>in the above code, the function <code class="inline">example/0</code> is exported and it referenced the
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="2069771893-3">(</span><span class="p" data-group-id="2069771893-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="2069771893-4">(</span><span class="p" data-group-id="2069771893-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="2069771893-5">(</span><span class="p" data-group-id="2069771893-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="2069771893-6">(</span><span class="p" data-group-id="2069771893-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>in the above code, the function <code class="inline">example/0</code> is exported and it referenced the
│ │ │  un-exported type <code class="inline">private/0</code>. Therefore both <code class="inline">example/0</code> and <code class="inline">private/0</code> will be
│ │ │  marked as visible. The <code class="inline">private/0</code> type will have the metadata field <code class="inline">exported</code>
│ │ │  set to <code class="inline">false</code> to show that it is not part of the public API.</p><p>If you want to make a visible entity hidden you need to set the <code class="inline">-doc</code> attribute
│ │ │ -to <code class="inline">false</code>. Let us revisit our previous example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5955427641-1">(</span><span class="p" data-group-id="5955427641-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5955427641-2">]</span><span class="p" data-group-id="5955427641-1">)</span><span class="p">.</span><span class="w">
│ │ │ +to <code class="inline">false</code>. Let us revisit our previous example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3717263081-1">(</span><span class="p" data-group-id="3717263081-2">[</span><span class="ss">example</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3717263081-2">]</span><span class="p" data-group-id="3717263081-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="5955427641-3">(</span><span class="p" data-group-id="5955427641-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="5955427641-4">(</span><span class="p" data-group-id="5955427641-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="5955427641-5">(</span><span class="p" data-group-id="5955427641-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="3717263081-3">(</span><span class="p" data-group-id="3717263081-3">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">example</span><span class="p" data-group-id="3717263081-4">(</span><span class="p" data-group-id="3717263081-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">private</span><span class="p" data-group-id="3717263081-5">(</span><span class="p" data-group-id="3717263081-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="ss">false</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="5955427641-6">(</span><span class="p" data-group-id="5955427641-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>The function <code class="inline">example/0</code> is exported but explicitly marked as hidden; therefore
│ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="3717263081-6">(</span><span class="p" data-group-id="3717263081-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">one</span><span class="p">.</span></code></pre><p>The function <code class="inline">example/0</code> is exported but explicitly marked as hidden; therefore
│ │ │  both <code class="inline">example/0</code> and <code class="inline">private/0</code> will be hidden.</p><p>Any documentation added to an automatically hidden entity (non-exported function
│ │ │  or type) is ignored and will generate a warning. Such functions can be
│ │ │  documented using comments.</p><h2 id="compiling-and-getting-documentation" class="section-heading">
│ │ │    <a href="#compiling-and-getting-documentation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Compiling and getting documentation</span>
│ │ │ @@ -375,21 +375,21 @@
│ │ │    <span class="text">Using ExDoc to generate HTML/ePub documentation</span>
│ │ │  </h2>
│ │ │  <p><a href="https://hexdocs.pm/ex_doc/">ExDoc</a> has built-in support to generate
│ │ │  documentation from Markdown. The simplest way is by using the
│ │ │  <a href="https://hexdocs.pm/rebar3_ex_doc">rebar3_ex_doc</a> plugin. To set up a
│ │ │  rebar3 project to use <a href="https://hexdocs.pm/ex_doc/">ExDoc</a> to generate
│ │ │  documentation add the following to your <code class="inline">rebar3.config</code>.</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Enable the plugin</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9384878941-1">{</span><span class="ss">plugins</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9384878941-2">[</span><span class="ss">rebar3_ex_doc</span><span class="p" data-group-id="9384878941-2">]</span><span class="p" data-group-id="9384878941-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9045983373-1">{</span><span class="ss">plugins</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9045983373-2">[</span><span class="ss">rebar3_ex_doc</span><span class="p" data-group-id="9045983373-2">]</span><span class="p" data-group-id="9045983373-1">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="9384878941-3">{</span><span class="ss">ex_doc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9384878941-4">[</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9384878941-5">{</span><span class="ss">extras</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9384878941-6">[</span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="9384878941-6">]</span><span class="p" data-group-id="9384878941-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9384878941-7">{</span><span class="ss">main</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="9384878941-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9384878941-8">{</span><span class="ss">source_url</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;https://github.com/namespace/your_app&quot;</span><span class="p" data-group-id="9384878941-8">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9384878941-4">]</span><span class="p" data-group-id="9384878941-3">}</span><span class="p">.</span></code></pre><p>When configured you can run <code class="inline">rebar3 ex_doc</code> to generate the
│ │ │ +</span><span class="p" data-group-id="9045983373-3">{</span><span class="ss">ex_doc</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9045983373-4">[</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9045983373-5">{</span><span class="ss">extras</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9045983373-6">[</span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="9045983373-6">]</span><span class="p" data-group-id="9045983373-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9045983373-7">{</span><span class="ss">main</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;README.md&quot;</span><span class="p" data-group-id="9045983373-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9045983373-8">{</span><span class="ss">source_url</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;https://github.com/namespace/your_app&quot;</span><span class="p" data-group-id="9045983373-8">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9045983373-4">]</span><span class="p" data-group-id="9045983373-3">}</span><span class="p">.</span></code></pre><p>When configured you can run <code class="inline">rebar3 ex_doc</code> to generate the
│ │ │  documentation to <code class="inline">doc/index.html</code>. For more details and options see
│ │ │  the <a href="https://hexdocs.pm/rebar3_ex_doc">rebar3_ex_doc</a> documentation.</p><p>You can also download the
│ │ │  <a href="https://github.com/elixir/ex_doc/releases/latest">release escript bundle</a> from
│ │ │  github and run it from the command line. The documentation for using the escript
│ │ │  is found by running <code class="inline">ex_doc --help</code>.</p><p>If you are writing documentation that will be using
│ │ │  <a href="https://hexdocs.pm/ex_doc/">ExDoc</a> to generate HTML/ePub it is highly
│ │ │  recommended to read its documentation.</p>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/drivers.html
│ │ │ @@ -122,23 +122,23 @@
│ │ │    <span class="text">Drivers and Concurrency</span>
│ │ │  </h2>
│ │ │  <p>The runtime system always takes a lock before running any code in a driver.</p><p>By default, that lock is at the driver level, that is, if several ports have
│ │ │  been opened to the same driver, only code for one port at the same time can be
│ │ │  running.</p><p>A driver can be configured to have one lock for each port instead.</p><p>If a driver is used in a functional way (that is, holds no state, but only does
│ │ │  some heavy calculation and returns a result), several ports with registered
│ │ │  names can be opened beforehand, and the port to be used can be chosen based on
│ │ │ -the scheduler ID as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6400542730-1">(</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="6400542730-2">(</span><span class="p" data-group-id="6400542730-2">)</span><span class="p">,</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="6400542730-3">{</span><span class="ss">some_driver_01</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_02</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_03</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_04</span><span class="p">,</span><span class="w">
│ │ │ +the scheduler ID as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4545121889-1">(</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="4545121889-2">(</span><span class="p" data-group-id="4545121889-2">)</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="4545121889-3">{</span><span class="ss">some_driver_01</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_02</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_03</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_04</span><span class="p">,</span><span class="w">
│ │ │  	 </span><span class="ss">some_driver_05</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_06</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_07</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_08</span><span class="p">,</span><span class="w">
│ │ │  	 </span><span class="ss">some_driver_09</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_10</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_11</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_12</span><span class="p">,</span><span class="w">
│ │ │ -	 </span><span class="ss">some_driver_13</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_14</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_15</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_16</span><span class="p" data-group-id="6400542730-3">}</span><span class="p" data-group-id="6400542730-1">)</span><span class="p">.</span><span class="w">
│ │ │ +	 </span><span class="ss">some_driver_13</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_14</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_15</span><span class="p">,</span><span class="w"> </span><span class="ss">some_driver_16</span><span class="p" data-group-id="4545121889-3">}</span><span class="p" data-group-id="4545121889-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client_port</span><span class="p" data-group-id="6400542730-4">(</span><span class="p" data-group-id="6400542730-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="6400542730-5">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="6400542730-6">(</span><span class="ss">scheduler_id</span><span class="p" data-group-id="6400542730-6">)</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="6400542730-7">(</span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="6400542730-8">(</span><span class="p" data-group-id="6400542730-8">)</span><span class="p" data-group-id="6400542730-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="6400542730-9">(</span><span class="p" data-group-id="6400542730-9">)</span><span class="p" data-group-id="6400542730-5">)</span><span class="p">.</span></code></pre><p>As long as there are no more than 16 schedulers, there will never be any lock
│ │ │ +</span><span class="nf">client_port</span><span class="p" data-group-id="4545121889-4">(</span><span class="p" data-group-id="4545121889-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="4545121889-5">(</span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="4545121889-6">(</span><span class="ss">scheduler_id</span><span class="p" data-group-id="4545121889-6">)</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="nf">tuple_size</span><span class="p" data-group-id="4545121889-7">(</span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="4545121889-8">(</span><span class="p" data-group-id="4545121889-8">)</span><span class="p" data-group-id="4545121889-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="o">?</span><span class="n">PORT_NAMES</span><span class="p" data-group-id="4545121889-9">(</span><span class="p" data-group-id="4545121889-9">)</span><span class="p" data-group-id="4545121889-5">)</span><span class="p">.</span></code></pre><p>As long as there are no more than 16 schedulers, there will never be any lock
│ │ │  contention on the port lock for the driver.</p><h2 id="avoiding-copying-binaries-when-calling-a-driver" class="section-heading">
│ │ │    <a href="#avoiding-copying-binaries-when-calling-a-driver" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Avoiding Copying Binaries When Calling a Driver</span>
│ │ │  </h2>
│ │ │  <p>There are basically two ways to avoid copying a binary that is sent to a driver:</p><ul><li><p>If the <code class="inline">Data</code> argument for <a href="../../erts-15.2.7.8/doc/html/erlang.html#port_control/3"><code class="inline">port_control/3</code></a> is a
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/eff_guide_functions.html
│ │ │ @@ -122,67 +122,67 @@
│ │ │    <span class="text">Pattern Matching</span>
│ │ │  </h2>
│ │ │  <p>Pattern matching in function head as well as in <code class="inline">case</code> and <code class="inline">receive</code> clauses are
│ │ │  optimized by the compiler. With a few exceptions, there is nothing to gain by
│ │ │  rearranging clauses.</p><p>One exception is pattern matching of binaries. The compiler does not rearrange
│ │ │  clauses that match binaries. Placing the clause that matches against the empty
│ │ │  binary <em>last</em> is usually slightly faster than placing it <em>first</em>.</p><p>The following is a rather unnatural example to show another exception where
│ │ │ -rearranging clauses is beneficial:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map1</span><span class="p" data-group-id="6953814817-1">(</span><span class="ss">one</span><span class="p" data-group-id="6953814817-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="6953814817-2">(</span><span class="ss">two</span><span class="p" data-group-id="6953814817-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="6953814817-3">(</span><span class="ss">three</span><span class="p" data-group-id="6953814817-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="6953814817-4">(</span><span class="n">Int</span><span class="p" data-group-id="6953814817-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6953814817-5">(</span><span class="n">Int</span><span class="p" data-group-id="6953814817-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="6953814817-6">(</span><span class="ss">four</span><span class="p" data-group-id="6953814817-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="6953814817-7">(</span><span class="ss">five</span><span class="p" data-group-id="6953814817-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map1</span><span class="p" data-group-id="6953814817-8">(</span><span class="ss">six</span><span class="p" data-group-id="6953814817-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>The problem is the clause with the variable <code class="inline">Int</code>. As a variable can match
│ │ │ +rearranging clauses is beneficial:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map1</span><span class="p" data-group-id="3705223437-1">(</span><span class="ss">one</span><span class="p" data-group-id="3705223437-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="3705223437-2">(</span><span class="ss">two</span><span class="p" data-group-id="3705223437-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="3705223437-3">(</span><span class="ss">three</span><span class="p" data-group-id="3705223437-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="3705223437-4">(</span><span class="n">Int</span><span class="p" data-group-id="3705223437-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="3705223437-5">(</span><span class="n">Int</span><span class="p" data-group-id="3705223437-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="3705223437-6">(</span><span class="ss">four</span><span class="p" data-group-id="3705223437-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="3705223437-7">(</span><span class="ss">five</span><span class="p" data-group-id="3705223437-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map1</span><span class="p" data-group-id="3705223437-8">(</span><span class="ss">six</span><span class="p" data-group-id="3705223437-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>The problem is the clause with the variable <code class="inline">Int</code>. As a variable can match
│ │ │  anything, including the atoms <code class="inline">four</code>, <code class="inline">five</code>, and <code class="inline">six</code>, which the following
│ │ │  clauses also match, the compiler must generate suboptimal code that executes as
│ │ │  follows:</p><ul><li>First, the input value is compared to <code class="inline">one</code>, <code class="inline">two</code>, and <code class="inline">three</code> (using a
│ │ │  single instruction that does a binary search; thus, quite efficient even if
│ │ │  there are many values) to select which one of the first three clauses to
│ │ │  execute (if any).</li><li>If none of the first three clauses match, the fourth clause match as a
│ │ │  variable always matches.</li><li>If the guard test <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_integer/1"><code class="inline">is_integer(Int)</code></a> succeeds, the fourth
│ │ │  clause is executed.</li><li>If the guard test fails, the input value is compared to <code class="inline">four</code>, <code class="inline">five</code>, and
│ │ │  <code class="inline">six</code>, and the appropriate clause is selected. (There is a <code class="inline">function_clause</code>
│ │ │ -exception if none of the values matched.)</li></ul><p>Rewriting to either:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map2</span><span class="p" data-group-id="6508655986-1">(</span><span class="ss">one</span><span class="p" data-group-id="6508655986-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="6508655986-2">(</span><span class="ss">two</span><span class="p" data-group-id="6508655986-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="6508655986-3">(</span><span class="ss">three</span><span class="p" data-group-id="6508655986-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="6508655986-4">(</span><span class="ss">four</span><span class="p" data-group-id="6508655986-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="6508655986-5">(</span><span class="ss">five</span><span class="p" data-group-id="6508655986-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="6508655986-6">(</span><span class="ss">six</span><span class="p" data-group-id="6508655986-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map2</span><span class="p" data-group-id="6508655986-7">(</span><span class="n">Int</span><span class="p" data-group-id="6508655986-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6508655986-8">(</span><span class="n">Int</span><span class="p" data-group-id="6508655986-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>or:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map3</span><span class="p" data-group-id="4910966051-1">(</span><span class="n">Int</span><span class="p" data-group-id="4910966051-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="4910966051-2">(</span><span class="n">Int</span><span class="p" data-group-id="4910966051-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="4910966051-3">(</span><span class="ss">one</span><span class="p" data-group-id="4910966051-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="4910966051-4">(</span><span class="ss">two</span><span class="p" data-group-id="4910966051-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="4910966051-5">(</span><span class="ss">three</span><span class="p" data-group-id="4910966051-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="4910966051-6">(</span><span class="ss">four</span><span class="p" data-group-id="4910966051-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="4910966051-7">(</span><span class="ss">five</span><span class="p" data-group-id="4910966051-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">atom_map3</span><span class="p" data-group-id="4910966051-8">(</span><span class="ss">six</span><span class="p" data-group-id="4910966051-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>gives slightly more efficient matching code.</p><p>Another example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs1</span><span class="p" data-group-id="9691801031-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9691801031-2">[</span><span class="p" data-group-id="9691801031-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="9691801031-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +exception if none of the values matched.)</li></ul><p>Rewriting to either:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map2</span><span class="p" data-group-id="1870689579-1">(</span><span class="ss">one</span><span class="p" data-group-id="1870689579-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="1870689579-2">(</span><span class="ss">two</span><span class="p" data-group-id="1870689579-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="1870689579-3">(</span><span class="ss">three</span><span class="p" data-group-id="1870689579-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="1870689579-4">(</span><span class="ss">four</span><span class="p" data-group-id="1870689579-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="1870689579-5">(</span><span class="ss">five</span><span class="p" data-group-id="1870689579-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="1870689579-6">(</span><span class="ss">six</span><span class="p" data-group-id="1870689579-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map2</span><span class="p" data-group-id="1870689579-7">(</span><span class="n">Int</span><span class="p" data-group-id="1870689579-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="1870689579-8">(</span><span class="n">Int</span><span class="p" data-group-id="1870689579-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>or:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">atom_map3</span><span class="p" data-group-id="9779118890-1">(</span><span class="n">Int</span><span class="p" data-group-id="9779118890-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="9779118890-2">(</span><span class="n">Int</span><span class="p" data-group-id="9779118890-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9779118890-3">(</span><span class="ss">one</span><span class="p" data-group-id="9779118890-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9779118890-4">(</span><span class="ss">two</span><span class="p" data-group-id="9779118890-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9779118890-5">(</span><span class="ss">three</span><span class="p" data-group-id="9779118890-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9779118890-6">(</span><span class="ss">four</span><span class="p" data-group-id="9779118890-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9779118890-7">(</span><span class="ss">five</span><span class="p" data-group-id="9779118890-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">atom_map3</span><span class="p" data-group-id="9779118890-8">(</span><span class="ss">six</span><span class="p" data-group-id="9779118890-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span></code></pre><p>gives slightly more efficient matching code.</p><p>Another example:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs1</span><span class="p" data-group-id="5624662711-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5624662711-2">[</span><span class="p" data-group-id="5624662711-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5624662711-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Ys</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map_pairs1</span><span class="p" data-group-id="9691801031-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9691801031-4">[</span><span class="p" data-group-id="9691801031-4">]</span><span class="p" data-group-id="9691801031-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">map_pairs1</span><span class="p" data-group-id="5624662711-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5624662711-4">[</span><span class="p" data-group-id="5624662711-4">]</span><span class="p" data-group-id="5624662711-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Xs</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map_pairs1</span><span class="p" data-group-id="9691801031-5">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9691801031-6">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="9691801031-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9691801031-7">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="9691801031-7">]</span><span class="p" data-group-id="9691801031-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9691801031-8">[</span><span class="n">Map</span><span class="p" data-group-id="9691801031-9">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9691801031-9">)</span><span class="p">|</span><span class="nf">map_pairs1</span><span class="p" data-group-id="9691801031-10">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="9691801031-10">)</span><span class="p" data-group-id="9691801031-8">]</span><span class="p">.</span></code></pre><p>The first argument is <em>not</em> a problem. It is variable, but it is a variable in
│ │ │ +</span><span class="nf">map_pairs1</span><span class="p" data-group-id="5624662711-5">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5624662711-6">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="5624662711-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5624662711-7">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="5624662711-7">]</span><span class="p" data-group-id="5624662711-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5624662711-8">[</span><span class="n">Map</span><span class="p" data-group-id="5624662711-9">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5624662711-9">)</span><span class="p">|</span><span class="nf">map_pairs1</span><span class="p" data-group-id="5624662711-10">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="5624662711-10">)</span><span class="p" data-group-id="5624662711-8">]</span><span class="p">.</span></code></pre><p>The first argument is <em>not</em> a problem. It is variable, but it is a variable in
│ │ │  all clauses. The problem is the variable in the second argument, <code class="inline">Xs</code>, in the
│ │ │  middle clause. Because the variable can match anything, the compiler is not
│ │ │  allowed to rearrange the clauses, but must generate code that matches them in
│ │ │  the order written.</p><p>If the function is rewritten as follows, the compiler is free to rearrange the
│ │ │ -clauses:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs2</span><span class="p" data-group-id="3589589229-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3589589229-2">[</span><span class="p" data-group-id="3589589229-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="3589589229-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +clauses:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">map_pairs2</span><span class="p" data-group-id="0283110101-1">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0283110101-2">[</span><span class="p" data-group-id="0283110101-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="0283110101-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Ys</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map_pairs2</span><span class="p" data-group-id="3589589229-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3589589229-4">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="3589589229-4">]</span><span class="o">=</span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3589589229-5">[</span><span class="p" data-group-id="3589589229-5">]</span><span class="w"> </span><span class="p" data-group-id="3589589229-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">map_pairs2</span><span class="p" data-group-id="0283110101-3">(</span><span class="p">_</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0283110101-4">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="0283110101-4">]</span><span class="o">=</span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0283110101-5">[</span><span class="p" data-group-id="0283110101-5">]</span><span class="w"> </span><span class="p" data-group-id="0283110101-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Xs</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map_pairs2</span><span class="p" data-group-id="3589589229-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3589589229-7">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="3589589229-7">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3589589229-8">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="3589589229-8">]</span><span class="p" data-group-id="3589589229-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3589589229-9">[</span><span class="n">Map</span><span class="p" data-group-id="3589589229-10">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3589589229-10">)</span><span class="p">|</span><span class="nf">map_pairs2</span><span class="p" data-group-id="3589589229-11">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="3589589229-11">)</span><span class="p" data-group-id="3589589229-9">]</span><span class="p">.</span></code></pre><p>The compiler will generate code similar to this:</p><p><strong>DO NOT (already done by the compiler)</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="3538073906-1">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs0</span><span class="p">,</span><span class="w"> </span><span class="n">Ys0</span><span class="p" data-group-id="3538073906-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">map_pairs2</span><span class="p" data-group-id="0283110101-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0283110101-7">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="0283110101-7">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0283110101-8">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="0283110101-8">]</span><span class="p" data-group-id="0283110101-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0283110101-9">[</span><span class="n">Map</span><span class="p" data-group-id="0283110101-10">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0283110101-10">)</span><span class="p">|</span><span class="nf">map_pairs2</span><span class="p" data-group-id="0283110101-11">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="0283110101-11">)</span><span class="p" data-group-id="0283110101-9">]</span><span class="p">.</span></code></pre><p>The compiler will generate code similar to this:</p><p><strong>DO NOT (already done by the compiler)</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="4501125138-1">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs0</span><span class="p">,</span><span class="w"> </span><span class="n">Ys0</span><span class="p" data-group-id="4501125138-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Xs0</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="3538073906-2">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="3538073906-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="4501125138-2">[</span><span class="n">X</span><span class="p">|</span><span class="n">Xs</span><span class="p" data-group-id="4501125138-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="k">case</span><span class="w"> </span><span class="n">Ys0</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="3538073906-3">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="3538073906-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="p" data-group-id="3538073906-4">[</span><span class="n">Map</span><span class="p" data-group-id="3538073906-5">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3538073906-5">)</span><span class="p">|</span><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="3538073906-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="3538073906-6">)</span><span class="p" data-group-id="3538073906-4">]</span><span class="p">;</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="3538073906-7">[</span><span class="p" data-group-id="3538073906-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="4501125138-3">[</span><span class="n">Y</span><span class="p">|</span><span class="n">Ys</span><span class="p" data-group-id="4501125138-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="p" data-group-id="4501125138-4">[</span><span class="n">Map</span><span class="p" data-group-id="4501125138-5">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4501125138-5">)</span><span class="p">|</span><span class="nf">explicit_map_pairs</span><span class="p" data-group-id="4501125138-6">(</span><span class="n">Map</span><span class="p">,</span><span class="w"> </span><span class="n">Xs</span><span class="p">,</span><span class="w"> </span><span class="n">Ys</span><span class="p" data-group-id="4501125138-6">)</span><span class="p" data-group-id="4501125138-4">]</span><span class="p">;</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="4501125138-7">[</span><span class="p" data-group-id="4501125138-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  		    </span><span class="n">Xs0</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="3538073906-8">[</span><span class="p" data-group-id="3538073906-8">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="4501125138-8">[</span><span class="p" data-group-id="4501125138-8">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Ys0</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>This is slightly faster for probably the most common case that the input lists
│ │ │  are not empty or very short. (Another advantage is that Dialyzer can deduce a
│ │ │  better type for the <code class="inline">Xs</code> variable.)</p><h2 id="function-calls" class="section-heading">
│ │ │    <a href="#function-calls" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/eff_guide_processes.html
│ │ │ @@ -119,45 +119,45 @@
│ │ │    <a href="#creating-an-erlang-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating an Erlang Process</span>
│ │ │  </h2>
│ │ │  <p>An Erlang process is lightweight compared to threads and processes in operating
│ │ │  systems.</p><p>A newly spawned Erlang process uses 327 words of memory. The size can be found
│ │ │ -as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="1804436068-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p">.</span><span class="mi">3</span><span class="p" data-group-id="1804436068-1">]</span><span class="w"> </span><span class="p" data-group-id="1804436068-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="1804436068-2">]</span><span class="w"> </span><span class="p" data-group-id="1804436068-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="1804436068-3">]</span><span class="w"> </span><span class="p" data-group-id="1804436068-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="1804436068-4">]</span><span class="w"> </span><span class="p" data-group-id="1804436068-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1804436068-5">]</span><span class="w"> </span><span class="p" data-group-id="1804436068-6">[</span><span class="ss">jit</span><span class="p" data-group-id="1804436068-6">]</span><span class="w">
│ │ │ +as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="2544467025-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p">.</span><span class="mi">3</span><span class="p" data-group-id="2544467025-1">]</span><span class="w"> </span><span class="p" data-group-id="2544467025-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="2544467025-2">]</span><span class="w"> </span><span class="p" data-group-id="2544467025-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="2544467025-3">]</span><span class="w"> </span><span class="p" data-group-id="2544467025-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="2544467025-4">]</span><span class="w"> </span><span class="p" data-group-id="2544467025-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2544467025-5">]</span><span class="w"> </span><span class="p" data-group-id="2544467025-6">[</span><span class="ss">jit</span><span class="p" data-group-id="2544467025-6">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mf">2.3</span><span class="w"> </span><span class="p" data-group-id="1804436068-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="1804436068-8">(</span><span class="p" data-group-id="1804436068-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="1804436068-7">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1804436068-9">(</span><span class="p" data-group-id="1804436068-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="ss">infinity</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mf">2.3</span><span class="w"> </span><span class="p" data-group-id="2544467025-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="2544467025-8">(</span><span class="p" data-group-id="2544467025-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="2544467025-7">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="2544467025-9">(</span><span class="p" data-group-id="2544467025-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="ss">infinity</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">43.39164016</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="1804436068-10">{</span><span class="p">_</span><span class="p">,</span><span class="n">Bytes</span><span class="p" data-group-id="1804436068-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">process_info</span><span class="p" data-group-id="1804436068-11">(</span><span class="nf">spawn</span><span class="p" data-group-id="1804436068-12">(</span><span class="n">Fun</span><span class="p" data-group-id="1804436068-12">)</span><span class="p">,</span><span class="w"> </span><span class="nb">memory</span><span class="p" data-group-id="1804436068-11">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1804436068-13">{</span><span class="nb">memory</span><span class="p">,</span><span class="mi">2616</span><span class="p" data-group-id="1804436068-13">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="n">Bytes</span><span class="w"> </span><span class="ow">div</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="1804436068-14">(</span><span class="ss">wordsize</span><span class="p" data-group-id="1804436068-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="2544467025-10">{</span><span class="p">_</span><span class="p">,</span><span class="n">Bytes</span><span class="p" data-group-id="2544467025-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">process_info</span><span class="p" data-group-id="2544467025-11">(</span><span class="nf">spawn</span><span class="p" data-group-id="2544467025-12">(</span><span class="n">Fun</span><span class="p" data-group-id="2544467025-12">)</span><span class="p">,</span><span class="w"> </span><span class="nb">memory</span><span class="p" data-group-id="2544467025-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2544467025-13">{</span><span class="nb">memory</span><span class="p">,</span><span class="mi">2616</span><span class="p" data-group-id="2544467025-13">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="n">Bytes</span><span class="w"> </span><span class="ow">div</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="2544467025-14">(</span><span class="ss">wordsize</span><span class="p" data-group-id="2544467025-14">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">327</span></code></pre><p>The size includes 233 words for the heap area (which includes the stack). The
│ │ │  garbage collector increases the heap as needed.</p><p>The main (outer) loop for a process <em>must</em> be tail-recursive. Otherwise, the
│ │ │ -stack grows until the process terminates.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="8873047744-1">(</span><span class="p" data-group-id="8873047744-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +stack grows until the process terminates.</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="0680651178-1">(</span><span class="p" data-group-id="0680651178-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │    </span><span class="k">receive</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="8873047744-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8873047744-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="8873047744-3">(</span><span class="n">Msg</span><span class="p" data-group-id="8873047744-3">)</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="8873047744-4">(</span><span class="p" data-group-id="8873047744-4">)</span><span class="p">;</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="8873047744-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="8873047744-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -          </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="8873047744-6">(</span><span class="n">Msg</span><span class="p" data-group-id="8873047744-6">)</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0680651178-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="0680651178-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="0680651178-3">(</span><span class="n">Msg</span><span class="p" data-group-id="0680651178-3">)</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="0680651178-4">(</span><span class="p" data-group-id="0680651178-4">)</span><span class="p">;</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0680651178-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="0680651178-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +          </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="0680651178-6">(</span><span class="n">Msg</span><span class="p" data-group-id="0680651178-6">)</span><span class="p">,</span><span class="w">
│ │ │            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Reply</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="nf">loop</span><span class="p" data-group-id="8873047744-7">(</span><span class="p" data-group-id="8873047744-7">)</span><span class="w">
│ │ │ +          </span><span class="nf">loop</span><span class="p" data-group-id="0680651178-7">(</span><span class="p" data-group-id="0680651178-7">)</span><span class="w">
│ │ │    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8873047744-8">(</span><span class="s">&quot;Message is processed</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8873047744-9">[</span><span class="p" data-group-id="8873047744-9">]</span><span class="p" data-group-id="8873047744-8">)</span><span class="p">.</span></code></pre><p>The call to <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> will never be executed, but a return address will
│ │ │ +  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0680651178-8">(</span><span class="s">&quot;Message is processed</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0680651178-9">[</span><span class="p" data-group-id="0680651178-9">]</span><span class="p" data-group-id="0680651178-8">)</span><span class="p">.</span></code></pre><p>The call to <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> will never be executed, but a return address will
│ │ │  still be pushed to the stack each time <code class="inline">loop/0</code> is called recursively. The
│ │ │ -correct tail-recursive version of the function looks as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="2768182636-1">(</span><span class="p" data-group-id="2768182636-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +correct tail-recursive version of the function looks as follows:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="6214857317-1">(</span><span class="p" data-group-id="6214857317-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │     </span><span class="k">receive</span><span class="w">
│ │ │ -      </span><span class="p" data-group-id="2768182636-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="2768182636-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="2768182636-3">(</span><span class="n">Msg</span><span class="p" data-group-id="2768182636-3">)</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="2768182636-4">(</span><span class="p" data-group-id="2768182636-4">)</span><span class="p">;</span><span class="w">
│ │ │ -      </span><span class="p" data-group-id="2768182636-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="2768182636-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -         </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="2768182636-6">(</span><span class="n">Msg</span><span class="p" data-group-id="2768182636-6">)</span><span class="p">,</span><span class="w">
│ │ │ +      </span><span class="p" data-group-id="6214857317-2">{</span><span class="ss">sys</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6214857317-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +         </span><span class="nf">handle_sys_msg</span><span class="p" data-group-id="6214857317-3">(</span><span class="n">Msg</span><span class="p" data-group-id="6214857317-3">)</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="6214857317-4">(</span><span class="p" data-group-id="6214857317-4">)</span><span class="p">;</span><span class="w">
│ │ │ +      </span><span class="p" data-group-id="6214857317-5">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="6214857317-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +         </span><span class="n">Reply</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="6214857317-6">(</span><span class="n">Msg</span><span class="p" data-group-id="6214857317-6">)</span><span class="p">,</span><span class="w">
│ │ │           </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Reply</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="nf">loop</span><span class="p" data-group-id="2768182636-7">(</span><span class="p" data-group-id="2768182636-7">)</span><span class="w">
│ │ │ +         </span><span class="nf">loop</span><span class="p" data-group-id="6214857317-7">(</span><span class="p" data-group-id="6214857317-7">)</span><span class="w">
│ │ │   </span><span class="k">end</span><span class="p">.</span></code></pre><h3 id="initial-heap-size" class="section-heading">
│ │ │    <a href="#initial-heap-size" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Initial Heap Size</span>
│ │ │  </h3>
│ │ │  <p>The default initial heap size of 233 words is quite conservative to support
│ │ │ @@ -189,30 +189,30 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Receiving messages</span>
│ │ │  </h2>
│ │ │  <p>The cost of receiving messages depends on how complicated the <code class="inline">receive</code>
│ │ │  expression is. A simple expression that matches any message is very cheap
│ │ │  because it retrieves the first message in the message queue:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="4987051592-1">(</span><span class="n">Message</span><span class="p" data-group-id="4987051592-1">)</span><span class="w">
│ │ │ +    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="3259475884-1">(</span><span class="n">Message</span><span class="p" data-group-id="3259475884-1">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>However, this is not always convenient: we can receive a message that we do not
│ │ │  know how to handle at this point, so it is common to only match the messages we
│ │ │  expect:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5137758493-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5137758493-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="5137758493-2">(</span><span class="n">Message</span><span class="p" data-group-id="5137758493-2">)</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4522054085-1">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4522054085-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="4522054085-2">(</span><span class="n">Message</span><span class="p" data-group-id="4522054085-2">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>While this is convenient it means that the entire message queue must be searched
│ │ │  until it finds a matching message. This is very expensive for processes with
│ │ │  long message queues, so there is an optimization for the common case of
│ │ │ -sending a request and waiting for a response shortly after:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="2403567697-1">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="2403567697-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2403567697-2">{</span><span class="nf">self</span><span class="p" data-group-id="2403567697-3">(</span><span class="p" data-group-id="2403567697-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="2403567697-2">}</span><span class="p">,</span><span class="w">
│ │ │ +sending a request and waiting for a response shortly after:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="5070129997-1">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="5070129997-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="5070129997-2">{</span><span class="nf">self</span><span class="p" data-group-id="5070129997-3">(</span><span class="p" data-group-id="5070129997-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="5070129997-2">}</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2403567697-4">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="2403567697-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="2403567697-5">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2403567697-6">[</span><span class="ss">flush</span><span class="p" data-group-id="2403567697-6">]</span><span class="p" data-group-id="2403567697-5">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="nf">handle_reply</span><span class="p" data-group-id="2403567697-7">(</span><span class="n">Reply</span><span class="p" data-group-id="2403567697-7">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2403567697-8">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="2403567697-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nf">handle_error</span><span class="p" data-group-id="2403567697-9">(</span><span class="n">Reason</span><span class="p" data-group-id="2403567697-9">)</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5070129997-4">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="5070129997-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="5070129997-5">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5070129997-6">[</span><span class="ss">flush</span><span class="p" data-group-id="5070129997-6">]</span><span class="p" data-group-id="5070129997-5">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="nf">handle_reply</span><span class="p" data-group-id="5070129997-7">(</span><span class="n">Reply</span><span class="p" data-group-id="5070129997-7">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5070129997-8">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5070129997-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">handle_error</span><span class="p" data-group-id="5070129997-9">(</span><span class="n">Reason</span><span class="p" data-group-id="5070129997-9">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p>Since the compiler knows that the reference created by
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#monitor/2"><code class="inline">monitor/2</code></a> cannot exist before the call (since it is a globally
│ │ │  unique identifier), and that the <code class="inline">receive</code> only matches messages that contain
│ │ │  said reference, it will tell the emulator to search only the messages that
│ │ │  arrived after the call to <a href="../../erts-15.2.7.8/doc/html/erlang.html#monitor/2"><code class="inline">monitor/2</code></a>.</p><p>The above is a simple example where one is but guaranteed that the optimization
│ │ │  will take, but what about more complicated code?</p><p><a href="" id="recv_opt_info"></a></p><h3 id="option-recv_opt_info" class="section-heading">
│ │ │    <a href="#option-recv_opt_info" class="hover-link">
│ │ │ @@ -228,101 +228,101 @@
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">200</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">NOT</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">do</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">suitable</span><span class="w"> </span><span class="ss">reference</span><span class="w">
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">206</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">used</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">mark</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">message</span><span class="w"> </span><span class="ss">queue</span><span class="w"> </span><span class="ss">position</span><span class="w">
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">208</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">created</span><span class="w"> </span><span class="ss">by</span><span class="w"> </span><span class="nb">monitor</span><span class="p">/</span><span class="mi">2</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">206</span><span class="w">
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">219</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">INFO</span><span class="p">:</span><span class="w"> </span><span class="ss">passing</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">created</span><span class="w"> </span><span class="ss">by</span><span class="w"> </span><span class="ss">make_ref</span><span class="p">/</span><span class="mi">0</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">218</span><span class="w">
│ │ │  </span><span class="ss">efficiency_guide</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">222</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="n">OPTIMIZED</span><span class="p">:</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">clauses</span><span class="w"> </span><span class="ss">match</span><span class="w"> </span><span class="ss">reference</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">function</span><span class="w"> </span><span class="ss">parameter</span><span class="w"> </span><span class="mi">1</span></code></pre><p>To make it clearer exactly what code the warnings refer to, the warnings in the
│ │ │  following examples are inserted as comments after the clause they refer to, for
│ │ │  example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% DO</span><span class="w">
│ │ │ -</span><span class="nf">simple_receive</span><span class="p" data-group-id="4338437643-1">(</span><span class="p" data-group-id="4338437643-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">simple_receive</span><span class="p" data-group-id="7151976231-1">(</span><span class="p" data-group-id="7151976231-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="c1">%% efficiency_guide.erl:194: Warning: INFO: not a selective receive, this is always fast</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="4338437643-2">(</span><span class="n">Message</span><span class="p" data-group-id="4338437643-2">)</span><span class="w">
│ │ │ +    </span><span class="n">Message</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7151976231-2">(</span><span class="n">Message</span><span class="p" data-group-id="7151976231-2">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% DO NOT, unless Tag is known to be a suitable reference: see</span><span class="w">
│ │ │  </span><span class="c1">%% cross_function_receive/0 further down.</span><span class="w">
│ │ │ -</span><span class="nf">selective_receive</span><span class="p" data-group-id="4338437643-3">(</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4338437643-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">selective_receive</span><span class="p" data-group-id="7151976231-3">(</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7151976231-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="c1">%% efficiency_guide.erl:200: Warning: NOT OPTIMIZED: all clauses do not match a suitable reference</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4338437643-4">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4338437643-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="4338437643-5">(</span><span class="n">Message</span><span class="p" data-group-id="4338437643-5">)</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7151976231-4">{</span><span class="n">Tag</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7151976231-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7151976231-5">(</span><span class="n">Message</span><span class="p" data-group-id="7151976231-5">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% DO</span><span class="w">
│ │ │ -</span><span class="nf">optimized_receive</span><span class="p" data-group-id="4338437643-6">(</span><span class="n">Process</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="4338437643-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">optimized_receive</span><span class="p" data-group-id="7151976231-6">(</span><span class="n">Process</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="7151976231-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="c1">%% efficiency_guide.erl:206: Warning: OPTIMIZED: reference used to mark a message queue position</span><span class="w">
│ │ │ -    </span><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="4338437643-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="4338437643-7">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4338437643-8">{</span><span class="nf">self</span><span class="p" data-group-id="4338437643-9">(</span><span class="p" data-group-id="4338437643-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="4338437643-8">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">MRef</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">monitor</span><span class="p" data-group-id="7151976231-7">(</span><span class="ss">process</span><span class="p">,</span><span class="w"> </span><span class="n">Process</span><span class="p" data-group-id="7151976231-7">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Process</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7151976231-8">{</span><span class="nf">self</span><span class="p" data-group-id="7151976231-9">(</span><span class="p" data-group-id="7151976231-9">)</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="7151976231-8">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% efficiency_guide.erl:208: Warning: OPTIMIZED: matches reference created by monitor/2 at efficiency_guide.erl:206</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4338437643-10">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="4338437643-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="4338437643-11">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4338437643-12">[</span><span class="ss">flush</span><span class="p" data-group-id="4338437643-12">]</span><span class="p" data-group-id="4338437643-11">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="nf">handle_reply</span><span class="p" data-group-id="4338437643-13">(</span><span class="n">Reply</span><span class="p" data-group-id="4338437643-13">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4338437643-14">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="4338437643-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">handle_error</span><span class="p" data-group-id="4338437643-15">(</span><span class="n">Reason</span><span class="p" data-group-id="4338437643-15">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7151976231-10">{</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="p" data-group-id="7151976231-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">demonitor</span><span class="p" data-group-id="7151976231-11">(</span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7151976231-12">[</span><span class="ss">flush</span><span class="p" data-group-id="7151976231-12">]</span><span class="p" data-group-id="7151976231-11">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="nf">handle_reply</span><span class="p" data-group-id="7151976231-13">(</span><span class="n">Reply</span><span class="p" data-group-id="7151976231-13">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7151976231-14">{</span><span class="ss">&#39;DOWN&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">MRef</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7151976231-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">handle_error</span><span class="p" data-group-id="7151976231-15">(</span><span class="n">Reason</span><span class="p" data-group-id="7151976231-15">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% DO</span><span class="w">
│ │ │ -</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="4338437643-16">(</span><span class="p" data-group-id="4338437643-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="7151976231-16">(</span><span class="p" data-group-id="7151976231-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% efficiency_guide.erl:218: Warning: OPTIMIZED: reference used to mark a message queue position</span><span class="w">
│ │ │ -    </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="4338437643-17">(</span><span class="p" data-group-id="4338437643-17">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Ref</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_ref</span><span class="p" data-group-id="7151976231-17">(</span><span class="p" data-group-id="7151976231-17">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="c1">%% efficiency_guide.erl:219: Warning: INFO: passing reference created by make_ref/0 at efficiency_guide.erl:218</span><span class="w">
│ │ │ -    </span><span class="nf">cross_function_receive</span><span class="p" data-group-id="4338437643-18">(</span><span class="n">Ref</span><span class="p" data-group-id="4338437643-18">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">cross_function_receive</span><span class="p" data-group-id="7151976231-18">(</span><span class="n">Ref</span><span class="p" data-group-id="7151976231-18">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="4338437643-19">(</span><span class="n">Ref</span><span class="p" data-group-id="4338437643-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">cross_function_receive</span><span class="p" data-group-id="7151976231-19">(</span><span class="n">Ref</span><span class="p" data-group-id="7151976231-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% efficiency_guide.erl:222: Warning: OPTIMIZED: all clauses match reference in function parameter 1</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4338437643-20">{</span><span class="n">Ref</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4338437643-20">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="4338437643-21">(</span><span class="n">Message</span><span class="p" data-group-id="4338437643-21">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7151976231-20">{</span><span class="n">Ref</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7151976231-20">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_msg</span><span class="p" data-group-id="7151976231-21">(</span><span class="n">Message</span><span class="p" data-group-id="7151976231-21">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="literal-pool" class="section-heading">
│ │ │    <a href="#literal-pool" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Literal Pool</span>
│ │ │  </h2>
│ │ │  <p>Constant Erlang terms (hereafter called <em>literals</em>) are kept in <em>literal pools</em>;
│ │ │  each loaded module has its own pool. The following function does not build the
│ │ │  tuple every time it is called (only to have it discarded the next time the
│ │ │  garbage collector was run), but the tuple is located in the module's literal
│ │ │ -pool:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">days_in_month</span><span class="p" data-group-id="5628546213-1">(</span><span class="n">M</span><span class="p" data-group-id="5628546213-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="5628546213-2">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5628546213-3">{</span><span class="mi">31</span><span class="p">,</span><span class="mi">28</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p" data-group-id="5628546213-3">}</span><span class="p" data-group-id="5628546213-2">)</span><span class="p">.</span></code></pre><p>If a literal, or a term that contains a literal, is inserted into an Ets table,
│ │ │ +pool:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">days_in_month</span><span class="p" data-group-id="9582453241-1">(</span><span class="n">M</span><span class="p" data-group-id="9582453241-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="9582453241-2">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9582453241-3">{</span><span class="mi">31</span><span class="p">,</span><span class="mi">28</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p">,</span><span class="mi">30</span><span class="p">,</span><span class="mi">31</span><span class="p" data-group-id="9582453241-3">}</span><span class="p" data-group-id="9582453241-2">)</span><span class="p">.</span></code></pre><p>If a literal, or a term that contains a literal, is inserted into an Ets table,
│ │ │  it is <em>copied</em>. The reason is that the module containing the literal can be
│ │ │  unloaded in the future.</p><p>When a literal is sent to another process, it is <em>not</em> copied. When a module
│ │ │  holding a literal is unloaded, the literal will be copied to the heap of all
│ │ │  processes that hold references to that literal.</p><p>There also exists a global literal pool that is managed by the
│ │ │  <a href="../../erts-15.2.7.8/doc/html/persistent_term.html"><code class="inline">persistent_term</code></a> module.</p><p>By default, 1 GB of virtual address space is reserved for all literal pools (in
│ │ │  BEAM code and persistent terms). The amount of virtual address space reserved
│ │ │  for literals can be changed by using the
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erts_alloc.html#MIscs"><code class="inline">+MIscs option</code></a> when starting the emulator.</p><p>Here is an example how the reserved virtual address space for literals can be
│ │ │  raised to 2 GB (2048 MB):</p><pre><code class="text">erl +MIscs 2048</code></pre><h2 id="loss-of-sharing" class="section-heading">
│ │ │    <a href="#loss-of-sharing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Loss of Sharing</span>
│ │ │  </h2>
│ │ │ -<p>An Erlang term can have shared subterms. Here is a simple example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1460255188-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="1460255188-1">}</span></code></pre><p>Shared subterms are <em>not</em> preserved in the following cases:</p><ul><li>When a term is sent to another process</li><li>When a term is passed as the initial process arguments in the <code class="inline">spawn</code> call</li><li>When a term is stored in an Ets table</li></ul><p>That is an optimization. Most applications do not send messages with shared
│ │ │ -subterms.</p><p>The following example shows how a shared subterm can be created:</p><pre><code class="makeup erlang" translate="no"><span class="nf">kilo_byte</span><span class="p" data-group-id="9671612272-1">(</span><span class="p" data-group-id="9671612272-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="9671612272-2">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9671612272-3">[</span><span class="mi">42</span><span class="p" data-group-id="9671612272-3">]</span><span class="p" data-group-id="9671612272-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>An Erlang term can have shared subterms. Here is a simple example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9305953172-1">{</span><span class="n">SubTerm</span><span class="p">,</span><span class="w"> </span><span class="n">SubTerm</span><span class="p" data-group-id="9305953172-1">}</span></code></pre><p>Shared subterms are <em>not</em> preserved in the following cases:</p><ul><li>When a term is sent to another process</li><li>When a term is passed as the initial process arguments in the <code class="inline">spawn</code> call</li><li>When a term is stored in an Ets table</li></ul><p>That is an optimization. Most applications do not send messages with shared
│ │ │ +subterms.</p><p>The following example shows how a shared subterm can be created:</p><pre><code class="makeup erlang" translate="no"><span class="nf">kilo_byte</span><span class="p" data-group-id="6934723700-1">(</span><span class="p" data-group-id="6934723700-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="6934723700-2">(</span><span class="mi">10</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6934723700-3">[</span><span class="mi">42</span><span class="p" data-group-id="6934723700-3">]</span><span class="p" data-group-id="6934723700-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">kilo_byte</span><span class="p" data-group-id="9671612272-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9671612272-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">kilo_byte</span><span class="p" data-group-id="6934723700-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6934723700-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Acc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">kilo_byte</span><span class="p" data-group-id="9671612272-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="9671612272-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="9671612272-6">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9671612272-7">[</span><span class="n">Acc</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="9671612272-7">]</span><span class="p" data-group-id="9671612272-6">)</span><span class="p">.</span></code></pre><p><code class="inline">kilo_byte/1</code> creates a deep list. If <a href="../../erts-15.2.7.8/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a>
│ │ │ +</span><span class="nf">kilo_byte</span><span class="p" data-group-id="6934723700-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="6934723700-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">kilo_byte</span><span class="p" data-group-id="6934723700-6">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6934723700-7">[</span><span class="n">Acc</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="6934723700-7">]</span><span class="p" data-group-id="6934723700-6">)</span><span class="p">.</span></code></pre><p><code class="inline">kilo_byte/1</code> creates a deep list. If <a href="../../erts-15.2.7.8/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a>
│ │ │  is called, the deep list can be converted to a binary of 1024 bytes:</p><pre><code class="text">1&gt; byte_size(list_to_binary(efficiency_guide:kilo_byte())).
│ │ │  1024</code></pre><p>Using the <code class="inline">erts_debug:size/1</code> BIF, it can be seen that the deep list only
│ │ │ -requires 22 words of heap space:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="7537997330-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="7537997330-2">(</span><span class="p" data-group-id="7537997330-2">)</span><span class="p" data-group-id="7537997330-1">)</span><span class="p">.</span><span class="w">
│ │ │ +requires 22 words of heap space:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="1815466344-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="1815466344-2">(</span><span class="p" data-group-id="1815466344-2">)</span><span class="p" data-group-id="1815466344-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">22</span></code></pre><p>Using the <code class="inline">erts_debug:flat_size/1</code> BIF, the size of the deep list can be
│ │ │  calculated if sharing is ignored. It becomes the size of the list when it has
│ │ │ -been sent to another process or stored in an Ets table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="8210019633-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="8210019633-2">(</span><span class="p" data-group-id="8210019633-2">)</span><span class="p" data-group-id="8210019633-1">)</span><span class="p">.</span><span class="w">
│ │ │ +been sent to another process or stored in an Ets table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="6399540949-1">(</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="6399540949-2">(</span><span class="p" data-group-id="6399540949-2">)</span><span class="p" data-group-id="6399540949-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4094</span></code></pre><p>It can be verified that sharing will be lost if the data is inserted into an Ets
│ │ │ -table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2788710003-1">(</span><span class="ss">tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2788710003-2">[</span><span class="p" data-group-id="2788710003-2">]</span><span class="p" data-group-id="2788710003-1">)</span><span class="p">.</span><span class="w">
│ │ │ +table:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="1448406569-1">(</span><span class="ss">tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1448406569-2">[</span><span class="p" data-group-id="1448406569-2">]</span><span class="p" data-group-id="1448406569-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Ref</span><span class="o">&lt;</span><span class="mf">0.1662103692</span><span class="p">.</span><span class="mf">2407923716.214181</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">ets</span><span class="p">:</span><span class="nf">insert</span><span class="p" data-group-id="2788710003-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2788710003-4">{</span><span class="ss">key</span><span class="p">,</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="2788710003-5">(</span><span class="p" data-group-id="2788710003-5">)</span><span class="p" data-group-id="2788710003-4">}</span><span class="p" data-group-id="2788710003-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">ets</span><span class="p">:</span><span class="nf">insert</span><span class="p" data-group-id="1448406569-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1448406569-4">{</span><span class="ss">key</span><span class="p">,</span><span class="nc">efficiency_guide</span><span class="p">:</span><span class="nf">kilo_byte</span><span class="p" data-group-id="1448406569-5">(</span><span class="p" data-group-id="1448406569-5">)</span><span class="p" data-group-id="1448406569-4">}</span><span class="p" data-group-id="1448406569-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="2788710003-6">(</span><span class="nf">element</span><span class="p" data-group-id="2788710003-7">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="2788710003-8">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="2788710003-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="2788710003-9">)</span><span class="p" data-group-id="2788710003-8">)</span><span class="p" data-group-id="2788710003-7">)</span><span class="p" data-group-id="2788710003-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">size</span><span class="p" data-group-id="1448406569-6">(</span><span class="nf">element</span><span class="p" data-group-id="1448406569-7">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="1448406569-8">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="1448406569-9">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="1448406569-9">)</span><span class="p" data-group-id="1448406569-8">)</span><span class="p" data-group-id="1448406569-7">)</span><span class="p" data-group-id="1448406569-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4094</span><span class="w">
│ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="2788710003-10">(</span><span class="nf">element</span><span class="p" data-group-id="2788710003-11">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="2788710003-12">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="2788710003-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="2788710003-13">)</span><span class="p" data-group-id="2788710003-12">)</span><span class="p" data-group-id="2788710003-11">)</span><span class="p" data-group-id="2788710003-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nc">erts_debug</span><span class="p">:</span><span class="nf">flat_size</span><span class="p" data-group-id="1448406569-10">(</span><span class="nf">element</span><span class="p" data-group-id="1448406569-11">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="nf">hd</span><span class="p" data-group-id="1448406569-12">(</span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="1448406569-13">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="ss">key</span><span class="p" data-group-id="1448406569-13">)</span><span class="p" data-group-id="1448406569-12">)</span><span class="p" data-group-id="1448406569-11">)</span><span class="p" data-group-id="1448406569-10">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4094</span></code></pre><p>When the data has passed through an Ets table, <code class="inline">erts_debug:size/1</code> and
│ │ │  <code class="inline">erts_debug:flat_size/1</code> return the same value. Sharing has been lost.</p><p>It is possible to build an <em>experimental</em> variant of the runtime system that
│ │ │  will preserve sharing when copying terms by giving the
│ │ │  <code class="inline">--enable-sharing-preserving</code> option to the <code class="inline">configure</code> script.</p><h2 id="smp-run-time-system" class="section-heading">
│ │ │    <a href="#smp-run-time-system" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/erl_interface.html
│ │ │ @@ -120,119 +120,119 @@
│ │ │  to read the port example in <a href="c_port.html">Ports</a> before reading this section.</p><h2 id="erlang-program" class="section-heading">
│ │ │    <a href="#erlang-program" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Erlang Program</span>
│ │ │  </h2>
│ │ │  <p>The following example shows an Erlang program communicating with a C program
│ │ │ -over a plain port with home made encoding:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1754495431-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="1754495431-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1754495431-2">(</span><span class="p" data-group-id="1754495431-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1754495431-3">]</span><span class="p" data-group-id="1754495431-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1754495431-4">(</span><span class="p" data-group-id="1754495431-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1754495431-5">]</span><span class="p" data-group-id="1754495431-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="1754495431-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1754495431-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1754495431-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1754495431-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="1754495431-8">]</span><span class="p" data-group-id="1754495431-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="1754495431-9">(</span><span class="p" data-group-id="1754495431-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +over a plain port with home made encoding:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9057943717-1">(</span><span class="ss">complex1</span><span class="p" data-group-id="9057943717-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9057943717-2">(</span><span class="p" data-group-id="9057943717-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9057943717-3">]</span><span class="p" data-group-id="9057943717-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9057943717-4">(</span><span class="p" data-group-id="9057943717-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9057943717-5">]</span><span class="p" data-group-id="9057943717-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="9057943717-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9057943717-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="9057943717-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9057943717-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="9057943717-8">]</span><span class="p" data-group-id="9057943717-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="9057943717-9">(</span><span class="p" data-group-id="9057943717-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="1754495431-10">(</span><span class="n">X</span><span class="p" data-group-id="1754495431-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="1754495431-11">(</span><span class="p" data-group-id="1754495431-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1754495431-12">}</span><span class="p" data-group-id="1754495431-11">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="1754495431-13">(</span><span class="n">Y</span><span class="p" data-group-id="1754495431-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="1754495431-14">(</span><span class="p" data-group-id="1754495431-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1754495431-15">}</span><span class="p" data-group-id="1754495431-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="9057943717-10">(</span><span class="n">X</span><span class="p" data-group-id="9057943717-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="9057943717-11">(</span><span class="p" data-group-id="9057943717-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9057943717-12">}</span><span class="p" data-group-id="9057943717-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="9057943717-13">(</span><span class="n">Y</span><span class="p" data-group-id="9057943717-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="9057943717-14">(</span><span class="p" data-group-id="9057943717-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9057943717-15">}</span><span class="p" data-group-id="9057943717-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="1754495431-16">(</span><span class="n">Msg</span><span class="p" data-group-id="1754495431-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1754495431-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1754495431-18">(</span><span class="p" data-group-id="1754495431-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1754495431-17">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="9057943717-16">(</span><span class="n">Msg</span><span class="p" data-group-id="9057943717-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9057943717-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9057943717-18">(</span><span class="p" data-group-id="9057943717-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9057943717-17">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="1754495431-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1754495431-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="9057943717-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="9057943717-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1754495431-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1754495431-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="1754495431-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1754495431-22">(</span><span class="p" data-group-id="1754495431-22">)</span><span class="p" data-group-id="1754495431-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="1754495431-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1754495431-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="1754495431-24">(</span><span class="p" data-group-id="1754495431-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="1754495431-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1754495431-26">[</span><span class="p" data-group-id="1754495431-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1754495431-27">}</span><span class="p" data-group-id="1754495431-26">]</span><span class="p" data-group-id="1754495431-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="1754495431-28">(</span><span class="n">Port</span><span class="p" data-group-id="1754495431-28">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="9057943717-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="9057943717-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="9057943717-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="9057943717-22">(</span><span class="p" data-group-id="9057943717-22">)</span><span class="p" data-group-id="9057943717-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="9057943717-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9057943717-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="9057943717-24">(</span><span class="p" data-group-id="9057943717-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="9057943717-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9057943717-26">[</span><span class="p" data-group-id="9057943717-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9057943717-27">}</span><span class="p" data-group-id="9057943717-26">]</span><span class="p" data-group-id="9057943717-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="9057943717-28">(</span><span class="n">Port</span><span class="p" data-group-id="9057943717-28">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="1754495431-29">(</span><span class="n">Port</span><span class="p" data-group-id="1754495431-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="9057943717-29">(</span><span class="n">Port</span><span class="p" data-group-id="9057943717-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="1754495431-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1754495431-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1754495431-31">{</span><span class="nf">self</span><span class="p" data-group-id="1754495431-32">(</span><span class="p" data-group-id="1754495431-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1754495431-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="1754495431-34">(</span><span class="n">Msg</span><span class="p" data-group-id="1754495431-34">)</span><span class="p" data-group-id="1754495431-33">}</span><span class="p" data-group-id="1754495431-31">}</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="9057943717-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="9057943717-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9057943717-31">{</span><span class="nf">self</span><span class="p" data-group-id="9057943717-32">(</span><span class="p" data-group-id="9057943717-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9057943717-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="9057943717-34">(</span><span class="n">Msg</span><span class="p" data-group-id="9057943717-34">)</span><span class="p" data-group-id="9057943717-33">}</span><span class="p" data-group-id="9057943717-31">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="1754495431-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1754495431-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1754495431-36">}</span><span class="p" data-group-id="1754495431-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1754495431-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="1754495431-38">(</span><span class="n">Data</span><span class="p" data-group-id="1754495431-38">)</span><span class="p" data-group-id="1754495431-37">}</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="9057943717-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9057943717-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9057943717-36">}</span><span class="p" data-group-id="9057943717-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9057943717-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="9057943717-38">(</span><span class="n">Data</span><span class="p" data-group-id="9057943717-38">)</span><span class="p" data-group-id="9057943717-37">}</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="1754495431-39">(</span><span class="n">Port</span><span class="p" data-group-id="1754495431-39">)</span><span class="p">;</span><span class="w">
│ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="9057943717-39">(</span><span class="n">Port</span><span class="p" data-group-id="9057943717-39">)</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1754495431-40">{</span><span class="nf">self</span><span class="p" data-group-id="1754495431-41">(</span><span class="p" data-group-id="1754495431-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="1754495431-40">}</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9057943717-40">{</span><span class="nf">self</span><span class="p" data-group-id="9057943717-41">(</span><span class="p" data-group-id="9057943717-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="9057943717-40">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="1754495431-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="1754495431-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="1754495431-43">(</span><span class="ss">normal</span><span class="p" data-group-id="1754495431-43">)</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="9057943717-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="9057943717-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="9057943717-43">(</span><span class="ss">normal</span><span class="p" data-group-id="9057943717-43">)</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="1754495431-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1754495431-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="1754495431-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="1754495431-45">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="9057943717-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9057943717-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="9057943717-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="9057943717-45">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="1754495431-46">(</span><span class="p" data-group-id="1754495431-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1754495431-47">}</span><span class="p" data-group-id="1754495431-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1754495431-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1754495431-48">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">encode</span><span class="p" data-group-id="1754495431-49">(</span><span class="p" data-group-id="1754495431-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1754495431-50">}</span><span class="p" data-group-id="1754495431-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1754495431-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1754495431-51">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="9057943717-46">(</span><span class="p" data-group-id="9057943717-47">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9057943717-47">}</span><span class="p" data-group-id="9057943717-46">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9057943717-48">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9057943717-48">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">encode</span><span class="p" data-group-id="9057943717-49">(</span><span class="p" data-group-id="9057943717-50">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9057943717-50">}</span><span class="p" data-group-id="9057943717-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9057943717-51">[</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9057943717-51">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">decode</span><span class="p" data-group-id="1754495431-52">(</span><span class="p" data-group-id="1754495431-53">[</span><span class="n">Int</span><span class="p" data-group-id="1754495431-53">]</span><span class="p" data-group-id="1754495431-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>There are two differences when using Erl_Interface on the C side compared to the
│ │ │ +</span><span class="nf">decode</span><span class="p" data-group-id="9057943717-52">(</span><span class="p" data-group-id="9057943717-53">[</span><span class="n">Int</span><span class="p" data-group-id="9057943717-53">]</span><span class="p" data-group-id="9057943717-52">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span></code></pre><p>There are two differences when using Erl_Interface on the C side compared to the
│ │ │  example in <a href="c_port.html">Ports</a>, using only the plain port:</p><ul><li>As Erl_Interface operates on the Erlang external term format, the port must be
│ │ │  set to use binaries.</li><li>Instead of inventing an encoding/decoding scheme, the
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#term_to_binary/1"><code class="inline">term_to_binary/1</code></a> and
│ │ │ -<a href="../../erts-15.2.7.8/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a> BIFs are to be used.</li></ul><p>That is:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="8436380365-1">(</span><span class="p" data-group-id="8436380365-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="8436380365-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8436380365-3">[</span><span class="p" data-group-id="8436380365-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8436380365-4">}</span><span class="p" data-group-id="8436380365-3">]</span><span class="p" data-group-id="8436380365-1">)</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="9127517582-1">(</span><span class="p" data-group-id="9127517582-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="9127517582-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9127517582-3">[</span><span class="p" data-group-id="9127517582-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9127517582-4">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="9127517582-3">]</span><span class="p" data-group-id="9127517582-1">)</span></code></pre><p>And:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8662080675-1">{</span><span class="nf">self</span><span class="p" data-group-id="8662080675-2">(</span><span class="p" data-group-id="8662080675-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8662080675-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="8662080675-4">(</span><span class="n">Msg</span><span class="p" data-group-id="8662080675-4">)</span><span class="p" data-group-id="8662080675-3">}</span><span class="p" data-group-id="8662080675-1">}</span><span class="p">,</span><span class="w">
│ │ │ +<a href="../../erts-15.2.7.8/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a> BIFs are to be used.</li></ul><p>That is:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="3549037303-1">(</span><span class="p" data-group-id="3549037303-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="3549037303-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3549037303-3">[</span><span class="p" data-group-id="3549037303-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3549037303-4">}</span><span class="p" data-group-id="3549037303-3">]</span><span class="p" data-group-id="3549037303-1">)</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open_port</span><span class="p" data-group-id="2405247906-1">(</span><span class="p" data-group-id="2405247906-2">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="2405247906-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2405247906-3">[</span><span class="p" data-group-id="2405247906-4">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2405247906-4">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="2405247906-3">]</span><span class="p" data-group-id="2405247906-1">)</span></code></pre><p>And:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4164828494-1">{</span><span class="nf">self</span><span class="p" data-group-id="4164828494-2">(</span><span class="p" data-group-id="4164828494-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4164828494-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">encode</span><span class="p" data-group-id="4164828494-4">(</span><span class="n">Msg</span><span class="p" data-group-id="4164828494-4">)</span><span class="p" data-group-id="4164828494-3">}</span><span class="p" data-group-id="4164828494-1">}</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8662080675-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8662080675-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8662080675-6">}</span><span class="p" data-group-id="8662080675-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8662080675-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="8662080675-8">(</span><span class="n">Data</span><span class="p" data-group-id="8662080675-8">)</span><span class="p" data-group-id="8662080675-7">}</span><span class="w">
│ │ │ -</span><span class="k">end</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3916317342-1">{</span><span class="nf">self</span><span class="p" data-group-id="3916317342-2">(</span><span class="p" data-group-id="3916317342-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3916317342-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="3916317342-4">(</span><span class="n">Msg</span><span class="p" data-group-id="3916317342-4">)</span><span class="p" data-group-id="3916317342-3">}</span><span class="p" data-group-id="3916317342-1">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4164828494-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4164828494-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4164828494-6">}</span><span class="p" data-group-id="4164828494-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4164828494-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">decode</span><span class="p" data-group-id="4164828494-8">(</span><span class="n">Data</span><span class="p" data-group-id="4164828494-8">)</span><span class="p" data-group-id="4164828494-7">}</span><span class="w">
│ │ │ +</span><span class="k">end</span></code></pre><p>is replaced with:</p><pre><code class="makeup erlang" translate="no"><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7962445983-1">{</span><span class="nf">self</span><span class="p" data-group-id="7962445983-2">(</span><span class="p" data-group-id="7962445983-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7962445983-3">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="7962445983-4">(</span><span class="n">Msg</span><span class="p" data-group-id="7962445983-4">)</span><span class="p" data-group-id="7962445983-3">}</span><span class="p" data-group-id="7962445983-1">}</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="k">receive</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="3916317342-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3916317342-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3916317342-6">}</span><span class="p" data-group-id="3916317342-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3916317342-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="3916317342-8">(</span><span class="n">Data</span><span class="p" data-group-id="3916317342-8">)</span><span class="p" data-group-id="3916317342-7">}</span><span class="w">
│ │ │ -</span><span class="k">end</span></code></pre><p>The resulting Erlang program is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1243359003-1">(</span><span class="ss">complex2</span><span class="p" data-group-id="1243359003-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1243359003-2">(</span><span class="p" data-group-id="1243359003-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1243359003-3">]</span><span class="p" data-group-id="1243359003-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1243359003-4">(</span><span class="p" data-group-id="1243359003-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1243359003-5">]</span><span class="p" data-group-id="1243359003-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="1243359003-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1243359003-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1243359003-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1243359003-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="1243359003-8">]</span><span class="p" data-group-id="1243359003-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="1243359003-9">(</span><span class="p" data-group-id="1243359003-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7962445983-5">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7962445983-6">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7962445983-6">}</span><span class="p" data-group-id="7962445983-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7962445983-7">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="7962445983-8">(</span><span class="n">Data</span><span class="p" data-group-id="7962445983-8">)</span><span class="p" data-group-id="7962445983-7">}</span><span class="w">
│ │ │ +</span><span class="k">end</span></code></pre><p>The resulting Erlang program is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3975535263-1">(</span><span class="ss">complex2</span><span class="p" data-group-id="3975535263-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3975535263-2">(</span><span class="p" data-group-id="3975535263-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3975535263-3">]</span><span class="p" data-group-id="3975535263-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3975535263-4">(</span><span class="p" data-group-id="3975535263-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3975535263-5">]</span><span class="p" data-group-id="3975535263-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="3975535263-6">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="3975535263-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="3975535263-7">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3975535263-8">[</span><span class="n">ExtPrg</span><span class="p" data-group-id="3975535263-8">]</span><span class="p" data-group-id="3975535263-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="3975535263-9">(</span><span class="p" data-group-id="3975535263-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">stop</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="1243359003-10">(</span><span class="n">X</span><span class="p" data-group-id="1243359003-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="1243359003-11">(</span><span class="p" data-group-id="1243359003-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1243359003-12">}</span><span class="p" data-group-id="1243359003-11">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="1243359003-13">(</span><span class="n">Y</span><span class="p" data-group-id="1243359003-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">call_port</span><span class="p" data-group-id="1243359003-14">(</span><span class="p" data-group-id="1243359003-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1243359003-15">}</span><span class="p" data-group-id="1243359003-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="3975535263-10">(</span><span class="n">X</span><span class="p" data-group-id="3975535263-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="3975535263-11">(</span><span class="p" data-group-id="3975535263-12">{</span><span class="ss">foo</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3975535263-12">}</span><span class="p" data-group-id="3975535263-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="3975535263-13">(</span><span class="n">Y</span><span class="p" data-group-id="3975535263-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">call_port</span><span class="p" data-group-id="3975535263-14">(</span><span class="p" data-group-id="3975535263-15">{</span><span class="ss">bar</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3975535263-15">}</span><span class="p" data-group-id="3975535263-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">call_port</span><span class="p" data-group-id="1243359003-16">(</span><span class="n">Msg</span><span class="p" data-group-id="1243359003-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1243359003-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1243359003-18">(</span><span class="p" data-group-id="1243359003-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1243359003-17">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">call_port</span><span class="p" data-group-id="3975535263-16">(</span><span class="n">Msg</span><span class="p" data-group-id="3975535263-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">complex</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3975535263-17">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3975535263-18">(</span><span class="p" data-group-id="3975535263-18">)</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3975535263-17">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="1243359003-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="1243359003-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="3975535263-19">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="3975535263-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">Result</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1243359003-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="1243359003-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="1243359003-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1243359003-22">(</span><span class="p" data-group-id="1243359003-22">)</span><span class="p" data-group-id="1243359003-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="1243359003-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1243359003-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="1243359003-24">(</span><span class="p" data-group-id="1243359003-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="1243359003-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1243359003-26">[</span><span class="p" data-group-id="1243359003-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1243359003-27">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="1243359003-26">]</span><span class="p" data-group-id="1243359003-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="1243359003-28">(</span><span class="n">Port</span><span class="p" data-group-id="1243359003-28">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="3975535263-20">(</span><span class="n">ExtPrg</span><span class="p" data-group-id="3975535263-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="3975535263-21">(</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3975535263-22">(</span><span class="p" data-group-id="3975535263-22">)</span><span class="p" data-group-id="3975535263-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="3975535263-23">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="3975535263-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">open_port</span><span class="p" data-group-id="3975535263-24">(</span><span class="p" data-group-id="3975535263-25">{</span><span class="nb">spawn</span><span class="p">,</span><span class="w"> </span><span class="n">ExtPrg</span><span class="p" data-group-id="3975535263-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3975535263-26">[</span><span class="p" data-group-id="3975535263-27">{</span><span class="ss">packet</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3975535263-27">}</span><span class="p">,</span><span class="w"> </span><span class="ss">binary</span><span class="p" data-group-id="3975535263-26">]</span><span class="p" data-group-id="3975535263-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="3975535263-28">(</span><span class="n">Port</span><span class="p" data-group-id="3975535263-28">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="1243359003-29">(</span><span class="n">Port</span><span class="p" data-group-id="1243359003-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="3975535263-29">(</span><span class="n">Port</span><span class="p" data-group-id="3975535263-29">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="1243359003-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="1243359003-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1243359003-31">{</span><span class="nf">self</span><span class="p" data-group-id="1243359003-32">(</span><span class="p" data-group-id="1243359003-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1243359003-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="1243359003-34">(</span><span class="n">Msg</span><span class="p" data-group-id="1243359003-34">)</span><span class="p" data-group-id="1243359003-33">}</span><span class="p" data-group-id="1243359003-31">}</span><span class="p">,</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="3975535263-30">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="n">Caller</span><span class="p">,</span><span class="w"> </span><span class="n">Msg</span><span class="p" data-group-id="3975535263-30">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3975535263-31">{</span><span class="nf">self</span><span class="p" data-group-id="3975535263-32">(</span><span class="p" data-group-id="3975535263-32">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3975535263-33">{</span><span class="ss">command</span><span class="p">,</span><span class="w"> </span><span class="nf">term_to_binary</span><span class="p" data-group-id="3975535263-34">(</span><span class="n">Msg</span><span class="p" data-group-id="3975535263-34">)</span><span class="p" data-group-id="3975535263-33">}</span><span class="p" data-group-id="3975535263-31">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="1243359003-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1243359003-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1243359003-36">}</span><span class="p" data-group-id="1243359003-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1243359003-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="1243359003-38">(</span><span class="n">Data</span><span class="p" data-group-id="1243359003-38">)</span><span class="p" data-group-id="1243359003-37">}</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="3975535263-35">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3975535263-36">{</span><span class="ss">data</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3975535263-36">}</span><span class="p" data-group-id="3975535263-35">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="n">Caller</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3975535263-37">{</span><span class="ss">complex</span><span class="p">,</span><span class="w"> </span><span class="nf">binary_to_term</span><span class="p" data-group-id="3975535263-38">(</span><span class="n">Data</span><span class="p" data-group-id="3975535263-38">)</span><span class="p" data-group-id="3975535263-37">}</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">loop</span><span class="p" data-group-id="1243359003-39">(</span><span class="n">Port</span><span class="p" data-group-id="1243359003-39">)</span><span class="p">;</span><span class="w">
│ │ │ +	    </span><span class="nf">loop</span><span class="p" data-group-id="3975535263-39">(</span><span class="n">Port</span><span class="p" data-group-id="3975535263-39">)</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">stop</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1243359003-40">{</span><span class="nf">self</span><span class="p" data-group-id="1243359003-41">(</span><span class="p" data-group-id="1243359003-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="1243359003-40">}</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="n">Port</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3975535263-40">{</span><span class="nf">self</span><span class="p" data-group-id="3975535263-41">(</span><span class="p" data-group-id="3975535263-41">)</span><span class="p">,</span><span class="w"> </span><span class="ss">close</span><span class="p" data-group-id="3975535263-40">}</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="k">receive</span><span class="w">
│ │ │ -		</span><span class="p" data-group-id="1243359003-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="1243359003-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -		    </span><span class="nf">exit</span><span class="p" data-group-id="1243359003-43">(</span><span class="ss">normal</span><span class="p" data-group-id="1243359003-43">)</span><span class="w">
│ │ │ +		</span><span class="p" data-group-id="3975535263-42">{</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="ss">closed</span><span class="p" data-group-id="3975535263-42">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +		    </span><span class="nf">exit</span><span class="p" data-group-id="3975535263-43">(</span><span class="ss">normal</span><span class="p" data-group-id="3975535263-43">)</span><span class="w">
│ │ │  	    </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="1243359003-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1243359003-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="nf">exit</span><span class="p" data-group-id="1243359003-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="1243359003-45">)</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="3975535263-44">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="3975535263-44">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	    </span><span class="nf">exit</span><span class="p" data-group-id="3975535263-45">(</span><span class="ss">port_terminated</span><span class="p" data-group-id="3975535263-45">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Notice that calling <code class="inline">complex2:foo/1</code> and <code class="inline">complex2:bar/1</code> results in the tuple
│ │ │  <code class="inline">{foo,X}</code> or <code class="inline">{bar,Y}</code> being sent to the <code class="inline">complex</code> process, which codes them as
│ │ │  binaries and sends them to the port. This means that the C program must be able
│ │ │  to handle these two tuples.</p><h2 id="c-program" class="section-heading">
│ │ │    <a href="#c-program" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -244,145 +244,145 @@
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="s">&quot;ei.h&quot;</span><span class="w">
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">unistd</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">string</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdlib</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  
│ │ │  </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="kt">byte</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="6019997194-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="6019997194-1">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="6019997194-2">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="6019997194-2">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="6019997194-3">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="6019997194-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="6019997194-4">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="6019997194-4">)</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">fail</span><span class="p" data-group-id="6019997194-5">(</span><span class="kt">int</span><span class="w"> </span><span class="n">place</span><span class="p" data-group-id="6019997194-5">)</span><span class="w"> </span><span class="p" data-group-id="6019997194-6">{</span><span class="w">
│ │ │ -    </span><span class="nf">fprintf</span><span class="p" data-group-id="6019997194-7">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Something went wrong %d</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">place</span><span class="p" data-group-id="6019997194-7">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="6019997194-8">(</span><span class="mi">1</span><span class="p" data-group-id="6019997194-8">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6019997194-6">}</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="2152062275-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="2152062275-1">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="2152062275-2">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="2152062275-2">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="2152062275-3">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="2152062275-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="2152062275-4">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="2152062275-4">)</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">fail</span><span class="p" data-group-id="2152062275-5">(</span><span class="kt">int</span><span class="w"> </span><span class="n">place</span><span class="p" data-group-id="2152062275-5">)</span><span class="w"> </span><span class="p" data-group-id="2152062275-6">{</span><span class="w">
│ │ │ +    </span><span class="nf">fprintf</span><span class="p" data-group-id="2152062275-7">(</span><span class="n">stderr</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Something went wrong %d</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">place</span><span class="p" data-group-id="2152062275-7">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="2152062275-8">(</span><span class="mi">1</span><span class="p" data-group-id="2152062275-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2152062275-6">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p" data-group-id="6019997194-9">(</span><span class="p" data-group-id="6019997194-9">)</span><span class="w"> </span><span class="p" data-group-id="6019997194-10">{</span><span class="w">
│ │ │ -    </span><span class="kt">byte</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="6019997194-11">[</span><span class="mi">100</span><span class="p" data-group-id="6019997194-11">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p" data-group-id="2152062275-9">(</span><span class="p" data-group-id="2152062275-9">)</span><span class="w"> </span><span class="p" data-group-id="2152062275-10">{</span><span class="w">
│ │ │ +    </span><span class="kt">byte</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="2152062275-11">[</span><span class="mi">100</span><span class="p" data-group-id="2152062275-11">]</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">index</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">version</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">arity</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="kt">char</span><span class="w"> </span><span class="n">atom</span><span class="p" data-group-id="6019997194-12">[</span><span class="mi">128</span><span class="p" data-group-id="6019997194-12">]</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="kt">char</span><span class="w"> </span><span class="n">atom</span><span class="p" data-group-id="2152062275-12">[</span><span class="mi">128</span><span class="p" data-group-id="2152062275-12">]</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="kt">long</span><span class="w"> </span><span class="n">in</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">ei_x_buff</span><span class="w"> </span><span class="n">res_buf</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">ei_init</span><span class="p" data-group-id="6019997194-13">(</span><span class="p" data-group-id="6019997194-13">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="6019997194-14">(</span><span class="nf">read_cmd</span><span class="p" data-group-id="6019997194-15">(</span><span class="n">buf</span><span class="p" data-group-id="6019997194-15">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-14">)</span><span class="w"> </span><span class="p" data-group-id="6019997194-16">{</span><span class="w">
│ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-17">(</span><span class="nf">ei_decode_version</span><span class="p" data-group-id="6019997194-18">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">version</span><span class="p" data-group-id="6019997194-18">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-17">)</span><span class="w">
│ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="6019997194-19">(</span><span class="mi">1</span><span class="p" data-group-id="6019997194-19">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-20">(</span><span class="nf">ei_decode_tuple_header</span><span class="p" data-group-id="6019997194-21">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">arity</span><span class="p" data-group-id="6019997194-21">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-20">)</span><span class="w">
│ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="6019997194-22">(</span><span class="mi">2</span><span class="p" data-group-id="6019997194-22">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-23">(</span><span class="n">arity</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6019997194-23">)</span><span class="w">
│ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="6019997194-24">(</span><span class="mi">3</span><span class="p" data-group-id="6019997194-24">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-25">(</span><span class="nf">ei_decode_atom</span><span class="p" data-group-id="6019997194-26">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="n">atom</span><span class="p" data-group-id="6019997194-26">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-25">)</span><span class="w">
│ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="6019997194-27">(</span><span class="mi">4</span><span class="p" data-group-id="6019997194-27">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-28">(</span><span class="nf">ei_decode_long</span><span class="p" data-group-id="6019997194-29">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">in</span><span class="p" data-group-id="6019997194-29">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-28">)</span><span class="w">
│ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="6019997194-30">(</span><span class="mi">5</span><span class="p" data-group-id="6019997194-30">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-31">(</span><span class="nf">strncmp</span><span class="p" data-group-id="6019997194-32">(</span><span class="n">atom</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6019997194-32">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-31">)</span><span class="w"> </span><span class="p" data-group-id="6019997194-33">{</span><span class="w">
│ │ │ -            </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="6019997194-34">(</span><span class="p" data-group-id="6019997194-35">(</span><span class="kt">int</span><span class="p" data-group-id="6019997194-35">)</span><span class="n">in</span><span class="p" data-group-id="6019997194-34">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6019997194-33">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-36">(</span><span class="nf">strncmp</span><span class="p" data-group-id="6019997194-37">(</span><span class="n">atom</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bar&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6019997194-37">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-36">)</span><span class="w"> </span><span class="p" data-group-id="6019997194-38">{</span><span class="w">
│ │ │ -            </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="6019997194-39">(</span><span class="p" data-group-id="6019997194-40">(</span><span class="kt">int</span><span class="p" data-group-id="6019997194-40">)</span><span class="n">in</span><span class="p" data-group-id="6019997194-39">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6019997194-38">}</span><span class="w">
│ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-41">(</span><span class="nf">ei_x_new_with_version</span><span class="p" data-group-id="6019997194-42">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p" data-group-id="6019997194-42">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-41">)</span><span class="w">
│ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="6019997194-43">(</span><span class="mi">6</span><span class="p" data-group-id="6019997194-43">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-44">(</span><span class="nf">ei_x_encode_long</span><span class="p" data-group-id="6019997194-45">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p" data-group-id="6019997194-45">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-44">)</span><span class="w">
│ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="6019997194-46">(</span><span class="mi">7</span><span class="p" data-group-id="6019997194-46">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">write_cmd</span><span class="p" data-group-id="6019997194-47">(</span><span class="n">res_buf</span><span class="p">.</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="n">res_buf</span><span class="p">.</span><span class="n">index</span><span class="p" data-group-id="6019997194-47">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">ei_init</span><span class="p" data-group-id="2152062275-13">(</span><span class="p" data-group-id="2152062275-13">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="2152062275-14">(</span><span class="nf">read_cmd</span><span class="p" data-group-id="2152062275-15">(</span><span class="n">buf</span><span class="p" data-group-id="2152062275-15">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-14">)</span><span class="w"> </span><span class="p" data-group-id="2152062275-16">{</span><span class="w">
│ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-17">(</span><span class="nf">ei_decode_version</span><span class="p" data-group-id="2152062275-18">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">version</span><span class="p" data-group-id="2152062275-18">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-17">)</span><span class="w">
│ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2152062275-19">(</span><span class="mi">1</span><span class="p" data-group-id="2152062275-19">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-20">(</span><span class="nf">ei_decode_tuple_header</span><span class="p" data-group-id="2152062275-21">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">arity</span><span class="p" data-group-id="2152062275-21">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-20">)</span><span class="w">
│ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2152062275-22">(</span><span class="mi">2</span><span class="p" data-group-id="2152062275-22">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-23">(</span><span class="n">arity</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2152062275-23">)</span><span class="w">
│ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2152062275-24">(</span><span class="mi">3</span><span class="p" data-group-id="2152062275-24">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-25">(</span><span class="nf">ei_decode_atom</span><span class="p" data-group-id="2152062275-26">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="n">atom</span><span class="p" data-group-id="2152062275-26">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-25">)</span><span class="w">
│ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2152062275-27">(</span><span class="mi">4</span><span class="p" data-group-id="2152062275-27">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-28">(</span><span class="nf">ei_decode_long</span><span class="p" data-group-id="2152062275-29">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">index</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">in</span><span class="p" data-group-id="2152062275-29">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-28">)</span><span class="w">
│ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2152062275-30">(</span><span class="mi">5</span><span class="p" data-group-id="2152062275-30">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-31">(</span><span class="nf">strncmp</span><span class="p" data-group-id="2152062275-32">(</span><span class="n">atom</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2152062275-32">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-31">)</span><span class="w"> </span><span class="p" data-group-id="2152062275-33">{</span><span class="w">
│ │ │ +            </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="2152062275-34">(</span><span class="p" data-group-id="2152062275-35">(</span><span class="kt">int</span><span class="p" data-group-id="2152062275-35">)</span><span class="n">in</span><span class="p" data-group-id="2152062275-34">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2152062275-33">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-36">(</span><span class="nf">strncmp</span><span class="p" data-group-id="2152062275-37">(</span><span class="n">atom</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;bar&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2152062275-37">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-36">)</span><span class="w"> </span><span class="p" data-group-id="2152062275-38">{</span><span class="w">
│ │ │ +            </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="2152062275-39">(</span><span class="p" data-group-id="2152062275-40">(</span><span class="kt">int</span><span class="p" data-group-id="2152062275-40">)</span><span class="n">in</span><span class="p" data-group-id="2152062275-39">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2152062275-38">}</span><span class="w">
│ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-41">(</span><span class="nf">ei_x_new_with_version</span><span class="p" data-group-id="2152062275-42">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p" data-group-id="2152062275-42">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-41">)</span><span class="w">
│ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2152062275-43">(</span><span class="mi">6</span><span class="p" data-group-id="2152062275-43">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-44">(</span><span class="nf">ei_x_encode_long</span><span class="p" data-group-id="2152062275-45">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p" data-group-id="2152062275-45">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-44">)</span><span class="w">
│ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2152062275-46">(</span><span class="mi">7</span><span class="p" data-group-id="2152062275-46">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="nf">write_cmd</span><span class="p" data-group-id="2152062275-47">(</span><span class="n">res_buf</span><span class="p">.</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="n">res_buf</span><span class="p">.</span><span class="n">index</span><span class="p" data-group-id="2152062275-47">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="6019997194-48">(</span><span class="nf">ei_x_free</span><span class="p" data-group-id="6019997194-49">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p" data-group-id="6019997194-49">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6019997194-48">)</span><span class="w">
│ │ │ -            </span><span class="nf">fail</span><span class="p" data-group-id="6019997194-50">(</span><span class="mi">8</span><span class="p" data-group-id="6019997194-50">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2152062275-48">(</span><span class="nf">ei_x_free</span><span class="p" data-group-id="2152062275-49">(</span><span class="o">&amp;</span><span class="n">res_buf</span><span class="p" data-group-id="2152062275-49">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2152062275-48">)</span><span class="w">
│ │ │ +            </span><span class="nf">fail</span><span class="p" data-group-id="2152062275-50">(</span><span class="mi">8</span><span class="p" data-group-id="2152062275-50">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">index</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6019997194-16">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6019997194-10">}</span></code></pre><p>The following functions, <code class="inline">read_cmd()</code> and <code class="inline">write_cmd()</code>, from the <code class="inline">erl_comm.c</code>
│ │ │ +    </span><span class="p" data-group-id="2152062275-16">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2152062275-10">}</span></code></pre><p>The following functions, <code class="inline">read_cmd()</code> and <code class="inline">write_cmd()</code>, from the <code class="inline">erl_comm.c</code>
│ │ │  example in <a href="c_port.html">Ports</a> can still be used for reading from and writing to
│ │ │  the port:</p><pre><code class="makeup c" translate="no"><span class="cm">/* erl_comm.c */</span><span class="w">
│ │ │  
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdio</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">unistd</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  
│ │ │  </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="kt">byte</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="8141108730-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="8141108730-1">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8141108730-2">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="7923207045-1">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="7923207045-1">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7923207045-2">{</span><span class="w">
│ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">got</span><span class="o">=</span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="8141108730-3">{</span><span class="w">
│ │ │ -      </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8141108730-4">(</span><span class="p" data-group-id="8141108730-5">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read</span><span class="p" data-group-id="8141108730-6">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">got</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">got</span><span class="p" data-group-id="8141108730-6">)</span><span class="p" data-group-id="8141108730-5">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8141108730-4">)</span><span class="p" data-group-id="8141108730-7">{</span><span class="w">
│ │ │ -          </span><span class="nf">return</span><span class="p" data-group-id="8141108730-8">(</span><span class="n">i</span><span class="p" data-group-id="8141108730-8">)</span><span class="p">;</span><span class="w">
│ │ │ -      </span><span class="p" data-group-id="8141108730-7">}</span><span class="w">
│ │ │ +  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="7923207045-3">{</span><span class="w">
│ │ │ +      </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="7923207045-4">(</span><span class="p" data-group-id="7923207045-5">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">read</span><span class="p" data-group-id="7923207045-6">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">got</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">got</span><span class="p" data-group-id="7923207045-6">)</span><span class="p" data-group-id="7923207045-5">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7923207045-4">)</span><span class="p" data-group-id="7923207045-7">{</span><span class="w">
│ │ │ +          </span><span class="nf">return</span><span class="p" data-group-id="7923207045-8">(</span><span class="n">i</span><span class="p" data-group-id="7923207045-8">)</span><span class="p">;</span><span class="w">
│ │ │ +      </span><span class="p" data-group-id="7923207045-7">}</span><span class="w">
│ │ │      </span><span class="n">got</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8141108730-3">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="8141108730-9">(</span><span class="n">got</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="8141108730-9">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7923207045-3">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="7923207045-9">(</span><span class="n">got</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="7923207045-9">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="nf">return</span><span class="p" data-group-id="8141108730-10">(</span><span class="n">len</span><span class="p" data-group-id="8141108730-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8141108730-2">}</span><span class="w">
│ │ │ +  </span><span class="nf">return</span><span class="p" data-group-id="7923207045-10">(</span><span class="n">len</span><span class="p" data-group-id="7923207045-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7923207045-2">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="8141108730-11">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="8141108730-11">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8141108730-12">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="7923207045-11">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="7923207045-11">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7923207045-12">{</span><span class="w">
│ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">wrote</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="8141108730-13">{</span><span class="w">
│ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8141108730-14">(</span><span class="p" data-group-id="8141108730-15">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">write</span><span class="p" data-group-id="8141108730-16">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">wrote</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">wrote</span><span class="p" data-group-id="8141108730-16">)</span><span class="p" data-group-id="8141108730-15">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8141108730-14">)</span><span class="w">
│ │ │ -      </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="8141108730-17">(</span><span class="n">i</span><span class="p" data-group-id="8141108730-17">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="7923207045-13">{</span><span class="w">
│ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="7923207045-14">(</span><span class="p" data-group-id="7923207045-15">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">write</span><span class="p" data-group-id="7923207045-16">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">buf</span><span class="o">+</span><span class="n">wrote</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="o">-</span><span class="n">wrote</span><span class="p" data-group-id="7923207045-16">)</span><span class="p" data-group-id="7923207045-15">)</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7923207045-14">)</span><span class="w">
│ │ │ +      </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="7923207045-17">(</span><span class="n">i</span><span class="p" data-group-id="7923207045-17">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">wrote</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8141108730-13">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="8141108730-18">(</span><span class="n">wrote</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="8141108730-18">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7923207045-13">}</span><span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p" data-group-id="7923207045-18">(</span><span class="n">wrote</span><span class="o">&lt;</span><span class="n">len</span><span class="p" data-group-id="7923207045-18">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="8141108730-19">(</span><span class="n">len</span><span class="p" data-group-id="8141108730-19">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8141108730-12">}</span><span class="w">
│ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="7923207045-19">(</span><span class="n">len</span><span class="p" data-group-id="7923207045-19">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7923207045-12">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="8141108730-20">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="8141108730-20">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8141108730-21">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">read_cmd</span><span class="p" data-group-id="7923207045-20">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p" data-group-id="7923207045-20">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7923207045-21">{</span><span class="w">
│ │ │    </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8141108730-22">(</span><span class="nf">read_exact</span><span class="p" data-group-id="8141108730-23">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8141108730-23">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8141108730-22">)</span><span class="w">
│ │ │ -    </span><span class="nf">return</span><span class="p" data-group-id="8141108730-24">(</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="8141108730-24">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8141108730-25">(</span><span class="n">buf</span><span class="p" data-group-id="8141108730-26">[</span><span class="mi">0</span><span class="p" data-group-id="8141108730-26">]</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="8141108730-25">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="8141108730-27">[</span><span class="mi">1</span><span class="p" data-group-id="8141108730-27">]</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="8141108730-28">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="8141108730-28">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8141108730-21">}</span><span class="w">
│ │ │ +  </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="7923207045-22">(</span><span class="nf">read_exact</span><span class="p" data-group-id="7923207045-23">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7923207045-23">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7923207045-22">)</span><span class="w">
│ │ │ +    </span><span class="nf">return</span><span class="p" data-group-id="7923207045-24">(</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="7923207045-24">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7923207045-25">(</span><span class="n">buf</span><span class="p" data-group-id="7923207045-26">[</span><span class="mi">0</span><span class="p" data-group-id="7923207045-26">]</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="7923207045-25">)</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">buf</span><span class="p" data-group-id="7923207045-27">[</span><span class="mi">1</span><span class="p" data-group-id="7923207045-27">]</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="nf">read_exact</span><span class="p" data-group-id="7923207045-28">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="7923207045-28">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7923207045-21">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="8141108730-29">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="8141108730-29">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8141108730-30">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">write_cmd</span><span class="p" data-group-id="7923207045-29">(</span><span class="kt">byte</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="7923207045-29">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7923207045-30">{</span><span class="w">
│ │ │    </span><span class="kt">byte</span><span class="w"> </span><span class="n">li</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8141108730-31">(</span><span class="n">len</span><span class="w"> </span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="8141108730-31">)</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">write_exact</span><span class="p" data-group-id="8141108730-32">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8141108730-32">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7923207045-31">(</span><span class="n">len</span><span class="w"> </span><span class="o">&gt;&gt;</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="7923207045-31">)</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">write_exact</span><span class="p" data-group-id="7923207045-32">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7923207045-32">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │    </span><span class="n">li</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">len</span><span class="w"> </span><span class="o">&amp;</span><span class="w"> </span><span class="mh">0xff</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">write_exact</span><span class="p" data-group-id="8141108730-33">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8141108730-33">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">write_exact</span><span class="p" data-group-id="7923207045-33">(</span><span class="o">&amp;</span><span class="n">li</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7923207045-33">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="k">return</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="8141108730-34">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="8141108730-34">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8141108730-30">}</span></code></pre><h2 id="running-the-example" class="section-heading">
│ │ │ +  </span><span class="k">return</span><span class="w"> </span><span class="nf">write_exact</span><span class="p" data-group-id="7923207045-34">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="7923207045-34">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7923207045-30">}</span></code></pre><h2 id="running-the-example" class="section-heading">
│ │ │    <a href="#running-the-example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running the Example</span>
│ │ │  </h2>
│ │ │  <p><em>Step 1.</em> Compile the C code. This provides the paths to the include file
│ │ │  <code class="inline">ei.h</code>, and also to the library <code class="inline">ei</code>:</p><pre><code class="text">$ gcc -o extprg -I/usr/local/otp/lib/erl_interface-3.9.2/include \
│ │ │      -L/usr/local/otp/lib/erl_interface-3.9.2/lib \
│ │ │      complex.c erl_comm.c ei.c -lei -lpthread</code></pre><p>In Erlang/OTP R5B and later versions of OTP, the <code class="inline">include</code> and <code class="inline">lib</code> directories
│ │ │  are situated under <code class="inline">$OTPROOT/lib/erl_interface-VSN</code>, where <code class="inline">$OTPROOT</code> is the
│ │ │  root directory of the OTP installation (<code class="inline">/usr/local/otp</code> in the recent example)
│ │ │  and <code class="inline">VSN</code> is the version of the Erl_interface application (3.2.1 in the recent
│ │ │  example).</p><p>In R4B and earlier versions of OTP, <code class="inline">include</code> and <code class="inline">lib</code> are situated under
│ │ │  <code class="inline">$OTPROOT/usr</code>.</p><p><em>Step 2.</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$ </span><span class="ss">erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="5467264621-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="5467264621-1">]</span><span class="w"> </span><span class="p" data-group-id="5467264621-2">[</span><span class="ss">source</span><span class="p" data-group-id="5467264621-2">]</span><span class="w"> </span><span class="p" data-group-id="5467264621-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="5467264621-3">]</span><span class="w"> </span><span class="p" data-group-id="5467264621-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="5467264621-4">]</span><span class="w"> </span><span class="p" data-group-id="5467264621-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="5467264621-5">]</span><span class="w"> </span><span class="p" data-group-id="5467264621-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5467264621-6">]</span><span class="w"> </span><span class="p" data-group-id="5467264621-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="5467264621-7">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="p" data-group-id="0323205937-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">14.2</span><span class="p" data-group-id="0323205937-1">]</span><span class="w"> </span><span class="p" data-group-id="0323205937-2">[</span><span class="ss">source</span><span class="p" data-group-id="0323205937-2">]</span><span class="w"> </span><span class="p" data-group-id="0323205937-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0323205937-3">]</span><span class="w"> </span><span class="p" data-group-id="0323205937-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0323205937-4">]</span><span class="w"> </span><span class="p" data-group-id="0323205937-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="0323205937-5">]</span><span class="w"> </span><span class="p" data-group-id="0323205937-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0323205937-6">]</span><span class="w"> </span><span class="p" data-group-id="0323205937-7">[</span><span class="nc">jit</span><span class="p">:</span><span class="ss">ns</span><span class="p" data-group-id="0323205937-7">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="5467264621-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="5467264621-9">(</span><span class="p" data-group-id="5467264621-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="5467264621-8">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="5467264621-10">(</span><span class="ss">complex2</span><span class="p" data-group-id="5467264621-10">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5467264621-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex2</span><span class="p" data-group-id="5467264621-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="8513549671-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="8513549671-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V14</span><span class="p">.</span><span class="mi">2</span><span class="w"> </span><span class="p" data-group-id="0323205937-8">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="0323205937-9">(</span><span class="p" data-group-id="0323205937-9">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="0323205937-8">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="0323205937-10">(</span><span class="ss">complex2</span><span class="p" data-group-id="0323205937-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0323205937-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex2</span><span class="p" data-group-id="0323205937-11">}</span></code></pre><p><em>Step 3.</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3561773925-1">(</span><span class="s">&quot;./extprg&quot;</span><span class="p" data-group-id="3561773925-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="o">&lt;</span><span class="mf">0.34</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="8513549671-2">(</span><span class="mi">3</span><span class="p" data-group-id="8513549671-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="3561773925-2">(</span><span class="mi">3</span><span class="p" data-group-id="3561773925-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="8513549671-3">(</span><span class="mi">5</span><span class="p" data-group-id="8513549671-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="3561773925-3">(</span><span class="mi">5</span><span class="p" data-group-id="3561773925-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="8513549671-4">(</span><span class="mi">352</span><span class="p" data-group-id="8513549671-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="3561773925-4">(</span><span class="mi">352</span><span class="p" data-group-id="3561773925-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">704</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="8513549671-5">(</span><span class="p" data-group-id="8513549671-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">complex2</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="3561773925-5">(</span><span class="p" data-group-id="3561773925-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">stop</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="c_port.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/error_logging.html
│ │ │ @@ -143,39 +143,39 @@
│ │ │  reports and other error and information reports are by default logged through
│ │ │  the log handler which is set up when the Kernel application is started.</p><p>Prior to Erlang/OTP 21.0, supervisor, crash, and progress reports were only
│ │ │  logged when the SASL application was running. This behaviour can, for backwards
│ │ │  compatibility, be enabled by setting the Kernel configuration parameter
│ │ │  <a href="../../lib/kernel-10.2.7.4/doc/html/kernel_app.html#logger_sasl_compatible"><code class="inline">logger_sasl_compatible</code></a> to
│ │ │  <code class="inline">true</code>. For more information, see
│ │ │  <a href="../../lib/sasl-4.2.2.1/doc/html/error_logging.html">SASL Error Logging</a> in the SASL User's Guide.</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl -kernel logger_level info</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">21</span><span class="w"> </span><span class="p" data-group-id="2064510262-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">10.0</span><span class="p" data-group-id="2064510262-1">]</span><span class="w"> </span><span class="p" data-group-id="2064510262-2">[</span><span class="ss">source</span><span class="o">-</span><span class="mi">13</span><span class="ss">c50db</span><span class="p" data-group-id="2064510262-2">]</span><span class="w"> </span><span class="p" data-group-id="2064510262-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="2064510262-3">]</span><span class="w"> </span><span class="p" data-group-id="2064510262-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="2064510262-4">]</span><span class="w"> </span><span class="p" data-group-id="2064510262-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="2064510262-5">]</span><span class="w"> </span><span class="p" data-group-id="2064510262-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="2064510262-6">]</span><span class="w"> </span><span class="p" data-group-id="2064510262-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="2064510262-7">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">21</span><span class="w"> </span><span class="p" data-group-id="4195028644-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">10.0</span><span class="p" data-group-id="4195028644-1">]</span><span class="w"> </span><span class="p" data-group-id="4195028644-2">[</span><span class="ss">source</span><span class="o">-</span><span class="mi">13</span><span class="ss">c50db</span><span class="p" data-group-id="4195028644-2">]</span><span class="w"> </span><span class="p" data-group-id="4195028644-3">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="4195028644-3">]</span><span class="w"> </span><span class="p" data-group-id="4195028644-4">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="4195028644-4">]</span><span class="w"> </span><span class="p" data-group-id="4195028644-5">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="4195028644-5">]</span><span class="w"> </span><span class="p" data-group-id="4195028644-6">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="4195028644-6">]</span><span class="w"> </span><span class="p" data-group-id="4195028644-7">[</span><span class="ss">hipe</span><span class="p" data-group-id="4195028644-7">]</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.916404</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │      </span><span class="nc">application</span><span class="p">:</span><span class="w"> </span><span class="ss">kernel</span><span class="w">
│ │ │      </span><span class="nc">started_at</span><span class="p">:</span><span class="w"> </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.922908</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │      </span><span class="nc">application</span><span class="p">:</span><span class="w"> </span><span class="ss">stdlib</span><span class="w">
│ │ │      </span><span class="nc">started_at</span><span class="p">:</span><span class="w"> </span><span class="ss">nonode@nohost</span><span class="w">
│ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.925755</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="2064510262-8">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="2064510262-8">}</span><span class="w">
│ │ │ -    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="2064510262-9">[</span><span class="p" data-group-id="2064510262-10">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.74</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2064510262-10">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-11">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_sup</span><span class="p" data-group-id="2064510262-11">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-12">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="2064510262-13">{</span><span class="ss">disk_log_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="2064510262-14">[</span><span class="p" data-group-id="2064510262-14">]</span><span class="p" data-group-id="2064510262-13">}</span><span class="p" data-group-id="2064510262-12">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-15">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="2064510262-15">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-16">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">1000</span><span class="p" data-group-id="2064510262-16">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-17">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">supervisor</span><span class="p" data-group-id="2064510262-17">}</span><span class="p" data-group-id="2064510262-9">]</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4195028644-8">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="4195028644-8">}</span><span class="w">
│ │ │ +    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4195028644-9">[</span><span class="p" data-group-id="4195028644-10">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.74</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4195028644-10">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-11">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_sup</span><span class="p" data-group-id="4195028644-11">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-12">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="4195028644-13">{</span><span class="ss">disk_log_sup</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="4195028644-14">[</span><span class="p" data-group-id="4195028644-14">]</span><span class="p" data-group-id="4195028644-13">}</span><span class="p" data-group-id="4195028644-12">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-15">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="4195028644-15">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-16">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">1000</span><span class="p" data-group-id="4195028644-16">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-17">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">supervisor</span><span class="p" data-group-id="4195028644-17">}</span><span class="p" data-group-id="4195028644-9">]</span><span class="w">
│ │ │  </span><span class="o">=</span><span class="n">PROGRESS</span><span class="w"> </span><span class="n">REPORT</span><span class="o">==</span><span class="o">==</span><span class="w"> </span><span class="mi">8</span><span class="o">-</span><span class="n">Jun</span><span class="o">-</span><span class="mi">2018</span><span class="p">:</span><span class="p">:</span><span class="mi">16</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">19.926056</span><span class="w"> </span><span class="o">==</span><span class="o">=</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="2064510262-18">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="2064510262-18">}</span><span class="w">
│ │ │ -    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="2064510262-19">[</span><span class="p" data-group-id="2064510262-20">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.75</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2064510262-20">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-21">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_server</span><span class="p" data-group-id="2064510262-21">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-22">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="2064510262-23">{</span><span class="ss">disk_log_server</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="2064510262-24">[</span><span class="p" data-group-id="2064510262-24">]</span><span class="p" data-group-id="2064510262-23">}</span><span class="p" data-group-id="2064510262-22">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-25">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="2064510262-25">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-26">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">2000</span><span class="p" data-group-id="2064510262-26">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="2064510262-27">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">worker</span><span class="p" data-group-id="2064510262-27">}</span><span class="p" data-group-id="2064510262-19">]</span><span class="w">
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V10</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="2064510262-28">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="2064510262-28">)</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4195028644-18">{</span><span class="ss">local</span><span class="p">,</span><span class="ss">kernel_safe_sup</span><span class="p" data-group-id="4195028644-18">}</span><span class="w">
│ │ │ +    </span><span class="nc">started</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4195028644-19">[</span><span class="p" data-group-id="4195028644-20">{</span><span class="ss">pid</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.75</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="4195028644-20">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-21">{</span><span class="ss">id</span><span class="p">,</span><span class="ss">disk_log_server</span><span class="p" data-group-id="4195028644-21">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-22">{</span><span class="ss">mfargs</span><span class="p">,</span><span class="p" data-group-id="4195028644-23">{</span><span class="ss">disk_log_server</span><span class="p">,</span><span class="ss">start_link</span><span class="p">,</span><span class="p" data-group-id="4195028644-24">[</span><span class="p" data-group-id="4195028644-24">]</span><span class="p" data-group-id="4195028644-23">}</span><span class="p" data-group-id="4195028644-22">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-25">{</span><span class="ss">restart_type</span><span class="p">,</span><span class="ss">permanent</span><span class="p" data-group-id="4195028644-25">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-26">{</span><span class="ss">shutdown</span><span class="p">,</span><span class="mi">2000</span><span class="p" data-group-id="4195028644-26">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="4195028644-27">{</span><span class="ss">child_type</span><span class="p">,</span><span class="ss">worker</span><span class="p" data-group-id="4195028644-27">}</span><span class="p" data-group-id="4195028644-19">]</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V10</span><span class="p">.</span><span class="mi">0</span><span class="w">  </span><span class="p" data-group-id="4195028644-28">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="4195028644-28">)</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="o">&gt;</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="system_principles.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/errors.html
│ │ │ @@ -151,22 +151,22 @@
│ │ │  classes, with different origins. The <a href="expressions.html#try">try</a> expression can
│ │ │  distinguish between the different classes, whereas the
│ │ │  <a href="expressions.html#catch-and-throw">catch</a> expression cannot. <code class="inline">try</code> and <code class="inline">catch</code> are described
│ │ │  in <a href="expressions.html">Expressions</a>.</p><table><thead><tr><th style="text-align: left;"><em>Class</em></th><th style="text-align: left;"><em>Origin</em></th></tr></thead><tbody><tr><td style="text-align: left;"><code class="inline">error</code></td><td style="text-align: left;">Run-time error, for example, <code class="inline">1+a</code>, or the process called <a href="../../erts-15.2.7.8/doc/html/erlang.html#error/1"><code class="inline">error/1</code></a></td></tr><tr><td style="text-align: left;"><code class="inline">exit</code></td><td style="text-align: left;">The process called <a href="../../erts-15.2.7.8/doc/html/erlang.html#exit/1"><code class="inline">exit/1</code></a></td></tr><tr><td style="text-align: left;"><code class="inline">throw</code></td><td style="text-align: left;">The process called <a href="../../erts-15.2.7.8/doc/html/erlang.html#throw/1"><code class="inline">throw/1</code></a></td></tr></tbody></table><p><em>Table: Exception Classes.</em></p><p>All of the above exceptions can also be generated by calling <a href="../../erts-15.2.7.8/doc/html/erlang.html#raise/3"><code class="inline">erlang:raise/3</code></a>.</p><p>An exception consists of its class, an exit reason (see
│ │ │  <a href="errors.html#exit_reasons">Exit Reason</a>), and a stack trace (which aids in finding
│ │ │  the code location of the exception).</p><p>The stack trace can be bound to a variable from within a <code class="inline">try</code> expression for
│ │ │  any exception class, or as part of the exit reason when a run-time error is
│ │ │ -caught by a <code class="inline">catch</code>. Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="4999574170-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="4999574170-2">{</span><span class="ss">test</span><span class="p">,</span><span class="n">Stacktrace</span><span class="p" data-group-id="4999574170-2">}</span><span class="p" data-group-id="4999574170-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4999574170-3">(</span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="4999574170-4">(</span><span class="ss">test</span><span class="p" data-group-id="4999574170-4">)</span><span class="p" data-group-id="4999574170-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Stacktrace</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4999574170-5">[</span><span class="p" data-group-id="4999574170-6">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="4999574170-7">[</span><span class="p" data-group-id="4999574170-7">]</span><span class="p" data-group-id="4999574170-6">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4999574170-8">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="4999574170-9">[</span><span class="p" data-group-id="4999574170-9">]</span><span class="p" data-group-id="4999574170-8">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4999574170-5">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="k">try</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="4999574170-10">(</span><span class="ss">test</span><span class="p" data-group-id="4999574170-10">)</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="n">Class</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stacktrace</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Stacktrace</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4999574170-11">[</span><span class="p" data-group-id="4999574170-12">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="4999574170-13">[</span><span class="p" data-group-id="4999574170-13">]</span><span class="p" data-group-id="4999574170-12">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4999574170-14">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="4999574170-15">[</span><span class="p" data-group-id="4999574170-15">]</span><span class="p" data-group-id="4999574170-14">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4999574170-11">]</span></code></pre><p><a href="" id="stacktrace"></a></p><h3 id="the-call-stack-back-trace-stacktrace" class="section-heading">
│ │ │ +caught by a <code class="inline">catch</code>. Example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="5616518901-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="5616518901-2">{</span><span class="ss">test</span><span class="p">,</span><span class="n">Stacktrace</span><span class="p" data-group-id="5616518901-2">}</span><span class="p" data-group-id="5616518901-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5616518901-3">(</span><span class="k">catch</span><span class="w"> </span><span class="nf">error</span><span class="p" data-group-id="5616518901-4">(</span><span class="ss">test</span><span class="p" data-group-id="5616518901-4">)</span><span class="p" data-group-id="5616518901-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Stacktrace</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5616518901-5">[</span><span class="p" data-group-id="5616518901-6">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="5616518901-7">[</span><span class="p" data-group-id="5616518901-7">]</span><span class="p" data-group-id="5616518901-6">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5616518901-8">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="5616518901-9">[</span><span class="p" data-group-id="5616518901-9">]</span><span class="p" data-group-id="5616518901-8">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5616518901-5">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="k">try</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="5616518901-10">(</span><span class="ss">test</span><span class="p" data-group-id="5616518901-10">)</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="n">Class</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stacktrace</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Stacktrace</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5616518901-11">[</span><span class="p" data-group-id="5616518901-12">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">apply_fun</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="p" data-group-id="5616518901-13">[</span><span class="p" data-group-id="5616518901-13">]</span><span class="p" data-group-id="5616518901-12">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5616518901-14">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="p" data-group-id="5616518901-15">[</span><span class="p" data-group-id="5616518901-15">]</span><span class="p" data-group-id="5616518901-14">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5616518901-11">]</span></code></pre><p><a href="" id="stacktrace"></a></p><h3 id="the-call-stack-back-trace-stacktrace" class="section-heading">
│ │ │    <a href="#the-call-stack-back-trace-stacktrace" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The call-stack back trace (stacktrace)</span>
│ │ │  </h3>
│ │ │  <p>The stack back-trace (<a href="../../erts-15.2.7.8/doc/html/erlang.html#t:stacktrace/0"><em>stacktrace</em></a>) is a list that
│ │ │  contains <code class="inline">{Module, Function, Arity, ExtraInfo}</code> and/or <code class="inline">{Fun, Arity, ExtraInfo}</code>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/events.html
│ │ │ @@ -135,43 +135,43 @@
│ │ │  event handler.</p><h2 id="example" class="section-heading">
│ │ │    <a href="#example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example</span>
│ │ │  </h2>
│ │ │  <p>The callback module for the event handler writing error messages to the terminal
│ │ │ -can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1080909705-1">(</span><span class="ss">terminal_logger</span><span class="p" data-group-id="1080909705-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1080909705-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="1080909705-2">)</span><span class="p">.</span><span class="w">
│ │ │ +can look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1709403016-1">(</span><span class="ss">terminal_logger</span><span class="p" data-group-id="1709403016-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="1709403016-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="1709403016-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1080909705-3">(</span><span class="p" data-group-id="1080909705-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1080909705-4">]</span><span class="p" data-group-id="1080909705-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1709403016-3">(</span><span class="p" data-group-id="1709403016-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1709403016-4">]</span><span class="p" data-group-id="1709403016-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1080909705-5">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="1080909705-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1080909705-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1080909705-7">[</span><span class="p" data-group-id="1080909705-7">]</span><span class="p" data-group-id="1080909705-6">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="1709403016-5">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="1709403016-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1709403016-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1709403016-7">[</span><span class="p" data-group-id="1709403016-7">]</span><span class="p" data-group-id="1709403016-6">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1080909705-8">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1080909705-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1080909705-9">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1080909705-10">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="1080909705-10">]</span><span class="p" data-group-id="1080909705-9">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1080909705-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1080909705-11">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="1709403016-8">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1709403016-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1709403016-9">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1709403016-10">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="1709403016-10">]</span><span class="p" data-group-id="1709403016-9">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1709403016-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1709403016-11">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="1080909705-12">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="1080909705-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="1709403016-12">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="1709403016-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The callback module for the event handler writing error messages to a file can
│ │ │ -look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5755287260-1">(</span><span class="ss">file_logger</span><span class="p" data-group-id="5755287260-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5755287260-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="5755287260-2">)</span><span class="p">.</span><span class="w">
│ │ │ +look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5766850210-1">(</span><span class="ss">file_logger</span><span class="p" data-group-id="5766850210-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5766850210-2">(</span><span class="ss">gen_event</span><span class="p" data-group-id="5766850210-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5755287260-3">(</span><span class="p" data-group-id="5755287260-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5755287260-4">]</span><span class="p" data-group-id="5755287260-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5766850210-3">(</span><span class="p" data-group-id="5766850210-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5766850210-4">]</span><span class="p" data-group-id="5766850210-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="5755287260-5">(</span><span class="n">File</span><span class="p" data-group-id="5755287260-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5755287260-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5755287260-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="5755287260-7">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="5755287260-7">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5755287260-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5755287260-8">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5755287260-9">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5755287260-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5755287260-10">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5755287260-11">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="5755287260-11">]</span><span class="p" data-group-id="5755287260-10">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5755287260-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5755287260-12">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="5766850210-5">(</span><span class="n">File</span><span class="p" data-group-id="5766850210-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5766850210-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5766850210-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="5766850210-7">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="5766850210-7">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5766850210-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5766850210-8">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="5766850210-9">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5766850210-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5766850210-10">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5766850210-11">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="5766850210-11">]</span><span class="p" data-group-id="5766850210-10">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5766850210-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5766850210-12">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="5755287260-13">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5755287260-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="5755287260-14">(</span><span class="n">Fd</span><span class="p" data-group-id="5755287260-14">)</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><p><a href="" id="mgr"></a></p><h2 id="starting-an-event-manager" class="section-heading">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="5766850210-13">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="5766850210-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="5766850210-14">(</span><span class="n">Fd</span><span class="p" data-group-id="5766850210-14">)</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><p><a href="" id="mgr"></a></p><h2 id="starting-an-event-manager" class="section-heading">
│ │ │    <a href="#starting-an-event-manager" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting an Event Manager</span>
│ │ │  </h2>
│ │ │  <p>To start an event manager for handling errors, as described in the previous
│ │ │  example, call the following function:</p><pre><code class="text">gen_event:start_link({local, error_man})</code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/gen_event.html#start_link/1"><code class="inline">gen_event:start_link/1</code></a> spawns and links to a new event manager process.</p><p>The argument, <code class="inline">{local, error_man}</code>, specifies the name under which the
│ │ │ @@ -184,57 +184,57 @@
│ │ │  manager that is not part of a supervision tree.</p><h2 id="adding-an-event-handler" class="section-heading">
│ │ │    <a href="#adding-an-event-handler" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Adding an Event Handler</span>
│ │ │  </h2>
│ │ │  <p>The following example shows how to start an event manager and add an event
│ │ │ -handler to it by using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="2471085471-1">(</span><span class="p" data-group-id="2471085471-2">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="2471085471-2">}</span><span class="p" data-group-id="2471085471-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2471085471-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.31</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="2471085471-3">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">add_handler</span><span class="p" data-group-id="2471085471-4">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2471085471-5">[</span><span class="p" data-group-id="2471085471-5">]</span><span class="p" data-group-id="2471085471-4">)</span><span class="p">.</span><span class="w">
│ │ │ +handler to it by using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3543760965-1">(</span><span class="p" data-group-id="3543760965-2">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="3543760965-2">}</span><span class="p" data-group-id="3543760965-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3543760965-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.31</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="3543760965-3">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">add_handler</span><span class="p" data-group-id="3543760965-4">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3543760965-5">[</span><span class="p" data-group-id="3543760965-5">]</span><span class="p" data-group-id="3543760965-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>This function sends a message to the event manager registered as <code class="inline">error_man</code>,
│ │ │  telling it to add the event handler <code class="inline">terminal_logger</code>. The event manager calls
│ │ │  the callback function <code class="inline">terminal_logger:init([])</code>, where the argument <code class="inline">[]</code> is the
│ │ │  third argument to <code class="inline">add_handler</code>. <code class="inline">init/1</code> is expected to return <code class="inline">{ok, State}</code>,
│ │ │ -where <code class="inline">State</code> is the internal state of the event handler.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6497598200-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6497598200-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6497598200-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6497598200-3">[</span><span class="p" data-group-id="6497598200-3">]</span><span class="p" data-group-id="6497598200-2">}</span><span class="p">.</span></code></pre><p>Here, <code class="inline">init/1</code> does not need any input data and ignores its argument. For
│ │ │ +where <code class="inline">State</code> is the internal state of the event handler.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5201485716-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5201485716-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5201485716-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5201485716-3">[</span><span class="p" data-group-id="5201485716-3">]</span><span class="p" data-group-id="5201485716-2">}</span><span class="p">.</span></code></pre><p>Here, <code class="inline">init/1</code> does not need any input data and ignores its argument. For
│ │ │  <code class="inline">terminal_logger</code>, the internal state is not used. For <code class="inline">file_logger</code>, the
│ │ │ -internal state is used to save the open file descriptor.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8584983072-1">(</span><span class="n">File</span><span class="p" data-group-id="8584983072-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8584983072-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8584983072-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="8584983072-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="8584983072-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8584983072-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8584983072-4">}</span><span class="p">.</span></code></pre><h2 id="notifying-about-events" class="section-heading">
│ │ │ +internal state is used to save the open file descriptor.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4386885336-1">(</span><span class="n">File</span><span class="p" data-group-id="4386885336-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4386885336-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="4386885336-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="4386885336-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">read</span><span class="p" data-group-id="4386885336-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4386885336-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="4386885336-4">}</span><span class="p">.</span></code></pre><h2 id="notifying-about-events" class="section-heading">
│ │ │    <a href="#notifying-about-events" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Notifying about Events</span>
│ │ │  </h2>
│ │ │  <pre><code class="text">3&gt; gen_event:notify(error_man, no_reply).
│ │ │  ***Error*** no_reply
│ │ │  ok</code></pre><p><code class="inline">error_man</code> is the name of the event manager and <code class="inline">no_reply</code> is the event.</p><p>The event is made into a message and sent to the event manager. When the event
│ │ │  is received, the event manager calls <code class="inline">handle_event(Event, State)</code> for each
│ │ │  installed event handler, in the same order as they were added. The function is
│ │ │  expected to return a tuple <code class="inline">{ok,State1}</code>, where <code class="inline">State1</code> is a new value for the
│ │ │ -state of the event handler.</p><p>In <code class="inline">terminal_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="8141200417-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8141200417-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8141200417-2">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8141200417-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="8141200417-3">]</span><span class="p" data-group-id="8141200417-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8141200417-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8141200417-4">}</span><span class="p">.</span></code></pre><p>In <code class="inline">file_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="6880252694-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="6880252694-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6880252694-2">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6880252694-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="6880252694-3">]</span><span class="p" data-group-id="6880252694-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6880252694-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="6880252694-4">}</span><span class="p">.</span></code></pre><h2 id="deleting-an-event-handler" class="section-heading">
│ │ │ +state of the event handler.</p><p>In <code class="inline">terminal_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="1089609009-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1089609009-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1089609009-2">(</span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1089609009-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="1089609009-3">]</span><span class="p" data-group-id="1089609009-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1089609009-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1089609009-4">}</span><span class="p">.</span></code></pre><p>In <code class="inline">file_logger</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_event</span><span class="p" data-group-id="7999777067-1">(</span><span class="n">ErrorMsg</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="7999777067-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7999777067-2">(</span><span class="n">Fd</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;***Error*** </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7999777067-3">[</span><span class="n">ErrorMsg</span><span class="p" data-group-id="7999777067-3">]</span><span class="p" data-group-id="7999777067-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7999777067-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="7999777067-4">}</span><span class="p">.</span></code></pre><h2 id="deleting-an-event-handler" class="section-heading">
│ │ │    <a href="#deleting-an-event-handler" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Deleting an Event Handler</span>
│ │ │  </h2>
│ │ │ -<pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">delete_handler</span><span class="p" data-group-id="4253058893-1">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4253058893-2">[</span><span class="p" data-group-id="4253058893-2">]</span><span class="p" data-group-id="4253058893-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">delete_handler</span><span class="p" data-group-id="4434998470-1">(</span><span class="ss">error_man</span><span class="p">,</span><span class="w"> </span><span class="ss">terminal_logger</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4434998470-2">[</span><span class="p" data-group-id="4434998470-2">]</span><span class="p" data-group-id="4434998470-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>This function sends a message to the event manager registered as <code class="inline">error_man</code>,
│ │ │  telling it to delete the event handler <code class="inline">terminal_logger</code>. The event manager
│ │ │  calls the callback function <code class="inline">terminal_logger:terminate([], State)</code>, where the
│ │ │  argument <code class="inline">[]</code> is the third argument to <code class="inline">delete_handler</code>. <code class="inline">terminate/2</code> is to be
│ │ │  the opposite of <code class="inline">init/1</code> and do any necessary cleaning up. Its return value is
│ │ │ -ignored.</p><p>For <code class="inline">terminal_logger</code>, no cleaning up is necessary:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="7469083664-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="7469083664-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>For <code class="inline">file_logger</code>, the file descriptor opened in <code class="inline">init</code> must be closed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="4399699248-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="4399699248-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="4399699248-2">(</span><span class="n">Fd</span><span class="p" data-group-id="4399699248-2">)</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │ +ignored.</p><p>For <code class="inline">terminal_logger</code>, no cleaning up is necessary:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="5405497112-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p" data-group-id="5405497112-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>For <code class="inline">file_logger</code>, the file descriptor opened in <code class="inline">init</code> must be closed:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="8406434272-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p">,</span><span class="w"> </span><span class="n">Fd</span><span class="p" data-group-id="8406434272-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="8406434272-2">(</span><span class="n">Fd</span><span class="p" data-group-id="8406434272-2">)</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │    <a href="#stopping" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Stopping</span>
│ │ │  </h2>
│ │ │  <p>When an event manager is stopped, it gives each of the installed event handlers
│ │ │  the chance to clean up by calling <code class="inline">terminate/2</code>, the same way as when deleting a
│ │ │ @@ -249,33 +249,33 @@
│ │ │  this is done is defined by a <a href="sup_princ.html#shutdown">shutdown strategy</a> set in
│ │ │  the supervisor.</p><h3 id="standalone-event-managers" class="section-heading">
│ │ │    <a href="#standalone-event-managers" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Standalone Event Managers</span>
│ │ │  </h3>
│ │ │ -<p>An event manager can also be stopped by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="2562377959-1">(</span><span class="ss">error_man</span><span class="p" data-group-id="2562377959-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>An event manager can also be stopped by calling:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">gen_event</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="7159501297-1">(</span><span class="ss">error_man</span><span class="p" data-group-id="7159501297-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><h2 id="handling-other-messages" class="section-heading">
│ │ │    <a href="#handling-other-messages" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Handling Other Messages</span>
│ │ │  </h2>
│ │ │  <p>If the <code class="inline">gen_event</code> process is to be able to receive other messages
│ │ │  than events, the callback function <code class="inline">handle_info(Info, State)</code> must be
│ │ │  implemented to handle them. Examples of other messages are exit
│ │ │  messages if the event manager is linked to other processes than the
│ │ │  supervisor (for example via <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_event.html#add_sup_handler/3"><code class="inline">gen_event:add_sup_handler/3</code></a>) and is
│ │ │ -trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="4682303369-1">(</span><span class="p" data-group-id="4682303369-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="4682303369-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4682303369-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="4348913796-1">(</span><span class="p" data-group-id="4348913796-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="4348913796-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4348913796-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code to handle exits here.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4682303369-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="4682303369-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="7118222676-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="7118222676-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4348913796-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="4348913796-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="4630173189-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="4630173189-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code to convert state (and more) during code change.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7118222676-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="7118222676-2">}</span><span class="p">.</span></code></pre>
│ │ │ +    </span><span class="p" data-group-id="4630173189-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="4630173189-2">}</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="statem.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/example.html
│ │ │ @@ -121,25 +121,25 @@
│ │ │    </a>
│ │ │    <span class="text">Description</span>
│ │ │  </h2>
│ │ │  <p>A common interoperability situation is when you want to incorporate a piece of
│ │ │  code, solving a complex problem, in your Erlang program. Suppose for example,
│ │ │  that you have the following C functions that you would like to call from Erlang:</p><pre><code class="makeup c" translate="no"><span class="cm">/* complex.c */</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="6902683739-1">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="6902683739-1">)</span><span class="w"> </span><span class="p" data-group-id="6902683739-2">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="5214412989-1">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="5214412989-1">)</span><span class="w"> </span><span class="p" data-group-id="5214412989-2">{</span><span class="w">
│ │ │    </span><span class="k">return</span><span class="w"> </span><span class="n">x</span><span class="o">+</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6902683739-2">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5214412989-2">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="6902683739-3">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="6902683739-3">)</span><span class="w"> </span><span class="p" data-group-id="6902683739-4">{</span><span class="w">
│ │ │ +</span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="5214412989-3">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="5214412989-3">)</span><span class="w"> </span><span class="p" data-group-id="5214412989-4">{</span><span class="w">
│ │ │    </span><span class="k">return</span><span class="w"> </span><span class="n">y</span><span class="o">*</span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6902683739-4">}</span></code></pre><p>The functions are deliberately kept as simple as possible, for readability
│ │ │ +</span><span class="p" data-group-id="5214412989-4">}</span></code></pre><p>The functions are deliberately kept as simple as possible, for readability
│ │ │  reasons.</p><p>From an Erlang perspective, it is preferable to be able to call <code class="inline">foo</code> and <code class="inline">bar</code>
│ │ │  without having to bother about that they are C functions:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% Erlang code</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="n">Res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">complex</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="2117621560-1">(</span><span class="n">X</span><span class="p" data-group-id="2117621560-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">complex</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="5027920150-1">(</span><span class="n">X</span><span class="p" data-group-id="5027920150-1">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Here, the communication with C is hidden in the implementation of <code class="inline">complex.erl</code>.
│ │ │  In the following sections, it is shown how this module can be implemented using
│ │ │  the different interoperability mechanisms.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/expressions.html
│ │ │ @@ -151,81 +151,81 @@
│ │ │  </span><span class="n">Phone_number</span><span class="w">
│ │ │  </span><span class="p">_</span><span class="w">
│ │ │  </span><span class="p">_</span><span class="n">Height</span><span class="w">
│ │ │  </span><span class="ss">name@node</span></code></pre><p>Variables are bound to values using <a href="patterns.html">pattern matching</a>. Erlang uses
│ │ │  <em>single assignment</em>, that is, a variable can only be bound once.</p><p>The <em>anonymous variable</em> is denoted by underscore (_) and can be used when a
│ │ │  variable is required but its value can be ignored.</p><p><em>Example:</em></p><pre><code class="text">[H|_] = [1,2,3]</code></pre><p>Variables starting with underscore (<code class="inline">_</code>), for example, <code class="inline">_Height</code>, are normal
│ │ │  variables, not anonymous. However, they are ignored by the compiler in the sense
│ │ │ -that they do not generate warnings.</p><p><em>Example:</em></p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="4914246955-1">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4914246955-2">[</span><span class="p" data-group-id="4914246955-2">]</span><span class="p" data-group-id="4914246955-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4914246955-3">[</span><span class="p" data-group-id="4914246955-3">]</span><span class="p">.</span></code></pre><p>can be rewritten to be more readable:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="1246915081-1">(</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1246915081-2">[</span><span class="p" data-group-id="1246915081-2">]</span><span class="p" data-group-id="1246915081-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1246915081-3">[</span><span class="p" data-group-id="1246915081-3">]</span><span class="p">.</span></code></pre><p>This causes a warning for an unused variable, <code class="inline">Elem</code>. To avoid the warning,
│ │ │ -the code can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="4793001263-1">(</span><span class="p">_</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4793001263-2">[</span><span class="p" data-group-id="4793001263-2">]</span><span class="p" data-group-id="4793001263-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4793001263-3">[</span><span class="p" data-group-id="4793001263-3">]</span><span class="p">.</span></code></pre><p>Notice that since variables starting with an underscore are not anonymous, the
│ │ │ -following example matches:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2052062731-1">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2052062731-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2052062731-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2052062731-2">}</span></code></pre><p>But this example fails:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6322529973-1">{</span><span class="p">_</span><span class="n">N</span><span class="p">,</span><span class="p">_</span><span class="n">N</span><span class="p" data-group-id="6322529973-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6322529973-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6322529973-2">}</span></code></pre><p>The scope for a variable is its function clause. Variables bound in a branch of
│ │ │ +that they do not generate warnings.</p><p><em>Example:</em></p><p>The following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="2377950623-1">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2377950623-2">[</span><span class="p" data-group-id="2377950623-2">]</span><span class="p" data-group-id="2377950623-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2377950623-3">[</span><span class="p" data-group-id="2377950623-3">]</span><span class="p">.</span></code></pre><p>can be rewritten to be more readable:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="0819620250-1">(</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0819620250-2">[</span><span class="p" data-group-id="0819620250-2">]</span><span class="p" data-group-id="0819620250-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0819620250-3">[</span><span class="p" data-group-id="0819620250-3">]</span><span class="p">.</span></code></pre><p>This causes a warning for an unused variable, <code class="inline">Elem</code>. To avoid the warning,
│ │ │ +the code can be rewritten to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">member</span><span class="p" data-group-id="6175705174-1">(</span><span class="p">_</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6175705174-2">[</span><span class="p" data-group-id="6175705174-2">]</span><span class="p" data-group-id="6175705174-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6175705174-3">[</span><span class="p" data-group-id="6175705174-3">]</span><span class="p">.</span></code></pre><p>Notice that since variables starting with an underscore are not anonymous, the
│ │ │ +following example matches:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9411431925-1">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9411431925-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9411431925-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9411431925-2">}</span></code></pre><p>But this example fails:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9229891307-1">{</span><span class="p">_</span><span class="n">N</span><span class="p">,</span><span class="p">_</span><span class="n">N</span><span class="p" data-group-id="9229891307-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9229891307-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="9229891307-2">}</span></code></pre><p>The scope for a variable is its function clause. Variables bound in a branch of
│ │ │  an <code class="inline">if</code>, <code class="inline">case</code>, or <code class="inline">receive</code> expression must be bound in all branches to have a
│ │ │  value outside the expression. Otherwise they are regarded as unsafe outside
│ │ │  the expression.</p><p>For the <code class="inline">try</code> expression variable scoping is limited so that variables bound in
│ │ │  the expression are always unsafe outside the expression.</p><h2 id="patterns" class="section-heading">
│ │ │    <a href="#patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Patterns</span>
│ │ │  </h2>
│ │ │  <p>A pattern has the same structure as a term but can contain unbound variables.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">Name1</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3656412274-1">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3656412274-1">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3656412274-2">{</span><span class="ss">error</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="3656412274-2">}</span></code></pre><p>Patterns are allowed in clause heads, <a href="expressions.html#case">case expressions</a>,
│ │ │ +</span><span class="p" data-group-id="7813056331-1">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7813056331-1">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7813056331-2">{</span><span class="ss">error</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="7813056331-2">}</span></code></pre><p>Patterns are allowed in clause heads, <a href="expressions.html#case">case expressions</a>,
│ │ │  <a href="expressions.html#receive">receive expressions</a>, and
│ │ │  <a href="expressions.html#the-match-operator">match expressions</a>.</p><h3 id="the-compound-pattern-operator" class="section-heading">
│ │ │    <a href="#the-compound-pattern-operator" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The Compound Pattern Operator</span>
│ │ │  </h3>
│ │ │  <p>If <code class="inline">Pattern1</code> and <code class="inline">Pattern2</code> are valid patterns, the following is also a valid
│ │ │  pattern:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Pattern2</span></code></pre><p>When matched against a term, both <code class="inline">Pattern1</code> and <code class="inline">Pattern2</code> are matched against
│ │ │ -the term. The idea behind this feature is to avoid reconstruction of terms.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="1986921391-1">(</span><span class="p" data-group-id="1986921391-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="1986921391-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="1986921391-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Signal</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1986921391-3">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="1986921391-3">}</span><span class="p">,</span><span class="w">
│ │ │ +the term. The idea behind this feature is to avoid reconstruction of terms.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4472580237-1">(</span><span class="p" data-group-id="4472580237-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="4472580237-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="4472580237-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Signal</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4472580237-3">{</span><span class="ss">connect</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="n">Number</span><span class="p">,</span><span class="n">Options</span><span class="p" data-group-id="4472580237-3">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="1986921391-4">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="1986921391-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>can instead be written as</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="6696331267-1">(</span><span class="p" data-group-id="6696331267-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6696331267-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6696331267-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="4472580237-4">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="4472580237-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>can instead be written as</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="6576938854-1">(</span><span class="p" data-group-id="6576938854-2">{</span><span class="ss">connect</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="n">To</span><span class="p">,</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6576938854-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6576938854-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="6696331267-3">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6696331267-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="6576938854-3">(</span><span class="n">Signal</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="6576938854-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ignore</span><span class="p">.</span></code></pre><p>The compound pattern operator does not imply that its operands are matched in
│ │ │  any particular order. That means that it is not legal to bind a variable in
│ │ │  <code class="inline">Pattern1</code> and use it in <code class="inline">Pattern2</code>, or vice versa.</p><h3 id="string-prefix-in-patterns" class="section-heading">
│ │ │    <a href="#string-prefix-in-patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">String Prefix in Patterns</span>
│ │ │  </h3>
│ │ │ -<p>When matching strings, the following is a valid pattern:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="7635344548-1">(</span><span class="s">&quot;prefix&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="7635344548-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This is syntactic sugar for the equivalent, but harder to read:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="0710228809-1">(</span><span class="p" data-group-id="0710228809-2">[</span><span class="sc">$p</span><span class="p">,</span><span class="sc">$r</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$f</span><span class="p">,</span><span class="sc">$i</span><span class="p">,</span><span class="sc">$x</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="0710228809-2">]</span><span class="p" data-group-id="0710228809-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h3 id="expressions-in-patterns" class="section-heading">
│ │ │ +<p>When matching strings, the following is a valid pattern:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="7894285664-1">(</span><span class="s">&quot;prefix&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="7894285664-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This is syntactic sugar for the equivalent, but harder to read:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="7510316130-1">(</span><span class="p" data-group-id="7510316130-2">[</span><span class="sc">$p</span><span class="p">,</span><span class="sc">$r</span><span class="p">,</span><span class="sc">$e</span><span class="p">,</span><span class="sc">$f</span><span class="p">,</span><span class="sc">$i</span><span class="p">,</span><span class="sc">$x</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Str</span><span class="p" data-group-id="7510316130-2">]</span><span class="p" data-group-id="7510316130-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h3 id="expressions-in-patterns" class="section-heading">
│ │ │    <a href="#expressions-in-patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Expressions in Patterns</span>
│ │ │  </h3>
│ │ │  <p>An arithmetic expression can be used within a pattern if it meets both of the
│ │ │ -following two conditions:</p><ul><li>It uses only numeric or bitwise operators.</li><li>Its value can be evaluated to a constant when complied.</li></ul><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="p" data-group-id="8021499646-1">{</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="8021499646-1">}</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8021499646-2">{</span><span class="o">?</span><span class="n">THRESHOLD</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="8021499646-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="the-match-operator" class="section-heading">
│ │ │ +following two conditions:</p><ul><li>It uses only numeric or bitwise operators.</li><li>Its value can be evaluated to a constant when complied.</li></ul><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="p" data-group-id="7082253164-1">{</span><span class="n">Value</span><span class="p">,</span><span class="w"> </span><span class="n">Result</span><span class="p" data-group-id="7082253164-1">}</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7082253164-2">{</span><span class="o">?</span><span class="n">THRESHOLD</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="7082253164-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="the-match-operator" class="section-heading">
│ │ │    <a href="#the-match-operator" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The Match Operator</span>
│ │ │  </h2>
│ │ │  <p>The following matches <code class="inline">Pattern</code> against <code class="inline">Expr</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>If the matching succeeds, any unbound variable in the pattern becomes bound and
│ │ │  the value of <code class="inline">Expr</code> is returned.</p><p>If multiple match operators are applied in sequence, they will be evaluated from
│ │ │ -right to left.</p><p>If the matching fails, a <code class="inline">badmatch</code> run-time error occurs.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6457815561-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="6457815561-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6457815561-2">{</span><span class="ss">answer</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="6457815561-2">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6457815561-3">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6457815561-3">}</span><span class="w">
│ │ │ +right to left.</p><p>If the matching fails, a <code class="inline">badmatch</code> run-time error occurs.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2556414109-1">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2556414109-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2556414109-2">{</span><span class="ss">answer</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="2556414109-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2556414109-3">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="2556414109-3">}</span><span class="w">
│ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">answer</span><span class="w">
│ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="w">
│ │ │  </span><span class="gp unselectable">4&gt; </span><span class="n">T</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6457815561-4">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6457815561-4">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="6457815561-5">{</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="6457815561-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6457815561-6">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6457815561-6">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2556414109-4">{</span><span class="ss">answer</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="2556414109-4">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="2556414109-5">{</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="2556414109-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2556414109-6">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2556414109-6">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right-hand side value [1,2]</span></code></pre><p>Because multiple match operators are evaluated from right to left, it means
│ │ │  that:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Pattern2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">PatternN</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expression</span></code></pre><p>is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="n">Temporary</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expression</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">PatternN</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Temporary</span><span class="p">,</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">Pattern2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Temporary</span><span class="p">,</span><span class="w">
│ │ │ @@ -239,30 +239,30 @@
│ │ │  can safely be skipped on a first reading.</p></section><p>The <code class="inline">=</code> character is used to denote two similar but distinct operators: the
│ │ │  match operator and the compound pattern operator. Which one is meant is
│ │ │  determined by context.</p><p>The <em>compound pattern operator</em> is used to construct a compound pattern from two
│ │ │  patterns. Compound patterns are accepted everywhere a pattern is accepted. A
│ │ │  compound pattern matches if all of its constituent patterns match. It is not
│ │ │  legal for a pattern that is part of a compound pattern to use variables (as keys
│ │ │  in map patterns or sizes in binary patterns) bound in other sub patterns of the
│ │ │ -same compound pattern.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">fun</span><span class="p" data-group-id="4419444436-1">(</span><span class="p" data-group-id="4419444436-2">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="4419444436-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4419444436-3">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="4419444436-3">}</span><span class="p" data-group-id="4419444436-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +same compound pattern.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">fun</span><span class="p" data-group-id="0449026677-1">(</span><span class="p" data-group-id="0449026677-2">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="0449026677-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0449026677-3">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="0449026677-3">}</span><span class="p" data-group-id="0449026677-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">* 1:7: variable &#39;Key&#39; is unbound</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4419444436-4">(</span><span class="p" data-group-id="4419444436-5">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4419444436-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="4419444436-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4419444436-6">{</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4419444436-6">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="4419444436-7">(</span><span class="p" data-group-id="4419444436-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4419444436-8">}</span><span class="p" data-group-id="4419444436-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4419444436-9">{</span><span class="p" data-group-id="4419444436-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4419444436-10">}</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4419444436-9">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="n">G</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4419444436-11">(</span><span class="p" data-group-id="4419444436-12">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">B</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="4419444436-12">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4419444436-13">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="4419444436-13">&gt;&gt;</span><span class="p" data-group-id="4419444436-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4419444436-14">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="4419444436-14">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">G</span><span class="p" data-group-id="4419444436-15">(</span><span class="p" data-group-id="4419444436-16">&lt;&lt;</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p" data-group-id="4419444436-16">&gt;&gt;</span><span class="p" data-group-id="4419444436-15">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4419444436-17">{</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p">,</span><span class="mi">10795</span><span class="p" data-group-id="4419444436-17">}</span></code></pre><p>The <em>match operator</em> is allowed everywhere an expression is allowed. It is used
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0449026677-4">(</span><span class="p" data-group-id="0449026677-5">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="0449026677-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">E</span><span class="p" data-group-id="0449026677-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0449026677-6">{</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="0449026677-6">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="0449026677-7">(</span><span class="p" data-group-id="0449026677-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0449026677-8">}</span><span class="p" data-group-id="0449026677-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0449026677-9">{</span><span class="p" data-group-id="0449026677-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0449026677-10">}</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0449026677-9">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="n">G</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0449026677-11">(</span><span class="p" data-group-id="0449026677-12">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="n">B</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0449026677-12">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0449026677-13">&lt;&lt;</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="0449026677-13">&gt;&gt;</span><span class="p" data-group-id="0449026677-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0449026677-14">{</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="0449026677-14">}</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">G</span><span class="p" data-group-id="0449026677-15">(</span><span class="p" data-group-id="0449026677-16">&lt;&lt;</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p" data-group-id="0449026677-16">&gt;&gt;</span><span class="p" data-group-id="0449026677-15">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0449026677-17">{</span><span class="mi">42</span><span class="p">,</span><span class="mi">43</span><span class="p">,</span><span class="mi">10795</span><span class="p" data-group-id="0449026677-17">}</span></code></pre><p>The <em>match operator</em> is allowed everywhere an expression is allowed. It is used
│ │ │  to match the value of an expression to a pattern. If multiple match operators
│ │ │ -are applied in sequence, they will be evaluated from right to left.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0217256417-1">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="0217256417-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0217256417-2">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="0217256417-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">f</span><span class="p" data-group-id="0217256417-3">(</span><span class="n">Key</span><span class="p" data-group-id="0217256417-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0217256417-4">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="0217256417-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0217256417-5">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="0217256417-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ +are applied in sequence, they will be evaluated from right to left.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9777053342-1">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="w"> </span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="9777053342-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9777053342-2">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">key2</span><span class="p">,</span><span class="ss">key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">value</span><span class="p" data-group-id="9777053342-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">f</span><span class="p" data-group-id="9777053342-3">(</span><span class="n">Key</span><span class="p" data-group-id="9777053342-3">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9777053342-4">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9777053342-4">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9777053342-5">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9777053342-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">value</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nf">f</span><span class="p" data-group-id="0217256417-6">(</span><span class="n">Key</span><span class="p" data-group-id="0217256417-6">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0217256417-7">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="0217256417-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0217256417-8">(</span><span class="p" data-group-id="0217256417-9">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="0217256417-9">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="0217256417-8">)</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nf">f</span><span class="p" data-group-id="9777053342-6">(</span><span class="n">Key</span><span class="p" data-group-id="9777053342-6">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9777053342-7">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9777053342-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9777053342-8">(</span><span class="p" data-group-id="9777053342-9">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9777053342-9">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p" data-group-id="9777053342-8">)</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">value</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nf">f</span><span class="p" data-group-id="0217256417-10">(</span><span class="n">Key</span><span class="p" data-group-id="0217256417-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0217256417-11">(</span><span class="p" data-group-id="0217256417-12">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="0217256417-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0217256417-13">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="0217256417-13">}</span><span class="p" data-group-id="0217256417-11">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nf">f</span><span class="p" data-group-id="9777053342-10">(</span><span class="n">Key</span><span class="p" data-group-id="9777053342-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9777053342-11">(</span><span class="p" data-group-id="9777053342-12">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="9777053342-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9777053342-13">#{</span><span class="ss">key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="9777053342-13">}</span><span class="p" data-group-id="9777053342-11">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="n">Value</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">* 1:12: variable &#39;Key&#39; is unbound</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="0217256417-14">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">Y</span><span class="p" data-group-id="0217256417-14">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">begin</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0217256417-15">&lt;&lt;</span><span class="mi">42</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0217256417-15">&gt;&gt;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="9777053342-14">&lt;&lt;</span><span class="n">X</span><span class="p">:</span><span class="n">Y</span><span class="p" data-group-id="9777053342-14">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">begin</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9777053342-15">&lt;&lt;</span><span class="mi">42</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="9777053342-15">&gt;&gt;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span></code></pre><p>The expression at prompt <code class="inline">2&gt;</code> first matches the value of variable <code class="inline">M</code> against
│ │ │  pattern <code class="inline">#{key := Key}</code>, binding variable <code class="inline">Key</code>. It then matches the value of
│ │ │  <code class="inline">M</code> against pattern <code class="inline">#{Key := Value}</code> using variable <code class="inline">Key</code> as the key, binding
│ │ │  variable <code class="inline">Value</code>.</p><p>The expression at prompt <code class="inline">3&gt;</code> matches expression <code class="inline">(#{key := Key} = M)</code> against
│ │ │  pattern <code class="inline">#{Key := Value}</code>. The expression inside the parentheses is evaluated
│ │ │  first. That is, <code class="inline">M</code> is matched against <code class="inline">#{key := Key}</code>, and then the value of
│ │ │  <code class="inline">M</code> is matched against pattern <code class="inline">#{Key := Value}</code>. That is the same evaluation
│ │ │ @@ -276,30 +276,30 @@
│ │ │  binding variable <code class="inline">Y</code> and creating a binary. The binary is then matched against
│ │ │  pattern <code class="inline">&lt;&lt;X:Y&gt;&gt;</code> using the value of <code class="inline">Y</code> as the size of the segment.</p><h2 id="function-calls" class="section-heading">
│ │ │    <a href="#function-calls" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Function Calls</span>
│ │ │  </h2>
│ │ │ -<pre><code class="makeup erlang" translate="no"><span class="n">ExprF</span><span class="p" data-group-id="0224864303-1">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="0224864303-1">)</span><span class="w">
│ │ │ -</span><span class="n">ExprM</span><span class="p">:</span><span class="n">ExprF</span><span class="p" data-group-id="0224864303-2">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="0224864303-2">)</span></code></pre><p>In the first form of function calls, <code class="inline">ExprM:ExprF(Expr1,...,ExprN)</code>, each of
│ │ │ +<pre><code class="makeup erlang" translate="no"><span class="n">ExprF</span><span class="p" data-group-id="2904325784-1">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="2904325784-1">)</span><span class="w">
│ │ │ +</span><span class="n">ExprM</span><span class="p">:</span><span class="n">ExprF</span><span class="p" data-group-id="2904325784-2">(</span><span class="n">Expr1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ExprN</span><span class="p" data-group-id="2904325784-2">)</span></code></pre><p>In the first form of function calls, <code class="inline">ExprM:ExprF(Expr1,...,ExprN)</code>, each of
│ │ │  <code class="inline">ExprM</code> and <code class="inline">ExprF</code> must be an atom or an expression that evaluates to an atom.
│ │ │  The function is said to be called by using the <em>fully qualified function name</em>.
│ │ │ -This is often referred to as a <em>remote</em> or <em>external function call</em>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="9328842667-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9328842667-1">)</span></code></pre><p>In the second form of function calls, <code class="inline">ExprF(Expr1,...,ExprN)</code>, <code class="inline">ExprF</code> must be
│ │ │ +This is often referred to as a <em>remote</em> or <em>external function call</em>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="1739725770-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1739725770-1">)</span></code></pre><p>In the second form of function calls, <code class="inline">ExprF(Expr1,...,ExprN)</code>, <code class="inline">ExprF</code> must be
│ │ │  an atom or evaluate to a fun.</p><p>If <code class="inline">ExprF</code> is an atom, the function is said to be called by using the
│ │ │  <em>implicitly qualified function name</em>. If the function <code class="inline">ExprF</code> is locally
│ │ │  defined, it is called. Alternatively, if <code class="inline">ExprF</code> is explicitly imported from the
│ │ │  <code class="inline">M</code> module, <code class="inline">M:ExprF(Expr1,...,ExprN)</code> is called. If <code class="inline">ExprF</code> is neither declared
│ │ │  locally nor explicitly imported, <code class="inline">ExprF</code> must be the name of an automatically
│ │ │ -imported BIF.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="5204221646-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5204221646-1">)</span><span class="w">
│ │ │ -</span><span class="nf">spawn</span><span class="p" data-group-id="5204221646-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5204221646-3">[</span><span class="p" data-group-id="5204221646-3">]</span><span class="p" data-group-id="5204221646-2">)</span></code></pre><p><em>Examples</em> where <code class="inline">ExprF</code> is a fun:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0958164159-1">(</span><span class="n">X</span><span class="p" data-group-id="0958164159-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Fun1</span><span class="p" data-group-id="0958164159-2">(</span><span class="mi">3</span><span class="p" data-group-id="0958164159-2">)</span><span class="p">.</span><span class="w">
│ │ │ +imported BIF.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="5502282351-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5502282351-1">)</span><span class="w">
│ │ │ +</span><span class="nf">spawn</span><span class="p" data-group-id="5502282351-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5502282351-3">[</span><span class="p" data-group-id="5502282351-3">]</span><span class="p" data-group-id="5502282351-2">)</span></code></pre><p><em>Examples</em> where <code class="inline">ExprF</code> is a fun:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="0003741352-1">(</span><span class="n">X</span><span class="p" data-group-id="0003741352-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Fun1</span><span class="p" data-group-id="0003741352-2">(</span><span class="mi">3</span><span class="p" data-group-id="0003741352-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="k">fun</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="ss">append</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0958164159-3">(</span><span class="p" data-group-id="0958164159-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0958164159-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0958164159-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0958164159-5">]</span><span class="p" data-group-id="0958164159-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0958164159-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0958164159-6">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="k">fun</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="ss">append</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0003741352-3">(</span><span class="p" data-group-id="0003741352-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0003741352-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0003741352-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0003741352-5">]</span><span class="p" data-group-id="0003741352-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0003741352-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0003741352-6">]</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="o">&gt;</span></code></pre><p>Notice that when calling a local function, there is a difference between using
│ │ │  the implicitly or fully qualified function name. The latter always refers to the
│ │ │  latest version of the module. See
│ │ │  <a href="code_loading.html">Compilation and Code Loading </a>and
│ │ │  <a href="ref_man_functions.html#eval">Function Evaluation</a>.</p><h3 id="local-function-names-clashing-with-auto-imported-bifs" class="section-heading">
│ │ │    <a href="#local-function-names-clashing-with-auto-imported-bifs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -316,40 +316,40 @@
│ │ │  called instead. This is to avoid that future additions to the set of
│ │ │  auto-imported BIFs do not silently change the behavior of old code.</p></section><p>However, to avoid that old (pre R14) code changed its behavior when compiled
│ │ │  with Erlang/OTP version R14A or later, the following restriction applies: If you
│ │ │  override the name of a BIF that was auto-imported in OTP versions prior to R14A
│ │ │  (ERTS version 5.8) and have an implicitly qualified call to that function in
│ │ │  your code, you either need to explicitly remove the auto-import using a compiler
│ │ │  directive, or replace the call with a fully qualified function call. Otherwise
│ │ │ -you get a compilation error. See the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7810803699-1">(</span><span class="p" data-group-id="7810803699-2">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7810803699-2">]</span><span class="p" data-group-id="7810803699-1">)</span><span class="p">.</span><span class="w">
│ │ │ +you get a compilation error. See the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7313633078-1">(</span><span class="p" data-group-id="7313633078-2">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7313633078-2">]</span><span class="p" data-group-id="7313633078-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="7810803699-3">(</span><span class="p" data-group-id="7810803699-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="7810803699-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7810803699-5">]</span><span class="p" data-group-id="7810803699-4">}</span><span class="p" data-group-id="7810803699-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="7313633078-3">(</span><span class="p" data-group-id="7313633078-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="7313633078-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7313633078-5">]</span><span class="p" data-group-id="7313633078-4">}</span><span class="p" data-group-id="7313633078-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">length</span><span class="p" data-group-id="7810803699-6">(</span><span class="p" data-group-id="7810803699-7">[</span><span class="p" data-group-id="7810803699-7">]</span><span class="p" data-group-id="7810803699-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">length</span><span class="p" data-group-id="7313633078-6">(</span><span class="p" data-group-id="7313633078-7">[</span><span class="p" data-group-id="7313633078-7">]</span><span class="p" data-group-id="7313633078-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">length</span><span class="p" data-group-id="7810803699-8">(</span><span class="p" data-group-id="7810803699-9">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7810803699-9">]</span><span class="p" data-group-id="7810803699-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7810803699-10">(</span><span class="n">T</span><span class="p" data-group-id="7810803699-10">)</span><span class="p">.</span><span class="w"> </span><span class="c1">%% Calls the local function length/1</span><span class="w">
│ │ │ +</span><span class="nf">length</span><span class="p" data-group-id="7313633078-8">(</span><span class="p" data-group-id="7313633078-9">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7313633078-9">]</span><span class="p" data-group-id="7313633078-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7313633078-10">(</span><span class="n">T</span><span class="p" data-group-id="7313633078-10">)</span><span class="p">.</span><span class="w"> </span><span class="c1">%% Calls the local function length/1</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="7810803699-11">(</span><span class="n">X</span><span class="p" data-group-id="7810803699-11">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="7810803699-12">(</span><span class="n">X</span><span class="p" data-group-id="7810803699-12">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="7313633078-11">(</span><span class="n">X</span><span class="p" data-group-id="7313633078-11">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="7313633078-12">(</span><span class="n">X</span><span class="p" data-group-id="7313633078-12">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │                                    </span><span class="c1">%% which is allowed in guards</span><span class="w">
│ │ │      </span><span class="ss">long</span><span class="p">.</span></code></pre><p>The same logic applies to explicitly imported functions from other modules, as
│ │ │  to locally defined functions. It is not allowed to both import a function from
│ │ │ -another module and have the function declared in the module at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0041170120-1">(</span><span class="p" data-group-id="0041170120-2">[</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0041170120-2">]</span><span class="p" data-group-id="0041170120-1">)</span><span class="p">.</span><span class="w">
│ │ │ +another module and have the function declared in the module at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6737014139-1">(</span><span class="p" data-group-id="6737014139-2">[</span><span class="ss">f</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6737014139-2">]</span><span class="p" data-group-id="6737014139-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="0041170120-3">(</span><span class="p" data-group-id="0041170120-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="0041170120-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0041170120-5">]</span><span class="p" data-group-id="0041170120-4">}</span><span class="p" data-group-id="0041170120-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="6737014139-3">(</span><span class="p" data-group-id="6737014139-4">{</span><span class="ss">no_auto_import</span><span class="p">,</span><span class="p" data-group-id="6737014139-5">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6737014139-5">]</span><span class="p" data-group-id="6737014139-4">}</span><span class="p" data-group-id="6737014139-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% erlang:length/1 no longer autoimported</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="0041170120-6">(</span><span class="ss">mod</span><span class="p">,</span><span class="p" data-group-id="0041170120-7">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0041170120-7">]</span><span class="p" data-group-id="0041170120-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="6737014139-6">(</span><span class="ss">mod</span><span class="p">,</span><span class="p" data-group-id="6737014139-7">[</span><span class="nb">length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6737014139-7">]</span><span class="p" data-group-id="6737014139-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="0041170120-8">(</span><span class="n">X</span><span class="p" data-group-id="0041170120-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="0041170120-9">(</span><span class="n">X</span><span class="p" data-group-id="0041170120-9">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">33</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="6737014139-8">(</span><span class="n">X</span><span class="p" data-group-id="6737014139-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="6737014139-9">(</span><span class="n">X</span><span class="p" data-group-id="6737014139-9">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">33</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">%% Calls erlang:length/1,</span><span class="w">
│ │ │                                     </span><span class="c1">%% which is allowed in guards</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="0041170120-10">(</span><span class="n">X</span><span class="p" data-group-id="0041170120-10">)</span><span class="p">;</span><span class="w">              </span><span class="c1">%% Explicit call to erlang:length in body</span><span class="w">
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">length</span><span class="p" data-group-id="6737014139-10">(</span><span class="n">X</span><span class="p" data-group-id="6737014139-10">)</span><span class="p">;</span><span class="w">              </span><span class="c1">%% Explicit call to erlang:length in body</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="0041170120-11">(</span><span class="n">X</span><span class="p" data-group-id="0041170120-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">length</span><span class="p" data-group-id="0041170120-12">(</span><span class="n">X</span><span class="p" data-group-id="0041170120-12">)</span><span class="p">.</span><span class="w">                     </span><span class="c1">%% mod:length/1 is called</span></code></pre><p>For auto-imported BIFs added in Erlang/OTP R14A and thereafter, overriding the
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="6737014139-11">(</span><span class="n">X</span><span class="p" data-group-id="6737014139-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">length</span><span class="p" data-group-id="6737014139-12">(</span><span class="n">X</span><span class="p" data-group-id="6737014139-12">)</span><span class="p">.</span><span class="w">                     </span><span class="c1">%% mod:length/1 is called</span></code></pre><p>For auto-imported BIFs added in Erlang/OTP R14A and thereafter, overriding the
│ │ │  name with a local function or explicit import is always allowed. However, if the
│ │ │  <code class="inline">-compile({no_auto_import,[F/A])</code> directive is not used, the compiler issues a
│ │ │  warning whenever the function is called in the module using the implicitly
│ │ │  qualified function name.</p><h2 id="if" class="section-heading">
│ │ │    <a href="#if" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -361,40 +361,40 @@
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">GuardSeqN</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The branches of an <code class="inline">if</code>-expression are scanned sequentially until a guard
│ │ │  sequence <code class="inline">GuardSeq</code> that evaluates to true is found. Then the corresponding
│ │ │  <code class="inline">Body</code> (a sequence of expressions separated by <code class="inline">,</code>) is evaluated.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">if</code> expression.</p><p>If no guard sequence is evaluated as true, an <code class="inline">if_clause</code> run-time error occurs.
│ │ │  If necessary, the guard expression <code class="inline">true</code> can be used in the last branch, as
│ │ │ -that guard sequence is always true.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_greater_than</span><span class="p" data-group-id="8295947507-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8295947507-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +that guard sequence is always true.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_greater_than</span><span class="p" data-group-id="4141128502-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4141128502-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% works as an &#39;else&#39; branch</span><span class="w">
│ │ │              </span><span class="ss">false</span><span class="w">
│ │ │      </span><span class="k">end</span></code></pre><h2 id="case" class="section-heading">
│ │ │    <a href="#case" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Case</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">Expr</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="6331149350-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="6331149350-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="0832211110-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="0832211110-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="6331149350-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="6331149350-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="0832211110-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="0832211110-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The expression <code class="inline">Expr</code> is evaluated and the patterns <code class="inline">Pattern</code> are sequentially
│ │ │  matched against the result. If a match succeeds and the optional guard sequence
│ │ │  <code class="inline">GuardSeq</code> is true, the corresponding <code class="inline">Body</code> is evaluated.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">case</code> expression.</p><p>If there is no matching pattern with a true guard sequence, a <code class="inline">case_clause</code>
│ │ │ -run-time error occurs.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_valid_signal</span><span class="p" data-group-id="0547773469-1">(</span><span class="n">Signal</span><span class="p" data-group-id="0547773469-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +run-time error occurs.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_valid_signal</span><span class="p" data-group-id="9269407990-1">(</span><span class="n">Signal</span><span class="p" data-group-id="9269407990-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Signal</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0547773469-2">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="0547773469-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="9269407990-2">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="9269407990-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0547773469-3">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="0547773469-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="9269407990-3">{</span><span class="ss">signal</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">What</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">To</span><span class="p" data-group-id="9269407990-3">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">_</span><span class="n">Else</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">false</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="maybe" class="section-heading">
│ │ │    <a href="#maybe" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -412,57 +412,57 @@
│ │ │  the top-level of a <code class="inline">maybe</code> block. It matches the pattern <code class="inline">Expr1</code> against
│ │ │  <code class="inline">Expr2</code>. If the matching succeeds, any unbound variable in the pattern becomes
│ │ │  bound. If the expression is the last expression in the <code class="inline">maybe</code> block, it also
│ │ │  returns the value of <code class="inline">Expr2</code>. If the matching is unsuccessful, the rest of the
│ │ │  expressions in the <code class="inline">maybe</code> block are skipped and the return value of the <code class="inline">maybe</code>
│ │ │  block is <code class="inline">Expr2</code>.</p><p>None of the variables bound in a <code class="inline">maybe</code> block must be used in the code that
│ │ │  follows the block.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9298738735-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="9298738735-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="9298738735-2">(</span><span class="p" data-group-id="9298738735-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9461073627-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="9461073627-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="9461073627-2">(</span><span class="p" data-group-id="9461073627-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9298738735-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9298738735-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="9298738735-4">(</span><span class="p" data-group-id="9298738735-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9461073627-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="9461073627-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="9461073627-4">(</span><span class="p" data-group-id="9461073627-4">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>Let us first assume that <code class="inline">a()</code> returns <code class="inline">{ok,42}</code> and <code class="inline">b()</code> returns <code class="inline">{ok,58}</code>.
│ │ │  With those return values, all of the match operators will succeed, and the
│ │ │  return value of the <code class="inline">maybe</code> block is <code class="inline">A + B</code>, which is equal to <code class="inline">42 + 58 = 100</code>.</p><p>Now let us assume that <code class="inline">a()</code> returns <code class="inline">error</code>. The conditional match operator in
│ │ │  <code class="inline">{ok, A} ?= a()</code> fails to match, and the return value of the <code class="inline">maybe</code> block is
│ │ │  the value of the expression that failed to match, namely <code class="inline">error</code>. Similarly, if
│ │ │  <code class="inline">b()</code> returns <code class="inline">wrong</code>, the return value of the <code class="inline">maybe</code> block is <code class="inline">wrong</code>.</p><p>Finally, let us assume that <code class="inline">a()</code> returns <code class="inline">{ok,-1}</code>. Because <code class="inline">true = A &gt;= 0</code> uses
│ │ │  the match operator <code class="inline">=</code>, a <code class="inline">{badmatch,false}</code> run-time error occurs when the
│ │ │ -expression fails to match the pattern.</p><p>The example can be written in a less succient way using nested case expressions:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="4279210053-1">(</span><span class="p" data-group-id="4279210053-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4279210053-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="4279210053-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +expression fails to match the pattern.</p><p>The example can be written in a less succient way using nested case expressions:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="3838617637-1">(</span><span class="p" data-group-id="3838617637-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3838617637-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="3838617637-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="4279210053-3">(</span><span class="p" data-group-id="4279210053-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4279210053-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4279210053-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="3838617637-3">(</span><span class="p" data-group-id="3838617637-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="3838617637-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="3838617637-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="n">Other1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Other1</span><span class="w">
│ │ │          </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Other2</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Other2</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">maybe</code> block can be augmented with <code class="inline">else</code> clauses:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │      </span><span class="n">Expr1</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">ExprN</span><span class="w">
│ │ │  </span><span class="k">else</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="3330257173-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="3330257173-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="7749471981-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="7749471981-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="3330257173-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="3330257173-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="7749471981-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="7749471981-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>If a conditional match operator fails, the failed expression is matched against
│ │ │  the patterns in all clauses between the <code class="inline">else</code> and <code class="inline">end</code> keywords. If a match
│ │ │  succeeds and the optional guard sequence <code class="inline">GuardSeq</code> is true, the corresponding
│ │ │  <code class="inline">Body</code> is evaluated. The value returned from the body is the return value of the
│ │ │  <code class="inline">maybe</code> block.</p><p>If there is no matching pattern with a true guard sequence, an <code class="inline">else_clause</code>
│ │ │  run-time error occurs.</p><p>None of the variables bound in a <code class="inline">maybe</code> block must be used in the <code class="inline">else</code>
│ │ │  clauses. None of the variables bound in the <code class="inline">else</code> clauses must be used in the
│ │ │  code that follows the <code class="inline">maybe</code> block.</p><p>Here is the previous example augmented with <code class="inline">else</code> clauses:</p><pre><code class="makeup erlang" translate="no"><span class="k">maybe</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2296835622-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2296835622-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="2296835622-2">(</span><span class="p" data-group-id="2296835622-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7596544544-1">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="7596544544-1">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">a</span><span class="p" data-group-id="7596544544-2">(</span><span class="p" data-group-id="7596544544-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2296835622-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2296835622-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="2296835622-4">(</span><span class="p" data-group-id="2296835622-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7596544544-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="7596544544-3">}</span><span class="w"> </span><span class="o">?</span><span class="o">=</span><span class="w"> </span><span class="nf">b</span><span class="p" data-group-id="7596544544-4">(</span><span class="p" data-group-id="7596544544-4">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">A</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">B</span><span class="w">
│ │ │  </span><span class="k">else</span><span class="w">
│ │ │      </span><span class="ss">error</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">wrong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">else</code> clauses translate the failing value from the conditional match
│ │ │  operators to the value <code class="inline">error</code>. If the failing value is not one of the
│ │ │  recognized values, a <code class="inline">else_clause</code> run-time error occurs.</p><h2 id="send" class="section-heading">
│ │ │ @@ -481,75 +481,75 @@
│ │ │  <code class="inline">{Name,Node}</code> (or a pid located at another node), also never fails.</li></ul><h2 id="receive" class="section-heading">
│ │ │    <a href="#receive" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Receive</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="6623726572-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="6623726572-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="0652957583-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="0652957583-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="6623726572-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="6623726572-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="0652957583-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="0652957583-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>Fetches a received message present in the message queue of the process. The
│ │ │  first message in the message queue is matched sequentially against the patterns
│ │ │  from top to bottom. If no match was found, the matching sequence is repeated for
│ │ │  the second message in the queue, and so on. Messages are queued in the
│ │ │  <a href="ref_man_processes.html#message-queue-order">order they were received</a>. If a match
│ │ │  succeeds, that is, if the <code class="inline">Pattern</code> matches and the optional guard sequence
│ │ │  <code class="inline">GuardSeq</code> is true, then the message is removed from the message queue and the
│ │ │  corresponding <code class="inline">Body</code> is evaluated. All other messages in the message queue
│ │ │  remain unchanged.</p><p>The return value of <code class="inline">Body</code> is the return value of the <code class="inline">receive</code> expression.</p><p><code class="inline">receive</code> never fails. The execution is suspended, possibly indefinitely, until
│ │ │  a message arrives that matches one of the patterns and with a true guard
│ │ │ -sequence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="2959729543-1">(</span><span class="p" data-group-id="2959729543-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +sequence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="7052149412-1">(</span><span class="p" data-group-id="7052149412-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">onhook</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="2959729543-2">(</span><span class="p" data-group-id="2959729543-2">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">idle</span><span class="p" data-group-id="2959729543-3">(</span><span class="p" data-group-id="2959729543-3">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2959729543-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="2959729543-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2959729543-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2959729543-6">(</span><span class="p" data-group-id="2959729543-6">)</span><span class="p" data-group-id="2959729543-5">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="2959729543-7">(</span><span class="p" data-group-id="2959729543-7">)</span><span class="w">
│ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="7052149412-2">(</span><span class="p" data-group-id="7052149412-2">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">idle</span><span class="p" data-group-id="7052149412-3">(</span><span class="p" data-group-id="7052149412-3">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7052149412-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="7052149412-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7052149412-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7052149412-6">(</span><span class="p" data-group-id="7052149412-6">)</span><span class="p" data-group-id="7052149412-5">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="7052149412-7">(</span><span class="p" data-group-id="7052149412-7">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The <code class="inline">receive</code> expression can be augmented with a timeout:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="3482637261-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="3482637261-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="5463799135-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="5463799135-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="3482637261-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="3482637261-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="5463799135-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="5463799135-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w">
│ │ │      </span><span class="n">ExprT</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyT</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p><code class="inline">receive...after</code> works exactly as <code class="inline">receive</code>, except that if no matching message
│ │ │  has arrived within <code class="inline">ExprT</code> milliseconds, then <code class="inline">BodyT</code> is evaluated instead. The
│ │ │  return value of <code class="inline">BodyT</code> then becomes the return value of the <code class="inline">receive...after</code>
│ │ │  expression. <code class="inline">ExprT</code> is to evaluate to an integer, or the atom <code class="inline">infinity</code>. The
│ │ │  allowed integer range is from 0 to 4294967295, that is, the longest possible
│ │ │  timeout is almost 50 days. With a zero value the timeout occurs immediately if
│ │ │  there is no matching message in the message queue.</p><p>The atom <code class="inline">infinity</code> will make the process wait indefinitely for a matching
│ │ │  message. This is the same as not using a timeout. It can be useful for timeout
│ │ │ -values that are calculated at runtime.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="4655190276-1">(</span><span class="p" data-group-id="4655190276-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +values that are calculated at runtime.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">wait_for_onhook</span><span class="p" data-group-id="1906628650-1">(</span><span class="p" data-group-id="1906628650-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">onhook</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="4655190276-2">(</span><span class="p" data-group-id="4655190276-2">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">idle</span><span class="p" data-group-id="4655190276-3">(</span><span class="p" data-group-id="4655190276-3">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4655190276-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="4655190276-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4655190276-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4655190276-6">(</span><span class="p" data-group-id="4655190276-6">)</span><span class="p" data-group-id="4655190276-5">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="4655190276-7">(</span><span class="p" data-group-id="4655190276-7">)</span><span class="w">
│ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="1906628650-2">(</span><span class="p" data-group-id="1906628650-2">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">idle</span><span class="p" data-group-id="1906628650-3">(</span><span class="p" data-group-id="1906628650-3">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="1906628650-4">{</span><span class="ss">connect</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="1906628650-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">B</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1906628650-5">{</span><span class="ss">busy</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1906628650-6">(</span><span class="p" data-group-id="1906628650-6">)</span><span class="p" data-group-id="1906628650-5">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">wait_for_onhook</span><span class="p" data-group-id="1906628650-7">(</span><span class="p" data-group-id="1906628650-7">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w">
│ │ │          </span><span class="mi">60000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">disconnect</span><span class="p" data-group-id="4655190276-8">(</span><span class="p" data-group-id="4655190276-8">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">error</span><span class="p" data-group-id="4655190276-9">(</span><span class="p" data-group-id="4655190276-9">)</span><span class="w">
│ │ │ +            </span><span class="nf">disconnect</span><span class="p" data-group-id="1906628650-8">(</span><span class="p" data-group-id="1906628650-8">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">error</span><span class="p" data-group-id="1906628650-9">(</span><span class="p" data-group-id="1906628650-9">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>It is legal to use a <code class="inline">receive...after</code> expression with no branches:</p><pre><code class="makeup erlang" translate="no"><span class="k">receive</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w">
│ │ │      </span><span class="n">ExprT</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyT</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>This construction does not consume any messages, only suspends execution in the
│ │ │ -process for <code class="inline">ExprT</code> milliseconds. This can be used to implement simple timers.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">timer</span><span class="p" data-group-id="7332169674-1">(</span><span class="p" data-group-id="7332169674-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="7332169674-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7332169674-3">[</span><span class="nf">self</span><span class="p" data-group-id="7332169674-4">(</span><span class="p" data-group-id="7332169674-4">)</span><span class="p" data-group-id="7332169674-3">]</span><span class="p" data-group-id="7332169674-2">)</span><span class="p">.</span><span class="w">
│ │ │ +process for <code class="inline">ExprT</code> milliseconds. This can be used to implement simple timers.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">timer</span><span class="p" data-group-id="3774213518-1">(</span><span class="p" data-group-id="3774213518-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="3774213518-2">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3774213518-3">[</span><span class="nf">self</span><span class="p" data-group-id="3774213518-4">(</span><span class="p" data-group-id="3774213518-4">)</span><span class="p" data-group-id="3774213518-3">]</span><span class="p" data-group-id="3774213518-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">timer</span><span class="p" data-group-id="7332169674-5">(</span><span class="n">Pid</span><span class="p" data-group-id="7332169674-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">timer</span><span class="p" data-group-id="3774213518-5">(</span><span class="n">Pid</span><span class="p" data-group-id="3774213518-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w">
│ │ │          </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">timeout</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>For more information on timers in Erlang in general, see the
│ │ │  <a href="../../erts-15.2.7.8/doc/html/time_correction.html#timers"><em>Timers</em></a> section of the
│ │ │  <a href="../../erts-15.2.7.8/doc/html/time_correction.html"><em>Time and Time Correction in Erlang</em></a>
│ │ │ @@ -591,21 +591,21 @@
│ │ │  </span><span class="ss">false</span><span class="w">
│ │ │  </span><span class="gp unselectable">4&gt; </span><span class="mf">0.0</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">-</span><span class="mf">0.0</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="w">
│ │ │  </span><span class="gp unselectable">5&gt; </span><span class="mf">0.0</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">+</span><span class="mf">0.0</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │  </span><span class="gp unselectable">6&gt; </span><span class="mi">1</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="p" data-group-id="1533803803-1">#{</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1533803803-1">}</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="1533803803-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1533803803-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="p" data-group-id="2146833999-1">#{</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2146833999-1">}</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="2146833999-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2146833999-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ -</span><span class="gp unselectable">8&gt; </span><span class="p" data-group-id="1533803803-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1533803803-3">}</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="p" data-group-id="1533803803-4">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">2.0</span><span class="p" data-group-id="1533803803-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">8&gt; </span><span class="p" data-group-id="2146833999-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2146833999-3">}</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="p" data-group-id="2146833999-4">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">2.0</span><span class="p" data-group-id="2146833999-4">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="p" data-group-id="1533803803-5">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="1533803803-5">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="1533803803-6">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="1533803803-6">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="p" data-group-id="2146833999-5">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="2146833999-5">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="2146833999-6">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="2146833999-6">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="p" data-group-id="1533803803-7">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="1533803803-7">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="1533803803-8">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="1533803803-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="p" data-group-id="2146833999-7">&lt;&lt;</span><span class="mi">3</span><span class="p">:</span><span class="mi">2</span><span class="p" data-group-id="2146833999-7">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="p" data-group-id="2146833999-8">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="2146833999-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Prior to OTP 27, the term equivalence operators considered <code class="inline">0.0</code>
│ │ │  and <code class="inline">-0.0</code> to be the same term.</p><p>This was changed in OTP 27 but legacy code may have expected them to be
│ │ │  considered the same. To help users catch errors that may arise from an
│ │ │  upgrade, the compiler raises a warning when <code class="inline">0.0</code> is pattern-matched or used
│ │ │  in a term equivalence test.</p><p>If you need to match <code class="inline">0.0</code> specifically, the warning can be silenced by
│ │ │  writing <code class="inline">+0.0</code> instead, which produces the same term but makes the compiler
│ │ │  interpret the match as being done on purpose.</p></section><h2 id="arithmetic-expressions" class="section-heading">
│ │ │ @@ -631,15 +631,15 @@
│ │ │  </span><span class="mi">0</span><span class="w">
│ │ │  </span><span class="gp unselectable">8&gt; </span><span class="mi">2#10</span><span class="w"> </span><span class="ow">bor</span><span class="w"> </span><span class="mi">2#01</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │  </span><span class="gp unselectable">9&gt; </span><span class="ss">a</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">10</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: an error occurred when evaluating an arithmetic expression
│ │ │       in operator  +/2
│ │ │          called as a + 10</span><span class="w">
│ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="mi">1</span><span class="w"> </span><span class="nf">bsl</span><span class="w"> </span><span class="p" data-group-id="9641674174-1">(</span><span class="mi">1</span><span class="w"> </span><span class="ow">bsl</span><span class="w"> </span><span class="mi">64</span><span class="p" data-group-id="9641674174-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="mi">1</span><span class="w"> </span><span class="nf">bsl</span><span class="w"> </span><span class="p" data-group-id="0781780448-1">(</span><span class="mi">1</span><span class="w"> </span><span class="ow">bsl</span><span class="w"> </span><span class="mi">64</span><span class="p" data-group-id="0781780448-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: a system limit has been reached
│ │ │       in operator  bsl/2
│ │ │          called as 1 bsl 18446744073709551616</span></code></pre><h2 id="boolean-expressions" class="section-heading">
│ │ │    <a href="#boolean-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Boolean Expressions</span>
│ │ │ @@ -658,136 +658,136 @@
│ │ │    <a href="#short-circuit-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Short-Circuit Expressions</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="n">Expr1</span><span class="w"> </span><span class="ow">orelse</span><span class="w"> </span><span class="n">Expr2</span><span class="w">
│ │ │  </span><span class="n">Expr1</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">Expr2</span></code></pre><p><code class="inline">Expr2</code> is evaluated only if necessary. That is, <code class="inline">Expr2</code> is evaluated only if:</p><ul><li><code class="inline">Expr1</code> evaluates to <code class="inline">false</code> in an <code class="inline">orelse</code> expression.</li></ul><p>or</p><ul><li><code class="inline">Expr1</code> evaluates to <code class="inline">true</code> in an <code class="inline">andalso</code> expression.</li></ul><p>Returns either the value of <code class="inline">Expr1</code> (that is, <code class="inline">true</code> or <code class="inline">false</code>) or the value of
│ │ │ -<code class="inline">Expr2</code> (if <code class="inline">Expr2</code> is evaluated).</p><p><em>Example 1:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="o">-</span><span class="mf">1.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nc">math</span><span class="p">:</span><span class="nf">sqrt</span><span class="p" data-group-id="1937665454-1">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="1937665454-1">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span></code></pre><p>This works even if <code class="inline">A</code> is less than <code class="inline">-1.0</code>, since in that case, <a href="../../lib/stdlib-6.2.2.3/doc/html/math.html#sqrt/1"><code class="inline">math:sqrt/1</code></a> is
│ │ │ -never evaluated.</p><p><em>Example 2:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">OnlyOne</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">is_atom</span><span class="p" data-group-id="8543249137-1">(</span><span class="n">L</span><span class="p" data-group-id="8543249137-1">)</span><span class="w"> </span><span class="nf">orelse</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="8543249137-2">(</span><span class="nf">is_list</span><span class="p" data-group-id="8543249137-3">(</span><span class="n">L</span><span class="p" data-group-id="8543249137-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8543249137-4">(</span><span class="n">L</span><span class="p" data-group-id="8543249137-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8543249137-2">)</span><span class="p">,</span></code></pre><p><code class="inline">Expr2</code> is not required to evaluate to a Boolean value. Because of that,
│ │ │ -<code class="inline">andalso</code> and <code class="inline">orelse</code> are tail-recursive.</p><p><em>Example 3 (tail-recursive function):</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="7758272866-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7758272866-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="7758272866-2">]</span><span class="p" data-group-id="7758272866-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pred</span><span class="p" data-group-id="7758272866-3">(</span><span class="n">Hd</span><span class="p" data-group-id="7758272866-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">all</span><span class="p" data-group-id="7758272866-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="7758272866-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">all</span><span class="p" data-group-id="7758272866-5">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7758272866-6">[</span><span class="p" data-group-id="7758272866-6">]</span><span class="p" data-group-id="7758272866-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<code class="inline">Expr2</code> (if <code class="inline">Expr2</code> is evaluated).</p><p><em>Example 1:</em></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="o">-</span><span class="mf">1.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nc">math</span><span class="p">:</span><span class="nf">sqrt</span><span class="p" data-group-id="2367364246-1">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="2367364246-1">)</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span></code></pre><p>This works even if <code class="inline">A</code> is less than <code class="inline">-1.0</code>, since in that case, <a href="../../lib/stdlib-6.2.2.3/doc/html/math.html#sqrt/1"><code class="inline">math:sqrt/1</code></a> is
│ │ │ +never evaluated.</p><p><em>Example 2:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">OnlyOne</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">is_atom</span><span class="p" data-group-id="7949668952-1">(</span><span class="n">L</span><span class="p" data-group-id="7949668952-1">)</span><span class="w"> </span><span class="nf">orelse</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="7949668952-2">(</span><span class="nf">is_list</span><span class="p" data-group-id="7949668952-3">(</span><span class="n">L</span><span class="p" data-group-id="7949668952-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7949668952-4">(</span><span class="n">L</span><span class="p" data-group-id="7949668952-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7949668952-2">)</span><span class="p">,</span></code></pre><p><code class="inline">Expr2</code> is not required to evaluate to a Boolean value. Because of that,
│ │ │ +<code class="inline">andalso</code> and <code class="inline">orelse</code> are tail-recursive.</p><p><em>Example 3 (tail-recursive function):</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="6922873001-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6922873001-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="6922873001-2">]</span><span class="p" data-group-id="6922873001-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pred</span><span class="p" data-group-id="6922873001-3">(</span><span class="n">Hd</span><span class="p" data-group-id="6922873001-3">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">all</span><span class="p" data-group-id="6922873001-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6922873001-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">all</span><span class="p" data-group-id="6922873001-5">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6922873001-6">[</span><span class="p" data-group-id="6922873001-6">]</span><span class="p" data-group-id="6922873001-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="p">.</span></code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R13A, <code class="inline">Expr2</code> was required to evaluate to a Boolean value,
│ │ │  and as consequence, <code class="inline">andalso</code> and <code class="inline">orelse</code> were <strong>not</strong> tail-recursive.</p></section><h2 id="list-operations" class="section-heading">
│ │ │    <a href="#list-operations" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">List Operations</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="n">Expr1</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">Expr2</span><span class="w">
│ │ │  </span><span class="n">Expr1</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="n">Expr2</span></code></pre><p>The list concatenation operator <code class="inline">++</code> appends its second argument to its first
│ │ │  and returns the resulting list.</p><p>The list subtraction operator <code class="inline">--</code> produces a list that is a copy of the first
│ │ │  argument. The procedure is as follows: for each element in the second argument,
│ │ │ -the first occurrence of this element (if any) is removed.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1824449637-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1824449637-1">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1824449637-2">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1824449637-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1824449637-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1824449637-3">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="1824449637-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1824449637-4">]</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="p" data-group-id="1824449637-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1824449637-5">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1824449637-6">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1824449637-6">]</span></code></pre><h2 id="map-expressions" class="section-heading">
│ │ │ +the first occurrence of this element (if any) is removed.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0440720401-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0440720401-1">]</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0440720401-2">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0440720401-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0440720401-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0440720401-3">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="0440720401-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0440720401-4">]</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="p" data-group-id="0440720401-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0440720401-5">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0440720401-6">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0440720401-6">]</span></code></pre><h2 id="map-expressions" class="section-heading">
│ │ │    <a href="#map-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Map Expressions</span>
│ │ │  </h2>
│ │ │  <h3 id="creating-maps" class="section-heading">
│ │ │    <a href="#creating-maps" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating Maps</span>
│ │ │  </h3>
│ │ │  <p>Constructing a new map is done by letting an expression <code class="inline">K</code> be associated with
│ │ │ -another expression <code class="inline">V</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2570091887-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="2570091887-1">}</span></code></pre><p>New maps can include multiple associations at construction by listing every
│ │ │ -association:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0553161359-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="0553161359-1">}</span></code></pre><p>An empty map is constructed by not associating any terms with each other:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0571940800-1">#{</span><span class="p" data-group-id="0571940800-1">}</span></code></pre><p>All keys and values in the map are terms. Any expression is first evaluated and
│ │ │ +another expression <code class="inline">V</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2612159811-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="2612159811-1">}</span></code></pre><p>New maps can include multiple associations at construction by listing every
│ │ │ +association:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6482193059-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="6482193059-1">}</span></code></pre><p>An empty map is constructed by not associating any terms with each other:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0824868107-1">#{</span><span class="p" data-group-id="0824868107-1">}</span></code></pre><p>All keys and values in the map are terms. Any expression is first evaluated and
│ │ │  then the resulting terms are used as <em>key</em> and <em>value</em> respectively.</p><p>Keys and values are separated by the <code class="inline">=&gt;</code> arrow and associations are separated
│ │ │ -by a comma (<code class="inline">,</code>).</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9505669379-1">#{</span><span class="p" data-group-id="9505669379-1">}</span><span class="p">,</span><span class="w">                 </span><span class="c1">% empty map</span><span class="w">
│ │ │ -</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9505669379-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9505669379-3">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="9505669379-3">&gt;&gt;</span><span class="p" data-group-id="9505669379-2">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% single association with literals</span><span class="w">
│ │ │ -</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9505669379-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="9505669379-4">}</span><span class="p">,</span><span class="w">   </span><span class="c1">% multiple associations with literals</span><span class="w">
│ │ │ -</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9505669379-5">#{</span><span class="ss">k</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9505669379-6">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="9505669379-6">}</span><span class="p" data-group-id="9505669379-5">}</span><span class="p">,</span><span class="w">       </span><span class="c1">% single association with variables</span><span class="w">
│ │ │ -</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9505669379-7">#{</span><span class="p" data-group-id="9505669379-8">{</span><span class="s">&quot;w&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9505669379-8">}</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="9505669379-9">(</span><span class="p" data-group-id="9505669379-9">)</span><span class="p" data-group-id="9505669379-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% compound key associated with an evaluated expression</span></code></pre><p>Here, <code class="inline">A</code> and <code class="inline">B</code> are any expressions and <code class="inline">M0</code> through <code class="inline">M4</code> are the resulting
│ │ │ -map terms.</p><p>If two matching keys are declared, the latter key takes precedence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4403344427-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="4403344427-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4403344427-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p" data-group-id="4403344427-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4403344427-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="4403344427-3">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4403344427-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="4403344427-4">}</span></code></pre><p>The order in which the expressions constructing the keys (and their associated
│ │ │ +by a comma (<code class="inline">,</code>).</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2135624778-1">#{</span><span class="p" data-group-id="2135624778-1">}</span><span class="p">,</span><span class="w">                 </span><span class="c1">% empty map</span><span class="w">
│ │ │ +</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2135624778-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2135624778-3">&lt;&lt;</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="2135624778-3">&gt;&gt;</span><span class="p" data-group-id="2135624778-2">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% single association with literals</span><span class="w">
│ │ │ +</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2135624778-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="2135624778-4">}</span><span class="p">,</span><span class="w">   </span><span class="c1">% multiple associations with literals</span><span class="w">
│ │ │ +</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2135624778-5">#{</span><span class="ss">k</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2135624778-6">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="2135624778-6">}</span><span class="p" data-group-id="2135624778-5">}</span><span class="p">,</span><span class="w">       </span><span class="c1">% single association with variables</span><span class="w">
│ │ │ +</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2135624778-7">#{</span><span class="p" data-group-id="2135624778-8">{</span><span class="s">&quot;w&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2135624778-8">}</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="2135624778-9">(</span><span class="p" data-group-id="2135624778-9">)</span><span class="p" data-group-id="2135624778-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% compound key associated with an evaluated expression</span></code></pre><p>Here, <code class="inline">A</code> and <code class="inline">B</code> are any expressions and <code class="inline">M0</code> through <code class="inline">M4</code> are the resulting
│ │ │ +map terms.</p><p>If two matching keys are declared, the latter key takes precedence.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3272077632-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3272077632-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3272077632-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p" data-group-id="3272077632-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="3272077632-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3272077632-3">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3272077632-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="3272077632-4">}</span></code></pre><p>The order in which the expressions constructing the keys (and their associated
│ │ │  values) are evaluated is not defined. The syntactic order of the key-value pairs
│ │ │  in the construction is of no relevance, except in the recently mentioned case of
│ │ │  two matching keys.</p><h3 id="updating-maps" class="section-heading">
│ │ │    <a href="#updating-maps" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Updating Maps</span>
│ │ │  </h3>
│ │ │  <p>Updating a map has a similar syntax as constructing it.</p><p>An expression defining the map to be updated is put in front of the expression
│ │ │ -defining the keys to be updated and their respective values:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="8711410021-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="8711410021-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map and <code class="inline">K</code> and <code class="inline">V</code> are any expression.</p><p>If key <code class="inline">K</code> does not match any existing key in the map, a new association is
│ │ │ +defining the keys to be updated and their respective values:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="5526408438-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="5526408438-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map and <code class="inline">K</code> and <code class="inline">V</code> are any expression.</p><p>If key <code class="inline">K</code> does not match any existing key in the map, a new association is
│ │ │  created from key <code class="inline">K</code> to value <code class="inline">V</code>.</p><p>If key <code class="inline">K</code> matches an existing key in map <code class="inline">M</code>, its associated value is replaced
│ │ │  by the new value <code class="inline">V</code>. In both cases, the evaluated map expression returns a new
│ │ │ -map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p>To only update an existing value, the following syntax is used:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="0456541696-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="0456541696-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map, <code class="inline">V</code> is an expression and <code class="inline">K</code> is an expression
│ │ │ +map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p>To only update an existing value, the following syntax is used:</p><pre><code class="makeup erlang" translate="no"><span class="n">M</span><span class="p" data-group-id="4595342554-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="4595342554-1">}</span></code></pre><p>Here <code class="inline">M</code> is a term of type map, <code class="inline">V</code> is an expression and <code class="inline">K</code> is an expression
│ │ │  that evaluates to an existing key in <code class="inline">M</code>.</p><p>If key <code class="inline">K</code> does not match any existing keys in map <code class="inline">M</code>, an exception of type
│ │ │  <code class="inline">badkey</code> is raised at runtime. If a matching key <code class="inline">K</code> is present in map <code class="inline">M</code>,
│ │ │  its associated value is replaced by the new value <code class="inline">V</code>, and the evaluated map
│ │ │ -expression returns a new map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8601714851-1">#{</span><span class="p" data-group-id="8601714851-1">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M0</span><span class="p" data-group-id="8601714851-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8601714851-2">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="8601714851-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8601714851-3">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M2</span><span class="p" data-group-id="8601714851-4">#{</span><span class="s">&quot;function&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8601714851-5">(</span><span class="p" data-group-id="8601714851-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="8601714851-6">(</span><span class="p" data-group-id="8601714851-6">)</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="8601714851-4">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M3</span><span class="p" data-group-id="8601714851-7">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8601714851-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% &#39;a&#39; and &#39;b&#39; was added in `M1` and `M2`.</span></code></pre><p>Here <code class="inline">M0</code> is any map. It follows that <code class="inline">M1</code> through <code class="inline">M4</code> are maps as well.</p><p><em>More examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1978019061-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="1978019061-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1978019061-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="p" data-group-id="1978019061-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">M</span><span class="p" data-group-id="1978019061-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1978019061-3">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1978019061-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1978019061-4">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="n">M</span><span class="p" data-group-id="1978019061-5">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1978019061-5">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1978019061-6">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1978019061-6">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">M</span><span class="p" data-group-id="1978019061-7">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="1978019061-7">}</span><span class="p">.</span><span class="w">
│ │ │ +expression returns a new map.</p><p>If <code class="inline">M</code> is not of type map, an exception of type <code class="inline">badmap</code> is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="n">M0</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5874068541-1">#{</span><span class="p" data-group-id="5874068541-1">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">M1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M0</span><span class="p" data-group-id="5874068541-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5874068541-2">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">M2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M1</span><span class="p" data-group-id="5874068541-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5874068541-3">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">M3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M2</span><span class="p" data-group-id="5874068541-4">#{</span><span class="s">&quot;function&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="5874068541-5">(</span><span class="p" data-group-id="5874068541-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="5874068541-6">(</span><span class="p" data-group-id="5874068541-6">)</span><span class="w"> </span><span class="k">end</span><span class="p" data-group-id="5874068541-4">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">M4</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M3</span><span class="p" data-group-id="5874068541-7">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5874068541-7">}</span><span class="p">.</span><span class="w">  </span><span class="c1">% &#39;a&#39; and &#39;b&#39; was added in `M1` and `M2`.</span></code></pre><p>Here <code class="inline">M0</code> is any map. It follows that <code class="inline">M1</code> through <code class="inline">M4</code> are maps as well.</p><p><em>More examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7499479961-1">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p" data-group-id="7499479961-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7499479961-2">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="p" data-group-id="7499479961-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">M</span><span class="p" data-group-id="7499479961-3">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7499479961-3">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7499479961-4">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="mf">1.0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7499479961-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="n">M</span><span class="p" data-group-id="7499479961-5">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7499479961-5">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7499479961-6">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7499479961-6">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">M</span><span class="p" data-group-id="7499479961-7">#{</span><span class="mf">1.0</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="7499479961-7">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: bad argument</span></code></pre><p>As in construction, the order in which the key and value expressions are
│ │ │  evaluated is not defined. The syntactic order of the key-value pairs in the
│ │ │  update is of no relevance, except in the case where two keys match. In that
│ │ │  case, the latter value is used.</p><h3 id="maps-in-patterns" class="section-heading">
│ │ │    <a href="#maps-in-patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Maps in Patterns</span>
│ │ │  </h3>
│ │ │ -<p>Matching of key-value associations from maps is done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2120110894-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="2120110894-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here <code class="inline">M</code> is any map. The key <code class="inline">K</code> must be a
│ │ │ +<p>Matching of key-value associations from maps is done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0042715565-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="0042715565-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here <code class="inline">M</code> is any map. The key <code class="inline">K</code> must be a
│ │ │  <a href="expressions.html#guard-expressions">guard expression</a>, with all variables already
│ │ │  bound. <code class="inline">V</code> can be any pattern with either bound or unbound variables.</p><p>If the variable <code class="inline">V</code> is unbound, it becomes bound to the value associated with
│ │ │  the key <code class="inline">K</code>, which must exist in the map <code class="inline">M</code>. If the variable <code class="inline">V</code> is bound, it
│ │ │  must match the value associated with <code class="inline">K</code> in <code class="inline">M</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 23, the expression defining the key <code class="inline">K</code> was restricted to be
│ │ │ -either a single variable or a literal.</p></section><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5810156340-1">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5810156340-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5810156340-2">}</span><span class="p" data-group-id="5810156340-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5810156340-3">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5810156340-4">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5810156340-4">}</span><span class="p" data-group-id="5810156340-3">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="5810156340-5">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5810156340-6">{</span><span class="mi">1</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="5810156340-6">}</span><span class="p" data-group-id="5810156340-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5810156340-7">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5810156340-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5810156340-8">}</span><span class="p" data-group-id="5810156340-7">}</span><span class="w">
│ │ │ +either a single variable or a literal.</p></section><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2018073667-1">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2018073667-2">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2018073667-2">}</span><span class="p" data-group-id="2018073667-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2018073667-3">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2018073667-4">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2018073667-4">}</span><span class="p" data-group-id="2018073667-3">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="2018073667-5">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2018073667-6">{</span><span class="mi">1</span><span class="p">,</span><span class="n">B</span><span class="p" data-group-id="2018073667-6">}</span><span class="p" data-group-id="2018073667-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2018073667-7">#{</span><span class="s">&quot;tuple&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2018073667-8">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2018073667-8">}</span><span class="p" data-group-id="2018073667-7">}</span><span class="w">
│ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">2</span><span class="p">.</span></code></pre><p>This binds variable <code class="inline">B</code> to integer <code class="inline">2</code>.</p><p>Similarly, multiple values from the map can be matched:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3595566162-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="3595566162-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here keys <code class="inline">K1</code> through <code class="inline">Kn</code> are any expressions with literals or bound
│ │ │ +</span><span class="mi">2</span><span class="p">.</span></code></pre><p>This binds variable <code class="inline">B</code> to integer <code class="inline">2</code>.</p><p>Similarly, multiple values from the map can be matched:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3775350745-1">#{</span><span class="n">K1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Kn</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Vn</span><span class="p" data-group-id="3775350745-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>Here keys <code class="inline">K1</code> through <code class="inline">Kn</code> are any expressions with literals or bound
│ │ │  variables. If all key expressions evaluate successfully and all keys
│ │ │  exist in map <code class="inline">M</code>, all variables in <code class="inline">V1 .. Vn</code> is matched to the
│ │ │  associated values of their respective keys.</p><p>If the matching conditions are not met the match fails.</p><p>Note that when matching a map, only the <code class="inline">:=</code> operator (not the <code class="inline">=&gt;</code>) is allowed
│ │ │  as a delimiter for the associations.</p><p>The order in which keys are declared in matching has no relevance.</p><p>Duplicate keys are allowed in matching and match each pattern associated to the
│ │ │ -keys:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4374668471-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V2</span><span class="p" data-group-id="4374668471-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>The empty map literal (<code class="inline">#{}</code>) matches any map when used as a pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8112424941-1">#{</span><span class="p" data-group-id="8112424941-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>This expression matches if the expression <code class="inline">Expr</code> is of type map, otherwise it
│ │ │ -fails with an exception <code class="inline">badmatch</code>.</p><p>Here the key to be retrieved is constructed from an expression:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7138546537-1">#{</span><span class="p" data-group-id="7138546537-2">{</span><span class="ss">tag</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="7138546537-3">(</span><span class="n">List</span><span class="p" data-group-id="7138546537-3">)</span><span class="p" data-group-id="7138546537-2">}</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="7138546537-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map</span></code></pre><p><code class="inline">List</code> must be an already bound variable.</p><h4>Matching Syntax</h4><p>Matching of literals as keys are allowed in function heads:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% only start if not_started</span><span class="w">
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="6244450026-1">(</span><span class="ss">start</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6244450026-2">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">not_started</span><span class="p" data-group-id="6244450026-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="6244450026-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +keys:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6927822318-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V2</span><span class="p" data-group-id="6927822318-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span></code></pre><p>The empty map literal (<code class="inline">#{}</code>) matches any map when used as a pattern:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0595609413-1">#{</span><span class="p" data-group-id="0595609413-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>This expression matches if the expression <code class="inline">Expr</code> is of type map, otherwise it
│ │ │ +fails with an exception <code class="inline">badmatch</code>.</p><p>Here the key to be retrieved is constructed from an expression:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5856657801-1">#{</span><span class="p" data-group-id="5856657801-2">{</span><span class="ss">tag</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="5856657801-3">(</span><span class="n">List</span><span class="p" data-group-id="5856657801-3">)</span><span class="p" data-group-id="5856657801-2">}</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="p" data-group-id="5856657801-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map</span></code></pre><p><code class="inline">List</code> must be an already bound variable.</p><h4>Matching Syntax</h4><p>Matching of literals as keys are allowed in function heads:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% only start if not_started</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="7541544855-1">(</span><span class="ss">start</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541544855-2">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">not_started</span><span class="p" data-group-id="7541544855-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7541544855-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6244450026-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="6244450026-4">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="6244450026-4">}</span><span class="p" data-group-id="6244450026-3">}</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7541544855-3">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7541544855-4">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="7541544855-4">}</span><span class="p" data-group-id="7541544855-3">}</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% only change if started</span><span class="w">
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="6244450026-5">(</span><span class="ss">change</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6244450026-6">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="6244450026-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="6244450026-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="7541544855-5">(</span><span class="ss">change</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7541544855-6">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">start</span><span class="p" data-group-id="7541544855-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7541544855-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6244450026-7">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="6244450026-8">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">changed</span><span class="p" data-group-id="6244450026-8">}</span><span class="p" data-group-id="6244450026-7">}</span><span class="p">;</span></code></pre><h3 id="maps-in-guards" class="section-heading">
│ │ │ +    </span><span class="p" data-group-id="7541544855-7">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">S</span><span class="p" data-group-id="7541544855-8">#{</span><span class="ss">state</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">changed</span><span class="p" data-group-id="7541544855-8">}</span><span class="p" data-group-id="7541544855-7">}</span><span class="p">;</span></code></pre><h3 id="maps-in-guards" class="section-heading">
│ │ │    <a href="#maps-in-guards" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Maps in Guards</span>
│ │ │  </h3>
│ │ │  <p>Maps are allowed in guards as long as all subexpressions are valid guard
│ │ │  expressions.</p><p>The following guard BIFs handle maps:</p><ul><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#is_map/1">is_map/1</a> in the <code class="inline">erlang</code> module</li><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#is_map_key/2">is_map_key/2</a> in the <code class="inline">erlang</code> module</li><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#map_get/2">map_get/2</a> in the <code class="inline">erlang</code> module</li><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#map_size/1">map_size/1</a> in the <code class="inline">erlang</code> module</li></ul><h2 id="bit-syntax-expressions" class="section-heading">
│ │ │    <a href="#bit-syntax-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Bit Syntax Expressions</span>
│ │ │  </h2>
│ │ │  <p>The bit syntax operates on <em>bit strings</em>. A bit string is a sequence of bits
│ │ │ -ordered from the most significant bit to the least significant bit.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7192575102-1">&lt;&lt;</span><span class="p" data-group-id="7192575102-1">&gt;&gt;</span><span class="w">  </span><span class="c1">% The empty bit string, zero length</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7192575102-2">&lt;&lt;</span><span class="n">E1</span><span class="p" data-group-id="7192575102-2">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7192575102-3">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">En</span><span class="p" data-group-id="7192575102-3">&gt;&gt;</span></code></pre><p>Each element <code class="inline">Ei</code> specifies a <em>segment</em> of the bit string. The segments are
│ │ │ +ordered from the most significant bit to the least significant bit.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7927171763-1">&lt;&lt;</span><span class="p" data-group-id="7927171763-1">&gt;&gt;</span><span class="w">  </span><span class="c1">% The empty bit string, zero length</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7927171763-2">&lt;&lt;</span><span class="n">E1</span><span class="p" data-group-id="7927171763-2">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7927171763-3">&lt;&lt;</span><span class="n">E1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">En</span><span class="p" data-group-id="7927171763-3">&gt;&gt;</span></code></pre><p>Each element <code class="inline">Ei</code> specifies a <em>segment</em> of the bit string. The segments are
│ │ │  ordered left to right from the most significant bit to the least significant bit
│ │ │  of the bit string.</p><p>Each segment specification <code class="inline">Ei</code> is a value, whose default type is <code class="inline">integer</code>,
│ │ │  followed by an optional <em>size expression</em> and an optional <em>type specifier list</em>.</p><pre><code class="makeup erlang" translate="no"><span class="n">Ei</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Value</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │       </span><span class="n">Value</span><span class="p">:</span><span class="n">Size</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │       </span><span class="n">Value</span><span class="o">/</span><span class="n">TypeSpecifierList</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │       </span><span class="n">Value</span><span class="p">:</span><span class="n">Size</span><span class="o">/</span><span class="n">TypeSpecifierList</span></code></pre><p>When used in a bit string construction, <code class="inline">Value</code> is an expression that is to
│ │ │  evaluate to an integer, float, or bit string. If the expression is not a single
│ │ │ @@ -798,34 +798,34 @@
│ │ │  <a href="expressions.html#guard-expressions">guard expression</a> that evaluates to an
│ │ │  integer. All variables in the guard expression must be already bound.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 23, <code class="inline">Size</code> was restricted to be an integer or a variable
│ │ │  bound to an integer.</p></section><p>The value of <code class="inline">Size</code> specifies the size of the segment in units (see below). The
│ │ │  default value depends on the type (see below):</p><ul><li>For <code class="inline">integer</code> it is 8.</li><li>For <code class="inline">float</code> it is 64.</li><li>For <code class="inline">binary</code> and <code class="inline">bitstring</code> it is the whole binary or bit string.</li></ul><p>In matching, the default value for a binary or bit string segment is only valid
│ │ │  for the last element. All other bit string or binary elements in the matching
│ │ │  must have a size specification.</p><p><a href="" id="binaries"></a></p><p><strong>Binaries</strong></p><p>A bit string with a length that is a multiple of 8 bits is known as a <em>binary</em>,
│ │ │  which is the most common and useful type of bit string.</p><p>A binary has a canonical representation in memory. Here follows a sequence of
│ │ │ -bytes where each byte's value is its sequence number:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4453337737-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p" data-group-id="4453337737-1">&gt;&gt;</span></code></pre><p>Bit strings are a later generalization of binaries, so many texts and much
│ │ │ -information about binaries apply just as well for bit strings.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9876293116-1">&lt;&lt;</span><span class="n">A</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9876293116-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9876293116-2">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="9876293116-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +bytes where each byte's value is its sequence number:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3944133809-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">10</span><span class="p" data-group-id="3944133809-1">&gt;&gt;</span></code></pre><p>Bit strings are a later generalization of binaries, so many texts and much
│ │ │ +information about binaries apply just as well for bit strings.</p><p><strong>Example:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3515667625-1">&lt;&lt;</span><span class="n">A</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3515667625-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3515667625-2">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="3515667625-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">* 1:3: a binary field without size is only allowed at the end of a binary pattern</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="9876293116-3">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">3</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9876293116-3">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9876293116-4">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="9876293116-4">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9876293116-5">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="9876293116-5">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="3515667625-3">&lt;&lt;</span><span class="n">A</span><span class="p">:</span><span class="mi">3</span><span class="o">/</span><span class="ss">binary</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3515667625-3">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3515667625-4">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="3515667625-4">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3515667625-5">&lt;&lt;</span><span class="s">&quot;abcde&quot;</span><span class="p" data-group-id="3515667625-5">&gt;&gt;</span><span class="w">
│ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9876293116-6">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9876293116-6">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3515667625-6">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3515667625-6">&gt;&gt;</span><span class="w">
│ │ │  </span><span class="gp unselectable">4&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9876293116-7">&lt;&lt;</span><span class="s">&quot;de&quot;</span><span class="p" data-group-id="9876293116-7">&gt;&gt;</span></code></pre><p>For the <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code> types, <code class="inline">Size</code> must not be given. The size
│ │ │ +</span><span class="p" data-group-id="3515667625-7">&lt;&lt;</span><span class="s">&quot;de&quot;</span><span class="p" data-group-id="3515667625-7">&gt;&gt;</span></code></pre><p>For the <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code> types, <code class="inline">Size</code> must not be given. The size
│ │ │  of the segment is implicitly determined by the type and value itself.</p><p><code class="inline">TypeSpecifierList</code> is a list of type specifiers, in any order, separated by
│ │ │  hyphens (-). Default values are used for any omitted type specifiers.</p><ul><li><p><strong><code class="inline">Type</code>= <code class="inline">integer</code> | <code class="inline">float</code> | <code class="inline">binary</code> | <code class="inline">bytes</code> | <code class="inline">bitstring</code> | <code class="inline">bits</code> |
│ │ │  <code class="inline">utf8</code> | <code class="inline">utf16</code> | <code class="inline">utf32</code></strong> - The default is <code class="inline">integer</code>. <code class="inline">bytes</code> is a
│ │ │  shorthand for <code class="inline">binary</code> and <code class="inline">bits</code> is a shorthand for <code class="inline">bitstring</code>. See below
│ │ │  for more information about the <code class="inline">utf</code> types.</p></li><li><p><strong><code class="inline">Signedness</code>= <code class="inline">signed</code> | <code class="inline">unsigned</code></strong> - Only matters for matching and when
│ │ │  the type is <code class="inline">integer</code>. The default is <code class="inline">unsigned</code>.</p></li><li><p><strong><code class="inline">Endianness</code>= <code class="inline">big</code> | <code class="inline">little</code> | <code class="inline">native</code></strong> - Specifies byte level (octet
│ │ │  level) endianness (byte order). Native-endian means that the endianness is
│ │ │  resolved at load time to be either big-endian or little-endian, depending on
│ │ │  what is native for the CPU that the Erlang machine is run on. Endianness only
│ │ │  matters when the <strong>Type</strong> is either <code class="inline">integer</code>, <code class="inline">utf16</code>, <code class="inline">utf32</code>, or <code class="inline">float</code>. The
│ │ │ -default is <code class="inline">big</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1705972394-1">&lt;&lt;</span><span class="mi">16#1234</span><span class="p">:</span><span class="mi">16</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="1705972394-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1705972394-2">&lt;&lt;</span><span class="mi">16#3412</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1705972394-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1705972394-3">&lt;&lt;</span><span class="mi">16#34</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">16#12</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="1705972394-3">&gt;&gt;</span></code></pre></li><li><p><strong><code class="inline">Unit</code>= <code class="inline">unit:IntegerLiteral</code></strong> - The allowed range is 1 through 256.
│ │ │ +default is <code class="inline">big</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9077796271-1">&lt;&lt;</span><span class="mi">16#1234</span><span class="p">:</span><span class="mi">16</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="9077796271-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9077796271-2">&lt;&lt;</span><span class="mi">16#3412</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="9077796271-2">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9077796271-3">&lt;&lt;</span><span class="mi">16#34</span><span class="p">:</span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">16#12</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="9077796271-3">&gt;&gt;</span></code></pre></li><li><p><strong><code class="inline">Unit</code>= <code class="inline">unit:IntegerLiteral</code></strong> - The allowed range is 1 through 256.
│ │ │  Defaults to 1 for <code class="inline">integer</code>, <code class="inline">float</code>, and <code class="inline">bitstring</code>, and to 8 for <code class="inline">binary</code>.
│ │ │  For types <code class="inline">bitstring</code>, <code class="inline">bits</code>, and <code class="inline">bytes</code>, it is not allowed to specify a
│ │ │  unit value different from the default value. No unit specifier must be given
│ │ │  for the types <code class="inline">utf8</code>, <code class="inline">utf16</code>, and <code class="inline">utf32</code>.</p></li></ul><h3 id="integer-segments" class="section-heading">
│ │ │    <a href="#integer-segments" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -850,41 +850,41 @@
│ │ │    </a>
│ │ │    <span class="text">Binary segments</span>
│ │ │  </h3>
│ │ │  <p>In this section, the phrase &quot;binary segment&quot; refers to any one of the segment
│ │ │  types <code class="inline">binary</code>, <code class="inline">bitstring</code>, <code class="inline">bytes</code>, and <code class="inline">bits</code>.</p><p>See also the paragraphs about <a href="expressions.html#binaries">Binaries</a>.</p><p>When constructing binaries and no size is specified for a binary segment, the
│ │ │  entire binary value is interpolated into the binary being constructed. However,
│ │ │  the size in bits of the binary being interpolated must be evenly divisible by
│ │ │ -the unit value for the segment; otherwise an exception is raised.</p><p>For example, the following examples all succeed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9706137442-1">&lt;&lt;</span><span class="p" data-group-id="9706137442-2">(</span><span class="p" data-group-id="9706137442-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9706137442-3">&gt;&gt;</span><span class="p" data-group-id="9706137442-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="9706137442-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9706137442-4">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9706137442-4">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="9706137442-5">&lt;&lt;</span><span class="p" data-group-id="9706137442-6">(</span><span class="p" data-group-id="9706137442-7">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9706137442-7">&gt;&gt;</span><span class="p" data-group-id="9706137442-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="9706137442-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9706137442-8">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9706137442-8">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="9706137442-9">&lt;&lt;</span><span class="p" data-group-id="9706137442-10">(</span><span class="p" data-group-id="9706137442-11">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9706137442-11">&gt;&gt;</span><span class="p" data-group-id="9706137442-10">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="9706137442-9">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9706137442-12">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="9706137442-12">&gt;&gt;</span></code></pre><p>The first two examples have a unit value of 1 for the segment, while the third
│ │ │ +the unit value for the segment; otherwise an exception is raised.</p><p>For example, the following examples all succeed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3873433706-1">&lt;&lt;</span><span class="p" data-group-id="3873433706-2">(</span><span class="p" data-group-id="3873433706-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3873433706-3">&gt;&gt;</span><span class="p" data-group-id="3873433706-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="3873433706-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3873433706-4">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3873433706-4">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="3873433706-5">&lt;&lt;</span><span class="p" data-group-id="3873433706-6">(</span><span class="p" data-group-id="3873433706-7">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3873433706-7">&gt;&gt;</span><span class="p" data-group-id="3873433706-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="3873433706-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3873433706-8">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3873433706-8">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="3873433706-9">&lt;&lt;</span><span class="p" data-group-id="3873433706-10">(</span><span class="p" data-group-id="3873433706-11">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3873433706-11">&gt;&gt;</span><span class="p" data-group-id="3873433706-10">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="3873433706-9">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3873433706-12">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="3873433706-12">&gt;&gt;</span></code></pre><p>The first two examples have a unit value of 1 for the segment, while the third
│ │ │  segment has a unit value of 8.</p><p>Attempting to interpolate a bit string of size 1 into a binary segment with unit
│ │ │ -8 (the default unit for <code class="inline">binary</code>) fails as shown in this example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1344375189-1">&lt;&lt;</span><span class="p" data-group-id="1344375189-2">(</span><span class="p" data-group-id="1344375189-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1344375189-3">&gt;&gt;</span><span class="p" data-group-id="1344375189-2">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1344375189-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="gt">** exception error: bad argument</span></code></pre><p>For the construction to succeed, the unit value of the segment must be 1:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="0102929799-1">&lt;&lt;</span><span class="p" data-group-id="0102929799-2">(</span><span class="p" data-group-id="0102929799-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0102929799-3">&gt;&gt;</span><span class="p" data-group-id="0102929799-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="0102929799-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0102929799-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0102929799-4">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="0102929799-5">&lt;&lt;</span><span class="p" data-group-id="0102929799-6">(</span><span class="p" data-group-id="0102929799-7">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0102929799-7">&gt;&gt;</span><span class="p" data-group-id="0102929799-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0102929799-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0102929799-8">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0102929799-8">&gt;&gt;</span></code></pre><p>Similarly, when matching a binary segment with no size specified, the match
│ │ │ +8 (the default unit for <code class="inline">binary</code>) fails as shown in this example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1663309408-1">&lt;&lt;</span><span class="p" data-group-id="1663309408-2">(</span><span class="p" data-group-id="1663309408-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="1663309408-3">&gt;&gt;</span><span class="p" data-group-id="1663309408-2">)</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="1663309408-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gt">** exception error: bad argument</span></code></pre><p>For the construction to succeed, the unit value of the segment must be 1:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="8155656295-1">&lt;&lt;</span><span class="p" data-group-id="8155656295-2">(</span><span class="p" data-group-id="8155656295-3">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8155656295-3">&gt;&gt;</span><span class="p" data-group-id="8155656295-2">)</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="8155656295-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8155656295-4">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8155656295-4">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="8155656295-5">&lt;&lt;</span><span class="p" data-group-id="8155656295-6">(</span><span class="p" data-group-id="8155656295-7">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8155656295-7">&gt;&gt;</span><span class="p" data-group-id="8155656295-6">)</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8155656295-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8155656295-8">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8155656295-8">&gt;&gt;</span></code></pre><p>Similarly, when matching a binary segment with no size specified, the match
│ │ │  succeeds if and only if the size in bits of the rest of the binary is evenly
│ │ │ -divisible by the unit value:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1282349066-1">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1282349066-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1282349066-2">&lt;&lt;</span><span class="s">&quot;&quot;</span><span class="p" data-group-id="1282349066-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1282349066-3">&lt;&lt;</span><span class="p" data-group-id="1282349066-3">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="1282349066-4">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1282349066-4">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1282349066-5">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="1282349066-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +divisible by the unit value:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5879807730-1">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5879807730-1">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5879807730-2">&lt;&lt;</span><span class="s">&quot;&quot;</span><span class="p" data-group-id="5879807730-2">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5879807730-3">&lt;&lt;</span><span class="p" data-group-id="5879807730-3">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="5879807730-4">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5879807730-4">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5879807730-5">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="5879807730-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value &lt;&lt;&quot;a&quot;&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="1282349066-6">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1282349066-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1282349066-7">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="1282349066-7">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1282349066-8">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="1282349066-8">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="1282349066-9">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1282349066-9">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1282349066-10">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="1282349066-10">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="5879807730-6">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5879807730-6">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5879807730-7">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="5879807730-7">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5879807730-8">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="5879807730-8">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="5879807730-9">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5879807730-9">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5879807730-10">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="5879807730-10">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value &lt;&lt;&quot;abc&quot;&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="1282349066-11">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="1282349066-11">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1282349066-12">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="1282349066-12">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1282349066-13">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="1282349066-13">&gt;&gt;</span></code></pre><p>When a size is explicitly specified for a binary segment, the segment size in
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="5879807730-11">&lt;&lt;</span><span class="p">_</span><span class="o">/</span><span class="ss">binary</span><span class="o">-</span><span class="nc">unit</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5879807730-11">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5879807730-12">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="5879807730-12">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5879807730-13">&lt;&lt;</span><span class="s">&quot;abcd&quot;</span><span class="p" data-group-id="5879807730-13">&gt;&gt;</span></code></pre><p>When a size is explicitly specified for a binary segment, the segment size in
│ │ │  bits is the value of <code class="inline">Size</code> multiplied by the default or explicit unit value.</p><p>When constructing binaries, the size of the binary being interpolated into the
│ │ │ -constructed binary must be at least as large as the size of the binary segment.</p><p><strong>Examples:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8712496366-1">&lt;&lt;</span><span class="p" data-group-id="8712496366-2">(</span><span class="p" data-group-id="8712496366-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="8712496366-3">&gt;&gt;</span><span class="p" data-group-id="8712496366-2">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8712496366-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8712496366-4">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="8712496366-4">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="8712496366-5">&lt;&lt;</span><span class="p" data-group-id="8712496366-6">(</span><span class="p" data-group-id="8712496366-7">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="8712496366-7">&gt;&gt;</span><span class="p" data-group-id="8712496366-6">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="8712496366-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +constructed binary must be at least as large as the size of the binary segment.</p><p><strong>Examples:</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7591357195-1">&lt;&lt;</span><span class="p" data-group-id="7591357195-2">(</span><span class="p" data-group-id="7591357195-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="7591357195-3">&gt;&gt;</span><span class="p" data-group-id="7591357195-2">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7591357195-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7591357195-4">&lt;&lt;</span><span class="s">&quot;ab&quot;</span><span class="p" data-group-id="7591357195-4">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="7591357195-5">&lt;&lt;</span><span class="p" data-group-id="7591357195-6">(</span><span class="p" data-group-id="7591357195-7">&lt;&lt;</span><span class="s">&quot;a&quot;</span><span class="p" data-group-id="7591357195-7">&gt;&gt;</span><span class="p" data-group-id="7591357195-6">)</span><span class="p">:</span><span class="mi">2</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="7591357195-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: construction of binary failed
│ │ │          *** segment 1 of type &#39;binary&#39;: the value &lt;&lt;&quot;a&quot;&gt;&gt; is shorter than the size of the segment</span></code></pre><h3 id="unicode-segments" class="section-heading">
│ │ │    <a href="#unicode-segments" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Unicode segments</span>
│ │ │  </h3>
│ │ │ @@ -900,78 +900,78 @@
│ │ │  range <code class="inline">0</code> through <code class="inline">16#D7FF</code> or <code class="inline">16#E000</code> through <code class="inline">16#10FFFF</code>. The match fails if the
│ │ │  returned value falls outside those ranges.</p><p>A segment of type <code class="inline">utf8</code> matches 1-4 bytes in the bit string, if the bit string
│ │ │  at the match position contains a valid UTF-8 sequence. (See RFC-3629 or the
│ │ │  Unicode standard.)</p><p>A segment of type <code class="inline">utf16</code> can match 2 or 4 bytes in the bit string. The match
│ │ │  fails if the bit string at the match position does not contain a legal UTF-16
│ │ │  encoding of a Unicode code point. (See RFC-2781 or the Unicode standard.)</p><p>A segment of type <code class="inline">utf32</code> can match 4 bytes in the bit string in the same way as
│ │ │  an <code class="inline">integer</code> segment matches 32 bits. The match fails if the resulting integer
│ │ │ -is outside the legal ranges previously mentioned.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6078267765-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6078267765-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6078267765-2">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6078267765-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="6078267765-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-4">&lt;&lt;</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="6078267765-4">&gt;&gt;</span><span class="w">
│ │ │ +is outside the legal ranges previously mentioned.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Bin1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5037130846-1">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5037130846-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-2">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5037130846-2">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">Bin2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5037130846-3">&lt;&lt;</span><span class="s">&quot;abc&quot;</span><span class="p" data-group-id="5037130846-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-4">&lt;&lt;</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="5037130846-4">&gt;&gt;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6078267765-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6078267765-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-6">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6078267765-6">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="6078267765-7">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6078267765-7">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6078267765-8">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6078267765-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-9">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6078267765-9">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="mi">3</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Bin3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5037130846-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5037130846-5">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-6">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5037130846-6">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="5037130846-7">&lt;&lt;</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5037130846-7">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5037130846-8">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5037130846-8">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-9">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5037130846-9">&gt;&gt;</span><span class="w">
│ │ │  </span><span class="gp unselectable">5&gt; </span><span class="n">C</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="p" data-group-id="6078267765-10">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="n">E</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="6078267765-10">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6078267765-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6078267765-11">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-12">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6078267765-12">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="p" data-group-id="5037130846-10">&lt;&lt;</span><span class="n">D</span><span class="p">:</span><span class="mi">16</span><span class="p">,</span><span class="n">E</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="5037130846-10">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5037130846-11">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5037130846-11">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-12">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5037130846-12">&gt;&gt;</span><span class="w">
│ │ │  </span><span class="gp unselectable">7&gt; </span><span class="n">D</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">273</span><span class="w">
│ │ │  </span><span class="gp unselectable">8&gt; </span><span class="n">F</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="w">
│ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="p" data-group-id="6078267765-13">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">H</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="6078267765-13">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6078267765-14">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="6078267765-14">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-15">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6078267765-15">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="p" data-group-id="5037130846-13">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">H</span><span class="o">/</span><span class="ss">binary</span><span class="p" data-group-id="5037130846-13">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5037130846-14">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">16</span><span class="p" data-group-id="5037130846-14">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-15">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5037130846-15">&gt;&gt;</span><span class="w">
│ │ │  </span><span class="gp unselectable">10&gt; </span><span class="n">H</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-16">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="6078267765-16">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">11&gt; </span><span class="p" data-group-id="6078267765-17">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">J</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="6078267765-17">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6078267765-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="6078267765-18">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-19">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="6078267765-19">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-16">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">42</span><span class="p" data-group-id="5037130846-16">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">11&gt; </span><span class="p" data-group-id="5037130846-17">&lt;&lt;</span><span class="n">G</span><span class="p">,</span><span class="n">J</span><span class="o">/</span><span class="ss">bitstring</span><span class="p" data-group-id="5037130846-17">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5037130846-18">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">42</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="5037130846-18">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-19">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5037130846-19">&gt;&gt;</span><span class="w">
│ │ │  </span><span class="gp unselectable">12&gt; </span><span class="n">J</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-20">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="6078267765-20">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-20">&lt;&lt;</span><span class="mi">17</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">10</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5037130846-20">&gt;&gt;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">13</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="6078267765-21">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="6078267765-21">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-22">&lt;&lt;</span><span class="mi">208</span><span class="p">,</span><span class="mi">128</span><span class="p" data-group-id="6078267765-22">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="mi">13</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="5037130846-21">&lt;&lt;</span><span class="mi">1024</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="5037130846-21">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-22">&lt;&lt;</span><span class="mi">208</span><span class="p">,</span><span class="mi">128</span><span class="p" data-group-id="5037130846-22">&gt;&gt;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">14</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="6078267765-23">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">:</span><span class="mi">7</span><span class="p" data-group-id="6078267765-23">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-24">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="6078267765-24">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">15&gt; </span><span class="p" data-group-id="6078267765-25">&lt;&lt;</span><span class="mi">16#123</span><span class="p">:</span><span class="mi">12</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="6078267765-25">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6078267765-26">&lt;&lt;</span><span class="mi">16#231</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="6078267765-26">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6078267765-27">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="6078267765-27">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6078267765-28">&lt;&lt;</span><span class="mi">35</span><span class="p">,</span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="6078267765-28">&gt;&gt;</span></code></pre><p>Notice that bit string patterns cannot be nested.</p><p>Notice also that &quot;<code class="inline">B=&lt;&lt;1&gt;&gt;</code>&quot; is interpreted as &quot;<code class="inline">B =&lt; &lt;1&gt;&gt;</code>&quot; which is a syntax
│ │ │ +</span><span class="mi">14</span><span class="o">&gt;</span><span class="w"> </span><span class="p" data-group-id="5037130846-23">&lt;&lt;</span><span class="mi">1</span><span class="p">:</span><span class="mi">1</span><span class="p">,</span><span class="mi">0</span><span class="p">:</span><span class="mi">7</span><span class="p" data-group-id="5037130846-23">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-24">&lt;&lt;</span><span class="mi">128</span><span class="p" data-group-id="5037130846-24">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">15&gt; </span><span class="p" data-group-id="5037130846-25">&lt;&lt;</span><span class="mi">16#123</span><span class="p">:</span><span class="mi">12</span><span class="o">/</span><span class="ss">little</span><span class="p" data-group-id="5037130846-25">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5037130846-26">&lt;&lt;</span><span class="mi">16#231</span><span class="p">:</span><span class="mi">12</span><span class="p" data-group-id="5037130846-26">&gt;&gt;</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5037130846-27">&lt;&lt;</span><span class="mi">2</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">:</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5037130846-27">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5037130846-28">&lt;&lt;</span><span class="mi">35</span><span class="p">,</span><span class="mi">1</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="5037130846-28">&gt;&gt;</span></code></pre><p>Notice that bit string patterns cannot be nested.</p><p>Notice also that &quot;<code class="inline">B=&lt;&lt;1&gt;&gt;</code>&quot; is interpreted as &quot;<code class="inline">B =&lt; &lt;1&gt;&gt;</code>&quot; which is a syntax
│ │ │  error. The correct way is to write a space after <code class="inline">=</code>: &quot;<code class="inline">B = &lt;&lt;1&gt;&gt;</code>.</p><p>More examples are provided in <a href="../../doc/system/bit_syntax.html">Programming Examples</a>.</p><h2 id="fun-expressions" class="section-heading">
│ │ │    <a href="#fun-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Fun Expressions</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">fun</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9687755611-1">[</span><span class="n">Name</span><span class="p" data-group-id="9687755611-1">]</span><span class="p" data-group-id="9687755611-2">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="9687755611-2">)</span><span class="w"> </span><span class="p" data-group-id="9687755611-3">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="9687755611-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7205389318-1">[</span><span class="n">Name</span><span class="p" data-group-id="7205389318-1">]</span><span class="p" data-group-id="7205389318-2">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="7205389318-2">)</span><span class="w"> </span><span class="p" data-group-id="7205389318-3">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="7205389318-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9687755611-4">[</span><span class="n">Name</span><span class="p" data-group-id="9687755611-4">]</span><span class="p" data-group-id="9687755611-5">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="9687755611-5">)</span><span class="w"> </span><span class="p" data-group-id="9687755611-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="9687755611-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7205389318-4">[</span><span class="n">Name</span><span class="p" data-group-id="7205389318-4">]</span><span class="p" data-group-id="7205389318-5">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="7205389318-5">)</span><span class="w"> </span><span class="p" data-group-id="7205389318-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="7205389318-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                </span><span class="n">BodyK</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>A fun expression begins with the keyword <code class="inline">fun</code> and ends with the keyword <code class="inline">end</code>.
│ │ │  Between them is to be a function declaration, similar to a
│ │ │  <a href="ref_man_functions.html#function-declaration-syntax">regular function declaration</a>,
│ │ │  except that the function name is optional and is to be a variable, if any.</p><p>Variables in a fun head shadow the function name and both shadow variables in
│ │ │  the function clause surrounding the fun expression. Variables bound in a fun
│ │ │ -body are local to the fun body.</p><p>The return value of the expression is the resulting fun.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8756173396-1">(</span><span class="n">X</span><span class="p" data-group-id="8756173396-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +body are local to the fun body.</p><p>The return value of the expression is the resulting fun.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">Fun1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7014086318-1">(</span><span class="n">X</span><span class="p" data-group-id="7014086318-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">+</span><span class="mi">1</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="8756173396-2">(</span><span class="mi">2</span><span class="p" data-group-id="8756173396-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">Fun1</span><span class="p" data-group-id="7014086318-2">(</span><span class="mi">2</span><span class="p" data-group-id="7014086318-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="n">Fun2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8756173396-3">(</span><span class="n">X</span><span class="p" data-group-id="8756173396-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="o">&gt;=</span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">gt</span><span class="p">;</span><span class="w"> </span><span class="p" data-group-id="8756173396-4">(</span><span class="n">X</span><span class="p" data-group-id="8756173396-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">lt</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="n">Fun2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7014086318-3">(</span><span class="n">X</span><span class="p" data-group-id="7014086318-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="o">&gt;=</span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">gt</span><span class="p">;</span><span class="w"> </span><span class="p" data-group-id="7014086318-4">(</span><span class="n">X</span><span class="p" data-group-id="7014086318-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">lt</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">Fun2</span><span class="p" data-group-id="8756173396-5">(</span><span class="mi">7</span><span class="p" data-group-id="8756173396-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">Fun2</span><span class="p" data-group-id="7014086318-5">(</span><span class="mi">7</span><span class="p" data-group-id="7014086318-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">gt</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="n">Fun3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="8756173396-6">(</span><span class="mi">1</span><span class="p" data-group-id="8756173396-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="8756173396-7">(</span><span class="n">X</span><span class="p" data-group-id="8756173396-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="8756173396-8">(</span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8756173396-8">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="n">Fun3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="7014086318-6">(</span><span class="mi">1</span><span class="p" data-group-id="7014086318-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="7014086318-7">(</span><span class="n">X</span><span class="p" data-group-id="7014086318-7">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Fact</span><span class="p" data-group-id="7014086318-8">(</span><span class="n">X</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7014086318-8">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.39074546</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="n">Fun3</span><span class="p" data-group-id="8756173396-9">(</span><span class="mi">4</span><span class="p" data-group-id="8756173396-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="n">Fun3</span><span class="p" data-group-id="7014086318-9">(</span><span class="mi">4</span><span class="p" data-group-id="7014086318-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">24</span></code></pre><p>The following fun expressions are also allowed:</p><pre><code class="makeup erlang" translate="no"><span class="k">fun</span><span class="w"> </span><span class="n">Name</span><span class="o">/</span><span class="n">Arity</span><span class="w">
│ │ │  </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">Name</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In <code class="inline">Name/Arity</code>, <code class="inline">Name</code> is an atom and <code class="inline">Arity</code> is an integer. <code class="inline">Name/Arity</code> must
│ │ │ -specify an existing local function. The expression is syntactic sugar for:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0557080115-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="0557080115-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0557080115-2">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="0557080115-2">)</span><span class="w"> </span><span class="k">end</span></code></pre><p>In <code class="inline">Module:Name/Arity</code>, <code class="inline">Module</code>, and <code class="inline">Name</code> are atoms and <code class="inline">Arity</code> is an
│ │ │ +specify an existing local function. The expression is syntactic sugar for:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4975103369-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="4975103369-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4975103369-2">(</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="4975103369-2">)</span><span class="w"> </span><span class="k">end</span></code></pre><p>In <code class="inline">Module:Name/Arity</code>, <code class="inline">Module</code>, and <code class="inline">Name</code> are atoms and <code class="inline">Arity</code> is an
│ │ │  integer. <code class="inline">Module</code>, <code class="inline">Name</code>, and <code class="inline">Arity</code> can also be variables. A fun defined in
│ │ │  this way refers to the function <code class="inline">Name</code> with arity <code class="inline">Arity</code> in the <em>latest</em>
│ │ │  version of module <code class="inline">Module</code>. A fun defined in this way is not dependent on the
│ │ │  code for the module in which it is defined.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R15, <code class="inline">Module</code>, <code class="inline">Name</code>, and <code class="inline">Arity</code> were not allowed to be
│ │ │  variables.</p></section><p>More examples are provided in <a href="../../doc/system/funs.html">Programming Examples</a>.</p><h2 id="catch-and-throw" class="section-heading">
│ │ │    <a href="#catch-and-throw" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -981,35 +981,35 @@
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">catch</span><span class="w"> </span><span class="n">Expr</span></code></pre><p>Returns the value of <code class="inline">Expr</code> unless an exception is raised during the evaluation. In
│ │ │  that case, the exception is caught. The return value depends on the class of the
│ │ │  exception:</p><ul><li><p><strong><code class="inline">error</code></strong> (a run-time error or the code called <a href="../../erts-15.2.7.8/doc/html/erlang.html#error/1"><code class="inline">error(Term)</code></a>) -
│ │ │  <code class="inline">{'EXIT',{Reason,Stack}}</code> is returned.</p></li><li><p><strong><code class="inline">exit</code></strong> (the code called <a href="../../erts-15.2.7.8/doc/html/erlang.html#exit/1"><code class="inline">exit(Term)</code></a>) - <code class="inline">{'EXIT',Term}</code> is returned.</p></li><li><p><strong><code class="inline">throw</code></strong> (the code called <a href="../../erts-15.2.7.8/doc/html/erlang.html#throw/1"><code class="inline">throw(Term)</code></a>): <code class="inline">Term</code> is returned.</p></li></ul><p><code class="inline">Reason</code> depends on the type of error that occurred, and <code class="inline">Stack</code> is the stack of
│ │ │  recent function calls, see <a href="errors.html#exit_reasons">Exit Reasons</a>.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="k">catch</span><span class="w"> </span><span class="mi">1</span><span class="o">+</span><span class="mi">2</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │  </span><span class="gp unselectable">2&gt; </span><span class="k">catch</span><span class="w"> </span><span class="mi">1</span><span class="o">+</span><span class="ss">a</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8219950944-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="8219950944-2">{</span><span class="ss">badarith</span><span class="p">,</span><span class="p" data-group-id="8219950944-3">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8219950944-3">]</span><span class="p" data-group-id="8219950944-2">}</span><span class="p" data-group-id="8219950944-1">}</span></code></pre><p>The BIF <a href="../../erts-15.2.7.8/doc/html/erlang.html#throw/1"><code class="inline">throw(Any)</code></a> can be used for non-local return from a
│ │ │ -function. It must be evaluated within a <code class="inline">catch</code>, which returns the value <code class="inline">Any</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="5933322663-1">(</span><span class="ss">hello</span><span class="p" data-group-id="5933322663-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9054025149-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="9054025149-2">{</span><span class="ss">badarith</span><span class="p">,</span><span class="p" data-group-id="9054025149-3">[</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9054025149-3">]</span><span class="p" data-group-id="9054025149-2">}</span><span class="p" data-group-id="9054025149-1">}</span></code></pre><p>The BIF <a href="../../erts-15.2.7.8/doc/html/erlang.html#throw/1"><code class="inline">throw(Any)</code></a> can be used for non-local return from a
│ │ │ +function. It must be evaluated within a <code class="inline">catch</code>, which returns the value <code class="inline">Any</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="k">catch</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="6812133235-1">(</span><span class="ss">hello</span><span class="p" data-group-id="6812133235-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span></code></pre><p>If <a href="../../erts-15.2.7.8/doc/html/erlang.html#throw/1"><code class="inline">throw/1</code></a> is not evaluated within a catch, a <code class="inline">nocatch</code> run-time
│ │ │  error occurs.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 24, the <code class="inline">catch</code> operator had the lowest precedence, making
│ │ │ -it necessary to add parentheses when combining it with the <code class="inline">match</code> operator:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3354493703-1">(</span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="3354493703-1">)</span><span class="p">.</span><span class="w">
│ │ │ +it necessary to add parentheses when combining it with the <code class="inline">match</code> operator:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6264123525-1">(</span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="6264123525-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="w">
│ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span></code></pre><p>Starting from Erlang/OTP 24, the parentheses can be omitted:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">catch</span><span class="w"> </span><span class="mi">42</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span><span class="w">
│ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">42</span></code></pre></section><h2 id="try" class="section-heading">
│ │ │    <a href="#try" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Try</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="4846649127-1">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="4846649127-1">]</span><span class="w"> </span><span class="p" data-group-id="4846649127-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="4846649127-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="3293985871-1">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="3293985871-1">]</span><span class="w"> </span><span class="p" data-group-id="3293985871-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="3293985871-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="4846649127-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="4846649127-3">]</span><span class="w"> </span><span class="p" data-group-id="4846649127-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="4846649127-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="3293985871-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="3293985871-3">]</span><span class="w"> </span><span class="p" data-group-id="3293985871-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="3293985871-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>This is an enhancement of <a href="expressions.html#catch-and-throw">catch</a>. It gives the
│ │ │  possibility to:</p><ul><li>Distinguish between different exception classes.</li><li>Choose to handle only the desired ones.</li><li>Passing the others on to an enclosing <code class="inline">try</code> or <code class="inline">catch</code>, or to default error
│ │ │  handling.</li></ul><p>Notice that although the keyword <code class="inline">catch</code> is used in the <code class="inline">try</code> expression, there
│ │ │  is not a <code class="inline">catch</code> expression within the <code class="inline">try</code> expression.</p><p>It returns the value of <code class="inline">Exprs</code> (a sequence of expressions <code class="inline">Expr1, ..., ExprN</code>)
│ │ │  unless an exception occurs during the evaluation. In that case the exception is
│ │ │  caught and the patterns <code class="inline">ExceptionPattern</code> with the right exception class
│ │ │ @@ -1019,47 +1019,47 @@
│ │ │  stack trace is bound to the variable when the corresponding <code class="inline">ExceptionPattern</code>
│ │ │  matches.</p><p>If an exception occurs during evaluation of <code class="inline">Exprs</code> but there is no matching
│ │ │  <code class="inline">ExceptionPattern</code> of the right <code class="inline">Class</code> with a true guard sequence, the
│ │ │  exception is passed on as if <code class="inline">Exprs</code> had not been enclosed in a <code class="inline">try</code>
│ │ │  expression.</p><p>If an exception occurs during evaluation of <code class="inline">ExceptionBody</code>, it is not caught.</p><p>It is allowed to omit <code class="inline">Class</code> and <code class="inline">Stacktrace</code>. An omitted <code class="inline">Class</code> is shorthand
│ │ │  for <code class="inline">throw</code>:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ -    </span><span class="n">ExceptionPattern1</span><span class="w"> </span><span class="p" data-group-id="4462694765-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="4462694765-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ExceptionPattern1</span><span class="w"> </span><span class="p" data-group-id="8612094430-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="8612094430-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ExceptionPatternN</span><span class="w"> </span><span class="p" data-group-id="4462694765-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="4462694765-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ExceptionPatternN</span><span class="w"> </span><span class="p" data-group-id="8612094430-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="8612094430-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>The <code class="inline">try</code> expression can have an <code class="inline">of</code> section:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="3275712438-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="3275712438-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="5693718804-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="5693718804-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="3275712438-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="3275712438-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="5693718804-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="5693718804-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="3275712438-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="3275712438-3">]</span><span class="w"> </span><span class="p" data-group-id="3275712438-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="3275712438-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="5693718804-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="5693718804-3">]</span><span class="w"> </span><span class="p" data-group-id="5693718804-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="5693718804-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="3275712438-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="3275712438-5">]</span><span class="w"> </span><span class="p" data-group-id="3275712438-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="3275712438-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="5693718804-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="5693718804-5">]</span><span class="w"> </span><span class="p" data-group-id="5693718804-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="5693718804-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>If the evaluation of <code class="inline">Exprs</code> succeeds without an exception, the patterns
│ │ │  <code class="inline">Pattern</code> are sequentially matched against the result in the same way as for a
│ │ │  <a href="expressions.html#case">case</a> expression, except that if the matching fails, a
│ │ │  <code class="inline">try_clause</code> run-time error occurs instead of a <code class="inline">case_clause</code>.</p><p>Only exceptions occurring during the evaluation of <code class="inline">Exprs</code> can be caught by the
│ │ │  <code class="inline">catch</code> section. Exceptions occurring in a <code class="inline">Body</code> or due to a failed match are
│ │ │  not caught.</p><p>The <code class="inline">try</code> expression can also be augmented with an <code class="inline">after</code> section, intended to
│ │ │  be used for cleanup with side effects:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="6401679977-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="6401679977-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pattern1</span><span class="w"> </span><span class="p" data-group-id="8894014434-1">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="8894014434-1">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="6401679977-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="6401679977-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PatternN</span><span class="w"> </span><span class="p" data-group-id="8894014434-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqN</span><span class="p" data-group-id="8894014434-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">BodyN</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │ -    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="6401679977-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="6401679977-3">]</span><span class="w"> </span><span class="p" data-group-id="6401679977-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="6401679977-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Class1</span><span class="p">:</span><span class="n">ExceptionPattern1</span><span class="p" data-group-id="8894014434-3">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="8894014434-3">]</span><span class="w"> </span><span class="p" data-group-id="8894014434-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeq1</span><span class="p" data-group-id="8894014434-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBody1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="6401679977-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="6401679977-5">]</span><span class="w"> </span><span class="p" data-group-id="6401679977-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="6401679977-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">ClassN</span><span class="p">:</span><span class="n">ExceptionPatternN</span><span class="p" data-group-id="8894014434-5">[</span><span class="p">:</span><span class="n">Stacktrace</span><span class="p" data-group-id="8894014434-5">]</span><span class="w"> </span><span class="p" data-group-id="8894014434-6">[</span><span class="k">when</span><span class="w"> </span><span class="n">ExceptionGuardSeqN</span><span class="p" data-group-id="8894014434-6">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="n">ExceptionBodyN</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w">
│ │ │      </span><span class="n">AfterBody</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p><code class="inline">AfterBody</code> is evaluated after either <code class="inline">Body</code> or <code class="inline">ExceptionBody</code>, no matter which
│ │ │  one. The evaluated value of <code class="inline">AfterBody</code> is lost; the return value of the <code class="inline">try</code>
│ │ │  expression is the same with an <code class="inline">after</code> section as without.</p><p>Even if an exception occurs during evaluation of <code class="inline">Body</code> or <code class="inline">ExceptionBody</code>,
│ │ │  <code class="inline">AfterBody</code> is evaluated. In this case the exception is passed on after
│ │ │ @@ -1082,40 +1082,40 @@
│ │ │          </span><span class="n">ExpressionBody</span><span class="w">
│ │ │  </span><span class="k">after</span><span class="w">
│ │ │      </span><span class="n">AfterBody</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="w">
│ │ │  
│ │ │  </span><span class="k">try</span><span class="w"> </span><span class="n">Exprs</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="n">AfterBody</span><span class="w"> </span><span class="k">end</span></code></pre><p>Next is an example of using <code class="inline">after</code>. This closes the file, even in the event of
│ │ │  exceptions in <a href="../../lib/kernel-10.2.7.4/doc/html/file.html#read/2"><code class="inline">file:read/2</code></a> or in <a href="../../erts-15.2.7.8/doc/html/erlang.html#binary_to_term/1"><code class="inline">binary_to_term/1</code></a>. The
│ │ │ -exceptions are the same as without the <code class="inline">try</code>...<code class="inline">after</code>...<code class="inline">end</code> expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">termize_file</span><span class="p" data-group-id="8700629213-1">(</span><span class="n">Name</span><span class="p" data-group-id="8700629213-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8700629213-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="8700629213-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="8700629213-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8700629213-4">[</span><span class="ss">read</span><span class="p">,</span><span class="ss">binary</span><span class="p" data-group-id="8700629213-4">]</span><span class="p" data-group-id="8700629213-3">)</span><span class="p">,</span><span class="w">
│ │ │ +exceptions are the same as without the <code class="inline">try</code>...<code class="inline">after</code>...<code class="inline">end</code> expression:</p><pre><code class="makeup erlang" translate="no"><span class="nf">termize_file</span><span class="p" data-group-id="3586875147-1">(</span><span class="n">Name</span><span class="p" data-group-id="3586875147-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3586875147-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">F</span><span class="p" data-group-id="3586875147-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="3586875147-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3586875147-4">[</span><span class="ss">read</span><span class="p">,</span><span class="ss">binary</span><span class="p" data-group-id="3586875147-4">]</span><span class="p" data-group-id="3586875147-3">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">try</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8700629213-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">Bin</span><span class="p" data-group-id="8700629213-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="8700629213-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p" data-group-id="8700629213-6">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="nf">binary_to_term</span><span class="p" data-group-id="8700629213-7">(</span><span class="n">Bin</span><span class="p" data-group-id="8700629213-7">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3586875147-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="n">Bin</span><span class="p" data-group-id="3586875147-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="3586875147-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p" data-group-id="3586875147-6">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="nf">binary_to_term</span><span class="p" data-group-id="3586875147-7">(</span><span class="n">Bin</span><span class="p" data-group-id="3586875147-7">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w">
│ │ │ -        </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="8700629213-8">(</span><span class="n">F</span><span class="p" data-group-id="8700629213-8">)</span><span class="w">
│ │ │ +        </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="3586875147-8">(</span><span class="n">F</span><span class="p" data-group-id="3586875147-8">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Next is an example of using <code class="inline">try</code> to emulate <code class="inline">catch Expr</code>:</p><pre><code class="makeup erlang" translate="no"><span class="k">try</span><span class="w"> </span><span class="n">Expr</span><span class="w">
│ │ │  </span><span class="k">catch</span><span class="w">
│ │ │      </span><span class="nc">throw</span><span class="p">:</span><span class="n">Term</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Term</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nc">exit</span><span class="p">:</span><span class="n">Reason</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3300859238-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="3300859238-1">}</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nc">error</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stk</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3300859238-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="3300859238-3">{</span><span class="n">Reason</span><span class="p">,</span><span class="n">Stk</span><span class="p" data-group-id="3300859238-3">}</span><span class="p" data-group-id="3300859238-2">}</span><span class="w">
│ │ │ +    </span><span class="nc">exit</span><span class="p">:</span><span class="n">Reason</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1981551269-1">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="n">Reason</span><span class="p" data-group-id="1981551269-1">}</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nc">error</span><span class="p">:</span><span class="n">Reason</span><span class="p">:</span><span class="n">Stk</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1981551269-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="1981551269-3">{</span><span class="n">Reason</span><span class="p">,</span><span class="n">Stk</span><span class="p" data-group-id="1981551269-3">}</span><span class="p" data-group-id="1981551269-2">}</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><p>Variables bound in the various parts of these expressions have different scopes.
│ │ │  Variables bound just after the <code class="inline">try</code> keyword are:</p><ul><li>bound in the <code class="inline">of</code> section</li><li>unsafe in both the <code class="inline">catch</code> and <code class="inline">after</code> sections, as well as after the whole
│ │ │  construct</li></ul><p>Variables bound in <code class="inline">of</code> section are:</p><ul><li>unbound in the <code class="inline">catch</code> section</li><li>unsafe in both the <code class="inline">after</code> section, as well as after the whole construct</li></ul><p>Variables bound in the <code class="inline">catch</code> section are unsafe in the <code class="inline">after</code> section, as
│ │ │  well as after the whole construct.</p><p>Variables bound in the <code class="inline">after</code> section are unsafe after the whole construct.</p><h2 id="parenthesized-expressions" class="section-heading">
│ │ │    <a href="#parenthesized-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Parenthesized Expressions</span>
│ │ │  </h2>
│ │ │ -<pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0954790164-1">(</span><span class="n">Expr</span><span class="p" data-group-id="0954790164-1">)</span></code></pre><p>Parenthesized expressions are useful to override
│ │ │ +<pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6857476895-1">(</span><span class="n">Expr</span><span class="p" data-group-id="6857476895-1">)</span></code></pre><p>Parenthesized expressions are useful to override
│ │ │  <a href="expressions.html#prec">operator precedences</a>, for example, in arithmetic
│ │ │  expressions:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">7</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="0082196797-1">(</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0082196797-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4534757316-1">(</span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4534757316-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">9</span></code></pre><h2 id="block-expressions" class="section-heading">
│ │ │    <a href="#block-expressions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Block Expressions</span>
│ │ │  </h2>
│ │ │  <pre><code class="makeup erlang" translate="no"><span class="k">begin</span><span class="w">
│ │ │ @@ -1127,71 +1127,71 @@
│ │ │    <a href="#comprehensions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Comprehensions</span>
│ │ │  </h2>
│ │ │  <p>Comprehensions provide a succinct notation for iterating over one or more terms
│ │ │  and constructing a new term. Comprehensions come in three different flavors,
│ │ │ -depending on the type of term they build.</p><p>List comprehensions construct lists. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1126350184-1">[</span><span class="n">Expr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="1126350184-1">]</span></code></pre><p>Here, <code class="inline">Expr</code> is an arbitrary expression, and each <code class="inline">Qualifier</code> is either a
│ │ │ +depending on the type of term they build.</p><p>List comprehensions construct lists. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7765206295-1">[</span><span class="n">Expr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="7765206295-1">]</span></code></pre><p>Here, <code class="inline">Expr</code> is an arbitrary expression, and each <code class="inline">Qualifier</code> is either a
│ │ │  <strong>generator</strong> or a <strong>filter</strong>.</p><p>Bit string comprehensions construct bit strings or binaries. They have the
│ │ │ -following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3438746847-1">&lt;&lt;</span><span class="w"> </span><span class="n">BitStringExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="w"> </span><span class="p" data-group-id="3438746847-1">&gt;&gt;</span></code></pre><p><code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string. If
│ │ │ +following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6342347712-1">&lt;&lt;</span><span class="w"> </span><span class="n">BitStringExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="w"> </span><span class="p" data-group-id="6342347712-1">&gt;&gt;</span></code></pre><p><code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string. If
│ │ │  <code class="inline">BitStringExpr</code> is a function call, it must be enclosed in parentheses. Each
│ │ │ -<code class="inline">Qualifier</code> is either a <strong>generator</strong> or a <strong>filter</strong>.</p><p>Map comprehensions construct maps. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2319199244-1">#{</span><span class="n">KeyExpr</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="2319199244-1">}</span></code></pre><p>Here, <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> are arbitrary expressions, and each <code class="inline">Qualifier</code>
│ │ │ +<code class="inline">Qualifier</code> is either a <strong>generator</strong> or a <strong>filter</strong>.</p><p>Map comprehensions construct maps. They have the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9094939886-1">#{</span><span class="n">KeyExpr</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueExpr</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Qualifier1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">QualifierN</span><span class="p" data-group-id="9094939886-1">}</span></code></pre><p>Here, <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> are arbitrary expressions, and each <code class="inline">Qualifier</code>
│ │ │  is either a <strong>generator</strong> or a <strong>filter</strong>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Map comprehensions and map generators were introduced in Erlang/OTP 26.</p></section><p>There are three kinds of generators.</p><p>A <em>list generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">Pattern</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">ListExpr</span></code></pre><p>where <code class="inline">ListExpr</code> is an expression that evaluates to a list of terms.</p><p>A <em>bit string generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">BitstringPattern</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="n">BitStringExpr</span></code></pre><p>where <code class="inline">BitStringExpr</code> is an expression that evaluates to a bit string.</p><p>A <em>map generator</em> has the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">KeyPattern</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">ValuePattern</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">MapExpression</span></code></pre><p>where <code class="inline">MapExpr</code> is an expression that evaluates to a map, or a map iterator
│ │ │  obtained by calling <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html#iterator/1"><code class="inline">maps:iterator/1</code></a> or <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html#iterator/2"><code class="inline">maps:iterator/2</code></a>.</p><p>A <em>filter</em> is an expression that evaluates to <code class="inline">true</code> or <code class="inline">false</code>.</p><p>The variables in the generator patterns shadow previously bound variables,
│ │ │  including variables bound in a previous generator pattern.</p><p>Variables bound in a generator expression are not visible outside the
│ │ │ -expression:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6312880842-1">[</span><span class="p" data-group-id="6312880842-2">{</span><span class="n">E</span><span class="p">,</span><span class="n">L</span><span class="p" data-group-id="6312880842-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="o">=</span><span class="p" data-group-id="6312880842-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6312880842-3">]</span><span class="p" data-group-id="6312880842-1">]</span><span class="p">.</span><span class="w">
│ │ │ +expression:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6964833679-1">[</span><span class="p" data-group-id="6964833679-2">{</span><span class="n">E</span><span class="p">,</span><span class="n">L</span><span class="p" data-group-id="6964833679-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="o">=</span><span class="p" data-group-id="6964833679-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6964833679-3">]</span><span class="p" data-group-id="6964833679-1">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">* 1:5: variable &#39;L&#39; is unbound</span></code></pre><p>A <strong>list comprehension</strong> returns a list, where the list elements are the result
│ │ │  of evaluating <code class="inline">Expr</code> for each combination of generator elements for which all
│ │ │  filters are true.</p><p>A <strong>bit string comprehension</strong> returns a bit string, which is created by
│ │ │  concatenating the results of evaluating <code class="inline">BitStringExpr</code> for each combination of
│ │ │  bit string generator elements for which all filters are true.</p><p>A <strong>map comprehension</strong> returns a map, where the map elements are the result of
│ │ │  evaluating <code class="inline">KeyExpr</code> and <code class="inline">ValueExpr</code> for each combination of generator elements
│ │ │  for which all filters are true. If the key expressions are not unique, the last
│ │ │ -occurrence is stored in the map.</p><p><strong>Examples:</strong></p><p>Multiplying each element in a list by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9891434146-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9891434146-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9891434146-2">]</span><span class="p" data-group-id="9891434146-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9891434146-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9891434146-3">]</span></code></pre><p>Multiplying each byte in a binary by two, returning a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5059984717-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="5059984717-2">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="5059984717-2">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="5059984717-3">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5059984717-3">&gt;&gt;</span><span class="p" data-group-id="5059984717-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5059984717-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5059984717-4">]</span></code></pre><p>Multiplying each byte in a binary by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0627809495-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="0627809495-2">&lt;&lt;</span><span class="p" data-group-id="0627809495-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="0627809495-3">)</span><span class="p" data-group-id="0627809495-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="0627809495-4">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="0627809495-4">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="0627809495-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0627809495-5">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="0627809495-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0627809495-6">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="0627809495-6">&gt;&gt;</span></code></pre><p>Multiplying each element in a list by two, returning a binary:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4427911568-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="4427911568-2">&lt;&lt;</span><span class="p" data-group-id="4427911568-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="4427911568-3">)</span><span class="p" data-group-id="4427911568-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4427911568-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="4427911568-4">]</span><span class="w"> </span><span class="p" data-group-id="4427911568-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4427911568-5">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4427911568-5">&gt;&gt;</span></code></pre><p>Creating a mapping from an integer to its square:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9327683104-1">#{</span><span class="n">X</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="9327683104-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9327683104-2">]</span><span class="p" data-group-id="9327683104-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9327683104-3">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9327683104-3">}</span></code></pre><p>Multiplying the value of each element in a map by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="7315923095-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">V</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="7315923095-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="7315923095-2">}</span><span class="p" data-group-id="7315923095-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7315923095-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="7315923095-3">}</span></code></pre><p>Filtering a list, keeping odd numbers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8371123805-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8371123805-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8371123805-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8371123805-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8371123805-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8371123805-3">]</span></code></pre><p>Filtering a list, keeping only elements that match:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2617440425-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="2617440425-2">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2617440425-2">}</span><span class="o">=</span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="2617440425-3">[</span><span class="p" data-group-id="2617440425-4">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2617440425-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2617440425-5">[</span><span class="ss">a</span><span class="p" data-group-id="2617440425-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2617440425-6">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="2617440425-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2617440425-7">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2617440425-7">}</span><span class="p" data-group-id="2617440425-3">]</span><span class="p" data-group-id="2617440425-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2617440425-8">[</span><span class="p" data-group-id="2617440425-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2617440425-9">}</span><span class="p">,</span><span class="p" data-group-id="2617440425-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2617440425-10">}</span><span class="p" data-group-id="2617440425-8">]</span></code></pre><p>Combining elements from two list generators:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4022979626-1">[</span><span class="p" data-group-id="4022979626-2">{</span><span class="n">P</span><span class="p">,</span><span class="n">Q</span><span class="p" data-group-id="4022979626-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4022979626-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4022979626-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4022979626-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4022979626-4">]</span><span class="p" data-group-id="4022979626-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4022979626-5">[</span><span class="p" data-group-id="4022979626-6">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4022979626-6">}</span><span class="p">,</span><span class="p" data-group-id="4022979626-7">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4022979626-7">}</span><span class="p">,</span><span class="p" data-group-id="4022979626-8">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4022979626-8">}</span><span class="p">,</span><span class="p" data-group-id="4022979626-9">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4022979626-9">}</span><span class="p">,</span><span class="p" data-group-id="4022979626-10">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4022979626-10">}</span><span class="p">,</span><span class="p" data-group-id="4022979626-11">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4022979626-11">}</span><span class="p" data-group-id="4022979626-5">]</span></code></pre><p>More examples are provided in
│ │ │ +occurrence is stored in the map.</p><p><strong>Examples:</strong></p><p>Multiplying each element in a list by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2315769926-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="2315769926-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2315769926-2">]</span><span class="p" data-group-id="2315769926-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2315769926-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2315769926-3">]</span></code></pre><p>Multiplying each byte in a binary by two, returning a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2125494035-1">[</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="2125494035-2">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="2125494035-2">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="2125494035-3">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2125494035-3">&gt;&gt;</span><span class="p" data-group-id="2125494035-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2125494035-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2125494035-4">]</span></code></pre><p>Multiplying each byte in a binary by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9334282614-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="9334282614-2">&lt;&lt;</span><span class="p" data-group-id="9334282614-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="9334282614-3">)</span><span class="p" data-group-id="9334282614-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="9334282614-4">&lt;&lt;</span><span class="n">X</span><span class="p" data-group-id="9334282614-4">&gt;&gt;</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="p" data-group-id="9334282614-5">&lt;&lt;</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="9334282614-5">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="9334282614-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9334282614-6">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9334282614-6">&gt;&gt;</span></code></pre><p>Multiplying each element in a list by two, returning a binary:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="6867760250-1">&lt;&lt;</span><span class="w"> </span><span class="p" data-group-id="6867760250-2">&lt;&lt;</span><span class="p" data-group-id="6867760250-3">(</span><span class="n">X</span><span class="o">*</span><span class="mi">2</span><span class="p" data-group-id="6867760250-3">)</span><span class="p" data-group-id="6867760250-2">&gt;&gt;</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6867760250-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6867760250-4">]</span><span class="w"> </span><span class="p" data-group-id="6867760250-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6867760250-5">&lt;&lt;</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6867760250-5">&gt;&gt;</span></code></pre><p>Creating a mapping from an integer to its square:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2968099018-1">#{</span><span class="n">X</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="2968099018-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2968099018-2">]</span><span class="p" data-group-id="2968099018-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2968099018-3">#{</span><span class="mi">1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="2968099018-3">}</span></code></pre><p>Multiplying the value of each element in a map by two:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="2403987934-1">#{</span><span class="n">K</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">V</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="2403987934-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2403987934-2">}</span><span class="p" data-group-id="2403987934-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2403987934-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="2403987934-3">}</span></code></pre><p>Filtering a list, keeping odd numbers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="5055352591-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5055352591-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5055352591-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5055352591-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5055352591-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="5055352591-3">]</span></code></pre><p>Filtering a list, keeping only elements that match:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="0353225592-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="0353225592-2">{</span><span class="p">_</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0353225592-2">}</span><span class="o">=</span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="0353225592-3">[</span><span class="p" data-group-id="0353225592-4">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="0353225592-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0353225592-5">[</span><span class="ss">a</span><span class="p" data-group-id="0353225592-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0353225592-6">{</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="0353225592-6">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0353225592-7">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0353225592-7">}</span><span class="p" data-group-id="0353225592-3">]</span><span class="p" data-group-id="0353225592-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0353225592-8">[</span><span class="p" data-group-id="0353225592-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="0353225592-9">}</span><span class="p">,</span><span class="p" data-group-id="0353225592-10">{</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0353225592-10">}</span><span class="p" data-group-id="0353225592-8">]</span></code></pre><p>Combining elements from two list generators:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="8889179313-1">[</span><span class="p" data-group-id="8889179313-2">{</span><span class="n">P</span><span class="p">,</span><span class="n">Q</span><span class="p" data-group-id="8889179313-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8889179313-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8889179313-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="8889179313-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8889179313-4">]</span><span class="p" data-group-id="8889179313-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8889179313-5">[</span><span class="p" data-group-id="8889179313-6">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8889179313-6">}</span><span class="p">,</span><span class="p" data-group-id="8889179313-7">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8889179313-7">}</span><span class="p">,</span><span class="p" data-group-id="8889179313-8">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8889179313-8">}</span><span class="p">,</span><span class="p" data-group-id="8889179313-9">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8889179313-9">}</span><span class="p">,</span><span class="p" data-group-id="8889179313-10">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8889179313-10">}</span><span class="p">,</span><span class="p" data-group-id="8889179313-11">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8889179313-11">}</span><span class="p" data-group-id="8889179313-5">]</span></code></pre><p>More examples are provided in
│ │ │  <a href="../../doc/system/list_comprehensions.html">Programming Examples.</a></p><p>When there are no generators, a comprehension returns either a term constructed
│ │ │  from a single element (the result of evaluating <code class="inline">Expr</code>) if all filters are true,
│ │ │  or a term constructed from no elements (that is, <code class="inline">[]</code> for list comprehension,
│ │ │ -<code class="inline">&lt;&lt;&gt;&gt;</code> for a bit string comprehension, and <code class="inline">#{}</code> for a map comprehension).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="1497510124-1">[</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="1497510124-2">(</span><span class="mi">2</span><span class="p" data-group-id="1497510124-2">)</span><span class="p" data-group-id="1497510124-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1497510124-3">[</span><span class="mi">2</span><span class="p" data-group-id="1497510124-3">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="1497510124-4">[</span><span class="ss">x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="1497510124-5">(</span><span class="ss">x</span><span class="p" data-group-id="1497510124-5">)</span><span class="p" data-group-id="1497510124-4">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1497510124-6">[</span><span class="p" data-group-id="1497510124-6">]</span></code></pre><p>What happens when the filter expression does not evaluate to a boolean value
│ │ │ +<code class="inline">&lt;&lt;&gt;&gt;</code> for a bit string comprehension, and <code class="inline">#{}</code> for a map comprehension).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="3403948466-1">[</span><span class="mi">2</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="3403948466-2">(</span><span class="mi">2</span><span class="p" data-group-id="3403948466-2">)</span><span class="p" data-group-id="3403948466-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3403948466-3">[</span><span class="mi">2</span><span class="p" data-group-id="3403948466-3">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="3403948466-4">[</span><span class="ss">x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="3403948466-5">(</span><span class="ss">x</span><span class="p" data-group-id="3403948466-5">)</span><span class="p" data-group-id="3403948466-4">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3403948466-6">[</span><span class="p" data-group-id="3403948466-6">]</span></code></pre><p>What happens when the filter expression does not evaluate to a boolean value
│ │ │  depends on the expression:</p><ul><li>If the expression is a <a href="expressions.html#guard-expressions">guard expression</a>,
│ │ │  failure to evaluate or evaluating to a non-boolean value is equivalent to
│ │ │  evaluating to <code class="inline">false</code>.</li><li>If the expression is not a guard expression and evaluates to a non-Boolean
│ │ │  value <code class="inline">Val</code>, an exception <code class="inline">{bad_filter, Val}</code> is triggered at runtime. If the
│ │ │  evaluation of the expression raises an exception, it is not caught by the
│ │ │ -comprehension.</li></ul><p><strong>Examples</strong> (using a guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6397439874-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="6397439874-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6397439874-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="6397439874-2">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="6397439874-3">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6397439874-3">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6397439874-4">[</span><span class="p" data-group-id="6397439874-4">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="6397439874-5">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6397439874-5">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6397439874-6">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="6397439874-6">]</span></code></pre><p><strong>Examples</strong> (using a non-guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6524510241-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="6524510241-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6524510241-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="6524510241-2">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="n">FaultyIsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6524510241-3">(</span><span class="n">E</span><span class="p" data-group-id="6524510241-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +comprehension.</li></ul><p><strong>Examples</strong> (using a guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7695539659-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7695539659-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7695539659-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7695539659-2">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="7695539659-3">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7695539659-3">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7695539659-4">[</span><span class="p" data-group-id="7695539659-4">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="7695539659-5">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7695539659-5">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7695539659-6">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7695539659-6">]</span></code></pre><p><strong>Examples</strong> (using a non-guard expression as filter):</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1895520481-1">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1895520481-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1895520481-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1895520481-2">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="n">FaultyIsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1895520481-3">(</span><span class="n">E</span><span class="p" data-group-id="1895520481-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">42.17316486</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="6524510241-4">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">FaultyIsEven</span><span class="p" data-group-id="6524510241-5">(</span><span class="n">E</span><span class="p" data-group-id="6524510241-5">)</span><span class="p" data-group-id="6524510241-4">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="p" data-group-id="1895520481-4">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">FaultyIsEven</span><span class="p" data-group-id="1895520481-5">(</span><span class="n">E</span><span class="p" data-group-id="1895520481-5">)</span><span class="p" data-group-id="1895520481-4">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: bad filter 1</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="n">IsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6524510241-6">(</span><span class="n">E</span><span class="p" data-group-id="6524510241-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="n">IsEven</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1895520481-6">(</span><span class="n">E</span><span class="p" data-group-id="1895520481-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">42.17316486</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="6524510241-7">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="6524510241-8">(</span><span class="n">E</span><span class="p" data-group-id="6524510241-8">)</span><span class="p" data-group-id="6524510241-7">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="1895520481-7">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="1895520481-8">(</span><span class="n">E</span><span class="p" data-group-id="1895520481-8">)</span><span class="p" data-group-id="1895520481-7">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: an error occurred when evaluating an arithmetic expression
│ │ │       in operator  rem/2
│ │ │          called as a rem 2</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="p" data-group-id="6524510241-9">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6524510241-10">(</span><span class="n">E</span><span class="p" data-group-id="6524510241-10">)</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="6524510241-11">(</span><span class="n">E</span><span class="p" data-group-id="6524510241-11">)</span><span class="p" data-group-id="6524510241-9">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6524510241-12">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="6524510241-12">]</span></code></pre><p><a href="" id="guards"></a></p><h2 id="guard-sequences" class="section-heading">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="p" data-group-id="1895520481-9">[</span><span class="n">E</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="1895520481-10">(</span><span class="n">E</span><span class="p" data-group-id="1895520481-10">)</span><span class="p">,</span><span class="w"> </span><span class="n">IsEven</span><span class="p" data-group-id="1895520481-11">(</span><span class="n">E</span><span class="p" data-group-id="1895520481-11">)</span><span class="p" data-group-id="1895520481-9">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1895520481-12">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1895520481-12">]</span></code></pre><p><a href="" id="guards"></a></p><h2 id="guard-sequences" class="section-heading">
│ │ │    <a href="#guard-sequences" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Guard Sequences</span>
│ │ │  </h2>
│ │ │  <p>A <em>guard sequence</em> is a sequence of guards, separated by semicolon (<code class="inline">;</code>). The
│ │ │  guard sequence is true if at least one of the guards is true. (The remaining
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/funs.html
│ │ │ @@ -117,402 +117,402 @@
│ │ │  
│ │ │  <h2 id="map" class="section-heading">
│ │ │    <a href="#map" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">map</span>
│ │ │  </h2>
│ │ │ -<p>The following function, <code class="inline">double</code>, doubles every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="0810059228-1">(</span><span class="p" data-group-id="0810059228-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0810059228-2">]</span><span class="p" data-group-id="0810059228-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0810059228-3">[</span><span class="mi">2</span><span class="o">*</span><span class="n">H</span><span class="p">|</span><span class="nf">double</span><span class="p" data-group-id="0810059228-4">(</span><span class="n">T</span><span class="p" data-group-id="0810059228-4">)</span><span class="p" data-group-id="0810059228-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="0810059228-5">(</span><span class="p" data-group-id="0810059228-6">[</span><span class="p" data-group-id="0810059228-6">]</span><span class="p" data-group-id="0810059228-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0810059228-7">[</span><span class="p" data-group-id="0810059228-7">]</span><span class="p">.</span></code></pre><p>Hence, the argument entered as input is doubled as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">double</span><span class="p" data-group-id="0835101506-1">(</span><span class="p" data-group-id="0835101506-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0835101506-2">]</span><span class="p" data-group-id="0835101506-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0835101506-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p" data-group-id="0835101506-3">]</span></code></pre><p>The following function, <code class="inline">add_one</code>, adds one to every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add_one</span><span class="p" data-group-id="8767530053-1">(</span><span class="p" data-group-id="8767530053-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8767530053-2">]</span><span class="p" data-group-id="8767530053-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8767530053-3">[</span><span class="n">H</span><span class="o">+</span><span class="mi">1</span><span class="p">|</span><span class="nf">add_one</span><span class="p" data-group-id="8767530053-4">(</span><span class="n">T</span><span class="p" data-group-id="8767530053-4">)</span><span class="p" data-group-id="8767530053-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">add_one</span><span class="p" data-group-id="8767530053-5">(</span><span class="p" data-group-id="8767530053-6">[</span><span class="p" data-group-id="8767530053-6">]</span><span class="p" data-group-id="8767530053-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8767530053-7">[</span><span class="p" data-group-id="8767530053-7">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> have a similar structure. This can be used
│ │ │ -by writing a function <code class="inline">map</code> that expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="4004740402-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4004740402-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4004740402-2">]</span><span class="p" data-group-id="4004740402-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4004740402-3">[</span><span class="n">F</span><span class="p" data-group-id="4004740402-4">(</span><span class="n">H</span><span class="p" data-group-id="4004740402-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="4004740402-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4004740402-5">)</span><span class="p" data-group-id="4004740402-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="4004740402-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4004740402-7">[</span><span class="p" data-group-id="4004740402-7">]</span><span class="p" data-group-id="4004740402-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4004740402-8">[</span><span class="p" data-group-id="4004740402-8">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> can now be expressed in terms of <code class="inline">map</code> as
│ │ │ -follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="6770629906-1">(</span><span class="n">L</span><span class="p" data-group-id="6770629906-1">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="6770629906-2">(</span><span class="nf">fun</span><span class="p" data-group-id="6770629906-3">(</span><span class="n">X</span><span class="p" data-group-id="6770629906-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6770629906-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">add_one</span><span class="p" data-group-id="6770629906-4">(</span><span class="n">L</span><span class="p" data-group-id="6770629906-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="6770629906-5">(</span><span class="nf">fun</span><span class="p" data-group-id="6770629906-6">(</span><span class="n">X</span><span class="p" data-group-id="6770629906-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6770629906-5">)</span><span class="p">.</span></code></pre><p><code class="inline">map(F, List)</code> is a function that takes a function <code class="inline">F</code> and a list <code class="inline">L</code> as
│ │ │ +<p>The following function, <code class="inline">double</code>, doubles every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="1471562974-1">(</span><span class="p" data-group-id="1471562974-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1471562974-2">]</span><span class="p" data-group-id="1471562974-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1471562974-3">[</span><span class="mi">2</span><span class="o">*</span><span class="n">H</span><span class="p">|</span><span class="nf">double</span><span class="p" data-group-id="1471562974-4">(</span><span class="n">T</span><span class="p" data-group-id="1471562974-4">)</span><span class="p" data-group-id="1471562974-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="1471562974-5">(</span><span class="p" data-group-id="1471562974-6">[</span><span class="p" data-group-id="1471562974-6">]</span><span class="p" data-group-id="1471562974-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1471562974-7">[</span><span class="p" data-group-id="1471562974-7">]</span><span class="p">.</span></code></pre><p>Hence, the argument entered as input is doubled as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">double</span><span class="p" data-group-id="9351452940-1">(</span><span class="p" data-group-id="9351452940-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="9351452940-2">]</span><span class="p" data-group-id="9351452940-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9351452940-3">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p" data-group-id="9351452940-3">]</span></code></pre><p>The following function, <code class="inline">add_one</code>, adds one to every element in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">add_one</span><span class="p" data-group-id="8995633419-1">(</span><span class="p" data-group-id="8995633419-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8995633419-2">]</span><span class="p" data-group-id="8995633419-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8995633419-3">[</span><span class="n">H</span><span class="o">+</span><span class="mi">1</span><span class="p">|</span><span class="nf">add_one</span><span class="p" data-group-id="8995633419-4">(</span><span class="n">T</span><span class="p" data-group-id="8995633419-4">)</span><span class="p" data-group-id="8995633419-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">add_one</span><span class="p" data-group-id="8995633419-5">(</span><span class="p" data-group-id="8995633419-6">[</span><span class="p" data-group-id="8995633419-6">]</span><span class="p" data-group-id="8995633419-5">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8995633419-7">[</span><span class="p" data-group-id="8995633419-7">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> have a similar structure. This can be used
│ │ │ +by writing a function <code class="inline">map</code> that expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="8625611221-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8625611221-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8625611221-2">]</span><span class="p" data-group-id="8625611221-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8625611221-3">[</span><span class="n">F</span><span class="p" data-group-id="8625611221-4">(</span><span class="n">H</span><span class="p" data-group-id="8625611221-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="8625611221-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8625611221-5">)</span><span class="p" data-group-id="8625611221-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="8625611221-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8625611221-7">[</span><span class="p" data-group-id="8625611221-7">]</span><span class="p" data-group-id="8625611221-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8625611221-8">[</span><span class="p" data-group-id="8625611221-8">]</span><span class="p">.</span></code></pre><p>The functions <code class="inline">double</code> and <code class="inline">add_one</code> can now be expressed in terms of <code class="inline">map</code> as
│ │ │ +follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">double</span><span class="p" data-group-id="8111098215-1">(</span><span class="n">L</span><span class="p" data-group-id="8111098215-1">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="8111098215-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8111098215-3">(</span><span class="n">X</span><span class="p" data-group-id="8111098215-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="8111098215-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">add_one</span><span class="p" data-group-id="8111098215-4">(</span><span class="n">L</span><span class="p" data-group-id="8111098215-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="8111098215-5">(</span><span class="nf">fun</span><span class="p" data-group-id="8111098215-6">(</span><span class="n">X</span><span class="p" data-group-id="8111098215-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="8111098215-5">)</span><span class="p">.</span></code></pre><p><code class="inline">map(F, List)</code> is a function that takes a function <code class="inline">F</code> and a list <code class="inline">L</code> as
│ │ │  arguments and returns a new list, obtained by applying <code class="inline">F</code> to each of the
│ │ │  elements in <code class="inline">L</code>.</p><p>The process of abstracting out the common features of a number of different
│ │ │  programs is called <em>procedural abstraction</em>. Procedural abstraction can be used
│ │ │  to write several different functions that have a similar structure, but differ
│ │ │  in some minor detail. This is done as follows:</p><ol><li><em>Step 1.</em> Write one function that represents the common features of these
│ │ │  functions.</li><li><em>Step 2.</em> Parameterize the difference in terms of functions that are passed
│ │ │  as arguments to the common function.</li></ol><h2 id="foreach" class="section-heading">
│ │ │    <a href="#foreach" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">foreach</span>
│ │ │  </h2>
│ │ │  <p>This section illustrates procedural abstraction. Initially, the following two
│ │ │ -examples are written as conventional functions.</p><p>This function prints all elements of a list onto a stream:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="3209451929-1">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3209451929-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3209451929-2">]</span><span class="p" data-group-id="3209451929-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3209451929-3">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3209451929-4">[</span><span class="n">H</span><span class="p" data-group-id="3209451929-4">]</span><span class="p" data-group-id="3209451929-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_list</span><span class="p" data-group-id="3209451929-5">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3209451929-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">print_list</span><span class="p" data-group-id="3209451929-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3209451929-7">[</span><span class="p" data-group-id="3209451929-7">]</span><span class="p" data-group-id="3209451929-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>This function broadcasts a message to a list of processes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">broadcast</span><span class="p" data-group-id="5966804176-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5966804176-2">[</span><span class="n">Pid</span><span class="p">|</span><span class="n">Pids</span><span class="p" data-group-id="5966804176-2">]</span><span class="p" data-group-id="5966804176-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +examples are written as conventional functions.</p><p>This function prints all elements of a list onto a stream:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="6101101673-1">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6101101673-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6101101673-2">]</span><span class="p" data-group-id="6101101673-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6101101673-3">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6101101673-4">[</span><span class="n">H</span><span class="p" data-group-id="6101101673-4">]</span><span class="p" data-group-id="6101101673-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_list</span><span class="p" data-group-id="6101101673-5">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6101101673-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">print_list</span><span class="p" data-group-id="6101101673-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6101101673-7">[</span><span class="p" data-group-id="6101101673-7">]</span><span class="p" data-group-id="6101101673-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>This function broadcasts a message to a list of processes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">broadcast</span><span class="p" data-group-id="4510256336-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4510256336-2">[</span><span class="n">Pid</span><span class="p">|</span><span class="n">Pids</span><span class="p" data-group-id="4510256336-2">]</span><span class="p" data-group-id="4510256336-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">Msg</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">broadcast</span><span class="p" data-group-id="5966804176-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">Pids</span><span class="p" data-group-id="5966804176-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">broadcast</span><span class="p" data-group-id="5966804176-4">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5966804176-5">[</span><span class="p" data-group-id="5966804176-5">]</span><span class="p" data-group-id="5966804176-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">broadcast</span><span class="p" data-group-id="4510256336-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">Pids</span><span class="p" data-group-id="4510256336-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">broadcast</span><span class="p" data-group-id="4510256336-4">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4510256336-5">[</span><span class="p" data-group-id="4510256336-5">]</span><span class="p" data-group-id="4510256336-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="p">.</span></code></pre><p>These two functions have a similar structure. They both iterate over a list and
│ │ │  do something to each element in the list. The &quot;something&quot; is passed on as an
│ │ │ -extra argument to the function that does this.</p><p>The function <code class="inline">foreach</code> expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="0636543333-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0636543333-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0636543333-2">]</span><span class="p" data-group-id="0636543333-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">F</span><span class="p" data-group-id="0636543333-3">(</span><span class="n">H</span><span class="p" data-group-id="0636543333-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="0636543333-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="0636543333-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="0636543333-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0636543333-6">[</span><span class="p" data-group-id="0636543333-6">]</span><span class="p" data-group-id="0636543333-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">print_list</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="1764281542-1">(</span><span class="nf">fun</span><span class="p" data-group-id="1764281542-2">(</span><span class="n">H</span><span class="p" data-group-id="1764281542-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1764281542-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="1764281542-4">[</span><span class="n">H</span><span class="p" data-group-id="1764281542-4">]</span><span class="p" data-group-id="1764281542-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1764281542-1">)</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">broadcast</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="9158049011-1">(</span><span class="nf">fun</span><span class="p" data-group-id="9158049011-2">(</span><span class="n">Pid</span><span class="p" data-group-id="9158049011-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="9158049011-1">)</span></code></pre><p><code class="inline">foreach</code> is evaluated for its side-effect and not its value. <code class="inline">foreach(Fun ,L)</code>
│ │ │ +extra argument to the function that does this.</p><p>The function <code class="inline">foreach</code> expresses this similarity:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="0096746018-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0096746018-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0096746018-2">]</span><span class="p" data-group-id="0096746018-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">F</span><span class="p" data-group-id="0096746018-3">(</span><span class="n">H</span><span class="p" data-group-id="0096746018-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="0096746018-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="0096746018-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="0096746018-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0096746018-6">[</span><span class="p" data-group-id="0096746018-6">]</span><span class="p" data-group-id="0096746018-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">print_list</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="2217185510-1">(</span><span class="nf">fun</span><span class="p" data-group-id="2217185510-2">(</span><span class="n">H</span><span class="p" data-group-id="2217185510-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2217185510-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="2217185510-4">[</span><span class="n">H</span><span class="p" data-group-id="2217185510-4">]</span><span class="p" data-group-id="2217185510-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2217185510-1">)</span></code></pre><p>Using the function <code class="inline">foreach</code>, the function <code class="inline">broadcast</code> becomes:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="8619143625-1">(</span><span class="nf">fun</span><span class="p" data-group-id="8619143625-2">(</span><span class="n">Pid</span><span class="p" data-group-id="8619143625-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="8619143625-1">)</span></code></pre><p><code class="inline">foreach</code> is evaluated for its side-effect and not its value. <code class="inline">foreach(Fun ,L)</code>
│ │ │  calls <code class="inline">Fun(X)</code> for each element <code class="inline">X</code> in <code class="inline">L</code> and the processing occurs in the
│ │ │  order that the elements were defined in <code class="inline">L</code>. <code class="inline">map</code> does not define the order in
│ │ │  which its elements are processed.</p><h2 id="syntax-of-funs" class="section-heading">
│ │ │    <a href="#syntax-of-funs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Syntax of Funs</span>
│ │ │  </h2>
│ │ │  <p>Funs are written with the following syntax (see
│ │ │ -<a href="../../doc/system/expressions.html#fun-expressions">Fun Expressions </a>for full description):</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2308336496-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">ArgN</span><span class="p" data-group-id="2308336496-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<a href="../../doc/system/expressions.html#fun-expressions">Fun Expressions </a>for full description):</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7607106852-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="n">ArgN</span><span class="p" data-group-id="7607106852-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">end</span></code></pre><p>This creates an anonymous function of <code class="inline">N</code> arguments and binds it to the variable
│ │ │  <code class="inline">F</code>.</p><p>Another function, <code class="inline">FunctionName</code>, written in the same module, can be passed as
│ │ │  an argument, using the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>With this form of function reference, the function that is referred to does not
│ │ │  need to be exported from the module.</p><p>It is also possible to refer to a function defined in a different module, with
│ │ │ -the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In this case, the function must be exported from the module in question.</p><p>The following program illustrates the different ways of creating funs:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6758080295-1">(</span><span class="ss">fun_test</span><span class="p" data-group-id="6758080295-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6758080295-2">(</span><span class="p" data-group-id="6758080295-3">[</span><span class="ss">t1</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">t2</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6758080295-3">]</span><span class="p" data-group-id="6758080295-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="6758080295-4">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6758080295-5">[</span><span class="ss">map</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="6758080295-5">]</span><span class="p" data-group-id="6758080295-4">)</span><span class="p">.</span><span class="w">
│ │ │ +the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">Module</span><span class="p">:</span><span class="n">FunctionName</span><span class="o">/</span><span class="n">Arity</span></code></pre><p>In this case, the function must be exported from the module in question.</p><p>The following program illustrates the different ways of creating funs:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7863248049-1">(</span><span class="ss">fun_test</span><span class="p" data-group-id="7863248049-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7863248049-2">(</span><span class="p" data-group-id="7863248049-3">[</span><span class="ss">t1</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">t2</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7863248049-3">]</span><span class="p" data-group-id="7863248049-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">import</span><span class="p" data-group-id="7863248049-4">(</span><span class="ss">lists</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7863248049-5">[</span><span class="ss">map</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7863248049-5">]</span><span class="p" data-group-id="7863248049-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">t1</span><span class="p" data-group-id="6758080295-6">(</span><span class="p" data-group-id="6758080295-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="6758080295-7">(</span><span class="nf">fun</span><span class="p" data-group-id="6758080295-8">(</span><span class="n">X</span><span class="p" data-group-id="6758080295-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6758080295-9">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="6758080295-9">]</span><span class="p" data-group-id="6758080295-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">t1</span><span class="p" data-group-id="7863248049-6">(</span><span class="p" data-group-id="7863248049-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="7863248049-7">(</span><span class="nf">fun</span><span class="p" data-group-id="7863248049-8">(</span><span class="n">X</span><span class="p" data-group-id="7863248049-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7863248049-9">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7863248049-9">]</span><span class="p" data-group-id="7863248049-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">t2</span><span class="p" data-group-id="6758080295-10">(</span><span class="p" data-group-id="6758080295-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="6758080295-11">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6758080295-12">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="6758080295-12">]</span><span class="p" data-group-id="6758080295-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">t2</span><span class="p" data-group-id="7863248049-10">(</span><span class="p" data-group-id="7863248049-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">map</span><span class="p" data-group-id="7863248049-11">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7863248049-12">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7863248049-12">]</span><span class="p" data-group-id="7863248049-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="6758080295-13">(</span><span class="n">X</span><span class="p" data-group-id="6758080295-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span></code></pre><p>The fun <code class="inline">F</code> can be evaluated with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="p" data-group-id="1804379687-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Argn</span><span class="p" data-group-id="1804379687-1">)</span></code></pre><p>To check whether a term is a fun, use the test
│ │ │ -<a href="../../erts-15.2.7.8/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> in a guard.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="3916268086-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="3916268086-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_function</span><span class="p" data-group-id="3916268086-2">(</span><span class="n">F</span><span class="p" data-group-id="3916268086-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="nf">apply</span><span class="p" data-group-id="3916268086-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="3916268086-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="3916268086-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3916268086-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="3916268086-5">(</span><span class="n">N</span><span class="p" data-group-id="3916268086-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="7863248049-13">(</span><span class="n">X</span><span class="p" data-group-id="7863248049-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span></code></pre><p>The fun <code class="inline">F</code> can be evaluated with the following syntax:</p><pre><code class="makeup erlang" translate="no"><span class="n">F</span><span class="p" data-group-id="8693122942-1">(</span><span class="n">Arg1</span><span class="p">,</span><span class="w"> </span><span class="n">Arg2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Argn</span><span class="p" data-group-id="8693122942-1">)</span></code></pre><p>To check whether a term is a fun, use the test
│ │ │ +<a href="../../erts-15.2.7.8/doc/html/erlang.html#is_function/1"><code class="inline">is_function/1</code></a> in a guard.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="2465010621-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="2465010621-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_function</span><span class="p" data-group-id="2465010621-2">(</span><span class="n">F</span><span class="p" data-group-id="2465010621-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="nf">apply</span><span class="p" data-group-id="2465010621-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="2465010621-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="2465010621-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2465010621-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="2465010621-5">(</span><span class="n">N</span><span class="p" data-group-id="2465010621-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │     </span><span class="n">N</span><span class="p">.</span></code></pre><p>Funs are a distinct type. The BIFs <code class="inline">erlang:fun_info/1,2</code> can be used to retrieve
│ │ │  information about a fun, and the BIF <a href="../../erts-15.2.7.8/doc/html/erlang.html#fun_to_list/1"><code class="inline">erlang:fun_to_list/1</code></a> returns a textual
│ │ │  representation of a fun. The <a href="../../erts-15.2.7.8/doc/html/erlang.html#check_process_code/2"><code class="inline">check_process_code/2</code></a>
│ │ │  BIF returns <code class="inline">true</code> if the process contains funs that depend on the old version
│ │ │  of a module.</p><h2 id="variable-bindings-within-a-fun" class="section-heading">
│ │ │    <a href="#variable-bindings-within-a-fun" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Variable Bindings Within a Fun</span>
│ │ │  </h2>
│ │ │  <p>The scope rules for variables that occur in funs are as follows:</p><ul><li>All variables that occur in the head of a fun are assumed to be &quot;fresh&quot;
│ │ │  variables.</li><li>Variables that are defined before the fun, and that occur in function calls or
│ │ │ -guard tests within the fun, have the values they had outside the fun.</li><li>Variables cannot be exported from a fun.</li></ul><p>The following examples illustrate these rules:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="7444609882-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7444609882-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7444609882-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="7444609882-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="7444609882-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="7444609882-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="7444609882-4">(</span><span class="nf">fun</span><span class="p" data-group-id="7444609882-5">(</span><span class="n">X</span><span class="p" data-group-id="7444609882-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7444609882-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="7444609882-7">[</span><span class="n">X</span><span class="p" data-group-id="7444609882-7">]</span><span class="p" data-group-id="7444609882-6">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7444609882-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="7444609882-8">(</span><span class="n">Stream</span><span class="p" data-group-id="7444609882-8">)</span><span class="p">.</span></code></pre><p>Here, the variable <code class="inline">X</code>, defined in the head of the fun, is a new variable. The
│ │ │ +guard tests within the fun, have the values they had outside the fun.</li><li>Variables cannot be exported from a fun.</li></ul><p>The following examples illustrate these rules:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="3751014535-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3751014535-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3751014535-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="3751014535-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="3751014535-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="3751014535-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="3751014535-4">(</span><span class="nf">fun</span><span class="p" data-group-id="3751014535-5">(</span><span class="n">X</span><span class="p" data-group-id="3751014535-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3751014535-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3751014535-7">[</span><span class="n">X</span><span class="p" data-group-id="3751014535-7">]</span><span class="p" data-group-id="3751014535-6">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3751014535-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="3751014535-8">(</span><span class="n">Stream</span><span class="p" data-group-id="3751014535-8">)</span><span class="p">.</span></code></pre><p>Here, the variable <code class="inline">X</code>, defined in the head of the fun, is a new variable. The
│ │ │  variable <code class="inline">Stream</code>, which is used within the fun, gets its value from the
│ │ │  <code class="inline">file:open</code> line.</p><p>As any variable that occurs in the head of a fun is considered a new variable,
│ │ │ -it is equally valid to write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="9910071119-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9910071119-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9910071119-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="9910071119-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="9910071119-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="9910071119-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="9910071119-4">(</span><span class="nf">fun</span><span class="p" data-group-id="9910071119-5">(</span><span class="n">File</span><span class="p" data-group-id="9910071119-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9910071119-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="9910071119-7">[</span><span class="n">File</span><span class="p" data-group-id="9910071119-7">]</span><span class="p" data-group-id="9910071119-6">)</span><span class="w">
│ │ │ -            </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9910071119-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="9910071119-8">(</span><span class="n">Stream</span><span class="p" data-group-id="9910071119-8">)</span><span class="p">.</span></code></pre><p>Here, <code class="inline">File</code> is used as the new variable instead of <code class="inline">X</code>. This is not so wise
│ │ │ +it is equally valid to write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">print_list</span><span class="p" data-group-id="1371272170-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1371272170-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1371272170-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Stream</span><span class="p" data-group-id="1371272170-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">file</span><span class="p">:</span><span class="nf">open</span><span class="p" data-group-id="1371272170-3">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="ss">write</span><span class="p" data-group-id="1371272170-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="1371272170-4">(</span><span class="nf">fun</span><span class="p" data-group-id="1371272170-5">(</span><span class="n">File</span><span class="p" data-group-id="1371272170-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1371272170-6">(</span><span class="n">Stream</span><span class="p">,</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="1371272170-7">[</span><span class="n">File</span><span class="p" data-group-id="1371272170-7">]</span><span class="p" data-group-id="1371272170-6">)</span><span class="w">
│ │ │ +            </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1371272170-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">file</span><span class="p">:</span><span class="nf">close</span><span class="p" data-group-id="1371272170-8">(</span><span class="n">Stream</span><span class="p" data-group-id="1371272170-8">)</span><span class="p">.</span></code></pre><p>Here, <code class="inline">File</code> is used as the new variable instead of <code class="inline">X</code>. This is not so wise
│ │ │  because code in the fun body cannot refer to the variable <code class="inline">File</code>, which is
│ │ │  defined outside of the fun. Compiling this example gives the following
│ │ │  diagnostic:</p><pre><code class="text">./FileName.erl:Line: Warning: variable 'File'
│ │ │        shadowed in 'fun'</code></pre><p>This indicates that the variable <code class="inline">File</code>, which is defined inside the fun,
│ │ │  collides with the variable <code class="inline">File</code>, which is defined outside the fun.</p><p>The rules for importing variables into a fun has the consequence that certain
│ │ │  pattern matching operations must be moved into guard expressions and cannot be
│ │ │  written in the head of the fun. For example, you might write the following code
│ │ │  if you intend the first clause of <code class="inline">F</code> to be evaluated when the value of its
│ │ │ -argument is <code class="inline">Y</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="2377626012-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2377626012-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +argument is <code class="inline">Y</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4266431979-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4266431979-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="nf">map</span><span class="p" data-group-id="2377626012-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2377626012-3">(</span><span class="n">X</span><span class="p" data-group-id="2377626012-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">map</span><span class="p" data-group-id="4266431979-2">(</span><span class="nf">fun</span><span class="p" data-group-id="4266431979-3">(</span><span class="n">X</span><span class="p" data-group-id="4266431979-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │               </span><span class="p">;</span><span class="w">
│ │ │ -           </span><span class="p" data-group-id="2377626012-4">(</span><span class="p">_</span><span class="p" data-group-id="2377626012-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +           </span><span class="p" data-group-id="4266431979-4">(</span><span class="p">_</span><span class="p" data-group-id="4266431979-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │               </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2377626012-2">)</span><span class="w">
│ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>instead of writing the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4402133187-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4402133187-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4266431979-2">)</span><span class="w">
│ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>instead of writing the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="1668527117-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1668527117-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="nf">map</span><span class="p" data-group-id="4402133187-2">(</span><span class="nf">fun</span><span class="p" data-group-id="4402133187-3">(</span><span class="n">Y</span><span class="p" data-group-id="4402133187-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">map</span><span class="p" data-group-id="1668527117-2">(</span><span class="nf">fun</span><span class="p" data-group-id="1668527117-3">(</span><span class="n">Y</span><span class="p" data-group-id="1668527117-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │               </span><span class="p">;</span><span class="w">
│ │ │ -           </span><span class="p" data-group-id="4402133187-4">(</span><span class="p">_</span><span class="p" data-group-id="4402133187-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +           </span><span class="p" data-group-id="1668527117-4">(</span><span class="p">_</span><span class="p" data-group-id="1668527117-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │               </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4402133187-2">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1668527117-2">)</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="funs-and-module-lists" class="section-heading">
│ │ │    <a href="#funs-and-module-lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Funs and Module Lists</span>
│ │ │  </h2>
│ │ │  <p>The following examples show a dialogue with the Erlang shell. All the higher
│ │ │  order functions discussed are exported from the module <a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html"><code class="inline">lists</code></a>.</p><h3 id="map-1" class="section-heading">
│ │ │    <a href="#map-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">map</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="5409363821-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5409363821-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5409363821-2">]</span><span class="p" data-group-id="5409363821-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5409363821-3">[</span><span class="n">F</span><span class="p" data-group-id="5409363821-4">(</span><span class="n">H</span><span class="p" data-group-id="5409363821-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="5409363821-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5409363821-5">)</span><span class="p" data-group-id="5409363821-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="5409363821-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5409363821-7">[</span><span class="p" data-group-id="5409363821-7">]</span><span class="p" data-group-id="5409363821-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5409363821-8">[</span><span class="p" data-group-id="5409363821-8">]</span><span class="p">.</span></code></pre><p>It returns the list obtained by applying the function to every argument in the
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">map</span><span class="p" data-group-id="3198224736-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3198224736-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3198224736-2">]</span><span class="p" data-group-id="3198224736-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3198224736-3">[</span><span class="n">F</span><span class="p" data-group-id="3198224736-4">(</span><span class="n">H</span><span class="p" data-group-id="3198224736-4">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="3198224736-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3198224736-5">)</span><span class="p" data-group-id="3198224736-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="3198224736-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3198224736-7">[</span><span class="p" data-group-id="3198224736-7">]</span><span class="p" data-group-id="3198224736-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3198224736-8">[</span><span class="p" data-group-id="3198224736-8">]</span><span class="p">.</span></code></pre><p>It returns the list obtained by applying the function to every argument in the
│ │ │  list.</p><p>When a new fun is defined in the shell, the value of the fun is printed as
│ │ │ -<code class="inline">Fun#&lt;erl_eval&gt;</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Double</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="4975652487-1">(</span><span class="n">X</span><span class="p" data-group-id="4975652487-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">Fun#&lt;erl_eval&gt;</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Double</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="2069427638-1">(</span><span class="n">X</span><span class="p" data-group-id="2069427638-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="4975652487-2">(</span><span class="n">Double</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4975652487-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4975652487-3">]</span><span class="p" data-group-id="4975652487-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4975652487-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="4975652487-4">]</span></code></pre><h3 id="any" class="section-heading">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="2069427638-2">(</span><span class="n">Double</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2069427638-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2069427638-3">]</span><span class="p" data-group-id="2069427638-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2069427638-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="2069427638-4">]</span></code></pre><h3 id="any" class="section-heading">
│ │ │    <a href="#any" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">any</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#any/2"><code class="inline">lists:any/2</code></a> takes a predicate <code class="inline">P</code> of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">any</span><span class="p" data-group-id="3658898463-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3658898463-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3658898463-2">]</span><span class="p" data-group-id="3658898463-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="3658898463-3">(</span><span class="n">H</span><span class="p" data-group-id="3658898463-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#any/2"><code class="inline">lists:any/2</code></a> takes a predicate <code class="inline">P</code> of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">any</span><span class="p" data-group-id="7864782250-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7864782250-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7864782250-2">]</span><span class="p" data-group-id="7864782250-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="7864782250-3">(</span><span class="n">H</span><span class="p" data-group-id="7864782250-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">any</span><span class="p" data-group-id="3658898463-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="3658898463-4">)</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">any</span><span class="p" data-group-id="7864782250-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="7864782250-4">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">any</span><span class="p" data-group-id="3658898463-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3658898463-6">[</span><span class="p" data-group-id="3658898463-6">]</span><span class="p" data-group-id="3658898463-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">any</span><span class="p" data-group-id="7864782250-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7864782250-6">[</span><span class="p" data-group-id="7864782250-6">]</span><span class="p" data-group-id="7864782250-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">false</span><span class="p">.</span></code></pre><p>A predicate is a function that returns <code class="inline">true</code> or <code class="inline">false</code>. <code class="inline">any</code> is <code class="inline">true</code> if
│ │ │  there is a term <code class="inline">X</code> in the list such that <code class="inline">P(X)</code> is <code class="inline">true</code>.</p><p>A predicate <code class="inline">Big(X)</code> is defined, which is <code class="inline">true</code> if its argument is greater that
│ │ │ -10:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Big</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="7236742420-1">(</span><span class="n">X</span><span class="p" data-group-id="7236742420-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="p">;</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +10:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Big</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="9263604844-1">(</span><span class="n">X</span><span class="p" data-group-id="9263604844-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="p">;</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="7236742420-2">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7236742420-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7236742420-3">]</span><span class="p" data-group-id="7236742420-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="9263604844-2">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9263604844-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="9263604844-3">]</span><span class="p" data-group-id="9263604844-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="7236742420-4">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7236742420-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7236742420-5">]</span><span class="p" data-group-id="7236742420-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">any</span><span class="p" data-group-id="9263604844-4">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9263604844-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="9263604844-5">]</span><span class="p" data-group-id="9263604844-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><h3 id="all" class="section-heading">
│ │ │    <a href="#all" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">all</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#all/2"><code class="inline">lists:all/2</code></a> has the same arguments as <code class="inline">any</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="8988253284-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8988253284-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8988253284-2">]</span><span class="p" data-group-id="8988253284-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="8988253284-3">(</span><span class="n">H</span><span class="p" data-group-id="8988253284-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">all</span><span class="p" data-group-id="8988253284-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="8988253284-4">)</span><span class="p">;</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#all/2"><code class="inline">lists:all/2</code></a> has the same arguments as <code class="inline">any</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">all</span><span class="p" data-group-id="4818667852-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4818667852-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4818667852-2">]</span><span class="p" data-group-id="4818667852-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="4818667852-3">(</span><span class="n">H</span><span class="p" data-group-id="4818667852-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">  </span><span class="nf">all</span><span class="p" data-group-id="4818667852-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4818667852-4">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="ss">false</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">all</span><span class="p" data-group-id="8988253284-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8988253284-6">[</span><span class="p" data-group-id="8988253284-6">]</span><span class="p" data-group-id="8988253284-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>It is <code class="inline">true</code> if the predicate applied to all elements in the list is <code class="inline">true</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="5693056763-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5693056763-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5693056763-2">]</span><span class="p" data-group-id="5693056763-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">all</span><span class="p" data-group-id="4818667852-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4818667852-6">[</span><span class="p" data-group-id="4818667852-6">]</span><span class="p" data-group-id="4818667852-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">true</span><span class="p">.</span></code></pre><p>It is <code class="inline">true</code> if the predicate applied to all elements in the list is <code class="inline">true</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="2335445700-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2335445700-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="2335445700-2">]</span><span class="p" data-group-id="2335445700-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="5693056763-3">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5693056763-4">[</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="5693056763-4">]</span><span class="p" data-group-id="5693056763-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">all</span><span class="p" data-group-id="2335445700-3">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2335445700-4">[</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="2335445700-4">]</span><span class="p" data-group-id="2335445700-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span></code></pre><h3 id="foreach-1" class="section-heading">
│ │ │    <a href="#foreach-1" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">foreach</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#foreach/2"><code class="inline">lists:foreach/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="0714772487-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0714772487-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0714772487-2">]</span><span class="p" data-group-id="0714772487-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">F</span><span class="p" data-group-id="0714772487-3">(</span><span class="n">H</span><span class="p" data-group-id="0714772487-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="0714772487-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="0714772487-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="0714772487-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0714772487-6">[</span><span class="p" data-group-id="0714772487-6">]</span><span class="p" data-group-id="0714772487-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#foreach/2"><code class="inline">lists:foreach/2</code></a> takes a function of one argument and a list of terms:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="1616644922-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1616644922-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1616644922-2">]</span><span class="p" data-group-id="1616644922-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">F</span><span class="p" data-group-id="1616644922-3">(</span><span class="n">H</span><span class="p" data-group-id="1616644922-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="1616644922-4">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="1616644922-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="1616644922-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1616644922-6">[</span><span class="p" data-group-id="1616644922-6">]</span><span class="p" data-group-id="1616644922-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The function is applied to each argument in the list. <code class="inline">foreach</code> returns <code class="inline">ok</code>. It
│ │ │ -is only used for its side-effect:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="8316594213-1">(</span><span class="nf">fun</span><span class="p" data-group-id="8316594213-2">(</span><span class="n">X</span><span class="p" data-group-id="8316594213-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8316594213-3">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="8316594213-4">[</span><span class="n">X</span><span class="p" data-group-id="8316594213-4">]</span><span class="p" data-group-id="8316594213-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8316594213-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8316594213-5">]</span><span class="p" data-group-id="8316594213-1">)</span><span class="p">.</span><span class="w">
│ │ │ +is only used for its side-effect:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="8983504042-1">(</span><span class="nf">fun</span><span class="p" data-group-id="8983504042-2">(</span><span class="n">X</span><span class="p" data-group-id="8983504042-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8983504042-3">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="8983504042-4">[</span><span class="n">X</span><span class="p" data-group-id="8983504042-4">]</span><span class="p" data-group-id="8983504042-3">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8983504042-5">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8983504042-5">]</span><span class="p" data-group-id="8983504042-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="w">
│ │ │  </span><span class="mi">2</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><h3 id="foldl" class="section-heading">
│ │ │    <a href="#foldl" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">foldl</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> takes a function of two arguments, an accumulator and a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foldl</span><span class="p" data-group-id="2184393797-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2184393797-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="2184393797-2">]</span><span class="p" data-group-id="2184393797-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">foldl</span><span class="p" data-group-id="2184393797-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="2184393797-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="2184393797-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="2184393797-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foldl</span><span class="p" data-group-id="2184393797-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2184393797-6">[</span><span class="p" data-group-id="2184393797-6">]</span><span class="p" data-group-id="2184393797-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Accu</span><span class="p">.</span></code></pre><p>The function is called with two arguments. The first argument is the successive
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> takes a function of two arguments, an accumulator and a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foldl</span><span class="p" data-group-id="0498497081-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0498497081-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="0498497081-2">]</span><span class="p" data-group-id="0498497081-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">foldl</span><span class="p" data-group-id="0498497081-3">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="0498497081-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="0498497081-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="0498497081-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foldl</span><span class="p" data-group-id="0498497081-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0498497081-6">[</span><span class="p" data-group-id="0498497081-6">]</span><span class="p" data-group-id="0498497081-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Accu</span><span class="p">.</span></code></pre><p>The function is called with two arguments. The first argument is the successive
│ │ │  elements in the list. The second argument is the accumulator. The function must
│ │ │  return a new accumulator, which is used the next time the function is called.</p><p>If you have a list of lists <code class="inline">L = [&quot;I&quot;,&quot;like&quot;,&quot;Erlang&quot;]</code>, then you can sum the
│ │ │ -lengths of all the strings in <code class="inline">L</code> as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6299863788-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="6299863788-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6299863788-2">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="6299863788-2">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="6299863788-3">(</span><span class="nf">fun</span><span class="p" data-group-id="6299863788-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="6299863788-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="6299863788-5">(</span><span class="n">X</span><span class="p" data-group-id="6299863788-5">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6299863788-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">11</span></code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> works like a <code class="inline">while</code> loop in an imperative language:</p><pre><code class="makeup erlang" translate="no"><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="p" data-group-id="2535067492-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="2535067492-1">]</span><span class="p">,</span><span class="w">
│ │ │ +lengths of all the strings in <code class="inline">L</code> as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4545879674-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="4545879674-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4545879674-2">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="4545879674-2">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="4545879674-3">(</span><span class="nf">fun</span><span class="p" data-group-id="4545879674-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="4545879674-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="4545879674-5">(</span><span class="n">X</span><span class="p" data-group-id="4545879674-5">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4545879674-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">11</span></code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#foldl/3"><code class="inline">lists:foldl/3</code></a> works like a <code class="inline">while</code> loop in an imperative language:</p><pre><code class="makeup erlang" translate="no"><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="p" data-group-id="4482033512-1">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;like&quot;</span><span class="p">,</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="4482033512-1">]</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">Sum</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">while</span><span class="p" data-group-id="2535067492-2">(</span><span class="w"> </span><span class="n">L</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2535067492-3">[</span><span class="p" data-group-id="2535067492-3">]</span><span class="p" data-group-id="2535067492-2">)</span><span class="p" data-group-id="2535067492-4">{</span><span class="w">
│ │ │ -    </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="2535067492-5">(</span><span class="nf">head</span><span class="p" data-group-id="2535067492-6">(</span><span class="n">L</span><span class="p" data-group-id="2535067492-6">)</span><span class="p" data-group-id="2535067492-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tail</span><span class="p" data-group-id="2535067492-7">(</span><span class="n">L</span><span class="p" data-group-id="2535067492-7">)</span><span class="w">
│ │ │ +</span><span class="nf">while</span><span class="p" data-group-id="4482033512-2">(</span><span class="w"> </span><span class="n">L</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4482033512-3">[</span><span class="p" data-group-id="4482033512-3">]</span><span class="p" data-group-id="4482033512-2">)</span><span class="p" data-group-id="4482033512-4">{</span><span class="w">
│ │ │ +    </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="4482033512-5">(</span><span class="nf">head</span><span class="p" data-group-id="4482033512-6">(</span><span class="n">L</span><span class="p" data-group-id="4482033512-6">)</span><span class="p" data-group-id="4482033512-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">L</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tail</span><span class="p" data-group-id="4482033512-7">(</span><span class="n">L</span><span class="p" data-group-id="4482033512-7">)</span><span class="w">
│ │ │  </span><span class="k">end</span></code></pre><h3 id="mapfoldl" class="section-heading">
│ │ │    <a href="#mapfoldl" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">mapfoldl</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#mapfoldl/3"><code class="inline">lists:mapfoldl/3</code></a> simultaneously maps and folds over a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mapfoldl</span><span class="p" data-group-id="1756520823-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1756520823-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="1756520823-2">]</span><span class="p" data-group-id="1756520823-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1756520823-3">{</span><span class="n">R</span><span class="p">,</span><span class="n">Accu1</span><span class="p" data-group-id="1756520823-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="1756520823-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p" data-group-id="1756520823-4">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1756520823-5">{</span><span class="n">Rs</span><span class="p">,</span><span class="n">Accu2</span><span class="p" data-group-id="1756520823-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">mapfoldl</span><span class="p" data-group-id="1756520823-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu1</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1756520823-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1756520823-7">{</span><span class="p" data-group-id="1756520823-8">[</span><span class="n">R</span><span class="p">|</span><span class="n">Rs</span><span class="p" data-group-id="1756520823-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu2</span><span class="p" data-group-id="1756520823-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">mapfoldl</span><span class="p" data-group-id="1756520823-9">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1756520823-10">[</span><span class="p" data-group-id="1756520823-10">]</span><span class="p" data-group-id="1756520823-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1756520823-11">{</span><span class="p" data-group-id="1756520823-12">[</span><span class="p" data-group-id="1756520823-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="1756520823-11">}</span><span class="p">.</span></code></pre><p>The following example shows how to change all letters in <code class="inline">L</code> to upper case and
│ │ │ -then count them.</p><p>First the change to upper case:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Upcase</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="7821646375-1">(</span><span class="n">X</span><span class="p" data-group-id="7821646375-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w">  </span><span class="n">X</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="sc">$a</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7821646375-2">(</span><span class="n">X</span><span class="p" data-group-id="7821646375-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#mapfoldl/3"><code class="inline">lists:mapfoldl/3</code></a> simultaneously maps and folds over a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mapfoldl</span><span class="p" data-group-id="1375782695-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1375782695-2">[</span><span class="n">Hd</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="1375782695-2">]</span><span class="p" data-group-id="1375782695-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1375782695-3">{</span><span class="n">R</span><span class="p">,</span><span class="n">Accu1</span><span class="p" data-group-id="1375782695-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="1375782695-4">(</span><span class="n">Hd</span><span class="p">,</span><span class="w"> </span><span class="n">Accu0</span><span class="p" data-group-id="1375782695-4">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1375782695-5">{</span><span class="n">Rs</span><span class="p">,</span><span class="n">Accu2</span><span class="p" data-group-id="1375782695-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">mapfoldl</span><span class="p" data-group-id="1375782695-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu1</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="1375782695-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1375782695-7">{</span><span class="p" data-group-id="1375782695-8">[</span><span class="n">R</span><span class="p">|</span><span class="n">Rs</span><span class="p" data-group-id="1375782695-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu2</span><span class="p" data-group-id="1375782695-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">mapfoldl</span><span class="p" data-group-id="1375782695-9">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1375782695-10">[</span><span class="p" data-group-id="1375782695-10">]</span><span class="p" data-group-id="1375782695-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1375782695-11">{</span><span class="p" data-group-id="1375782695-12">[</span><span class="p" data-group-id="1375782695-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Accu</span><span class="p" data-group-id="1375782695-11">}</span><span class="p">.</span></code></pre><p>The following example shows how to change all letters in <code class="inline">L</code> to upper case and
│ │ │ +then count them.</p><p>First the change to upper case:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Upcase</span><span class="w"> </span><span class="o">=</span><span class="w">  </span><span class="nf">fun</span><span class="p" data-group-id="6714472953-1">(</span><span class="n">X</span><span class="p" data-group-id="6714472953-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="sc">$a</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w">  </span><span class="n">X</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="sc">$z</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$A</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="sc">$a</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6714472953-2">(</span><span class="n">X</span><span class="p" data-group-id="6714472953-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │  </span><span class="gp unselectable">&gt; </span><span class="n">Upcase_word</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -</span><span class="nf">fun</span><span class="p" data-group-id="7821646375-3">(</span><span class="n">X</span><span class="p" data-group-id="7821646375-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7821646375-4">(</span><span class="n">Upcase</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="7821646375-4">)</span><span class="w">
│ │ │ +</span><span class="nf">fun</span><span class="p" data-group-id="6714472953-3">(</span><span class="n">X</span><span class="p" data-group-id="6714472953-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="6714472953-4">(</span><span class="n">Upcase</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="6714472953-4">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">Upcase_word</span><span class="p" data-group-id="7821646375-5">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="7821646375-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">Upcase_word</span><span class="p" data-group-id="6714472953-5">(</span><span class="s">&quot;Erlang&quot;</span><span class="p" data-group-id="6714472953-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;ERLANG&quot;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="7821646375-6">(</span><span class="n">Upcase_word</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="7821646375-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7821646375-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="7821646375-7">]</span></code></pre><p>Now, the fold and the map can be done at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">mapfoldl</span><span class="p" data-group-id="3758317393-1">(</span><span class="nf">fun</span><span class="p" data-group-id="3758317393-2">(</span><span class="n">Word</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="3758317393-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3758317393-3">{</span><span class="n">Upcase_word</span><span class="p" data-group-id="3758317393-4">(</span><span class="n">Word</span><span class="p" data-group-id="3758317393-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="3758317393-5">(</span><span class="n">Word</span><span class="p" data-group-id="3758317393-5">)</span><span class="p" data-group-id="3758317393-3">}</span><span class="w">
│ │ │ -</span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="3758317393-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3758317393-6">{</span><span class="p" data-group-id="3758317393-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="3758317393-7">]</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="3758317393-6">}</span></code></pre><h3 id="filter" class="section-heading">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="6714472953-6">(</span><span class="n">Upcase_word</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="6714472953-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6714472953-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="6714472953-7">]</span></code></pre><p>Now, the fold and the map can be done at the same time:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">mapfoldl</span><span class="p" data-group-id="0651488635-1">(</span><span class="nf">fun</span><span class="p" data-group-id="0651488635-2">(</span><span class="n">Word</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="0651488635-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0651488635-3">{</span><span class="n">Upcase_word</span><span class="p" data-group-id="0651488635-4">(</span><span class="n">Word</span><span class="p" data-group-id="0651488635-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0651488635-5">(</span><span class="n">Word</span><span class="p" data-group-id="0651488635-5">)</span><span class="p" data-group-id="0651488635-3">}</span><span class="w">
│ │ │ +</span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="0651488635-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0651488635-6">{</span><span class="p" data-group-id="0651488635-7">[</span><span class="s">&quot;I&quot;</span><span class="p">,</span><span class="s">&quot;LIKE&quot;</span><span class="p">,</span><span class="s">&quot;ERLANG&quot;</span><span class="p" data-group-id="0651488635-7">]</span><span class="p">,</span><span class="mi">11</span><span class="p" data-group-id="0651488635-6">}</span></code></pre><h3 id="filter" class="section-heading">
│ │ │    <a href="#filter" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">filter</span>
│ │ │  </h3>
│ │ │  <p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#filter/2"><code class="inline">lists:filter/2</code></a> takes a predicate of one argument and a list and returns all elements
│ │ │ -in the list that satisfy the predicate:</p><pre><code class="makeup erlang" translate="no"><span class="nf">filter</span><span class="p" data-group-id="5228778386-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5228778386-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5228778386-2">]</span><span class="p" data-group-id="5228778386-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="5228778386-3">(</span><span class="n">H</span><span class="p" data-group-id="5228778386-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5228778386-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">filter</span><span class="p" data-group-id="5228778386-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5228778386-5">)</span><span class="p" data-group-id="5228778386-4">]</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="5228778386-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5228778386-6">)</span><span class="w">
│ │ │ +in the list that satisfy the predicate:</p><pre><code class="makeup erlang" translate="no"><span class="nf">filter</span><span class="p" data-group-id="6601770868-1">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6601770868-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6601770868-2">]</span><span class="p" data-group-id="6601770868-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="6601770868-3">(</span><span class="n">H</span><span class="p" data-group-id="6601770868-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6601770868-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">filter</span><span class="p" data-group-id="6601770868-5">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6601770868-5">)</span><span class="p" data-group-id="6601770868-4">]</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="6601770868-6">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6601770868-6">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">filter</span><span class="p" data-group-id="5228778386-7">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5228778386-8">[</span><span class="p" data-group-id="5228778386-8">]</span><span class="p" data-group-id="5228778386-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5228778386-9">[</span><span class="p" data-group-id="5228778386-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="7723107797-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7723107797-2">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7723107797-2">]</span><span class="p" data-group-id="7723107797-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7723107797-3">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="7723107797-3">]</span></code></pre><p>Combining maps and filters enables writing of very succinct code. For example,
│ │ │ +</span><span class="nf">filter</span><span class="p" data-group-id="6601770868-7">(</span><span class="n">F</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6601770868-8">[</span><span class="p" data-group-id="6601770868-8">]</span><span class="p" data-group-id="6601770868-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6601770868-9">[</span><span class="p" data-group-id="6601770868-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="1576321595-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1576321595-2">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="1576321595-2">]</span><span class="p" data-group-id="1576321595-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1576321595-3">[</span><span class="mi">500</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="1576321595-3">]</span></code></pre><p>Combining maps and filters enables writing of very succinct code. For example,
│ │ │  to define a set difference function <code class="inline">diff(L1, L2)</code> to be the difference between
│ │ │ -the lists <code class="inline">L1</code> and <code class="inline">L2</code>, the code can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">diff</span><span class="p" data-group-id="1241314330-1">(</span><span class="n">L1</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="1241314330-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">filter</span><span class="p" data-group-id="1241314330-2">(</span><span class="nf">fun</span><span class="p" data-group-id="1241314330-3">(</span><span class="n">X</span><span class="p" data-group-id="1241314330-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="1241314330-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="1241314330-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="1241314330-2">)</span><span class="p">.</span></code></pre><p>This gives the list of all elements in L1 that are not contained in L2.</p><p>The AND intersection of the list <code class="inline">L1</code> and <code class="inline">L2</code> is also easily defined:</p><pre><code class="makeup erlang" translate="no"><span class="nf">intersection</span><span class="p" data-group-id="6877002042-1">(</span><span class="n">L1</span><span class="p">,</span><span class="n">L2</span><span class="p" data-group-id="6877002042-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="6877002042-2">(</span><span class="nf">fun</span><span class="p" data-group-id="6877002042-3">(</span><span class="n">X</span><span class="p" data-group-id="6877002042-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="6877002042-4">(</span><span class="n">X</span><span class="p">,</span><span class="n">L1</span><span class="p" data-group-id="6877002042-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="6877002042-2">)</span><span class="p">.</span></code></pre><h3 id="takewhile" class="section-heading">
│ │ │ +the lists <code class="inline">L1</code> and <code class="inline">L2</code>, the code can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">diff</span><span class="p" data-group-id="9905955618-1">(</span><span class="n">L1</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="9905955618-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">filter</span><span class="p" data-group-id="9905955618-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9905955618-3">(</span><span class="n">X</span><span class="p" data-group-id="9905955618-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ow">not</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="9905955618-4">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="9905955618-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="9905955618-2">)</span><span class="p">.</span></code></pre><p>This gives the list of all elements in L1 that are not contained in L2.</p><p>The AND intersection of the list <code class="inline">L1</code> and <code class="inline">L2</code> is also easily defined:</p><pre><code class="makeup erlang" translate="no"><span class="nf">intersection</span><span class="p" data-group-id="9344346335-1">(</span><span class="n">L1</span><span class="p">,</span><span class="n">L2</span><span class="p" data-group-id="9344346335-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">filter</span><span class="p" data-group-id="9344346335-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9344346335-3">(</span><span class="n">X</span><span class="p" data-group-id="9344346335-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">member</span><span class="p" data-group-id="9344346335-4">(</span><span class="n">X</span><span class="p">,</span><span class="n">L1</span><span class="p" data-group-id="9344346335-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">L2</span><span class="p" data-group-id="9344346335-2">)</span><span class="p">.</span></code></pre><h3 id="takewhile" class="section-heading">
│ │ │    <a href="#takewhile" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">takewhile</span>
│ │ │  </h3>
│ │ │  <p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#takewhile/2"><code class="inline">lists:takewhile/2</code></a> takes elements <code class="inline">X</code> from a list <code class="inline">L</code> as long as the predicate
│ │ │ -<code class="inline">P(X)</code> is true:</p><pre><code class="makeup erlang" translate="no"><span class="nf">takewhile</span><span class="p" data-group-id="6729626840-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6729626840-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6729626840-2">]</span><span class="p" data-group-id="6729626840-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="6729626840-3">(</span><span class="n">H</span><span class="p" data-group-id="6729626840-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6729626840-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">takewhile</span><span class="p" data-group-id="6729626840-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="6729626840-5">)</span><span class="p" data-group-id="6729626840-4">]</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6729626840-6">[</span><span class="p" data-group-id="6729626840-6">]</span><span class="w">
│ │ │ +<code class="inline">P(X)</code> is true:</p><pre><code class="makeup erlang" translate="no"><span class="nf">takewhile</span><span class="p" data-group-id="7227646624-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7227646624-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7227646624-2">]</span><span class="p" data-group-id="7227646624-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="7227646624-3">(</span><span class="n">H</span><span class="p" data-group-id="7227646624-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7227646624-4">[</span><span class="n">H</span><span class="p">|</span><span class="nf">takewhile</span><span class="p" data-group-id="7227646624-5">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="7227646624-5">)</span><span class="p" data-group-id="7227646624-4">]</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7227646624-6">[</span><span class="p" data-group-id="7227646624-6">]</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">takewhile</span><span class="p" data-group-id="6729626840-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6729626840-8">[</span><span class="p" data-group-id="6729626840-8">]</span><span class="p" data-group-id="6729626840-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6729626840-9">[</span><span class="p" data-group-id="6729626840-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">takewhile</span><span class="p" data-group-id="9921040531-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9921040531-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9921040531-2">]</span><span class="p" data-group-id="9921040531-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9921040531-3">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="9921040531-3">]</span></code></pre><h3 id="dropwhile" class="section-heading">
│ │ │ +</span><span class="nf">takewhile</span><span class="p" data-group-id="7227646624-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7227646624-8">[</span><span class="p" data-group-id="7227646624-8">]</span><span class="p" data-group-id="7227646624-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7227646624-9">[</span><span class="p" data-group-id="7227646624-9">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">takewhile</span><span class="p" data-group-id="9288004460-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9288004460-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="9288004460-2">]</span><span class="p" data-group-id="9288004460-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9288004460-3">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="9288004460-3">]</span></code></pre><h3 id="dropwhile" class="section-heading">
│ │ │    <a href="#dropwhile" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">dropwhile</span>
│ │ │  </h3>
│ │ │ -<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#dropwhile/2"><code class="inline">lists:dropwhile/2</code></a> is the complement of <code class="inline">takewhile</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">dropwhile</span><span class="p" data-group-id="9581605184-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9581605184-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9581605184-2">]</span><span class="p" data-group-id="9581605184-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="9581605184-3">(</span><span class="n">H</span><span class="p" data-group-id="9581605184-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">dropwhile</span><span class="p" data-group-id="9581605184-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="9581605184-4">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9581605184-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9581605184-5">]</span><span class="w">
│ │ │ +<p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#dropwhile/2"><code class="inline">lists:dropwhile/2</code></a> is the complement of <code class="inline">takewhile</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">dropwhile</span><span class="p" data-group-id="5775063620-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5775063620-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5775063620-2">]</span><span class="p" data-group-id="5775063620-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="5775063620-3">(</span><span class="n">H</span><span class="p" data-group-id="5775063620-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">dropwhile</span><span class="p" data-group-id="5775063620-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="5775063620-4">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5775063620-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5775063620-5">]</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">dropwhile</span><span class="p" data-group-id="9581605184-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9581605184-7">[</span><span class="p" data-group-id="9581605184-7">]</span><span class="p" data-group-id="9581605184-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9581605184-8">[</span><span class="p" data-group-id="9581605184-8">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">dropwhile</span><span class="p" data-group-id="8470328395-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8470328395-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8470328395-2">]</span><span class="p" data-group-id="8470328395-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8470328395-3">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8470328395-3">]</span></code></pre><h3 id="splitwith" class="section-heading">
│ │ │ +</span><span class="nf">dropwhile</span><span class="p" data-group-id="5775063620-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5775063620-7">[</span><span class="p" data-group-id="5775063620-7">]</span><span class="p" data-group-id="5775063620-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5775063620-8">[</span><span class="p" data-group-id="5775063620-8">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">dropwhile</span><span class="p" data-group-id="1148740485-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1148740485-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1148740485-2">]</span><span class="p" data-group-id="1148740485-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1148740485-3">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1148740485-3">]</span></code></pre><h3 id="splitwith" class="section-heading">
│ │ │    <a href="#splitwith" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">splitwith</span>
│ │ │  </h3>
│ │ │  <p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#splitwith/2"><code class="inline">lists:splitwith/2</code></a> splits the list <code class="inline">L</code> into the two sublists <code class="inline">{L1, L2}</code>, where
│ │ │ -<code class="inline">L = takewhile(P, L)</code> and <code class="inline">L2 = dropwhile(P, L)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">splitwith</span><span class="p" data-group-id="2455849691-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2455849691-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">splitwith</span><span class="p" data-group-id="2455849691-2">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2455849691-3">[</span><span class="p" data-group-id="2455849691-3">]</span><span class="p" data-group-id="2455849691-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">L = takewhile(P, L)</code> and <code class="inline">L2 = dropwhile(P, L)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">splitwith</span><span class="p" data-group-id="4401755611-1">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4401755611-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">splitwith</span><span class="p" data-group-id="4401755611-2">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4401755611-3">[</span><span class="p" data-group-id="4401755611-3">]</span><span class="p" data-group-id="4401755611-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">splitwith</span><span class="p" data-group-id="2455849691-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2455849691-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2455849691-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2455849691-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="2455849691-6">(</span><span class="n">H</span><span class="p" data-group-id="2455849691-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">splitwith</span><span class="p" data-group-id="2455849691-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2455849691-8">[</span><span class="n">H</span><span class="p">|</span><span class="n">L</span><span class="p" data-group-id="2455849691-8">]</span><span class="p" data-group-id="2455849691-7">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2455849691-9">{</span><span class="nf">reverse</span><span class="p" data-group-id="2455849691-10">(</span><span class="n">L</span><span class="p" data-group-id="2455849691-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2455849691-11">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="2455849691-11">]</span><span class="p" data-group-id="2455849691-9">}</span><span class="w">
│ │ │ +</span><span class="nf">splitwith</span><span class="p" data-group-id="4401755611-4">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4401755611-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4401755611-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4401755611-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="4401755611-6">(</span><span class="n">H</span><span class="p" data-group-id="4401755611-6">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="ss">true</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">splitwith</span><span class="p" data-group-id="4401755611-7">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4401755611-8">[</span><span class="n">H</span><span class="p">|</span><span class="n">L</span><span class="p" data-group-id="4401755611-8">]</span><span class="p" data-group-id="4401755611-7">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4401755611-9">{</span><span class="nf">reverse</span><span class="p" data-group-id="4401755611-10">(</span><span class="n">L</span><span class="p" data-group-id="4401755611-10">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4401755611-11">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="4401755611-11">]</span><span class="p" data-group-id="4401755611-9">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">splitwith</span><span class="p" data-group-id="2455849691-12">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2455849691-13">[</span><span class="p" data-group-id="2455849691-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2455849691-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2455849691-14">{</span><span class="nf">reverse</span><span class="p" data-group-id="2455849691-15">(</span><span class="n">L</span><span class="p" data-group-id="2455849691-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2455849691-16">[</span><span class="p" data-group-id="2455849691-16">]</span><span class="p" data-group-id="2455849691-14">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">splitwith</span><span class="p" data-group-id="7635729290-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7635729290-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7635729290-2">]</span><span class="p" data-group-id="7635729290-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7635729290-3">{</span><span class="p" data-group-id="7635729290-4">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="7635729290-4">]</span><span class="p">,</span><span class="p" data-group-id="7635729290-5">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="7635729290-5">]</span><span class="p" data-group-id="7635729290-3">}</span></code></pre><h2 id="funs-returning-funs" class="section-heading">
│ │ │ +</span><span class="nf">splitwith</span><span class="p" data-group-id="4401755611-12">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4401755611-13">[</span><span class="p" data-group-id="4401755611-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="4401755611-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4401755611-14">{</span><span class="nf">reverse</span><span class="p" data-group-id="4401755611-15">(</span><span class="n">L</span><span class="p" data-group-id="4401755611-15">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4401755611-16">[</span><span class="p" data-group-id="4401755611-16">]</span><span class="p" data-group-id="4401755611-14">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">splitwith</span><span class="p" data-group-id="8306857300-1">(</span><span class="n">Big</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8306857300-2">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8306857300-2">]</span><span class="p" data-group-id="8306857300-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8306857300-3">{</span><span class="p" data-group-id="8306857300-4">[</span><span class="mi">200</span><span class="p">,</span><span class="mi">500</span><span class="p">,</span><span class="mi">45</span><span class="p" data-group-id="8306857300-4">]</span><span class="p">,</span><span class="p" data-group-id="8306857300-5">[</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">45</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8306857300-5">]</span><span class="p" data-group-id="8306857300-3">}</span></code></pre><h2 id="funs-returning-funs" class="section-heading">
│ │ │    <a href="#funs-returning-funs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Funs Returning Funs</span>
│ │ │  </h2>
│ │ │  <p>So far, only functions that take funs as arguments have been described. More
│ │ │  powerful functions, that themselves return funs, can also be written. The
│ │ │  following examples illustrate these type of functions.</p><h3 id="simple-higher-order-functions" class="section-heading">
│ │ │    <a href="#simple-higher-order-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simple Higher Order Functions</span>
│ │ │  </h3>
│ │ │  <p><code class="inline">Adder(X)</code> is a function that given <code class="inline">X</code>, returns a new function <code class="inline">G</code> such that
│ │ │ -<code class="inline">G(K)</code> returns <code class="inline">K + X</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Adder</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6941642610-1">(</span><span class="n">X</span><span class="p" data-group-id="6941642610-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6941642610-2">(</span><span class="n">Y</span><span class="p" data-group-id="6941642610-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">G(K)</code> returns <code class="inline">K + X</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">Adder</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1817379165-1">(</span><span class="n">X</span><span class="p" data-group-id="1817379165-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1817379165-2">(</span><span class="n">Y</span><span class="p" data-group-id="1817379165-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">Add6</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Adder</span><span class="p" data-group-id="6941642610-3">(</span><span class="mi">6</span><span class="p" data-group-id="6941642610-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">Add6</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Adder</span><span class="p" data-group-id="1817379165-3">(</span><span class="mi">6</span><span class="p" data-group-id="1817379165-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">6.72228031</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">Add6</span><span class="p" data-group-id="6941642610-4">(</span><span class="mi">10</span><span class="p" data-group-id="6941642610-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">Add6</span><span class="p" data-group-id="1817379165-4">(</span><span class="mi">10</span><span class="p" data-group-id="1817379165-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">16</span></code></pre><h3 id="infinite-lists" class="section-heading">
│ │ │    <a href="#infinite-lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Infinite Lists</span>
│ │ │  </h3>
│ │ │ -<p>The idea is to write something like:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7861520319-1">(</span><span class="ss">lazy</span><span class="p" data-group-id="7861520319-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7861520319-2">(</span><span class="p" data-group-id="7861520319-3">[</span><span class="ss">ints_from</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7861520319-3">]</span><span class="p" data-group-id="7861520319-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">ints_from</span><span class="p" data-group-id="7861520319-4">(</span><span class="n">N</span><span class="p" data-group-id="7861520319-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">fun</span><span class="p" data-group-id="7861520319-5">(</span><span class="p" data-group-id="7861520319-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="7861520319-6">[</span><span class="n">N</span><span class="p">|</span><span class="nf">ints_from</span><span class="p" data-group-id="7861520319-7">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="7861520319-7">)</span><span class="p" data-group-id="7861520319-6">]</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Then proceed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lazy</span><span class="p">:</span><span class="nf">ints_from</span><span class="p" data-group-id="0689935301-1">(</span><span class="mi">1</span><span class="p" data-group-id="0689935301-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>The idea is to write something like:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8722007247-1">(</span><span class="ss">lazy</span><span class="p" data-group-id="8722007247-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8722007247-2">(</span><span class="p" data-group-id="8722007247-3">[</span><span class="ss">ints_from</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8722007247-3">]</span><span class="p" data-group-id="8722007247-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">ints_from</span><span class="p" data-group-id="8722007247-4">(</span><span class="n">N</span><span class="p" data-group-id="8722007247-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">fun</span><span class="p" data-group-id="8722007247-5">(</span><span class="p" data-group-id="8722007247-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8722007247-6">[</span><span class="n">N</span><span class="p">|</span><span class="nf">ints_from</span><span class="p" data-group-id="8722007247-7">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="8722007247-7">)</span><span class="p" data-group-id="8722007247-6">]</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Then proceed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lazy</span><span class="p">:</span><span class="nf">ints_from</span><span class="p" data-group-id="5491694396-1">(</span><span class="mi">1</span><span class="p" data-group-id="5491694396-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="p" data-group-id="0689935301-2">(</span><span class="p" data-group-id="0689935301-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0689935301-3">[</span><span class="mi">1</span><span class="p">|</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="p" data-group-id="0689935301-3">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="0689935301-4">(</span><span class="n">XX</span><span class="p" data-group-id="0689935301-5">(</span><span class="p" data-group-id="0689935301-5">)</span><span class="p" data-group-id="0689935301-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">XX</span><span class="p" data-group-id="5491694396-2">(</span><span class="p" data-group-id="5491694396-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5491694396-3">[</span><span class="mi">1</span><span class="p">|</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="p" data-group-id="5491694396-3">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="5491694396-4">(</span><span class="n">XX</span><span class="p" data-group-id="5491694396-5">(</span><span class="p" data-group-id="5491694396-5">)</span><span class="p" data-group-id="5491694396-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tl</span><span class="p" data-group-id="0689935301-6">(</span><span class="n">XX</span><span class="p" data-group-id="0689935301-7">(</span><span class="p" data-group-id="0689935301-7">)</span><span class="p" data-group-id="0689935301-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">tl</span><span class="p" data-group-id="5491694396-6">(</span><span class="n">XX</span><span class="p" data-group-id="5491694396-7">(</span><span class="p" data-group-id="5491694396-7">)</span><span class="p" data-group-id="5491694396-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">lazy</span><span class="p">.</span><span class="mf">0.29874839</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="0689935301-8">(</span><span class="n">Y</span><span class="p" data-group-id="0689935301-9">(</span><span class="p" data-group-id="0689935301-9">)</span><span class="p" data-group-id="0689935301-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">hd</span><span class="p" data-group-id="5491694396-8">(</span><span class="n">Y</span><span class="p" data-group-id="5491694396-9">(</span><span class="p" data-group-id="5491694396-9">)</span><span class="p" data-group-id="5491694396-8">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">2</span></code></pre><p>And so on. This is an example of &quot;lazy embedding&quot;.</p><h3 id="parsing" class="section-heading">
│ │ │    <a href="#parsing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Parsing</span>
│ │ │  </h3>
│ │ │ -<p>The following examples show parsers of the following type:</p><pre><code class="makeup erlang" translate="no"><span class="n">Parser</span><span class="p" data-group-id="4729820840-1">(</span><span class="n">Toks</span><span class="p" data-group-id="4729820840-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4729820840-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tree</span><span class="p">,</span><span class="w"> </span><span class="n">Toks1</span><span class="p" data-group-id="4729820840-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">fail</span></code></pre><p><code class="inline">Toks</code> is the list of tokens to be parsed. A successful parse returns
│ │ │ +<p>The following examples show parsers of the following type:</p><pre><code class="makeup erlang" translate="no"><span class="n">Parser</span><span class="p" data-group-id="9512243632-1">(</span><span class="n">Toks</span><span class="p" data-group-id="9512243632-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9512243632-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Tree</span><span class="p">,</span><span class="w"> </span><span class="n">Toks1</span><span class="p" data-group-id="9512243632-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">fail</span></code></pre><p><code class="inline">Toks</code> is the list of tokens to be parsed. A successful parse returns
│ │ │  <code class="inline">{ok, Tree, Toks1}</code>.</p><ul><li><code class="inline">Tree</code> is a parse tree.</li><li><code class="inline">Toks1</code> is a tail of <code class="inline">Tree</code> that contains symbols encountered after the
│ │ │  structure that was correctly parsed.</li></ul><p>An unsuccessful parse returns <code class="inline">fail</code>.</p><p>The following example illustrates a simple, functional parser that parses the
│ │ │  grammar:</p><pre><code class="text">(a | b) &amp; (c | d)</code></pre><p>The following code defines a function <code class="inline">pconst(X)</code> in the module <code class="inline">funparse</code>,
│ │ │ -which returns a fun that parses a list of tokens:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pconst</span><span class="p" data-group-id="4112748376-1">(</span><span class="n">X</span><span class="p" data-group-id="4112748376-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4112748376-2">(</span><span class="n">T</span><span class="p" data-group-id="4112748376-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +which returns a fun that parses a list of tokens:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pconst</span><span class="p" data-group-id="8216477047-1">(</span><span class="n">X</span><span class="p" data-group-id="8216477047-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8216477047-2">(</span><span class="n">T</span><span class="p" data-group-id="8216477047-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │         </span><span class="k">case</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -           </span><span class="p" data-group-id="4112748376-3">[</span><span class="n">X</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="4112748376-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4112748376-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4112748376-5">{</span><span class="ss">const</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4112748376-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="4112748376-4">}</span><span class="p">;</span><span class="w">
│ │ │ +           </span><span class="p" data-group-id="8216477047-3">[</span><span class="n">X</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="8216477047-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8216477047-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8216477047-5">{</span><span class="ss">const</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8216477047-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="8216477047-4">}</span><span class="p">;</span><span class="w">
│ │ │             </span><span class="p">_</span><span class="w">      </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">fail</span><span class="w">
│ │ │         </span><span class="k">end</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>This function can be used as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">pconst</span><span class="p" data-group-id="8671875054-1">(</span><span class="ss">a</span><span class="p" data-group-id="8671875054-1">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>This function can be used as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">pconst</span><span class="p" data-group-id="4957608758-1">(</span><span class="ss">a</span><span class="p" data-group-id="4957608758-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">funparse</span><span class="p">.</span><span class="mf">0.22674075</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="p" data-group-id="8671875054-2">(</span><span class="p" data-group-id="8671875054-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8671875054-3">]</span><span class="p" data-group-id="8671875054-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8671875054-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="8671875054-5">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="8671875054-5">}</span><span class="p">,</span><span class="p" data-group-id="8671875054-6">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="8671875054-6">]</span><span class="p" data-group-id="8671875054-4">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="p" data-group-id="8671875054-7">(</span><span class="p" data-group-id="8671875054-8">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="8671875054-8">]</span><span class="p" data-group-id="8671875054-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="p" data-group-id="4957608758-2">(</span><span class="p" data-group-id="4957608758-3">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4957608758-3">]</span><span class="p" data-group-id="4957608758-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4957608758-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="4957608758-5">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4957608758-5">}</span><span class="p">,</span><span class="p" data-group-id="4957608758-6">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="4957608758-6">]</span><span class="p" data-group-id="4957608758-4">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="p" data-group-id="4957608758-7">(</span><span class="p" data-group-id="4957608758-8">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="4957608758-8">]</span><span class="p" data-group-id="4957608758-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">fail</span></code></pre><p>Next, the two higher order functions <code class="inline">pand</code> and <code class="inline">por</code> are defined. They combine
│ │ │ -primitive parsers to produce more complex parsers.</p><p>First <code class="inline">pand</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pand</span><span class="p" data-group-id="5956873876-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="5956873876-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5956873876-2">(</span><span class="n">T</span><span class="p" data-group-id="5956873876-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="5956873876-3">(</span><span class="n">T</span><span class="p" data-group-id="5956873876-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="5956873876-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="5956873876-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="5956873876-5">(</span><span class="n">T1</span><span class="p" data-group-id="5956873876-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="5956873876-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="5956873876-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                        </span><span class="p" data-group-id="5956873876-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5956873876-8">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="5956873876-8">}</span><span class="p" data-group-id="5956873876-7">}</span><span class="p">;</span><span class="w">
│ │ │ +primitive parsers to produce more complex parsers.</p><p>First <code class="inline">pand</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pand</span><span class="p" data-group-id="2348755333-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="2348755333-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2348755333-2">(</span><span class="n">T</span><span class="p" data-group-id="2348755333-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="2348755333-3">(</span><span class="n">T</span><span class="p" data-group-id="2348755333-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2348755333-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="2348755333-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="2348755333-5">(</span><span class="n">T1</span><span class="p" data-group-id="2348755333-5">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="2348755333-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="2348755333-6">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                        </span><span class="p" data-group-id="2348755333-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2348755333-8">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="2348755333-8">}</span><span class="p" data-group-id="2348755333-7">}</span><span class="p">;</span><span class="w">
│ │ │                      </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                          </span><span class="ss">fail</span><span class="w">
│ │ │                  </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="ss">fail</span><span class="w">
│ │ │          </span><span class="k">end</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>Given a parser <code class="inline">P1</code> for grammar <code class="inline">G1</code>, and a parser <code class="inline">P2</code> for grammar <code class="inline">G2</code>,
│ │ │  <code class="inline">pand(P1, P2)</code> returns a parser for the grammar, which consists of sequences of
│ │ │  tokens that satisfy <code class="inline">G1</code>, followed by sequences of tokens that satisfy <code class="inline">G2</code>.</p><p><code class="inline">por(P1, P2)</code> returns a parser for the language described by the grammar <code class="inline">G1</code> or
│ │ │ -<code class="inline">G2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">por</span><span class="p" data-group-id="3852174740-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="3852174740-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3852174740-2">(</span><span class="n">T</span><span class="p" data-group-id="3852174740-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="3852174740-3">(</span><span class="n">T</span><span class="p" data-group-id="3852174740-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3852174740-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3852174740-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="3852174740-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3852174740-6">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="n">R</span><span class="p" data-group-id="3852174740-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3852174740-5">}</span><span class="p">;</span><span class="w">
│ │ │ +<code class="inline">G2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">por</span><span class="p" data-group-id="5574927689-1">(</span><span class="n">P1</span><span class="p">,</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="5574927689-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5574927689-2">(</span><span class="n">T</span><span class="p" data-group-id="5574927689-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="n">P1</span><span class="p" data-group-id="5574927689-3">(</span><span class="n">T</span><span class="p" data-group-id="5574927689-3">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="5574927689-4">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="5574927689-4">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="5574927689-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5574927689-6">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="n">R</span><span class="p" data-group-id="5574927689-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="5574927689-5">}</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="3852174740-7">(</span><span class="n">T</span><span class="p" data-group-id="3852174740-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="3852174740-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3852174740-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                        </span><span class="p" data-group-id="3852174740-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3852174740-10">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="n">R1</span><span class="p" data-group-id="3852174740-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="3852174740-9">}</span><span class="p">;</span><span class="w">
│ │ │ +                </span><span class="k">case</span><span class="w"> </span><span class="n">P2</span><span class="p" data-group-id="5574927689-7">(</span><span class="n">T</span><span class="p" data-group-id="5574927689-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="5574927689-8">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="5574927689-8">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                        </span><span class="p" data-group-id="5574927689-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5574927689-10">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="n">R1</span><span class="p" data-group-id="5574927689-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="5574927689-9">}</span><span class="p">;</span><span class="w">
│ │ │                      </span><span class="ss">fail</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                          </span><span class="ss">fail</span><span class="w">
│ │ │                  </span><span class="k">end</span><span class="w">
│ │ │          </span><span class="k">end</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The original problem was to parse the grammar <code class="inline">(a | b) &amp; (c | d)</code>. The following
│ │ │ -code addresses this problem:</p><pre><code class="makeup erlang" translate="no"><span class="nf">grammar</span><span class="p" data-group-id="2807091497-1">(</span><span class="p" data-group-id="2807091497-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">pand</span><span class="p" data-group-id="2807091497-2">(</span><span class="w">
│ │ │ -         </span><span class="nf">por</span><span class="p" data-group-id="2807091497-3">(</span><span class="nf">pconst</span><span class="p" data-group-id="2807091497-4">(</span><span class="ss">a</span><span class="p" data-group-id="2807091497-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="2807091497-5">(</span><span class="ss">b</span><span class="p" data-group-id="2807091497-5">)</span><span class="p" data-group-id="2807091497-3">)</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="nf">por</span><span class="p" data-group-id="2807091497-6">(</span><span class="nf">pconst</span><span class="p" data-group-id="2807091497-7">(</span><span class="ss">c</span><span class="p" data-group-id="2807091497-7">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="2807091497-8">(</span><span class="ss">d</span><span class="p" data-group-id="2807091497-8">)</span><span class="p" data-group-id="2807091497-6">)</span><span class="p" data-group-id="2807091497-2">)</span><span class="p">.</span></code></pre><p>The following code adds a parser interface to the grammar:</p><pre><code class="makeup erlang" translate="no"><span class="nf">parse</span><span class="p" data-group-id="2808875157-1">(</span><span class="n">List</span><span class="p" data-group-id="2808875157-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2808875157-2">(</span><span class="nf">grammar</span><span class="p" data-group-id="2808875157-3">(</span><span class="p" data-group-id="2808875157-3">)</span><span class="p" data-group-id="2808875157-2">)</span><span class="p" data-group-id="2808875157-4">(</span><span class="n">List</span><span class="p" data-group-id="2808875157-4">)</span><span class="p">.</span></code></pre><p>The parser can be tested as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1148409608-1">(</span><span class="p" data-group-id="1148409608-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1148409608-2">]</span><span class="p" data-group-id="1148409608-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1148409608-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="1148409608-4">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="1148409608-5">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="1148409608-6">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1148409608-6">}</span><span class="p" data-group-id="1148409608-5">}</span><span class="p">,</span><span class="p" data-group-id="1148409608-7">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="1148409608-8">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1148409608-8">}</span><span class="p" data-group-id="1148409608-7">}</span><span class="p" data-group-id="1148409608-4">}</span><span class="p" data-group-id="1148409608-3">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1148409608-9">(</span><span class="p" data-group-id="1148409608-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="1148409608-10">]</span><span class="p" data-group-id="1148409608-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1148409608-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="1148409608-12">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="1148409608-13">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="1148409608-14">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1148409608-14">}</span><span class="p" data-group-id="1148409608-13">}</span><span class="p">,</span><span class="p" data-group-id="1148409608-15">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1148409608-16">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="1148409608-16">}</span><span class="p" data-group-id="1148409608-15">}</span><span class="p" data-group-id="1148409608-12">}</span><span class="p" data-group-id="1148409608-11">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1148409608-17">(</span><span class="p" data-group-id="1148409608-18">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1148409608-18">]</span><span class="p" data-group-id="1148409608-17">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1148409608-19">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="1148409608-20">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="1148409608-21">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1148409608-22">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1148409608-22">}</span><span class="p" data-group-id="1148409608-21">}</span><span class="p">,</span><span class="p" data-group-id="1148409608-23">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="1148409608-24">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1148409608-24">}</span><span class="p" data-group-id="1148409608-23">}</span><span class="p" data-group-id="1148409608-20">}</span><span class="p" data-group-id="1148409608-19">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1148409608-25">(</span><span class="p" data-group-id="1148409608-26">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="1148409608-26">]</span><span class="p" data-group-id="1148409608-25">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1148409608-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="1148409608-28">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="1148409608-29">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1148409608-30">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1148409608-30">}</span><span class="p" data-group-id="1148409608-29">}</span><span class="p">,</span><span class="p" data-group-id="1148409608-31">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1148409608-32">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="1148409608-32">}</span><span class="p" data-group-id="1148409608-31">}</span><span class="p" data-group-id="1148409608-28">}</span><span class="p" data-group-id="1148409608-27">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1148409608-33">(</span><span class="p" data-group-id="1148409608-34">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1148409608-34">]</span><span class="p" data-group-id="1148409608-33">)</span><span class="p">.</span><span class="w">
│ │ │ +code addresses this problem:</p><pre><code class="makeup erlang" translate="no"><span class="nf">grammar</span><span class="p" data-group-id="5597024014-1">(</span><span class="p" data-group-id="5597024014-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">pand</span><span class="p" data-group-id="5597024014-2">(</span><span class="w">
│ │ │ +         </span><span class="nf">por</span><span class="p" data-group-id="5597024014-3">(</span><span class="nf">pconst</span><span class="p" data-group-id="5597024014-4">(</span><span class="ss">a</span><span class="p" data-group-id="5597024014-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="5597024014-5">(</span><span class="ss">b</span><span class="p" data-group-id="5597024014-5">)</span><span class="p" data-group-id="5597024014-3">)</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="nf">por</span><span class="p" data-group-id="5597024014-6">(</span><span class="nf">pconst</span><span class="p" data-group-id="5597024014-7">(</span><span class="ss">c</span><span class="p" data-group-id="5597024014-7">)</span><span class="p">,</span><span class="w"> </span><span class="nf">pconst</span><span class="p" data-group-id="5597024014-8">(</span><span class="ss">d</span><span class="p" data-group-id="5597024014-8">)</span><span class="p" data-group-id="5597024014-6">)</span><span class="p" data-group-id="5597024014-2">)</span><span class="p">.</span></code></pre><p>The following code adds a parser interface to the grammar:</p><pre><code class="makeup erlang" translate="no"><span class="nf">parse</span><span class="p" data-group-id="1989025029-1">(</span><span class="n">List</span><span class="p" data-group-id="1989025029-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1989025029-2">(</span><span class="nf">grammar</span><span class="p" data-group-id="1989025029-3">(</span><span class="p" data-group-id="1989025029-3">)</span><span class="p" data-group-id="1989025029-2">)</span><span class="p" data-group-id="1989025029-4">(</span><span class="n">List</span><span class="p" data-group-id="1989025029-4">)</span><span class="p">.</span></code></pre><p>The parser can be tested as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1047690274-1">(</span><span class="p" data-group-id="1047690274-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1047690274-2">]</span><span class="p" data-group-id="1047690274-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1047690274-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="1047690274-4">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="1047690274-5">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="1047690274-6">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1047690274-6">}</span><span class="p" data-group-id="1047690274-5">}</span><span class="p">,</span><span class="p" data-group-id="1047690274-7">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="1047690274-8">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1047690274-8">}</span><span class="p" data-group-id="1047690274-7">}</span><span class="p" data-group-id="1047690274-4">}</span><span class="p" data-group-id="1047690274-3">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1047690274-9">(</span><span class="p" data-group-id="1047690274-10">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="1047690274-10">]</span><span class="p" data-group-id="1047690274-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1047690274-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="1047690274-12">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="1047690274-13">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="1047690274-14">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1047690274-14">}</span><span class="p" data-group-id="1047690274-13">}</span><span class="p">,</span><span class="p" data-group-id="1047690274-15">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1047690274-16">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="1047690274-16">}</span><span class="p" data-group-id="1047690274-15">}</span><span class="p" data-group-id="1047690274-12">}</span><span class="p" data-group-id="1047690274-11">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1047690274-17">(</span><span class="p" data-group-id="1047690274-18">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1047690274-18">]</span><span class="p" data-group-id="1047690274-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1047690274-19">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="1047690274-20">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="1047690274-21">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1047690274-22">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1047690274-22">}</span><span class="p" data-group-id="1047690274-21">}</span><span class="p">,</span><span class="p" data-group-id="1047690274-23">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="p" data-group-id="1047690274-24">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1047690274-24">}</span><span class="p" data-group-id="1047690274-23">}</span><span class="p" data-group-id="1047690274-20">}</span><span class="p" data-group-id="1047690274-19">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1047690274-25">(</span><span class="p" data-group-id="1047690274-26">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="1047690274-26">]</span><span class="p" data-group-id="1047690274-25">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1047690274-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="1047690274-28">{</span><span class="ss">&#39;and&#39;</span><span class="p">,</span><span class="p" data-group-id="1047690274-29">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1047690274-30">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1047690274-30">}</span><span class="p" data-group-id="1047690274-29">}</span><span class="p">,</span><span class="p" data-group-id="1047690274-31">{</span><span class="ss">&#39;or&#39;</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="p" data-group-id="1047690274-32">{</span><span class="ss">const</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="1047690274-32">}</span><span class="p" data-group-id="1047690274-31">}</span><span class="p" data-group-id="1047690274-28">}</span><span class="p" data-group-id="1047690274-27">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">funparse</span><span class="p">:</span><span class="nf">parse</span><span class="p" data-group-id="1047690274-33">(</span><span class="p" data-group-id="1047690274-34">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1047690274-34">]</span><span class="p" data-group-id="1047690274-33">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">fail</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="prog_ex_records.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/gen_server_concepts.html
│ │ │ @@ -157,63 +157,63 @@
│ │ │    <a href="#example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example</span>
│ │ │  </h2>
│ │ │  <p>An example of a simple server written in plain Erlang is provided in
│ │ │  <a href="design_principles.html#ch1">Overview</a>. The server can be reimplemented using
│ │ │ -<code class="inline">gen_server</code>, resulting in this callback module:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9953482346-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="9953482346-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="9953482346-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="9953482346-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">gen_server</code>, resulting in this callback module:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2620667362-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="2620667362-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2620667362-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="2620667362-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9953482346-3">(</span><span class="p" data-group-id="9953482346-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9953482346-4">]</span><span class="p" data-group-id="9953482346-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9953482346-5">(</span><span class="p" data-group-id="9953482346-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9953482346-6">]</span><span class="p" data-group-id="9953482346-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9953482346-7">(</span><span class="p" data-group-id="9953482346-8">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9953482346-8">]</span><span class="p" data-group-id="9953482346-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2620667362-3">(</span><span class="p" data-group-id="2620667362-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2620667362-4">]</span><span class="p" data-group-id="2620667362-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2620667362-5">(</span><span class="p" data-group-id="2620667362-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2620667362-6">]</span><span class="p" data-group-id="2620667362-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2620667362-7">(</span><span class="p" data-group-id="2620667362-8">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2620667362-8">]</span><span class="p" data-group-id="2620667362-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="9953482346-9">(</span><span class="p" data-group-id="9953482346-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9953482346-10">(</span><span class="p" data-group-id="9953482346-11">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9953482346-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9953482346-12">[</span><span class="p" data-group-id="9953482346-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9953482346-13">[</span><span class="p" data-group-id="9953482346-13">]</span><span class="p" data-group-id="9953482346-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="2620667362-9">(</span><span class="p" data-group-id="2620667362-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2620667362-10">(</span><span class="p" data-group-id="2620667362-11">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2620667362-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2620667362-12">[</span><span class="p" data-group-id="2620667362-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2620667362-13">[</span><span class="p" data-group-id="2620667362-13">]</span><span class="p" data-group-id="2620667362-10">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="9953482346-14">(</span><span class="p" data-group-id="9953482346-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="9953482346-15">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="9953482346-15">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="2620667362-14">(</span><span class="p" data-group-id="2620667362-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="2620667362-15">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="2620667362-15">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="9953482346-16">(</span><span class="n">Ch</span><span class="p" data-group-id="9953482346-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="9953482346-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9953482346-18">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9953482346-18">}</span><span class="p" data-group-id="9953482346-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="2620667362-16">(</span><span class="n">Ch</span><span class="p" data-group-id="2620667362-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="2620667362-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2620667362-18">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="2620667362-18">}</span><span class="p" data-group-id="2620667362-17">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="9953482346-19">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="9953482346-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9953482346-20">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="9953482346-21">(</span><span class="p" data-group-id="9953482346-21">)</span><span class="p" data-group-id="9953482346-20">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2620667362-19">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="2620667362-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2620667362-20">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="2620667362-21">(</span><span class="p" data-group-id="2620667362-21">)</span><span class="p" data-group-id="2620667362-20">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="9953482346-22">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9953482346-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9953482346-23">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="9953482346-23">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="9953482346-24">(</span><span class="n">Chs</span><span class="p" data-group-id="9953482346-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9953482346-25">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="9953482346-25">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="2620667362-22">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2620667362-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2620667362-23">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="2620667362-23">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="2620667362-24">(</span><span class="n">Chs</span><span class="p" data-group-id="2620667362-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2620667362-25">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="2620667362-25">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="9953482346-26">(</span><span class="p" data-group-id="9953482346-27">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="9953482346-27">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9953482346-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="9953482346-28">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="9953482346-28">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9953482346-29">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="9953482346-29">}</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-a-gen_server" class="section-heading">
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="2620667362-26">(</span><span class="p" data-group-id="2620667362-27">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="2620667362-27">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2620667362-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="2620667362-28">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="2620667362-28">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2620667362-29">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="2620667362-29">}</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-a-gen_server" class="section-heading">
│ │ │    <a href="#starting-a-gen_server" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting a Gen_Server</span>
│ │ │  </h2>
│ │ │  <p>In the example in the previous section, <code class="inline">gen_server</code> is started by calling
│ │ │ -<code class="inline">ch3:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="2597302340-1">(</span><span class="p" data-group-id="2597302340-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2597302340-2">(</span><span class="p" data-group-id="2597302340-3">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2597302340-3">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2597302340-4">[</span><span class="p" data-group-id="2597302340-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2597302340-5">[</span><span class="p" data-group-id="2597302340-5">]</span><span class="p" data-group-id="2597302340-2">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2597302340-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="2597302340-6">}</span></code></pre><p><code class="inline">start_link/0</code> calls function <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a>.  This function
│ │ │ +<code class="inline">ch3:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="7896129782-1">(</span><span class="p" data-group-id="7896129782-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="7896129782-2">(</span><span class="p" data-group-id="7896129782-3">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7896129782-3">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7896129782-4">[</span><span class="p" data-group-id="7896129782-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7896129782-5">[</span><span class="p" data-group-id="7896129782-5">]</span><span class="p" data-group-id="7896129782-2">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7896129782-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p" data-group-id="7896129782-6">}</span></code></pre><p><code class="inline">start_link/0</code> calls function <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a>.  This function
│ │ │  spawns and links to a new process, a <code class="inline">gen_server</code>.</p><ul><li><p>The first argument, <code class="inline">{local, ch3}</code>, specifies the name.
│ │ │  The gen_server is then locally registered as <code class="inline">ch3</code>.</p><p>If the name is omitted, the <code class="inline">gen_server</code> is not registered. Instead its pid
│ │ │  must be used. The name can also be given as <code class="inline">{global, Name}</code>, in which case
│ │ │  the <code class="inline">gen_server</code> is registered using <a href="../../lib/kernel-10.2.7.4/doc/html/global.html#register_name/2"><code class="inline">global:register_name/2</code></a>.</p></li><li><p>The second argument, <code class="inline">ch3</code>, is the name of the callback module, which is
│ │ │  the module where the callback functions are located.</p><p>The interface functions (<code class="inline">start_link/0</code>, <code class="inline">alloc/0</code>, and <code class="inline">free/1</code>) are located
│ │ │  in the same module as the callback functions (<code class="inline">init/1</code>, <code class="inline">handle_call/3</code>, and
│ │ │  <code class="inline">handle_cast/2</code>). It is usually good programming practice to have the code
│ │ │  corresponding to one process contained in a single module.</p></li><li><p>The third argument, <code class="inline">[]</code>, is a term that is passed as is to the callback
│ │ │  function <code class="inline">init</code>. Here, <code class="inline">init</code> does not need any indata and ignores the
│ │ │  argument.</p></li><li><p>The fourth argument, <code class="inline">[]</code>, is a list of options. See <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html"><code class="inline">gen_server</code></a>
│ │ │  for the available options.</p></li></ul><p>If name registration succeeds, the new <code class="inline">gen_server</code> process calls the callback
│ │ │  function <code class="inline">ch3:init([])</code>. <code class="inline">init</code> is expected to return <code class="inline">{ok, State}</code>, where
│ │ │  <code class="inline">State</code> is the internal state of the <code class="inline">gen_server</code>. In this case, the state is
│ │ │ -the available channels.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4451493578-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="4451493578-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4451493578-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="4451493578-3">(</span><span class="p" data-group-id="4451493578-3">)</span><span class="p" data-group-id="4451493578-2">}</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> is synchronous. It does not return until the
│ │ │ +the available channels.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9193519712-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="9193519712-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9193519712-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="9193519712-3">(</span><span class="p" data-group-id="9193519712-3">)</span><span class="p" data-group-id="9193519712-2">}</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> is synchronous. It does not return until the
│ │ │  <code class="inline">gen_server</code> has been initialized and is ready to receive requests.</p><p><a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/4</code></a> must be used if the <code class="inline">gen_server</code> is part of
│ │ │  a supervision tree, meaning that it was started by a supervisor. There
│ │ │  is another function, <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#start/4"><code class="inline">gen_server:start/4</code></a>, to start a standalone
│ │ │  <code class="inline">gen_server</code> that is not part of a supervision tree.</p><h2 id="synchronous-requests-call" class="section-heading">
│ │ │    <a href="#synchronous-requests-call" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -221,32 +221,32 @@
│ │ │  </h2>
│ │ │  <p>The synchronous request <code class="inline">alloc()</code> is implemented using <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#call/2"><code class="inline">gen_server:call/2</code></a>:</p><pre><code class="text">alloc() -&gt;
│ │ │      gen_server:call(ch3, alloc).</code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code> and must agree with the name
│ │ │  used to start it. <code class="inline">alloc</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │  When the request is received, the <code class="inline">gen_server</code> calls
│ │ │  <code class="inline">handle_call(Request, From, State)</code>, which is expected to return
│ │ │  a tuple <code class="inline">{reply,Reply,State1}</code>. <code class="inline">Reply</code> is the reply that is to be sent back
│ │ │ -to the client, and <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="8217358225-1">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8217358225-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8217358225-2">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8217358225-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="8217358225-3">(</span><span class="n">Chs</span><span class="p" data-group-id="8217358225-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8217358225-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8217358225-4">}</span><span class="p">.</span></code></pre><p>In this case, the reply is the allocated channel <code class="inline">Ch</code> and the new state is the
│ │ │ +to the client, and <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_call</span><span class="p" data-group-id="6979616298-1">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6979616298-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6979616298-2">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6979616298-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="6979616298-3">(</span><span class="n">Chs</span><span class="p" data-group-id="6979616298-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6979616298-4">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6979616298-4">}</span><span class="p">.</span></code></pre><p>In this case, the reply is the allocated channel <code class="inline">Ch</code> and the new state is the
│ │ │  set of remaining available channels <code class="inline">Chs2</code>.</p><p>Thus, the call <code class="inline">ch3:alloc()</code> returns the allocated channel <code class="inline">Ch</code> and the
│ │ │  <code class="inline">gen_server</code> then waits for new requests, now with an updated list of
│ │ │  available channels.</p><h2 id="asynchronous-requests-cast" class="section-heading">
│ │ │    <a href="#asynchronous-requests-cast" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Asynchronous Requests - Cast</span>
│ │ │  </h2>
│ │ │ -<p>The asynchronous request <code class="inline">free(Ch)</code> is implemented using <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#cast/2"><code class="inline">gen_server:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">free</span><span class="p" data-group-id="6634869590-1">(</span><span class="n">Ch</span><span class="p" data-group-id="6634869590-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="6634869590-2">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6634869590-3">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6634869590-3">}</span><span class="p" data-group-id="6634869590-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code>. <code class="inline">{free, Ch}</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │ +<p>The asynchronous request <code class="inline">free(Ch)</code> is implemented using <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#cast/2"><code class="inline">gen_server:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">free</span><span class="p" data-group-id="8987017950-1">(</span><span class="n">Ch</span><span class="p" data-group-id="8987017950-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8987017950-2">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8987017950-3">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8987017950-3">}</span><span class="p" data-group-id="8987017950-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch3</code> is the name of the <code class="inline">gen_server</code>. <code class="inline">{free, Ch}</code> is the actual request.</p><p>The request is made into a message and sent to the <code class="inline">gen_server</code>.
│ │ │  <code class="inline">cast</code>, and thus <code class="inline">free</code>, then returns <code class="inline">ok</code>.</p><p>When the request is received, the <code class="inline">gen_server</code> calls
│ │ │  <code class="inline">handle_cast(Request, State)</code>, which is expected to return a tuple
│ │ │ -<code class="inline">{noreply,State1}</code>. <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_cast</span><span class="p" data-group-id="1403032416-1">(</span><span class="p" data-group-id="1403032416-2">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="1403032416-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1403032416-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="1403032416-3">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="1403032416-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1403032416-4">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="1403032416-4">}</span><span class="p">.</span></code></pre><p>In this case, the new state is the updated list of available channels <code class="inline">Chs2</code>.
│ │ │ +<code class="inline">{noreply,State1}</code>. <code class="inline">State1</code> is a new value for the state of the <code class="inline">gen_server</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_cast</span><span class="p" data-group-id="6690991217-1">(</span><span class="p" data-group-id="6690991217-2">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="6690991217-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6690991217-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="6690991217-3">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6690991217-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6690991217-4">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="6690991217-4">}</span><span class="p">.</span></code></pre><p>In this case, the new state is the updated list of available channels <code class="inline">Chs2</code>.
│ │ │  The <code class="inline">gen_server</code> is now ready for new requests.</p><h2 id="stopping" class="section-heading">
│ │ │    <a href="#stopping" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Stopping</span>
│ │ │  </h2>
│ │ │  <h3 id="in-a-supervision-tree" class="section-heading">
│ │ │ @@ -257,69 +257,69 @@
│ │ │  </h3>
│ │ │  <p>If the <code class="inline">gen_server</code> is part of a supervision tree, no stop function is needed.
│ │ │  The <code class="inline">gen_server</code> is automatically terminated by its supervisor.  Exactly how
│ │ │  this is done is defined by a <a href="sup_princ.html#shutdown">shutdown strategy</a>
│ │ │  set in the supervisor.</p><p>If it is necessary to clean up before termination, the shutdown strategy
│ │ │  must be a time-out value and the <code class="inline">gen_server</code> must be set to trap exit signals
│ │ │  in function <code class="inline">init</code>. When ordered to shutdown, the <code class="inline">gen_server</code> then calls
│ │ │ -the callback function <code class="inline">terminate(shutdown, State)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6581963024-1">(</span><span class="n">Args</span><span class="p" data-group-id="6581963024-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +the callback function <code class="inline">terminate(shutdown, State)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8656897647-1">(</span><span class="n">Args</span><span class="p" data-group-id="8656897647-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="6581963024-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6581963024-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="8656897647-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8656897647-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6581963024-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6581963024-3">}</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8656897647-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8656897647-3">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="6581963024-4">(</span><span class="ss">shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="6581963024-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="8656897647-4">(</span><span class="ss">shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8656897647-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code for cleaning up here</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="standalone-gen_servers" class="section-heading">
│ │ │    <a href="#standalone-gen_servers" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Standalone Gen_Servers</span>
│ │ │  </h3>
│ │ │  <p>If the <code class="inline">gen_server</code> is not part of a supervision tree, a stop function
│ │ │  can be useful, for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">export</span><span class="p" data-group-id="8656246960-1">(</span><span class="p" data-group-id="8656246960-2">[</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8656246960-2">]</span><span class="p" data-group-id="8656246960-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">export</span><span class="p" data-group-id="7835258761-1">(</span><span class="p" data-group-id="7835258761-2">[</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7835258761-2">]</span><span class="p" data-group-id="7835258761-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="8656246960-3">(</span><span class="p" data-group-id="8656246960-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8656246960-4">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p" data-group-id="8656246960-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="7835258761-3">(</span><span class="p" data-group-id="7835258761-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="7835258761-4">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p" data-group-id="7835258761-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="8656246960-5">(</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8656246960-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8656246960-6">{</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8656246960-6">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="8656246960-7">(</span><span class="p" data-group-id="8656246960-8">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8656246960-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8656246960-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="7835258761-5">(</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7835258761-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7835258761-6">{</span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7835258761-6">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="7835258761-7">(</span><span class="p" data-group-id="7835258761-8">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7835258761-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7835258761-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="8656246960-9">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="8656246960-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="7835258761-9">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7835258761-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The callback function handling the <code class="inline">stop</code> request returns a tuple
│ │ │  <code class="inline">{stop,normal,State1}</code>, where <code class="inline">normal</code> specifies that it is
│ │ │  a normal termination and <code class="inline">State1</code> is a new value for the state
│ │ │  of the <code class="inline">gen_server</code>.  This causes the <code class="inline">gen_server</code> to call
│ │ │  <code class="inline">terminate(normal, State1)</code> and then it terminates gracefully.</p><h2 id="handling-other-messages" class="section-heading">
│ │ │    <a href="#handling-other-messages" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Handling Other Messages</span>
│ │ │  </h2>
│ │ │  <p>If the <code class="inline">gen_server</code> is to be able to receive other messages than requests,
│ │ │  the callback function <code class="inline">handle_info(Info, State)</code> must be implemented
│ │ │  to handle them.  Examples of other messages are exit messages,
│ │ │  if the <code class="inline">gen_server</code> is linked to other processes than the supervisor
│ │ │ -and it is trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="7865583290-1">(</span><span class="p" data-group-id="7865583290-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7865583290-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7865583290-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +and it is trapping exit signals.</p><pre><code class="makeup erlang" translate="no"><span class="nf">handle_info</span><span class="p" data-group-id="4673150988-1">(</span><span class="p" data-group-id="4673150988-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Pid</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="4673150988-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4673150988-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code to handle exits here.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7865583290-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="7865583290-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="4664021662-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="4664021662-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4673150988-3">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">State1</span><span class="p" data-group-id="4673150988-3">}</span><span class="p">.</span></code></pre><p>The final function to implement is <code class="inline">code_change/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">code_change</span><span class="p" data-group-id="8644663455-1">(</span><span class="n">OldVsn</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="8644663455-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Code to convert state (and more) during code change.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4664021662-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="4664021662-2">}</span><span class="p">.</span></code></pre>
│ │ │ +    </span><span class="p" data-group-id="8644663455-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NewState</span><span class="p" data-group-id="8644663455-2">}</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="design_principles.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/included_applications.html
│ │ │ @@ -161,75 +161,75 @@
│ │ │  belonging to the primary application.</p><h2 id="specifying-included-applications" class="section-heading">
│ │ │    <a href="#specifying-included-applications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Specifying Included Applications</span>
│ │ │  </h2>
│ │ │  <p>Which applications to include is defined by the <code class="inline">included_applications</code> key in
│ │ │ -the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1397496150-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1397496150-2">[</span><span class="p" data-group-id="1397496150-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="1397496150-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1397496150-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="1397496150-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1397496150-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1397496150-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="1397496150-6">]</span><span class="p" data-group-id="1397496150-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1397496150-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1397496150-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="1397496150-8">]</span><span class="p" data-group-id="1397496150-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1397496150-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1397496150-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="1397496150-10">]</span><span class="p" data-group-id="1397496150-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1397496150-11">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1397496150-12">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="1397496150-12">]</span><span class="p" data-group-id="1397496150-11">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1397496150-13">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1397496150-14">{</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="1397496150-15">[</span><span class="p" data-group-id="1397496150-15">]</span><span class="p" data-group-id="1397496150-14">}</span><span class="p" data-group-id="1397496150-13">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1397496150-16">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1397496150-17">[</span><span class="p" data-group-id="1397496150-18">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="1397496150-18">}</span><span class="p" data-group-id="1397496150-17">]</span><span class="p" data-group-id="1397496150-16">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="1397496150-2">]</span><span class="p" data-group-id="1397496150-1">}</span><span class="p">.</span></code></pre><h2 id="synchronizing-processes-during-startup" class="section-heading">
│ │ │ +the <code class="inline">.app</code> file:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9787513574-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9787513574-2">[</span><span class="p" data-group-id="9787513574-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="9787513574-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9787513574-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9787513574-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9787513574-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9787513574-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="9787513574-6">]</span><span class="p" data-group-id="9787513574-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9787513574-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9787513574-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="9787513574-8">]</span><span class="p" data-group-id="9787513574-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9787513574-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9787513574-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="9787513574-10">]</span><span class="p" data-group-id="9787513574-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9787513574-11">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9787513574-12">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="9787513574-12">]</span><span class="p" data-group-id="9787513574-11">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9787513574-13">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9787513574-14">{</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="9787513574-15">[</span><span class="p" data-group-id="9787513574-15">]</span><span class="p" data-group-id="9787513574-14">}</span><span class="p" data-group-id="9787513574-13">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9787513574-16">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9787513574-17">[</span><span class="p" data-group-id="9787513574-18">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="9787513574-18">}</span><span class="p" data-group-id="9787513574-17">]</span><span class="p" data-group-id="9787513574-16">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9787513574-2">]</span><span class="p" data-group-id="9787513574-1">}</span><span class="p">.</span></code></pre><h2 id="synchronizing-processes-during-startup" class="section-heading">
│ │ │    <a href="#synchronizing-processes-during-startup" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Synchronizing Processes during Startup</span>
│ │ │  </h2>
│ │ │  <p>The supervisor tree of an included application is started as part of the
│ │ │  supervisor tree of the including application. If there is a need for
│ │ │  synchronization between processes in the including and included applications,
│ │ │  this can be achieved by using <em>start phases</em>.</p><p>Start phases are defined by the <code class="inline">start_phases</code> key in the <code class="inline">.app</code> file as a list
│ │ │  of tuples <code class="inline">{Phase,PhaseArgs}</code>, where <code class="inline">Phase</code> is an atom and <code class="inline">PhaseArgs</code> is a
│ │ │  term.</p><p>The value of the <code class="inline">mod</code> key of the including application must be set to
│ │ │  <code class="inline">{application_starter,[Module,StartArgs]}</code>, where <code class="inline">Module</code> as usual is the
│ │ │  application callback module. <code class="inline">StartArgs</code> is a term provided as argument to the
│ │ │ -callback function <code class="inline">Module:start/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0773196796-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0773196796-2">[</span><span class="p" data-group-id="0773196796-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="0773196796-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0773196796-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="0773196796-6">]</span><span class="p" data-group-id="0773196796-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="0773196796-8">]</span><span class="p" data-group-id="0773196796-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="0773196796-10">]</span><span class="p" data-group-id="0773196796-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-11">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-12">[</span><span class="p" data-group-id="0773196796-13">{</span><span class="ss">init</span><span class="p">,</span><span class="p" data-group-id="0773196796-14">[</span><span class="p" data-group-id="0773196796-14">]</span><span class="p" data-group-id="0773196796-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-15">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="0773196796-16">[</span><span class="p" data-group-id="0773196796-16">]</span><span class="p" data-group-id="0773196796-15">}</span><span class="p" data-group-id="0773196796-12">]</span><span class="p" data-group-id="0773196796-11">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-17">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-18">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="0773196796-18">]</span><span class="p" data-group-id="0773196796-17">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-19">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-20">{</span><span class="ss">application_starter</span><span class="p">,</span><span class="p" data-group-id="0773196796-21">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="0773196796-22">[</span><span class="p" data-group-id="0773196796-22">]</span><span class="p" data-group-id="0773196796-21">]</span><span class="p" data-group-id="0773196796-20">}</span><span class="p" data-group-id="0773196796-19">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-23">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-24">[</span><span class="p" data-group-id="0773196796-25">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="0773196796-25">}</span><span class="p" data-group-id="0773196796-24">]</span><span class="p" data-group-id="0773196796-23">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0773196796-2">]</span><span class="p" data-group-id="0773196796-1">}</span><span class="p">.</span><span class="w">
│ │ │ +callback function <code class="inline">Module:start/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3699974331-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3699974331-2">[</span><span class="p" data-group-id="3699974331-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Tree application&quot;</span><span class="p" data-group-id="3699974331-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="3699974331-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-6">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">prim_app_server</span><span class="p" data-group-id="3699974331-6">]</span><span class="p" data-group-id="3699974331-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-8">[</span><span class="ss">prim_app_server</span><span class="p" data-group-id="3699974331-8">]</span><span class="p" data-group-id="3699974331-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-9">{</span><span class="ss">included_applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-10">[</span><span class="ss">incl_app</span><span class="p" data-group-id="3699974331-10">]</span><span class="p" data-group-id="3699974331-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-11">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-12">[</span><span class="p" data-group-id="3699974331-13">{</span><span class="ss">init</span><span class="p">,</span><span class="p" data-group-id="3699974331-14">[</span><span class="p" data-group-id="3699974331-14">]</span><span class="p" data-group-id="3699974331-13">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-15">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="3699974331-16">[</span><span class="p" data-group-id="3699974331-16">]</span><span class="p" data-group-id="3699974331-15">}</span><span class="p" data-group-id="3699974331-12">]</span><span class="p" data-group-id="3699974331-11">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-17">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-18">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="3699974331-18">]</span><span class="p" data-group-id="3699974331-17">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-19">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-20">{</span><span class="ss">application_starter</span><span class="p">,</span><span class="p" data-group-id="3699974331-21">[</span><span class="ss">prim_app_cb</span><span class="p">,</span><span class="p" data-group-id="3699974331-22">[</span><span class="p" data-group-id="3699974331-22">]</span><span class="p" data-group-id="3699974331-21">]</span><span class="p" data-group-id="3699974331-20">}</span><span class="p" data-group-id="3699974331-19">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-23">{</span><span class="ss">env</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-24">[</span><span class="p" data-group-id="3699974331-25">{</span><span class="ss">file</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;/usr/local/log&quot;</span><span class="p" data-group-id="3699974331-25">}</span><span class="p" data-group-id="3699974331-24">]</span><span class="p" data-group-id="3699974331-23">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3699974331-2">]</span><span class="p" data-group-id="3699974331-1">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="0773196796-26">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0773196796-27">[</span><span class="p" data-group-id="0773196796-28">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Included application&quot;</span><span class="p" data-group-id="0773196796-28">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-29">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="0773196796-29">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-30">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-31">[</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_server</span><span class="p" data-group-id="0773196796-31">]</span><span class="p" data-group-id="0773196796-30">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-32">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-33">[</span><span class="p" data-group-id="0773196796-33">]</span><span class="p" data-group-id="0773196796-32">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-34">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-35">[</span><span class="p" data-group-id="0773196796-36">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="0773196796-37">[</span><span class="p" data-group-id="0773196796-37">]</span><span class="p" data-group-id="0773196796-36">}</span><span class="p" data-group-id="0773196796-35">]</span><span class="p" data-group-id="0773196796-34">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-38">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-39">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="0773196796-39">]</span><span class="p" data-group-id="0773196796-38">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0773196796-40">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0773196796-41">{</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="p" data-group-id="0773196796-42">[</span><span class="p" data-group-id="0773196796-42">]</span><span class="p" data-group-id="0773196796-41">}</span><span class="p" data-group-id="0773196796-40">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="0773196796-27">]</span><span class="p" data-group-id="0773196796-26">}</span><span class="p">.</span></code></pre><p>When starting a primary application with included applications, the primary
│ │ │ +</span><span class="p" data-group-id="3699974331-26">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3699974331-27">[</span><span class="p" data-group-id="3699974331-28">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Included application&quot;</span><span class="p" data-group-id="3699974331-28">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-29">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="3699974331-29">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-30">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-31">[</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">incl_app_server</span><span class="p" data-group-id="3699974331-31">]</span><span class="p" data-group-id="3699974331-30">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-32">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-33">[</span><span class="p" data-group-id="3699974331-33">]</span><span class="p" data-group-id="3699974331-32">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-34">{</span><span class="ss">start_phases</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-35">[</span><span class="p" data-group-id="3699974331-36">{</span><span class="ss">go</span><span class="p">,</span><span class="p" data-group-id="3699974331-37">[</span><span class="p" data-group-id="3699974331-37">]</span><span class="p" data-group-id="3699974331-36">}</span><span class="p" data-group-id="3699974331-35">]</span><span class="p" data-group-id="3699974331-34">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-38">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-39">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="3699974331-39">]</span><span class="p" data-group-id="3699974331-38">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="3699974331-40">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3699974331-41">{</span><span class="ss">incl_app_cb</span><span class="p">,</span><span class="p" data-group-id="3699974331-42">[</span><span class="p" data-group-id="3699974331-42">]</span><span class="p" data-group-id="3699974331-41">}</span><span class="p" data-group-id="3699974331-40">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="3699974331-27">]</span><span class="p" data-group-id="3699974331-26">}</span><span class="p">.</span></code></pre><p>When starting a primary application with included applications, the primary
│ │ │  application is started the normal way, that is:</p><ul><li>The application controller creates an application master for the application</li><li>The application master calls <code class="inline">Module:start(normal, StartArgs)</code> to start the
│ │ │  top supervisor.</li></ul><p>Then, for the primary application and each included application in top-down,
│ │ │  left-to-right order, the application master calls
│ │ │  <code class="inline">Module:start_phase(Phase, Type, PhaseArgs)</code> for each phase defined for the
│ │ │  primary application, in that order. If a phase is not defined for an included
│ │ │  application, the function is not called for this phase and application.</p><p>The following requirements apply to the <code class="inline">.app</code> file for an included application:</p><ul><li>The <code class="inline">{mod, {Module,StartArgs}}</code> option must be included. This option is used
│ │ │  to find the callback module <code class="inline">Module</code> of the application. <code class="inline">StartArgs</code> is
│ │ │  ignored, as <code class="inline">Module:start/2</code> is called only for the primary application.</li><li>If the included application itself contains included applications, instead the
│ │ │  <code class="inline">{mod, {application_starter, [Module,StartArgs]}}</code> option must be included.</li><li>The <code class="inline">{start_phases, [{Phase,PhaseArgs}]}</code> option must be included, and the set
│ │ │  of specified phases must be a subset of the set of phases specified for the
│ │ │  primary application.</li></ul><p>When starting <code class="inline">prim_app</code> as defined above, the application controller calls the
│ │ │  following callback functions before <code class="inline">application:start(prim_app)</code> returns a
│ │ │ -value:</p><pre><code class="makeup erlang" translate="no"><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3325279387-1">(</span><span class="ss">prim_app</span><span class="p" data-group-id="3325279387-1">)</span><span class="w">
│ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="3325279387-2">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3325279387-3">[</span><span class="p" data-group-id="3325279387-3">]</span><span class="p" data-group-id="3325279387-2">)</span><span class="w">
│ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="3325279387-4">(</span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3325279387-5">[</span><span class="p" data-group-id="3325279387-5">]</span><span class="p" data-group-id="3325279387-4">)</span><span class="w">
│ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="3325279387-6">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3325279387-7">[</span><span class="p" data-group-id="3325279387-7">]</span><span class="p" data-group-id="3325279387-6">)</span><span class="w">
│ │ │ - </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">incl_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="3325279387-8">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3325279387-9">[</span><span class="p" data-group-id="3325279387-9">]</span><span class="p" data-group-id="3325279387-8">)</span><span class="w">
│ │ │ +value:</p><pre><code class="makeup erlang" translate="no"><span class="nc">application</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9073633264-1">(</span><span class="ss">prim_app</span><span class="p" data-group-id="9073633264-1">)</span><span class="w">
│ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start</span><span class="p" data-group-id="9073633264-2">(</span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9073633264-3">[</span><span class="p" data-group-id="9073633264-3">]</span><span class="p" data-group-id="9073633264-2">)</span><span class="w">
│ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="9073633264-4">(</span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9073633264-5">[</span><span class="p" data-group-id="9073633264-5">]</span><span class="p" data-group-id="9073633264-4">)</span><span class="w">
│ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">prim_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="9073633264-6">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9073633264-7">[</span><span class="p" data-group-id="9073633264-7">]</span><span class="p" data-group-id="9073633264-6">)</span><span class="w">
│ │ │ + </span><span class="p">=&gt;</span><span class="w"> </span><span class="nc">incl_app_cb</span><span class="p">:</span><span class="nf">start_phase</span><span class="p" data-group-id="9073633264-8">(</span><span class="ss">go</span><span class="p">,</span><span class="w"> </span><span class="ss">normal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9073633264-9">[</span><span class="p" data-group-id="9073633264-9">]</span><span class="p" data-group-id="9073633264-8">)</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="applications.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/install-win32.html
│ │ │ @@ -295,15 +295,15 @@
│ │ │  </span><span class="gp unselectable">$ </span><span class="">cd erts/emulator
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make debug
│ │ │  </span><span class="gp unselectable">$ </span><span class="">cd ../etc
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make debug
│ │ │  </span></code></pre><p>and sometimes</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make local_setup
│ │ │  </span></code></pre><p>So now when you run <code class="inline">$ERL_TOP/erl.exe</code>, you should have a debug compiled
│ │ │ -emulator, which you will see if you do a:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="5367963359-1">(</span><span class="ss">system_version</span><span class="p" data-group-id="5367963359-1">)</span><span class="p">.</span></code></pre><p>in the erlang shell. If the returned string contains <code class="inline">[debug]</code>, you
│ │ │ +emulator, which you will see if you do a:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">system_info</span><span class="p" data-group-id="2552126543-1">(</span><span class="ss">system_version</span><span class="p" data-group-id="2552126543-1">)</span><span class="p">.</span></code></pre><p>in the erlang shell. If the returned string contains <code class="inline">[debug]</code>, you
│ │ │  got a debug compiled emulator.</p><p>To hack the erlang libraries, you simply do a <code class="inline">make opt</code> in the
│ │ │  specific &quot;applications&quot; directory, like:</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make opt
│ │ │  </span></code></pre><p>or even in the source directory...</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib/src
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make opt
│ │ │  </span></code></pre><p>Note that you're expected to have a fresh Erlang in your path when
│ │ │  doing this, preferably the plain 27 you have built in the previous
│ │ │ @@ -318,19 +318,19 @@
│ │ │  </span><span class="">:$ERL_TOP/erts/etc/win32/wsl_tools:$ERL_TOP/bootstrap/bin:$PATH
│ │ │  </span></code></pre><p>That should make it possible to rebuild any library without hassle...</p><p>If you want to copy a library (an application) newly built, to a
│ │ │  release area, you do like with the emulator:</p><pre><code class="makeup shell" translate="no"><span class="gp unselectable">$ </span><span class="">cd $ERL_TOP/lib/stdlib
│ │ │  </span><span class="gp unselectable">$ </span><span class="">make TESTROOT=/tmp/erlang_release release
│ │ │  </span></code></pre><p>Remember that:</p><ul><li><p>  Windows specific C-code goes in the <code class="inline">$ERL_TOP/erts/emulator/sys/win32</code>,
│ │ │  <code class="inline">$ERL_TOP/erts/emulator/drivers/win32</code> or <code class="inline">$ERL_TOP/erts/etc/win32</code>.</p></li><li><p>  Windows specific erlang code should be used conditionally and the
│ │ │  host OS tested in <em>runtime</em>, the exactly same beam files should be
│ │ │ -distributed for every platform! So write code like:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">os</span><span class="p">:</span><span class="nf">type</span><span class="p" data-group-id="0548584637-1">(</span><span class="p" data-group-id="0548584637-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0548584637-2">{</span><span class="ss">win32</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0548584637-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nf">do_windows_specific</span><span class="p" data-group-id="0548584637-3">(</span><span class="p" data-group-id="0548584637-3">)</span><span class="p">;</span><span class="w">
│ │ │ +distributed for every platform! So write code like:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">os</span><span class="p">:</span><span class="nf">type</span><span class="p" data-group-id="8901665230-1">(</span><span class="p" data-group-id="8901665230-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8901665230-2">{</span><span class="ss">win32</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8901665230-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">do_windows_specific</span><span class="p" data-group-id="8901665230-3">(</span><span class="p" data-group-id="8901665230-3">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Other</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nf">do_fallback_or_exit</span><span class="p" data-group-id="0548584637-4">(</span><span class="p" data-group-id="0548584637-4">)</span><span class="w">
│ │ │ +        </span><span class="nf">do_fallback_or_exit</span><span class="p" data-group-id="8901665230-4">(</span><span class="p" data-group-id="8901665230-4">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre></li></ul><p>That's basically all you need to get going.</p><h2 id="frequently-asked-questions" class="section-heading">
│ │ │    <a href="#frequently-asked-questions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Frequently Asked Questions</span>
│ │ │  </h2>
│ │ │  <ul><li><p>  Q: So, now I can build Erlang using GCC on Windows?</p><p>A: No, unfortunately not. You'll need Microsoft's Visual C++
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/list_comprehensions.html
│ │ │ @@ -117,33 +117,33 @@
│ │ │  
│ │ │  <h2 id="simple-examples" class="section-heading">
│ │ │    <a href="#simple-examples" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simple Examples</span>
│ │ │  </h2>
│ │ │ -<p>This section starts with a simple example, showing a generator and a filter:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="5705651241-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5705651241-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5705651241-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5705651241-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5705651241-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5705651241-3">]</span></code></pre><p>This is read as follows: The list of X such that X is taken from the list
│ │ │ +<p>This section starts with a simple example, showing a generator and a filter:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="4243823549-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="4243823549-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4243823549-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4243823549-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4243823549-3">[</span><span class="ss">a</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4243823549-3">]</span></code></pre><p>This is read as follows: The list of X such that X is taken from the list
│ │ │  <code class="inline">[1,2,a,...]</code> and X is greater than 3.</p><p>The notation <code class="inline">X &lt;- [1,2,a,...]</code> is a generator and the expression <code class="inline">X &gt; 3</code> is a
│ │ │  filter.</p><p>An additional filter, <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_integer/1"><code class="inline">is_integer(X)</code></a>, can be added to
│ │ │ -restrict the result to integers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="5472063969-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="5472063969-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5472063969-2">]</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="5472063969-3">(</span><span class="n">X</span><span class="p" data-group-id="5472063969-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5472063969-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5472063969-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="5472063969-4">]</span></code></pre><p>Generators can be combined. For example, the Cartesian product of two lists can
│ │ │ -be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="3718980518-1">[</span><span class="p" data-group-id="3718980518-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3718980518-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="3718980518-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3718980518-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="3718980518-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3718980518-4">]</span><span class="p" data-group-id="3718980518-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3718980518-5">[</span><span class="p" data-group-id="3718980518-6">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="3718980518-6">}</span><span class="p">,</span><span class="p" data-group-id="3718980518-7">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3718980518-7">}</span><span class="p">,</span><span class="p" data-group-id="3718980518-8">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="3718980518-8">}</span><span class="p">,</span><span class="p" data-group-id="3718980518-9">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3718980518-9">}</span><span class="p">,</span><span class="p" data-group-id="3718980518-10">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="3718980518-10">}</span><span class="p">,</span><span class="p" data-group-id="3718980518-11">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3718980518-11">}</span><span class="p" data-group-id="3718980518-5">]</span></code></pre><h2 id="quick-sort" class="section-heading">
│ │ │ +restrict the result to integers:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="6315028383-1">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6315028383-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6315028383-2">]</span><span class="p">,</span><span class="w"> </span><span class="nf">is_integer</span><span class="p" data-group-id="6315028383-3">(</span><span class="n">X</span><span class="p" data-group-id="6315028383-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6315028383-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6315028383-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="6315028383-4">]</span></code></pre><p>Generators can be combined. For example, the Cartesian product of two lists can
│ │ │ +be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="1542104293-1">[</span><span class="p" data-group-id="1542104293-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1542104293-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1542104293-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1542104293-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1542104293-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1542104293-4">]</span><span class="p" data-group-id="1542104293-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1542104293-5">[</span><span class="p" data-group-id="1542104293-6">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1542104293-6">}</span><span class="p">,</span><span class="p" data-group-id="1542104293-7">{</span><span class="mi">1</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1542104293-7">}</span><span class="p">,</span><span class="p" data-group-id="1542104293-8">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1542104293-8">}</span><span class="p">,</span><span class="p" data-group-id="1542104293-9">{</span><span class="mi">2</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1542104293-9">}</span><span class="p">,</span><span class="p" data-group-id="1542104293-10">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1542104293-10">}</span><span class="p">,</span><span class="p" data-group-id="1542104293-11">{</span><span class="mi">3</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1542104293-11">}</span><span class="p" data-group-id="1542104293-5">]</span></code></pre><h2 id="quick-sort" class="section-heading">
│ │ │    <a href="#quick-sort" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Quick Sort</span>
│ │ │  </h2>
│ │ │ -<p>The well-known quick sort routine can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sort</span><span class="p" data-group-id="1179913648-1">(</span><span class="p" data-group-id="1179913648-2">[</span><span class="p" data-group-id="1179913648-2">]</span><span class="p" data-group-id="1179913648-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1179913648-3">[</span><span class="p" data-group-id="1179913648-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">sort</span><span class="p" data-group-id="1179913648-4">(</span><span class="p" data-group-id="1179913648-5">[</span><span class="p">_</span><span class="p" data-group-id="1179913648-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1179913648-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">L</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">sort</span><span class="p" data-group-id="1179913648-6">(</span><span class="p" data-group-id="1179913648-7">[</span><span class="n">Pivot</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1179913648-7">]</span><span class="p" data-group-id="1179913648-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">sort</span><span class="p" data-group-id="1179913648-8">(</span><span class="p" data-group-id="1179913648-9">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="1179913648-9">]</span><span class="p" data-group-id="1179913648-8">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1179913648-10">[</span><span class="n">Pivot</span><span class="p" data-group-id="1179913648-10">]</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ -    </span><span class="nf">sort</span><span class="p" data-group-id="1179913648-11">(</span><span class="p" data-group-id="1179913648-12">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="1179913648-12">]</span><span class="p" data-group-id="1179913648-11">)</span><span class="p">.</span></code></pre><p>The expression <code class="inline">[X || X &lt;- T, X &lt; Pivot]</code> is the list of all elements in <code class="inline">T</code>
│ │ │ +<p>The well-known quick sort routine can be written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sort</span><span class="p" data-group-id="1140497368-1">(</span><span class="p" data-group-id="1140497368-2">[</span><span class="p" data-group-id="1140497368-2">]</span><span class="p" data-group-id="1140497368-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1140497368-3">[</span><span class="p" data-group-id="1140497368-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">sort</span><span class="p" data-group-id="1140497368-4">(</span><span class="p" data-group-id="1140497368-5">[</span><span class="p">_</span><span class="p" data-group-id="1140497368-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1140497368-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">L</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">sort</span><span class="p" data-group-id="1140497368-6">(</span><span class="p" data-group-id="1140497368-7">[</span><span class="n">Pivot</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1140497368-7">]</span><span class="p" data-group-id="1140497368-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">sort</span><span class="p" data-group-id="1140497368-8">(</span><span class="p" data-group-id="1140497368-9">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="1140497368-9">]</span><span class="p" data-group-id="1140497368-8">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1140497368-10">[</span><span class="n">Pivot</span><span class="p" data-group-id="1140497368-10">]</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ +    </span><span class="nf">sort</span><span class="p" data-group-id="1140497368-11">(</span><span class="p" data-group-id="1140497368-12">[</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="n">Pivot</span><span class="p" data-group-id="1140497368-12">]</span><span class="p" data-group-id="1140497368-11">)</span><span class="p">.</span></code></pre><p>The expression <code class="inline">[X || X &lt;- T, X &lt; Pivot]</code> is the list of all elements in <code class="inline">T</code>
│ │ │  that are less than <code class="inline">Pivot</code>.</p><p><code class="inline">[X || X &lt;- T, X &gt;= Pivot]</code> is the list of all elements in <code class="inline">T</code> that are greater
│ │ │  than or equal to <code class="inline">Pivot</code>.</p><p>With the algorithm above, a list is sorted as follows:</p><ul><li>A list with zero or one element is trivially sorted.</li><li>For lists with more than one element:<ol><li>The first element in the list is isolated as the pivot element.</li><li>The remaining list is partitioned into two sublists, such that:</li></ol><ul><li>The first sublist contains all elements that are smaller than the pivot
│ │ │  element.</li><li>The second sublist contains all elements that are greater than or equal to
│ │ │  the pivot element.</li></ul><ol><li>The sublists are recursively sorted by the same algorithm and the results
│ │ │  are combined, resulting in a list consisting of:</li></ol><ul><li>All elements from the first sublist, that is all elements smaller than the
│ │ │  pivot element, in sorted order.</li><li>The pivot element.</li><li>All elements from the second sublist, that is all elements greater than or
│ │ │  equal to the pivot element, in sorted order.</li></ul></li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>While the sorting algorithm as shown above serves as a nice example to
│ │ │ @@ -151,93 +151,93 @@
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html"><code class="inline">lists</code></a> module contains sorting functions that are implemented in a more
│ │ │  efficient way.</p></section><h2 id="permutations" class="section-heading">
│ │ │    <a href="#permutations" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Permutations</span>
│ │ │  </h2>
│ │ │ -<p>The following example generates all permutations of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">perms</span><span class="p" data-group-id="0069412384-1">(</span><span class="p" data-group-id="0069412384-2">[</span><span class="p" data-group-id="0069412384-2">]</span><span class="p" data-group-id="0069412384-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0069412384-3">[</span><span class="p" data-group-id="0069412384-4">[</span><span class="p" data-group-id="0069412384-4">]</span><span class="p" data-group-id="0069412384-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">perms</span><span class="p" data-group-id="0069412384-5">(</span><span class="n">L</span><span class="p" data-group-id="0069412384-5">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0069412384-6">[</span><span class="p" data-group-id="0069412384-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0069412384-7">]</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nf">perms</span><span class="p" data-group-id="0069412384-8">(</span><span class="n">L</span><span class="o">--</span><span class="p" data-group-id="0069412384-9">[</span><span class="n">H</span><span class="p" data-group-id="0069412384-9">]</span><span class="p" data-group-id="0069412384-8">)</span><span class="p" data-group-id="0069412384-6">]</span><span class="p">.</span></code></pre><p>This takes <code class="inline">H</code> from <code class="inline">L</code> in all possible ways. The result is the set of all lists
│ │ │ +<p>The following example generates all permutations of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="nf">perms</span><span class="p" data-group-id="0199747514-1">(</span><span class="p" data-group-id="0199747514-2">[</span><span class="p" data-group-id="0199747514-2">]</span><span class="p" data-group-id="0199747514-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0199747514-3">[</span><span class="p" data-group-id="0199747514-4">[</span><span class="p" data-group-id="0199747514-4">]</span><span class="p" data-group-id="0199747514-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">perms</span><span class="p" data-group-id="0199747514-5">(</span><span class="n">L</span><span class="p" data-group-id="0199747514-5">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0199747514-6">[</span><span class="p" data-group-id="0199747514-7">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0199747514-7">]</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nf">perms</span><span class="p" data-group-id="0199747514-8">(</span><span class="n">L</span><span class="o">--</span><span class="p" data-group-id="0199747514-9">[</span><span class="n">H</span><span class="p" data-group-id="0199747514-9">]</span><span class="p" data-group-id="0199747514-8">)</span><span class="p" data-group-id="0199747514-6">]</span><span class="p">.</span></code></pre><p>This takes <code class="inline">H</code> from <code class="inline">L</code> in all possible ways. The result is the set of all lists
│ │ │  <code class="inline">[H|T]</code>, where <code class="inline">T</code> is the set of all possible permutations of <code class="inline">L</code>, with <code class="inline">H</code>
│ │ │ -removed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">perms</span><span class="p" data-group-id="9841347649-1">(</span><span class="p" data-group-id="9841347649-2">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="9841347649-2">]</span><span class="p" data-group-id="9841347649-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9841347649-3">[</span><span class="p" data-group-id="9841347649-4">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="9841347649-4">]</span><span class="p">,</span><span class="p" data-group-id="9841347649-5">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="9841347649-5">]</span><span class="p">,</span><span class="p" data-group-id="9841347649-6">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="9841347649-6">]</span><span class="p">,</span><span class="p" data-group-id="9841347649-7">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9841347649-7">]</span><span class="p">,</span><span class="p" data-group-id="9841347649-8">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="9841347649-8">]</span><span class="p">,</span><span class="p" data-group-id="9841347649-9">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="9841347649-9">]</span><span class="p" data-group-id="9841347649-3">]</span></code></pre><h2 id="pythagorean-triplets" class="section-heading">
│ │ │ +removed:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">perms</span><span class="p" data-group-id="2738197520-1">(</span><span class="p" data-group-id="2738197520-2">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="2738197520-2">]</span><span class="p" data-group-id="2738197520-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2738197520-3">[</span><span class="p" data-group-id="2738197520-4">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="2738197520-4">]</span><span class="p">,</span><span class="p" data-group-id="2738197520-5">[</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="2738197520-5">]</span><span class="p">,</span><span class="p" data-group-id="2738197520-6">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">g</span><span class="p" data-group-id="2738197520-6">]</span><span class="p">,</span><span class="p" data-group-id="2738197520-7">[</span><span class="ss">u</span><span class="p">,</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2738197520-7">]</span><span class="p">,</span><span class="p" data-group-id="2738197520-8">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">u</span><span class="p" data-group-id="2738197520-8">]</span><span class="p">,</span><span class="p" data-group-id="2738197520-9">[</span><span class="ss">g</span><span class="p">,</span><span class="ss">u</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2738197520-9">]</span><span class="p" data-group-id="2738197520-3">]</span></code></pre><h2 id="pythagorean-triplets" class="section-heading">
│ │ │    <a href="#pythagorean-triplets" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Pythagorean Triplets</span>
│ │ │  </h2>
│ │ │  <p>Pythagorean triplets are sets of integers <code class="inline">{A,B,C}</code> such that
│ │ │  <code class="inline">A**2 + B**2 = C**2</code>.</p><p>The function <code class="inline">pyth(N)</code> generates a list of all integers <code class="inline">{A,B,C}</code> such that
│ │ │  <code class="inline">A**2 + B**2 = C**2</code> and where the sum of the sides is equal to, or less than,
│ │ │ -<code class="inline">N</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth</span><span class="p" data-group-id="4615713017-1">(</span><span class="n">N</span><span class="p" data-group-id="4615713017-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4615713017-2">[</span><span class="w"> </span><span class="p" data-group-id="4615713017-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="4615713017-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ -        </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="4615713017-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="4615713017-4">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="4615713017-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="4615713017-5">)</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="4615713017-6">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="4615713017-6">)</span><span class="p">,</span><span class="w">
│ │ │ +<code class="inline">N</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth</span><span class="p" data-group-id="7888673863-1">(</span><span class="n">N</span><span class="p" data-group-id="7888673863-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7888673863-2">[</span><span class="w"> </span><span class="p" data-group-id="7888673863-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="7888673863-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ +        </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="7888673863-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="7888673863-4">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="7888673863-5">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="7888673863-5">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="7888673863-6">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="7888673863-6">)</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">+</span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4615713017-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="3729286299-1">(</span><span class="mi">3</span><span class="p" data-group-id="3729286299-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3729286299-2">[</span><span class="p" data-group-id="3729286299-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="3729286299-3">(</span><span class="mi">11</span><span class="p" data-group-id="3729286299-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3729286299-4">[</span><span class="p" data-group-id="3729286299-4">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="3729286299-5">(</span><span class="mi">12</span><span class="p" data-group-id="3729286299-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3729286299-6">[</span><span class="p" data-group-id="3729286299-7">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3729286299-7">}</span><span class="p">,</span><span class="p" data-group-id="3729286299-8">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3729286299-8">}</span><span class="p" data-group-id="3729286299-6">]</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="3729286299-9">(</span><span class="mi">50</span><span class="p" data-group-id="3729286299-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3729286299-10">[</span><span class="p" data-group-id="3729286299-11">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3729286299-11">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-12">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3729286299-12">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-13">{</span><span class="mi">5</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="3729286299-13">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-14">{</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="3729286299-14">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-15">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="3729286299-15">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-16">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="3729286299-16">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-17">{</span><span class="mi">9</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="3729286299-17">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-18">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="3729286299-18">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-19">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="3729286299-19">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-20">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="3729286299-20">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-21">{</span><span class="mi">15</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="3729286299-21">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="3729286299-22">{</span><span class="mi">16</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="3729286299-22">}</span><span class="p" data-group-id="3729286299-10">]</span></code></pre><p>The following code reduces the search space and is more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth1</span><span class="p" data-group-id="8796214492-1">(</span><span class="n">N</span><span class="p" data-group-id="8796214492-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="p" data-group-id="8796214492-2">[</span><span class="p" data-group-id="8796214492-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="8796214492-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ -       </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="8796214492-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="8796214492-4">)</span><span class="p">,</span><span class="w">
│ │ │ -       </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="8796214492-5">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="8796214492-5">)</span><span class="p">,</span><span class="w">
│ │ │ -       </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="8796214492-6">(</span><span class="n">B</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="8796214492-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7888673863-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="2087367128-1">(</span><span class="mi">3</span><span class="p" data-group-id="2087367128-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2087367128-2">[</span><span class="p" data-group-id="2087367128-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="2087367128-3">(</span><span class="mi">11</span><span class="p" data-group-id="2087367128-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2087367128-4">[</span><span class="p" data-group-id="2087367128-4">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="2087367128-5">(</span><span class="mi">12</span><span class="p" data-group-id="2087367128-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2087367128-6">[</span><span class="p" data-group-id="2087367128-7">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2087367128-7">}</span><span class="p">,</span><span class="p" data-group-id="2087367128-8">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2087367128-8">}</span><span class="p" data-group-id="2087367128-6">]</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nf">pyth</span><span class="p" data-group-id="2087367128-9">(</span><span class="mi">50</span><span class="p" data-group-id="2087367128-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2087367128-10">[</span><span class="p" data-group-id="2087367128-11">{</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2087367128-11">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-12">{</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="2087367128-12">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-13">{</span><span class="mi">5</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="2087367128-13">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-14">{</span><span class="mi">6</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="2087367128-14">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-15">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">10</span><span class="p" data-group-id="2087367128-15">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-16">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="2087367128-16">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-17">{</span><span class="mi">9</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="2087367128-17">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-18">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="2087367128-18">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-19">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">15</span><span class="p" data-group-id="2087367128-19">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-20">{</span><span class="mi">12</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="2087367128-20">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-21">{</span><span class="mi">15</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">17</span><span class="p" data-group-id="2087367128-21">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2087367128-22">{</span><span class="mi">16</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">20</span><span class="p" data-group-id="2087367128-22">}</span><span class="p" data-group-id="2087367128-10">]</span></code></pre><p>The following code reduces the search space and is more efficient:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pyth1</span><span class="p" data-group-id="3453927687-1">(</span><span class="n">N</span><span class="p" data-group-id="3453927687-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="p" data-group-id="3453927687-2">[</span><span class="p" data-group-id="3453927687-3">{</span><span class="n">A</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">C</span><span class="p" data-group-id="3453927687-3">}</span><span class="w"> </span><span class="p">||</span><span class="w">
│ │ │ +       </span><span class="n">A</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="3453927687-4">(</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="3453927687-4">)</span><span class="p">,</span><span class="w">
│ │ │ +       </span><span class="n">B</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="3453927687-5">(</span><span class="n">A</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="3453927687-5">)</span><span class="p">,</span><span class="w">
│ │ │ +       </span><span class="n">C</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">seq</span><span class="p" data-group-id="3453927687-6">(</span><span class="n">B</span><span class="o">+</span><span class="mi">1</span><span class="p">,</span><span class="n">N</span><span class="p" data-group-id="3453927687-6">)</span><span class="p">,</span><span class="w">
│ │ │         </span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">+</span><span class="n">C</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w">
│ │ │ -       </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w"> </span><span class="p" data-group-id="8796214492-2">]</span><span class="p">.</span></code></pre><h2 id="simplifications-with-list-comprehensions" class="section-heading">
│ │ │ +       </span><span class="n">A</span><span class="o">*</span><span class="n">A</span><span class="o">+</span><span class="n">B</span><span class="o">*</span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">C</span><span class="o">*</span><span class="n">C</span><span class="w"> </span><span class="p" data-group-id="3453927687-2">]</span><span class="p">.</span></code></pre><h2 id="simplifications-with-list-comprehensions" class="section-heading">
│ │ │    <a href="#simplifications-with-list-comprehensions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simplifications With List Comprehensions</span>
│ │ │  </h2>
│ │ │  <p>As an example, list comprehensions can be used to simplify some of the functions
│ │ │ -in <code class="inline">lists.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="2564455422-1">(</span><span class="n">L</span><span class="p" data-group-id="2564455422-1">)</span><span class="w">   </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="2564455422-2">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">L1</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="2564455422-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="2564455422-3">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2564455422-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2564455422-4">[</span><span class="n">Fun</span><span class="p" data-group-id="2564455422-5">(</span><span class="n">X</span><span class="p" data-group-id="2564455422-5">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2564455422-4">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">filter</span><span class="p" data-group-id="2564455422-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="2564455422-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2564455422-7">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="2564455422-8">(</span><span class="n">X</span><span class="p" data-group-id="2564455422-8">)</span><span class="p" data-group-id="2564455422-7">]</span><span class="p">.</span></code></pre><h2 id="variable-bindings-in-list-comprehensions" class="section-heading">
│ │ │ +in <code class="inline">lists.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="1285292236-1">(</span><span class="n">L</span><span class="p" data-group-id="1285292236-1">)</span><span class="w">   </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="1285292236-2">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">L1</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L1</span><span class="p" data-group-id="1285292236-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="1285292236-3">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1285292236-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1285292236-4">[</span><span class="n">Fun</span><span class="p" data-group-id="1285292236-5">(</span><span class="n">X</span><span class="p" data-group-id="1285292236-5">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1285292236-4">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">filter</span><span class="p" data-group-id="1285292236-6">(</span><span class="n">Pred</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="1285292236-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1285292236-7">[</span><span class="n">X</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">Pred</span><span class="p" data-group-id="1285292236-8">(</span><span class="n">X</span><span class="p" data-group-id="1285292236-8">)</span><span class="p" data-group-id="1285292236-7">]</span><span class="p">.</span></code></pre><h2 id="variable-bindings-in-list-comprehensions" class="section-heading">
│ │ │    <a href="#variable-bindings-in-list-comprehensions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Variable Bindings in List Comprehensions</span>
│ │ │  </h2>
│ │ │  <p>The scope rules for variables that occur in list comprehensions are as follows:</p><ul><li>All variables that occur in a generator pattern are assumed to be &quot;fresh&quot;
│ │ │  variables.</li><li>Any variables that are defined before the list comprehension, and that are
│ │ │  used in filters, have the values they had before the list comprehension.</li><li>Variables cannot be exported from a list comprehension.</li></ul><p>As an example of these rules, suppose you want to write the function <code class="inline">select</code>,
│ │ │  which selects certain elements from a list of tuples. Suppose you write
│ │ │  <code class="inline">select(X, L) -&gt; [Y || {X, Y} &lt;- L].</code> with the intention of extracting all
│ │ │  tuples from <code class="inline">L</code>, where the first item is <code class="inline">X</code>.</p><p>Compiling this gives the following diagnostic:</p><pre><code class="text">./FileName.erl:Line: Warning: variable 'X' shadowed in generate</code></pre><p>This diagnostic warns that the variable <code class="inline">X</code> in the pattern is not the same as
│ │ │ -the variable <code class="inline">X</code> that occurs in the function head.</p><p>Evaluating <code class="inline">select</code> gives the following result:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="3744129879-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="3744129879-2">[</span><span class="p" data-group-id="3744129879-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3744129879-3">}</span><span class="p">,</span><span class="p" data-group-id="3744129879-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3744129879-4">}</span><span class="p">,</span><span class="p" data-group-id="3744129879-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3744129879-5">}</span><span class="p">,</span><span class="p" data-group-id="3744129879-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3744129879-6">}</span><span class="p" data-group-id="3744129879-2">]</span><span class="p" data-group-id="3744129879-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3744129879-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="3744129879-7">]</span></code></pre><p>This is not the wanted result. To achieve the desired effect, <code class="inline">select</code> must be
│ │ │ -written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="5824376415-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5824376415-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="5824376415-2">[</span><span class="n">Y</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="5824376415-3">{</span><span class="n">X1</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5824376415-3">}</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">X1</span><span class="p" data-group-id="5824376415-2">]</span><span class="p">.</span></code></pre><p>The generator now contains unbound variables and the test has been moved into
│ │ │ -the filter.</p><p>This now works as expected:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="2859741864-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="2859741864-2">[</span><span class="p" data-group-id="2859741864-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2859741864-3">}</span><span class="p">,</span><span class="p" data-group-id="2859741864-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2859741864-4">}</span><span class="p">,</span><span class="p" data-group-id="2859741864-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2859741864-5">}</span><span class="p">,</span><span class="p" data-group-id="2859741864-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="2859741864-6">}</span><span class="p" data-group-id="2859741864-2">]</span><span class="p" data-group-id="2859741864-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2859741864-7">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="2859741864-7">]</span></code></pre><p>Also note that a variable in a generator pattern will shadow a variable with the
│ │ │ -same name bound in a previous generator pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="1899513724-1">[</span><span class="p" data-group-id="1899513724-2">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p" data-group-id="1899513724-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1899513724-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1899513724-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="o">=</span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="1899513724-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1899513724-4">]</span><span class="p" data-group-id="1899513724-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1899513724-5">[</span><span class="p" data-group-id="1899513724-6">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1899513724-6">}</span><span class="p">,</span><span class="p" data-group-id="1899513724-7">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1899513724-7">}</span><span class="p">,</span><span class="p" data-group-id="1899513724-8">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1899513724-8">}</span><span class="p">,</span><span class="p" data-group-id="1899513724-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1899513724-9">}</span><span class="p">,</span><span class="p" data-group-id="1899513724-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1899513724-10">}</span><span class="p">,</span><span class="p" data-group-id="1899513724-11">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1899513724-11">}</span><span class="p">,</span><span class="p" data-group-id="1899513724-12">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1899513724-12">}</span><span class="p">,</span><span class="p" data-group-id="1899513724-13">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1899513724-13">}</span><span class="p">,</span><span class="p" data-group-id="1899513724-14">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1899513724-14">}</span><span class="p" data-group-id="1899513724-5">]</span></code></pre><p>A consequence of the rules for importing variables into a list comprehensions is
│ │ │ +the variable <code class="inline">X</code> that occurs in the function head.</p><p>Evaluating <code class="inline">select</code> gives the following result:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="7807180481-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="7807180481-2">[</span><span class="p" data-group-id="7807180481-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7807180481-3">}</span><span class="p">,</span><span class="p" data-group-id="7807180481-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7807180481-4">}</span><span class="p">,</span><span class="p" data-group-id="7807180481-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7807180481-5">}</span><span class="p">,</span><span class="p" data-group-id="7807180481-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7807180481-6">}</span><span class="p" data-group-id="7807180481-2">]</span><span class="p" data-group-id="7807180481-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7807180481-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7807180481-7">]</span></code></pre><p>This is not the wanted result. To achieve the desired effect, <code class="inline">select</code> must be
│ │ │ +written as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="5860131638-1">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">L</span><span class="p" data-group-id="5860131638-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="p" data-group-id="5860131638-2">[</span><span class="n">Y</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="p" data-group-id="5860131638-3">{</span><span class="n">X1</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5860131638-3">}</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">X1</span><span class="p" data-group-id="5860131638-2">]</span><span class="p">.</span></code></pre><p>The generator now contains unbound variables and the test has been moved into
│ │ │ +the filter.</p><p>This now works as expected:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">select</span><span class="p" data-group-id="5328695132-1">(</span><span class="ss">b</span><span class="p">,</span><span class="p" data-group-id="5328695132-2">[</span><span class="p" data-group-id="5328695132-3">{</span><span class="ss">a</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5328695132-3">}</span><span class="p">,</span><span class="p" data-group-id="5328695132-4">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5328695132-4">}</span><span class="p">,</span><span class="p" data-group-id="5328695132-5">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5328695132-5">}</span><span class="p">,</span><span class="p" data-group-id="5328695132-6">{</span><span class="ss">b</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="5328695132-6">}</span><span class="p" data-group-id="5328695132-2">]</span><span class="p" data-group-id="5328695132-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5328695132-7">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="5328695132-7">]</span></code></pre><p>Also note that a variable in a generator pattern will shadow a variable with the
│ │ │ +same name bound in a previous generator pattern. For example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="6802695102-1">[</span><span class="p" data-group-id="6802695102-2">{</span><span class="n">X</span><span class="p">,</span><span class="n">Y</span><span class="p" data-group-id="6802695102-2">}</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6802695102-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6802695102-3">]</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="o">=</span><span class="n">Y</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="p" data-group-id="6802695102-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6802695102-4">]</span><span class="p" data-group-id="6802695102-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6802695102-5">[</span><span class="p" data-group-id="6802695102-6">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="6802695102-6">}</span><span class="p">,</span><span class="p" data-group-id="6802695102-7">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6802695102-7">}</span><span class="p">,</span><span class="p" data-group-id="6802695102-8">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6802695102-8">}</span><span class="p">,</span><span class="p" data-group-id="6802695102-9">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="6802695102-9">}</span><span class="p">,</span><span class="p" data-group-id="6802695102-10">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6802695102-10">}</span><span class="p">,</span><span class="p" data-group-id="6802695102-11">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6802695102-11">}</span><span class="p">,</span><span class="p" data-group-id="6802695102-12">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="6802695102-12">}</span><span class="p">,</span><span class="p" data-group-id="6802695102-13">{</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6802695102-13">}</span><span class="p">,</span><span class="p" data-group-id="6802695102-14">{</span><span class="ss">c</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6802695102-14">}</span><span class="p" data-group-id="6802695102-5">]</span></code></pre><p>A consequence of the rules for importing variables into a list comprehensions is
│ │ │  that certain pattern matching operations must be moved into the filters and
│ │ │ -cannot be written directly in the generators.</p><p>To illustrate this, do <em>not</em> write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4273003309-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4273003309-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +cannot be written directly in the generators.</p><p>To illustrate this, do <em>not</em> write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="5168229949-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5168229949-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4273003309-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="4273003309-2">]</span><span class="w">
│ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Instead, write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="9122637849-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9122637849-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5168229949-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5168229949-2">]</span><span class="w">
│ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Instead, write as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="9420784821-1">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9420784821-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9122637849-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y1</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9122637849-2">]</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9420784821-2">[</span><span class="w"> </span><span class="n">Expression</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">PatternInvolving</span><span class="w"> </span><span class="n">Y1</span><span class="w">  </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">Expr</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Y1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="9420784821-2">]</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="funs.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/listhandling.html
│ │ │ @@ -120,105 +120,105 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating a List</span>
│ │ │  </h2>
│ │ │  <p>Lists can only be built starting from the end and attaching list elements at the
│ │ │  beginning. If you use the <code class="inline">++</code> operator as follows, a new list is created that
│ │ │  is a copy of the elements in <code class="inline">List1</code>, followed by <code class="inline">List2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">List1</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="n">List2</span></code></pre><p>Looking at how <a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#append/2"><code class="inline">lists:append/2</code></a> or <code class="inline">++</code> would be implemented in plain Erlang,
│ │ │ -clearly the first list is copied:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="9259551103-1">(</span><span class="p" data-group-id="9259551103-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9259551103-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="9259551103-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9259551103-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">append</span><span class="p" data-group-id="9259551103-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="9259551103-4">)</span><span class="p" data-group-id="9259551103-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">append</span><span class="p" data-group-id="9259551103-5">(</span><span class="p" data-group-id="9259551103-6">[</span><span class="p" data-group-id="9259551103-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="9259551103-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +clearly the first list is copied:</p><pre><code class="makeup erlang" translate="no"><span class="nf">append</span><span class="p" data-group-id="6789595067-1">(</span><span class="p" data-group-id="6789595067-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="6789595067-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6789595067-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6789595067-3">[</span><span class="n">H</span><span class="p">|</span><span class="nf">append</span><span class="p" data-group-id="6789595067-4">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6789595067-4">)</span><span class="p" data-group-id="6789595067-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">append</span><span class="p" data-group-id="6789595067-5">(</span><span class="p" data-group-id="6789595067-6">[</span><span class="p" data-group-id="6789595067-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Tail</span><span class="p" data-group-id="6789595067-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Tail</span><span class="p">.</span></code></pre><p>When recursing and building a list, it is important to ensure that you attach
│ │ │  the new elements to the beginning of the list. In this way, you will build <em>one</em>
│ │ │ -list, not hundreds or thousands of copies of the growing result list.</p><p>Let us first see how it is not to be done:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">bad_fib</span><span class="p" data-group-id="6555497939-1">(</span><span class="n">N</span><span class="p" data-group-id="6555497939-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">bad_fib</span><span class="p" data-group-id="6555497939-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6555497939-3">[</span><span class="p" data-group-id="6555497939-3">]</span><span class="p" data-group-id="6555497939-2">)</span><span class="p">.</span><span class="w">
│ │ │ +list, not hundreds or thousands of copies of the growing result list.</p><p>Let us first see how it is not to be done:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">bad_fib</span><span class="p" data-group-id="4143425555-1">(</span><span class="n">N</span><span class="p" data-group-id="4143425555-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">bad_fib</span><span class="p" data-group-id="4143425555-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4143425555-3">[</span><span class="p" data-group-id="4143425555-3">]</span><span class="p" data-group-id="4143425555-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">bad_fib</span><span class="p" data-group-id="6555497939-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="6555497939-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">bad_fib</span><span class="p" data-group-id="4143425555-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="4143425555-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Fibs</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">bad_fib</span><span class="p" data-group-id="6555497939-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="6555497939-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">bad_fib</span><span class="p" data-group-id="6555497939-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6555497939-7">[</span><span class="n">Current</span><span class="p" data-group-id="6555497939-7">]</span><span class="p" data-group-id="6555497939-6">)</span><span class="p">.</span></code></pre><p>Here more than one list is built. In each iteration step a new list is created
│ │ │ +</span><span class="nf">bad_fib</span><span class="p" data-group-id="4143425555-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="4143425555-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">bad_fib</span><span class="p" data-group-id="4143425555-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4143425555-7">[</span><span class="n">Current</span><span class="p" data-group-id="4143425555-7">]</span><span class="p" data-group-id="4143425555-6">)</span><span class="p">.</span></code></pre><p>Here more than one list is built. In each iteration step a new list is created
│ │ │  that is one element longer than the new previous list.</p><p>To avoid copying the result in each iteration, build the list in reverse order
│ │ │ -and reverse the list when you are done:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8846662505-1">(</span><span class="n">N</span><span class="p" data-group-id="8846662505-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8846662505-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8846662505-3">[</span><span class="p" data-group-id="8846662505-3">]</span><span class="p" data-group-id="8846662505-2">)</span><span class="p">.</span><span class="w">
│ │ │ +and reverse the list when you are done:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="2876962058-1">(</span><span class="n">N</span><span class="p" data-group-id="2876962058-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="2876962058-2">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2876962058-3">[</span><span class="p" data-group-id="2876962058-3">]</span><span class="p" data-group-id="2876962058-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8846662505-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="8846662505-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="8846662505-5">(</span><span class="n">Fibs</span><span class="p" data-group-id="8846662505-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8846662505-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="8846662505-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="8846662505-7">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8846662505-8">[</span><span class="n">Current</span><span class="p">|</span><span class="n">Fibs</span><span class="p" data-group-id="8846662505-8">]</span><span class="p" data-group-id="8846662505-7">)</span><span class="p">.</span></code></pre><h2 id="list-comprehensions" class="section-heading">
│ │ │ +</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="2876962058-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="2876962058-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="2876962058-5">(</span><span class="n">Fibs</span><span class="p" data-group-id="2876962058-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="2876962058-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Fibs</span><span class="p" data-group-id="2876962058-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">tail_recursive_fib</span><span class="p" data-group-id="2876962058-7">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Next</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2876962058-8">[</span><span class="n">Current</span><span class="p">|</span><span class="n">Fibs</span><span class="p" data-group-id="2876962058-8">]</span><span class="p" data-group-id="2876962058-7">)</span><span class="p">.</span></code></pre><h2 id="list-comprehensions" class="section-heading">
│ │ │    <a href="#list-comprehensions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">List Comprehensions</span>
│ │ │  </h2>
│ │ │ -<p>A list comprehension:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7377944212-1">[</span><span class="n">Expr</span><span class="p" data-group-id="7377944212-2">(</span><span class="n">E</span><span class="p" data-group-id="7377944212-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7377944212-1">]</span></code></pre><p>is basically translated to a local function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5756636567-1">(</span><span class="p" data-group-id="5756636567-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="5756636567-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="5756636567-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5756636567-3">[</span><span class="n">Expr</span><span class="p" data-group-id="5756636567-4">(</span><span class="n">E</span><span class="p" data-group-id="5756636567-4">)</span><span class="p">|</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5756636567-5">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="5756636567-5">)</span><span class="p" data-group-id="5756636567-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="5756636567-6">(</span><span class="p" data-group-id="5756636567-7">[</span><span class="p" data-group-id="5756636567-7">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="5756636567-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5756636567-8">[</span><span class="p" data-group-id="5756636567-8">]</span><span class="p">.</span></code></pre><p>If the result of the list comprehension will <em>obviously</em> not be used, a list
│ │ │ -will not be constructed. For example, in this code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0177773004-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="0177773004-2">(</span><span class="n">E</span><span class="p" data-group-id="0177773004-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="0177773004-1">]</span><span class="p">,</span><span class="w">
│ │ │ +<p>A list comprehension:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9795045036-1">[</span><span class="n">Expr</span><span class="p" data-group-id="9795045036-2">(</span><span class="n">E</span><span class="p" data-group-id="9795045036-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9795045036-1">]</span></code></pre><p>is basically translated to a local function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="2227023058-1">(</span><span class="p" data-group-id="2227023058-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="2227023058-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="2227023058-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2227023058-3">[</span><span class="n">Expr</span><span class="p" data-group-id="2227023058-4">(</span><span class="n">E</span><span class="p" data-group-id="2227023058-4">)</span><span class="p">|</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="2227023058-5">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="2227023058-5">)</span><span class="p" data-group-id="2227023058-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="2227023058-6">(</span><span class="p" data-group-id="2227023058-7">[</span><span class="p" data-group-id="2227023058-7">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="2227023058-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2227023058-8">[</span><span class="p" data-group-id="2227023058-8">]</span><span class="p">.</span></code></pre><p>If the result of the list comprehension will <em>obviously</em> not be used, a list
│ │ │ +will not be constructed. For example, in this code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7475737374-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="7475737374-2">(</span><span class="n">E</span><span class="p" data-group-id="7475737374-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="7475737374-1">]</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>or in this code:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="n">Var</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="1869638504-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="1869638504-2">(</span><span class="n">E</span><span class="p" data-group-id="1869638504-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1869638504-1">]</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="6451182559-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="6451182559-2">(</span><span class="n">E</span><span class="p" data-group-id="6451182559-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6451182559-1">]</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">some_function</span><span class="p" data-group-id="1869638504-3">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="1869638504-3">)</span><span class="p">,</span></code></pre><p>the value is not assigned to a variable, not passed to another function, and not
│ │ │ +</span><span class="nf">some_function</span><span class="p" data-group-id="6451182559-3">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="6451182559-3">)</span><span class="p">,</span></code></pre><p>the value is not assigned to a variable, not passed to another function, and not
│ │ │  returned. This means that there is no need to construct a list and the compiler
│ │ │ -will simplify the code for the list comprehension to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="7895402282-1">(</span><span class="p" data-group-id="7895402282-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="7895402282-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="7895402282-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Expr</span><span class="p" data-group-id="7895402282-3">(</span><span class="n">E</span><span class="p" data-group-id="7895402282-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="7895402282-4">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="7895402282-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="7895402282-5">(</span><span class="p" data-group-id="7895402282-6">[</span><span class="p" data-group-id="7895402282-6">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="7895402282-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="7895402282-7">[</span><span class="p" data-group-id="7895402282-7">]</span><span class="p">.</span></code></pre><p>The compiler also understands that assigning to <code class="inline">_</code> means that the value will
│ │ │ -not be used. Therefore, the code in the following example will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8675287680-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="8675287680-2">(</span><span class="n">E</span><span class="p" data-group-id="8675287680-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="8675287680-1">]</span><span class="p">,</span><span class="w">
│ │ │ +will simplify the code for the list comprehension to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="6492602573-1">(</span><span class="p" data-group-id="6492602573-2">[</span><span class="n">E</span><span class="p">|</span><span class="n">Tail</span><span class="p" data-group-id="6492602573-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="6492602573-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Expr</span><span class="p" data-group-id="6492602573-3">(</span><span class="n">E</span><span class="p" data-group-id="6492602573-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="6492602573-4">(</span><span class="n">Tail</span><span class="p">,</span><span class="w"> </span><span class="n">Expr</span><span class="p" data-group-id="6492602573-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">&#39;lc^0&#39;</span><span class="p" data-group-id="6492602573-5">(</span><span class="p" data-group-id="6492602573-6">[</span><span class="p" data-group-id="6492602573-6">]</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Expr</span><span class="p" data-group-id="6492602573-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="6492602573-7">[</span><span class="p" data-group-id="6492602573-7">]</span><span class="p">.</span></code></pre><p>The compiler also understands that assigning to <code class="inline">_</code> means that the value will
│ │ │ +not be used. Therefore, the code in the following example will also be optimized:</p><pre><code class="makeup erlang" translate="no"><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6147755072-1">[</span><span class="nc">io</span><span class="p">:</span><span class="nf">put_chars</span><span class="p" data-group-id="6147755072-2">(</span><span class="n">E</span><span class="p" data-group-id="6147755072-2">)</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">&lt;-</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="6147755072-1">]</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="p">.</span></code></pre><h2 id="deep-and-flat-lists" class="section-heading">
│ │ │    <a href="#deep-and-flat-lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Deep and Flat Lists</span>
│ │ │  </h2>
│ │ │  <p><a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#flatten/1"><code class="inline">lists:flatten/1</code></a> builds an entirely new list. It is therefore expensive, and
│ │ │  even <em>more</em> expensive than the <code class="inline">++</code> operator (which copies its left argument,
│ │ │  but not its right argument).</p><p>In the following situations it is unnecessary to call <a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#flatten/1"><code class="inline">lists:flatten/1</code></a>:</p><ul><li>When sending data to a port. Ports understand deep lists so there is no reason
│ │ │  to flatten the list before sending it to the port.</li><li>When calling BIFs that accept deep lists, such as
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#list_to_binary/1"><code class="inline">list_to_binary/1</code></a> or
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#iolist_to_binary/1"><code class="inline">iolist_to_binary/1</code></a>.</li><li>When you know that your list is only one level deep. Use <a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#append/1"><code class="inline">lists:append/1</code></a>
│ │ │ -instead.</li></ul><p><em>Examples:</em></p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="5802895082-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">DeepList</span><span class="p" data-group-id="5802895082-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="2163732969-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="2163732969-2">(</span><span class="n">DeepList</span><span class="p" data-group-id="2163732969-2">)</span><span class="p" data-group-id="2163732969-1">)</span></code></pre><p>A common way to send a zero-terminated string to a port is the following:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2337408484-1">[</span><span class="mi">0</span><span class="p" data-group-id="2337408484-1">]</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">port_command</span><span class="p" data-group-id="2337408484-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="2337408484-2">)</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0859796799-1">[</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0859796799-1">]</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nf">port_command</span><span class="p" data-group-id="0859796799-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="0859796799-2">)</span></code></pre><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">append</span><span class="p" data-group-id="6634670495-1">(</span><span class="p" data-group-id="6634670495-2">[</span><span class="p" data-group-id="6634670495-3">[</span><span class="mi">1</span><span class="p" data-group-id="6634670495-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6634670495-4">[</span><span class="mi">2</span><span class="p" data-group-id="6634670495-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6634670495-5">[</span><span class="mi">3</span><span class="p" data-group-id="6634670495-5">]</span><span class="p" data-group-id="6634670495-2">]</span><span class="p" data-group-id="6634670495-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6634670495-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6634670495-6">]</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="0780753782-1">(</span><span class="p" data-group-id="0780753782-2">[</span><span class="p" data-group-id="0780753782-3">[</span><span class="mi">1</span><span class="p" data-group-id="0780753782-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0780753782-4">[</span><span class="mi">2</span><span class="p" data-group-id="0780753782-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0780753782-5">[</span><span class="mi">3</span><span class="p" data-group-id="0780753782-5">]</span><span class="p" data-group-id="0780753782-2">]</span><span class="p" data-group-id="0780753782-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0780753782-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0780753782-6">]</span></code></pre><h2 id="recursive-list-functions" class="section-heading">
│ │ │ +instead.</li></ul><p><em>Examples:</em></p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="2722547225-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">DeepList</span><span class="p" data-group-id="2722547225-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">port_command</span><span class="p" data-group-id="7674538930-1">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="7674538930-2">(</span><span class="n">DeepList</span><span class="p" data-group-id="7674538930-2">)</span><span class="p" data-group-id="7674538930-1">)</span></code></pre><p>A common way to send a zero-terminated string to a port is the following:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">String</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="6283126400-1">[</span><span class="mi">0</span><span class="p" data-group-id="6283126400-1">]</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">port_command</span><span class="p" data-group-id="6283126400-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="6283126400-2">)</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TerminatedStr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0926462918-1">[</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0926462918-1">]</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">port_command</span><span class="p" data-group-id="0926462918-2">(</span><span class="n">Port</span><span class="p">,</span><span class="w"> </span><span class="n">TerminatedStr</span><span class="p" data-group-id="0926462918-2">)</span></code></pre><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">append</span><span class="p" data-group-id="2490410465-1">(</span><span class="p" data-group-id="2490410465-2">[</span><span class="p" data-group-id="2490410465-3">[</span><span class="mi">1</span><span class="p" data-group-id="2490410465-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2490410465-4">[</span><span class="mi">2</span><span class="p" data-group-id="2490410465-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2490410465-5">[</span><span class="mi">3</span><span class="p" data-group-id="2490410465-5">]</span><span class="p" data-group-id="2490410465-2">]</span><span class="p" data-group-id="2490410465-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2490410465-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="2490410465-6">]</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">flatten</span><span class="p" data-group-id="6983913256-1">(</span><span class="p" data-group-id="6983913256-2">[</span><span class="p" data-group-id="6983913256-3">[</span><span class="mi">1</span><span class="p" data-group-id="6983913256-3">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6983913256-4">[</span><span class="mi">2</span><span class="p" data-group-id="6983913256-4">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6983913256-5">[</span><span class="mi">3</span><span class="p" data-group-id="6983913256-5">]</span><span class="p" data-group-id="6983913256-2">]</span><span class="p" data-group-id="6983913256-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6983913256-6">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6983913256-6">]</span></code></pre><h2 id="recursive-list-functions" class="section-heading">
│ │ │    <a href="#recursive-list-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Recursive List Functions</span>
│ │ │  </h2>
│ │ │  <p>There are two basic ways to write a function that traverses a list and
│ │ │  produces a new list.</p><p>The first way is writing a <em>body-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ -</span><span class="nf">add_42_body</span><span class="p" data-group-id="3861732057-1">(</span><span class="p" data-group-id="3861732057-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="3861732057-2">]</span><span class="p" data-group-id="3861732057-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3861732057-3">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">add_42_body</span><span class="p" data-group-id="3861732057-4">(</span><span class="n">T</span><span class="p" data-group-id="3861732057-4">)</span><span class="p" data-group-id="3861732057-3">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">add_42_body</span><span class="p" data-group-id="3861732057-5">(</span><span class="p" data-group-id="3861732057-6">[</span><span class="p" data-group-id="3861732057-6">]</span><span class="p" data-group-id="3861732057-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3861732057-7">[</span><span class="p" data-group-id="3861732057-7">]</span><span class="p">.</span></code></pre><p>The second way is writing a <em>tail-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="1637850854-1">(</span><span class="n">List</span><span class="p" data-group-id="1637850854-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="1637850854-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1637850854-3">[</span><span class="p" data-group-id="1637850854-3">]</span><span class="p" data-group-id="1637850854-2">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="1637850854-4">(</span><span class="p" data-group-id="1637850854-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="1637850854-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1637850854-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="1637850854-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1637850854-7">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1637850854-7">]</span><span class="p" data-group-id="1637850854-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">add_42_tail</span><span class="p" data-group-id="1637850854-8">(</span><span class="p" data-group-id="1637850854-9">[</span><span class="p" data-group-id="1637850854-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="1637850854-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="1637850854-10">(</span><span class="n">Acc</span><span class="p" data-group-id="1637850854-10">)</span><span class="p">.</span></code></pre><p>In early version of Erlang the tail-recursive function would typically
│ │ │ +</span><span class="nf">add_42_body</span><span class="p" data-group-id="7597551266-1">(</span><span class="p" data-group-id="7597551266-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7597551266-2">]</span><span class="p" data-group-id="7597551266-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7597551266-3">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">add_42_body</span><span class="p" data-group-id="7597551266-4">(</span><span class="n">T</span><span class="p" data-group-id="7597551266-4">)</span><span class="p" data-group-id="7597551266-3">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">add_42_body</span><span class="p" data-group-id="7597551266-5">(</span><span class="p" data-group-id="7597551266-6">[</span><span class="p" data-group-id="7597551266-6">]</span><span class="p" data-group-id="7597551266-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7597551266-7">[</span><span class="p" data-group-id="7597551266-7">]</span><span class="p">.</span></code></pre><p>The second way is writing a <em>tail-recursive</em> function:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% Add 42 to each integer in the list.</span><span class="w">
│ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="0214791931-1">(</span><span class="n">List</span><span class="p" data-group-id="0214791931-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="0214791931-2">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0214791931-3">[</span><span class="p" data-group-id="0214791931-3">]</span><span class="p" data-group-id="0214791931-2">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="0214791931-4">(</span><span class="p" data-group-id="0214791931-5">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="0214791931-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0214791931-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">add_42_tail</span><span class="p" data-group-id="0214791931-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0214791931-7">[</span><span class="n">H</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0214791931-7">]</span><span class="p" data-group-id="0214791931-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">add_42_tail</span><span class="p" data-group-id="0214791931-8">(</span><span class="p" data-group-id="0214791931-9">[</span><span class="p" data-group-id="0214791931-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="0214791931-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="0214791931-10">(</span><span class="n">Acc</span><span class="p" data-group-id="0214791931-10">)</span><span class="p">.</span></code></pre><p>In early version of Erlang the tail-recursive function would typically
│ │ │  be more efficient. In modern versions of Erlang, there is usually not
│ │ │  much difference in performance between a body-recursive list function and
│ │ │  tail-recursive function that reverses the list at the end. Therefore,
│ │ │  concentrate on writing beautiful code and forget about the performance
│ │ │  of your list functions. In the time-critical parts of your code,
│ │ │  <em>measure</em> before rewriting your code.</p><p>For a thorough discussion about tail and body recursion, see
│ │ │  <a href="http://ferd.ca/erlang-s-tail-recursion-is-not-a-silver-bullet.html">Erlang's Tail Recursion is Not a Silver Bullet</a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>This section is about list functions that <em>construct</em> lists. A tail-recursive
│ │ │  function that does not construct a list runs in constant space, while the
│ │ │  corresponding body-recursive function uses stack space proportional to the
│ │ │  length of the list.</p></section><p>For example, a function that sums a list of integers, is <em>not</em> to be written as
│ │ │ -follows:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">recursive_sum</span><span class="p" data-group-id="7070089221-1">(</span><span class="p" data-group-id="7070089221-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="7070089221-2">]</span><span class="p" data-group-id="7070089221-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">H</span><span class="o">+</span><span class="nf">recursive_sum</span><span class="p" data-group-id="7070089221-3">(</span><span class="n">T</span><span class="p" data-group-id="7070089221-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">recursive_sum</span><span class="p" data-group-id="7070089221-4">(</span><span class="p" data-group-id="7070089221-5">[</span><span class="p" data-group-id="7070089221-5">]</span><span class="p" data-group-id="7070089221-4">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">sum</span><span class="p" data-group-id="5587662707-1">(</span><span class="n">L</span><span class="p" data-group-id="5587662707-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="5587662707-2">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5587662707-2">)</span><span class="p">.</span><span class="w">
│ │ │ +follows:</p><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">recursive_sum</span><span class="p" data-group-id="9928279714-1">(</span><span class="p" data-group-id="9928279714-2">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="9928279714-2">]</span><span class="p" data-group-id="9928279714-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">H</span><span class="o">+</span><span class="nf">recursive_sum</span><span class="p" data-group-id="9928279714-3">(</span><span class="n">T</span><span class="p" data-group-id="9928279714-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">recursive_sum</span><span class="p" data-group-id="9928279714-4">(</span><span class="p" data-group-id="9928279714-5">[</span><span class="p" data-group-id="9928279714-5">]</span><span class="p" data-group-id="9928279714-4">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">.</span></code></pre><p>Instead:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nf">sum</span><span class="p" data-group-id="8528923480-1">(</span><span class="n">L</span><span class="p" data-group-id="8528923480-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="8528923480-2">(</span><span class="n">L</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8528923480-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">sum</span><span class="p" data-group-id="5587662707-3">(</span><span class="p" data-group-id="5587662707-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="5587662707-4">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="5587662707-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="5587662707-5">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">H</span><span class="p" data-group-id="5587662707-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">sum</span><span class="p" data-group-id="5587662707-6">(</span><span class="p" data-group-id="5587662707-7">[</span><span class="p" data-group-id="5587662707-7">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="5587662707-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Sum</span><span class="p">.</span></code></pre>
│ │ │ +</span><span class="nf">sum</span><span class="p" data-group-id="8528923480-3">(</span><span class="p" data-group-id="8528923480-4">[</span><span class="n">H</span><span class="p">|</span><span class="n">T</span><span class="p" data-group-id="8528923480-4">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="8528923480-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">sum</span><span class="p" data-group-id="8528923480-5">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">H</span><span class="p" data-group-id="8528923480-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">sum</span><span class="p" data-group-id="8528923480-6">(</span><span class="p" data-group-id="8528923480-7">[</span><span class="p" data-group-id="8528923480-7">]</span><span class="p">,</span><span class="w"> </span><span class="n">Sum</span><span class="p" data-group-id="8528923480-6">)</span><span class="w">    </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Sum</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="maps.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/macros.html
│ │ │ @@ -117,56 +117,56 @@
│ │ │  
│ │ │  <h2 id="file-inclusion" class="section-heading">
│ │ │    <a href="#file-inclusion" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">File Inclusion</span>
│ │ │  </h2>
│ │ │ -<p>A file can be included as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="3762441424-1">(</span><span class="n">File</span><span class="p" data-group-id="3762441424-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="3762441424-2">(</span><span class="n">File</span><span class="p" data-group-id="3762441424-2">)</span><span class="p">.</span></code></pre><p><code class="inline">File</code>, a string, is to point out a file. The contents of this file are included
│ │ │ +<p>A file can be included as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1918467217-1">(</span><span class="n">File</span><span class="p" data-group-id="1918467217-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="1918467217-2">(</span><span class="n">File</span><span class="p" data-group-id="1918467217-2">)</span><span class="p">.</span></code></pre><p><code class="inline">File</code>, a string, is to point out a file. The contents of this file are included
│ │ │  as is, at the position of the directive.</p><p>Include files are typically used for record and macro definitions that are
│ │ │  shared by several modules. It is recommended to use the file name extension
│ │ │  <code class="inline">.hrl</code> for include files.</p><p><code class="inline">File</code> can start with a path component <code class="inline">$VAR</code>, for some string <code class="inline">VAR</code>. If that is
│ │ │  the case, the value of the environment variable <code class="inline">VAR</code> as returned by
│ │ │  <code class="inline">os:getenv(VAR)</code> is substituted for <code class="inline">$VAR</code>. If <code class="inline">os:getenv(VAR)</code> returns <code class="inline">false</code>,
│ │ │  <code class="inline">$VAR</code> is left as is.</p><p>If the filename <code class="inline">File</code> is absolute (possibly after variable substitution), the
│ │ │  include file with that name is included. Otherwise, the specified file is
│ │ │  searched for in the following directories, and in this order:</p><ol><li>The current working directory</li><li>The directory where the module is being compiled</li><li>The directories given by the <code class="inline">include</code> option</li></ol><p>For details, see <a href="../../erts-15.2.7.8/doc/html/erlc_cmd.html">erlc</a> in ERTS and
│ │ │ -<a href="../../lib/compiler-8.6.1.4/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2563295459-1">(</span><span class="s">&quot;my_records.hrl&quot;</span><span class="p" data-group-id="2563295459-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2563295459-2">(</span><span class="s">&quot;incdir/my_records.hrl&quot;</span><span class="p" data-group-id="2563295459-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2563295459-3">(</span><span class="s">&quot;/home/user/proj/my_records.hrl&quot;</span><span class="p" data-group-id="2563295459-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2563295459-4">(</span><span class="s">&quot;$PROJ_ROOT/my_records.hrl&quot;</span><span class="p" data-group-id="2563295459-4">)</span><span class="p">.</span></code></pre><p><code class="inline">include_lib</code> is similar to <code class="inline">include</code>, but is not to point out an absolute file.
│ │ │ +<a href="../../lib/compiler-8.6.1.4/doc/html/compile.html"><code class="inline">compile</code></a> in Compiler.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5365514236-1">(</span><span class="s">&quot;my_records.hrl&quot;</span><span class="p" data-group-id="5365514236-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5365514236-2">(</span><span class="s">&quot;incdir/my_records.hrl&quot;</span><span class="p" data-group-id="5365514236-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5365514236-3">(</span><span class="s">&quot;/home/user/proj/my_records.hrl&quot;</span><span class="p" data-group-id="5365514236-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5365514236-4">(</span><span class="s">&quot;$PROJ_ROOT/my_records.hrl&quot;</span><span class="p" data-group-id="5365514236-4">)</span><span class="p">.</span></code></pre><p><code class="inline">include_lib</code> is similar to <code class="inline">include</code>, but is not to point out an absolute file.
│ │ │  Instead, the first path component (possibly after variable substitution) is
│ │ │ -assumed to be the name of an application.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="0434266151-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="0434266151-1">)</span><span class="p">.</span></code></pre><p>The code server uses <code class="inline">code:lib_dir(kernel)</code> to find the directory of the current
│ │ │ +assumed to be the name of an application.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include_lib</span><span class="p" data-group-id="5148518945-1">(</span><span class="s">&quot;kernel/include/file.hrl&quot;</span><span class="p" data-group-id="5148518945-1">)</span><span class="p">.</span></code></pre><p>The code server uses <code class="inline">code:lib_dir(kernel)</code> to find the directory of the current
│ │ │  (latest) version of Kernel, and then the subdirectory <code class="inline">include</code> is searched for
│ │ │  the file <code class="inline">file.hrl</code>.</p><h2 id="defining-and-using-macros" class="section-heading">
│ │ │    <a href="#defining-and-using-macros" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Defining and Using Macros</span>
│ │ │  </h2>
│ │ │ -<p>A macro is defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0012410577-1">(</span><span class="n">Const</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="0012410577-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0012410577-2">(</span><span class="n">Func</span><span class="p" data-group-id="0012410577-3">(</span><span class="n">Var1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">VarN</span><span class="p" data-group-id="0012410577-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="0012410577-2">)</span><span class="p">.</span></code></pre><p>A macro definition can be placed anywhere among the attributes and function
│ │ │ +<p>A macro is defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2602879318-1">(</span><span class="n">Const</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="2602879318-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2602879318-2">(</span><span class="n">Func</span><span class="p" data-group-id="2602879318-3">(</span><span class="n">Var1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">VarN</span><span class="p" data-group-id="2602879318-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="2602879318-2">)</span><span class="p">.</span></code></pre><p>A macro definition can be placed anywhere among the attributes and function
│ │ │  declarations of a module, but the definition must come before any usage of the
│ │ │  macro.</p><p>If a macro is used in several modules, it is recommended that the macro
│ │ │  definition is placed in an include file.</p><p>A macro is used as follows:</p><pre><code class="text">?Const
│ │ │  ?Func(Arg1,...,ArgN)</code></pre><p>Macros are expanded during compilation. A simple macro <code class="inline">?Const</code> is replaced with
│ │ │ -<code class="inline">Replacement</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3502272005-1">(</span><span class="n">TIMEOUT</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="3502272005-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">Replacement</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4363699895-1">(</span><span class="n">TIMEOUT</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="4363699895-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">call</span><span class="p" data-group-id="3502272005-2">(</span><span class="n">Request</span><span class="p" data-group-id="3502272005-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3502272005-3">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">TIMEOUT</span><span class="p" data-group-id="3502272005-3">)</span><span class="p">.</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">call</span><span class="p" data-group-id="1354754682-1">(</span><span class="n">Request</span><span class="p" data-group-id="1354754682-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="1354754682-2">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="1354754682-2">)</span><span class="p">.</span></code></pre><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> is replaced with <code class="inline">Replacement</code>, where all
│ │ │ +</span><span class="nf">call</span><span class="p" data-group-id="4363699895-2">(</span><span class="n">Request</span><span class="p" data-group-id="4363699895-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4363699895-3">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">TIMEOUT</span><span class="p" data-group-id="4363699895-3">)</span><span class="p">.</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">call</span><span class="p" data-group-id="0029953882-1">(</span><span class="n">Request</span><span class="p" data-group-id="0029953882-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="0029953882-2">(</span><span class="ss">refserver</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="mi">200</span><span class="p" data-group-id="0029953882-2">)</span><span class="p">.</span></code></pre><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> is replaced with <code class="inline">Replacement</code>, where all
│ │ │  occurrences of a variable <code class="inline">Var</code> from the macro definition are replaced with the
│ │ │ -corresponding argument <code class="inline">Arg</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8112380296-1">(</span><span class="n">MACRO1</span><span class="p" data-group-id="8112380296-2">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8112380296-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8112380296-3">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8112380296-3">}</span><span class="p" data-group-id="8112380296-1">)</span><span class="p">.</span><span class="w">
│ │ │ +corresponding argument <code class="inline">Arg</code>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3372062666-1">(</span><span class="n">MACRO1</span><span class="p" data-group-id="3372062666-2">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3372062666-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3372062666-3">{</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3372062666-3">}</span><span class="p" data-group-id="3372062666-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="8112380296-4">(</span><span class="n">X</span><span class="p" data-group-id="8112380296-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="8112380296-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="8112380296-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="8112380296-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="p" data-group-id="8112380296-6">)</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="6360818195-1">(</span><span class="n">X</span><span class="p" data-group-id="6360818195-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6360818195-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6360818195-2">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6360818195-3">{</span><span class="ss">a</span><span class="p">,</span><span class="n">X</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">123</span><span class="p" data-group-id="6360818195-3">}</span><span class="p">.</span></code></pre><p>It is good programming practice, but not mandatory, to ensure that a macro
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="3372062666-4">(</span><span class="n">X</span><span class="p" data-group-id="3372062666-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="3372062666-5">(</span><span class="ss">a</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="p" data-group-id="3372062666-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">MACRO1</span><span class="p" data-group-id="3372062666-6">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="mi">123</span><span class="p" data-group-id="3372062666-6">)</span></code></pre><p>This is expanded to:</p><pre><code class="makeup erlang" translate="no"><span class="nf">bar</span><span class="p" data-group-id="2440261627-1">(</span><span class="n">X</span><span class="p" data-group-id="2440261627-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2440261627-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="2440261627-2">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2440261627-3">{</span><span class="ss">a</span><span class="p">,</span><span class="n">X</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="mi">123</span><span class="p" data-group-id="2440261627-3">}</span><span class="p">.</span></code></pre><p>It is good programming practice, but not mandatory, to ensure that a macro
│ │ │  definition is a valid Erlang syntactic form.</p><p>To view the result of macro expansion, a module can be compiled with the <code class="inline">'P'</code>
│ │ │  option. <code class="inline">compile:file(File, ['P'])</code>. This produces a listing of the parsed code
│ │ │  after preprocessing and parse transforms, in the file <code class="inline">File.P</code>.</p><h2 id="predefined-macros" class="section-heading">
│ │ │    <a href="#predefined-macros" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Predefined Macros</span>
│ │ │ @@ -185,29 +185,29 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Macros Overloading</span>
│ │ │  </h2>
│ │ │  <p>It is possible to overload macros, except for predefined macros. An overloaded
│ │ │  macro has more than one definition, each with a different number of arguments.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Support for overloading of macros was added in Erlang 5.7.5/OTP R13B04.</p></section><p>A macro <code class="inline">?Func(Arg1,...,ArgN)</code> with a (possibly empty) list of arguments results
│ │ │  in an error message if there is at least one definition of <code class="inline">Func</code> with
│ │ │ -arguments, but none with N arguments.</p><p>Assuming these definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6229160504-1">(</span><span class="n">F0</span><span class="p" data-group-id="6229160504-2">(</span><span class="p" data-group-id="6229160504-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="6229160504-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6229160504-3">(</span><span class="n">F1</span><span class="p" data-group-id="6229160504-4">(</span><span class="n">A</span><span class="p" data-group-id="6229160504-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="6229160504-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6229160504-5">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="nc">m</span><span class="p">:</span><span class="ss">f</span><span class="p" data-group-id="6229160504-5">)</span><span class="p">.</span></code></pre><p>the following does not work:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f0</span><span class="p" data-group-id="0884322964-1">(</span><span class="p" data-group-id="0884322964-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +arguments, but none with N arguments.</p><p>Assuming these definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1990819579-1">(</span><span class="n">F0</span><span class="p" data-group-id="1990819579-2">(</span><span class="p" data-group-id="1990819579-2">)</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="p" data-group-id="1990819579-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1990819579-3">(</span><span class="n">F1</span><span class="p" data-group-id="1990819579-4">(</span><span class="n">A</span><span class="p" data-group-id="1990819579-4">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="1990819579-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1990819579-5">(</span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="nc">m</span><span class="p">:</span><span class="ss">f</span><span class="p" data-group-id="1990819579-5">)</span><span class="p">.</span></code></pre><p>the following does not work:</p><pre><code class="makeup erlang" translate="no"><span class="nf">f0</span><span class="p" data-group-id="6732708969-1">(</span><span class="p" data-group-id="6732708969-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="o">?</span><span class="n">F0</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, an empty list of arguments expected.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">f1</span><span class="p" data-group-id="0884322964-2">(</span><span class="n">A</span><span class="p" data-group-id="0884322964-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">F1</span><span class="p" data-group-id="0884322964-3">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="0884322964-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, exactly one argument expected.</span></code></pre><p>On the other hand,</p><pre><code class="text">f() -&gt;
│ │ │ -    ?C().</code></pre><p>is expanded to</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="4795446989-1">(</span><span class="p" data-group-id="4795446989-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">m</span><span class="p">:</span><span class="nf">f</span><span class="p" data-group-id="4795446989-2">(</span><span class="p" data-group-id="4795446989-2">)</span><span class="p">.</span></code></pre><h2 id="removing-a-macro-definition" class="section-heading">
│ │ │ +</span><span class="nf">f1</span><span class="p" data-group-id="6732708969-2">(</span><span class="n">A</span><span class="p" data-group-id="6732708969-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">F1</span><span class="p" data-group-id="6732708969-3">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="6732708969-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% No, exactly one argument expected.</span></code></pre><p>On the other hand,</p><pre><code class="text">f() -&gt;
│ │ │ +    ?C().</code></pre><p>is expanded to</p><pre><code class="makeup erlang" translate="no"><span class="nf">f</span><span class="p" data-group-id="8285016337-1">(</span><span class="p" data-group-id="8285016337-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">m</span><span class="p">:</span><span class="nf">f</span><span class="p" data-group-id="8285016337-2">(</span><span class="p" data-group-id="8285016337-2">)</span><span class="p">.</span></code></pre><h2 id="removing-a-macro-definition" class="section-heading">
│ │ │    <a href="#removing-a-macro-definition" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Removing a macro definition</span>
│ │ │  </h2>
│ │ │ -<p>A definition of macro can be removed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">undef</span><span class="p" data-group-id="9114340716-1">(</span><span class="n">Macro</span><span class="p" data-group-id="9114340716-1">)</span><span class="p">.</span></code></pre><h2 id="conditional-compilation" class="section-heading">
│ │ │ +<p>A definition of macro can be removed as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">undef</span><span class="p" data-group-id="8001086937-1">(</span><span class="n">Macro</span><span class="p" data-group-id="8001086937-1">)</span><span class="p">.</span></code></pre><h2 id="conditional-compilation" class="section-heading">
│ │ │    <a href="#conditional-compilation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Conditional Compilation</span>
│ │ │  </h2>
│ │ │  <p>The following macro directives support conditional compilation:</p><ul><li><p><strong><code class="inline">-ifdef(Macro).</code></strong> - Evaluate the following lines only if <code class="inline">Macro</code> is
│ │ │  defined.</p></li><li><p><strong><code class="inline">-ifndef(Macro).</code></strong> - Evaluate the following lines only if <code class="inline">Macro</code> is not
│ │ │ @@ -219,43 +219,43 @@
│ │ │  true, and the <code class="inline">Condition</code> evaluates to true, the lines following the <code class="inline">elif</code>
│ │ │  are evaluated instead.</p></li><li><p><strong><code class="inline">-endif.</code></strong> - Specifies the end of a series of control flow directives.</p></li></ul><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Macro directives cannot be used inside functions.</p></section><p>Syntactically, the <code class="inline">Condition</code> in <code class="inline">if</code> and <code class="inline">elif</code> must be a
│ │ │  <a href="expressions.html#guard-expressions">guard expression</a>. Other constructs (such as
│ │ │  a <code class="inline">case</code> expression) result in a compilation error.</p><p>As opposed to the standard guard expressions, an expression in an <code class="inline">if</code> and
│ │ │  <code class="inline">elif</code> also supports calling the psuedo-function <code class="inline">defined(Name)</code>, which tests
│ │ │  whether the <code class="inline">Name</code> argument is the name of a previously defined macro.
│ │ │  <code class="inline">defined(Name)</code> evaluates to <code class="inline">true</code> if the macro is defined and <code class="inline">false</code>
│ │ │ -otherwise. An attempt to call other functions results in a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6097665146-1">(</span><span class="ss">m</span><span class="p" data-group-id="6097665146-1">)</span><span class="p">.</span><span class="w">
│ │ │ +otherwise. An attempt to call other functions results in a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3593980361-1">(</span><span class="ss">m</span><span class="p" data-group-id="3593980361-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="6097665146-2">(</span><span class="ss">debug</span><span class="p" data-group-id="6097665146-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6097665146-3">(</span><span class="n">LOG</span><span class="p" data-group-id="6097665146-4">(</span><span class="n">X</span><span class="p" data-group-id="6097665146-4">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6097665146-5">(</span><span class="s">&quot;{</span><span class="si">~p</span><span class="s">,</span><span class="si">~p</span><span class="s">}: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6097665146-6">[</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="o">?</span><span class="n">LINE</span><span class="p">,</span><span class="n">X</span><span class="p" data-group-id="6097665146-6">]</span><span class="p" data-group-id="6097665146-5">)</span><span class="p" data-group-id="6097665146-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="3593980361-2">(</span><span class="ss">debug</span><span class="p" data-group-id="3593980361-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3593980361-3">(</span><span class="n">LOG</span><span class="p" data-group-id="3593980361-4">(</span><span class="n">X</span><span class="p" data-group-id="3593980361-4">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3593980361-5">(</span><span class="s">&quot;{</span><span class="si">~p</span><span class="s">,</span><span class="si">~p</span><span class="s">}: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3593980361-6">[</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="o">?</span><span class="n">LINE</span><span class="p">,</span><span class="n">X</span><span class="p" data-group-id="3593980361-6">]</span><span class="p" data-group-id="3593980361-5">)</span><span class="p" data-group-id="3593980361-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6097665146-7">(</span><span class="n">LOG</span><span class="p" data-group-id="6097665146-8">(</span><span class="n">X</span><span class="p" data-group-id="6097665146-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6097665146-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3593980361-7">(</span><span class="n">LOG</span><span class="p" data-group-id="3593980361-8">(</span><span class="n">X</span><span class="p" data-group-id="3593980361-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="3593980361-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>When trace output is desired, <code class="inline">debug</code> is to be defined when the module <code class="inline">m</code> is
│ │ │  compiled:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erlc -Ddebug m.erl</span><span class="w">
│ │ │  
│ │ │  </span><span class="ow">or</span><span class="w">
│ │ │  
│ │ │ -</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="4161358811-1">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161358811-2">{</span><span class="ss">d</span><span class="p">,</span><span class="w"> </span><span class="ss">debug</span><span class="p" data-group-id="4161358811-2">}</span><span class="p" data-group-id="4161358811-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4161358811-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">m</span><span class="p" data-group-id="4161358811-3">}</span></code></pre><p><code class="inline">?LOG(Arg)</code> is then expanded to a call to <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> and provide the user
│ │ │ -with some simple trace output.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1900938148-1">(</span><span class="ss">m</span><span class="p" data-group-id="1900938148-1">)</span><span class="w">
│ │ │ +</span><span class="mi">1</span><span class="o">&gt;</span><span class="w"> </span><span class="nf">c</span><span class="p" data-group-id="2365173205-1">(</span><span class="ss">m</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2365173205-2">{</span><span class="ss">d</span><span class="p">,</span><span class="w"> </span><span class="ss">debug</span><span class="p" data-group-id="2365173205-2">}</span><span class="p" data-group-id="2365173205-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2365173205-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">m</span><span class="p" data-group-id="2365173205-3">}</span></code></pre><p><code class="inline">?LOG(Arg)</code> is then expanded to a call to <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> and provide the user
│ │ │ +with some simple trace output.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8981541437-1">(</span><span class="ss">m</span><span class="p" data-group-id="8981541437-1">)</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="1900938148-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">25</span><span class="p" data-group-id="1900938148-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="8981541437-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">25</span><span class="p" data-group-id="8981541437-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Code that will work in OTP 25 or higher</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">elif</span><span class="p" data-group-id="1900938148-3">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="p" data-group-id="1900938148-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">elif</span><span class="p" data-group-id="8981541437-3">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="p" data-group-id="8981541437-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Code that will work in OTP 26 or higher</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Code that will work in OTP 24 or lower.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This code uses the <code class="inline">OTP_RELEASE</code> macro to conditionally select code depending on
│ │ │ -release.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1875982409-1">(</span><span class="ss">m</span><span class="p" data-group-id="1875982409-1">)</span><span class="w">
│ │ │ +release.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2301889926-1">(</span><span class="ss">m</span><span class="p" data-group-id="2301889926-1">)</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="1875982409-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">defined</span><span class="p" data-group-id="1875982409-3">(</span><span class="ss">debug</span><span class="p" data-group-id="1875982409-3">)</span><span class="p" data-group-id="1875982409-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">if</span><span class="p" data-group-id="2301889926-2">(</span><span class="o">?</span><span class="n">OTP_RELEASE</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mi">26</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">defined</span><span class="p" data-group-id="2301889926-3">(</span><span class="ss">debug</span><span class="p" data-group-id="2301889926-3">)</span><span class="p" data-group-id="2301889926-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Debugging code that requires OTP 26 or later.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Non-debug code that works in any release.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>This code uses the <code class="inline">OTP_RELEASE</code> macro and <code class="inline">defined(debug)</code> to compile debug
│ │ │  code only for OTP 26 or later.</p><h2 id="the-feature-directive" class="section-heading">
│ │ │    <a href="#the-feature-directive" class="hover-link">
│ │ │ @@ -270,44 +270,44 @@
│ │ │  used. In practice this means it should appear before any <code class="inline">-export(..)</code> or record
│ │ │  definitions.</p><h2 id="error-and-warning-directives" class="section-heading">
│ │ │    <a href="#error-and-warning-directives" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">-error() and -warning() directives</span>
│ │ │  </h2>
│ │ │ -<p>The directive <code class="inline">-error(Term)</code> causes a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3417894104-1">(</span><span class="ss">t</span><span class="p" data-group-id="3417894104-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3417894104-2">(</span><span class="p" data-group-id="3417894104-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3417894104-3">]</span><span class="p" data-group-id="3417894104-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>The directive <code class="inline">-error(Term)</code> causes a compilation error.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2774607336-1">(</span><span class="ss">t</span><span class="p" data-group-id="2774607336-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2774607336-2">(</span><span class="p" data-group-id="2774607336-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2774607336-3">]</span><span class="p" data-group-id="2774607336-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="3417894104-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="3417894104-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="3417894104-5">(</span><span class="p" data-group-id="3417894104-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">ifdef</span><span class="p" data-group-id="2774607336-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="2774607336-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="2774607336-5">(</span><span class="p" data-group-id="2774607336-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">else</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">error</span><span class="p" data-group-id="3417894104-6">(</span><span class="s">&quot;Macro VERSION must be defined.&quot;</span><span class="p" data-group-id="3417894104-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="3417894104-7">(</span><span class="p" data-group-id="3417894104-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">error</span><span class="p" data-group-id="2774607336-6">(</span><span class="s">&quot;Macro VERSION must be defined.&quot;</span><span class="p" data-group-id="2774607336-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="2774607336-7">(</span><span class="p" data-group-id="2774607336-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span></code></pre><p>The error message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ -t.erl:7: -error(&quot;Macro VERSION must be defined.&quot;).</code></pre><p>The directive <code class="inline">-warning(Term)</code> causes a compilation warning.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9003832082-1">(</span><span class="ss">t</span><span class="p" data-group-id="9003832082-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9003832082-2">(</span><span class="p" data-group-id="9003832082-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9003832082-3">]</span><span class="p" data-group-id="9003832082-2">)</span><span class="p">.</span><span class="w">
│ │ │ +t.erl:7: -error(&quot;Macro VERSION must be defined.&quot;).</code></pre><p>The directive <code class="inline">-warning(Term)</code> causes a compilation warning.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9605841413-1">(</span><span class="ss">t</span><span class="p" data-group-id="9605841413-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9605841413-2">(</span><span class="p" data-group-id="9605841413-3">[</span><span class="ss">version</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9605841413-3">]</span><span class="p" data-group-id="9605841413-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">ifndef</span><span class="p" data-group-id="9003832082-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="9003832082-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">warning</span><span class="p" data-group-id="9003832082-5">(</span><span class="s">&quot;Macro VERSION not defined -- using default version.&quot;</span><span class="p" data-group-id="9003832082-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9003832082-6">(</span><span class="n">VERSION</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;0&quot;</span><span class="p" data-group-id="9003832082-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">ifndef</span><span class="p" data-group-id="9605841413-4">(</span><span class="n">VERSION</span><span class="p" data-group-id="9605841413-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">warning</span><span class="p" data-group-id="9605841413-5">(</span><span class="s">&quot;Macro VERSION not defined -- using default version.&quot;</span><span class="p" data-group-id="9605841413-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9605841413-6">(</span><span class="n">VERSION</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;0&quot;</span><span class="p" data-group-id="9605841413-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">endif</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">version</span><span class="p" data-group-id="9003832082-7">(</span><span class="p" data-group-id="9003832082-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span></code></pre><p>The warning message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │ +</span><span class="nf">version</span><span class="p" data-group-id="9605841413-7">(</span><span class="p" data-group-id="9605841413-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VERSION</span><span class="p">.</span></code></pre><p>The warning message will look like this:</p><pre><code class="text">% erlc t.erl
│ │ │  t.erl:5: Warning: -warning(&quot;Macro VERSION not defined -- using default version.&quot;).</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>The <code class="inline">-error()</code> and <code class="inline">-warning()</code> directives were added in Erlang/OTP 19.</p></section><h2 id="stringifying-macro-arguments" class="section-heading">
│ │ │    <a href="#stringifying-macro-arguments" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Stringifying Macro Arguments</span>
│ │ │  </h2>
│ │ │  <p>The construction <code class="inline">??Arg</code>, where <code class="inline">Arg</code> is a macro argument, is expanded to a
│ │ │  string containing the tokens of the argument. This is similar to the <code class="inline">#arg</code>
│ │ │ -stringifying construction in C.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6070286926-1">(</span><span class="n">TESTCALL</span><span class="p" data-group-id="6070286926-2">(</span><span class="n">Call</span><span class="p" data-group-id="6070286926-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6070286926-3">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6070286926-4">[</span><span class="o">?</span><span class="o">?</span><span class="n">Call</span><span class="p">,</span><span class="w"> </span><span class="n">Call</span><span class="p" data-group-id="6070286926-4">]</span><span class="p" data-group-id="6070286926-3">)</span><span class="p" data-group-id="6070286926-1">)</span><span class="p">.</span><span class="w">
│ │ │ +stringifying construction in C.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2078865209-1">(</span><span class="n">TESTCALL</span><span class="p" data-group-id="2078865209-2">(</span><span class="n">Call</span><span class="p" data-group-id="2078865209-2">)</span><span class="p">,</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2078865209-3">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2078865209-4">[</span><span class="o">?</span><span class="o">?</span><span class="n">Call</span><span class="p">,</span><span class="w"> </span><span class="n">Call</span><span class="p" data-group-id="2078865209-4">]</span><span class="p" data-group-id="2078865209-3">)</span><span class="p" data-group-id="2078865209-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="6070286926-5">(</span><span class="nf">myfunction</span><span class="p" data-group-id="6070286926-6">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6070286926-6">)</span><span class="p" data-group-id="6070286926-5">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="6070286926-7">(</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="6070286926-8">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6070286926-8">)</span><span class="p" data-group-id="6070286926-7">)</span><span class="p">.</span></code></pre><p>results in</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3457990031-1">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3457990031-2">[</span><span class="s">&quot;myfunction ( 1 , 2 )&quot;</span><span class="p">,</span><span class="nf">myfunction</span><span class="p" data-group-id="3457990031-3">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3457990031-3">)</span><span class="p" data-group-id="3457990031-2">]</span><span class="p" data-group-id="3457990031-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3457990031-4">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3457990031-5">[</span><span class="s">&quot;you : function ( 2 , 1 )&quot;</span><span class="p">,</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="3457990031-6">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3457990031-6">)</span><span class="p" data-group-id="3457990031-5">]</span><span class="p" data-group-id="3457990031-4">)</span><span class="p">.</span></code></pre><p>That is, a trace output, with both the function called and the resulting value.</p>
│ │ │ +</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="2078865209-5">(</span><span class="nf">myfunction</span><span class="p" data-group-id="2078865209-6">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2078865209-6">)</span><span class="p" data-group-id="2078865209-5">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="o">?</span><span class="n">TESTCALL</span><span class="p" data-group-id="2078865209-7">(</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="2078865209-8">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2078865209-8">)</span><span class="p" data-group-id="2078865209-7">)</span><span class="p">.</span></code></pre><p>results in</p><pre><code class="makeup erlang" translate="no"><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3779528720-1">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3779528720-2">[</span><span class="s">&quot;myfunction ( 1 , 2 )&quot;</span><span class="p">,</span><span class="nf">myfunction</span><span class="p" data-group-id="3779528720-3">(</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="3779528720-3">)</span><span class="p" data-group-id="3779528720-2">]</span><span class="p" data-group-id="3779528720-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3779528720-4">(</span><span class="s">&quot;Call </span><span class="si">~s</span><span class="s">: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="p" data-group-id="3779528720-5">[</span><span class="s">&quot;you : function ( 2 , 1 )&quot;</span><span class="p">,</span><span class="nc">you</span><span class="p">:</span><span class="nf">function</span><span class="p" data-group-id="3779528720-6">(</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3779528720-6">)</span><span class="p" data-group-id="3779528720-5">]</span><span class="p" data-group-id="3779528720-4">)</span><span class="p">.</span></code></pre><p>That is, a trace output, with both the function called and the resulting value.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="expressions.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/maps.html
│ │ │ @@ -148,16 +148,16 @@
│ │ │  single function that constructs the map using the map syntax and always use
│ │ │  it.</p></li><li><p>Always update the map using the <code class="inline">:=</code> operator (that is, requiring that an
│ │ │  element with that key already exists). The <code class="inline">:=</code> operator is slightly more
│ │ │  efficient, and it helps catching mispellings of keys.</p></li><li><p>Whenever possible, match multiple map elements at once.</p></li><li><p>Whenever possible, update multiple map elements at once.</p></li><li><p>Avoid default values and the <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> function. If there are default
│ │ │  values, sharing of keys between different instances of the map will be less
│ │ │  effective, and it is not possible to match multiple elements having default
│ │ │  values in one go.</p></li><li><p>To avoid having to deal with a map that may lack some keys, <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html#merge/2"><code class="inline">maps:merge/2</code></a> can
│ │ │ -efficiently add multiple default values. For example:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1865302731-1">#{</span><span class="ss">shoe_size</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="ss">editor</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">emacs</span><span class="p" data-group-id="1865302731-1">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="1865302731-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="1865302731-2">)</span></code></pre></li></ul><h2 id="using-maps-as-dictionaries" class="section-heading">
│ │ │ +efficiently add multiple default values. For example:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4887390844-1">#{</span><span class="ss">shoe_size</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="ss">editor</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">emacs</span><span class="p" data-group-id="4887390844-1">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="4887390844-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="4887390844-2">)</span></code></pre></li></ul><h2 id="using-maps-as-dictionaries" class="section-heading">
│ │ │    <a href="#using-maps-as-dictionaries" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Using Maps as Dictionaries</span>
│ │ │  </h2>
│ │ │  <p>Using a map as a dictionary implies the following usage pattern:</p><ul><li>Keys are usually variables not known at compile-time.</li><li>There can be any number of elements in the map.</li><li>Usually, no more than one element is looked up or updated at once.</li></ul><p>Given that usage pattern, the difference in performance between using the map
│ │ │  syntax and the maps module is usually small. Therefore, which one to use is
│ │ │ @@ -167,18 +167,18 @@
│ │ │  choice.</li></ul><h2 id="using-maps-as-sets" class="section-heading">
│ │ │    <a href="#using-maps-as-sets" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Using Maps as Sets</span>
│ │ │  </h2>
│ │ │  <p>Starting in OTP 24, the <a href="../../lib/stdlib-6.2.2.3/doc/html/sets.html"><code class="inline">sets</code></a> module has an option to represent sets as maps.
│ │ │ -Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="2892823144-1">(</span><span class="p" data-group-id="2892823144-2">[</span><span class="p" data-group-id="2892823144-3">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2892823144-3">}</span><span class="p" data-group-id="2892823144-2">]</span><span class="p" data-group-id="2892823144-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2892823144-4">#{</span><span class="p" data-group-id="2892823144-4">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">from_list</span><span class="p" data-group-id="2892823144-5">(</span><span class="p" data-group-id="2892823144-6">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="2892823144-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2892823144-7">[</span><span class="p" data-group-id="2892823144-8">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2892823144-8">}</span><span class="p" data-group-id="2892823144-7">]</span><span class="p" data-group-id="2892823144-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2892823144-9">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2892823144-10">[</span><span class="p" data-group-id="2892823144-10">]</span><span class="p">,</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2892823144-11">[</span><span class="p" data-group-id="2892823144-11">]</span><span class="p">,</span><span class="ss">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2892823144-12">[</span><span class="p" data-group-id="2892823144-12">]</span><span class="p" data-group-id="2892823144-9">}</span></code></pre><p><code class="inline">sets</code> backed by maps is generally the most efficient set representation, with a
│ │ │ +Examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="6448859568-1">(</span><span class="p" data-group-id="6448859568-2">[</span><span class="p" data-group-id="6448859568-3">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6448859568-3">}</span><span class="p" data-group-id="6448859568-2">]</span><span class="p" data-group-id="6448859568-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6448859568-4">#{</span><span class="p" data-group-id="6448859568-4">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">sets</span><span class="p">:</span><span class="nf">from_list</span><span class="p" data-group-id="6448859568-5">(</span><span class="p" data-group-id="6448859568-6">[</span><span class="ss">x</span><span class="p">,</span><span class="ss">y</span><span class="p">,</span><span class="ss">z</span><span class="p" data-group-id="6448859568-6">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6448859568-7">[</span><span class="p" data-group-id="6448859568-8">{</span><span class="ss">version</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6448859568-8">}</span><span class="p" data-group-id="6448859568-7">]</span><span class="p" data-group-id="6448859568-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6448859568-9">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6448859568-10">[</span><span class="p" data-group-id="6448859568-10">]</span><span class="p">,</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6448859568-11">[</span><span class="p" data-group-id="6448859568-11">]</span><span class="p">,</span><span class="ss">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6448859568-12">[</span><span class="p" data-group-id="6448859568-12">]</span><span class="p" data-group-id="6448859568-9">}</span></code></pre><p><code class="inline">sets</code> backed by maps is generally the most efficient set representation, with a
│ │ │  few possible exceptions:</p><ul><li><a href="../../lib/stdlib-6.2.2.3/doc/html/ordsets.html#intersection/2"><code class="inline">ordsets:intersection/2</code></a> can be more efficient than <a href="../../lib/stdlib-6.2.2.3/doc/html/sets.html#intersection/2"><code class="inline">sets:intersection/2</code></a>. If
│ │ │  the intersection operation is frequently used and operations that operate on a
│ │ │  single element in a set (such as <code class="inline">is_element/2</code>) are avoided, <a href="../../lib/stdlib-6.2.2.3/doc/html/ordsets.html"><code class="inline">ordsets</code></a> can
│ │ │  be a better choice than <a href="../../lib/stdlib-6.2.2.3/doc/html/sets.html"><code class="inline">sets</code></a>.</li><li>If the intersection operation is frequently used and operations that operate
│ │ │  on a single element in a set (such as <code class="inline">is_element/2</code>) must also be efficient,
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gb_sets.html"><code class="inline">gb_sets</code></a> can potentially be a better choice than <a href="../../lib/stdlib-6.2.2.3/doc/html/sets.html"><code class="inline">sets</code></a>.</li><li>If the elements of the set are integers in a fairly compact range, the set can
│ │ │  be represented as an integer where each bit represents an element in the set.
│ │ │ @@ -203,18 +203,18 @@
│ │ │  for the runtime system).</p></li><li><p><strong>N</strong> - The number of elements in the map.</p></li><li><p><strong>Keys</strong> - A tuple with keys of the map: <code class="inline">{Key1,...,KeyN}</code>. The keys are
│ │ │  sorted.</p></li><li><p><strong>Value1</strong> - The value corresponding to the first key in the key tuple.</p></li><li><p><strong>ValueN</strong> - The value corresponding to the last key in the key tuple.</p></li></ul><p>As an example, let us look at how the map <code class="inline">#{a =&gt; foo, z =&gt; bar}</code> is
│ │ │  represented:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: left;">4</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>2</em></td><td style="text-align: center;"><code class="inline">{a,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: left;"><code class="inline">bar</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, z =&gt; bar}</em></p><p>Let us update the map: <code class="inline">M#{q =&gt; baz}</code>. The map now looks like this:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: center;">4</th><th style="text-align: center;">5</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>3</em></td><td style="text-align: center;"><code class="inline">{a,q,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: center;"><code class="inline">baz</code></td><td style="text-align: center;"><code class="inline">bar</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, q =&gt; baz, z =&gt; bar}</em></p><p>Finally, change the value of one element: <code class="inline">M#{z := bird}</code>. The map now looks
│ │ │  like this:</p><table><thead><tr><th style="text-align: center;">0</th><th style="text-align: left;">1</th><th style="text-align: center;">2</th><th style="text-align: center;">3</th><th style="text-align: center;">4</th><th style="text-align: center;">5</th></tr></thead><tbody><tr><td style="text-align: center;"><strong>FLATMAP</strong></td><td style="text-align: left;"><em>3</em></td><td style="text-align: center;"><code class="inline">{a,q,z}</code></td><td style="text-align: center;"><code class="inline">foo</code></td><td style="text-align: center;"><code class="inline">baz</code></td><td style="text-align: center;"><code class="inline">bird</code></td></tr></tbody></table><p><em>Table: #{a =&gt; foo, q =&gt; baz, z =&gt; bird}</em></p><p>When the value for an existing key is updated, the key tuple is not updated,
│ │ │  allowing the key tuple to be shared with other instances of the map that have
│ │ │  the same keys. In fact, the key tuple can be shared between all maps with the
│ │ │  same keys with some care. To arrange that, define a function that returns a map.
│ │ │ -For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="0979817173-1">(</span><span class="p" data-group-id="0979817173-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0979817173-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p" data-group-id="0979817173-2">}</span><span class="p">.</span></code></pre><p>Defined like this, the key tuple <code class="inline">{a,b,c}</code> will be a global literal. To ensure
│ │ │ +For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="7670848456-1">(</span><span class="p" data-group-id="7670848456-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7670848456-2">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">b</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p">,</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">default</span><span class="p" data-group-id="7670848456-2">}</span><span class="p">.</span></code></pre><p>Defined like this, the key tuple <code class="inline">{a,b,c}</code> will be a global literal. To ensure
│ │ │  that the key tuple is shared when creating an instance of the map, always call
│ │ │ -<code class="inline">new()</code> and modify the returned map:</p><pre><code class="makeup erlang" translate="no"><span class="w">    </span><span class="p" data-group-id="0778626685-1">(</span><span class="n">SOME_MODULE</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0778626685-2">(</span><span class="p" data-group-id="0778626685-2">)</span><span class="p" data-group-id="0778626685-1">)</span><span class="p" data-group-id="0778626685-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="0778626685-3">}</span><span class="p">.</span></code></pre><p>Using the map syntax with small maps is particularly efficient. As long as the
│ │ │ +<code class="inline">new()</code> and modify the returned map:</p><pre><code class="makeup erlang" translate="no"><span class="w">    </span><span class="p" data-group-id="1013717601-1">(</span><span class="n">SOME_MODULE</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="1013717601-2">(</span><span class="p" data-group-id="1013717601-2">)</span><span class="p" data-group-id="1013717601-1">)</span><span class="p" data-group-id="1013717601-3">#{</span><span class="ss">a</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="1013717601-3">}</span><span class="p">.</span></code></pre><p>Using the map syntax with small maps is particularly efficient. As long as the
│ │ │  keys are known at compile-time, the map is updated in one go, making the time to
│ │ │  update a map essentially constant regardless of the number of keys updated. The
│ │ │  same goes for matching. (When the keys are variables, one or more of the keys
│ │ │  could be identical, so the operations need to be performed sequentially from
│ │ │  left to right.)</p><p>The memory size for a small map is the size of all keys and values plus 5 words.
│ │ │  See <a href="memory.html">Memory</a> for more information about memory sizes.</p><h3 id="how-large-maps-are-implemented" class="section-heading">
│ │ │    <a href="#how-large-maps-are-implemented" class="hover-link">
│ │ │ @@ -241,21 +241,21 @@
│ │ │    <a href="#using-the-map-syntax" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Using the Map Syntax</span>
│ │ │  </h2>
│ │ │  <p>Using the map syntax is usually slightly more efficient than using the
│ │ │  corresponding function in the <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html"><code class="inline">maps</code></a> module.</p><p>The gain in efficiency for the map syntax is more noticeable for the following
│ │ │ -operations that can only be achieved using the map syntax:</p><ul><li>Matching multiple literal keys</li><li>Updating multiple literal keys</li><li>Adding multiple literal keys to a map</li></ul><p>For example:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="2530283314-1">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="ss">z</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="2530283314-1">}</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="9841395224-1">(</span><span class="ss">x</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="9841395224-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="9841395224-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="9841395224-2">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="9841395224-3">(</span><span class="ss">z</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">,</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="9841395224-3">)</span></code></pre><p>If the map is a small map, the first example runs roughly three times as fast.</p><p>Note that for variable keys, the elements are updated sequentially from left to
│ │ │ -right. For example, given the following update with variable keys:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="5171377886-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="5171377886-1">}</span></code></pre><p>the compiler rewrites it like this to ensure that the updates are applied from
│ │ │ -left to right:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="3766338420-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3766338420-1">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="3766338420-2">#{</span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3766338420-2">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="3766338420-3">#{</span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="3766338420-3">}</span></code></pre><p>If a key is known to exist in a map, using the <code class="inline">:=</code> operator is slightly more
│ │ │ +operations that can only be achieved using the map syntax:</p><ul><li>Matching multiple literal keys</li><li>Updating multiple literal keys</li><li>Adding multiple literal keys to a map</li></ul><p>For example:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="3341604723-1">#{</span><span class="ss">x</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="ss">z</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="3341604723-1">}</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="5297337222-1">(</span><span class="ss">x</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="5297337222-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="5297337222-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="5297337222-2">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">update</span><span class="p" data-group-id="5297337222-3">(</span><span class="ss">z</span><span class="p">,</span><span class="w"> </span><span class="n">Z</span><span class="p">,</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="5297337222-3">)</span></code></pre><p>If the map is a small map, the first example runs roughly three times as fast.</p><p>Note that for variable keys, the elements are updated sequentially from left to
│ │ │ +right. For example, given the following update with variable keys:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="2543283842-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p">,</span><span class="w"> </span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="2543283842-1">}</span></code></pre><p>the compiler rewrites it like this to ensure that the updates are applied from
│ │ │ +left to right:</p><pre><code class="makeup erlang" translate="no"><span class="n">Map2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map1</span><span class="p" data-group-id="9556947534-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="9556947534-1">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Map3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map2</span><span class="p" data-group-id="9556947534-2">#{</span><span class="n">Key2</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9556947534-2">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Map</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Map3</span><span class="p" data-group-id="9556947534-3">#{</span><span class="n">Key3</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Z</span><span class="p" data-group-id="9556947534-3">}</span></code></pre><p>If a key is known to exist in a map, using the <code class="inline">:=</code> operator is slightly more
│ │ │  efficient than using the <code class="inline">=&gt;</code> operator for a small map.</p><h2 id="using-the-functions-in-the-maps-module" class="section-heading">
│ │ │    <a href="#using-the-functions-in-the-maps-module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Using the Functions in the maps Module</span>
│ │ │  </h2>
│ │ │  <p>Here follows some notes about most of the functions in the <code class="inline">maps</code> module. For
│ │ │ @@ -306,23 +306,23 @@
│ │ │    <a href="#maps-get-3" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">maps:get/3</span>
│ │ │  </h3>
│ │ │  <p>As an optimization, the compiler will rewrite a call to <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> to Erlang
│ │ │  code similar to the following:</p><pre><code class="makeup erlang" translate="no"><span class="n">Result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">Map</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="8098920675-1">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="8098920675-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="p">;</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="8098920675-2">#{</span><span class="p" data-group-id="8098920675-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Default</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="4042844062-1">#{</span><span class="n">Key</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Value</span><span class="p" data-group-id="4042844062-1">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Value</span><span class="p">;</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="4042844062-2">#{</span><span class="p" data-group-id="4042844062-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Default</span><span class="w">
│ │ │           </span><span class="k">end</span></code></pre><p>This is reasonably efficient, but if a small map is used as an alternative to
│ │ │  using a record it is often better not to rely on default values as it prevents
│ │ │  sharing of keys, which may in the end use more memory than what you save from
│ │ │  not storing default values in the map.</p><p>If default values are nevertheless required, instead of calling <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a>
│ │ │  multiple times, consider putting the default values in a map and merging that
│ │ │ -map with the other map:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9910396706-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">KeyN</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueN</span><span class="p" data-group-id="9910396706-1">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="9910396706-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="9910396706-2">)</span></code></pre><p>This helps share keys between the default map and the one you applied defaults
│ │ │ +map with the other map:</p><pre><code class="makeup erlang" translate="no"><span class="n">DefaultMap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0137171920-1">#{</span><span class="n">Key1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Value2</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">KeyN</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">ValueN</span><span class="p" data-group-id="0137171920-1">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">MapWithDefaultsApplied</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">merge</span><span class="p" data-group-id="0137171920-2">(</span><span class="n">DefaultMap</span><span class="p">,</span><span class="w"> </span><span class="n">OtherMap</span><span class="p" data-group-id="0137171920-2">)</span></code></pre><p>This helps share keys between the default map and the one you applied defaults
│ │ │  to, as long as the default map contains <em>all</em> the keys that will ever be used
│ │ │  and not just the ones with default values. Whether this is faster than calling
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> multiple times depends on the size of the map and the number of
│ │ │  default values.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before OTP 26.0 <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html#get/3"><code class="inline">maps:get/3</code></a> was implemented by calling the function instead
│ │ │  of rewriting it as an Erlang expression. It is now slightly faster but can no
│ │ │  longer be traced.</p></section><h3 id="maps-intersect-2-maps-intersect_with-3" class="section-heading">
│ │ │    <a href="#maps-intersect-2-maps-intersect_with-3" class="hover-link">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/modules.html
│ │ │ @@ -118,20 +118,20 @@
│ │ │  <h2 id="module-syntax" class="section-heading">
│ │ │    <a href="#module-syntax" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Module Syntax</span>
│ │ │  </h2>
│ │ │  <p>Erlang code is divided into <em>modules</em>. A module consists of a sequence of
│ │ │ -attributes and function declarations, each terminated by a period (<code class="inline">.</code>).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4385855243-1">(</span><span class="ss">m</span><span class="p" data-group-id="4385855243-1">)</span><span class="p">.</span><span class="w">          </span><span class="c1">% module attribute</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4385855243-2">(</span><span class="p" data-group-id="4385855243-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4385855243-3">]</span><span class="p" data-group-id="4385855243-2">)</span><span class="p">.</span><span class="w">   </span><span class="c1">% module attribute</span><span class="w">
│ │ │ +attributes and function declarations, each terminated by a period (<code class="inline">.</code>).</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1680519213-1">(</span><span class="ss">m</span><span class="p" data-group-id="1680519213-1">)</span><span class="p">.</span><span class="w">          </span><span class="c1">% module attribute</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1680519213-2">(</span><span class="p" data-group-id="1680519213-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1680519213-3">]</span><span class="p" data-group-id="1680519213-2">)</span><span class="p">.</span><span class="w">   </span><span class="c1">% module attribute</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="4385855243-4">(</span><span class="n">N</span><span class="p" data-group-id="4385855243-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% beginning of function declaration</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="4385855243-5">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="4385855243-5">)</span><span class="p">;</span><span class="w">   </span><span class="c1">%  |</span><span class="w">
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="4385855243-6">(</span><span class="mi">0</span><span class="p" data-group-id="4385855243-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">           </span><span class="c1">%  |</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="1680519213-4">(</span><span class="n">N</span><span class="p" data-group-id="1680519213-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="o">&gt;</span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% beginning of function declaration</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="1680519213-5">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="1680519213-5">)</span><span class="p">;</span><span class="w">   </span><span class="c1">%  |</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="1680519213-6">(</span><span class="mi">0</span><span class="p" data-group-id="1680519213-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">           </span><span class="c1">%  |</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">.</span><span class="w">               </span><span class="c1">% end of function declaration</span></code></pre><p>For a description of function declarations, see
│ │ │  <a href="ref_man_functions.html">Function Declaration Syntax</a>.</p><h2 id="module-attributes" class="section-heading">
│ │ │    <a href="#module-attributes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Module Attributes</span>
│ │ │  </h2>
│ │ │ @@ -176,71 +176,71 @@
│ │ │  meaning.</p></section></li></ul><h3 id="behaviour-module-attribute" class="section-heading">
│ │ │    <a href="#behaviour-module-attribute" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Behaviour Module Attribute</span>
│ │ │  </h3>
│ │ │  <p>It is possible to specify that the module is the callback module for a
│ │ │ -<em>behaviour</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6748720615-1">(</span><span class="n">Behaviour</span><span class="p" data-group-id="6748720615-1">)</span><span class="p">.</span></code></pre><p>The atom <code class="inline">Behaviour</code> gives the name of the behaviour, which can be a
│ │ │ +<em>behaviour</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="9697252806-1">(</span><span class="n">Behaviour</span><span class="p" data-group-id="9697252806-1">)</span><span class="p">.</span></code></pre><p>The atom <code class="inline">Behaviour</code> gives the name of the behaviour, which can be a
│ │ │  user-defined behaviour or one of the following OTP standard behaviours:</p><ul><li><code class="inline">gen_server</code></li><li><code class="inline">gen_statem</code></li><li><code class="inline">gen_event</code></li><li><code class="inline">supervisor</code></li></ul><p>The spelling <code class="inline">behavior</code> is also accepted.</p><p>The callback functions of the module can be specified either directly by the
│ │ │ -exported function <code class="inline">behaviour_info/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="3258400009-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="3258400009-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Callbacks</span><span class="p">.</span></code></pre><p>or by a <code class="inline">-callback</code> attribute for each callback function:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0598601945-1">(</span><span class="n">Arguments</span><span class="p" data-group-id="0598601945-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="p">.</span></code></pre><p>Here, <code class="inline">Arguments</code> is a list of zero or more arguments. The <code class="inline">-callback</code> attribute
│ │ │ +exported function <code class="inline">behaviour_info/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="4032115841-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="4032115841-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Callbacks</span><span class="p">.</span></code></pre><p>or by a <code class="inline">-callback</code> attribute for each callback function:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9081983314-1">(</span><span class="n">Arguments</span><span class="p" data-group-id="9081983314-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Result</span><span class="p">.</span></code></pre><p>Here, <code class="inline">Arguments</code> is a list of zero or more arguments. The <code class="inline">-callback</code> attribute
│ │ │  is to be preferred since the extra type information can be used by tools to
│ │ │  produce documentation or find discrepancies.</p><p>Read more about behaviours and callback modules in
│ │ │  <a href="../../doc/system/spec_proc.html#behaviours">OTP Design Principles</a>.</p><h3 id="record-definitions" class="section-heading">
│ │ │    <a href="#record-definitions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Record Definitions</span>
│ │ │  </h3>
│ │ │ -<p>The same syntax as for module attributes is used for record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3172533002-1">(</span><span class="n">Record</span><span class="p">,</span><span class="w"> </span><span class="n">Fields</span><span class="p" data-group-id="3172533002-1">)</span><span class="p">.</span></code></pre><p>Record definitions are allowed anywhere in a module, also among the function
│ │ │ +<p>The same syntax as for module attributes is used for record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0476117841-1">(</span><span class="n">Record</span><span class="p">,</span><span class="w"> </span><span class="n">Fields</span><span class="p" data-group-id="0476117841-1">)</span><span class="p">.</span></code></pre><p>Record definitions are allowed anywhere in a module, also among the function
│ │ │  declarations. Read more in <a href="ref_man_records.html">Records</a>.</p><h3 id="preprocessor" class="section-heading">
│ │ │    <a href="#preprocessor" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Preprocessor</span>
│ │ │  </h3>
│ │ │  <p>The same syntax as for module attributes is used by the preprocessor, which
│ │ │ -supports file inclusion, macros, and conditional compilation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5247697802-1">(</span><span class="s">&quot;SomeFile.hrl&quot;</span><span class="p" data-group-id="5247697802-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5247697802-2">(</span><span class="n">Macro</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="5247697802-2">)</span><span class="p">.</span></code></pre><p>Read more in <a href="macros.html">Preprocessor</a>.</p><h3 id="setting-file-and-line" class="section-heading">
│ │ │ +supports file inclusion, macros, and conditional compilation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="0094167989-1">(</span><span class="s">&quot;SomeFile.hrl&quot;</span><span class="p" data-group-id="0094167989-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0094167989-2">(</span><span class="n">Macro</span><span class="p">,</span><span class="w"> </span><span class="n">Replacement</span><span class="p" data-group-id="0094167989-2">)</span><span class="p">.</span></code></pre><p>Read more in <a href="macros.html">Preprocessor</a>.</p><h3 id="setting-file-and-line" class="section-heading">
│ │ │    <a href="#setting-file-and-line" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Setting File and Line</span>
│ │ │  </h3>
│ │ │  <p>The same syntax as for module attributes is used for changing the pre-defined
│ │ │ -macros <code class="inline">?FILE</code> and <code class="inline">?LINE</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">file</span><span class="p" data-group-id="8034121597-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">Line</span><span class="p" data-group-id="8034121597-1">)</span><span class="p">.</span></code></pre><p>This attribute is used by tools, such as Yecc, to inform the compiler that the
│ │ │ +macros <code class="inline">?FILE</code> and <code class="inline">?LINE</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">file</span><span class="p" data-group-id="8219896411-1">(</span><span class="n">File</span><span class="p">,</span><span class="w"> </span><span class="n">Line</span><span class="p" data-group-id="8219896411-1">)</span><span class="p">.</span></code></pre><p>This attribute is used by tools, such as Yecc, to inform the compiler that the
│ │ │  source program is generated by another tool. It also indicates the
│ │ │  correspondence of source files to lines of the original user-written file, from
│ │ │  which the source program is produced.</p><h3 id="types-and-function-specifications" class="section-heading">
│ │ │    <a href="#types-and-function-specifications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Types and function specifications</span>
│ │ │  </h3>
│ │ │  <p>A similar syntax as for module attributes is used for specifying types and
│ │ │ -function specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_type</span><span class="p" data-group-id="1247280728-1">(</span><span class="p" data-group-id="1247280728-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="1247280728-2">(</span><span class="p" data-group-id="1247280728-2">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1247280728-3">(</span><span class="p" data-group-id="1247280728-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">my_function</span><span class="p" data-group-id="1247280728-4">(</span><span class="nf">integer</span><span class="p" data-group-id="1247280728-5">(</span><span class="p" data-group-id="1247280728-5">)</span><span class="p" data-group-id="1247280728-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="1247280728-6">(</span><span class="p" data-group-id="1247280728-6">)</span><span class="p">.</span></code></pre><p>Read more in <a href="typespec.html">Types and Function specifications</a>.</p><p>The description is based on
│ │ │ +function specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_type</span><span class="p" data-group-id="0666064580-1">(</span><span class="p" data-group-id="0666064580-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="0666064580-2">(</span><span class="p" data-group-id="0666064580-2">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0666064580-3">(</span><span class="p" data-group-id="0666064580-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">my_function</span><span class="p" data-group-id="0666064580-4">(</span><span class="nf">integer</span><span class="p" data-group-id="0666064580-5">(</span><span class="p" data-group-id="0666064580-5">)</span><span class="p" data-group-id="0666064580-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0666064580-6">(</span><span class="p" data-group-id="0666064580-6">)</span><span class="p">.</span></code></pre><p>Read more in <a href="typespec.html">Types and Function specifications</a>.</p><p>The description is based on
│ │ │  <a href="http://www.erlang.org/eeps/eep-0008.html">EEP8 - Types and function specifications</a>,
│ │ │  which is not to be further updated.</p><h3 id="documentation-attributes" class="section-heading">
│ │ │    <a href="#documentation-attributes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Documentation attributes</span>
│ │ │  </h3>
│ │ │  <p>The module attribute <code class="inline">-doc(Documentation)</code> is used to provide user documentation
│ │ │ -for a function/type/callback:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="5382716590-1">(</span><span class="s">&quot;Example documentation&quot;</span><span class="p" data-group-id="5382716590-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">example</span><span class="p" data-group-id="5382716590-2">(</span><span class="p" data-group-id="5382716590-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The attribute should be placed just before the entity it documents.The
│ │ │ +for a function/type/callback:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="4215619534-1">(</span><span class="s">&quot;Example documentation&quot;</span><span class="p" data-group-id="4215619534-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">example</span><span class="p" data-group-id="4215619534-2">(</span><span class="p" data-group-id="4215619534-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The attribute should be placed just before the entity it documents.The
│ │ │  parenthesis are optional around <code class="inline">Documentation</code>. The allowed values for
│ │ │  <code class="inline">Documentation</code> are:</p><ul><li><p><strong><a href="data_types.html#string">literal string</a> or
│ │ │  <a href="expressions.html#unicode-segments">utf-8 encoded binary string</a></strong> - The string
│ │ │  documenting the entity. Any literal string is allowed, so both
│ │ │  <a href="data_types.html#tqstring">triple quoted strings</a> and
│ │ │  <a href="data_types.html#sigil">sigils</a> that translate to literal strings can be used.
│ │ │ -The following examples are equivalent:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="3473224628-1">(</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="p" data-group-id="3473224628-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="3473224628-2">(</span><span class="p" data-group-id="3473224628-3">&lt;&lt;</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="3473224628-3">&gt;&gt;</span><span class="p" data-group-id="3473224628-2">)</span><span class="p">.</span><span class="w">
│ │ │ +The following examples are equivalent:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7947092042-1">(</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="p" data-group-id="7947092042-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">doc</span><span class="p" data-group-id="7947092042-2">(</span><span class="p" data-group-id="7947092042-3">&lt;&lt;</span><span class="s">&quot;Example \&quot;docs\&quot;&quot;</span><span class="o">/</span><span class="ss">utf8</span><span class="p" data-group-id="7947092042-3">&gt;&gt;</span><span class="p" data-group-id="7947092042-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">~S/Example &quot;docs&quot;/</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="s">&quot;
│ │ │     Example &quot;</span><span class="ss">docs</span><span class="s">&quot;
│ │ │     &quot;</span><span class="s">&quot;&quot;</span><span class="w">
│ │ │  </span><span class="p">-</span><span class="na">doc</span><span class="w"> </span><span class="s">~B|Example &quot;docs&quot;|</span><span class="p">.</span></code></pre><p>For clarity it is recommended to use either normal <code class="inline">&quot;strings&quot;</code> or triple
│ │ │  quoted strings for documentation attributes.</p></li><li><p><strong><code class="inline">{file,</code> <a href="../../lib/kernel-10.2.7.4/doc/html/file.html#t:name/0"><code class="inline">file:name/0</code></a> <code class="inline">}</code></strong> - Read the contents of filename and use
│ │ │  that as the documentation string.</p></li><li><p><strong><code class="inline">false</code></strong> - Set the current entity as hidden, that is, it should not be
│ │ │ @@ -253,15 +253,15 @@
│ │ │    <a href="#the-feature-directive" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The feature directive</span>
│ │ │  </h2>
│ │ │  <p>While not a module attribute, but rather a directive (since it might affect
│ │ │  syntax), there is the <code class="inline">-feature(..)</code> directive used for enabling and disabling
│ │ │ -<a href="../../doc/system/features.html#features">features</a>.</p><p>The syntax is similar to that of an attribute, but has two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">feature</span><span class="p" data-group-id="6256671462-1">(</span><span class="n">FeatureName</span><span class="p">,</span><span class="w"> </span><span class="ss">enable</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">disable</span><span class="p" data-group-id="6256671462-1">)</span><span class="p">.</span></code></pre><p>Note that the <a href="macros.html#feature-directive">feature directive</a> can only appear
│ │ │ +<a href="../../doc/system/features.html#features">features</a>.</p><p>The syntax is similar to that of an attribute, but has two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">feature</span><span class="p" data-group-id="3184778328-1">(</span><span class="n">FeatureName</span><span class="p">,</span><span class="w"> </span><span class="ss">enable</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">disable</span><span class="p" data-group-id="3184778328-1">)</span><span class="p">.</span></code></pre><p>Note that the <a href="macros.html#feature-directive">feature directive</a> can only appear
│ │ │  in a prefix of the module.</p><h2 id="comments" class="section-heading">
│ │ │    <a href="#comments" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Comments</span>
│ │ │  </h2>
│ │ │  <p>Comments can be placed anywhere in a module except within strings and
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/nif.html
│ │ │ @@ -133,26 +133,26 @@
│ │ │    <span class="text">Erlang Program</span>
│ │ │  </h2>
│ │ │  <p>Even if all functions of a module are NIFs, an Erlang module is still needed for
│ │ │  two reasons:</p><ul><li>The NIF library must be explicitly loaded by Erlang code in the same module.</li><li>All NIFs of a module must have an Erlang implementation as well.</li></ul><p>Normally these are minimal stub implementations that throw an exception. But
│ │ │  they can also be used as fallback implementations for functions that do not have
│ │ │  native implementations on some architectures.</p><p>NIF libraries are loaded by calling <a href="../../erts-15.2.7.8/doc/html/erlang.html#load_nif/2"><code class="inline">erlang:load_nif/2</code></a>, with the name of the
│ │ │  shared library as argument. The second argument can be any term that will be
│ │ │ -passed on to the library and used for initialization:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1991554258-1">(</span><span class="ss">complex6</span><span class="p" data-group-id="1991554258-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1991554258-2">(</span><span class="p" data-group-id="1991554258-3">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1991554258-3">]</span><span class="p" data-group-id="1991554258-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="1991554258-4">(</span><span class="p" data-group-id="1991554258-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1991554258-5">]</span><span class="p" data-group-id="1991554258-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="1991554258-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="1991554258-6">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="1991554258-7">(</span><span class="p" data-group-id="1991554258-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="1991554258-8">(</span><span class="s">&quot;./complex6_nif&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1991554258-8">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="1991554258-9">(</span><span class="p">_</span><span class="n">X</span><span class="p" data-group-id="1991554258-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="1991554258-10">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="1991554258-10">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">bar</span><span class="p" data-group-id="1991554258-11">(</span><span class="p">_</span><span class="n">Y</span><span class="p" data-group-id="1991554258-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="1991554258-12">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="1991554258-12">)</span><span class="p">.</span></code></pre><p>Here, the directive <code class="inline">on_load</code> is used to get function <code class="inline">init</code> to be automatically
│ │ │ +passed on to the library and used for initialization:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7487646349-1">(</span><span class="ss">complex6</span><span class="p" data-group-id="7487646349-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7487646349-2">(</span><span class="p" data-group-id="7487646349-3">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7487646349-3">]</span><span class="p" data-group-id="7487646349-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">nifs</span><span class="p" data-group-id="7487646349-4">(</span><span class="p" data-group-id="7487646349-5">[</span><span class="ss">foo</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">bar</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7487646349-5">]</span><span class="p" data-group-id="7487646349-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">on_load</span><span class="p" data-group-id="7487646349-6">(</span><span class="ss">init</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7487646349-6">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="7487646349-7">(</span><span class="p" data-group-id="7487646349-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">load_nif</span><span class="p" data-group-id="7487646349-8">(</span><span class="s">&quot;./complex6_nif&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7487646349-8">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="7487646349-9">(</span><span class="p">_</span><span class="n">X</span><span class="p" data-group-id="7487646349-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="7487646349-10">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="7487646349-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">bar</span><span class="p" data-group-id="7487646349-11">(</span><span class="p">_</span><span class="n">Y</span><span class="p" data-group-id="7487646349-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">nif_error</span><span class="p" data-group-id="7487646349-12">(</span><span class="ss">nif_library_not_loaded</span><span class="p" data-group-id="7487646349-12">)</span><span class="p">.</span></code></pre><p>Here, the directive <code class="inline">on_load</code> is used to get function <code class="inline">init</code> to be automatically
│ │ │  called when the module is loaded. If <code class="inline">init</code> returns anything other than <code class="inline">ok</code>,
│ │ │  such when the loading of the NIF library fails in this example, the module is
│ │ │  unloaded and calls to functions within it, fail.</p><p>Loading the NIF library overrides the stub implementations and cause calls to
│ │ │  <code class="inline">foo</code> and <code class="inline">bar</code> to be dispatched to the NIF implementations instead.</p><h2 id="nif-library-code" class="section-heading">
│ │ │    <a href="#nif-library-code" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -165,43 +165,43 @@
│ │ │  is a shared module, not a program, no main function is to be present.</p><p>The function arguments passed to a NIF appears in an array <code class="inline">argv</code>, with <code class="inline">argc</code>
│ │ │  as the length of the array, and thus the arity of the function. The Nth argument
│ │ │  of the function can be accessed as <code class="inline">argv[N-1]</code>. NIFs also take an environment
│ │ │  argument that serves as an opaque handle that is needed to be passed on to most
│ │ │  API functions. The environment contains information about the calling Erlang
│ │ │  process:</p><pre><code class="makeup c" translate="no"><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">erl_nif</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="k">extern</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="7811820813-1">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="7811820813-1">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="k">extern</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="7811820813-2">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="7811820813-2">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="k">extern</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="9049855429-1">(</span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="9049855429-1">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="k">extern</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="9049855429-2">(</span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p" data-group-id="9049855429-2">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="nf">foo_nif</span><span class="p" data-group-id="7811820813-3">(</span><span class="no">ErlNifEnv</span><span class="o">*</span><span class="w"> </span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="7811820813-4">[</span><span class="p" data-group-id="7811820813-4">]</span><span class="p" data-group-id="7811820813-3">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7811820813-5">{</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="nf">foo_nif</span><span class="p" data-group-id="9049855429-3">(</span><span class="no">ErlNifEnv</span><span class="o">*</span><span class="w"> </span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9049855429-4">[</span><span class="p" data-group-id="9049855429-4">]</span><span class="p" data-group-id="9049855429-3">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9049855429-5">{</span><span class="w">
│ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="7811820813-6">(</span><span class="o">!</span><span class="nf">enif_get_int</span><span class="p" data-group-id="7811820813-7">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="7811820813-8">[</span><span class="mi">0</span><span class="p" data-group-id="7811820813-8">]</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="7811820813-7">)</span><span class="p" data-group-id="7811820813-6">)</span><span class="w"> </span><span class="p" data-group-id="7811820813-9">{</span><span class="w">
│ │ │ -</span><span class="err">	</span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_badarg</span><span class="p" data-group-id="7811820813-10">(</span><span class="n">env</span><span class="p" data-group-id="7811820813-10">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7811820813-9">}</span><span class="w">
│ │ │ -    </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="7811820813-11">(</span><span class="n">x</span><span class="p" data-group-id="7811820813-11">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_int</span><span class="p" data-group-id="7811820813-12">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p" data-group-id="7811820813-12">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7811820813-5">}</span><span class="w">
│ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9049855429-6">(</span><span class="o">!</span><span class="nf">enif_get_int</span><span class="p" data-group-id="9049855429-7">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9049855429-8">[</span><span class="mi">0</span><span class="p" data-group-id="9049855429-8">]</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="9049855429-7">)</span><span class="p" data-group-id="9049855429-6">)</span><span class="w"> </span><span class="p" data-group-id="9049855429-9">{</span><span class="w">
│ │ │ +</span><span class="err">	</span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_badarg</span><span class="p" data-group-id="9049855429-10">(</span><span class="n">env</span><span class="p" data-group-id="9049855429-10">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9049855429-9">}</span><span class="w">
│ │ │ +    </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="9049855429-11">(</span><span class="n">x</span><span class="p" data-group-id="9049855429-11">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_int</span><span class="p" data-group-id="9049855429-12">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p" data-group-id="9049855429-12">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9049855429-5">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="nf">bar_nif</span><span class="p" data-group-id="7811820813-13">(</span><span class="no">ErlNifEnv</span><span class="o">*</span><span class="w"> </span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="7811820813-14">[</span><span class="p" data-group-id="7811820813-14">]</span><span class="p" data-group-id="7811820813-13">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7811820813-15">{</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="nf">bar_nif</span><span class="p" data-group-id="9049855429-13">(</span><span class="no">ErlNifEnv</span><span class="o">*</span><span class="w"> </span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="no">ERL_NIF_TERM</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9049855429-14">[</span><span class="p" data-group-id="9049855429-14">]</span><span class="p" data-group-id="9049855429-13">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9049855429-15">{</span><span class="w">
│ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="7811820813-16">(</span><span class="o">!</span><span class="nf">enif_get_int</span><span class="p" data-group-id="7811820813-17">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="7811820813-18">[</span><span class="mi">0</span><span class="p" data-group-id="7811820813-18">]</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">y</span><span class="p" data-group-id="7811820813-17">)</span><span class="p" data-group-id="7811820813-16">)</span><span class="w"> </span><span class="p" data-group-id="7811820813-19">{</span><span class="w">
│ │ │ -</span><span class="err">	</span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_badarg</span><span class="p" data-group-id="7811820813-20">(</span><span class="n">env</span><span class="p" data-group-id="7811820813-20">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7811820813-19">}</span><span class="w">
│ │ │ -    </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="7811820813-21">(</span><span class="n">y</span><span class="p" data-group-id="7811820813-21">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_int</span><span class="p" data-group-id="7811820813-22">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p" data-group-id="7811820813-22">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7811820813-15">}</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ErlNifFunc</span><span class="w"> </span><span class="n">nif_funcs</span><span class="p" data-group-id="7811820813-23">[</span><span class="p" data-group-id="7811820813-23">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7811820813-24">{</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7811820813-25">{</span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">foo_nif</span><span class="p" data-group-id="7811820813-25">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7811820813-26">{</span><span class="s">&quot;bar&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">bar_nif</span><span class="p" data-group-id="7811820813-26">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7811820813-24">}</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9049855429-16">(</span><span class="o">!</span><span class="nf">enif_get_int</span><span class="p" data-group-id="9049855429-17">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">argv</span><span class="p" data-group-id="9049855429-18">[</span><span class="mi">0</span><span class="p" data-group-id="9049855429-18">]</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">y</span><span class="p" data-group-id="9049855429-17">)</span><span class="p" data-group-id="9049855429-16">)</span><span class="w"> </span><span class="p" data-group-id="9049855429-19">{</span><span class="w">
│ │ │ +</span><span class="err">	</span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_badarg</span><span class="p" data-group-id="9049855429-20">(</span><span class="n">env</span><span class="p" data-group-id="9049855429-20">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9049855429-19">}</span><span class="w">
│ │ │ +    </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">bar</span><span class="p" data-group-id="9049855429-21">(</span><span class="n">y</span><span class="p" data-group-id="9049855429-21">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="k">return</span><span class="w"> </span><span class="nf">enif_make_int</span><span class="p" data-group-id="9049855429-22">(</span><span class="n">env</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p" data-group-id="9049855429-22">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9049855429-15">}</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ErlNifFunc</span><span class="w"> </span><span class="n">nif_funcs</span><span class="p" data-group-id="9049855429-23">[</span><span class="p" data-group-id="9049855429-23">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9049855429-24">{</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9049855429-25">{</span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">foo_nif</span><span class="p" data-group-id="9049855429-25">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9049855429-26">{</span><span class="s">&quot;bar&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">bar_nif</span><span class="p" data-group-id="9049855429-26">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9049855429-24">}</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="no">ERL_NIF_INIT</span><span class="p" data-group-id="7811820813-27">(</span><span class="n">complex6</span><span class="p">,</span><span class="w"> </span><span class="n">nif_funcs</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="7811820813-27">)</span></code></pre><p>Here, <code class="inline">ERL_NIF_INIT</code> has the following arguments:</p><ul><li>The first argument must be the name of the Erlang module as a C-identifier. It
│ │ │ +</span><span class="no">ERL_NIF_INIT</span><span class="p" data-group-id="9049855429-27">(</span><span class="n">complex6</span><span class="p">,</span><span class="w"> </span><span class="n">nif_funcs</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="9049855429-27">)</span></code></pre><p>Here, <code class="inline">ERL_NIF_INIT</code> has the following arguments:</p><ul><li>The first argument must be the name of the Erlang module as a C-identifier. It
│ │ │  will be stringified by the macro.</li><li>The second argument is the array of <code class="inline">ErlNifFunc</code> structures containing name,
│ │ │  arity, and function pointer of each NIF.</li><li>The remaining arguments are pointers to callback functions that can be used to
│ │ │  initialize the library. They are not used in this simple example, hence they
│ │ │  are all set to <code class="inline">NULL</code>.</li></ul><p>Function arguments and return values are represented as values of type
│ │ │  <code class="inline">ERL_NIF_TERM</code>. Here, functions like <code class="inline">enif_get_int</code> and <code class="inline">enif_make_int</code> are used
│ │ │  to convert between Erlang term and C-type. If the function argument <code class="inline">argv[0]</code> is
│ │ │  not an integer, <code class="inline">enif_get_int</code> returns false, in which case it returns by
│ │ │ @@ -209,23 +209,23 @@
│ │ │    <a href="#running-the-example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running the Example</span>
│ │ │  </h2>
│ │ │  <p><em>Step 1.</em> Compile the C code:</p><pre><code class="text">unix&gt; gcc -o complex6_nif.so -fpic -shared complex.c complex6_nif.c
│ │ │  windows&gt; cl -LD -MD -Fe complex6_nif.dll complex.c complex6_nif.c</code></pre><p><em>Step 2:</em> Start Erlang and compile the Erlang code:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="ss">erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="w"> </span><span class="n">R13B04</span><span class="w"> </span><span class="p" data-group-id="0681618950-1">(</span><span class="ss">erts</span><span class="o">-</span><span class="mf">5.7</span><span class="p">.</span><span class="mi">5</span><span class="p" data-group-id="0681618950-1">)</span><span class="w"> </span><span class="p" data-group-id="0681618950-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0681618950-2">]</span><span class="w"> </span><span class="p" data-group-id="0681618950-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="0681618950-3">]</span><span class="w"> </span><span class="p" data-group-id="0681618950-4">[</span><span class="nc">rq</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="0681618950-4">]</span><span class="w"> </span><span class="p" data-group-id="0681618950-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="0681618950-5">]</span><span class="w"> </span><span class="p" data-group-id="0681618950-6">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="0681618950-6">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="w"> </span><span class="n">R13B04</span><span class="w"> </span><span class="p" data-group-id="0212546574-1">(</span><span class="ss">erts</span><span class="o">-</span><span class="mf">5.7</span><span class="p">.</span><span class="mi">5</span><span class="p" data-group-id="0212546574-1">)</span><span class="w"> </span><span class="p" data-group-id="0212546574-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0212546574-2">]</span><span class="w"> </span><span class="p" data-group-id="0212546574-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">4</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="0212546574-3">]</span><span class="w"> </span><span class="p" data-group-id="0212546574-4">[</span><span class="nc">rq</span><span class="p">:</span><span class="mi">4</span><span class="p" data-group-id="0212546574-4">]</span><span class="w"> </span><span class="p" data-group-id="0212546574-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">0</span><span class="p" data-group-id="0212546574-5">]</span><span class="w"> </span><span class="p" data-group-id="0212546574-6">[</span><span class="ss">kernel</span><span class="o">-</span><span class="nc">poll</span><span class="p">:</span><span class="ss">false</span><span class="p" data-group-id="0212546574-6">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">7.5</span><span class="w">  </span><span class="p" data-group-id="0681618950-7">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0681618950-7">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="0681618950-8">(</span><span class="ss">complex6</span><span class="p" data-group-id="0681618950-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0681618950-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex6</span><span class="p" data-group-id="0681618950-9">}</span></code></pre><p><em>Step 3:</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="4767393669-1">(</span><span class="mi">3</span><span class="p" data-group-id="4767393669-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V5</span><span class="p">.</span><span class="mf">7.5</span><span class="w">  </span><span class="p" data-group-id="0212546574-7">(</span><span class="ss">abort</span><span class="w"> </span><span class="ss">with</span><span class="w"> </span><span class="err">^</span><span class="n">G</span><span class="p" data-group-id="0212546574-7">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nf">c</span><span class="p" data-group-id="0212546574-8">(</span><span class="ss">complex6</span><span class="p" data-group-id="0212546574-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0212546574-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">complex6</span><span class="p" data-group-id="0212546574-9">}</span></code></pre><p><em>Step 3:</em> Run the example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="5199115368-1">(</span><span class="mi">3</span><span class="p" data-group-id="5199115368-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="4767393669-2">(</span><span class="mi">5</span><span class="p" data-group-id="4767393669-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">bar</span><span class="p" data-group-id="5199115368-2">(</span><span class="mi">5</span><span class="p" data-group-id="5199115368-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="4767393669-3">(</span><span class="s">&quot;not an integer&quot;</span><span class="p" data-group-id="4767393669-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">complex6</span><span class="p">:</span><span class="nf">foo</span><span class="p" data-group-id="5199115368-3">(</span><span class="s">&quot;not an integer&quot;</span><span class="p" data-group-id="5199115368-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: bad argument
│ │ │       in function  complex6:foo/1
│ │ │          called as comlpex6:foo(&quot;not an integer&quot;)</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/opaques.html
│ │ │ @@ -122,24 +122,24 @@
│ │ │    <span class="text">Opaque Type Aliases</span>
│ │ │  </h2>
│ │ │  <p>The main use case for opacity in Erlang is to hide the implementation of a data
│ │ │  type, enabling evolving the API while minimizing the risk of breaking consumers.
│ │ │  The runtime does not check opacity. Dialyzer provides some opacity-checking, but
│ │ │  the rest is up to convention.</p><p>This document explains what Erlang opacity is (and the trade-offs involved) via
│ │ │  the example of the <a href="../../lib/stdlib-6.2.2.3/doc/html/sets.html#t:set/0"><code class="inline">sets:set()</code></a> data type. This type <em>was</em>
│ │ │ -defined in the <code class="inline">sets</code> module like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="9332406485-1">(</span><span class="n">Element</span><span class="p" data-group-id="9332406485-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="9332406485-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="9332406485-3">(</span><span class="n">Element</span><span class="p" data-group-id="9332406485-3">)</span><span class="p" data-group-id="9332406485-2">}</span><span class="p">.</span></code></pre><p>OTP 24 changed the definition to the following in
│ │ │ -<a href="https://github.com/erlang/otp/commit/e66941e8d7c47b973dff94c0308ea85a6be1958e">this commit</a>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="6286610292-1">(</span><span class="n">Element</span><span class="p" data-group-id="6286610292-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="6286610292-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="6286610292-3">(</span><span class="n">Element</span><span class="p" data-group-id="6286610292-3">)</span><span class="p" data-group-id="6286610292-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="6286610292-4">#{</span><span class="n">Element</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VALUE</span><span class="p" data-group-id="6286610292-4">}</span><span class="p">.</span></code></pre><p>And this change was safer and more backwards-compatible than if the type had
│ │ │ +defined in the <code class="inline">sets</code> module like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="8775321272-1">(</span><span class="n">Element</span><span class="p" data-group-id="8775321272-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="8775321272-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="8775321272-3">(</span><span class="n">Element</span><span class="p" data-group-id="8775321272-3">)</span><span class="p" data-group-id="8775321272-2">}</span><span class="p">.</span></code></pre><p>OTP 24 changed the definition to the following in
│ │ │ +<a href="https://github.com/erlang/otp/commit/e66941e8d7c47b973dff94c0308ea85a6be1958e">this commit</a>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">set</span><span class="p" data-group-id="5531305711-1">(</span><span class="n">Element</span><span class="p" data-group-id="5531305711-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">set</span><span class="p" data-group-id="5531305711-2">{</span><span class="ss">segs</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">segs</span><span class="p" data-group-id="5531305711-3">(</span><span class="n">Element</span><span class="p" data-group-id="5531305711-3">)</span><span class="p" data-group-id="5531305711-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="5531305711-4">#{</span><span class="n">Element</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="o">?</span><span class="n">VALUE</span><span class="p" data-group-id="5531305711-4">}</span><span class="p">.</span></code></pre><p>And this change was safer and more backwards-compatible than if the type had
│ │ │  been defined with <code class="inline">-type</code> instead of <code class="inline">-opaque</code>. Here is why: when a module
│ │ │  defines an <code class="inline">-opaque</code>, the contract is that only the defining module should rely
│ │ │  on the definition of the type: no other modules should rely on the definition.</p><p>This means that code that pattern-matched on <code class="inline">set</code> as a record/tuple technically
│ │ │  broke the contract, and opted in to being potentially broken when the definition
│ │ │  of <code class="inline">set()</code> changed. Before OTP 24, this code printed <code class="inline">ok</code>. In OTP 24 it may
│ │ │ -error:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0726678060-1">(</span><span class="p" data-group-id="0726678060-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="n">Set</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_tuple</span><span class="p" data-group-id="0726678060-2">(</span><span class="n">Set</span><span class="p" data-group-id="0726678060-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0726678060-3">(</span><span class="s">&quot;ok&quot;</span><span class="p" data-group-id="0726678060-3">)</span><span class="w">
│ │ │ +error:</p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">sets</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="0734399476-1">(</span><span class="p" data-group-id="0734399476-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="n">Set</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_tuple</span><span class="p" data-group-id="0734399476-2">(</span><span class="n">Set</span><span class="p" data-group-id="0734399476-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0734399476-3">(</span><span class="s">&quot;ok&quot;</span><span class="p" data-group-id="0734399476-3">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span></code></pre><p><strong>When working with an opaque defined in another module, here are some
│ │ │  recommendations:</strong></p><ul><li>Don't examine the underlying type using pattern-matching, guards, or functions
│ │ │  that reveal the type, such as <a href="../../erts-15.2.7.8/doc/html/erlang.html#tuple_size/1"><code class="inline">tuple_size/1</code></a> .</li><li>Instead, use functions provided by the module for working with the type. For
│ │ │  example, <code class="inline">sets</code> module provides <a href="../../lib/stdlib-6.2.2.3/doc/html/sets.html#new/0"><code class="inline">sets:new/0</code></a>, <a href="../../lib/stdlib-6.2.2.3/doc/html/sets.html#add_element/2"><code class="inline">sets:add_element/2</code></a>,
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/sets.html#is_element/2"><code class="inline">sets:is_element/2</code></a>, and so on.</li><li><p><a href="../../lib/stdlib-6.2.2.3/doc/html/sets.html#t:set/1"><code class="inline">sets:set(a)</code></a> is a subtype of <code class="inline">sets:set(a | b)</code> and not the
│ │ │  other way around. Generally, you can rely on the property that <code class="inline">the_opaque(T)</code>
│ │ │  is a subtype of <code class="inline">the_opaque(U)</code> when T is a subtype of U.</p></li></ul><p><strong>When defining your own opaques, here are some recommendations:</strong></p><ul><li>Since consumers are expected to not rely on the definition of the opaque type,
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/otp-patch-apply.html
│ │ │ @@ -201,15 +201,15 @@
│ │ │    </a>
│ │ │    <span class="text">Sanity check</span>
│ │ │  </h2>
│ │ │  <p>The application dependencies can be checked using the Erlang shell.
│ │ │  Application dependencies are verified among installed applications by
│ │ │  <code class="inline">otp_patch_apply</code>, but these are not necessarily those actually loaded.
│ │ │  By calling <code class="inline">system_information:sanity_check()</code> one can validate
│ │ │ -dependencies among applications actually loaded.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">system_information</span><span class="p">:</span><span class="nf">sanity_check</span><span class="p" data-group-id="4088193083-1">(</span><span class="p" data-group-id="4088193083-1">)</span><span class="p">.</span><span class="w">
│ │ │ +dependencies among applications actually loaded.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">system_information</span><span class="p">:</span><span class="nf">sanity_check</span><span class="p" data-group-id="3127889578-1">(</span><span class="p" data-group-id="3127889578-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>Please take a look at the reference of <a href="../../lib/runtime_tools-2.1.1/doc/html/system_information.html#sanity_check/0" title="">sanity_check()</a> for more
│ │ │  information.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/patterns.html
│ │ │ @@ -128,18 +128,18 @@
│ │ │  succeeds, any unbound variables in the pattern become bound. If the matching
│ │ │  fails, an exception is raised.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** 1:1: variable &#39;X&#39; is unbound **</span><span class="w">
│ │ │  </span><span class="gp unselectable">2&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">2</span><span class="w">
│ │ │  </span><span class="gp unselectable">3&gt; </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="0776068264-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0776068264-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0776068264-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0776068264-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="p" data-group-id="5976194636-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5976194636-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5976194636-2">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5976194636-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value {1,2}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="0776068264-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0776068264-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0776068264-4">{</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="0776068264-4">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0776068264-5">{</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0776068264-5">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="p" data-group-id="5976194636-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5976194636-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5976194636-4">{</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5976194636-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5976194636-5">{</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5976194636-5">}</span><span class="w">
│ │ │  </span><span class="gp unselectable">6&gt; </span><span class="n">Y</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/prog_ex_records.html
│ │ │ @@ -122,105 +122,105 @@
│ │ │    <span class="text">Records and Tuples</span>
│ │ │  </h2>
│ │ │  <p>The main advantage of using records rather than tuples is that fields in a
│ │ │  record are accessed by name, whereas fields in a tuple are accessed by position.
│ │ │  To illustrate these differences, suppose that you want to represent a person
│ │ │  with the tuple <code class="inline">{Name, Address, Phone}</code>.</p><p>To write functions that manipulate this data, remember the following:</p><ul><li>The <code class="inline">Name</code> field is the first element of the tuple.</li><li>The <code class="inline">Address</code> field is the second element.</li><li>The <code class="inline">Phone</code> field is the third element.</li></ul><p>For example, to extract data from a variable <code class="inline">P</code> that contains such a tuple, you
│ │ │  can write the following code and then use pattern matching to extract the
│ │ │ -relevant fields:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="6877014355-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="6877014355-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="6877014355-2">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="6877014355-2">)</span><span class="p">,</span><span class="w">
│ │ │ +relevant fields:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="7278146684-1">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="7278146684-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">element</span><span class="p" data-group-id="7278146684-2">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">P</span><span class="p" data-group-id="7278146684-2">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Such code is difficult to read and understand, and errors occur if the numbering
│ │ │  of the elements in the tuple is wrong. If the data representation of the fields
│ │ │  is changed, by re-ordering, adding, or removing fields, all references to the
│ │ │  person tuple must be checked and possibly modified.</p><p>Records allow references to the fields by name, instead of by position. In the
│ │ │ -following example, a record instead of a tuple is used to store the data:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3718113585-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3718113585-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="3718113585-2">}</span><span class="p" data-group-id="3718113585-1">)</span><span class="p">.</span></code></pre><p>This enables references to the fields of the record by name. For example, if <code class="inline">P</code>
│ │ │ +following example, a record instead of a tuple is used to store the data:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4662933828-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4662933828-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="4662933828-2">}</span><span class="p" data-group-id="4662933828-1">)</span><span class="p">.</span></code></pre><p>This enables references to the fields of the record by name. For example, if <code class="inline">P</code>
│ │ │  is a variable whose value is a <code class="inline">person</code> record, the following code access the
│ │ │  name and address fields of the records:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="n">Address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">address</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Internally, records are represented using tagged tuples:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4220443018-1">{</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p" data-group-id="4220443018-1">}</span></code></pre><h2 id="defining-a-record" class="section-heading">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Internally, records are represented using tagged tuples:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6930109456-1">{</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p" data-group-id="6930109456-1">}</span></code></pre><h2 id="defining-a-record" class="section-heading">
│ │ │    <a href="#defining-a-record" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Defining a Record</span>
│ │ │  </h2>
│ │ │  <p>This following definition of a <code class="inline">person</code> is used in several examples in this
│ │ │  section. Three fields are included, <code class="inline">name</code>, <code class="inline">phone</code>, and <code class="inline">address</code>. The default
│ │ │  values for <code class="inline">name</code> and <code class="inline">phone</code> is &quot;&quot; and [], respectively. The default value for
│ │ │  <code class="inline">address</code> is the atom <code class="inline">undefined</code>, since no default value is supplied for this
│ │ │ -field:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9313821730-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9313821730-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9313821730-3">[</span><span class="p" data-group-id="9313821730-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="9313821730-2">}</span><span class="p" data-group-id="9313821730-1">)</span><span class="p">.</span></code></pre><p>The record must be defined in the shell to enable use of the record syntax in
│ │ │ -the examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">rd</span><span class="p" data-group-id="6304135665-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6304135665-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6304135665-3">[</span><span class="p" data-group-id="6304135665-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="6304135665-2">}</span><span class="p" data-group-id="6304135665-1">)</span><span class="p">.</span><span class="w">
│ │ │ +field:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2959648862-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2959648862-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2959648862-3">[</span><span class="p" data-group-id="2959648862-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="2959648862-2">}</span><span class="p" data-group-id="2959648862-1">)</span><span class="p">.</span></code></pre><p>The record must be defined in the shell to enable use of the record syntax in
│ │ │ +the examples:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">rd</span><span class="p" data-group-id="2170166366-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2170166366-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2170166366-3">[</span><span class="p" data-group-id="2170166366-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="2170166366-2">}</span><span class="p" data-group-id="2170166366-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">person</span></code></pre><p>This is because record definitions are only available at compile time, not at
│ │ │  runtime. For details on records in the shell, see the <a href="../../lib/stdlib-6.2.2.3/doc/html/shell.html"><code class="inline">shell</code></a> manual page in
│ │ │  STDLIB.</p><h2 id="creating-a-record" class="section-heading">
│ │ │    <a href="#creating-a-record" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating a Record</span>
│ │ │  </h2>
│ │ │ -<p>A new <code class="inline">person</code> record is created as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4840685704-1">{</span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="4840685704-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4840685704-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="4840685704-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4840685704-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4840685704-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4840685704-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="4840685704-3">}</span></code></pre><p>As the <code class="inline">address</code> field was omitted, its default value is used.</p><p>From Erlang 5.1/OTP R8B, a value to all fields in a record can be set with the
│ │ │ -special field <code class="inline">_</code>. <code class="inline">_</code> means &quot;all fields not explicitly specified&quot;.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3638026397-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="3638026397-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="3638026397-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="3638026397-2">}</span></code></pre><p>It is primarily intended to be used in <a href="../../lib/stdlib-6.2.2.3/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a> and
│ │ │ +<p>A new <code class="inline">person</code> record is created as follows:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8199876457-1">{</span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="8199876457-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8199876457-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="8199876457-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8199876457-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8199876457-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8199876457-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="8199876457-3">}</span></code></pre><p>As the <code class="inline">address</code> field was omitted, its default value is used.</p><p>From Erlang 5.1/OTP R8B, a value to all fields in a record can be set with the
│ │ │ +special field <code class="inline">_</code>. <code class="inline">_</code> means &quot;all fields not explicitly specified&quot;.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0616113518-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="0616113518-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0616113518-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Jakob&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="0616113518-2">}</span></code></pre><p>It is primarily intended to be used in <a href="../../lib/stdlib-6.2.2.3/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a> and
│ │ │  <a href="../../lib/mnesia-4.23.5.2/doc/html/mnesia.html#match_object/3"><code class="inline">mnesia:match_object/3</code></a>, to set record fields to the atom <code class="inline">'_'</code>. (This is a
│ │ │  wildcard in <a href="../../lib/stdlib-6.2.2.3/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>.)</p><h2 id="accessing-a-record-field" class="section-heading">
│ │ │    <a href="#accessing-a-record-field" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Accessing a Record Field</span>
│ │ │  </h2>
│ │ │ -<p>The following example shows how to access a record field:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2291645478-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2291645478-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2291645478-2">]</span><span class="p" data-group-id="2291645478-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2291645478-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2291645478-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2291645478-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="2291645478-3">}</span><span class="w">
│ │ │ +<p>The following example shows how to access a record field:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2126423502-1">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2126423502-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2126423502-2">]</span><span class="p" data-group-id="2126423502-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2126423502-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2126423502-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2126423502-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">undefined</span><span class="p" data-group-id="2126423502-3">}</span><span class="w">
│ │ │  </span><span class="gp unselectable">&gt; </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;Joe&quot;</span></code></pre><h2 id="updating-a-record" class="section-heading">
│ │ │    <a href="#updating-a-record" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Updating a Record</span>
│ │ │  </h2>
│ │ │ -<p>The following example shows how to update a record:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5016082375-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="5016082375-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5016082375-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="5016082375-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5016082375-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5016082375-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5016082375-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="5016082375-3">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P1</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5016082375-5">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="5016082375-5">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5016082375-6">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5016082375-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5016082375-7">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="5016082375-6">}</span></code></pre><h2 id="type-testing" class="section-heading">
│ │ │ +<p>The following example shows how to update a record:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5253582713-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="5253582713-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5253582713-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="5253582713-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5253582713-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5253582713-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5253582713-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="5253582713-3">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">P2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P1</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5253582713-5">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p" data-group-id="5253582713-5">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5253582713-6">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5253582713-7">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5253582713-7">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="5253582713-6">}</span></code></pre><h2 id="type-testing" class="section-heading">
│ │ │    <a href="#type-testing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Type Testing</span>
│ │ │  </h2>
│ │ │  <p>The following example shows that the guard succeeds if <code class="inline">P</code> is record of type
│ │ │ -<code class="inline">person</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="2006954850-1">(</span><span class="n">P</span><span class="p" data-group-id="2006954850-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="2006954850-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="2006954850-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">a_person</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foo</span><span class="p" data-group-id="2006954850-3">(</span><span class="p">_</span><span class="p" data-group-id="2006954850-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">not_a_person</span><span class="p">.</span></code></pre><h2 id="pattern-matching" class="section-heading">
│ │ │ +<code class="inline">person</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foo</span><span class="p" data-group-id="6840079110-1">(</span><span class="n">P</span><span class="p" data-group-id="6840079110-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="6840079110-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="6840079110-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">a_person</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foo</span><span class="p" data-group-id="6840079110-3">(</span><span class="p">_</span><span class="p" data-group-id="6840079110-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">not_a_person</span><span class="p">.</span></code></pre><h2 id="pattern-matching" class="section-heading">
│ │ │    <a href="#pattern-matching" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Pattern Matching</span>
│ │ │  </h2>
│ │ │  <p>Matching can be used in combination with records, as shown in the following
│ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1076221174-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="1076221174-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="1076221174-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1076221174-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1076221174-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1076221174-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="1076221174-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="1076221174-3">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1076221174-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="1076221174-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P3</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">.</span><span class="w">
│ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="n">P3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7050295650-1">{</span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="p" data-group-id="7050295650-2">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7050295650-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="o">=</span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="7050295650-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7050295650-3">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7050295650-4">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="7050295650-4">]</span><span class="p">,</span><span class="ss">address</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;A street&quot;</span><span class="p" data-group-id="7050295650-3">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7050295650-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7050295650-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P3</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;Joe&quot;</span></code></pre><p>The following function takes a list of <code class="inline">person</code> records and searches for the
│ │ │ -phone number of a person with a particular name:</p><pre><code class="makeup erlang" translate="no"><span class="nf">find_phone</span><span class="p" data-group-id="7233551126-1">(</span><span class="p" data-group-id="7233551126-2">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7233551126-3">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="n">Phone</span><span class="p" data-group-id="7233551126-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7233551126-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7233551126-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7233551126-4">{</span><span class="ss">found</span><span class="p">,</span><span class="w">  </span><span class="n">Phone</span><span class="p" data-group-id="7233551126-4">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">find_phone</span><span class="p" data-group-id="7233551126-5">(</span><span class="p" data-group-id="7233551126-6">[</span><span class="p">_</span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="7233551126-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7233551126-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">find_phone</span><span class="p" data-group-id="7233551126-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7233551126-7">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">find_phone</span><span class="p" data-group-id="7233551126-8">(</span><span class="p" data-group-id="7233551126-9">[</span><span class="p" data-group-id="7233551126-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7233551126-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +phone number of a person with a particular name:</p><pre><code class="makeup erlang" translate="no"><span class="nf">find_phone</span><span class="p" data-group-id="4052110409-1">(</span><span class="p" data-group-id="4052110409-2">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4052110409-3">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="n">Phone</span><span class="p" data-group-id="4052110409-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="4052110409-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4052110409-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4052110409-4">{</span><span class="ss">found</span><span class="p">,</span><span class="w">  </span><span class="n">Phone</span><span class="p" data-group-id="4052110409-4">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">find_phone</span><span class="p" data-group-id="4052110409-5">(</span><span class="p" data-group-id="4052110409-6">[</span><span class="p">_</span><span class="p">|</span><span class="w"> </span><span class="n">T</span><span class="p" data-group-id="4052110409-6">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4052110409-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">find_phone</span><span class="p" data-group-id="4052110409-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4052110409-7">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">find_phone</span><span class="p" data-group-id="4052110409-8">(</span><span class="p" data-group-id="4052110409-9">[</span><span class="p" data-group-id="4052110409-9">]</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4052110409-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">not_found</span><span class="p">.</span></code></pre><p>The fields referred to in the pattern can be given in any order.</p><h2 id="nested-records" class="section-heading">
│ │ │    <a href="#nested-records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Nested Records</span>
│ │ │  </h2>
│ │ │  <p>The value of a field in a record can be an instance of a record. Retrieval of
│ │ │  nested data can be done stepwise, or in a single step, as shown in the following
│ │ │ -example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4456365163-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4456365163-2">{</span><span class="ss">first</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">last</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Ericsson&quot;</span><span class="p" data-group-id="4456365163-2">}</span><span class="p" data-group-id="4456365163-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4456365163-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4456365163-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="4456365163-5">{</span><span class="p" data-group-id="4456365163-5">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p" data-group-id="4456365163-4">}</span><span class="p" data-group-id="4456365163-3">)</span><span class="p">.</span><span class="w">
│ │ │ +example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0522541982-1">(</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0522541982-2">{</span><span class="ss">first</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">last</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Ericsson&quot;</span><span class="p" data-group-id="0522541982-2">}</span><span class="p" data-group-id="0522541982-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0522541982-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0522541982-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="0522541982-5">{</span><span class="p" data-group-id="0522541982-5">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p" data-group-id="0522541982-4">}</span><span class="p" data-group-id="0522541982-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">demo</span><span class="p" data-group-id="4456365163-6">(</span><span class="p" data-group-id="4456365163-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="4456365163-7">{</span><span class="ss">name</span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="4456365163-8">{</span><span class="ss">first</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">last</span><span class="o">=</span><span class="s">&quot;Virding&quot;</span><span class="p" data-group-id="4456365163-8">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="mi">123</span><span class="p" data-group-id="4456365163-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="n">First</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4456365163-9">(</span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="4456365163-9">)</span><span class="o">#</span><span class="ss">name</span><span class="p">.</span><span class="ss">first</span><span class="p">.</span></code></pre><p>Here, <code class="inline">demo()</code> evaluates to <code class="inline">&quot;Robert&quot;</code>.</p><h2 id="a-longer-example" class="section-heading">
│ │ │ +</span><span class="nf">demo</span><span class="p" data-group-id="0522541982-6">(</span><span class="p" data-group-id="0522541982-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="n">P</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0522541982-7">{</span><span class="ss">name</span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">name</span><span class="p" data-group-id="0522541982-8">{</span><span class="ss">first</span><span class="o">=</span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="ss">last</span><span class="o">=</span><span class="s">&quot;Virding&quot;</span><span class="p" data-group-id="0522541982-8">}</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="o">=</span><span class="mi">123</span><span class="p" data-group-id="0522541982-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="n">First</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0522541982-9">(</span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="0522541982-9">)</span><span class="o">#</span><span class="ss">name</span><span class="p">.</span><span class="ss">first</span><span class="p">.</span></code></pre><p>Here, <code class="inline">demo()</code> evaluates to <code class="inline">&quot;Robert&quot;</code>.</p><h2 id="a-longer-example" class="section-heading">
│ │ │    <a href="#a-longer-example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">A Longer Example</span>
│ │ │  </h2>
│ │ │  <p>Comments are embedded in the following example:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% File: person.hrl</span><span class="w">
│ │ │  
│ │ │ @@ -230,48 +230,48 @@
│ │ │  </span><span class="c1">%%    name:  A string (default is undefined).</span><span class="w">
│ │ │  </span><span class="c1">%%    age:   An integer (default is undefined).</span><span class="w">
│ │ │  </span><span class="c1">%%    phone: A list of integers (default is []).</span><span class="w">
│ │ │  </span><span class="c1">%%    dict:  A dictionary containing various information</span><span class="w">
│ │ │  </span><span class="c1">%%           about the person.</span><span class="w">
│ │ │  </span><span class="c1">%%           A {Key, Value} list (default is the empty list).</span><span class="w">
│ │ │  </span><span class="c1">%%------------------------------------------------------------</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8877857005-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8877857005-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8877857005-3">[</span><span class="p" data-group-id="8877857005-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8877857005-4">[</span><span class="p" data-group-id="8877857005-4">]</span><span class="p" data-group-id="8877857005-2">}</span><span class="p" data-group-id="8877857005-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1404029017-1">(</span><span class="ss">person</span><span class="p" data-group-id="1404029017-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1404029017-2">(</span><span class="s">&quot;person.hrl&quot;</span><span class="p" data-group-id="1404029017-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="1404029017-3">(</span><span class="ss">export_all</span><span class="p" data-group-id="1404029017-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% For test purposes only.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6673598630-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6673598630-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6673598630-3">[</span><span class="p" data-group-id="6673598630-3">]</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6673598630-4">[</span><span class="p" data-group-id="6673598630-4">]</span><span class="p" data-group-id="6673598630-2">}</span><span class="p" data-group-id="6673598630-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2600910034-1">(</span><span class="ss">person</span><span class="p" data-group-id="2600910034-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2600910034-2">(</span><span class="s">&quot;person.hrl&quot;</span><span class="p" data-group-id="2600910034-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">compile</span><span class="p" data-group-id="2600910034-3">(</span><span class="ss">export_all</span><span class="p" data-group-id="2600910034-3">)</span><span class="p">.</span><span class="w"> </span><span class="c1">% For test purposes only.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% This creates an instance of a person.</span><span class="w">
│ │ │  </span><span class="c1">%%   Note: The phone number is not supplied so the</span><span class="w">
│ │ │  </span><span class="c1">%%         default value [] will be used.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="1404029017-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="1404029017-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1404029017-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ -           </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1404029017-6">[</span><span class="p" data-group-id="1404029017-7">{</span><span class="ss">computer_knowledge</span><span class="p">,</span><span class="w"> </span><span class="ss">excellent</span><span class="p" data-group-id="1404029017-7">}</span><span class="p">,</span><span class="w">
│ │ │ -                   </span><span class="p" data-group-id="1404029017-8">{</span><span class="ss">drinks</span><span class="p">,</span><span class="w"> </span><span class="ss">coke</span><span class="p" data-group-id="1404029017-8">}</span><span class="p" data-group-id="1404029017-6">]</span><span class="p" data-group-id="1404029017-5">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="2600910034-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="2600910034-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2600910034-5">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ +           </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2600910034-6">[</span><span class="p" data-group-id="2600910034-7">{</span><span class="ss">computer_knowledge</span><span class="p">,</span><span class="w"> </span><span class="ss">excellent</span><span class="p" data-group-id="2600910034-7">}</span><span class="p">,</span><span class="w">
│ │ │ +                   </span><span class="p" data-group-id="2600910034-8">{</span><span class="ss">drinks</span><span class="p">,</span><span class="w"> </span><span class="ss">coke</span><span class="p" data-group-id="2600910034-8">}</span><span class="p" data-group-id="2600910034-6">]</span><span class="p" data-group-id="2600910034-5">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% This demonstrates matching in arguments</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">print</span><span class="p" data-group-id="1404029017-9">(</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1404029017-10">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="1404029017-10">}</span><span class="p" data-group-id="1404029017-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1404029017-11">(</span><span class="s">&quot;Name: </span><span class="si">~s</span><span class="s">, Age: </span><span class="si">~w</span><span class="s">, Phone: </span><span class="si">~w</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="w">
│ │ │ -            </span><span class="s">&quot;Dictionary: </span><span class="si">~w</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1404029017-12">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="1404029017-12">]</span><span class="p" data-group-id="1404029017-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">print</span><span class="p" data-group-id="2600910034-9">(</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2600910034-10">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="ss">dict</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="2600910034-10">}</span><span class="p" data-group-id="2600910034-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +  </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2600910034-11">(</span><span class="s">&quot;Name: </span><span class="si">~s</span><span class="s">, Age: </span><span class="si">~w</span><span class="s">, Phone: </span><span class="si">~w</span><span class="s"> </span><span class="si">~n</span><span class="s">&quot;</span><span class="w">
│ │ │ +            </span><span class="s">&quot;Dictionary: </span><span class="si">~w</span><span class="s">.</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2600910034-12">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Age</span><span class="p">,</span><span class="w"> </span><span class="n">Phone</span><span class="p">,</span><span class="w"> </span><span class="n">Dict</span><span class="p" data-group-id="2600910034-12">]</span><span class="p" data-group-id="2600910034-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Demonstrates type testing, selector, updating.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">birthday</span><span class="p" data-group-id="1404029017-13">(</span><span class="n">P</span><span class="p" data-group-id="1404029017-13">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="1404029017-14">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="1404029017-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1404029017-15">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1404029017-15">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">birthday</span><span class="p" data-group-id="2600910034-13">(</span><span class="n">P</span><span class="p" data-group-id="2600910034-13">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="2600910034-14">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="2600910034-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2600910034-15">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">P</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2600910034-15">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">register_two_hackers</span><span class="p" data-group-id="1404029017-16">(</span><span class="p" data-group-id="1404029017-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="n">Hacker1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="1404029017-17">(</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">29</span><span class="p" data-group-id="1404029017-17">)</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="n">OldHacker</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">birthday</span><span class="p" data-group-id="1404029017-18">(</span><span class="n">Hacker1</span><span class="p" data-group-id="1404029017-18">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">register_two_hackers</span><span class="p" data-group-id="2600910034-16">(</span><span class="p" data-group-id="2600910034-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="n">Hacker1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_hacker_without_phone</span><span class="p" data-group-id="2600910034-17">(</span><span class="s">&quot;Joe&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">29</span><span class="p" data-group-id="2600910034-17">)</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="n">OldHacker</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">birthday</span><span class="p" data-group-id="2600910034-18">(</span><span class="n">Hacker1</span><span class="p" data-group-id="2600910034-18">)</span><span class="p">,</span><span class="w">
│ │ │     </span><span class="c1">% The central_register_server should have</span><span class="w">
│ │ │     </span><span class="c1">% an interface function for this.</span><span class="w">
│ │ │ -   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1404029017-19">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w"> </span><span class="n">Hacker1</span><span class="p" data-group-id="1404029017-19">}</span><span class="p">,</span><span class="w">
│ │ │ -   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1404029017-20">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="n">OldHacker</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="1404029017-21">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w">
│ │ │ -                              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1404029017-22">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1404029017-22">]</span><span class="p" data-group-id="1404029017-21">}</span><span class="p" data-group-id="1404029017-20">}</span><span class="p">.</span></code></pre>
│ │ │ +   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2600910034-19">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w"> </span><span class="n">Hacker1</span><span class="p" data-group-id="2600910034-19">}</span><span class="p">,</span><span class="w">
│ │ │ +   </span><span class="ss">central_register_server</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2600910034-20">{</span><span class="ss">register_person</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="n">OldHacker</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2600910034-21">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;Robert&quot;</span><span class="p">,</span><span class="w">
│ │ │ +                              </span><span class="ss">phone</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2600910034-22">[</span><span class="mi">0</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="2600910034-22">]</span><span class="p" data-group-id="2600910034-21">}</span><span class="p" data-group-id="2600910034-20">}</span><span class="p">.</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="programming_examples.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/records_macros.html
│ │ │ @@ -124,40 +124,40 @@
│ │ │  </h2>
│ │ │  <p>To illustrate this, the messenger example from the previous section is divided
│ │ │  into the following five files:</p><ul><li><p><code class="inline">mess_config.hrl</code></p><p>Header file for configuration data</p></li><li><p><code class="inline">mess_interface.hrl</code></p><p>Interface definitions between the client and the messenger</p></li><li><p><code class="inline">user_interface.erl</code></p><p>Functions for the user interface</p></li><li><p><code class="inline">mess_client.erl</code></p><p>Functions for the client side of the messenger</p></li><li><p><code class="inline">mess_server.erl</code></p><p>Functions for the server side of the messenger</p></li></ul><p>While doing this, the message passing interface between the shell, the client,
│ │ │  and the server is cleaned up and is defined using <em>records</em>. Also, <em>macros</em> are
│ │ │  introduced:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_config.hrl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Configure the location of the server node,</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1085945513-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="1085945513-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5527521076-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="5527521076-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_interface.hrl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Message interface between client and server and client shell for</span><span class="w">
│ │ │  </span><span class="c1">%%% messenger program</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%Messages from Client to server received in server/1 function.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9068479358-1">(</span><span class="ss">logon</span><span class="p">,</span><span class="p" data-group-id="9068479358-2">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="p" data-group-id="9068479358-2">}</span><span class="p" data-group-id="9068479358-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9068479358-3">(</span><span class="ss">message</span><span class="p">,</span><span class="p" data-group-id="9068479358-4">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="9068479358-4">}</span><span class="p" data-group-id="9068479358-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0281689161-1">(</span><span class="ss">logon</span><span class="p">,</span><span class="p" data-group-id="0281689161-2">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="p" data-group-id="0281689161-2">}</span><span class="p" data-group-id="0281689161-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0281689161-3">(</span><span class="ss">message</span><span class="p">,</span><span class="p" data-group-id="0281689161-4">{</span><span class="ss">client_pid</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="0281689161-4">}</span><span class="p" data-group-id="0281689161-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% {&#39;EXIT&#39;, ClientPid, Reason}  (client terminated or unreachable.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Messages from Server to Client, received in await_result/0 function</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9068479358-5">(</span><span class="ss">abort_client</span><span class="p">,</span><span class="p" data-group-id="9068479358-6">{</span><span class="ss">message</span><span class="p" data-group-id="9068479358-6">}</span><span class="p" data-group-id="9068479358-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0281689161-5">(</span><span class="ss">abort_client</span><span class="p">,</span><span class="p" data-group-id="0281689161-6">{</span><span class="ss">message</span><span class="p" data-group-id="0281689161-6">}</span><span class="p" data-group-id="0281689161-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% Messages are: user_exists_at_other_node,</span><span class="w">
│ │ │  </span><span class="c1">%%%               you_are_not_logged_on</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9068479358-7">(</span><span class="ss">server_reply</span><span class="p">,</span><span class="p" data-group-id="9068479358-8">{</span><span class="ss">message</span><span class="p" data-group-id="9068479358-8">}</span><span class="p" data-group-id="9068479358-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0281689161-7">(</span><span class="ss">server_reply</span><span class="p">,</span><span class="p" data-group-id="0281689161-8">{</span><span class="ss">message</span><span class="p" data-group-id="0281689161-8">}</span><span class="p" data-group-id="0281689161-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% Messages are: logged_on</span><span class="w">
│ │ │  </span><span class="c1">%%%               receiver_not_found</span><span class="w">
│ │ │  </span><span class="c1">%%%               sent  (Message has been sent (no guarantee)</span><span class="w">
│ │ │  </span><span class="c1">%%% Messages from Server to Client received in client/1 function</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9068479358-9">(</span><span class="ss">message_from</span><span class="p">,</span><span class="p" data-group-id="9068479358-10">{</span><span class="ss">from_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="9068479358-10">}</span><span class="p" data-group-id="9068479358-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0281689161-9">(</span><span class="ss">message_from</span><span class="p">,</span><span class="p" data-group-id="0281689161-10">{</span><span class="ss">from_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="0281689161-10">}</span><span class="p" data-group-id="0281689161-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Messages from shell to Client received in client/1 function</span><span class="w">
│ │ │  </span><span class="c1">%%% spawn(mess_client, client, [server_node(), Name])</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9068479358-11">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="9068479358-12">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="9068479358-12">}</span><span class="p" data-group-id="9068479358-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0281689161-11">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="0281689161-12">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="0281689161-12">}</span><span class="p" data-group-id="0281689161-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% logoff</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE user_interface.erl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% User interface to the messenger program</span><span class="w">
│ │ │  </span><span class="c1">%%% login(Name)</span><span class="w">
│ │ │  </span><span class="c1">%%%     One user at a time can log in from each Erlang node in the</span><span class="w">
│ │ │ @@ -170,177 +170,177 @@
│ │ │  </span><span class="c1">%%%     Logs off anybody at that node</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% message(ToName, Message)</span><span class="w">
│ │ │  </span><span class="c1">%%%     sends Message to ToName. Error messages if the user of this</span><span class="w">
│ │ │  </span><span class="c1">%%%     function is not logged on or if ToName is not logged on at</span><span class="w">
│ │ │  </span><span class="c1">%%%     any node.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2101644477-1">(</span><span class="ss">user_interface</span><span class="p" data-group-id="2101644477-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2101644477-2">(</span><span class="p" data-group-id="2101644477-3">[</span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2101644477-3">]</span><span class="p" data-group-id="2101644477-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2101644477-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="2101644477-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2101644477-5">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="2101644477-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1210047894-1">(</span><span class="ss">user_interface</span><span class="p" data-group-id="1210047894-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1210047894-2">(</span><span class="p" data-group-id="1210047894-3">[</span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1210047894-3">]</span><span class="p" data-group-id="1210047894-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1210047894-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="1210047894-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1210047894-5">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="1210047894-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="2101644477-6">(</span><span class="n">Name</span><span class="p" data-group-id="2101644477-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="2101644477-7">(</span><span class="ss">mess_client</span><span class="p" data-group-id="2101644477-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="1210047894-6">(</span><span class="n">Name</span><span class="p" data-group-id="1210047894-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="1210047894-7">(</span><span class="ss">mess_client</span><span class="p" data-group-id="1210047894-7">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="2101644477-8">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="2101644477-9">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2101644477-10">[</span><span class="o">?</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2101644477-10">]</span><span class="p" data-group-id="2101644477-9">)</span><span class="p" data-group-id="2101644477-8">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="1210047894-8">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="1210047894-9">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1210047894-10">[</span><span class="o">?</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="1210047894-10">]</span><span class="p" data-group-id="1210047894-9">)</span><span class="p" data-group-id="1210047894-8">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="2101644477-11">(</span><span class="p" data-group-id="2101644477-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="1210047894-11">(</span><span class="p" data-group-id="1210047894-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="2101644477-12">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2101644477-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="2101644477-13">(</span><span class="ss">mess_client</span><span class="p" data-group-id="2101644477-13">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="1210047894-12">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="1210047894-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="1210047894-13">(</span><span class="ss">mess_client</span><span class="p" data-group-id="1210047894-13">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="2101644477-14">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="2101644477-14">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="1210047894-14">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="1210047894-14">}</span><span class="p">,</span><span class="w">
│ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE----</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_client.erl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% The client process which runs on each user node</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5752086689-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="5752086689-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5752086689-2">(</span><span class="p" data-group-id="5752086689-3">[</span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5752086689-3">]</span><span class="p" data-group-id="5752086689-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="5752086689-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="5752086689-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="5752086689-5">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="5752086689-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5752086689-6">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="5752086689-6">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="5752086689-7">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="5752086689-8">(</span><span class="p" data-group-id="5752086689-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="5752086689-7">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="5752086689-9">(</span><span class="p" data-group-id="5752086689-9">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="5752086689-10">(</span><span class="n">Server_Node</span><span class="p" data-group-id="5752086689-10">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9465675514-1">(</span><span class="ss">mess_client</span><span class="p" data-group-id="9465675514-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9465675514-2">(</span><span class="p" data-group-id="9465675514-3">[</span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9465675514-3">]</span><span class="p" data-group-id="9465675514-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="9465675514-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="9465675514-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="9465675514-5">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9465675514-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9465675514-6">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="9465675514-6">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="9465675514-7">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="9465675514-8">(</span><span class="p" data-group-id="9465675514-8">)</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="9465675514-7">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="9465675514-9">(</span><span class="p" data-group-id="9465675514-9">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="9465675514-10">(</span><span class="n">Server_Node</span><span class="p" data-group-id="9465675514-10">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="5752086689-11">(</span><span class="n">Server_Node</span><span class="p" data-group-id="5752086689-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="9465675514-11">(</span><span class="n">Server_Node</span><span class="p" data-group-id="9465675514-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="5752086689-12">(</span><span class="ss">normal</span><span class="p" data-group-id="5752086689-12">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="5752086689-13">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="5752086689-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="5752086689-14">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="5752086689-14">}</span><span class="w"> </span><span class="o">!</span><span class="w">
│ │ │ -                </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="5752086689-15">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="5752086689-16">(</span><span class="p" data-group-id="5752086689-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="5752086689-15">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="5752086689-17">(</span><span class="p" data-group-id="5752086689-17">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5752086689-18">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5752086689-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5752086689-19">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5752086689-20">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5752086689-20">]</span><span class="p" data-group-id="5752086689-19">)</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="9465675514-12">(</span><span class="ss">normal</span><span class="p" data-group-id="9465675514-12">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="9465675514-13">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="9465675514-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="9465675514-14">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="9465675514-14">}</span><span class="w"> </span><span class="o">!</span><span class="w">
│ │ │ +                </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="9465675514-15">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="nf">self</span><span class="p" data-group-id="9465675514-16">(</span><span class="p" data-group-id="9465675514-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="9465675514-15">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="9465675514-17">(</span><span class="p" data-group-id="9465675514-17">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="9465675514-18">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9465675514-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9465675514-19">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9465675514-20">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9465675514-20">]</span><span class="p" data-group-id="9465675514-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="5752086689-21">(</span><span class="n">Server_Node</span><span class="p" data-group-id="5752086689-21">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="9465675514-21">(</span><span class="n">Server_Node</span><span class="p" data-group-id="9465675514-21">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="5752086689-22">(</span><span class="p" data-group-id="5752086689-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="9465675514-22">(</span><span class="p" data-group-id="9465675514-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="5752086689-23">{</span><span class="ss">message</span><span class="o">=</span><span class="n">Why</span><span class="p" data-group-id="5752086689-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5752086689-24">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5752086689-25">[</span><span class="n">Why</span><span class="p" data-group-id="5752086689-25">]</span><span class="p" data-group-id="5752086689-24">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="5752086689-26">(</span><span class="ss">normal</span><span class="p" data-group-id="5752086689-26">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="5752086689-27">{</span><span class="ss">message</span><span class="o">=</span><span class="n">What</span><span class="p" data-group-id="5752086689-27">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5752086689-28">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5752086689-29">[</span><span class="n">What</span><span class="p" data-group-id="5752086689-29">]</span><span class="p" data-group-id="5752086689-28">)</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="9465675514-23">{</span><span class="ss">message</span><span class="o">=</span><span class="n">Why</span><span class="p" data-group-id="9465675514-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9465675514-24">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9465675514-25">[</span><span class="n">Why</span><span class="p" data-group-id="9465675514-25">]</span><span class="p" data-group-id="9465675514-24">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="9465675514-26">(</span><span class="ss">normal</span><span class="p" data-group-id="9465675514-26">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9465675514-27">{</span><span class="ss">message</span><span class="o">=</span><span class="n">What</span><span class="p" data-group-id="9465675514-27">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9465675514-28">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9465675514-29">[</span><span class="n">What</span><span class="p" data-group-id="9465675514-29">]</span><span class="p" data-group-id="9465675514-28">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="5752086689-30">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5752086689-31">[</span><span class="p" data-group-id="5752086689-31">]</span><span class="p" data-group-id="5752086689-30">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="5752086689-32">(</span><span class="ss">timeout</span><span class="p" data-group-id="5752086689-32">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9465675514-30">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9465675514-31">[</span><span class="p" data-group-id="9465675514-31">]</span><span class="p" data-group-id="9465675514-30">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="9465675514-32">(</span><span class="ss">timeout</span><span class="p" data-group-id="9465675514-32">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE---</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%%----FILE mess_server.erl----</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% This is the server process of the messenger service</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9236381368-1">(</span><span class="ss">mess_server</span><span class="p" data-group-id="9236381368-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9236381368-2">(</span><span class="p" data-group-id="9236381368-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="9236381368-3">]</span><span class="p" data-group-id="9236381368-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="9236381368-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="9236381368-4">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9236381368-5">(</span><span class="p" data-group-id="9236381368-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9236381368-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9236381368-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="9236381368-7">(</span><span class="p" data-group-id="9236381368-8">[</span><span class="p" data-group-id="9236381368-8">]</span><span class="p" data-group-id="9236381368-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2119733911-1">(</span><span class="ss">mess_server</span><span class="p" data-group-id="2119733911-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2119733911-2">(</span><span class="p" data-group-id="2119733911-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2119733911-3">]</span><span class="p" data-group-id="2119733911-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="2119733911-4">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="2119733911-4">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="2119733911-5">(</span><span class="p" data-group-id="2119733911-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="2119733911-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2119733911-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="2119733911-7">(</span><span class="p" data-group-id="2119733911-8">[</span><span class="p" data-group-id="2119733911-8">]</span><span class="p" data-group-id="2119733911-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9236381368-9">(</span><span class="n">User_List</span><span class="p" data-group-id="9236381368-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9236381368-10">(</span><span class="s">&quot;User list = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9236381368-11">[</span><span class="n">User_List</span><span class="p" data-group-id="9236381368-11">]</span><span class="p" data-group-id="9236381368-10">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="2119733911-9">(</span><span class="n">User_List</span><span class="p" data-group-id="2119733911-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2119733911-10">(</span><span class="s">&quot;User list = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2119733911-11">[</span><span class="n">User_List</span><span class="p" data-group-id="2119733911-11">]</span><span class="p" data-group-id="2119733911-10">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="9236381368-12">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="9236381368-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="9236381368-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-13">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9236381368-14">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9236381368-14">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9236381368-15">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9236381368-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="9236381368-16">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-16">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9236381368-17">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9236381368-17">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="9236381368-18">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="9236381368-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9236381368-19">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-19">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9236381368-20">(</span><span class="n">User_List</span><span class="p" data-group-id="9236381368-20">)</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">logon</span><span class="p" data-group-id="2119733911-12">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">username</span><span class="o">=</span><span class="n">Name</span><span class="p" data-group-id="2119733911-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="2119733911-13">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-13">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="2119733911-14">(</span><span class="n">New_User_List</span><span class="p" data-group-id="2119733911-14">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2119733911-15">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2119733911-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="2119733911-16">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-16">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="2119733911-17">(</span><span class="n">New_User_List</span><span class="p" data-group-id="2119733911-17">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="o">#</span><span class="ss">message</span><span class="p" data-group-id="2119733911-18">{</span><span class="ss">client_pid</span><span class="o">=</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="2119733911-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="2119733911-19">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-19">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="2119733911-20">(</span><span class="n">User_List</span><span class="p" data-group-id="2119733911-20">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="9236381368-21">(</span><span class="p" data-group-id="9236381368-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9236381368-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9236381368-23">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9236381368-24">[</span><span class="p" data-group-id="9236381368-24">]</span><span class="p" data-group-id="9236381368-23">)</span><span class="p" data-group-id="9236381368-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="2119733911-21">(</span><span class="p" data-group-id="2119733911-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="2119733911-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2119733911-23">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2119733911-24">[</span><span class="p" data-group-id="2119733911-24">]</span><span class="p" data-group-id="2119733911-23">)</span><span class="p" data-group-id="2119733911-22">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="9236381368-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="2119733911-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="9236381368-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="2119733911-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="9236381368-27">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="9236381368-27">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="2119733911-27">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="2119733911-27">}</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9236381368-28">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">logged_on</span><span class="p" data-group-id="9236381368-28">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">link</span><span class="p" data-group-id="9236381368-29">(</span><span class="n">From</span><span class="p" data-group-id="9236381368-29">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9236381368-30">[</span><span class="p" data-group-id="9236381368-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9236381368-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="2119733911-28">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">logged_on</span><span class="p" data-group-id="2119733911-28">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">link</span><span class="p" data-group-id="2119733911-29">(</span><span class="n">From</span><span class="p" data-group-id="2119733911-29">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2119733911-30">[</span><span class="p" data-group-id="2119733911-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2119733911-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="9236381368-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="9236381368-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-33">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="2119733911-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="2119733911-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-33">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9236381368-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="2119733911-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9236381368-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="2119733911-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="9236381368-36">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="9236381368-36">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9236381368-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9236381368-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9236381368-38">}</span><span class="p" data-group-id="9236381368-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9236381368-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-39">)</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">abort_client</span><span class="p" data-group-id="2119733911-36">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="2119733911-36">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2119733911-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2119733911-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2119733911-38">}</span><span class="p" data-group-id="2119733911-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="2119733911-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-39">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9236381368-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="2119733911-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9236381368-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9236381368-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="2119733911-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2119733911-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9236381368-42">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">receiver_not_found</span><span class="p" data-group-id="9236381368-42">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9236381368-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9236381368-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="9236381368-44">}</span><span class="p" data-group-id="9236381368-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_from</span><span class="p" data-group-id="9236381368-45">{</span><span class="ss">from_name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="9236381368-45">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="9236381368-46">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">sent</span><span class="p" data-group-id="9236381368-46">}</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="2119733911-42">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">receiver_not_found</span><span class="p" data-group-id="2119733911-42">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2119733911-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2119733911-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="2119733911-44">}</span><span class="p" data-group-id="2119733911-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="o">#</span><span class="ss">message_from</span><span class="p" data-group-id="2119733911-45">{</span><span class="ss">from_name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="2119733911-45">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w">  </span><span class="o">#</span><span class="ss">server_reply</span><span class="p" data-group-id="2119733911-46">{</span><span class="ss">message</span><span class="o">=</span><span class="ss">sent</span><span class="p" data-group-id="2119733911-46">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%%----END FILE---</span></code></pre><h2 id="header-files" class="section-heading">
│ │ │    <a href="#header-files" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Header Files</span>
│ │ │  </h2>
│ │ │  <p>As shown above, some files have extension <code class="inline">.hrl</code>. These are header files that
│ │ │ -are included in the <code class="inline">.erl</code> files by:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="7588935882-1">(</span><span class="s">&quot;File_Name&quot;</span><span class="p" data-group-id="7588935882-1">)</span><span class="p">.</span></code></pre><p>for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="1129505959-1">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="1129505959-1">)</span><span class="p">.</span></code></pre><p>In the case above the file is fetched from the same directory as all the other
│ │ │ +are included in the <code class="inline">.erl</code> files by:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4125971258-1">(</span><span class="s">&quot;File_Name&quot;</span><span class="p" data-group-id="4125971258-1">)</span><span class="p">.</span></code></pre><p>for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="7103749941-1">(</span><span class="s">&quot;mess_interface.hrl&quot;</span><span class="p" data-group-id="7103749941-1">)</span><span class="p">.</span></code></pre><p>In the case above the file is fetched from the same directory as all the other
│ │ │  files in the messenger example. (<em>manual</em>).</p><p>.hrl files can contain any valid Erlang code but are most often used for record
│ │ │  and macro definitions.</p><h2 id="records" class="section-heading">
│ │ │    <a href="#records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Records</span>
│ │ │  </h2>
│ │ │ -<p>A record is defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8186738808-1">(</span><span class="ss">name_of_record</span><span class="p">,</span><span class="p" data-group-id="8186738808-2">{</span><span class="ss">field_name1</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name2</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8186738808-2">}</span><span class="p" data-group-id="8186738808-1">)</span><span class="p">.</span></code></pre><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9331667049-1">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="9331667049-2">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="9331667049-2">}</span><span class="p" data-group-id="9331667049-1">)</span><span class="p">.</span></code></pre><p>This is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5438940835-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To_Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="5438940835-1">}</span></code></pre><p>Creating a record is best illustrated by an example:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="6256189663-1">{</span><span class="ss">message</span><span class="o">=</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="ss">fred</span><span class="p">)</span></code></pre><p>This creates:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7209062348-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="7209062348-1">}</span></code></pre><p>Notice that you do not have to worry about the order you assign values to the
│ │ │ +<p>A record is defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2847084433-1">(</span><span class="ss">name_of_record</span><span class="p">,</span><span class="p" data-group-id="2847084433-2">{</span><span class="ss">field_name1</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name2</span><span class="p">,</span><span class="w"> </span><span class="ss">field_name3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="2847084433-2">}</span><span class="p" data-group-id="2847084433-1">)</span><span class="p">.</span></code></pre><p>For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1024563130-1">(</span><span class="ss">message_to</span><span class="p">,</span><span class="p" data-group-id="1024563130-2">{</span><span class="ss">to_name</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p" data-group-id="1024563130-2">}</span><span class="p" data-group-id="1024563130-1">)</span><span class="p">.</span></code></pre><p>This is equivalent to:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7070781216-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To_Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="7070781216-1">}</span></code></pre><p>Creating a record is best illustrated by an example:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="2557146609-1">{</span><span class="ss">message</span><span class="o">=</span><span class="s">&quot;hello&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">to_name</span><span class="o">=</span><span class="ss">fred</span><span class="p">)</span></code></pre><p>This creates:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4397078589-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="ss">fred</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="4397078589-1">}</span></code></pre><p>Notice that you do not have to worry about the order you assign values to the
│ │ │  various parts of the records when you create it. The advantage of using records
│ │ │  is that by placing their definitions in header files you can conveniently define
│ │ │  interfaces that are easy to change. For example, if you want to add a new field
│ │ │  to the record, you only have to change the code where the new field is used and
│ │ │  not at every place the record is referred to. If you leave out a field when
│ │ │  creating a record, it gets the value of the atom <code class="inline">undefined</code>. (<em>manual</em>)</p><p>Pattern matching with records is very similar to creating records. For example,
│ │ │ -inside a <code class="inline">case</code> or <code class="inline">receive</code>:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="1887688280-1">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="1887688280-1">}</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>This is the same as:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4477549207-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="4477549207-1">}</span></code></pre><h2 id="macros" class="section-heading">
│ │ │ +inside a <code class="inline">case</code> or <code class="inline">receive</code>:</p><pre><code class="makeup erlang" translate="no"><span class="o">#</span><span class="ss">message_to</span><span class="p" data-group-id="3081563231-1">{</span><span class="ss">to_name</span><span class="o">=</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="o">=</span><span class="n">Message</span><span class="p" data-group-id="3081563231-1">}</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>This is the same as:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2619048038-1">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2619048038-1">}</span></code></pre><h2 id="macros" class="section-heading">
│ │ │    <a href="#macros" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Macros</span>
│ │ │  </h2>
│ │ │  <p>Another thing that has been added to the messenger is a macro. The file
│ │ │  <code class="inline">mess_config.hrl</code> contains the definition:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Configure the location of the server node,</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1839744666-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="1839744666-1">)</span><span class="p">.</span></code></pre><p>This file is included in <code class="inline">mess_server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="7770229922-1">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="7770229922-1">)</span><span class="p">.</span></code></pre><p>Every occurrence of <code class="inline">?server_node</code> in <code class="inline">mess_server.erl</code> is now replaced by
│ │ │ -<code class="inline">messenger@super</code>.</p><p>A macro is also used when spawning the server process:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="3840797983-1">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3840797983-2">[</span><span class="p" data-group-id="3840797983-2">]</span><span class="p" data-group-id="3840797983-1">)</span></code></pre><p>This is a standard macro (that is, defined by the system, not by the user).
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9094035015-1">(</span><span class="ss">server_node</span><span class="p">,</span><span class="w"> </span><span class="ss">messenger@super</span><span class="p" data-group-id="9094035015-1">)</span><span class="p">.</span></code></pre><p>This file is included in <code class="inline">mess_server.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">include</span><span class="p" data-group-id="4113633451-1">(</span><span class="s">&quot;mess_config.hrl&quot;</span><span class="p" data-group-id="4113633451-1">)</span><span class="p">.</span></code></pre><p>Every occurrence of <code class="inline">?server_node</code> in <code class="inline">mess_server.erl</code> is now replaced by
│ │ │ +<code class="inline">messenger@super</code>.</p><p>A macro is also used when spawning the server process:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="1581125088-1">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1581125088-2">[</span><span class="p" data-group-id="1581125088-2">]</span><span class="p" data-group-id="1581125088-1">)</span></code></pre><p>This is a standard macro (that is, defined by the system, not by the user).
│ │ │  <code class="inline">?MODULE</code> is always replaced by the name of the current module (that is, the
│ │ │  <code class="inline">-module</code> definition near the start of the file). There are more advanced ways
│ │ │  of using macros with, for example, <a href="macros.html#defining-and-using-macros">parameters</a>.</p><p>The three Erlang (<code class="inline">.erl</code>) files in the messenger example are individually
│ │ │  compiled into object code file (<code class="inline">.beam</code>). The Erlang system loads and links
│ │ │  these files into the system when they are referred to during execution of the
│ │ │  code. In this case, they are simply put in our current working directory (that
│ │ │  is, the place you have done &quot;cd&quot; to). There are ways of putting the <code class="inline">.beam</code>
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/ref_man_functions.html
│ │ │ @@ -120,51 +120,51 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Function Declaration Syntax</span>
│ │ │  </h2>
│ │ │  <p>A <em>function declaration</em> is a sequence of function clauses separated by
│ │ │  semicolons, and terminated by a period (<code class="inline">.</code>).</p><p>A <em>function clause</em> consists of a <em>clause head</em> and a <em>clause body</em>, separated by
│ │ │  <code class="inline">-&gt;</code>.</p><p>A clause <em>head</em> consists of the function name, an argument list, and an optional
│ │ │ -guard sequence beginning with the keyword <code class="inline">when</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="p" data-group-id="4500442904-1">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="4500442904-1">)</span><span class="w"> </span><span class="p" data-group-id="4500442904-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="4500442904-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +guard sequence beginning with the keyword <code class="inline">when</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">Name</span><span class="p" data-group-id="0966592188-1">(</span><span class="n">Pattern11</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">Pattern1N</span><span class="p" data-group-id="0966592188-1">)</span><span class="w"> </span><span class="p" data-group-id="0966592188-2">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeq1</span><span class="p" data-group-id="0966592188-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Body1</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">Name</span><span class="p" data-group-id="4500442904-3">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="4500442904-3">)</span><span class="w"> </span><span class="p" data-group-id="4500442904-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="4500442904-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="n">Name</span><span class="p" data-group-id="0966592188-3">(</span><span class="n">PatternK1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">PatternKN</span><span class="p" data-group-id="0966592188-3">)</span><span class="w"> </span><span class="p" data-group-id="0966592188-4">[</span><span class="k">when</span><span class="w"> </span><span class="n">GuardSeqK</span><span class="p" data-group-id="0966592188-4">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">BodyK</span><span class="p">.</span></code></pre><p>The function name is an atom. Each argument is a pattern.</p><p>The number of arguments <code class="inline">N</code> is the <em>arity</em> of the function. A function is
│ │ │  uniquely defined by the module name, function name, and arity. That is, two
│ │ │  functions with the same name and in the same module, but with different arities
│ │ │  are two different functions.</p><p>A function named <code class="inline">f</code> in module <code class="inline">mod</code> and with arity <code class="inline">N</code> is often denoted as
│ │ │  <code class="inline">mod:f/N</code>.</p><p>A clause <em>body</em> consists of a sequence of expressions separated by comma (<code class="inline">,</code>):</p><pre><code class="text">Expr1,
│ │ │  ...,
│ │ │  ExprN</code></pre><p>Valid Erlang expressions and guard sequences are described in
│ │ │ -<a href="expressions.html">Expressions</a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">fact</span><span class="p" data-group-id="6185508754-1">(</span><span class="n">N</span><span class="p" data-group-id="6185508754-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% first clause head</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="6185508754-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="6185508754-2">)</span><span class="p">;</span><span class="w">     </span><span class="c1">% first clause body</span><span class="w">
│ │ │ +<a href="expressions.html">Expressions</a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">fact</span><span class="p" data-group-id="8993865971-1">(</span><span class="n">N</span><span class="p" data-group-id="8993865971-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% first clause head</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="8993865971-2">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="8993865971-2">)</span><span class="p">;</span><span class="w">     </span><span class="c1">% first clause body</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="6185508754-3">(</span><span class="mi">0</span><span class="p" data-group-id="6185508754-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">             </span><span class="c1">% second clause head</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="8993865971-3">(</span><span class="mi">0</span><span class="p" data-group-id="8993865971-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">             </span><span class="c1">% second clause head</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">.</span><span class="w">                 </span><span class="c1">% second clause body</span></code></pre><p><a href="" id="eval"></a></p><h2 id="function-evaluation" class="section-heading">
│ │ │    <a href="#function-evaluation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Function Evaluation</span>
│ │ │  </h2>
│ │ │  <p>When a function <code class="inline">M:F/N</code> is called, first the code for the function is located.
│ │ │  If the function cannot be found, an <code class="inline">undef</code> runtime error occurs. Notice that
│ │ │  the function must be exported to be visible outside the module it is defined in.</p><p>If the function is found, the function clauses are scanned sequentially until a
│ │ │  clause is found that fulfills both of the following two conditions:</p><ol><li>The patterns in the clause head can be successfully matched against the given
│ │ │  arguments.</li><li>The guard sequence, if any, is true.</li></ol><p>If such a clause cannot be found, a <code class="inline">function_clause</code> runtime error occurs.</p><p>If such a clause is found, the corresponding clause body is evaluated. That is,
│ │ │  the expressions in the body are evaluated sequentially and the value of the last
│ │ │ -expression is returned.</p><p>Consider the function <code class="inline">fact</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0722355748-1">(</span><span class="ss">mod</span><span class="p" data-group-id="0722355748-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0722355748-2">(</span><span class="p" data-group-id="0722355748-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0722355748-3">]</span><span class="p" data-group-id="0722355748-2">)</span><span class="p">.</span><span class="w">
│ │ │ +expression is returned.</p><p>Consider the function <code class="inline">fact</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2762096711-1">(</span><span class="ss">mod</span><span class="p" data-group-id="2762096711-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2762096711-2">(</span><span class="p" data-group-id="2762096711-3">[</span><span class="ss">fact</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2762096711-3">]</span><span class="p" data-group-id="2762096711-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="0722355748-4">(</span><span class="n">N</span><span class="p" data-group-id="0722355748-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="0722355748-5">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0722355748-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">fact</span><span class="p" data-group-id="0722355748-6">(</span><span class="mi">0</span><span class="p" data-group-id="0722355748-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="2762096711-4">(</span><span class="n">N</span><span class="p" data-group-id="2762096711-4">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="2762096711-5">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2762096711-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">fact</span><span class="p" data-group-id="2762096711-6">(</span><span class="mi">0</span><span class="p" data-group-id="2762096711-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">.</span></code></pre><p>Assume that you want to calculate the factorial for 1:</p><pre><code class="text">1&gt; mod:fact(1).</code></pre><p>Evaluation starts at the first clause. The pattern <code class="inline">N</code> is matched against
│ │ │  argument 1. The matching succeeds and the guard (<code class="inline">N &gt; 0</code>) is true, thus <code class="inline">N</code> is
│ │ │ -bound to 1, and the corresponding body is evaluated:</p><pre><code class="makeup erlang" translate="no"><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="7609933643-1">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="7609933643-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7609933643-2">(</span><span class="n">N</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">bound</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="7609933643-2">)</span><span class="w">
│ │ │ -</span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="7609933643-3">(</span><span class="mi">0</span><span class="p" data-group-id="7609933643-3">)</span></code></pre><p>Now, <code class="inline">fact(0)</code> is called, and the function clauses are scanned
│ │ │ +bound to 1, and the corresponding body is evaluated:</p><pre><code class="makeup erlang" translate="no"><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="5160427698-1">(</span><span class="n">N</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5160427698-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5160427698-2">(</span><span class="n">N</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">bound</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5160427698-2">)</span><span class="w">
│ │ │ +</span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fact</span><span class="p" data-group-id="5160427698-3">(</span><span class="mi">0</span><span class="p" data-group-id="5160427698-3">)</span></code></pre><p>Now, <code class="inline">fact(0)</code> is called, and the function clauses are scanned
│ │ │  sequentially again. First, the pattern <code class="inline">N</code> is matched against 0. The
│ │ │  matching succeeds, but the guard (<code class="inline">N &gt; 0</code>) is false. Second, the
│ │ │  pattern <code class="inline">0</code> is matched against the argument <code class="inline">0</code>. The matching succeeds
│ │ │  and the body is evaluated:</p><pre><code class="text">1 * fact(0) =&gt;
│ │ │  1 * 1 =&gt;
│ │ │  1</code></pre><p>Evaluation has succeed and <code class="inline">mod:fact(1)</code> returns 1.</p><p>If <code class="inline">mod:fact/1</code> is called with a negative number as argument, no clause head
│ │ │  matches. A <code class="inline">function_clause</code> runtime error occurs.</p><h2 id="tail-recursion" class="section-heading">
│ │ │ @@ -173,17 +173,17 @@
│ │ │    </a>
│ │ │    <span class="text">Tail recursion</span>
│ │ │  </h2>
│ │ │  <p>If the last expression of a function body is a function call, a
│ │ │  <em>tail-recursive call</em> is done. This is to ensure that no system
│ │ │  resources, for example, call stack, are consumed. This means that an
│ │ │  infinite loop using tail-recursive calls will not exhaust the call
│ │ │ -stack and can (in principle) run forever.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="4161145751-1">(</span><span class="n">N</span><span class="p" data-group-id="4161145751-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4161145751-2">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161145751-3">[</span><span class="n">N</span><span class="p" data-group-id="4161145751-3">]</span><span class="p" data-group-id="4161145751-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="4161145751-4">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="4161145751-4">)</span><span class="p">.</span></code></pre><p>The earlier factorial example is a counter-example. It is not
│ │ │ +stack and can (in principle) run forever.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="0133350842-1">(</span><span class="n">N</span><span class="p" data-group-id="0133350842-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0133350842-2">(</span><span class="s">&quot;</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0133350842-3">[</span><span class="n">N</span><span class="p" data-group-id="0133350842-3">]</span><span class="p" data-group-id="0133350842-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="0133350842-4">(</span><span class="n">N</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0133350842-4">)</span><span class="p">.</span></code></pre><p>The earlier factorial example is a counter-example. It is not
│ │ │  tail-recursive, since a multiplication is done on the result of the recursive
│ │ │  call to <code class="inline">fact(N-1)</code>.</p><h2 id="built-in-functions-bifs" class="section-heading">
│ │ │    <a href="#built-in-functions-bifs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Built-In Functions (BIFs)</span>
│ │ │  </h2>
│ │ │ @@ -191,17 +191,17 @@
│ │ │  system. BIFs do things that are difficult or impossible to implement
│ │ │  in Erlang. Most of the BIFs belong to module <a href="../../erts-15.2.7.8/doc/html/erlang.html"><code class="inline">erlang</code></a>, but there
│ │ │  are also BIFs belonging to a few other modules, for example <a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html"><code class="inline">lists</code></a>
│ │ │  and <a href="../../lib/stdlib-6.2.2.3/doc/html/ets.html"><code class="inline">ets</code></a>.</p><p>The most commonly used BIFs belonging to <a href="../../erts-15.2.7.8/doc/html/erlang.html"><code class="inline">erlang</code></a> are <em>auto-imported</em>. They do
│ │ │  not need to be prefixed with the module name. Which BIFs that are auto-imported
│ │ │  is specified in the <a href="../../erts-15.2.7.8/doc/html/erlang.html"><code class="inline">erlang</code></a> module in ERTS. For example, standard-type
│ │ │  conversion BIFs like <code class="inline">atom_to_list</code> and BIFs allowed in guards can be called
│ │ │ -without specifying the module name.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="1933768742-1">(</span><span class="p" data-group-id="1933768742-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="1933768742-2">}</span><span class="p" data-group-id="1933768742-1">)</span><span class="p">.</span><span class="w">
│ │ │ +without specifying the module name.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nf">tuple_size</span><span class="p" data-group-id="5201380887-1">(</span><span class="p" data-group-id="5201380887-2">{</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="5201380887-2">}</span><span class="p" data-group-id="5201380887-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="1933768742-3">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="1933768742-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="5201380887-3">(</span><span class="ss">&#39;Erlang&#39;</span><span class="p" data-group-id="5201380887-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;Erlang&quot;</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="documentation.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/ref_man_processes.html
│ │ │ @@ -125,18 +125,18 @@
│ │ │  (grow and shrink dynamically) with small memory footprint, fast to create and
│ │ │  terminate, and the scheduling overhead is low.</p><h2 id="process-creation" class="section-heading">
│ │ │    <a href="#process-creation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Process Creation</span>
│ │ │  </h2>
│ │ │ -<p>A process is created by calling <a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn/3"><code class="inline">spawn()</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="7531803283-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="7531803283-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pid</span><span class="p" data-group-id="7531803283-2">(</span><span class="p" data-group-id="7531803283-2">)</span><span class="w">
│ │ │ -  </span><span class="n">Module</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="7531803283-3">(</span><span class="p" data-group-id="7531803283-3">)</span><span class="w">
│ │ │ -  </span><span class="n">Args</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7531803283-4">[</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="7531803283-4">]</span><span class="w">
│ │ │ -    </span><span class="n">ArgI</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7531803283-5">(</span><span class="p" data-group-id="7531803283-5">)</span></code></pre><p><code class="inline">spawn()</code> creates a new process and returns the pid.</p><p>The new process starts executing in <code class="inline">Module:Name(Arg1,...,ArgN)</code> where the
│ │ │ +<p>A process is created by calling <a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn/3"><code class="inline">spawn()</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">spawn</span><span class="p" data-group-id="3213275618-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Args</span><span class="p" data-group-id="3213275618-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pid</span><span class="p" data-group-id="3213275618-2">(</span><span class="p" data-group-id="3213275618-2">)</span><span class="w">
│ │ │ +  </span><span class="n">Module</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="3213275618-3">(</span><span class="p" data-group-id="3213275618-3">)</span><span class="w">
│ │ │ +  </span><span class="n">Args</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3213275618-4">[</span><span class="n">Arg1</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="n">ArgN</span><span class="p" data-group-id="3213275618-4">]</span><span class="w">
│ │ │ +    </span><span class="n">ArgI</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3213275618-5">(</span><span class="p" data-group-id="3213275618-5">)</span></code></pre><p><code class="inline">spawn()</code> creates a new process and returns the pid.</p><p>The new process starts executing in <code class="inline">Module:Name(Arg1,...,ArgN)</code> where the
│ │ │  arguments are the elements of the (possible empty) <code class="inline">Args</code> argument list.</p><p>There exist a number of different <code class="inline">spawn</code> BIFs:</p><ul><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn/4"><code class="inline">spawn/1,2,3,4</code></a></li><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn_link/4"><code class="inline">spawn_link/1,2,3,4</code></a></li><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn_monitor/4"><code class="inline">spawn_monitor/1,2,3,4</code></a></li><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn_opt/5"><code class="inline">spawn_opt/2,3,4,5</code></a></li><li><a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn_request/5"><code class="inline">spawn_request/1,2,3,4,5</code></a></li></ul><h2 id="registered-processes" class="section-heading">
│ │ │    <a href="#registered-processes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Registered Processes</span>
│ │ │  </h2>
│ │ │  <p>Besides addressing a process by using its pid, there are also BIFs for
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/ref_man_records.html
│ │ │ @@ -123,17 +123,17 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Defining Records</span>
│ │ │  </h2>
│ │ │  <p>A record definition consists of the name of the record, followed by the field
│ │ │  names of the record. Record and field names must be atoms. Each field can be
│ │ │  given an optional default value. If no default value is supplied, <code class="inline">undefined</code> is
│ │ │ -used.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9390016019-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9390016019-2">{</span><span class="n">Field1</span><span class="w"> </span><span class="p" data-group-id="9390016019-3">[</span><span class="o">=</span><span class="w"> </span><span class="n">Expr1</span><span class="p" data-group-id="9390016019-3">]</span><span class="p">,</span><span class="w">
│ │ │ +used.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3881045232-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3881045232-2">{</span><span class="n">Field1</span><span class="w"> </span><span class="p" data-group-id="3881045232-3">[</span><span class="o">=</span><span class="w"> </span><span class="n">Expr1</span><span class="p" data-group-id="3881045232-3">]</span><span class="p">,</span><span class="w">
│ │ │                 </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -               </span><span class="n">FieldN</span><span class="w"> </span><span class="p" data-group-id="9390016019-4">[</span><span class="o">=</span><span class="w"> </span><span class="n">ExprN</span><span class="p" data-group-id="9390016019-4">]</span><span class="p" data-group-id="9390016019-2">}</span><span class="p" data-group-id="9390016019-1">)</span><span class="p">.</span></code></pre><p>The default value for a field is an arbitrary expression, except that it must
│ │ │ +               </span><span class="n">FieldN</span><span class="w"> </span><span class="p" data-group-id="3881045232-4">[</span><span class="o">=</span><span class="w"> </span><span class="n">ExprN</span><span class="p" data-group-id="3881045232-4">]</span><span class="p" data-group-id="3881045232-2">}</span><span class="p" data-group-id="3881045232-1">)</span><span class="p">.</span></code></pre><p>The default value for a field is an arbitrary expression, except that it must
│ │ │  not use any variables.</p><p>A record definition can be placed anywhere among the attributes and function
│ │ │  declarations of a module, but the definition must come before any usage of the
│ │ │  record.</p><p>If a record is used in several modules, it is recommended that the record
│ │ │  definition is placed in an include file.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Starting from Erlang/OTP 26, records can be defined in the Erlang shell
│ │ │  using the syntax described in this section. In earlier releases, it was
│ │ │  necessary to use the <a href="../../lib/stdlib-6.2.2.3/doc/html/shell.html"><code class="inline">shell</code></a> built-in function <code class="inline">rd/2</code>.</p></section><h2 id="creating-records" class="section-heading">
│ │ │    <a href="#creating-records" class="hover-link">
│ │ │ @@ -143,32 +143,32 @@
│ │ │  </h2>
│ │ │  <p>The following expression creates a new <code class="inline">Name</code> record where the value of each
│ │ │  field <code class="inline">FieldI</code> is the value of evaluating the corresponding expression <code class="inline">ExprI</code>:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p>The fields can be in any order, not necessarily the same order as in the record
│ │ │  definition, and fields can be omitted. Omitted fields get their respective
│ │ │  default value instead.</p><p>If several fields are to be assigned the same value, the following construction
│ │ │  can be used:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK, _=ExprL}</code></pre><p>Omitted fields then get the value of evaluating <code class="inline">ExprL</code> instead of their default
│ │ │  values. This feature is primarily intended to be used to create patterns for ETS
│ │ │ -and Mnesia match functions.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9517540582-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9517540582-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="9517540582-2">}</span><span class="p" data-group-id="9517540582-1">)</span><span class="p">.</span><span class="w">
│ │ │ +and Mnesia match functions.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0349774290-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0349774290-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="0349774290-2">}</span><span class="p" data-group-id="0349774290-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="9517540582-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="9517540582-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="9517540582-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9517540582-5">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="9517540582-5">}</span><span class="p" data-group-id="9517540582-4">)</span><span class="p">.</span></code></pre><h2 id="accessing-record-fields" class="section-heading">
│ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="0349774290-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="0349774290-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="0349774290-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="0349774290-5">{</span><span class="ss">name</span><span class="o">=</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="0349774290-5">}</span><span class="p" data-group-id="0349774290-4">)</span><span class="p">.</span></code></pre><h2 id="accessing-record-fields" class="section-heading">
│ │ │    <a href="#accessing-record-fields" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Accessing Record Fields</span>
│ │ │  </h2>
│ │ │  <pre><code class="text">Expr#Name.Field</code></pre><p>Returns the value of the specified field. <code class="inline">Expr</code> is to evaluate to a <code class="inline">Name</code>
│ │ │ -record.</p><p><em>Example</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5963244487-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5963244487-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="5963244487-2">}</span><span class="p" data-group-id="5963244487-1">)</span><span class="p">.</span><span class="w">
│ │ │ +record.</p><p><em>Example</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="1066510637-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1066510637-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="1066510637-2">}</span><span class="p" data-group-id="1066510637-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">get_person_name</span><span class="p" data-group-id="5963244487-3">(</span><span class="n">Person</span><span class="p" data-group-id="5963244487-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">get_person_name</span><span class="p" data-group-id="1066510637-3">(</span><span class="n">Person</span><span class="p" data-group-id="1066510637-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">.</span></code></pre><p>The following expression returns the position of the specified field in the
│ │ │ -tuple representation of the record:</p><pre><code class="text">#Name.Field</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9808278585-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9808278585-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="9808278585-2">}</span><span class="p" data-group-id="9808278585-1">)</span><span class="p">.</span><span class="w">
│ │ │ +tuple representation of the record:</p><pre><code class="text">#Name.Field</code></pre><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9890126275-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9890126275-2">{</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">phone</span><span class="p">,</span><span class="w"> </span><span class="ss">address</span><span class="p" data-group-id="9890126275-2">}</span><span class="p" data-group-id="9890126275-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="9808278585-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9808278585-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="9808278585-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9808278585-4">)</span><span class="p">.</span></code></pre><h2 id="updating-records" class="section-heading">
│ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="9890126275-3">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9890126275-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keyfind</span><span class="p" data-group-id="9890126275-4">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="9890126275-4">)</span><span class="p">.</span></code></pre><h2 id="updating-records" class="section-heading">
│ │ │    <a href="#updating-records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Updating Records</span>
│ │ │  </h2>
│ │ │  <pre><code class="text">Expr#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p><code class="inline">Expr</code> is to evaluate to a <code class="inline">Name</code> record. A copy of this record is returned,
│ │ │  with the value of each specified field <code class="inline">FieldI</code> changed to the value of
│ │ │ @@ -178,51 +178,51 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Records in Guards</span>
│ │ │  </h2>
│ │ │  <p>Since record expressions are expanded to tuple expressions, creating
│ │ │  records and accessing record fields are allowed in guards. However,
│ │ │  all subexpressions (for initializing fields), must be valid guard
│ │ │ -expressions as well.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="1797313543-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1797313543-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Msg</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">#</span><span class="ss">msg</span><span class="p" data-group-id="1797313543-2">{</span><span class="ss">to</span><span class="o">=</span><span class="ss">void</span><span class="p">,</span><span class="w"> </span><span class="ss">no</span><span class="o">=</span><span class="mi">3</span><span class="p" data-group-id="1797313543-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +expressions as well.</p><p><em>Examples:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">handle</span><span class="p" data-group-id="5609111601-1">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5609111601-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Msg</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="o">#</span><span class="ss">msg</span><span class="p" data-group-id="5609111601-2">{</span><span class="ss">to</span><span class="o">=</span><span class="ss">void</span><span class="p">,</span><span class="w"> </span><span class="ss">no</span><span class="o">=</span><span class="mi">3</span><span class="p" data-group-id="5609111601-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle</span><span class="p" data-group-id="1797313543-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1797313543-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">running</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>There is also a type test BIF <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_record/2"><code class="inline">is_record(Term, RecordTag)</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_person</span><span class="p" data-group-id="3461751253-1">(</span><span class="n">P</span><span class="p" data-group-id="3461751253-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="3461751253-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="3461751253-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle</span><span class="p" data-group-id="5609111601-3">(</span><span class="n">Msg</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="5609111601-3">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">State</span><span class="o">#</span><span class="ss">state</span><span class="p">.</span><span class="ss">running</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>There is also a type test BIF <a href="../../erts-15.2.7.8/doc/html/erlang.html#is_record/2"><code class="inline">is_record(Term, RecordTag)</code></a>.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="nf">is_person</span><span class="p" data-group-id="1183654868-1">(</span><span class="n">P</span><span class="p" data-group-id="1183654868-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="nf">is_record</span><span class="p" data-group-id="1183654868-2">(</span><span class="n">P</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="1183654868-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">true</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">is_person</span><span class="p" data-group-id="3461751253-3">(</span><span class="p">_</span><span class="n">P</span><span class="p" data-group-id="3461751253-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">is_person</span><span class="p" data-group-id="1183654868-3">(</span><span class="p">_</span><span class="n">P</span><span class="p" data-group-id="1183654868-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">false</span><span class="p">.</span></code></pre><h2 id="records-in-patterns" class="section-heading">
│ │ │    <a href="#records-in-patterns" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Records in Patterns</span>
│ │ │  </h2>
│ │ │  <p>A pattern that matches a certain record is created in the same way as a record
│ │ │  is created:</p><pre><code class="text">#Name{Field1=Expr1, ..., FieldK=ExprK}</code></pre><p>In this case, one or more of <code class="inline">Expr1</code> ... <code class="inline">ExprK</code> can be unbound variables.</p><h2 id="nested-records" class="section-heading">
│ │ │    <a href="#nested-records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Nested Records</span>
│ │ │  </h2>
│ │ │ -<p>Assume the following record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5870396261-1">(</span><span class="ss">nrec0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5870396261-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested0&quot;</span><span class="p" data-group-id="5870396261-2">}</span><span class="p" data-group-id="5870396261-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5870396261-3">(</span><span class="ss">nrec1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5870396261-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec0</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec0</span><span class="p" data-group-id="5870396261-5">{</span><span class="p" data-group-id="5870396261-5">}</span><span class="p" data-group-id="5870396261-4">}</span><span class="p" data-group-id="5870396261-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5870396261-6">(</span><span class="ss">nrec2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5870396261-7">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested2&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec1</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec1</span><span class="p" data-group-id="5870396261-8">{</span><span class="p" data-group-id="5870396261-8">}</span><span class="p" data-group-id="5870396261-7">}</span><span class="p" data-group-id="5870396261-6">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Assume the following record definitions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4183790761-1">(</span><span class="ss">nrec0</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4183790761-2">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested0&quot;</span><span class="p" data-group-id="4183790761-2">}</span><span class="p" data-group-id="4183790761-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4183790761-3">(</span><span class="ss">nrec1</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4183790761-4">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested1&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec0</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec0</span><span class="p" data-group-id="4183790761-5">{</span><span class="p" data-group-id="4183790761-5">}</span><span class="p" data-group-id="4183790761-4">}</span><span class="p" data-group-id="4183790761-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4183790761-6">(</span><span class="ss">nrec2</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4183790761-7">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">&quot;nested2&quot;</span><span class="p">,</span><span class="w"> </span><span class="ss">nrec1</span><span class="o">=</span><span class="o">#</span><span class="ss">nrec1</span><span class="p" data-group-id="4183790761-8">{</span><span class="p" data-group-id="4183790761-8">}</span><span class="p" data-group-id="4183790761-7">}</span><span class="p" data-group-id="4183790761-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">N2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">nrec2</span><span class="p" data-group-id="5870396261-9">{</span><span class="p" data-group-id="5870396261-9">}</span><span class="p">,</span></code></pre><p>Accessing or updating nested records can be written without parentheses:</p><pre><code class="text">&quot;nested0&quot; = N2#nrec2.nrec1#nrec1.nrec0#nrec0.name,
│ │ │ +</span><span class="n">N2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">#</span><span class="ss">nrec2</span><span class="p" data-group-id="4183790761-9">{</span><span class="p" data-group-id="4183790761-9">}</span><span class="p">,</span></code></pre><p>Accessing or updating nested records can be written without parentheses:</p><pre><code class="text">&quot;nested0&quot; = N2#nrec2.nrec1#nrec1.nrec0#nrec0.name,
│ │ │      N0n = N2#nrec2.nrec1#nrec1.nrec0#nrec0{name = &quot;nested0a&quot;},</code></pre><p>which is equivalent to:</p><pre><code class="text">&quot;nested0&quot; = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0.name,
│ │ │  N0n = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0{name = &quot;nested0a&quot;},</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP R14, parentheses were necessary when accessing or updating
│ │ │  nested records.</p></section><h2 id="internal-representation-of-records" class="section-heading">
│ │ │    <a href="#internal-representation-of-records" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Internal Representation of Records</span>
│ │ │  </h2>
│ │ │  <p>Record expressions are translated to tuple expressions during compilation. A
│ │ │ -record defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9251396984-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9251396984-2">{</span><span class="n">Field1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">FieldN</span><span class="p" data-group-id="9251396984-2">}</span><span class="p" data-group-id="9251396984-1">)</span><span class="p">.</span></code></pre><p>is internally represented by the tuple:</p><pre><code class="text">{Name, Value1, ..., ValueN}</code></pre><p>Here each <code class="inline">ValueI</code> is the default value for <code class="inline">FieldI</code>.</p><p>To each module using records, a pseudo function is added during compilation to
│ │ │ -obtain information about records:</p><pre><code class="makeup erlang" translate="no"><span class="nf">record_info</span><span class="p" data-group-id="8799780534-1">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="8799780534-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8799780534-2">[</span><span class="n">Field</span><span class="p" data-group-id="8799780534-2">]</span><span class="w">
│ │ │ -</span><span class="nf">record_info</span><span class="p" data-group-id="8799780534-3">(</span><span class="nb">size</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="8799780534-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Size</span></code></pre><p><code class="inline">Size</code> is the size of the tuple representation, that is, one more than the
│ │ │ +record defined as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0110659164-1">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0110659164-2">{</span><span class="n">Field1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">FieldN</span><span class="p" data-group-id="0110659164-2">}</span><span class="p" data-group-id="0110659164-1">)</span><span class="p">.</span></code></pre><p>is internally represented by the tuple:</p><pre><code class="text">{Name, Value1, ..., ValueN}</code></pre><p>Here each <code class="inline">ValueI</code> is the default value for <code class="inline">FieldI</code>.</p><p>To each module using records, a pseudo function is added during compilation to
│ │ │ +obtain information about records:</p><pre><code class="makeup erlang" translate="no"><span class="nf">record_info</span><span class="p" data-group-id="4683962990-1">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="4683962990-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4683962990-2">[</span><span class="n">Field</span><span class="p" data-group-id="4683962990-2">]</span><span class="w">
│ │ │ +</span><span class="nf">record_info</span><span class="p" data-group-id="4683962990-3">(</span><span class="nb">size</span><span class="p">,</span><span class="w"> </span><span class="n">Record</span><span class="p" data-group-id="4683962990-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Size</span></code></pre><p><code class="inline">Size</code> is the size of the tuple representation, that is, one more than the
│ │ │  number of fields.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="macros.html" class="bottom-actions-button" rel="prev">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/release_handling.html
│ │ │ @@ -223,38 +223,38 @@
│ │ │    <span class="text">update</span>
│ │ │  </h3>
│ │ │  <p>If a more complex change has been made, for example, a change to the format of
│ │ │  the internal state of a <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html"><code class="inline">gen_server</code></a>, simple code replacement is not sufficient.
│ │ │  Instead, it is necessary to:</p><ul><li>Suspend the processes using the module (to avoid that they try to handle any
│ │ │  requests before the code replacement is completed).</li><li>Ask them to transform the internal state format and switch to the new version
│ │ │  of the module.</li><li>Remove the old version.</li><li>Resume the processes.</li></ul><p>This is called <em>synchronized code replacement</em> and for this the following
│ │ │ -instructions are used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1580057781-1">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1580057781-2">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="1580057781-2">}</span><span class="p" data-group-id="1580057781-1">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1580057781-3">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="1580057781-3">}</span></code></pre><p><code class="inline">update</code> with argument <code class="inline">{advanced,Extra}</code> is used when changing the internal
│ │ │ +instructions are used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4171615546-1">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4171615546-2">{</span><span class="ss">advanced</span><span class="p">,</span><span class="w"> </span><span class="n">Extra</span><span class="p" data-group-id="4171615546-2">}</span><span class="p" data-group-id="4171615546-1">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4171615546-3">{</span><span class="ss">update</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="4171615546-3">}</span></code></pre><p><code class="inline">update</code> with argument <code class="inline">{advanced,Extra}</code> is used when changing the internal
│ │ │  state of a behaviour as described above. It causes behaviour processes to call
│ │ │  the callback function <code class="inline">code_change/3</code>, passing the term <code class="inline">Extra</code> and some other
│ │ │  information as arguments. See the manual pages for the respective behaviours and
│ │ │  <a href="appup_cookbook.html#int_state">Appup Cookbook</a>.</p><p><code class="inline">update</code> with argument <code class="inline">supervisor</code> is used when changing the start
│ │ │  specification of a supervisor. See <a href="appup_cookbook.html#sup">Appup Cookbook</a>.</p><p>When a module is to be updated, the release handler finds which processes that
│ │ │  are <em>using</em> the module by traversing the supervision tree of each running
│ │ │ -application and checking all the child specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1965473330-1">{</span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="n">StartFunc</span><span class="p">,</span><span class="w"> </span><span class="n">Restart</span><span class="p">,</span><span class="w"> </span><span class="n">Shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Modules</span><span class="p" data-group-id="1965473330-1">}</span></code></pre><p>A process uses a module if the name is listed in <code class="inline">Modules</code> in the child
│ │ │ +application and checking all the child specifications:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2479395592-1">{</span><span class="n">Id</span><span class="p">,</span><span class="w"> </span><span class="n">StartFunc</span><span class="p">,</span><span class="w"> </span><span class="n">Restart</span><span class="p">,</span><span class="w"> </span><span class="n">Shutdown</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">Modules</span><span class="p" data-group-id="2479395592-1">}</span></code></pre><p>A process uses a module if the name is listed in <code class="inline">Modules</code> in the child
│ │ │  specification for the process.</p><p>If <code class="inline">Modules=dynamic</code>, which is the case for event managers, the event manager
│ │ │  process informs the release handler about the list of currently installed event
│ │ │  handlers (<code class="inline">gen_event</code>), and it is checked if the module name is in this list
│ │ │  instead.</p><p>The release handler suspends, asks for code change, and resumes processes by
│ │ │  calling the functions <code class="inline">sys:suspend/1,2</code>, <code class="inline">sys:change_code/4,5</code>, and
│ │ │  <code class="inline">sys:resume/1,2</code>, respectively.</p><h3 id="add_module-and-delete_module" class="section-heading">
│ │ │    <a href="#add_module-and-delete_module" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">add_module and delete_module</span>
│ │ │  </h3>
│ │ │ -<p>If a new module is introduced, the following instruction is used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0345542364-1">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="0345542364-1">}</span></code></pre><p>This instruction loads module <code class="inline">Module</code>. When running Erlang in
│ │ │ +<p>If a new module is introduced, the following instruction is used:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5291847711-1">{</span><span class="ss">add_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="5291847711-1">}</span></code></pre><p>This instruction loads module <code class="inline">Module</code>. When running Erlang in
│ │ │  embedded mode it is necessary to use this this instruction. It is not
│ │ │  strictly required when running Erlang in interactive mode, since the
│ │ │ -code server automatically searches for and loads unloaded modules.</p><p>The opposite of <code class="inline">add_module</code> is <code class="inline">delete_module</code>, which unloads a module:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6296465243-1">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="6296465243-1">}</span></code></pre><p>Any process, in any application, with <code class="inline">Module</code> as residence module, is
│ │ │ +code server automatically searches for and loads unloaded modules.</p><p>The opposite of <code class="inline">add_module</code> is <code class="inline">delete_module</code>, which unloads a module:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7591694103-1">{</span><span class="nb">delete_module</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="7591694103-1">}</span></code></pre><p>Any process, in any application, with <code class="inline">Module</code> as residence module, is
│ │ │  killed when the instruction is evaluated. Therefore, the user must
│ │ │  ensure that all such processes are terminated before deleting module
│ │ │  <code class="inline">Module</code> to avoid a situation with failing supervisor restarts.</p><h3 id="application-instructions" class="section-heading">
│ │ │    <a href="#application-instructions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Application Instructions</span>
│ │ │ @@ -327,74 +327,74 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Application Upgrade File</span>
│ │ │  </h2>
│ │ │  <p>To define how to upgrade/downgrade between the current version and previous
│ │ │  versions of an application, an <em>application upgrade file</em>, or in short
│ │ │  <code class="inline">.appup</code> file is created. The file is to be called <code class="inline">Application.appup</code>, where
│ │ │ -<code class="inline">Application</code> is the application name:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="4120115534-1">{</span><span class="no">Vsn</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4120115534-2">[</span><span class="p" data-group-id="4120115534-3">{</span><span class="no">UpFromVsn1</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsU1</span><span class="p" data-group-id="4120115534-3">}</span><span class="p">,</span><span class="w">
│ │ │ +<code class="inline">Application</code> is the application name:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="0801180443-1">{</span><span class="no">Vsn</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0801180443-2">[</span><span class="p" data-group-id="0801180443-3">{</span><span class="no">UpFromVsn1</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsU1</span><span class="p" data-group-id="0801180443-3">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4120115534-4">{</span><span class="no">UpFromVsnK</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsUK</span><span class="p" data-group-id="4120115534-4">}</span><span class="p" data-group-id="4120115534-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4120115534-5">[</span><span class="p" data-group-id="4120115534-6">{</span><span class="no">DownToVsn1</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsD1</span><span class="p" data-group-id="4120115534-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="0801180443-4">{</span><span class="no">UpFromVsnK</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsUK</span><span class="p" data-group-id="0801180443-4">}</span><span class="p" data-group-id="0801180443-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="0801180443-5">[</span><span class="p" data-group-id="0801180443-6">{</span><span class="no">DownToVsn1</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsD1</span><span class="p" data-group-id="0801180443-6">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4120115534-7">{</span><span class="no">DownToVsnK</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsDK</span><span class="p" data-group-id="4120115534-7">}</span><span class="p" data-group-id="4120115534-5">]</span><span class="p" data-group-id="4120115534-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">Vsn</code>, a string, is the current version of the application, as defined in the
│ │ │ +  </span><span class="p" data-group-id="0801180443-7">{</span><span class="no">DownToVsnK</span><span class="p">,</span><span class="w"> </span><span class="no">InstructionsDK</span><span class="p" data-group-id="0801180443-7">}</span><span class="p" data-group-id="0801180443-5">]</span><span class="p" data-group-id="0801180443-1">}</span><span class="p">.</span></code></pre><ul><li><code class="inline">Vsn</code>, a string, is the current version of the application, as defined in the
│ │ │  <code class="inline">.app</code> file.</li><li>Each <code class="inline">UpFromVsn</code> is a previous version of the application to upgrade from.</li><li>Each <code class="inline">DownToVsn</code> is a previous version of the application to downgrade to.</li><li>Each <code class="inline">Instructions</code> is a list of release handling instructions.</li></ul><p><code class="inline">UpFromVsn</code> and <code class="inline">DownToVsn</code> can also be specified as regular expressions. For
│ │ │  more information about the syntax and contents of the <code class="inline">.appup</code> file, see
│ │ │  <a href="../../lib/sasl-4.2.2.1/doc/html/appup.html"><code class="inline">appup</code></a> in SASL.</p><p><a href="appup_cookbook.html">Appup Cookbook</a> includes examples of <code class="inline">.appup</code> files for
│ │ │  typical upgrade/downgrade cases.</p><p><em>Example:</em> Consider the release <code class="inline">ch_rel-1</code> from
│ │ │  <a href="release_structure.html#ch_rel">Releases</a>. Assume you want to add a function
│ │ │  <code class="inline">available/0</code> to server <code class="inline">ch3</code>, which returns the number of available channels
│ │ │  (when trying out the example, make the change in a copy of the original
│ │ │ -directory, to ensure that the first version is still available):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0323634893-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="0323634893-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0323634893-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="0323634893-2">)</span><span class="p">.</span><span class="w">
│ │ │ +directory, to ensure that the first version is still available):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4881141368-1">(</span><span class="ss">ch3</span><span class="p" data-group-id="4881141368-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4881141368-2">(</span><span class="ss">gen_server</span><span class="p" data-group-id="4881141368-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0323634893-3">(</span><span class="p" data-group-id="0323634893-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0323634893-4">]</span><span class="p" data-group-id="0323634893-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0323634893-5">(</span><span class="p" data-group-id="0323634893-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0323634893-6">]</span><span class="p" data-group-id="0323634893-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0323634893-7">(</span><span class="p" data-group-id="0323634893-8">[</span><span class="ss">available</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0323634893-8">]</span><span class="p" data-group-id="0323634893-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0323634893-9">(</span><span class="p" data-group-id="0323634893-10">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0323634893-10">]</span><span class="p" data-group-id="0323634893-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4881141368-3">(</span><span class="p" data-group-id="4881141368-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4881141368-4">]</span><span class="p" data-group-id="4881141368-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4881141368-5">(</span><span class="p" data-group-id="4881141368-6">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4881141368-6">]</span><span class="p" data-group-id="4881141368-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4881141368-7">(</span><span class="p" data-group-id="4881141368-8">[</span><span class="ss">available</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4881141368-8">]</span><span class="p" data-group-id="4881141368-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4881141368-9">(</span><span class="p" data-group-id="4881141368-10">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_call</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_cast</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4881141368-10">]</span><span class="p" data-group-id="4881141368-9">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="0323634893-11">(</span><span class="p" data-group-id="0323634893-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0323634893-12">(</span><span class="p" data-group-id="0323634893-13">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="0323634893-13">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0323634893-14">[</span><span class="p" data-group-id="0323634893-14">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0323634893-15">[</span><span class="p" data-group-id="0323634893-15">]</span><span class="p" data-group-id="0323634893-12">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="4881141368-11">(</span><span class="p" data-group-id="4881141368-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4881141368-12">(</span><span class="p" data-group-id="4881141368-13">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="4881141368-13">}</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4881141368-14">[</span><span class="p" data-group-id="4881141368-14">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4881141368-15">[</span><span class="p" data-group-id="4881141368-15">]</span><span class="p" data-group-id="4881141368-12">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="0323634893-16">(</span><span class="p" data-group-id="0323634893-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="0323634893-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0323634893-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="4881141368-16">(</span><span class="p" data-group-id="4881141368-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4881141368-17">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="4881141368-17">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="0323634893-18">(</span><span class="n">Ch</span><span class="p" data-group-id="0323634893-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="0323634893-19">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0323634893-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0323634893-20">}</span><span class="p" data-group-id="0323634893-19">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="4881141368-18">(</span><span class="n">Ch</span><span class="p" data-group-id="4881141368-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4881141368-19">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4881141368-20">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4881141368-20">}</span><span class="p" data-group-id="4881141368-19">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">available</span><span class="p" data-group-id="0323634893-21">(</span><span class="p" data-group-id="0323634893-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="0323634893-22">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">available</span><span class="p" data-group-id="0323634893-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">available</span><span class="p" data-group-id="4881141368-21">(</span><span class="p" data-group-id="4881141368-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_server</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4881141368-22">(</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">available</span><span class="p" data-group-id="4881141368-22">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="0323634893-23">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="0323634893-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0323634893-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="0323634893-25">(</span><span class="p" data-group-id="0323634893-25">)</span><span class="p" data-group-id="0323634893-24">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="4881141368-23">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="4881141368-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4881141368-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="4881141368-25">(</span><span class="p" data-group-id="4881141368-25">)</span><span class="p" data-group-id="4881141368-24">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="0323634893-26">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0323634893-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0323634893-27">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="0323634893-27">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="0323634893-28">(</span><span class="n">Chs</span><span class="p" data-group-id="0323634893-28">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0323634893-29">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="0323634893-29">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_call</span><span class="p" data-group-id="0323634893-30">(</span><span class="ss">available</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0323634893-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">available</span><span class="p" data-group-id="0323634893-31">(</span><span class="n">Chs</span><span class="p" data-group-id="0323634893-31">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0323634893-32">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0323634893-32">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="4881141368-26">(</span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4881141368-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4881141368-27">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="4881141368-27">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="4881141368-28">(</span><span class="n">Chs</span><span class="p" data-group-id="4881141368-28">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4881141368-29">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="4881141368-29">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_call</span><span class="p" data-group-id="4881141368-30">(</span><span class="ss">available</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4881141368-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">available</span><span class="p" data-group-id="4881141368-31">(</span><span class="n">Chs</span><span class="p" data-group-id="4881141368-31">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4881141368-32">{</span><span class="ss">reply</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4881141368-32">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_cast</span><span class="p" data-group-id="0323634893-33">(</span><span class="p" data-group-id="0323634893-34">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0323634893-34">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0323634893-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="0323634893-35">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0323634893-35">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0323634893-36">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="0323634893-36">}</span><span class="p">.</span></code></pre><p>A new version of the <code class="inline">ch_app.app</code> file must now be created, where the version is
│ │ │ -updated:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5541161562-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5541161562-2">[</span><span class="p" data-group-id="5541161562-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="5541161562-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5541161562-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="5541161562-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5541161562-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5541161562-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="5541161562-6">]</span><span class="p" data-group-id="5541161562-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5541161562-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5541161562-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="5541161562-8">]</span><span class="p" data-group-id="5541161562-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5541161562-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5541161562-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="5541161562-10">]</span><span class="p" data-group-id="5541161562-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5541161562-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5541161562-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="5541161562-13">[</span><span class="p" data-group-id="5541161562-13">]</span><span class="p" data-group-id="5541161562-12">}</span><span class="p" data-group-id="5541161562-11">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5541161562-2">]</span><span class="p" data-group-id="5541161562-1">}</span><span class="p">.</span></code></pre><p>To upgrade <code class="inline">ch_app</code> from <code class="inline">&quot;1&quot;</code> to <code class="inline">&quot;2&quot;</code> (and to downgrade from <code class="inline">&quot;2&quot;</code> to <code class="inline">&quot;1&quot;</code>),
│ │ │ +</span><span class="nf">handle_cast</span><span class="p" data-group-id="4881141368-33">(</span><span class="p" data-group-id="4881141368-34">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4881141368-34">}</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4881141368-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="4881141368-35">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4881141368-35">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4881141368-36">{</span><span class="ss">noreply</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="4881141368-36">}</span><span class="p">.</span></code></pre><p>A new version of the <code class="inline">ch_app.app</code> file must now be created, where the version is
│ │ │ +updated:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="2979126782-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2979126782-2">[</span><span class="p" data-group-id="2979126782-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="2979126782-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2979126782-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="2979126782-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2979126782-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2979126782-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="2979126782-6">]</span><span class="p" data-group-id="2979126782-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2979126782-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2979126782-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="2979126782-8">]</span><span class="p" data-group-id="2979126782-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2979126782-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2979126782-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="2979126782-10">]</span><span class="p" data-group-id="2979126782-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2979126782-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2979126782-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="2979126782-13">[</span><span class="p" data-group-id="2979126782-13">]</span><span class="p" data-group-id="2979126782-12">}</span><span class="p" data-group-id="2979126782-11">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="2979126782-2">]</span><span class="p" data-group-id="2979126782-1">}</span><span class="p">.</span></code></pre><p>To upgrade <code class="inline">ch_app</code> from <code class="inline">&quot;1&quot;</code> to <code class="inline">&quot;2&quot;</code> (and to downgrade from <code class="inline">&quot;2&quot;</code> to <code class="inline">&quot;1&quot;</code>),
│ │ │  you only need to load the new (old) version of the <code class="inline">ch3</code> callback module. Create
│ │ │ -the application upgrade file <code class="inline">ch_app.appup</code> in the <code class="inline">ebin</code> directory:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7619611705-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7619611705-2">[</span><span class="p" data-group-id="7619611705-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7619611705-4">[</span><span class="p" data-group-id="7619611705-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7619611705-5">}</span><span class="p" data-group-id="7619611705-4">]</span><span class="p" data-group-id="7619611705-3">}</span><span class="p" data-group-id="7619611705-2">]</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7619611705-6">[</span><span class="p" data-group-id="7619611705-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7619611705-8">[</span><span class="p" data-group-id="7619611705-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7619611705-9">}</span><span class="p" data-group-id="7619611705-8">]</span><span class="p" data-group-id="7619611705-7">}</span><span class="p" data-group-id="7619611705-6">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7619611705-1">}</span><span class="p">.</span></code></pre><p><a href="" id="relup"></a></p><h2 id="release-upgrade-file" class="section-heading">
│ │ │ +the application upgrade file <code class="inline">ch_app.appup</code> in the <code class="inline">ebin</code> directory:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9983663860-1">{</span><span class="s">&quot;2&quot;</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9983663860-2">[</span><span class="p" data-group-id="9983663860-3">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9983663860-4">[</span><span class="p" data-group-id="9983663860-5">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9983663860-5">}</span><span class="p" data-group-id="9983663860-4">]</span><span class="p" data-group-id="9983663860-3">}</span><span class="p" data-group-id="9983663860-2">]</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9983663860-6">[</span><span class="p" data-group-id="9983663860-7">{</span><span class="s">&quot;1&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9983663860-8">[</span><span class="p" data-group-id="9983663860-9">{</span><span class="nb">load_module</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9983663860-9">}</span><span class="p" data-group-id="9983663860-8">]</span><span class="p" data-group-id="9983663860-7">}</span><span class="p" data-group-id="9983663860-6">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9983663860-1">}</span><span class="p">.</span></code></pre><p><a href="" id="relup"></a></p><h2 id="release-upgrade-file" class="section-heading">
│ │ │    <a href="#release-upgrade-file" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Release Upgrade File</span>
│ │ │  </h2>
│ │ │  <p>To define how to upgrade/downgrade between the new version and previous versions
│ │ │  of a release, a <em>release upgrade file</em>, or in short <code class="inline">.relup</code> file, is to be
│ │ │ @@ -405,22 +405,22 @@
│ │ │  are to be added and deleted, and which applications that must be upgraded and/or
│ │ │  downgraded. The instructions for this are fetched from the <code class="inline">.appup</code> files and
│ │ │  transformed into a single list of low-level instructions in the right order.</p><p>If the <code class="inline">relup</code> file is relatively simple, it can be created manually. It is only
│ │ │  to contain low-level instructions.</p><p>For details about the syntax and contents of the release upgrade file, see
│ │ │  <a href="../../lib/sasl-4.2.2.1/doc/html/relup.html"><code class="inline">relup</code></a> in SASL.</p><p><em>Example, continued from the previous section:</em> You have a new version &quot;2&quot; of
│ │ │  <code class="inline">ch_app</code> and an <code class="inline">.appup</code> file. A new version of the <code class="inline">.rel</code> file is also needed.
│ │ │  This time the file is called <code class="inline">ch_rel-2.rel</code> and the release version string is
│ │ │ -changed from &quot;A&quot; to &quot;B&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9590649235-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9590649235-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="9590649235-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9590649235-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="9590649235-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9590649235-4">[</span><span class="p" data-group-id="9590649235-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="9590649235-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9590649235-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="9590649235-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9590649235-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="9590649235-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9590649235-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="9590649235-8">}</span><span class="p" data-group-id="9590649235-4">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9590649235-1">}</span><span class="p">.</span></code></pre><p>Now the <code class="inline">relup</code> file can be generated:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;]).
│ │ │ +changed from &quot;A&quot; to &quot;B&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4740740471-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4740740471-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="4740740471-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4740740471-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="4740740471-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4740740471-4">[</span><span class="p" data-group-id="4740740471-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="4740740471-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4740740471-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="4740740471-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4740740471-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="4740740471-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4740740471-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;2&quot;</span><span class="p" data-group-id="4740740471-8">}</span><span class="p" data-group-id="4740740471-4">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4740740471-1">}</span><span class="p">.</span></code></pre><p>Now the <code class="inline">relup</code> file can be generated:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;]).
│ │ │  ok</code></pre><p>This generates a <code class="inline">relup</code> file with instructions for how to upgrade from version
│ │ │  &quot;A&quot; (&quot;ch_rel-1&quot;) to version &quot;B&quot; (&quot;ch_rel-2&quot;) and how to downgrade from version
│ │ │  &quot;B&quot; to version &quot;A&quot;.</p><p>Both the old and new versions of the <code class="inline">.app</code> and <code class="inline">.rel</code> files must be in the code
│ │ │  path, as well as the <code class="inline">.appup</code> and (new) <code class="inline">.beam</code> files. The code path can be
│ │ │  extended by using the option <code class="inline">path</code>:</p><pre><code class="text">1&gt; systools:make_relup(&quot;ch_rel-2&quot;, [&quot;ch_rel-1&quot;], [&quot;ch_rel-1&quot;],
│ │ │  [{path,[&quot;../ch_rel-1&quot;,
│ │ │  &quot;../ch_rel-1/lib/ch_app-1/ebin&quot;]}]).
│ │ │ @@ -433,25 +433,25 @@
│ │ │  <p>When you have made a new version of a release, a release package can be created
│ │ │  with this new version and transferred to the target environment.</p><p>To install the new version of the release in runtime, the <em>release
│ │ │  handler</em> is used. This is a process belonging to the SASL application,
│ │ │  which handles unpacking, installation, and removal of release
│ │ │  packages. The <a href="../../lib/sasl-4.2.2.1/doc/html/release_handler.html"><code class="inline">release_handler</code></a> module communicates with this process.</p><p>Assuming there is an operational target system with installation root directory
│ │ │  <code class="inline">$ROOT</code>, the release package with the new version of the release is to be copied
│ │ │  to <code class="inline">$ROOT/releases</code>.</p><p>First, <em>unpack</em> the release package. The files are then extracted from the
│ │ │ -package:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="4295313995-1">(</span><span class="n">ReleaseName</span><span class="p" data-group-id="4295313995-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4295313995-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p" data-group-id="4295313995-2">}</span></code></pre><ul><li><code class="inline">ReleaseName</code> is the name of the release package except the <code class="inline">.tar.gz</code>
│ │ │ +package:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="1982986064-1">(</span><span class="n">ReleaseName</span><span class="p" data-group-id="1982986064-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1982986064-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p" data-group-id="1982986064-2">}</span></code></pre><ul><li><code class="inline">ReleaseName</code> is the name of the release package except the <code class="inline">.tar.gz</code>
│ │ │  extension.</li><li><code class="inline">Vsn</code> is the version of the unpacked release, as defined in its <code class="inline">.rel</code> file.</li></ul><p>A directory <code class="inline">$ROOT/lib/releases/Vsn</code> is created, where the <code class="inline">.rel</code> file, the boot
│ │ │  script <code class="inline">start.boot</code>, the system configuration file <code class="inline">sys.config</code>, and <code class="inline">relup</code> are
│ │ │  placed. For applications with new version numbers, the application directories
│ │ │  are placed under <code class="inline">$ROOT/lib</code>. Unchanged applications are not affected.</p><p>An unpacked release can be <em>installed</em>. The release handler then evaluates the
│ │ │ -instructions in <code class="inline">relup</code>, step by step:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="6930579434-1">(</span><span class="n">Vsn</span><span class="p" data-group-id="6930579434-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6930579434-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FromVsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6930579434-3">[</span><span class="p" data-group-id="6930579434-3">]</span><span class="p" data-group-id="6930579434-2">}</span></code></pre><p>If an error occurs during the installation, the system is rebooted using the old
│ │ │ +instructions in <code class="inline">relup</code>, step by step:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="7045328322-1">(</span><span class="n">Vsn</span><span class="p" data-group-id="7045328322-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7045328322-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">FromVsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7045328322-3">[</span><span class="p" data-group-id="7045328322-3">]</span><span class="p" data-group-id="7045328322-2">}</span></code></pre><p>If an error occurs during the installation, the system is rebooted using the old
│ │ │  version of the release. If installation succeeds, the system is afterwards using
│ │ │  the new version of the release, but if anything happens and the system is
│ │ │  rebooted, it starts using the previous version again.</p><p>To be made the default version, the newly installed release must be made
│ │ │  <em>permanent</em>, which means the previous version becomes <em>old</em>:</p><pre><code class="text">release_handler:make_permanent(Vsn) =&gt; ok</code></pre><p>The system keeps information about which versions are old and permanent in the
│ │ │ -files <code class="inline">$ROOT/releases/RELEASES</code> and <code class="inline">$ROOT/releases/start_erl.data</code>.</p><p>To downgrade from <code class="inline">Vsn</code> to <code class="inline">FromVsn</code>, <code class="inline">install_release</code> must be called again:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="2405109165-1">(</span><span class="n">FromVsn</span><span class="p" data-group-id="2405109165-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2405109165-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2405109165-3">[</span><span class="p" data-group-id="2405109165-3">]</span><span class="p" data-group-id="2405109165-2">}</span></code></pre><p>An installed, but not permanent, release can be <em>removed</em>. Information about the
│ │ │ +files <code class="inline">$ROOT/releases/RELEASES</code> and <code class="inline">$ROOT/releases/start_erl.data</code>.</p><p>To downgrade from <code class="inline">Vsn</code> to <code class="inline">FromVsn</code>, <code class="inline">install_release</code> must be called again:</p><pre><code class="makeup erlang" translate="no"><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="0355037469-1">(</span><span class="n">FromVsn</span><span class="p" data-group-id="0355037469-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0355037469-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Vsn</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0355037469-3">[</span><span class="p" data-group-id="0355037469-3">]</span><span class="p" data-group-id="0355037469-2">}</span></code></pre><p>An installed, but not permanent, release can be <em>removed</em>. Information about the
│ │ │  release is then deleted from <code class="inline">$ROOT/releases/RELEASES</code> and the release-specific
│ │ │  code, that is, the new application directories and the <code class="inline">$ROOT/releases/Vsn</code>
│ │ │  directory, are removed.</p><pre><code class="text">release_handler:remove_release(Vsn) =&gt; ok</code></pre><h3 id="example-continued-from-the-previous-sections" class="section-heading">
│ │ │    <a href="#example-continued-from-the-previous-sections" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example (continued from the previous sections)</span>
│ │ │ @@ -462,17 +462,17 @@
│ │ │  is needed, the file is to contain the empty list:</p><pre><code class="text">[].</code></pre><p><em>Step 2)</em> Start the system as a simple target system. In reality, it is to be
│ │ │  started as an embedded system. However, using <code class="inline">erl</code> with the correct boot script
│ │ │  and config file is enough for illustration purposes:</p><pre><code class="text">% cd $ROOT
│ │ │  % bin/erl -boot $ROOT/releases/A/start -config $ROOT/releases/A/sys
│ │ │  ...</code></pre><p><code class="inline">$ROOT</code> is the installation directory of the target system.</p><p><em>Step 3)</em> In another Erlang shell, generate start scripts and create a release
│ │ │  package for the new version <code class="inline">&quot;B&quot;</code>. Remember to include (a possible updated)
│ │ │  <code class="inline">sys.config</code> and the <code class="inline">relup</code> file. For more information, see
│ │ │ -<a href="release_handling.html#relup">Release Upgrade File</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="2256199734-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="2256199734-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="release_handling.html#relup">Release Upgrade File</a>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="4025239574-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="4025239574-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="2256199734-2">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="2256199734-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="4025239574-2">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="4025239574-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>The new release package now also contains version &quot;2&quot; of <code class="inline">ch_app</code> and the
│ │ │  <code class="inline">relup</code> file:</p><pre><code class="text">% tar tf ch_rel-2.tar
│ │ │  lib/kernel-9.2.4/ebin/kernel.app
│ │ │  lib/kernel-9.2.4/ebin/application.beam
│ │ │  ...
│ │ │  lib/stdlib-5.2.3/ebin/stdlib.app
│ │ │  lib/stdlib-5.2.3/ebin/argparse.beam
│ │ │ @@ -485,31 +485,31 @@
│ │ │  lib/ch_app-2/ebin/ch_sup.beam
│ │ │  lib/ch_app-2/ebin/ch3.beam
│ │ │  releases/B/start.boot
│ │ │  releases/B/relup
│ │ │  releases/B/sys.config
│ │ │  releases/B/ch_rel-2.rel
│ │ │  releases/ch_rel-2.rel</code></pre><p><em>Step 4)</em> Copy the release package <code class="inline">ch_rel-2.tar.gz</code> to the <code class="inline">$ROOT/releases</code>
│ │ │ -directory.</p><p><em>Step 5)</em> In the running target system, unpack the release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="4401899291-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="4401899291-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4401899291-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="4401899291-2">}</span></code></pre><p>The new application version <code class="inline">ch_app-2</code> is installed under <code class="inline">$ROOT/lib</code> next to
│ │ │ +directory.</p><p><em>Step 5)</em> In the running target system, unpack the release package:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">unpack_release</span><span class="p" data-group-id="4689130236-1">(</span><span class="s">&quot;ch_rel-2&quot;</span><span class="p" data-group-id="4689130236-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4689130236-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="4689130236-2">}</span></code></pre><p>The new application version <code class="inline">ch_app-2</code> is installed under <code class="inline">$ROOT/lib</code> next to
│ │ │  <code class="inline">ch_app-1</code>. The <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code> directories are not affected, as
│ │ │  they have not changed.</p><p>Under <code class="inline">$ROOT/releases</code>, a new directory <code class="inline">B</code> is created, containing
│ │ │ -<code class="inline">ch_rel-2.rel</code>, <code class="inline">start.boot</code>, <code class="inline">sys.config</code>, and <code class="inline">relup</code>.</p><p><em>Step 6)</em> Check if the function <code class="inline">ch3:available/0</code> is available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="2690122882-1">(</span><span class="p" data-group-id="2690122882-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">ch_rel-2.rel</code>, <code class="inline">start.boot</code>, <code class="inline">sys.config</code>, and <code class="inline">relup</code>.</p><p><em>Step 6)</em> Check if the function <code class="inline">ch3:available/0</code> is available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="1227688117-1">(</span><span class="p" data-group-id="1227688117-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: undefined function ch3:available/0</span></code></pre><p><em>Step 7)</em> Install the new release. The instructions in <code class="inline">$ROOT/releases/B/relup</code>
│ │ │  are executed one by one, resulting in the new version of <code class="inline">ch3</code> being loaded. The
│ │ │ -function <code class="inline">ch3:available/0</code> is now available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="4584309289-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="4584309289-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4584309289-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="p" data-group-id="4584309289-3">[</span><span class="p" data-group-id="4584309289-3">]</span><span class="p" data-group-id="4584309289-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="4584309289-4">(</span><span class="p" data-group-id="4584309289-4">)</span><span class="p">.</span><span class="w">
│ │ │ +function <code class="inline">ch3:available/0</code> is now available:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">install_release</span><span class="p" data-group-id="1530928592-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="1530928592-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1530928592-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="p" data-group-id="1530928592-3">[</span><span class="p" data-group-id="1530928592-3">]</span><span class="p" data-group-id="1530928592-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">ch3</span><span class="p">:</span><span class="nf">available</span><span class="p" data-group-id="1530928592-4">(</span><span class="p" data-group-id="1530928592-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">3</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="4584309289-5">(</span><span class="ss">ch3</span><span class="p" data-group-id="4584309289-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="1530928592-5">(</span><span class="ss">ch3</span><span class="p" data-group-id="1530928592-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;.../lib/ch_app-2/ebin/ch3.beam&quot;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="4584309289-6">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="4584309289-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">code</span><span class="p">:</span><span class="nf">which</span><span class="p" data-group-id="1530928592-6">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="1530928592-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;.../lib/ch_app-1/ebin/ch_sup.beam&quot;</span></code></pre><p>Processes in <code class="inline">ch_app</code> for which code have not been updated, for example, the
│ │ │  supervisor, are still evaluating code from <code class="inline">ch_app-1</code>.</p><p><em>Step 8)</em> If the target system is now rebooted, it uses version &quot;A&quot; again. The
│ │ │ -&quot;B&quot; version must be made permanent, to be used when the system is rebooted.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">make_permanent</span><span class="p" data-group-id="5635121526-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="5635121526-1">)</span><span class="p">.</span><span class="w">
│ │ │ +&quot;B&quot; version must be made permanent, to be used when the system is rebooted.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nc">release_handler</span><span class="p">:</span><span class="nf">make_permanent</span><span class="p" data-group-id="3353452385-1">(</span><span class="s">&quot;B&quot;</span><span class="p" data-group-id="3353452385-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p><a href="" id="sys"></a></p><h2 id="updating-application-specifications" class="section-heading">
│ │ │    <a href="#updating-application-specifications" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Updating Application Specifications</span>
│ │ │  </h2>
│ │ │  <p>When a new version of a release is installed, the application specifications are
│ │ │ @@ -518,15 +518,15 @@
│ │ │  boot script is generated from the same <code class="inline">.rel</code> file as is used to build the
│ │ │  release package itself.</p></section><p>Specifically, the application configuration parameters are automatically updated
│ │ │  according to (in increasing priority order):</p><ul><li>The data in the boot script, fetched from the new application resource file
│ │ │  <code class="inline">App.app</code></li><li>The new <code class="inline">sys.config</code></li><li>Command-line arguments <code class="inline">-App Par Val</code></li></ul><p>This means that parameter values set in the other system configuration files and
│ │ │  values set using <a href="../../lib/kernel-10.2.7.4/doc/html/application.html#set_env/3"><code class="inline">application:set_env/3</code></a> are disregarded.</p><p>When an installed release is made permanent, the system process <code class="inline">init</code> is set to
│ │ │  point out the new <code class="inline">sys.config</code>.</p><p>After the installation, the application controller compares the old and new
│ │ │  configuration parameters for all running applications and call the callback
│ │ │ -function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">config_change</span><span class="p" data-group-id="2707679335-1">(</span><span class="n">Changed</span><span class="p">,</span><span class="w"> </span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Removed</span><span class="p" data-group-id="2707679335-1">)</span></code></pre><ul><li><code class="inline">Module</code> is the application callback module as defined by the <code class="inline">mod</code> key in the
│ │ │ +function:</p><pre><code class="makeup erlang" translate="no"><span class="n">Module</span><span class="p">:</span><span class="nf">config_change</span><span class="p" data-group-id="3695856431-1">(</span><span class="n">Changed</span><span class="p">,</span><span class="w"> </span><span class="n">New</span><span class="p">,</span><span class="w"> </span><span class="n">Removed</span><span class="p" data-group-id="3695856431-1">)</span></code></pre><ul><li><code class="inline">Module</code> is the application callback module as defined by the <code class="inline">mod</code> key in the
│ │ │  <code class="inline">.app</code> file.</li><li><code class="inline">Changed</code> and <code class="inline">New</code> are lists of <code class="inline">{Par,Val}</code> for all changed and added
│ │ │  configuration parameters, respectively.</li><li><code class="inline">Removed</code> is a list of all parameters <code class="inline">Par</code> that have been removed.</li></ul><p>The function is optional and can be omitted when implementing an application
│ │ │  callback module.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/release_structure.html
│ │ │ @@ -136,37 +136,37 @@
│ │ │    <a href="#release-resource-file" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Release Resource File</span>
│ │ │  </h2>
│ │ │  <p>To define a release, create a <em>release resource file</em>, or in short a <code class="inline">.rel</code>
│ │ │  file. In the file, specify the name and version of the release, which ERTS
│ │ │ -version it is based on, and which applications it consists of:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5566002299-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5566002299-2">{</span><span class="n">Name</span><span class="p">,</span><span class="n">Vsn</span><span class="p" data-group-id="5566002299-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5566002299-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">EVsn</span><span class="p" data-group-id="5566002299-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="5566002299-4">[</span><span class="p" data-group-id="5566002299-5">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsn1</span><span class="p" data-group-id="5566002299-5">}</span><span class="p">,</span><span class="w">
│ │ │ +version it is based on, and which applications it consists of:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9360369854-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9360369854-2">{</span><span class="n">Name</span><span class="p">,</span><span class="n">Vsn</span><span class="p" data-group-id="9360369854-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9360369854-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="n">EVsn</span><span class="p" data-group-id="9360369854-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9360369854-4">[</span><span class="p" data-group-id="9360369854-5">{</span><span class="n">Application1</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsn1</span><span class="p" data-group-id="9360369854-5">}</span><span class="p">,</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5566002299-6">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsnN</span><span class="p" data-group-id="5566002299-6">}</span><span class="p" data-group-id="5566002299-4">]</span><span class="p" data-group-id="5566002299-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Name</code>, <code class="inline">Vsn</code>, <code class="inline">EVsn</code>, and <code class="inline">AppVsn</code> are strings.</p><p>The file must be named <code class="inline">Rel.rel</code>, where <code class="inline">Rel</code> is a unique name.</p><p>Each <code class="inline">Application</code> (atom) and <code class="inline">AppVsn</code> is the name and version of an application
│ │ │ +  </span><span class="p" data-group-id="9360369854-6">{</span><span class="n">ApplicationN</span><span class="p">,</span><span class="w"> </span><span class="n">AppVsnN</span><span class="p" data-group-id="9360369854-6">}</span><span class="p" data-group-id="9360369854-4">]</span><span class="p" data-group-id="9360369854-1">}</span><span class="p">.</span></code></pre><p><code class="inline">Name</code>, <code class="inline">Vsn</code>, <code class="inline">EVsn</code>, and <code class="inline">AppVsn</code> are strings.</p><p>The file must be named <code class="inline">Rel.rel</code>, where <code class="inline">Rel</code> is a unique name.</p><p>Each <code class="inline">Application</code> (atom) and <code class="inline">AppVsn</code> is the name and version of an application
│ │ │  included in the release. The minimal release based on Erlang/OTP consists of the
│ │ │  Kernel and STDLIB applications, so these applications must be included in the
│ │ │  list.</p><p>If the release is to be upgraded, it must also include the SASL application.</p><p><a href="" id="ch_rel"></a></p><p>Here is an example showing the <code class="inline">.app</code> file for a release of <code class="inline">ch_app</code> from
│ │ │ -the <a href="applications.html#ch_app">Applications</a> section:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7490849801-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7490849801-2">[</span><span class="p" data-group-id="7490849801-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="7490849801-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="7490849801-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="7490849801-4">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="7490849801-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7490849801-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="7490849801-6">]</span><span class="p" data-group-id="7490849801-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="7490849801-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7490849801-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="7490849801-8">]</span><span class="p" data-group-id="7490849801-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="7490849801-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7490849801-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="7490849801-10">]</span><span class="p" data-group-id="7490849801-9">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="7490849801-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7490849801-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="7490849801-13">[</span><span class="p" data-group-id="7490849801-13">]</span><span class="p" data-group-id="7490849801-12">}</span><span class="p" data-group-id="7490849801-11">}</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="7490849801-2">]</span><span class="p" data-group-id="7490849801-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">.rel</code> file must also contain <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code>, as these
│ │ │ -applications are required by <code class="inline">ch_app</code>. The file is called <code class="inline">ch_rel-1.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8653120388-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8653120388-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;A&quot;</span><span class="p" data-group-id="8653120388-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8653120388-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="8653120388-3">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="8653120388-4">[</span><span class="p" data-group-id="8653120388-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="8653120388-5">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8653120388-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="8653120388-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8653120388-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="8653120388-7">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="8653120388-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="8653120388-8">}</span><span class="p" data-group-id="8653120388-4">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8653120388-1">}</span><span class="p">.</span></code></pre><p><a href="" id="boot"></a></p><h2 id="generating-boot-scripts" class="section-heading">
│ │ │ +the <a href="applications.html#ch_app">Applications</a> section:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9180904561-1">{</span><span class="ss">application</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_app</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9180904561-2">[</span><span class="p" data-group-id="9180904561-3">{</span><span class="ss">description</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Channel allocator&quot;</span><span class="p" data-group-id="9180904561-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9180904561-4">{</span><span class="ss">vsn</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="9180904561-4">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9180904561-5">{</span><span class="ss">modules</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9180904561-6">[</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="ss">ch3</span><span class="p" data-group-id="9180904561-6">]</span><span class="p" data-group-id="9180904561-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9180904561-7">{</span><span class="ss">registered</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9180904561-8">[</span><span class="ss">ch3</span><span class="p" data-group-id="9180904561-8">]</span><span class="p" data-group-id="9180904561-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9180904561-9">{</span><span class="ss">applications</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9180904561-10">[</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="ss">sasl</span><span class="p" data-group-id="9180904561-10">]</span><span class="p" data-group-id="9180904561-9">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="9180904561-11">{</span><span class="ss">mod</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9180904561-12">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="p" data-group-id="9180904561-13">[</span><span class="p" data-group-id="9180904561-13">]</span><span class="p" data-group-id="9180904561-12">}</span><span class="p" data-group-id="9180904561-11">}</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9180904561-2">]</span><span class="p" data-group-id="9180904561-1">}</span><span class="p">.</span></code></pre><p>The <code class="inline">.rel</code> file must also contain <code class="inline">kernel</code>, <code class="inline">stdlib</code>, and <code class="inline">sasl</code>, as these
│ │ │ +applications are required by <code class="inline">ch_app</code>. The file is called <code class="inline">ch_rel-1.rel</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="8464216453-1">{</span><span class="ss">release</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8464216453-2">{</span><span class="s">&quot;ch_rel&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;A&quot;</span><span class="p" data-group-id="8464216453-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8464216453-3">{</span><span class="ss">erts</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;14.2.5&quot;</span><span class="p" data-group-id="8464216453-3">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="8464216453-4">[</span><span class="p" data-group-id="8464216453-5">{</span><span class="ss">kernel</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;9.2.4&quot;</span><span class="p" data-group-id="8464216453-5">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8464216453-6">{</span><span class="ss">stdlib</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;5.2.3&quot;</span><span class="p" data-group-id="8464216453-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8464216453-7">{</span><span class="ss">sasl</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;4.2.1&quot;</span><span class="p" data-group-id="8464216453-7">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8464216453-8">{</span><span class="ss">ch_app</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;1&quot;</span><span class="p" data-group-id="8464216453-8">}</span><span class="p" data-group-id="8464216453-4">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8464216453-1">}</span><span class="p">.</span></code></pre><p><a href="" id="boot"></a></p><h2 id="generating-boot-scripts" class="section-heading">
│ │ │    <a href="#generating-boot-scripts" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Generating Boot Scripts</span>
│ │ │  </h2>
│ │ │  <p><a href="../../lib/sasl-4.2.2.1/doc/html/systools.html"><code class="inline">systools</code></a> in the SASL application includes tools to build and check
│ │ │  releases. The functions read the <code class="inline">.rel</code> and <code class="inline">.app</code> files and perform
│ │ │ @@ -190,17 +190,17 @@
│ │ │    <a href="#creating-a-release-package" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Creating a Release Package</span>
│ │ │  </h2>
│ │ │  <p>The <a href="../../lib/sasl-4.2.2.1/doc/html/systools.html#make_tar/2"><code class="inline">systools:make_tar/1,2</code></a> function takes a
│ │ │  <code class="inline">.rel</code> file as input and creates a zipped tar file with the code for
│ │ │ -the specified applications, a <em>release package</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="6395855303-1">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="6395855303-1">)</span><span class="p">.</span><span class="w">
│ │ │ +the specified applications, a <em>release package</em>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_script</span><span class="p" data-group-id="2817606346-1">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="2817606346-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="6395855303-2">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="6395855303-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">systools</span><span class="p">:</span><span class="nf">make_tar</span><span class="p" data-group-id="2817606346-2">(</span><span class="s">&quot;ch_rel-1&quot;</span><span class="p" data-group-id="2817606346-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>The release package by default contains:</p><ul><li>The <code class="inline">.app</code> files</li><li>The <code class="inline">.rel</code> file</li><li>The object code for all applications, structured according to the
│ │ │  <a href="applications.html#app_dir">application directory structure</a></li><li>The binary boot script renamed to <code class="inline">start.boot</code></li></ul><pre><code class="text">% tar tf ch_rel-1.tar
│ │ │  lib/kernel-9.2.4/ebin/kernel.app
│ │ │  lib/kernel-9.2.4/ebin/application.beam
│ │ │  ...
│ │ │  lib/stdlib-5.2.3/ebin/stdlib.app
│ │ │  lib/stdlib-5.2.3/ebin/argparse.beam
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/robustness.html
│ │ │ @@ -128,68 +128,68 @@
│ │ │  </h2>
│ │ │  <p>Before improving the messenger program, let us look at some general principles,
│ │ │  using the ping pong program as an example. Recall that when &quot;ping&quot; finishes, it
│ │ │  tells &quot;pong&quot; that it has done so by sending the atom <code class="inline">finished</code> as a message to
│ │ │  &quot;pong&quot; so that &quot;pong&quot; can also finish. Another way to let &quot;pong&quot; finish is to
│ │ │  make &quot;pong&quot; exit if it does not receive a message from ping within a certain
│ │ │  time. This can be done by adding a <em>time-out</em> to <code class="inline">pong</code> as shown in the
│ │ │ -following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3290758015-1">(</span><span class="ss">tut19</span><span class="p" data-group-id="3290758015-1">)</span><span class="p">.</span><span class="w">
│ │ │ +following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0673189905-1">(</span><span class="ss">tut19</span><span class="p" data-group-id="0673189905-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3290758015-2">(</span><span class="p" data-group-id="3290758015-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3290758015-3">]</span><span class="p" data-group-id="3290758015-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0673189905-2">(</span><span class="p" data-group-id="0673189905-3">[</span><span class="ss">start_ping</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">start_pong</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0673189905-3">]</span><span class="p" data-group-id="0673189905-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="3290758015-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="3290758015-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3290758015-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3290758015-6">[</span><span class="p" data-group-id="3290758015-6">]</span><span class="p" data-group-id="3290758015-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="0673189905-4">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0673189905-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0673189905-5">(</span><span class="s">&quot;ping finished</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0673189905-6">[</span><span class="p" data-group-id="0673189905-6">]</span><span class="p" data-group-id="0673189905-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="3290758015-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="3290758015-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3290758015-8">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="3290758015-8">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="3290758015-9">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="3290758015-10">(</span><span class="p" data-group-id="3290758015-10">)</span><span class="p" data-group-id="3290758015-9">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="0673189905-7">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0673189905-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0673189905-8">{</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0673189905-8">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0673189905-9">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0673189905-10">(</span><span class="p" data-group-id="0673189905-10">)</span><span class="p" data-group-id="0673189905-9">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3290758015-11">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3290758015-12">[</span><span class="p" data-group-id="3290758015-12">]</span><span class="p" data-group-id="3290758015-11">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0673189905-11">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0673189905-12">[</span><span class="p" data-group-id="0673189905-12">]</span><span class="p" data-group-id="0673189905-11">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping</span><span class="p" data-group-id="3290758015-13">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="3290758015-13">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping</span><span class="p" data-group-id="0673189905-13">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0673189905-13">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="3290758015-14">(</span><span class="p" data-group-id="3290758015-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="0673189905-14">(</span><span class="p" data-group-id="0673189905-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="3290758015-15">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="3290758015-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3290758015-16">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3290758015-17">[</span><span class="p" data-group-id="3290758015-17">]</span><span class="p" data-group-id="3290758015-16">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0673189905-15">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="0673189905-15">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0673189905-16">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0673189905-17">[</span><span class="p" data-group-id="0673189905-17">]</span><span class="p" data-group-id="0673189905-16">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="3290758015-18">(</span><span class="p" data-group-id="3290758015-18">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="0673189905-18">(</span><span class="p" data-group-id="0673189905-18">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3290758015-19">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3290758015-20">[</span><span class="p" data-group-id="3290758015-20">]</span><span class="p" data-group-id="3290758015-19">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0673189905-19">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0673189905-20">[</span><span class="p" data-group-id="0673189905-20">]</span><span class="p" data-group-id="0673189905-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_pong</span><span class="p" data-group-id="3290758015-21">(</span><span class="p" data-group-id="3290758015-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="3290758015-22">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="3290758015-23">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3290758015-24">[</span><span class="p" data-group-id="3290758015-24">]</span><span class="p" data-group-id="3290758015-23">)</span><span class="p" data-group-id="3290758015-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_pong</span><span class="p" data-group-id="0673189905-21">(</span><span class="p" data-group-id="0673189905-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="0673189905-22">(</span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="0673189905-23">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0673189905-24">[</span><span class="p" data-group-id="0673189905-24">]</span><span class="p" data-group-id="0673189905-23">)</span><span class="p" data-group-id="0673189905-22">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_ping</span><span class="p" data-group-id="3290758015-25">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="3290758015-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="3290758015-26">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3290758015-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="3290758015-27">]</span><span class="p" data-group-id="3290758015-26">)</span><span class="p">.</span></code></pre><p>After this is compiled and the file <code class="inline">tut19.beam</code> is copied to the necessary
│ │ │ +</span><span class="nf">start_ping</span><span class="p" data-group-id="0673189905-25">(</span><span class="n">Pong_Node</span><span class="p" data-group-id="0673189905-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="0673189905-26">(</span><span class="ss">tut19</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0673189905-27">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Node</span><span class="p" data-group-id="0673189905-27">]</span><span class="p" data-group-id="0673189905-26">)</span><span class="p">.</span></code></pre><p>After this is compiled and the file <code class="inline">tut19.beam</code> is copied to the necessary
│ │ │  directories, the following is seen on (pong@kosken):</p><pre><code class="text">(pong@kosken)1&gt; tut19:start_pong().
│ │ │  true
│ │ │  Pong received ping
│ │ │  Pong received ping
│ │ │  Pong received ping
│ │ │  Pong timed out</code></pre><p>And the following is seen on (ping@gollum):</p><pre><code class="text">(ping@gollum)1&gt; tut19:start_ping(pong@kosken).
│ │ │  &lt;0.36.0&gt;
│ │ │  Ping received pong
│ │ │  Ping received pong
│ │ │  Ping received pong
│ │ │ -ping finished</code></pre><p>The time-out is set in:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pong</span><span class="p" data-group-id="0600521377-1">(</span><span class="p" data-group-id="0600521377-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +ping finished</code></pre><p>The time-out is set in:</p><pre><code class="makeup erlang" translate="no"><span class="nf">pong</span><span class="p" data-group-id="2227455424-1">(</span><span class="p" data-group-id="2227455424-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0600521377-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="0600521377-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0600521377-3">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0600521377-4">[</span><span class="p" data-group-id="0600521377-4">]</span><span class="p" data-group-id="0600521377-3">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2227455424-2">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2227455424-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2227455424-3">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2227455424-4">[</span><span class="p" data-group-id="2227455424-4">]</span><span class="p" data-group-id="2227455424-3">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="0600521377-5">(</span><span class="p" data-group-id="0600521377-5">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="2227455424-5">(</span><span class="p" data-group-id="2227455424-5">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0600521377-6">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0600521377-7">[</span><span class="p" data-group-id="0600521377-7">]</span><span class="p" data-group-id="0600521377-6">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2227455424-6">(</span><span class="s">&quot;Pong timed out</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2227455424-7">[</span><span class="p" data-group-id="2227455424-7">]</span><span class="p" data-group-id="2227455424-6">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The time-out (<code class="inline">after 5000</code>) is started when <code class="inline">receive</code> is entered. The time-out
│ │ │  is canceled if <code class="inline">{ping,Ping_PID}</code> is received. If <code class="inline">{ping,Ping_PID}</code> is not
│ │ │  received, the actions following the time-out are done after 5000 milliseconds.
│ │ │  <code class="inline">after</code> must be last in the <code class="inline">receive</code>, that is, preceded by all other message
│ │ │  reception specifications in the <code class="inline">receive</code>. It is also possible to call a
│ │ │ -function that returned an integer for the time-out:</p><pre><code class="makeup erlang" translate="no"><span class="k">after</span><span class="w"> </span><span class="nf">pong_timeout</span><span class="p" data-group-id="9577343151-1">(</span><span class="p" data-group-id="9577343151-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>In general, there are better ways than using time-outs to supervise parts of a
│ │ │ +function that returned an integer for the time-out:</p><pre><code class="makeup erlang" translate="no"><span class="k">after</span><span class="w"> </span><span class="nf">pong_timeout</span><span class="p" data-group-id="5797447256-1">(</span><span class="p" data-group-id="5797447256-1">)</span><span class="w"> </span><span class="p">-&gt;</span></code></pre><p>In general, there are better ways than using time-outs to supervise parts of a
│ │ │  distributed Erlang system. Time-outs are usually appropriate to supervise
│ │ │  external events, for example, if you have expected a message from some external
│ │ │  system within a specified time. For example, a time-out can be used to log a
│ │ │  user out of the messenger system if they have not accessed it for, say, ten
│ │ │  minutes.</p><h2 id="error-handling" class="section-heading">
│ │ │    <a href="#error-handling" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -209,96 +209,96 @@
│ │ │  something called a <em>signal</em> to all the processes it has links to.</p><p>The signal carries information about the pid it was sent from and the exit
│ │ │  reason.</p><p>The default behaviour of a process that receives a normal exit is to ignore the
│ │ │  signal.</p><p>The default behaviour in the two other cases (that is, abnormal exit) above is
│ │ │  to:</p><ul><li>Bypass all messages to the receiving process.</li><li>Kill the receiving process.</li><li>Propagate the same error signal to the links of the killed process.</li></ul><p>In this way you can connect all processes in a transaction together using links.
│ │ │  If one of the processes exits abnormally, all the processes in the transaction
│ │ │  are killed. As it is often wanted to create a process and link to it at the same
│ │ │  time, there is a special BIF, <a href="../../erts-15.2.7.8/doc/html/erlang.html#spawn_link/1">spawn_link</a> that does the
│ │ │ -same as <code class="inline">spawn</code>, but also creates a link to the spawned process.</p><p>Now an example of the ping pong example using links to terminate &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2803015130-1">(</span><span class="ss">tut20</span><span class="p" data-group-id="2803015130-1">)</span><span class="p">.</span><span class="w">
│ │ │ +same as <code class="inline">spawn</code>, but also creates a link to the spawned process.</p><p>Now an example of the ping pong example using links to terminate &quot;pong&quot;:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2676805076-1">(</span><span class="ss">tut20</span><span class="p" data-group-id="2676805076-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2803015130-2">(</span><span class="p" data-group-id="2803015130-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2803015130-3">]</span><span class="p" data-group-id="2803015130-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2676805076-2">(</span><span class="p" data-group-id="2676805076-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2676805076-3">]</span><span class="p" data-group-id="2676805076-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2803015130-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2803015130-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">link</span><span class="p" data-group-id="2803015130-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="2803015130-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="2803015130-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2803015130-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="2676805076-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2676805076-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">link</span><span class="p" data-group-id="2676805076-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="2676805076-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="2676805076-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2676805076-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="2803015130-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2803015130-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="2803015130-8">(</span><span class="ss">ping</span><span class="p" data-group-id="2803015130-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="2676805076-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2676805076-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="2676805076-8">(</span><span class="ss">ping</span><span class="p" data-group-id="2676805076-8">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="2803015130-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2803015130-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2803015130-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2803015130-11">(</span><span class="p" data-group-id="2803015130-11">)</span><span class="p" data-group-id="2803015130-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="2676805076-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2676805076-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2676805076-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2676805076-11">(</span><span class="p" data-group-id="2676805076-11">)</span><span class="p" data-group-id="2676805076-10">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2803015130-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2803015130-13">[</span><span class="p" data-group-id="2803015130-13">]</span><span class="p" data-group-id="2803015130-12">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2676805076-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2676805076-13">[</span><span class="p" data-group-id="2676805076-13">]</span><span class="p" data-group-id="2676805076-12">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="2803015130-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2803015130-14">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="2676805076-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2676805076-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="2803015130-15">(</span><span class="p" data-group-id="2803015130-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="2676805076-15">(</span><span class="p" data-group-id="2676805076-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2803015130-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2803015130-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2803015130-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2803015130-18">[</span><span class="p" data-group-id="2803015130-18">]</span><span class="p" data-group-id="2803015130-17">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2676805076-16">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2676805076-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2676805076-17">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2676805076-18">[</span><span class="p" data-group-id="2676805076-18">]</span><span class="p" data-group-id="2676805076-17">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong</span><span class="p" data-group-id="2803015130-19">(</span><span class="p" data-group-id="2803015130-19">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong</span><span class="p" data-group-id="2676805076-19">(</span><span class="p" data-group-id="2676805076-19">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2803015130-20">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="2803015130-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2803015130-21">(</span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2803015130-22">[</span><span class="p" data-group-id="2803015130-22">]</span><span class="p" data-group-id="2803015130-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2803015130-23">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2803015130-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="2803015130-24">]</span><span class="p" data-group-id="2803015130-23">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)3&gt; tut20:start(s2@kosken).
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="2676805076-20">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="2676805076-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2676805076-21">(</span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2676805076-22">[</span><span class="p" data-group-id="2676805076-22">]</span><span class="p" data-group-id="2676805076-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="2676805076-23">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut20</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2676805076-24">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="2676805076-24">]</span><span class="p" data-group-id="2676805076-23">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)3&gt; tut20:start(s2@kosken).
│ │ │  Pong received ping
│ │ │  &lt;3820.41.0&gt;
│ │ │  Ping received pong
│ │ │  Pong received ping
│ │ │  Ping received pong
│ │ │  Pong received ping
│ │ │  Ping received pong</code></pre><p>This is a slight modification of the ping pong program where both processes are
│ │ │  spawned from the same <code class="inline">start/1</code> function, and the &quot;ping&quot; process can be spawned
│ │ │  on a separate node. Notice the use of the <code class="inline">link</code> BIF. &quot;Ping&quot; calls
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#exit/1"><code class="inline">exit(ping)</code></a> when it finishes and this causes an exit signal to be
│ │ │  sent to &quot;pong&quot;, which also terminates.</p><p>It is possible to modify the default behaviour of a process so that it does not
│ │ │  get killed when it receives abnormal exit signals. Instead, all signals are
│ │ │  turned into normal messages on the format <code class="inline">{'EXIT',FromPID,Reason}</code> and added to
│ │ │ -the end of the receiving process' message queue. This behaviour is set by:</p><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="4569272525-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4569272525-1">)</span></code></pre><p>There are several other process flags, see <a href="../../erts-15.2.7.8/doc/html/erlang.html#process_flag/2">erlang(3)</a>.
│ │ │ +the end of the receiving process' message queue. This behaviour is set by:</p><pre><code class="makeup erlang" translate="no"><span class="nf">process_flag</span><span class="p" data-group-id="4296967161-1">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4296967161-1">)</span></code></pre><p>There are several other process flags, see <a href="../../erts-15.2.7.8/doc/html/erlang.html#process_flag/2">erlang(3)</a>.
│ │ │  Changing the default behaviour of a process in this way is usually not done in
│ │ │  standard user programs, but is left to the supervisory programs in OTP. However,
│ │ │ -the ping pong program is modified to illustrate exit trapping.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2855430000-1">(</span><span class="ss">tut21</span><span class="p" data-group-id="2855430000-1">)</span><span class="p">.</span><span class="w">
│ │ │ +the ping pong program is modified to illustrate exit trapping.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7055718017-1">(</span><span class="ss">tut21</span><span class="p" data-group-id="7055718017-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2855430000-2">(</span><span class="p" data-group-id="2855430000-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2855430000-3">]</span><span class="p" data-group-id="2855430000-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7055718017-2">(</span><span class="p" data-group-id="7055718017-3">[</span><span class="ss">start</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w">  </span><span class="ss">ping</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7055718017-3">]</span><span class="p" data-group-id="7055718017-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping</span><span class="p" data-group-id="2855430000-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2855430000-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">link</span><span class="p" data-group-id="2855430000-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="2855430000-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="2855430000-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2855430000-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">ping</span><span class="p" data-group-id="7055718017-4">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="7055718017-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">link</span><span class="p" data-group-id="7055718017-5">(</span><span class="n">Pong_Pid</span><span class="p" data-group-id="7055718017-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="7055718017-6">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="7055718017-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="2855430000-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2855430000-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="2855430000-8">(</span><span class="ss">ping</span><span class="p" data-group-id="2855430000-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="7055718017-7">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="7055718017-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="7055718017-8">(</span><span class="ss">ping</span><span class="p" data-group-id="7055718017-8">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">ping1</span><span class="p" data-group-id="2855430000-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2855430000-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2855430000-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="2855430000-11">(</span><span class="p" data-group-id="2855430000-11">)</span><span class="p" data-group-id="2855430000-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">ping1</span><span class="p" data-group-id="7055718017-9">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="7055718017-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Pong_Pid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7055718017-10">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7055718017-11">(</span><span class="p" data-group-id="7055718017-11">)</span><span class="p" data-group-id="7055718017-10">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">pong</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2855430000-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2855430000-13">[</span><span class="p" data-group-id="2855430000-13">]</span><span class="p" data-group-id="2855430000-12">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7055718017-12">(</span><span class="s">&quot;Ping received pong</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7055718017-13">[</span><span class="p" data-group-id="7055718017-13">]</span><span class="p" data-group-id="7055718017-12">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">ping1</span><span class="p" data-group-id="2855430000-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="2855430000-14">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">ping1</span><span class="p" data-group-id="7055718017-14">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">Pong_Pid</span><span class="p" data-group-id="7055718017-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong</span><span class="p" data-group-id="2855430000-15">(</span><span class="p" data-group-id="2855430000-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="2855430000-16">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2855430000-16">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">pong1</span><span class="p" data-group-id="2855430000-17">(</span><span class="p" data-group-id="2855430000-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">pong</span><span class="p" data-group-id="7055718017-15">(</span><span class="p" data-group-id="7055718017-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="7055718017-16">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7055718017-16">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">pong1</span><span class="p" data-group-id="7055718017-17">(</span><span class="p" data-group-id="7055718017-17">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">pong1</span><span class="p" data-group-id="2855430000-18">(</span><span class="p" data-group-id="2855430000-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">pong1</span><span class="p" data-group-id="7055718017-18">(</span><span class="p" data-group-id="7055718017-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2855430000-19">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="2855430000-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2855430000-20">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2855430000-21">[</span><span class="p" data-group-id="2855430000-21">]</span><span class="p" data-group-id="2855430000-20">)</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7055718017-19">{</span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="n">Ping_PID</span><span class="p" data-group-id="7055718017-19">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7055718017-20">(</span><span class="s">&quot;Pong received ping</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7055718017-21">[</span><span class="p" data-group-id="7055718017-21">]</span><span class="p" data-group-id="7055718017-20">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">Ping_PID</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">pong1</span><span class="p" data-group-id="2855430000-22">(</span><span class="p" data-group-id="2855430000-22">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2855430000-23">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="2855430000-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2855430000-24">(</span><span class="s">&quot;pong exiting, got </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2855430000-25">[</span><span class="p" data-group-id="2855430000-26">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="2855430000-26">}</span><span class="p" data-group-id="2855430000-25">]</span><span class="p" data-group-id="2855430000-24">)</span><span class="w">
│ │ │ +            </span><span class="nf">pong1</span><span class="p" data-group-id="7055718017-22">(</span><span class="p" data-group-id="7055718017-22">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7055718017-23">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7055718017-23">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7055718017-24">(</span><span class="s">&quot;pong exiting, got </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7055718017-25">[</span><span class="p" data-group-id="7055718017-26">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="7055718017-26">}</span><span class="p" data-group-id="7055718017-25">]</span><span class="p" data-group-id="7055718017-24">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start</span><span class="p" data-group-id="2855430000-27">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="2855430000-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2855430000-28">(</span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2855430000-29">[</span><span class="p" data-group-id="2855430000-29">]</span><span class="p" data-group-id="2855430000-28">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="2855430000-30">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2855430000-31">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="2855430000-31">]</span><span class="p" data-group-id="2855430000-30">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)1&gt; tut21:start(s2@gollum).
│ │ │ +</span><span class="nf">start</span><span class="p" data-group-id="7055718017-27">(</span><span class="n">Ping_Node</span><span class="p" data-group-id="7055718017-27">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">PongPID</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="7055718017-28">(</span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">pong</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7055718017-29">[</span><span class="p" data-group-id="7055718017-29">]</span><span class="p" data-group-id="7055718017-28">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="7055718017-30">(</span><span class="n">Ping_Node</span><span class="p">,</span><span class="w"> </span><span class="ss">tut21</span><span class="p">,</span><span class="w"> </span><span class="ss">ping</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7055718017-31">[</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="n">PongPID</span><span class="p" data-group-id="7055718017-31">]</span><span class="p" data-group-id="7055718017-30">)</span><span class="p">.</span></code></pre><pre><code class="text">(s1@bill)1&gt; tut21:start(s2@gollum).
│ │ │  &lt;3820.39.0&gt;
│ │ │  Pong received ping
│ │ │  Ping received pong
│ │ │  Pong received ping
│ │ │  Ping received pong
│ │ │  Pong received ping
│ │ │  Ping received pong
│ │ │ @@ -351,135 +351,135 @@
│ │ │  </span><span class="c1">%%% Started: messenger:client(Server_Node, Name)</span><span class="w">
│ │ │  </span><span class="c1">%%% To client: logoff</span><span class="w">
│ │ │  </span><span class="c1">%%% To client: {message_to, ToName, Message}</span><span class="w">
│ │ │  </span><span class="c1">%%%</span><span class="w">
│ │ │  </span><span class="c1">%%% Configuration: change the server_node() function to return the</span><span class="w">
│ │ │  </span><span class="c1">%%% name of the node where the messenger server runs</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9454271889-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="9454271889-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9454271889-2">(</span><span class="p" data-group-id="9454271889-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9454271889-3">]</span><span class="p" data-group-id="9454271889-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2720645701-1">(</span><span class="ss">messenger</span><span class="p" data-group-id="2720645701-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2720645701-2">(</span><span class="p" data-group-id="2720645701-3">[</span><span class="ss">start_server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="ss">logon</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">logoff</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">message</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2720645701-3">]</span><span class="p" data-group-id="2720645701-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Change the function below to return the name of the node where the</span><span class="w">
│ │ │  </span><span class="c1">%%% messenger server runs</span><span class="w">
│ │ │ -</span><span class="nf">server_node</span><span class="p" data-group-id="9454271889-4">(</span><span class="p" data-group-id="9454271889-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_node</span><span class="p" data-group-id="2720645701-4">(</span><span class="p" data-group-id="2720645701-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">messenger@super</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% This is the server process for the &quot;messenger&quot;</span><span class="w">
│ │ │  </span><span class="c1">%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]</span><span class="w">
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9454271889-5">(</span><span class="p" data-group-id="9454271889-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9454271889-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9454271889-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">server</span><span class="p" data-group-id="9454271889-7">(</span><span class="p" data-group-id="9454271889-8">[</span><span class="p" data-group-id="9454271889-8">]</span><span class="p" data-group-id="9454271889-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="2720645701-5">(</span><span class="p" data-group-id="2720645701-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="2720645701-6">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="2720645701-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">server</span><span class="p" data-group-id="2720645701-7">(</span><span class="p" data-group-id="2720645701-8">[</span><span class="p" data-group-id="2720645701-8">]</span><span class="p" data-group-id="2720645701-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">server</span><span class="p" data-group-id="9454271889-9">(</span><span class="n">User_List</span><span class="p" data-group-id="9454271889-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server</span><span class="p" data-group-id="2720645701-9">(</span><span class="n">User_List</span><span class="p" data-group-id="2720645701-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9454271889-10">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9454271889-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="9454271889-11">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-11">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9454271889-12">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9454271889-12">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9454271889-13">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9454271889-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="9454271889-14">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-14">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9454271889-15">(</span><span class="n">New_User_List</span><span class="p" data-group-id="9454271889-15">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9454271889-16">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9454271889-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9454271889-17">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-17">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9454271889-18">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9454271889-19">[</span><span class="n">User_List</span><span class="p" data-group-id="9454271889-19">]</span><span class="p" data-group-id="9454271889-18">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">server</span><span class="p" data-group-id="9454271889-20">(</span><span class="n">User_List</span><span class="p" data-group-id="9454271889-20">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2720645701-10">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2720645701-10">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logon</span><span class="p" data-group-id="2720645701-11">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-11">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="2720645701-12">(</span><span class="n">New_User_List</span><span class="p" data-group-id="2720645701-12">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2720645701-13">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2720645701-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">New_User_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">server_logoff</span><span class="p" data-group-id="2720645701-14">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-14">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="2720645701-15">(</span><span class="n">New_User_List</span><span class="p" data-group-id="2720645701-15">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2720645701-16">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2720645701-16">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="2720645701-17">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-17">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2720645701-18">(</span><span class="s">&quot;list is now: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2720645701-19">[</span><span class="n">User_List</span><span class="p" data-group-id="2720645701-19">]</span><span class="p" data-group-id="2720645701-18">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">server</span><span class="p" data-group-id="2720645701-20">(</span><span class="n">User_List</span><span class="p" data-group-id="2720645701-20">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Start the server</span><span class="w">
│ │ │ -</span><span class="nf">start_server</span><span class="p" data-group-id="9454271889-21">(</span><span class="p" data-group-id="9454271889-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="9454271889-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="9454271889-23">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9454271889-24">[</span><span class="p" data-group-id="9454271889-24">]</span><span class="p" data-group-id="9454271889-23">)</span><span class="p" data-group-id="9454271889-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_server</span><span class="p" data-group-id="2720645701-21">(</span><span class="p" data-group-id="2720645701-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="2720645701-22">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="nf">spawn</span><span class="p" data-group-id="2720645701-23">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">server</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2720645701-24">[</span><span class="p" data-group-id="2720645701-24">]</span><span class="p" data-group-id="2720645701-23">)</span><span class="p" data-group-id="2720645701-22">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server adds a new user to the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logon</span><span class="p" data-group-id="9454271889-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_logon</span><span class="p" data-group-id="2720645701-25">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check if logged on anywhere else</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="9454271889-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keymember</span><span class="p" data-group-id="2720645701-26">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-26">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9454271889-27">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="9454271889-27">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2720645701-27">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">user_exists_at_other_node</span><span class="p" data-group-id="2720645701-27">}</span><span class="p">,</span><span class="w">  </span><span class="c1">%reject logon</span><span class="w">
│ │ │              </span><span class="n">User_List</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9454271889-28">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="9454271889-28">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">link</span><span class="p" data-group-id="9454271889-29">(</span><span class="n">From</span><span class="p" data-group-id="9454271889-29">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9454271889-30">[</span><span class="p" data-group-id="9454271889-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9454271889-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2720645701-28">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">logged_on</span><span class="p" data-group-id="2720645701-28">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">link</span><span class="p" data-group-id="2720645701-29">(</span><span class="n">From</span><span class="p" data-group-id="2720645701-29">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2720645701-30">[</span><span class="p" data-group-id="2720645701-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2720645701-31">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-30">]</span><span class="w">        </span><span class="c1">%add user to the list</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Server deletes a user from the user list</span><span class="w">
│ │ │ -</span><span class="nf">server_logoff</span><span class="p" data-group-id="9454271889-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="9454271889-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-33">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">server_logoff</span><span class="p" data-group-id="2720645701-32">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keydelete</span><span class="p" data-group-id="2720645701-33">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-33">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  
│ │ │  </span><span class="c1">%%% Server transfers a message between user</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9454271889-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="2720645701-34">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-34">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% check that the user is logged on and who he is</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9454271889-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="2720645701-35">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-35">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9454271889-36">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="9454271889-36">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9454271889-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9454271889-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9454271889-38">}</span><span class="p" data-group-id="9454271889-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">server_transfer</span><span class="p" data-group-id="9454271889-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-39">)</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2720645701-36">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="ss">you_are_not_logged_on</span><span class="p" data-group-id="2720645701-36">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2720645701-37">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2720645701-38">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2720645701-38">}</span><span class="p" data-group-id="2720645701-37">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">server_transfer</span><span class="p" data-group-id="2720645701-39">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-39">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% If the user exists, send the message</span><span class="w">
│ │ │ -</span><span class="nf">server_transfer</span><span class="p" data-group-id="9454271889-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">server_transfer</span><span class="p" data-group-id="2720645701-40">(</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-40">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Find the receiver and send the message</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="9454271889-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="9454271889-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">keysearch</span><span class="p" data-group-id="2720645701-41">(</span><span class="n">To</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">User_List</span><span class="p" data-group-id="2720645701-41">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">false</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9454271889-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="9454271889-42">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9454271889-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9454271889-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="9454271889-44">}</span><span class="p" data-group-id="9454271889-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9454271889-45">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9454271889-45">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9454271889-46">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="9454271889-46">}</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2720645701-42">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">receiver_not_found</span><span class="p" data-group-id="2720645701-42">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2720645701-43">{</span><span class="ss">value</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2720645701-44">{</span><span class="n">ToPid</span><span class="p">,</span><span class="w"> </span><span class="n">To</span><span class="p" data-group-id="2720645701-44">}</span><span class="p" data-group-id="2720645701-43">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">ToPid</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2720645701-45">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2720645701-45">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2720645701-46">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">sent</span><span class="p" data-group-id="2720645701-46">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% User Commands</span><span class="w">
│ │ │ -</span><span class="nf">logon</span><span class="p" data-group-id="9454271889-47">(</span><span class="n">Name</span><span class="p" data-group-id="9454271889-47">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="9454271889-48">(</span><span class="ss">mess_client</span><span class="p" data-group-id="9454271889-48">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +</span><span class="nf">logon</span><span class="p" data-group-id="2720645701-47">(</span><span class="n">Name</span><span class="p" data-group-id="2720645701-47">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="2720645701-48">(</span><span class="ss">mess_client</span><span class="p" data-group-id="2720645701-48">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">register</span><span class="p" data-group-id="9454271889-49">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ -                     </span><span class="nf">spawn</span><span class="p" data-group-id="9454271889-50">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9454271889-51">[</span><span class="nf">server_node</span><span class="p" data-group-id="9454271889-52">(</span><span class="p" data-group-id="9454271889-52">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9454271889-51">]</span><span class="p" data-group-id="9454271889-50">)</span><span class="p" data-group-id="9454271889-49">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nf">register</span><span class="p" data-group-id="2720645701-49">(</span><span class="ss">mess_client</span><span class="p">,</span><span class="w">
│ │ │ +                     </span><span class="nf">spawn</span><span class="p" data-group-id="2720645701-50">(</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">client</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2720645701-51">[</span><span class="nf">server_node</span><span class="p" data-group-id="2720645701-52">(</span><span class="p" data-group-id="2720645701-52">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2720645701-51">]</span><span class="p" data-group-id="2720645701-50">)</span><span class="p" data-group-id="2720645701-49">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">already_logged_on</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">logoff</span><span class="p" data-group-id="9454271889-53">(</span><span class="p" data-group-id="9454271889-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">logoff</span><span class="p" data-group-id="2720645701-53">(</span><span class="p" data-group-id="2720645701-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="ss">logoff</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">message</span><span class="p" data-group-id="9454271889-54">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9454271889-54">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="9454271889-55">(</span><span class="ss">mess_client</span><span class="p" data-group-id="9454271889-55">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │ +</span><span class="nf">message</span><span class="p" data-group-id="2720645701-54">(</span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2720645701-54">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nf">whereis</span><span class="p" data-group-id="2720645701-55">(</span><span class="ss">mess_client</span><span class="p" data-group-id="2720645701-55">)</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="c1">% Test if the client is running</span><span class="w">
│ │ │          </span><span class="ss">undefined</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_logged_on</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9454271889-56">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9454271889-56">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">mess_client</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2720645701-56">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2720645701-56">}</span><span class="p">,</span><span class="w">
│ │ │               </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% The client process which runs on each user node</span><span class="w">
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="9454271889-57">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9454271889-57">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9454271889-58">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="9454271889-58">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9454271889-59">{</span><span class="nf">self</span><span class="p" data-group-id="9454271889-60">(</span><span class="p" data-group-id="9454271889-60">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="9454271889-59">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">await_result</span><span class="p" data-group-id="9454271889-61">(</span><span class="p" data-group-id="9454271889-61">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="9454271889-62">(</span><span class="n">Server_Node</span><span class="p" data-group-id="9454271889-62">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="2720645701-57">(</span><span class="n">Server_Node</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2720645701-57">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2720645701-58">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="2720645701-58">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2720645701-59">{</span><span class="nf">self</span><span class="p" data-group-id="2720645701-60">(</span><span class="p" data-group-id="2720645701-60">)</span><span class="p">,</span><span class="w"> </span><span class="ss">logon</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="2720645701-59">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">await_result</span><span class="p" data-group-id="2720645701-61">(</span><span class="p" data-group-id="2720645701-61">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="2720645701-62">(</span><span class="n">Server_Node</span><span class="p" data-group-id="2720645701-62">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">client</span><span class="p" data-group-id="9454271889-63">(</span><span class="n">Server_Node</span><span class="p" data-group-id="9454271889-63">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">client</span><span class="p" data-group-id="2720645701-63">(</span><span class="n">Server_Node</span><span class="p" data-group-id="2720645701-63">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="ss">logoff</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="9454271889-64">(</span><span class="ss">normal</span><span class="p" data-group-id="9454271889-64">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9454271889-65">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9454271889-65">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9454271889-66">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="9454271889-66">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="9454271889-67">{</span><span class="nf">self</span><span class="p" data-group-id="9454271889-68">(</span><span class="p" data-group-id="9454271889-68">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9454271889-67">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">await_result</span><span class="p" data-group-id="9454271889-69">(</span><span class="p" data-group-id="9454271889-69">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9454271889-70">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9454271889-70">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9454271889-71">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9454271889-72">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="9454271889-72">]</span><span class="p" data-group-id="9454271889-71">)</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="2720645701-64">(</span><span class="ss">normal</span><span class="p" data-group-id="2720645701-64">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2720645701-65">{</span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2720645701-65">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2720645701-66">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">Server_Node</span><span class="p" data-group-id="2720645701-66">}</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="2720645701-67">{</span><span class="nf">self</span><span class="p" data-group-id="2720645701-68">(</span><span class="p" data-group-id="2720645701-68">)</span><span class="p">,</span><span class="w"> </span><span class="ss">message_to</span><span class="p">,</span><span class="w"> </span><span class="n">ToName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2720645701-67">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">await_result</span><span class="p" data-group-id="2720645701-69">(</span><span class="p" data-group-id="2720645701-69">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2720645701-70">{</span><span class="ss">message_from</span><span class="p">,</span><span class="w"> </span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2720645701-70">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2720645701-71">(</span><span class="s">&quot;Message from </span><span class="si">~p</span><span class="s">: </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2720645701-72">[</span><span class="n">FromName</span><span class="p">,</span><span class="w"> </span><span class="n">Message</span><span class="p" data-group-id="2720645701-72">]</span><span class="p" data-group-id="2720645701-71">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">client</span><span class="p" data-group-id="9454271889-73">(</span><span class="n">Server_Node</span><span class="p" data-group-id="9454271889-73">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">client</span><span class="p" data-group-id="2720645701-73">(</span><span class="n">Server_Node</span><span class="p" data-group-id="2720645701-73">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% wait for a response from the server</span><span class="w">
│ │ │ -</span><span class="nf">await_result</span><span class="p" data-group-id="9454271889-74">(</span><span class="p" data-group-id="9454271889-74">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">await_result</span><span class="p" data-group-id="2720645701-74">(</span><span class="p" data-group-id="2720645701-74">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9454271889-75">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="9454271889-75">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9454271889-76">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9454271889-77">[</span><span class="n">Why</span><span class="p" data-group-id="9454271889-77">]</span><span class="p" data-group-id="9454271889-76">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="9454271889-78">(</span><span class="ss">normal</span><span class="p" data-group-id="9454271889-78">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9454271889-79">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="9454271889-79">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9454271889-80">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9454271889-81">[</span><span class="n">What</span><span class="p" data-group-id="9454271889-81">]</span><span class="p" data-group-id="9454271889-80">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2720645701-75">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="ss">stop</span><span class="p">,</span><span class="w"> </span><span class="n">Why</span><span class="p" data-group-id="2720645701-75">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Stop the client</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2720645701-76">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2720645701-77">[</span><span class="n">Why</span><span class="p" data-group-id="2720645701-77">]</span><span class="p" data-group-id="2720645701-76">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="2720645701-78">(</span><span class="ss">normal</span><span class="p" data-group-id="2720645701-78">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2720645701-79">{</span><span class="ss">messenger</span><span class="p">,</span><span class="w"> </span><span class="n">What</span><span class="p" data-group-id="2720645701-79">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Normal response</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2720645701-80">(</span><span class="s">&quot;</span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2720645701-81">[</span><span class="n">What</span><span class="p" data-group-id="2720645701-81">]</span><span class="p" data-group-id="2720645701-80">)</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">5000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9454271889-82">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9454271889-83">[</span><span class="p" data-group-id="9454271889-83">]</span><span class="p" data-group-id="9454271889-82">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="9454271889-84">(</span><span class="ss">timeout</span><span class="p" data-group-id="9454271889-84">)</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2720645701-82">(</span><span class="s">&quot;No response from server</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2720645701-83">[</span><span class="p" data-group-id="2720645701-83">]</span><span class="p" data-group-id="2720645701-82">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="2720645701-84">(</span><span class="ss">timeout</span><span class="p" data-group-id="2720645701-84">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>The following changes are added:</p><p>The messenger server traps exits. If it receives an exit signal,
│ │ │  <code class="inline">{'EXIT',From,Reason}</code>, this means that a client process has terminated or is
│ │ │  unreachable for one of the following reasons:</p><ul><li>The user has logged off (the &quot;logoff&quot; message is removed).</li><li>The network connection to the client is broken.</li><li>The node on which the client process resides has gone down.</li><li>The client processes has done some illegal operation.</li></ul><p>If an exit signal is received as above, the tuple <code class="inline">{From,Name}</code> is deleted from
│ │ │  the servers <code class="inline">User_List</code> using the <code class="inline">server_logoff</code> function. If the node on which
│ │ │  the server runs goes down, an exit signal (automatically generated by the
│ │ │  system) is sent to all of the client processes:
│ │ │  <code class="inline">{'EXIT',MessengerPID,noconnection}</code> causing all the client processes to
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/seq_prog.html
│ │ │ @@ -136,293 +136,293 @@
│ │ │  </span><span class="mi">7</span><span class="w">
│ │ │  </span><span class="gp unselectable">2&gt; </span></code></pre><p>As shown, the Erlang shell numbers the lines that can be entered, (as 1&gt; 2&gt;) and
│ │ │  that it correctly says that 2 + 5 is 7. If you make writing mistakes in the
│ │ │  shell, you can delete with the backspace key, as in most shells. There are many
│ │ │  more editing commands in the shell (see
│ │ │  <a href="../../erts-15.2.7.8/doc/html/tty.html">tty - A command line interface</a> in ERTS User's Guide).</p><p>(Notice that many line numbers given by the shell in the following examples are
│ │ │  out of sequence. This is because this tutorial was written and code-tested in
│ │ │ -separate sessions).</p><p>Here is a bit more complex calculation:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="9328692688-1">(</span><span class="mi">42</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">77</span><span class="p" data-group-id="9328692688-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">66</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │ +separate sessions).</p><p>Here is a bit more complex calculation:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="1536957133-1">(</span><span class="mi">42</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">77</span><span class="p" data-group-id="1536957133-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">66</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">3</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">2618.0</span></code></pre><p>Notice the use of brackets, the multiplication operator <code class="inline">*</code>, and the division
│ │ │  operator <code class="inline">/</code>, as in normal arithmetic (see
│ │ │  <a href="../../doc/system/expressions.html">Expressions</a>).</p><p>Press Control-C to shut down the Erlang system and the Erlang shell.</p><p>The following output is shown:</p><pre><code class="text">BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
│ │ │         (v)ersion (k)ill (D)b-tables (d)istribution
│ │ │  a
│ │ │ -$</code></pre><p>Type <code class="inline">a</code> to leave the Erlang system.</p><p>Another way to shut down the Erlang system is by entering <a href="../../erts-15.2.7.8/doc/html/erlang.html#halt/0"><code class="inline">halt/0</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">halt</span><span class="p" data-group-id="2686339452-1">(</span><span class="p" data-group-id="2686339452-1">)</span><span class="p">.</span><span class="w">
│ │ │ +$</code></pre><p>Type <code class="inline">a</code> to leave the Erlang system.</p><p>Another way to shut down the Erlang system is by entering <a href="../../erts-15.2.7.8/doc/html/erlang.html#halt/0"><code class="inline">halt/0</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">halt</span><span class="p" data-group-id="0735775273-1">(</span><span class="p" data-group-id="0735775273-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="err">$</span></code></pre><h2 id="modules-and-functions" class="section-heading">
│ │ │    <a href="#modules-and-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Modules and Functions</span>
│ │ │  </h2>
│ │ │  <p>A programming language is not much use if you only can run code from the shell.
│ │ │  So here is a small Erlang program. Enter it into a file named <code class="inline">tut.erl</code> using a
│ │ │  suitable text editor. The file name <code class="inline">tut.erl</code> is important, and also that it is
│ │ │  in the same directory as the one where you started <code class="inline">erl</code>). If you are lucky your
│ │ │  editor has an Erlang mode that makes it easier for you to enter and format your
│ │ │  code nicely (see <a href="../../lib/tools-4.1.1/doc/html/erlang_mode_chapter.html">The Erlang mode for Emacs</a>
│ │ │  in Tools User's Guide), but you can manage perfectly well without. Here is the
│ │ │ -code to enter:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2701640909-1">(</span><span class="ss">tut</span><span class="p" data-group-id="2701640909-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2701640909-2">(</span><span class="p" data-group-id="2701640909-3">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2701640909-3">]</span><span class="p" data-group-id="2701640909-2">)</span><span class="p">.</span><span class="w">
│ │ │ +code to enter:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4034478616-1">(</span><span class="ss">tut</span><span class="p" data-group-id="4034478616-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4034478616-2">(</span><span class="p" data-group-id="4034478616-3">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4034478616-3">]</span><span class="p" data-group-id="4034478616-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">double</span><span class="p" data-group-id="2701640909-4">(</span><span class="n">X</span><span class="p" data-group-id="2701640909-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">double</span><span class="p" data-group-id="4034478616-4">(</span><span class="n">X</span><span class="p" data-group-id="4034478616-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">2</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">X</span><span class="p">.</span></code></pre><p>It is not hard to guess that this program doubles the value of numbers. The
│ │ │  first two lines of the code are described later. Let us compile the program.
│ │ │ -This can be done in an Erlang shell as follows, where <code class="inline">c</code> means compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">c</span><span class="p" data-group-id="4035190153-1">(</span><span class="ss">tut</span><span class="p" data-group-id="4035190153-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4035190153-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut</span><span class="p" data-group-id="4035190153-2">}</span></code></pre><p>The <code class="inline">{ok,tut}</code> means that the compilation is OK. If it says <code class="inline">error</code> it means
│ │ │ +This can be done in an Erlang shell as follows, where <code class="inline">c</code> means compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">3&gt; </span><span class="nf">c</span><span class="p" data-group-id="1694441404-1">(</span><span class="ss">tut</span><span class="p" data-group-id="1694441404-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1694441404-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut</span><span class="p" data-group-id="1694441404-2">}</span></code></pre><p>The <code class="inline">{ok,tut}</code> means that the compilation is OK. If it says <code class="inline">error</code> it means
│ │ │  that there is some mistake in the text that you entered. Additional error
│ │ │  messages gives an idea to what is wrong so you can modify the text and then try
│ │ │ -to compile the program again.</p><p>Now run the program:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="0905322528-1">(</span><span class="mi">10</span><span class="p" data-group-id="0905322528-1">)</span><span class="p">.</span><span class="w">
│ │ │ +to compile the program again.</p><p>Now run the program:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="3404750379-1">(</span><span class="mi">10</span><span class="p" data-group-id="3404750379-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">20</span></code></pre><p>As expected, double of 10 is 20.</p><p>Now let us get back to the first two lines of the code. Erlang programs are
│ │ │  written in files. Each file contains an Erlang <em>module</em>. The first line of code
│ │ │ -in the module is the module name (see <a href="../../doc/system/modules.html">Modules</a>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3172923387-1">(</span><span class="ss">tut</span><span class="p" data-group-id="3172923387-1">)</span><span class="p">.</span></code></pre><p>Thus, the module is called <em>tut</em>. Notice the full stop <code class="inline">.</code> at the end of the
│ │ │ +in the module is the module name (see <a href="../../doc/system/modules.html">Modules</a>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2699008159-1">(</span><span class="ss">tut</span><span class="p" data-group-id="2699008159-1">)</span><span class="p">.</span></code></pre><p>Thus, the module is called <em>tut</em>. Notice the full stop <code class="inline">.</code> at the end of the
│ │ │  line. The files which are used to store the module must have the same name as
│ │ │  the module but with the extension <code class="inline">.erl</code>. In this case the file name is
│ │ │  <code class="inline">tut.erl</code>. When using a function in another module, the syntax
│ │ │  <code class="inline">module_name:function_name(arguments)</code> is used. So the following means call
│ │ │ -function <code class="inline">double</code> in module <code class="inline">tut</code> with argument <code class="inline">10</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="8694795127-1">(</span><span class="mi">10</span><span class="p" data-group-id="8694795127-1">)</span><span class="p">.</span></code></pre><p>The second line says that the module <code class="inline">tut</code> contains a function called <code class="inline">double</code>,
│ │ │ -which takes one argument (<code class="inline">X</code> in our example):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5979746269-1">(</span><span class="p" data-group-id="5979746269-2">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5979746269-2">]</span><span class="p" data-group-id="5979746269-1">)</span><span class="p">.</span></code></pre><p>The second line also says that this function can be called from outside the
│ │ │ +function <code class="inline">double</code> in module <code class="inline">tut</code> with argument <code class="inline">10</code>.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">4&gt; </span><span class="nc">tut</span><span class="p">:</span><span class="nf">double</span><span class="p" data-group-id="3630518054-1">(</span><span class="mi">10</span><span class="p" data-group-id="3630518054-1">)</span><span class="p">.</span></code></pre><p>The second line says that the module <code class="inline">tut</code> contains a function called <code class="inline">double</code>,
│ │ │ +which takes one argument (<code class="inline">X</code> in our example):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7296494291-1">(</span><span class="p" data-group-id="7296494291-2">[</span><span class="ss">double</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7296494291-2">]</span><span class="p" data-group-id="7296494291-1">)</span><span class="p">.</span></code></pre><p>The second line also says that this function can be called from outside the
│ │ │  module <code class="inline">tut</code>. More about this later. Again, notice the <code class="inline">.</code> at the end of the
│ │ │  line.</p><p>Now for a more complicated example, the factorial of a number. For example, the
│ │ │ -factorial of 4 is 4 <em> 3 </em> 2 * 1, which equals 24.</p><p>Enter the following code in a file named <code class="inline">tut1.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9753651452-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="9753651452-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9753651452-2">(</span><span class="p" data-group-id="9753651452-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9753651452-3">]</span><span class="p" data-group-id="9753651452-2">)</span><span class="p">.</span><span class="w">
│ │ │ +factorial of 4 is 4 <em> 3 </em> 2 * 1, which equals 24.</p><p>Enter the following code in a file named <code class="inline">tut1.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4048479548-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="4048479548-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4048479548-2">(</span><span class="p" data-group-id="4048479548-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4048479548-3">]</span><span class="p" data-group-id="4048479548-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="9753651452-4">(</span><span class="mi">1</span><span class="p" data-group-id="9753651452-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="4048479548-4">(</span><span class="mi">1</span><span class="p" data-group-id="4048479548-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="9753651452-5">(</span><span class="n">N</span><span class="p" data-group-id="9753651452-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="9753651452-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9753651452-6">)</span><span class="p">.</span></code></pre><p>So this is a module, called <code class="inline">tut1</code> that contains a function called <code class="inline">fac&gt;</code>, which
│ │ │ -takes one argument, <code class="inline">N</code>.</p><p>The first part says that the factorial of 1 is 1.:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="3136526077-1">(</span><span class="mi">1</span><span class="p" data-group-id="3136526077-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="4048479548-5">(</span><span class="n">N</span><span class="p" data-group-id="4048479548-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="4048479548-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4048479548-6">)</span><span class="p">.</span></code></pre><p>So this is a module, called <code class="inline">tut1</code> that contains a function called <code class="inline">fac&gt;</code>, which
│ │ │ +takes one argument, <code class="inline">N</code>.</p><p>The first part says that the factorial of 1 is 1.:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="1763788426-1">(</span><span class="mi">1</span><span class="p" data-group-id="1763788426-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">;</span></code></pre><p>Notice that this part ends with a semicolon <code class="inline">;</code> that indicates that there is
│ │ │  more of the function <code class="inline">fac&gt;</code> to come.</p><p>The second part says that the factorial of N is N multiplied by the factorial of
│ │ │ -N - 1:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="1751782145-1">(</span><span class="n">N</span><span class="p" data-group-id="1751782145-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="1751782145-2">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1751782145-2">)</span><span class="p">.</span></code></pre><p>Notice that this part ends with a <code class="inline">.</code> saying that there are no more parts of
│ │ │ -this function.</p><p>Compile the file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="2410635521-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="2410635521-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2410635521-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="2410635521-2">}</span></code></pre><p>And now calculate the factorial of 4.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">fac</span><span class="p" data-group-id="2486856604-1">(</span><span class="mi">4</span><span class="p" data-group-id="2486856604-1">)</span><span class="p">.</span><span class="w">
│ │ │ +N - 1:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fac</span><span class="p" data-group-id="3441549733-1">(</span><span class="n">N</span><span class="p" data-group-id="3441549733-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="3441549733-2">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3441549733-2">)</span><span class="p">.</span></code></pre><p>Notice that this part ends with a <code class="inline">.</code> saying that there are no more parts of
│ │ │ +this function.</p><p>Compile the file:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">5&gt; </span><span class="nf">c</span><span class="p" data-group-id="4601023304-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="4601023304-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4601023304-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="4601023304-2">}</span></code></pre><p>And now calculate the factorial of 4.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">6&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">fac</span><span class="p" data-group-id="4188708325-1">(</span><span class="mi">4</span><span class="p" data-group-id="4188708325-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">24</span></code></pre><p>Here the function <code class="inline">fac&gt;</code> in module <code class="inline">tut1</code> is called with argument <code class="inline">4</code>.</p><p>A function can have many arguments. Let us expand the module <code class="inline">tut1</code> with the
│ │ │ -function to multiply two numbers:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5269517194-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="5269517194-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5269517194-2">(</span><span class="p" data-group-id="5269517194-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">mult</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5269517194-3">]</span><span class="p" data-group-id="5269517194-2">)</span><span class="p">.</span><span class="w">
│ │ │ +function to multiply two numbers:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9986088199-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="9986088199-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9986088199-2">(</span><span class="p" data-group-id="9986088199-3">[</span><span class="ss">fac</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">mult</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="9986088199-3">]</span><span class="p" data-group-id="9986088199-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="5269517194-4">(</span><span class="mi">1</span><span class="p" data-group-id="5269517194-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="9986088199-4">(</span><span class="mi">1</span><span class="p" data-group-id="9986088199-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">fac</span><span class="p" data-group-id="5269517194-5">(</span><span class="n">N</span><span class="p" data-group-id="5269517194-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="5269517194-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5269517194-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">fac</span><span class="p" data-group-id="9986088199-5">(</span><span class="n">N</span><span class="p" data-group-id="9986088199-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nf">fac</span><span class="p" data-group-id="9986088199-6">(</span><span class="n">N</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9986088199-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">mult</span><span class="p" data-group-id="5269517194-7">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5269517194-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">mult</span><span class="p" data-group-id="9986088199-7">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9986088199-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">Y</span><span class="p">.</span></code></pre><p>Notice that it is also required to expand the <code class="inline">-export</code> line with the
│ │ │ -information that there is another function <code class="inline">mult</code> with two arguments.</p><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nf">c</span><span class="p" data-group-id="0749443019-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="0749443019-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0749443019-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="0749443019-2">}</span></code></pre><p>Try out the new function <code class="inline">mult</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">8&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">mult</span><span class="p" data-group-id="7660580983-1">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="7660580983-1">)</span><span class="p">.</span><span class="w">
│ │ │ +information that there is another function <code class="inline">mult</code> with two arguments.</p><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">7&gt; </span><span class="nf">c</span><span class="p" data-group-id="6211174659-1">(</span><span class="ss">tut1</span><span class="p" data-group-id="6211174659-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6211174659-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut1</span><span class="p" data-group-id="6211174659-2">}</span></code></pre><p>Try out the new function <code class="inline">mult</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">8&gt; </span><span class="nc">tut1</span><span class="p">:</span><span class="nf">mult</span><span class="p" data-group-id="3451902900-1">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3451902900-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">12</span></code></pre><p>In this example the numbers are integers and the arguments in the functions in
│ │ │  the code <code class="inline">N</code>, <code class="inline">X</code>, and <code class="inline">Y</code> are called variables. Variables must start with a
│ │ │  capital letter (see <a href="../../doc/system/expressions.html">Variables</a>). Examples of
│ │ │  variables are <code class="inline">Number</code>, <code class="inline">ShoeSize</code>, and <code class="inline">Age</code>.</p><h2 id="atoms" class="section-heading">
│ │ │    <a href="#atoms" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Atoms</span>
│ │ │  </h2>
│ │ │  <p>Atom is another data type in Erlang. Atoms start with a small letter (see
│ │ │  <a href="../../doc/system/data_types.html">Atom</a>), for example, <code class="inline">charles</code>, <code class="inline">centimeter</code>, and
│ │ │  <code class="inline">inch</code>. Atoms are simply names, nothing else. They are not like variables, which
│ │ │  can have a value.</p><p>Enter the next program in a file named <code class="inline">tut2.erl</code>). It can be useful for
│ │ │ -converting from inches to centimeters and conversely:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0557390510-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="0557390510-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0557390510-2">(</span><span class="p" data-group-id="0557390510-3">[</span><span class="ss">convert</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0557390510-3">]</span><span class="p" data-group-id="0557390510-2">)</span><span class="p">.</span><span class="w">
│ │ │ +converting from inches to centimeters and conversely:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5452982596-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="5452982596-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5452982596-2">(</span><span class="p" data-group-id="5452982596-3">[</span><span class="ss">convert</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="5452982596-3">]</span><span class="p" data-group-id="5452982596-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert</span><span class="p" data-group-id="0557390510-4">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="0557390510-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">convert</span><span class="p" data-group-id="5452982596-4">(</span><span class="n">M</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="5452982596-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">M</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert</span><span class="p" data-group-id="0557390510-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="0557390510-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p">.</span></code></pre><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nf">c</span><span class="p" data-group-id="2450124477-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="2450124477-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2450124477-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut2</span><span class="p" data-group-id="2450124477-2">}</span></code></pre><p>Test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">10&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="5353823010-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="5353823010-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">convert</span><span class="p" data-group-id="5452982596-5">(</span><span class="n">N</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="5452982596-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">N</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p">.</span></code></pre><p>Compile:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">9&gt; </span><span class="nf">c</span><span class="p" data-group-id="7181115834-1">(</span><span class="ss">tut2</span><span class="p" data-group-id="7181115834-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7181115834-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut2</span><span class="p" data-group-id="7181115834-2">}</span></code></pre><p>Test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">10&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="4044052344-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="4044052344-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">1.1811023622047243</span><span class="w">
│ │ │ -</span><span class="gp unselectable">11&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="5353823010-2">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="5353823010-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">11&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="4044052344-2">(</span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="ss">centimeter</span><span class="p" data-group-id="4044052344-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">17.78</span></code></pre><p>Notice the introduction of decimals (floating point numbers) without any
│ │ │  explanation. Hopefully you can cope with that.</p><p>Let us see what happens if something other than <code class="inline">centimeter</code> or <code class="inline">inch</code> is
│ │ │ -entered in the <code class="inline">convert</code> function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">12&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="3363254033-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">miles</span><span class="p" data-group-id="3363254033-1">)</span><span class="p">.</span><span class="w">
│ │ │ +entered in the <code class="inline">convert</code> function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">12&gt; </span><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="3004548678-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">miles</span><span class="p" data-group-id="3004548678-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no function clause matching tut2:convert(3,miles) (tut2.erl, line 4)</span></code></pre><p>The two parts of the <code class="inline">convert</code> function are called its clauses. As shown,
│ │ │  <code class="inline">miles</code> is not part of either of the clauses. The Erlang system cannot <em>match</em>
│ │ │  either of the clauses so an error message <code class="inline">function_clause</code> is returned. The
│ │ │  shell formats the error message nicely, but the error tuple is saved in the
│ │ │ -shell's history list and can be output by the shell command <code class="inline">v/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">13&gt; </span><span class="nf">v</span><span class="p" data-group-id="0791980309-1">(</span><span class="mi">12</span><span class="p" data-group-id="0791980309-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0791980309-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="0791980309-3">{</span><span class="ss">function_clause</span><span class="p">,</span><span class="p" data-group-id="0791980309-4">[</span><span class="p" data-group-id="0791980309-5">{</span><span class="ss">tut2</span><span class="p">,</span><span class="ss">convert</span><span class="p">,</span><span class="w">
│ │ │ -                                </span><span class="p" data-group-id="0791980309-6">[</span><span class="mi">3</span><span class="p">,</span><span class="ss">miles</span><span class="p" data-group-id="0791980309-6">]</span><span class="p">,</span><span class="w">
│ │ │ -                                </span><span class="p" data-group-id="0791980309-7">[</span><span class="p" data-group-id="0791980309-8">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;tut2.erl&quot;</span><span class="p" data-group-id="0791980309-8">}</span><span class="p">,</span><span class="p" data-group-id="0791980309-9">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0791980309-9">}</span><span class="p" data-group-id="0791980309-7">]</span><span class="p" data-group-id="0791980309-5">}</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="0791980309-10">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="p" data-group-id="0791980309-11">[</span><span class="p" data-group-id="0791980309-12">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="0791980309-12">}</span><span class="p">,</span><span class="p" data-group-id="0791980309-13">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="0791980309-13">}</span><span class="p" data-group-id="0791980309-11">]</span><span class="p" data-group-id="0791980309-10">}</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="0791980309-14">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="0791980309-15">[</span><span class="p" data-group-id="0791980309-16">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="0791980309-16">}</span><span class="p">,</span><span class="p" data-group-id="0791980309-17">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="0791980309-17">}</span><span class="p" data-group-id="0791980309-15">]</span><span class="p" data-group-id="0791980309-14">}</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="0791980309-18">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="0791980309-19">[</span><span class="p" data-group-id="0791980309-20">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="0791980309-20">}</span><span class="p">,</span><span class="p" data-group-id="0791980309-21">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="0791980309-21">}</span><span class="p" data-group-id="0791980309-19">]</span><span class="p" data-group-id="0791980309-18">}</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="p" data-group-id="0791980309-22">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                 </span><span class="p" data-group-id="0791980309-23">[</span><span class="p" data-group-id="0791980309-24">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="0791980309-24">}</span><span class="p">,</span><span class="p" data-group-id="0791980309-25">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="0791980309-25">}</span><span class="p" data-group-id="0791980309-23">]</span><span class="p" data-group-id="0791980309-22">}</span><span class="p" data-group-id="0791980309-4">]</span><span class="p" data-group-id="0791980309-3">}</span><span class="p" data-group-id="0791980309-2">}</span></code></pre><h2 id="tuples" class="section-heading">
│ │ │ +shell's history list and can be output by the shell command <code class="inline">v/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">13&gt; </span><span class="nf">v</span><span class="p" data-group-id="8742237635-1">(</span><span class="mi">12</span><span class="p" data-group-id="8742237635-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8742237635-2">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="p" data-group-id="8742237635-3">{</span><span class="ss">function_clause</span><span class="p">,</span><span class="p" data-group-id="8742237635-4">[</span><span class="p" data-group-id="8742237635-5">{</span><span class="ss">tut2</span><span class="p">,</span><span class="ss">convert</span><span class="p">,</span><span class="w">
│ │ │ +                                </span><span class="p" data-group-id="8742237635-6">[</span><span class="mi">3</span><span class="p">,</span><span class="ss">miles</span><span class="p" data-group-id="8742237635-6">]</span><span class="p">,</span><span class="w">
│ │ │ +                                </span><span class="p" data-group-id="8742237635-7">[</span><span class="p" data-group-id="8742237635-8">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;tut2.erl&quot;</span><span class="p" data-group-id="8742237635-8">}</span><span class="p">,</span><span class="p" data-group-id="8742237635-9">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8742237635-9">}</span><span class="p" data-group-id="8742237635-7">]</span><span class="p" data-group-id="8742237635-5">}</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="8742237635-10">{</span><span class="ss">erl_eval</span><span class="p">,</span><span class="ss">do_apply</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="p" data-group-id="8742237635-11">[</span><span class="p" data-group-id="8742237635-12">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;erl_eval.erl&quot;</span><span class="p" data-group-id="8742237635-12">}</span><span class="p">,</span><span class="p" data-group-id="8742237635-13">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">677</span><span class="p" data-group-id="8742237635-13">}</span><span class="p" data-group-id="8742237635-11">]</span><span class="p" data-group-id="8742237635-10">}</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="8742237635-14">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="8742237635-15">[</span><span class="p" data-group-id="8742237635-16">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="8742237635-16">}</span><span class="p">,</span><span class="p" data-group-id="8742237635-17">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">687</span><span class="p" data-group-id="8742237635-17">}</span><span class="p" data-group-id="8742237635-15">]</span><span class="p" data-group-id="8742237635-14">}</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="8742237635-18">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_exprs</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="p" data-group-id="8742237635-19">[</span><span class="p" data-group-id="8742237635-20">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="8742237635-20">}</span><span class="p">,</span><span class="p" data-group-id="8742237635-21">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">642</span><span class="p" data-group-id="8742237635-21">}</span><span class="p" data-group-id="8742237635-19">]</span><span class="p" data-group-id="8742237635-18">}</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="p" data-group-id="8742237635-22">{</span><span class="ss">shell</span><span class="p">,</span><span class="ss">eval_loop</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                 </span><span class="p" data-group-id="8742237635-23">[</span><span class="p" data-group-id="8742237635-24">{</span><span class="ss">file</span><span class="p">,</span><span class="s">&quot;shell.erl&quot;</span><span class="p" data-group-id="8742237635-24">}</span><span class="p">,</span><span class="p" data-group-id="8742237635-25">{</span><span class="ss">line</span><span class="p">,</span><span class="mi">627</span><span class="p" data-group-id="8742237635-25">}</span><span class="p" data-group-id="8742237635-23">]</span><span class="p" data-group-id="8742237635-22">}</span><span class="p" data-group-id="8742237635-4">]</span><span class="p" data-group-id="8742237635-3">}</span><span class="p" data-group-id="8742237635-2">}</span></code></pre><h2 id="tuples" class="section-heading">
│ │ │    <a href="#tuples" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Tuples</span>
│ │ │  </h2>
│ │ │ -<p>Now the <code class="inline">tut2</code> program is hardly good programming style. Consider:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="4819870198-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="4819870198-1">)</span><span class="p">.</span></code></pre><p>Does this mean that 3 is in inches? Or does it mean that 3 is in centimeters and
│ │ │ +<p>Now the <code class="inline">tut2</code> program is hardly good programming style. Consider:</p><pre><code class="makeup erlang" translate="no"><span class="nc">tut2</span><span class="p">:</span><span class="nf">convert</span><span class="p" data-group-id="8723134930-1">(</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">inch</span><span class="p" data-group-id="8723134930-1">)</span><span class="p">.</span></code></pre><p>Does this mean that 3 is in inches? Or does it mean that 3 is in centimeters and
│ │ │  is to be converted to inches? Erlang has a way to group things together to make
│ │ │  things more understandable. These are called <em>tuples</em> and are surrounded by
│ │ │  curly brackets, <code class="inline">{</code> and <code class="inline">}</code>.</p><p>So, <code class="inline">{inch,3}</code> denotes 3 inches and <code class="inline">{centimeter,5}</code> denotes 5 centimeters. Now
│ │ │  let us write a new program that converts centimeters to inches and conversely.
│ │ │ -Enter the following code in a file called <code class="inline">tut3.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1646710534-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="1646710534-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1646710534-2">(</span><span class="p" data-group-id="1646710534-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1646710534-3">]</span><span class="p" data-group-id="1646710534-2">)</span><span class="p">.</span><span class="w">
│ │ │ +Enter the following code in a file called <code class="inline">tut3.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3950974550-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="3950974550-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3950974550-2">(</span><span class="p" data-group-id="3950974550-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3950974550-3">]</span><span class="p" data-group-id="3950974550-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="1646710534-4">(</span><span class="p" data-group-id="1646710534-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="1646710534-5">}</span><span class="p" data-group-id="1646710534-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1646710534-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="1646710534-6">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="1646710534-7">(</span><span class="p" data-group-id="1646710534-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="1646710534-8">}</span><span class="p" data-group-id="1646710534-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1646710534-9">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="1646710534-9">}</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">14&gt; </span><span class="nf">c</span><span class="p" data-group-id="2586307898-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="2586307898-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2586307898-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut3</span><span class="p" data-group-id="2586307898-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">15&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2586307898-3">(</span><span class="p" data-group-id="2586307898-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="2586307898-4">}</span><span class="p" data-group-id="2586307898-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2586307898-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">12.7</span><span class="p" data-group-id="2586307898-5">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">16&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2586307898-6">(</span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2586307898-7">(</span><span class="p" data-group-id="2586307898-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="2586307898-8">}</span><span class="p" data-group-id="2586307898-7">)</span><span class="p" data-group-id="2586307898-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2586307898-9">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">5.0</span><span class="p" data-group-id="2586307898-9">}</span></code></pre><p>Notice on line 16 that 5 inches is converted to centimeters and back again and
│ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="3950974550-4">(</span><span class="p" data-group-id="3950974550-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="3950974550-5">}</span><span class="p" data-group-id="3950974550-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3950974550-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="3950974550-6">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="3950974550-7">(</span><span class="p" data-group-id="3950974550-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3950974550-8">}</span><span class="p" data-group-id="3950974550-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3950974550-9">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="3950974550-9">}</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">14&gt; </span><span class="nf">c</span><span class="p" data-group-id="1974918512-1">(</span><span class="ss">tut3</span><span class="p" data-group-id="1974918512-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1974918512-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut3</span><span class="p" data-group-id="1974918512-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">15&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="1974918512-3">(</span><span class="p" data-group-id="1974918512-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="1974918512-4">}</span><span class="p" data-group-id="1974918512-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1974918512-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">12.7</span><span class="p" data-group-id="1974918512-5">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">16&gt; </span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="1974918512-6">(</span><span class="nc">tut3</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="1974918512-7">(</span><span class="p" data-group-id="1974918512-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="1974918512-8">}</span><span class="p" data-group-id="1974918512-7">)</span><span class="p" data-group-id="1974918512-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1974918512-9">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">5.0</span><span class="p" data-group-id="1974918512-9">}</span></code></pre><p>Notice on line 16 that 5 inches is converted to centimeters and back again and
│ │ │  reassuringly get back to the original value. That is, the argument to a function
│ │ │  can be the result of another function. Consider how line 16 (above) works. The
│ │ │  argument given to the function <code class="inline">{inch,5}</code> is first matched against the first
│ │ │  head clause of <code class="inline">convert_length</code>, that is, <code class="inline">convert_length({centimeter,X})</code>. It
│ │ │  can be seen that <code class="inline">{centimeter,X}</code> does not match <code class="inline">{inch,5}</code> (the head is the bit
│ │ │  before the <code class="inline">-&gt;</code>). This having failed, let us try the head of the next clause
│ │ │  that is, <code class="inline">convert_length({inch,Y})</code>. This matches, and <code class="inline">Y</code> gets the value 5.</p><p>Tuples can have more than two parts, in fact as many parts as you want, and
│ │ │  contain any valid Erlang <em>term</em>. For example, to represent the temperature of
│ │ │ -various cities of the world:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6749643955-1">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749643955-2">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6749643955-2">}</span><span class="p" data-group-id="6749643955-1">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6749643955-3">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749643955-4">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6749643955-4">}</span><span class="p" data-group-id="6749643955-3">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6749643955-5">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749643955-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6749643955-6">}</span><span class="p" data-group-id="6749643955-5">}</span></code></pre><p>Tuples have a fixed number of items in them. Each item in a tuple is called an
│ │ │ +various cities of the world:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6574900994-1">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6574900994-2">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6574900994-2">}</span><span class="p" data-group-id="6574900994-1">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6574900994-3">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6574900994-4">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6574900994-4">}</span><span class="p" data-group-id="6574900994-3">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6574900994-5">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6574900994-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6574900994-6">}</span><span class="p" data-group-id="6574900994-5">}</span></code></pre><p>Tuples have a fixed number of items in them. Each item in a tuple is called an
│ │ │  <em>element</em>. In the tuple <code class="inline">{moscow,{c,-10}}</code>, element 1 is <code class="inline">moscow</code> and element 2
│ │ │  is <code class="inline">{c,-10}</code>. Here <code class="inline">c</code> represents Celsius and <code class="inline">f</code> Fahrenheit.</p><h2 id="lists" class="section-heading">
│ │ │    <a href="#lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Lists</span>
│ │ │  </h2>
│ │ │  <p>Whereas tuples group things together, it is also needed to represent lists of
│ │ │  things. Lists in Erlang are surrounded by square brackets, <code class="inline">[</code> and <code class="inline">]</code>. For
│ │ │ -example, a list of the temperatures of various cities in the world can be:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4340701902-1">[</span><span class="p" data-group-id="4340701902-2">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4340701902-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4340701902-3">}</span><span class="p" data-group-id="4340701902-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4340701902-4">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4340701902-5">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4340701902-5">}</span><span class="p" data-group-id="4340701902-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4340701902-6">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4340701902-7">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4340701902-7">}</span><span class="p" data-group-id="4340701902-6">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4340701902-8">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4340701902-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4340701902-9">}</span><span class="p" data-group-id="4340701902-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4340701902-10">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4340701902-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4340701902-11">}</span><span class="p" data-group-id="4340701902-10">}</span><span class="p" data-group-id="4340701902-1">]</span></code></pre><p>Notice that this list was so long that it did not fit on one line. This does not
│ │ │ +example, a list of the temperatures of various cities in the world can be:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9049618653-1">[</span><span class="p" data-group-id="9049618653-2">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9049618653-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="9049618653-3">}</span><span class="p" data-group-id="9049618653-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9049618653-4">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9049618653-5">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="9049618653-5">}</span><span class="p" data-group-id="9049618653-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9049618653-6">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9049618653-7">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="9049618653-7">}</span><span class="p" data-group-id="9049618653-6">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="9049618653-8">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9049618653-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="9049618653-9">}</span><span class="p" data-group-id="9049618653-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9049618653-10">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9049618653-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="9049618653-11">}</span><span class="p" data-group-id="9049618653-10">}</span><span class="p" data-group-id="9049618653-1">]</span></code></pre><p>Notice that this list was so long that it did not fit on one line. This does not
│ │ │  matter, Erlang allows line breaks at all &quot;sensible places&quot; but not, for example,
│ │ │  in the middle of atoms, integers, and others.</p><p>A useful way of looking at parts of lists, is by using <code class="inline">|</code>. This is best
│ │ │ -explained by an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">17&gt; </span><span class="p" data-group-id="8076375882-1">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="n">TheRest</span><span class="p" data-group-id="8076375882-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8076375882-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8076375882-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8076375882-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8076375882-3">]</span><span class="w">
│ │ │ +explained by an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">17&gt; </span><span class="p" data-group-id="4322441824-1">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="n">TheRest</span><span class="p" data-group-id="4322441824-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4322441824-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4322441824-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4322441824-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4322441824-3">]</span><span class="w">
│ │ │  </span><span class="gp unselectable">18&gt; </span><span class="n">First</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="w">
│ │ │  </span><span class="gp unselectable">19&gt; </span><span class="n">TheRest</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8076375882-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8076375882-4">]</span></code></pre><p>To separate the first elements of the list from the rest of the list, <code class="inline">|</code> is
│ │ │ -used. <code class="inline">First</code> has got value <code class="inline">1</code> and <code class="inline">TheRest</code> has got the value <code class="inline">[2,3,4,5]</code>.</p><p>Another example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">20&gt; </span><span class="p" data-group-id="4548124589-1">[</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">R</span><span class="p" data-group-id="4548124589-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4548124589-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4548124589-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4548124589-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4548124589-3">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4322441824-4">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4322441824-4">]</span></code></pre><p>To separate the first elements of the list from the rest of the list, <code class="inline">|</code> is
│ │ │ +used. <code class="inline">First</code> has got value <code class="inline">1</code> and <code class="inline">TheRest</code> has got the value <code class="inline">[2,3,4,5]</code>.</p><p>Another example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">20&gt; </span><span class="p" data-group-id="8173102833-1">[</span><span class="n">E1</span><span class="p">,</span><span class="w"> </span><span class="n">E2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">R</span><span class="p" data-group-id="8173102833-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8173102833-2">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="8173102833-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8173102833-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="8173102833-3">]</span><span class="w">
│ │ │  </span><span class="gp unselectable">21&gt; </span><span class="n">E1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="w">
│ │ │  </span><span class="gp unselectable">22&gt; </span><span class="n">E2</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">2</span><span class="w">
│ │ │  </span><span class="gp unselectable">23&gt; </span><span class="n">R</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4548124589-4">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4548124589-4">]</span></code></pre><p>Here you see the use of <code class="inline">|</code> to get the first two elements from the list. If you
│ │ │ +</span><span class="p" data-group-id="8173102833-4">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="8173102833-4">]</span></code></pre><p>Here you see the use of <code class="inline">|</code> to get the first two elements from the list. If you
│ │ │  try to get more elements from the list than there are elements in the list, an
│ │ │  error is returned. Notice also the special case of the list with no elements,
│ │ │ -<code class="inline">[]</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">24&gt; </span><span class="p" data-group-id="7878890167-1">[</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="7878890167-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7878890167-2">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7878890167-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7878890167-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7878890167-3">]</span><span class="w">
│ │ │ +<code class="inline">[]</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">24&gt; </span><span class="p" data-group-id="7073836275-1">[</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="p" data-group-id="7073836275-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7073836275-2">[</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="7073836275-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7073836275-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7073836275-3">]</span><span class="w">
│ │ │  </span><span class="gp unselectable">25&gt; </span><span class="n">A</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="w">
│ │ │  </span><span class="gp unselectable">26&gt; </span><span class="n">B</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">2</span><span class="w">
│ │ │  </span><span class="gp unselectable">27&gt; </span><span class="n">C</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7878890167-4">[</span><span class="p" data-group-id="7878890167-4">]</span></code></pre><p>In the previous examples, new variable names are used, instead of reusing the
│ │ │ +</span><span class="p" data-group-id="7073836275-4">[</span><span class="p" data-group-id="7073836275-4">]</span></code></pre><p>In the previous examples, new variable names are used, instead of reusing the
│ │ │  old ones: <code class="inline">First</code>, <code class="inline">TheRest</code>, <code class="inline">E1</code>, <code class="inline">E2</code>, <code class="inline">R</code>, <code class="inline">A</code>, <code class="inline">B</code>, and <code class="inline">C</code>. The reason for
│ │ │  this is that a variable can only be given a value once in its context (scope).
│ │ │  More about this later.</p><p>The following example shows how to find the length of a list. Enter the
│ │ │ -following code in a file named <code class="inline">tut4.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2162767124-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="2162767124-1">)</span><span class="p">.</span><span class="w">
│ │ │ +following code in a file named <code class="inline">tut4.erl</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9328004045-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="9328004045-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2162767124-2">(</span><span class="p" data-group-id="2162767124-3">[</span><span class="ss">list_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2162767124-3">]</span><span class="p" data-group-id="2162767124-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9328004045-2">(</span><span class="p" data-group-id="9328004045-3">[</span><span class="ss">list_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9328004045-3">]</span><span class="p" data-group-id="9328004045-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">list_length</span><span class="p" data-group-id="2162767124-4">(</span><span class="p" data-group-id="2162767124-5">[</span><span class="p" data-group-id="2162767124-5">]</span><span class="p" data-group-id="2162767124-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">list_length</span><span class="p" data-group-id="9328004045-4">(</span><span class="p" data-group-id="9328004045-5">[</span><span class="p" data-group-id="9328004045-5">]</span><span class="p" data-group-id="9328004045-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">list_length</span><span class="p" data-group-id="2162767124-6">(</span><span class="p" data-group-id="2162767124-7">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2162767124-7">]</span><span class="p" data-group-id="2162767124-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="2162767124-8">(</span><span class="n">Rest</span><span class="p" data-group-id="2162767124-8">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">28&gt; </span><span class="nf">c</span><span class="p" data-group-id="2908148840-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="2908148840-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2908148840-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut4</span><span class="p" data-group-id="2908148840-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">29&gt; </span><span class="nc">tut4</span><span class="p">:</span><span class="nf">list_length</span><span class="p" data-group-id="2908148840-3">(</span><span class="p" data-group-id="2908148840-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="2908148840-4">]</span><span class="p" data-group-id="2908148840-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">7</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="9658470474-1">(</span><span class="p" data-group-id="9658470474-2">[</span><span class="p" data-group-id="9658470474-2">]</span><span class="p" data-group-id="9658470474-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="mi">0</span><span class="p">;</span></code></pre><p>The length of an empty list is obviously 0.</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="8359931059-1">(</span><span class="p" data-group-id="8359931059-2">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="8359931059-2">]</span><span class="p" data-group-id="8359931059-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="8359931059-3">(</span><span class="n">Rest</span><span class="p" data-group-id="8359931059-3">)</span><span class="p">.</span></code></pre><p>The length of a list with the first element <code class="inline">First</code> and the remaining elements
│ │ │ +</span><span class="nf">list_length</span><span class="p" data-group-id="9328004045-6">(</span><span class="p" data-group-id="9328004045-7">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9328004045-7">]</span><span class="p" data-group-id="9328004045-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="9328004045-8">(</span><span class="n">Rest</span><span class="p" data-group-id="9328004045-8">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">28&gt; </span><span class="nf">c</span><span class="p" data-group-id="4304873138-1">(</span><span class="ss">tut4</span><span class="p" data-group-id="4304873138-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4304873138-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut4</span><span class="p" data-group-id="4304873138-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">29&gt; </span><span class="nc">tut4</span><span class="p">:</span><span class="nf">list_length</span><span class="p" data-group-id="4304873138-3">(</span><span class="p" data-group-id="4304873138-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p" data-group-id="4304873138-4">]</span><span class="p" data-group-id="4304873138-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="mi">7</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="5353426337-1">(</span><span class="p" data-group-id="5353426337-2">[</span><span class="p" data-group-id="5353426337-2">]</span><span class="p" data-group-id="5353426337-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="mi">0</span><span class="p">;</span></code></pre><p>The length of an empty list is obviously 0.</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_length</span><span class="p" data-group-id="6207405197-1">(</span><span class="p" data-group-id="6207405197-2">[</span><span class="n">First</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="6207405197-2">]</span><span class="p" data-group-id="6207405197-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="mi">1</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="nf">list_length</span><span class="p" data-group-id="6207405197-3">(</span><span class="n">Rest</span><span class="p" data-group-id="6207405197-3">)</span><span class="p">.</span></code></pre><p>The length of a list with the first element <code class="inline">First</code> and the remaining elements
│ │ │  <code class="inline">Rest</code> is 1 + the length of <code class="inline">Rest</code>.</p><p>(Advanced readers only: This is not tail recursive, there is a better way to
│ │ │  write this function.)</p><p>In general, tuples are used where &quot;records&quot; or &quot;structs&quot; are used in other
│ │ │  languages. Also, lists are used when representing things with varying sizes,
│ │ │  that is, where linked lists are used in other languages.</p><p>Erlang does not have a string data type. Instead, strings can be represented by
│ │ │  lists of Unicode characters. This implies for example that the list <code class="inline">[97,98,99]</code>
│ │ │  is equivalent to <code class="inline">&quot;abc&quot;</code>. The Erlang shell is &quot;clever&quot; and guesses what list you
│ │ │ -mean and outputs it in what it thinks is the most appropriate form, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">30&gt; </span><span class="p" data-group-id="0710661819-1">[</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="0710661819-1">]</span><span class="p">.</span><span class="w">
│ │ │ +mean and outputs it in what it thinks is the most appropriate form, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">30&gt; </span><span class="p" data-group-id="6039541164-1">[</span><span class="mi">97</span><span class="p">,</span><span class="mi">98</span><span class="p">,</span><span class="mi">99</span><span class="p" data-group-id="6039541164-1">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;abc&quot;</span></code></pre><h2 id="maps" class="section-heading">
│ │ │    <a href="#maps" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Maps</span>
│ │ │  </h2>
│ │ │  <p>Maps are a set of key to value associations. These associations are encapsulated
│ │ │ -with <code class="inline">#{</code> and <code class="inline">}</code>. To create an association from <code class="inline">&quot;key&quot;</code> to value <code class="inline">42</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="0458051328-1">#{</span><span class="w"> </span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p" data-group-id="0458051328-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0458051328-2">#{</span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="0458051328-2">}</span></code></pre><p>Let us jump straight into the deep end with an example using some interesting
│ │ │ +with <code class="inline">#{</code> and <code class="inline">}</code>. To create an association from <code class="inline">&quot;key&quot;</code> to value <code class="inline">42</code>:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="p" data-group-id="7714677982-1">#{</span><span class="w"> </span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p" data-group-id="7714677982-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7714677982-2">#{</span><span class="s">&quot;key&quot;</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">42</span><span class="p" data-group-id="7714677982-2">}</span></code></pre><p>Let us jump straight into the deep end with an example using some interesting
│ │ │  features.</p><p>The following example shows how to calculate alpha blending using maps to
│ │ │ -reference color and alpha channels. Enter the code in a file named <code class="inline">color.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2312357586-1">(</span><span class="ss">color</span><span class="p" data-group-id="2312357586-1">)</span><span class="p">.</span><span class="w">
│ │ │ +reference color and alpha channels. Enter the code in a file named <code class="inline">color.erl</code>):</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4212399925-1">(</span><span class="ss">color</span><span class="p" data-group-id="4212399925-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2312357586-2">(</span><span class="p" data-group-id="2312357586-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="ss">blend</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="2312357586-3">]</span><span class="p" data-group-id="2312357586-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4212399925-2">(</span><span class="p" data-group-id="4212399925-3">[</span><span class="ss">new</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="ss">blend</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4212399925-3">]</span><span class="p" data-group-id="4212399925-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2312357586-4">(</span><span class="nf">is_channel</span><span class="p" data-group-id="2312357586-5">(</span><span class="n">V</span><span class="p" data-group-id="2312357586-5">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312357586-6">(</span><span class="nf">is_float</span><span class="p" data-group-id="2312357586-7">(</span><span class="n">V</span><span class="p" data-group-id="2312357586-7">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="2312357586-6">)</span><span class="p" data-group-id="2312357586-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4212399925-4">(</span><span class="nf">is_channel</span><span class="p" data-group-id="4212399925-5">(</span><span class="n">V</span><span class="p" data-group-id="4212399925-5">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4212399925-6">(</span><span class="nf">is_float</span><span class="p" data-group-id="4212399925-7">(</span><span class="n">V</span><span class="p" data-group-id="4212399925-7">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="4212399925-6">)</span><span class="p" data-group-id="4212399925-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">new</span><span class="p" data-group-id="2312357586-8">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="2312357586-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="2312357586-9">(</span><span class="n">R</span><span class="p" data-group-id="2312357586-9">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="2312357586-10">(</span><span class="n">G</span><span class="p" data-group-id="2312357586-10">)</span><span class="p">,</span><span class="w">
│ │ │ -                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="2312357586-11">(</span><span class="n">B</span><span class="p" data-group-id="2312357586-11">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="2312357586-12">(</span><span class="n">A</span><span class="p" data-group-id="2312357586-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2312357586-13">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="2312357586-13">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="2312357586-14">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="2312357586-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">blend</span><span class="p" data-group-id="2312357586-15">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="nf">alpha</span><span class="p" data-group-id="2312357586-16">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="2312357586-16">)</span><span class="p" data-group-id="2312357586-15">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="2312357586-17">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="2312357586-17">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="2312357586-18">#{</span><span class="w">
│ │ │ -        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="2312357586-19">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="2312357586-19">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="2312357586-20">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="2312357586-20">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="2312357586-21">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="2312357586-21">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">new</span><span class="p" data-group-id="4212399925-8">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="4212399925-8">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="4212399925-9">(</span><span class="n">R</span><span class="p" data-group-id="4212399925-9">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="4212399925-10">(</span><span class="n">G</span><span class="p" data-group-id="4212399925-10">)</span><span class="p">,</span><span class="w">
│ │ │ +                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="4212399925-11">(</span><span class="n">B</span><span class="p" data-group-id="4212399925-11">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="4212399925-12">(</span><span class="n">A</span><span class="p" data-group-id="4212399925-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4212399925-13">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="4212399925-13">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="4212399925-14">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="4212399925-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">blend</span><span class="p" data-group-id="4212399925-15">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="nf">alpha</span><span class="p" data-group-id="4212399925-16">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="4212399925-16">)</span><span class="p" data-group-id="4212399925-15">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="4212399925-17">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="4212399925-17">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="4212399925-18">#{</span><span class="w">
│ │ │ +        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="4212399925-19">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="4212399925-19">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="4212399925-20">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="4212399925-20">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="4212399925-21">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="4212399925-21">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Alpha</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2312357586-18">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">blend</span><span class="p" data-group-id="2312357586-22">(</span><span class="p">_</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2312357586-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="2312357586-23">#{</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4212399925-18">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">blend</span><span class="p" data-group-id="4212399925-22">(</span><span class="p">_</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4212399925-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="4212399925-23">#{</span><span class="w">
│ │ │          </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="mf">0.0</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2312357586-23">}</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4212399925-23">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alpha</span><span class="p" data-group-id="2312357586-24">(</span><span class="p" data-group-id="2312357586-25">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2312357586-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312357586-26">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="2312357586-26">}</span><span class="p" data-group-id="2312357586-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="2312357586-27">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2312357586-27">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">alpha</span><span class="p" data-group-id="4212399925-24">(</span><span class="p" data-group-id="4212399925-25">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="4212399925-25">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4212399925-26">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="4212399925-26">}</span><span class="p" data-group-id="4212399925-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="4212399925-27">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="4212399925-27">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">red</span><span class="p" data-group-id="2312357586-28">(</span><span class="p" data-group-id="2312357586-29">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2312357586-29">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312357586-30">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="2312357586-30">}</span><span class="p" data-group-id="2312357586-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="2312357586-31">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2312357586-31">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">green</span><span class="p" data-group-id="2312357586-32">(</span><span class="p" data-group-id="2312357586-33">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2312357586-33">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312357586-34">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="2312357586-34">}</span><span class="p" data-group-id="2312357586-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="2312357586-35">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2312357586-35">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">blue</span><span class="p" data-group-id="2312357586-36">(</span><span class="p" data-group-id="2312357586-37">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2312357586-37">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2312357586-38">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="2312357586-38">}</span><span class="p" data-group-id="2312357586-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="2312357586-39">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="2312357586-39">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">c</span><span class="p" data-group-id="4456290208-1">(</span><span class="ss">color</span><span class="p" data-group-id="4456290208-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4456290208-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">color</span><span class="p" data-group-id="4456290208-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">C1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="4456290208-3">(</span><span class="mf">0.3</span><span class="p">,</span><span class="mf">0.4</span><span class="p">,</span><span class="mf">0.5</span><span class="p">,</span><span class="mf">1.0</span><span class="p" data-group-id="4456290208-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4456290208-4">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="4456290208-4">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="n">C2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="4456290208-5">(</span><span class="mf">1.0</span><span class="p">,</span><span class="mf">0.8</span><span class="p">,</span><span class="mf">0.1</span><span class="p">,</span><span class="mf">0.3</span><span class="p" data-group-id="4456290208-5">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4456290208-6">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.1</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.8</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="4456290208-6">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="4456290208-7">(</span><span class="n">C1</span><span class="p">,</span><span class="n">C2</span><span class="p" data-group-id="4456290208-7">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4456290208-8">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="4456290208-8">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="4456290208-9">(</span><span class="n">C2</span><span class="p">,</span><span class="n">C1</span><span class="p" data-group-id="4456290208-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4456290208-10">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.38</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.52</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.51</span><span class="p" data-group-id="4456290208-10">}</span></code></pre><p>This example warrants some explanation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8015173036-1">(</span><span class="nf">is_channel</span><span class="p" data-group-id="8015173036-2">(</span><span class="n">V</span><span class="p" data-group-id="8015173036-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8015173036-3">(</span><span class="nf">is_float</span><span class="p" data-group-id="8015173036-4">(</span><span class="n">V</span><span class="p" data-group-id="8015173036-4">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="8015173036-3">)</span><span class="p" data-group-id="8015173036-1">)</span><span class="p">.</span></code></pre><p>First a macro <code class="inline">is_channel</code> is defined to help with the guard tests. This is only
│ │ │ +</span><span class="nf">red</span><span class="p" data-group-id="4212399925-28">(</span><span class="p" data-group-id="4212399925-29">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="4212399925-29">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4212399925-30">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="4212399925-30">}</span><span class="p" data-group-id="4212399925-28">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="4212399925-31">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="4212399925-31">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">green</span><span class="p" data-group-id="4212399925-32">(</span><span class="p" data-group-id="4212399925-33">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="4212399925-33">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4212399925-34">#{</span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="4212399925-34">}</span><span class="p" data-group-id="4212399925-32">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="4212399925-35">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="4212399925-35">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">blue</span><span class="p" data-group-id="4212399925-36">(</span><span class="p" data-group-id="4212399925-37">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="4212399925-37">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4212399925-38">#{</span><span class="ss">blue</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="4212399925-38">}</span><span class="p" data-group-id="4212399925-36">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="4212399925-39">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="4212399925-39">)</span><span class="p">.</span></code></pre><p>Compile and test:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">&gt; </span><span class="nf">c</span><span class="p" data-group-id="4115189695-1">(</span><span class="ss">color</span><span class="p" data-group-id="4115189695-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4115189695-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">color</span><span class="p" data-group-id="4115189695-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">C1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="4115189695-3">(</span><span class="mf">0.3</span><span class="p">,</span><span class="mf">0.4</span><span class="p">,</span><span class="mf">0.5</span><span class="p">,</span><span class="mf">1.0</span><span class="p" data-group-id="4115189695-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4115189695-4">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="4115189695-4">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="n">C2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">color</span><span class="p">:</span><span class="nf">new</span><span class="p" data-group-id="4115189695-5">(</span><span class="mf">1.0</span><span class="p">,</span><span class="mf">0.8</span><span class="p">,</span><span class="mf">0.1</span><span class="p">,</span><span class="mf">0.3</span><span class="p" data-group-id="4115189695-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4115189695-6">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.1</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.8</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="4115189695-6">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="4115189695-7">(</span><span class="n">C1</span><span class="p">,</span><span class="n">C2</span><span class="p" data-group-id="4115189695-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4115189695-8">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.5</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.4</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.3</span><span class="p" data-group-id="4115189695-8">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">&gt; </span><span class="nc">color</span><span class="p">:</span><span class="nf">blend</span><span class="p" data-group-id="4115189695-9">(</span><span class="n">C2</span><span class="p">,</span><span class="n">C1</span><span class="p" data-group-id="4115189695-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4115189695-10">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p">,</span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.38</span><span class="p">,</span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.52</span><span class="p">,</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mf">0.51</span><span class="p" data-group-id="4115189695-10">}</span></code></pre><p>This example warrants some explanation:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2709572176-1">(</span><span class="nf">is_channel</span><span class="p" data-group-id="2709572176-2">(</span><span class="n">V</span><span class="p" data-group-id="2709572176-2">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2709572176-3">(</span><span class="nf">is_float</span><span class="p" data-group-id="2709572176-4">(</span><span class="n">V</span><span class="p" data-group-id="2709572176-4">)</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">&gt;=</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">=&lt;</span><span class="w"> </span><span class="mf">1.0</span><span class="p" data-group-id="2709572176-3">)</span><span class="p" data-group-id="2709572176-1">)</span><span class="p">.</span></code></pre><p>First a macro <code class="inline">is_channel</code> is defined to help with the guard tests. This is only
│ │ │  here for convenience and to reduce syntax cluttering. For more information about
│ │ │ -macros, see <a href="../../doc/system/macros.html">The Preprocessor</a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="0764509359-1">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="0764509359-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0764509359-2">(</span><span class="n">R</span><span class="p" data-group-id="0764509359-2">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0764509359-3">(</span><span class="n">G</span><span class="p" data-group-id="0764509359-3">)</span><span class="p">,</span><span class="w">
│ │ │ -                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0764509359-4">(</span><span class="n">B</span><span class="p" data-group-id="0764509359-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="0764509359-5">(</span><span class="n">A</span><span class="p" data-group-id="0764509359-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0764509359-6">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="0764509359-6">}</span><span class="p">.</span></code></pre><p>The function <code class="inline">new/4</code> creates a new map term and lets the keys <code class="inline">red</code>, <code class="inline">green</code>,
│ │ │ +macros, see <a href="../../doc/system/macros.html">The Preprocessor</a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">new</span><span class="p" data-group-id="5679848057-1">(</span><span class="n">R</span><span class="p">,</span><span class="n">G</span><span class="p">,</span><span class="n">B</span><span class="p">,</span><span class="n">A</span><span class="p" data-group-id="5679848057-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="5679848057-2">(</span><span class="n">R</span><span class="p" data-group-id="5679848057-2">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="5679848057-3">(</span><span class="n">G</span><span class="p" data-group-id="5679848057-3">)</span><span class="p">,</span><span class="w">
│ │ │ +                  </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="5679848057-4">(</span><span class="n">B</span><span class="p" data-group-id="5679848057-4">)</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="nf">is_channel</span><span class="p" data-group-id="5679848057-5">(</span><span class="n">A</span><span class="p" data-group-id="5679848057-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5679848057-6">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">R</span><span class="p">,</span><span class="w"> </span><span class="ss">green</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">G</span><span class="p">,</span><span class="w"> </span><span class="ss">blue</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">A</span><span class="p" data-group-id="5679848057-6">}</span><span class="p">.</span></code></pre><p>The function <code class="inline">new/4</code> creates a new map term and lets the keys <code class="inline">red</code>, <code class="inline">green</code>,
│ │ │  <code class="inline">blue</code>, and <code class="inline">alpha</code> be associated with an initial value. In this case, only
│ │ │  float values between and including 0.0 and 1.0 are allowed, as ensured by the
│ │ │  <code class="inline">?is_channel/1</code> macro for each argument. Only the <code class="inline">=&gt;</code> operator is allowed when
│ │ │  creating a new map.</p><p>By calling <code class="inline">blend/2</code> on any color term created by <code class="inline">new/4</code>, the resulting color
│ │ │ -can be calculated as determined by the two map terms.</p><p>The first thing <code class="inline">blend/2</code> does is to calculate the resulting alpha channel:</p><pre><code class="makeup erlang" translate="no"><span class="nf">alpha</span><span class="p" data-group-id="3239122322-1">(</span><span class="p" data-group-id="3239122322-2">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3239122322-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3239122322-3">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="3239122322-3">}</span><span class="p" data-group-id="3239122322-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="3239122322-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3239122322-4">)</span><span class="p">.</span></code></pre><p>The value associated with key <code class="inline">alpha</code> is fetched for both arguments using the
│ │ │ +can be calculated as determined by the two map terms.</p><p>The first thing <code class="inline">blend/2</code> does is to calculate the resulting alpha channel:</p><pre><code class="makeup erlang" translate="no"><span class="nf">alpha</span><span class="p" data-group-id="6901620663-1">(</span><span class="p" data-group-id="6901620663-2">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6901620663-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6901620663-3">#{</span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="6901620663-3">}</span><span class="p" data-group-id="6901620663-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="6901620663-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="6901620663-4">)</span><span class="p">.</span></code></pre><p>The value associated with key <code class="inline">alpha</code> is fetched for both arguments using the
│ │ │  <code class="inline">:=</code> operator. The other keys in the map are ignored, only the key <code class="inline">alpha</code> is
│ │ │ -required and checked for.</p><p>This is also the case for functions <code class="inline">red/2</code>, <code class="inline">blue/2</code>, and <code class="inline">green/2</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">red</span><span class="p" data-group-id="8805964699-1">(</span><span class="p" data-group-id="8805964699-2">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="8805964699-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8805964699-3">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="8805964699-3">}</span><span class="p" data-group-id="8805964699-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="8805964699-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="8805964699-4">)</span><span class="p">.</span></code></pre><p>The difference here is that a check is made for two keys in each map argument.
│ │ │ -The other keys are ignored.</p><p>Finally, let us return the resulting color in <code class="inline">blend/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">blend</span><span class="p" data-group-id="9017040145-1">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="9017040145-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Dst</span><span class="p" data-group-id="9017040145-2">#{</span><span class="w">
│ │ │ -        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="9017040145-3">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="9017040145-3">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="9017040145-4">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="9017040145-4">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="9017040145-5">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="9017040145-5">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +required and checked for.</p><p>This is also the case for functions <code class="inline">red/2</code>, <code class="inline">blue/2</code>, and <code class="inline">green/2</code>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">red</span><span class="p" data-group-id="3416710831-1">(</span><span class="p" data-group-id="3416710831-2">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3416710831-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3416710831-3">#{</span><span class="ss">red</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DV</span><span class="p">,</span><span class="w"> </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">DA</span><span class="p" data-group-id="3416710831-3">}</span><span class="p" data-group-id="3416710831-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SV</span><span class="o">*</span><span class="n">SA</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">DV</span><span class="o">*</span><span class="n">DA</span><span class="o">*</span><span class="p" data-group-id="3416710831-4">(</span><span class="mf">1.0</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">SA</span><span class="p" data-group-id="3416710831-4">)</span><span class="p">.</span></code></pre><p>The difference here is that a check is made for two keys in each map argument.
│ │ │ +The other keys are ignored.</p><p>Finally, let us return the resulting color in <code class="inline">blend/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">blend</span><span class="p" data-group-id="0480622254-1">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p">,</span><span class="n">Alpha</span><span class="p" data-group-id="0480622254-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Alpha</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mf">0.0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Dst</span><span class="p" data-group-id="0480622254-2">#{</span><span class="w">
│ │ │ +        </span><span class="ss">red</span><span class="w">   </span><span class="p">:=</span><span class="w"> </span><span class="nf">red</span><span class="p" data-group-id="0480622254-3">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0480622254-3">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="ss">green</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="nf">green</span><span class="p" data-group-id="0480622254-4">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0480622254-4">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="ss">blue</span><span class="w">  </span><span class="p">:=</span><span class="w"> </span><span class="nf">blue</span><span class="p" data-group-id="0480622254-5">(</span><span class="n">Src</span><span class="p">,</span><span class="n">Dst</span><span class="p" data-group-id="0480622254-5">)</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">Alpha</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">alpha</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Alpha</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9017040145-2">}</span><span class="p">;</span></code></pre><p>The <code class="inline">Dst</code> map is updated with new channel values. The syntax for updating an
│ │ │ +    </span><span class="p" data-group-id="0480622254-2">}</span><span class="p">;</span></code></pre><p>The <code class="inline">Dst</code> map is updated with new channel values. The syntax for updating an
│ │ │  existing key with a new value is with the <code class="inline">:=</code> operator.</p><h2 id="standard-modules-and-manual-pages" class="section-heading">
│ │ │    <a href="#standard-modules-and-manual-pages" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Standard Modules and Manual Pages</span>
│ │ │  </h2>
│ │ │  <p>Erlang has many standard modules to help you do things. For example, the module
│ │ │ @@ -442,24 +442,24 @@
│ │ │    <a href="#writing-output-to-a-terminal" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Writing Output to a Terminal</span>
│ │ │  </h2>
│ │ │  <p>It is nice to be able to do formatted output in examples, so the next example
│ │ │  shows a simple way to use the <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function. Like all other exported
│ │ │ -functions, you can test the <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">31&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6231799151-1">(</span><span class="s">&quot;hello world</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6231799151-2">[</span><span class="p" data-group-id="6231799151-2">]</span><span class="p" data-group-id="6231799151-1">)</span><span class="p">.</span><span class="w">
│ │ │ +functions, you can test the <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">31&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6625028407-1">(</span><span class="s">&quot;hello world</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6625028407-2">[</span><span class="p" data-group-id="6625028407-2">]</span><span class="p" data-group-id="6625028407-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">hello</span><span class="w"> </span><span class="ss">world</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">32&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6231799151-3">(</span><span class="s">&quot;this outputs one Erlang term: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6231799151-4">[</span><span class="ss">hello</span><span class="p" data-group-id="6231799151-4">]</span><span class="p" data-group-id="6231799151-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">32&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6625028407-3">(</span><span class="s">&quot;this outputs one Erlang term: </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6625028407-4">[</span><span class="ss">hello</span><span class="p" data-group-id="6625028407-4">]</span><span class="p" data-group-id="6625028407-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">one</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">term</span><span class="p">:</span><span class="w"> </span><span class="ss">hello</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">33&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6231799151-5">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6231799151-6">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="6231799151-6">]</span><span class="p" data-group-id="6231799151-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">33&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6625028407-5">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6625028407-6">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="6625028407-6">]</span><span class="p" data-group-id="6625028407-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">terms</span><span class="p">:</span><span class="w"> </span><span class="ss">helloworld</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">34&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6231799151-7">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6231799151-8">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="6231799151-8">]</span><span class="p" data-group-id="6231799151-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">34&gt; </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6625028407-7">(</span><span class="s">&quot;this outputs two Erlang terms: </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6625028407-8">[</span><span class="ss">hello</span><span class="p">,</span><span class="w"> </span><span class="ss">world</span><span class="p" data-group-id="6625028407-8">]</span><span class="p" data-group-id="6625028407-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">this</span><span class="w"> </span><span class="ss">outputs</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="nc">terms</span><span class="p">:</span><span class="w"> </span><span class="ss">hello</span><span class="w"> </span><span class="ss">world</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>The function <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> (that is, <code class="inline">format</code> with two arguments) takes two lists.
│ │ │  The first one is nearly always a list written between <code class="inline">&quot; &quot;</code>. This list is printed
│ │ │  out as it is, except that each <code class="inline">~w</code> is replaced by a term taken in order from the
│ │ │  second list. Each ~n is replaced by a new line. The <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/2"><code class="inline">io:format/2</code></a> function
│ │ │  itself returns the atom <code class="inline">ok</code> if everything goes as planned. Like other functions
│ │ │  in Erlang, it crashes if an error occurs. This is not a fault in Erlang, it is a
│ │ │ @@ -473,34 +473,34 @@
│ │ │    <span class="text">A Larger Example</span>
│ │ │  </h2>
│ │ │  <p>Now for a larger example to consolidate what you have learnt so far. Assume that
│ │ │  you have a list of temperature readings from a number of cities in the world.
│ │ │  Some of them are in Celsius and some in Fahrenheit (as in the previous list).
│ │ │  First let us convert them all to Celsius, then let us print the data neatly.</p><pre><code class="makeup erlang" translate="no"><span class="c1">%% This module is in file tut5.erl</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="9479623111-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="9479623111-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="9479623111-2">(</span><span class="p" data-group-id="9479623111-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="9479623111-3">]</span><span class="p" data-group-id="9479623111-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2624882691-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="2624882691-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2624882691-2">(</span><span class="p" data-group-id="2624882691-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2624882691-3">]</span><span class="p" data-group-id="2624882691-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Only this function is exported</span><span class="w">
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="9479623111-4">(</span><span class="p" data-group-id="9479623111-5">[</span><span class="p" data-group-id="9479623111-5">]</span><span class="p" data-group-id="9479623111-4">)</span><span class="p">-&gt;</span><span class="w">                        </span><span class="c1">% No output for an empty list</span><span class="w">
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="2624882691-4">(</span><span class="p" data-group-id="2624882691-5">[</span><span class="p" data-group-id="2624882691-5">]</span><span class="p" data-group-id="2624882691-4">)</span><span class="p">-&gt;</span><span class="w">                        </span><span class="c1">% No output for an empty list</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="9479623111-6">(</span><span class="p" data-group-id="9479623111-7">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="9479623111-7">]</span><span class="p" data-group-id="9479623111-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="9479623111-8">(</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="9479623111-9">(</span><span class="n">City</span><span class="p" data-group-id="9479623111-9">)</span><span class="p" data-group-id="9479623111-8">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">format_temps</span><span class="p" data-group-id="9479623111-10">(</span><span class="n">Rest</span><span class="p" data-group-id="9479623111-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="9479623111-11">(</span><span class="p" data-group-id="9479623111-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479623111-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9479623111-13">}</span><span class="p" data-group-id="9479623111-12">}</span><span class="p" data-group-id="9479623111-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% No conversion needed</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9479623111-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479623111-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9479623111-15">}</span><span class="p" data-group-id="9479623111-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="9479623111-16">(</span><span class="p" data-group-id="9479623111-17">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479623111-18">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9479623111-18">}</span><span class="p" data-group-id="9479623111-17">}</span><span class="p" data-group-id="9479623111-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Do the conversion</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9479623111-19">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479623111-20">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479623111-21">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="9479623111-21">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9479623111-20">}</span><span class="p" data-group-id="9479623111-19">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="9479623111-22">(</span><span class="p" data-group-id="9479623111-23">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479623111-24">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9479623111-24">}</span><span class="p" data-group-id="9479623111-23">}</span><span class="p" data-group-id="9479623111-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9479623111-25">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9479623111-26">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="9479623111-26">]</span><span class="p" data-group-id="9479623111-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">35&gt; </span><span class="nf">c</span><span class="p" data-group-id="3479142195-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="3479142195-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3479142195-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut5</span><span class="p" data-group-id="3479142195-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">36&gt; </span><span class="nc">tut5</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="3479142195-3">(</span><span class="p" data-group-id="3479142195-4">[</span><span class="p" data-group-id="3479142195-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3479142195-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="3479142195-6">}</span><span class="p" data-group-id="3479142195-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3479142195-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3479142195-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="3479142195-8">}</span><span class="p" data-group-id="3479142195-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3479142195-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3479142195-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="3479142195-10">}</span><span class="p" data-group-id="3479142195-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3479142195-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3479142195-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="3479142195-12">}</span><span class="p" data-group-id="3479142195-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3479142195-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3479142195-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="3479142195-14">}</span><span class="p" data-group-id="3479142195-13">}</span><span class="p" data-group-id="3479142195-4">]</span><span class="p" data-group-id="3479142195-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="2624882691-6">(</span><span class="p" data-group-id="2624882691-7">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2624882691-7">]</span><span class="p" data-group-id="2624882691-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="2624882691-8">(</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="2624882691-9">(</span><span class="n">City</span><span class="p" data-group-id="2624882691-9">)</span><span class="p" data-group-id="2624882691-8">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">format_temps</span><span class="p" data-group-id="2624882691-10">(</span><span class="n">Rest</span><span class="p" data-group-id="2624882691-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="2624882691-11">(</span><span class="p" data-group-id="2624882691-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2624882691-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2624882691-13">}</span><span class="p" data-group-id="2624882691-12">}</span><span class="p" data-group-id="2624882691-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% No conversion needed</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2624882691-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2624882691-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2624882691-15">}</span><span class="p" data-group-id="2624882691-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_to_celsius</span><span class="p" data-group-id="2624882691-16">(</span><span class="p" data-group-id="2624882691-17">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2624882691-18">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2624882691-18">}</span><span class="p" data-group-id="2624882691-17">}</span><span class="p" data-group-id="2624882691-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">  </span><span class="c1">% Do the conversion</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2624882691-19">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2624882691-20">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2624882691-21">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="2624882691-21">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="2624882691-20">}</span><span class="p" data-group-id="2624882691-19">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="2624882691-22">(</span><span class="p" data-group-id="2624882691-23">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2624882691-24">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2624882691-24">}</span><span class="p" data-group-id="2624882691-23">}</span><span class="p" data-group-id="2624882691-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2624882691-25">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2624882691-26">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2624882691-26">]</span><span class="p" data-group-id="2624882691-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">35&gt; </span><span class="nf">c</span><span class="p" data-group-id="7647503527-1">(</span><span class="ss">tut5</span><span class="p" data-group-id="7647503527-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7647503527-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut5</span><span class="p" data-group-id="7647503527-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">36&gt; </span><span class="nc">tut5</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="7647503527-3">(</span><span class="p" data-group-id="7647503527-4">[</span><span class="p" data-group-id="7647503527-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7647503527-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="7647503527-6">}</span><span class="p" data-group-id="7647503527-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7647503527-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7647503527-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="7647503527-8">}</span><span class="p" data-group-id="7647503527-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7647503527-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7647503527-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="7647503527-10">}</span><span class="p" data-group-id="7647503527-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7647503527-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7647503527-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="7647503527-12">}</span><span class="p" data-group-id="7647503527-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7647503527-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7647503527-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="7647503527-14">}</span><span class="p" data-group-id="7647503527-13">}</span><span class="p" data-group-id="7647503527-4">]</span><span class="p" data-group-id="7647503527-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>Before looking at how this program works, notice that a few comments are added
│ │ │  to the code. A comment starts with a %-character and goes on to the end of the
│ │ │ @@ -528,28 +528,28 @@
│ │ │    <a href="#matching-guards-and-scope-of-variables" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Matching, Guards, and Scope of Variables</span>
│ │ │  </h2>
│ │ │  <p>It can be useful to find the maximum and minimum temperature in lists like this.
│ │ │  Before extending the program to do this, let us look at functions for finding
│ │ │ -the maximum value of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3356182177-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="3356182177-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3356182177-2">(</span><span class="p" data-group-id="3356182177-3">[</span><span class="ss">list_max</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3356182177-3">]</span><span class="p" data-group-id="3356182177-2">)</span><span class="p">.</span><span class="w">
│ │ │ +the maximum value of the elements in a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6005946818-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="6005946818-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6005946818-2">(</span><span class="p" data-group-id="6005946818-3">[</span><span class="ss">list_max</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6005946818-3">]</span><span class="p" data-group-id="6005946818-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="3356182177-4">(</span><span class="p" data-group-id="3356182177-5">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="3356182177-5">]</span><span class="p" data-group-id="3356182177-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -   </span><span class="nf">list_max</span><span class="p" data-group-id="3356182177-6">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="3356182177-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="6005946818-4">(</span><span class="p" data-group-id="6005946818-5">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="6005946818-5">]</span><span class="p" data-group-id="6005946818-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +   </span><span class="nf">list_max</span><span class="p" data-group-id="6005946818-6">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="6005946818-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="3356182177-7">(</span><span class="p" data-group-id="3356182177-8">[</span><span class="p" data-group-id="3356182177-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="3356182177-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="6005946818-7">(</span><span class="p" data-group-id="6005946818-8">[</span><span class="p" data-group-id="6005946818-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="6005946818-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">Res</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="3356182177-9">(</span><span class="p" data-group-id="3356182177-10">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="3356182177-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="3356182177-9">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="3356182177-11">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="3356182177-11">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">list_max</span><span class="p" data-group-id="3356182177-12">(</span><span class="p" data-group-id="3356182177-13">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="3356182177-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="3356182177-12">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="3356182177-14">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="3356182177-14">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">37&gt; </span><span class="nf">c</span><span class="p" data-group-id="1402786876-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="1402786876-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1402786876-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut6</span><span class="p" data-group-id="1402786876-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">38&gt; </span><span class="nc">tut6</span><span class="p">:</span><span class="nf">list_max</span><span class="p" data-group-id="1402786876-3">(</span><span class="p" data-group-id="1402786876-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1402786876-4">]</span><span class="p" data-group-id="1402786876-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="6005946818-9">(</span><span class="p" data-group-id="6005946818-10">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="6005946818-10">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="6005946818-9">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="6005946818-11">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Head</span><span class="p" data-group-id="6005946818-11">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">list_max</span><span class="p" data-group-id="6005946818-12">(</span><span class="p" data-group-id="6005946818-13">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="6005946818-13">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="6005946818-12">)</span><span class="w">  </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="6005946818-14">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="6005946818-14">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">37&gt; </span><span class="nf">c</span><span class="p" data-group-id="5819689838-1">(</span><span class="ss">tut6</span><span class="p" data-group-id="5819689838-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5819689838-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut6</span><span class="p" data-group-id="5819689838-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">38&gt; </span><span class="nc">tut6</span><span class="p">:</span><span class="nf">list_max</span><span class="p" data-group-id="5819689838-3">(</span><span class="p" data-group-id="5819689838-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5819689838-4">]</span><span class="p" data-group-id="5819689838-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">7</span></code></pre><p>First notice that two functions have the same name, <code class="inline">list_max</code>. However, each of
│ │ │  these takes a different number of arguments (parameters). In Erlang these are
│ │ │  regarded as completely different functions. Where you need to distinguish
│ │ │  between these functions, you write Name/Arity, where Name is the function name
│ │ │  and Arity is the number of arguments, in this case <code class="inline">list_max/1</code> and
│ │ │  <code class="inline">list_max/2</code>.</p><p>In this example you walk through a list &quot;carrying&quot; a value, in this case
│ │ │  <code class="inline">Result_so_far</code>. <code class="inline">list_max/1</code> simply assumes that the max value of the list is
│ │ │ @@ -578,180 +578,180 @@
│ │ │  </span><span class="mi">5</span><span class="w">
│ │ │  </span><span class="gp unselectable">40&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">6</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value 6</span><span class="w">
│ │ │  </span><span class="gp unselectable">41&gt; </span><span class="n">M</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value 6</span><span class="w">
│ │ │  </span><span class="gp unselectable">42&gt; </span><span class="n">N</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">6</span></code></pre><p>The use of the match operator is particularly useful for pulling apart Erlang
│ │ │ -terms and creating new ones.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">43&gt; </span><span class="p" data-group-id="3279006152-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="3279006152-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3279006152-2">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3279006152-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="3279006152-3">}</span><span class="p" data-group-id="3279006152-2">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3279006152-4">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="3279006152-5">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="3279006152-5">}</span><span class="p" data-group-id="3279006152-4">}</span><span class="w">
│ │ │ +terms and creating new ones.</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">43&gt; </span><span class="p" data-group-id="0721165550-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="0721165550-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0721165550-2">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0721165550-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="0721165550-3">}</span><span class="p" data-group-id="0721165550-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0721165550-4">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="0721165550-5">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="0721165550-5">}</span><span class="p" data-group-id="0721165550-4">}</span><span class="w">
│ │ │  </span><span class="gp unselectable">44&gt; </span><span class="n">X</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">
│ │ │  </span><span class="gp unselectable">45&gt; </span><span class="n">Y</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3279006152-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="3279006152-6">}</span></code></pre><p>Here <code class="inline">X</code> gets the value <code class="inline">paris</code> and <code class="inline">Y</code> the value <code class="inline">{f,28}</code>.</p><p>If you try to do the same again with another city, an error is returned:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">46&gt; </span><span class="p" data-group-id="9739849879-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="9739849879-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9739849879-2">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9739849879-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="9739849879-3">}</span><span class="p" data-group-id="9739849879-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0721165550-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">28</span><span class="p" data-group-id="0721165550-6">}</span></code></pre><p>Here <code class="inline">X</code> gets the value <code class="inline">paris</code> and <code class="inline">Y</code> the value <code class="inline">{f,28}</code>.</p><p>If you try to do the same again with another city, an error is returned:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">46&gt; </span><span class="p" data-group-id="7284442434-1">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="7284442434-1">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7284442434-2">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7284442434-3">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="7284442434-3">}</span><span class="p" data-group-id="7284442434-2">}</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no match of right hand side value {london,{f,36}}</span></code></pre><p>Variables can also be used to improve the readability of programs. For example,
│ │ │ -in function <code class="inline">list_max/2</code> above, you can write:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_max</span><span class="p" data-group-id="3288217728-1">(</span><span class="p" data-group-id="3288217728-2">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="3288217728-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="3288217728-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +in function <code class="inline">list_max/2</code> above, you can write:</p><pre><code class="makeup erlang" translate="no"><span class="nf">list_max</span><span class="p" data-group-id="5762166580-1">(</span><span class="p" data-group-id="5762166580-2">[</span><span class="n">Head</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="5762166580-2">]</span><span class="p">,</span><span class="w"> </span><span class="n">Result_so_far</span><span class="p" data-group-id="5762166580-1">)</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Head</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Result_so_far</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">New_result_far</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Head</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">list_max</span><span class="p" data-group-id="3288217728-3">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">New_result_far</span><span class="p" data-group-id="3288217728-3">)</span><span class="p">;</span></code></pre><p>This is possibly a little clearer.</p><h2 id="more-about-lists" class="section-heading">
│ │ │ +    </span><span class="nf">list_max</span><span class="p" data-group-id="5762166580-3">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">New_result_far</span><span class="p" data-group-id="5762166580-3">)</span><span class="p">;</span></code></pre><p>This is possibly a little clearer.</p><h2 id="more-about-lists" class="section-heading">
│ │ │    <a href="#more-about-lists" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">More About Lists</span>
│ │ │  </h2>
│ │ │ -<p>Remember that the <code class="inline">|</code> operator can be used to get the head of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">47&gt; </span><span class="p" data-group-id="3029811591-1">[</span><span class="n">M1</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="3029811591-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3029811591-2">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="ss">rome</span><span class="p" data-group-id="3029811591-2">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3029811591-3">[</span><span class="ss">paris</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="3029811591-3">]</span><span class="w">
│ │ │ +<p>Remember that the <code class="inline">|</code> operator can be used to get the head of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">47&gt; </span><span class="p" data-group-id="8004651825-1">[</span><span class="n">M1</span><span class="p">|</span><span class="n">T1</span><span class="p" data-group-id="8004651825-1">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8004651825-2">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="ss">rome</span><span class="p" data-group-id="8004651825-2">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8004651825-3">[</span><span class="ss">paris</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="8004651825-3">]</span><span class="w">
│ │ │  </span><span class="gp unselectable">48&gt; </span><span class="n">M1</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">
│ │ │  </span><span class="gp unselectable">49&gt; </span><span class="n">T1</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3029811591-4">[</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="3029811591-4">]</span></code></pre><p>The <code class="inline">|</code> operator can also be used to add a head to a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">50&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8620614117-1">[</span><span class="ss">madrid</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="8620614117-1">]</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8620614117-2">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="8620614117-2">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8004651825-4">[</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="8004651825-4">]</span></code></pre><p>The <code class="inline">|</code> operator can also be used to add a head to a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">50&gt; </span><span class="n">L1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8175203695-1">[</span><span class="ss">madrid</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">T1</span><span class="p" data-group-id="8175203695-1">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8175203695-2">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="8175203695-2">]</span><span class="w">
│ │ │  </span><span class="gp unselectable">51&gt; </span><span class="n">L1</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8620614117-3">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="8620614117-3">]</span></code></pre><p>Now an example of this when working with lists - reversing the order of a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0487094625-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="0487094625-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8175203695-3">[</span><span class="ss">madrid</span><span class="p">,</span><span class="ss">london</span><span class="p">,</span><span class="ss">rome</span><span class="p" data-group-id="8175203695-3">]</span></code></pre><p>Now an example of this when working with lists - reversing the order of a list:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2467907613-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="2467907613-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0487094625-2">(</span><span class="p" data-group-id="0487094625-3">[</span><span class="ss">reverse</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0487094625-3">]</span><span class="p" data-group-id="0487094625-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2467907613-2">(</span><span class="p" data-group-id="2467907613-3">[</span><span class="ss">reverse</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2467907613-3">]</span><span class="p" data-group-id="2467907613-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="0487094625-4">(</span><span class="n">List</span><span class="p" data-group-id="0487094625-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="0487094625-5">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0487094625-6">[</span><span class="p" data-group-id="0487094625-6">]</span><span class="p" data-group-id="0487094625-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="2467907613-4">(</span><span class="n">List</span><span class="p" data-group-id="2467907613-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="2467907613-5">(</span><span class="n">List</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2467907613-6">[</span><span class="p" data-group-id="2467907613-6">]</span><span class="p" data-group-id="2467907613-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="0487094625-7">(</span><span class="p" data-group-id="0487094625-8">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0487094625-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="0487094625-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="0487094625-9">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0487094625-10">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="0487094625-10">]</span><span class="p" data-group-id="0487094625-9">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="0487094625-11">(</span><span class="p" data-group-id="0487094625-12">[</span><span class="p" data-group-id="0487094625-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="0487094625-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Reversed_List</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">52&gt; </span><span class="nf">c</span><span class="p" data-group-id="6137352418-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="6137352418-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6137352418-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut8</span><span class="p" data-group-id="6137352418-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">53&gt; </span><span class="nc">tut8</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="6137352418-3">(</span><span class="p" data-group-id="6137352418-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6137352418-4">]</span><span class="p" data-group-id="6137352418-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6137352418-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6137352418-5">]</span></code></pre><p>Consider how <code class="inline">Reversed_List</code> is built. It starts as [], then successively the
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="2467907613-7">(</span><span class="p" data-group-id="2467907613-8">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="2467907613-8">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="2467907613-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="2467907613-9">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2467907613-10">[</span><span class="n">Head</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="2467907613-10">]</span><span class="p" data-group-id="2467907613-9">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="2467907613-11">(</span><span class="p" data-group-id="2467907613-12">[</span><span class="p" data-group-id="2467907613-12">]</span><span class="p">,</span><span class="w"> </span><span class="n">Reversed_List</span><span class="p" data-group-id="2467907613-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Reversed_List</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">52&gt; </span><span class="nf">c</span><span class="p" data-group-id="6708591649-1">(</span><span class="ss">tut8</span><span class="p" data-group-id="6708591649-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6708591649-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut8</span><span class="p" data-group-id="6708591649-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">53&gt; </span><span class="nc">tut8</span><span class="p">:</span><span class="nf">reverse</span><span class="p" data-group-id="6708591649-3">(</span><span class="p" data-group-id="6708591649-4">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="6708591649-4">]</span><span class="p" data-group-id="6708591649-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6708591649-5">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6708591649-5">]</span></code></pre><p>Consider how <code class="inline">Reversed_List</code> is built. It starts as [], then successively the
│ │ │  heads are taken off of the list to be reversed and added to the the
│ │ │ -<code class="inline">Reversed_List</code>, as shown in the following:</p><pre><code class="makeup erlang" translate="no"><span class="nf">reverse</span><span class="p" data-group-id="0769032511-1">(</span><span class="p" data-group-id="0769032511-2">[</span><span class="mi">1</span><span class="p">|</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0769032511-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0769032511-3">[</span><span class="p" data-group-id="0769032511-3">]</span><span class="p" data-group-id="0769032511-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="0769032511-4">(</span><span class="p" data-group-id="0769032511-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0769032511-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0769032511-6">[</span><span class="mi">1</span><span class="p">|</span><span class="p" data-group-id="0769032511-7">[</span><span class="p" data-group-id="0769032511-7">]</span><span class="p" data-group-id="0769032511-6">]</span><span class="p" data-group-id="0769032511-4">)</span><span class="w">
│ │ │ +<code class="inline">Reversed_List</code>, as shown in the following:</p><pre><code class="makeup erlang" translate="no"><span class="nf">reverse</span><span class="p" data-group-id="1963877740-1">(</span><span class="p" data-group-id="1963877740-2">[</span><span class="mi">1</span><span class="p">|</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1963877740-2">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1963877740-3">[</span><span class="p" data-group-id="1963877740-3">]</span><span class="p" data-group-id="1963877740-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="1963877740-4">(</span><span class="p" data-group-id="1963877740-5">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1963877740-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1963877740-6">[</span><span class="mi">1</span><span class="p">|</span><span class="p" data-group-id="1963877740-7">[</span><span class="p" data-group-id="1963877740-7">]</span><span class="p" data-group-id="1963877740-6">]</span><span class="p" data-group-id="1963877740-4">)</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="0769032511-8">(</span><span class="p" data-group-id="0769032511-9">[</span><span class="mi">2</span><span class="p">|</span><span class="mi">3</span><span class="p" data-group-id="0769032511-9">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0769032511-10">[</span><span class="mi">1</span><span class="p" data-group-id="0769032511-10">]</span><span class="p" data-group-id="0769032511-8">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="0769032511-11">(</span><span class="p" data-group-id="0769032511-12">[</span><span class="mi">3</span><span class="p" data-group-id="0769032511-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0769032511-13">[</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="0769032511-14">[</span><span class="mi">1</span><span class="p" data-group-id="0769032511-14">]</span><span class="p">)</span><span class="w">
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="1963877740-8">(</span><span class="p" data-group-id="1963877740-9">[</span><span class="mi">2</span><span class="p">|</span><span class="mi">3</span><span class="p" data-group-id="1963877740-9">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1963877740-10">[</span><span class="mi">1</span><span class="p" data-group-id="1963877740-10">]</span><span class="p" data-group-id="1963877740-8">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="1963877740-11">(</span><span class="p" data-group-id="1963877740-12">[</span><span class="mi">3</span><span class="p" data-group-id="1963877740-12">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1963877740-13">[</span><span class="mi">2</span><span class="p">|</span><span class="p" data-group-id="1963877740-14">[</span><span class="mi">1</span><span class="p" data-group-id="1963877740-14">]</span><span class="p">)</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="0769032511-15">(</span><span class="p" data-group-id="0769032511-16">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="0769032511-17">[</span><span class="p" data-group-id="0769032511-17">]</span><span class="p" data-group-id="0769032511-16">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0769032511-18">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0769032511-18">]</span><span class="p" data-group-id="0769032511-15">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">reverse</span><span class="p" data-group-id="0769032511-19">(</span><span class="p" data-group-id="0769032511-20">[</span><span class="p" data-group-id="0769032511-20">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0769032511-21">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="0769032511-22">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0769032511-22">]</span><span class="p" data-group-id="0769032511-21">]</span><span class="p" data-group-id="0769032511-19">)</span><span class="w">
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="1963877740-15">(</span><span class="p" data-group-id="1963877740-16">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="1963877740-17">[</span><span class="p" data-group-id="1963877740-17">]</span><span class="p" data-group-id="1963877740-16">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1963877740-18">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1963877740-18">]</span><span class="p" data-group-id="1963877740-15">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">reverse</span><span class="p" data-group-id="1963877740-19">(</span><span class="p" data-group-id="1963877740-20">[</span><span class="p" data-group-id="1963877740-20">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1963877740-21">[</span><span class="mi">3</span><span class="p">|</span><span class="p" data-group-id="1963877740-22">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1963877740-22">]</span><span class="p" data-group-id="1963877740-21">]</span><span class="p" data-group-id="1963877740-19">)</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">reverse</span><span class="p" data-group-id="0769032511-23">(</span><span class="p" data-group-id="0769032511-24">[</span><span class="p" data-group-id="0769032511-24">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0769032511-25">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0769032511-25">]</span><span class="p" data-group-id="0769032511-23">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0769032511-26">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0769032511-26">]</span></code></pre><p>The module <code class="inline">lists</code> contains many functions for manipulating lists, for example,
│ │ │ +</span><span class="nf">reverse</span><span class="p" data-group-id="1963877740-23">(</span><span class="p" data-group-id="1963877740-24">[</span><span class="p" data-group-id="1963877740-24">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1963877740-25">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1963877740-25">]</span><span class="p" data-group-id="1963877740-23">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1963877740-26">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1963877740-26">]</span></code></pre><p>The module <code class="inline">lists</code> contains many functions for manipulating lists, for example,
│ │ │  for reversing them. So before writing a list-manipulating function it is a good
│ │ │  idea to check if one not already is written for you (see the <a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html"><code class="inline">lists</code></a> manual
│ │ │  page in STDLIB).</p><p>Now let us get back to the cities and temperatures, but take a more structured
│ │ │ -approach this time. First let us convert the whole list to Celsius as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7513920811-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="7513920811-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7513920811-2">(</span><span class="p" data-group-id="7513920811-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7513920811-3">]</span><span class="p" data-group-id="7513920811-2">)</span><span class="p">.</span><span class="w">
│ │ │ +approach this time. First let us convert the whole list to Celsius as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4724168381-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="4724168381-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4724168381-2">(</span><span class="p" data-group-id="4724168381-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4724168381-3">]</span><span class="p" data-group-id="4724168381-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="7513920811-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="7513920811-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7513920811-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="7513920811-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="4724168381-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="4724168381-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4724168381-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="4724168381-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7513920811-6">(</span><span class="p" data-group-id="7513920811-7">[</span><span class="p" data-group-id="7513920811-8">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7513920811-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="7513920811-9">}</span><span class="p" data-group-id="7513920811-8">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7513920811-7">]</span><span class="p" data-group-id="7513920811-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7513920811-10">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7513920811-11">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7513920811-12">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="7513920811-12">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="7513920811-11">}</span><span class="p" data-group-id="7513920811-10">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7513920811-13">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7513920811-14">(</span><span class="n">Rest</span><span class="p" data-group-id="7513920811-14">)</span><span class="p" data-group-id="7513920811-13">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7513920811-15">(</span><span class="p" data-group-id="7513920811-16">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7513920811-16">]</span><span class="p" data-group-id="7513920811-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7513920811-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7513920811-18">(</span><span class="n">Rest</span><span class="p" data-group-id="7513920811-18">)</span><span class="p" data-group-id="7513920811-17">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7513920811-19">(</span><span class="p" data-group-id="7513920811-20">[</span><span class="p" data-group-id="7513920811-20">]</span><span class="p" data-group-id="7513920811-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7513920811-21">[</span><span class="p" data-group-id="7513920811-21">]</span><span class="p">.</span></code></pre><p>Test the function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">54&gt; </span><span class="nf">c</span><span class="p" data-group-id="4728150126-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="4728150126-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4728150126-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="4728150126-2">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="gp unselectable">55&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="4728150126-3">(</span><span class="p" data-group-id="4728150126-4">[</span><span class="p" data-group-id="4728150126-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4728150126-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4728150126-6">}</span><span class="p" data-group-id="4728150126-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4728150126-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4728150126-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4728150126-8">}</span><span class="p" data-group-id="4728150126-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4728150126-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4728150126-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4728150126-10">}</span><span class="p" data-group-id="4728150126-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4728150126-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4728150126-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4728150126-12">}</span><span class="p" data-group-id="4728150126-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4728150126-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4728150126-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4728150126-14">}</span><span class="p" data-group-id="4728150126-13">}</span><span class="p" data-group-id="4728150126-4">]</span><span class="p" data-group-id="4728150126-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4728150126-15">[</span><span class="p" data-group-id="4728150126-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="4728150126-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4728150126-17">}</span><span class="p" data-group-id="4728150126-16">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4728150126-18">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="4728150126-19">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">21.11111111111111</span><span class="p" data-group-id="4728150126-19">}</span><span class="p" data-group-id="4728150126-18">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4728150126-20">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="4728150126-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4728150126-21">}</span><span class="p" data-group-id="4728150126-20">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4728150126-22">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="4728150126-23">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="4728150126-23">}</span><span class="p" data-group-id="4728150126-22">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="4728150126-24">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="4728150126-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="4728150126-25">}</span><span class="p" data-group-id="4728150126-24">}</span><span class="p" data-group-id="4728150126-15">]</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">format_temps</span><span class="p" data-group-id="9699171466-1">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="9699171466-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9699171466-2">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="9699171466-2">)</span><span class="p">.</span></code></pre><p>Here <code class="inline">format_temps/1</code> calls <code class="inline">convert_list_to_c/1</code>. <code class="inline">convert_list_to_c/1</code> takes
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4724168381-6">(</span><span class="p" data-group-id="4724168381-7">[</span><span class="p" data-group-id="4724168381-8">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4724168381-9">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="4724168381-9">}</span><span class="p" data-group-id="4724168381-8">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4724168381-7">]</span><span class="p" data-group-id="4724168381-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4724168381-10">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4724168381-11">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4724168381-12">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="4724168381-12">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="4724168381-11">}</span><span class="p" data-group-id="4724168381-10">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4724168381-13">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4724168381-14">(</span><span class="n">Rest</span><span class="p" data-group-id="4724168381-14">)</span><span class="p" data-group-id="4724168381-13">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4724168381-15">(</span><span class="p" data-group-id="4724168381-16">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4724168381-16">]</span><span class="p" data-group-id="4724168381-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4724168381-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4724168381-18">(</span><span class="n">Rest</span><span class="p" data-group-id="4724168381-18">)</span><span class="p" data-group-id="4724168381-17">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4724168381-19">(</span><span class="p" data-group-id="4724168381-20">[</span><span class="p" data-group-id="4724168381-20">]</span><span class="p" data-group-id="4724168381-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4724168381-21">[</span><span class="p" data-group-id="4724168381-21">]</span><span class="p">.</span></code></pre><p>Test the function:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">54&gt; </span><span class="nf">c</span><span class="p" data-group-id="7393894788-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="7393894788-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7393894788-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="7393894788-2">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">55&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="7393894788-3">(</span><span class="p" data-group-id="7393894788-4">[</span><span class="p" data-group-id="7393894788-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7393894788-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="7393894788-6">}</span><span class="p" data-group-id="7393894788-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7393894788-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7393894788-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="7393894788-8">}</span><span class="p" data-group-id="7393894788-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7393894788-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7393894788-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="7393894788-10">}</span><span class="p" data-group-id="7393894788-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7393894788-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7393894788-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="7393894788-12">}</span><span class="p" data-group-id="7393894788-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7393894788-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7393894788-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="7393894788-14">}</span><span class="p" data-group-id="7393894788-13">}</span><span class="p" data-group-id="7393894788-4">]</span><span class="p" data-group-id="7393894788-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7393894788-15">[</span><span class="p" data-group-id="7393894788-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="7393894788-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="7393894788-17">}</span><span class="p" data-group-id="7393894788-16">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7393894788-18">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="7393894788-19">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">21.11111111111111</span><span class="p" data-group-id="7393894788-19">}</span><span class="p" data-group-id="7393894788-18">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7393894788-20">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="7393894788-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="7393894788-21">}</span><span class="p" data-group-id="7393894788-20">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7393894788-22">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="7393894788-23">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="7393894788-23">}</span><span class="p" data-group-id="7393894788-22">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="7393894788-24">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="7393894788-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mf">2.2222222222222223</span><span class="p" data-group-id="7393894788-25">}</span><span class="p" data-group-id="7393894788-24">}</span><span class="p" data-group-id="7393894788-15">]</span></code></pre><p>Explanation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">format_temps</span><span class="p" data-group-id="5369594240-1">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="5369594240-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="5369594240-2">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="5369594240-2">)</span><span class="p">.</span></code></pre><p>Here <code class="inline">format_temps/1</code> calls <code class="inline">convert_list_to_c/1</code>. <code class="inline">convert_list_to_c/1</code> takes
│ │ │  off the head of the <code class="inline">List_of_cities</code>, converts it to Celsius if needed. The <code class="inline">|</code>
│ │ │ -operator is used to add the (maybe) converted to the converted rest of the list:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7627928596-1">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7627928596-2">(</span><span class="n">Rest</span><span class="p" data-group-id="7627928596-2">)</span><span class="p" data-group-id="7627928596-1">]</span><span class="p">;</span></code></pre><p>or:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7783508016-1">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7783508016-2">(</span><span class="n">Rest</span><span class="p" data-group-id="7783508016-2">)</span><span class="p" data-group-id="7783508016-1">]</span><span class="p">;</span></code></pre><p>This is done until the end of the list is reached, that is, the list is empty:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3772319854-1">(</span><span class="p" data-group-id="3772319854-2">[</span><span class="p" data-group-id="3772319854-2">]</span><span class="p" data-group-id="3772319854-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3772319854-3">[</span><span class="p" data-group-id="3772319854-3">]</span><span class="p">.</span></code></pre><p>Now when the list is converted, a function to print it is added:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1155391145-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="1155391145-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1155391145-2">(</span><span class="p" data-group-id="1155391145-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1155391145-3">]</span><span class="p" data-group-id="1155391145-2">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="1155391145-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="1155391145-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1155391145-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="1155391145-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="1155391145-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="1155391145-6">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1155391145-7">(</span><span class="p" data-group-id="1155391145-8">[</span><span class="p" data-group-id="1155391145-9">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1155391145-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="1155391145-10">}</span><span class="p" data-group-id="1155391145-9">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1155391145-8">]</span><span class="p" data-group-id="1155391145-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1155391145-11">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1155391145-12">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1155391145-13">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="1155391145-13">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1155391145-12">}</span><span class="p" data-group-id="1155391145-11">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1155391145-14">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1155391145-15">(</span><span class="n">Rest</span><span class="p" data-group-id="1155391145-15">)</span><span class="p" data-group-id="1155391145-14">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1155391145-16">(</span><span class="p" data-group-id="1155391145-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1155391145-17">]</span><span class="p" data-group-id="1155391145-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1155391145-18">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1155391145-19">(</span><span class="n">Rest</span><span class="p" data-group-id="1155391145-19">)</span><span class="p" data-group-id="1155391145-18">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1155391145-20">(</span><span class="p" data-group-id="1155391145-21">[</span><span class="p" data-group-id="1155391145-21">]</span><span class="p" data-group-id="1155391145-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1155391145-22">[</span><span class="p" data-group-id="1155391145-22">]</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="1155391145-23">(</span><span class="p" data-group-id="1155391145-24">[</span><span class="p" data-group-id="1155391145-25">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1155391145-26">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1155391145-26">}</span><span class="p" data-group-id="1155391145-25">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="1155391145-24">]</span><span class="p" data-group-id="1155391145-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1155391145-27">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1155391145-28">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1155391145-28">]</span><span class="p" data-group-id="1155391145-27">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="1155391145-29">(</span><span class="n">Rest</span><span class="p" data-group-id="1155391145-29">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="1155391145-30">(</span><span class="p" data-group-id="1155391145-31">[</span><span class="p" data-group-id="1155391145-31">]</span><span class="p" data-group-id="1155391145-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ok</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">56&gt; </span><span class="nf">c</span><span class="p" data-group-id="9913849696-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="9913849696-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9913849696-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut7</span><span class="p" data-group-id="9913849696-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">57&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="9913849696-3">(</span><span class="p" data-group-id="9913849696-4">[</span><span class="p" data-group-id="9913849696-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9913849696-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="9913849696-6">}</span><span class="p" data-group-id="9913849696-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9913849696-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9913849696-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="9913849696-8">}</span><span class="p" data-group-id="9913849696-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9913849696-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9913849696-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="9913849696-10">}</span><span class="p" data-group-id="9913849696-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9913849696-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9913849696-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="9913849696-12">}</span><span class="p" data-group-id="9913849696-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9913849696-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9913849696-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="9913849696-14">}</span><span class="p" data-group-id="9913849696-13">}</span><span class="p" data-group-id="9913849696-4">]</span><span class="p" data-group-id="9913849696-3">)</span><span class="p">.</span><span class="w">
│ │ │ +operator is used to add the (maybe) converted to the converted rest of the list:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9625625026-1">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="9625625026-2">(</span><span class="n">Rest</span><span class="p" data-group-id="9625625026-2">)</span><span class="p" data-group-id="9625625026-1">]</span><span class="p">;</span></code></pre><p>or:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7096237862-1">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7096237862-2">(</span><span class="n">Rest</span><span class="p" data-group-id="7096237862-2">)</span><span class="p" data-group-id="7096237862-1">]</span><span class="p">;</span></code></pre><p>This is done until the end of the list is reached, that is, the list is empty:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4121884895-1">(</span><span class="p" data-group-id="4121884895-2">[</span><span class="p" data-group-id="4121884895-2">]</span><span class="p" data-group-id="4121884895-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4121884895-3">[</span><span class="p" data-group-id="4121884895-3">]</span><span class="p">.</span></code></pre><p>Now when the list is converted, a function to print it is added:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7360744689-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="7360744689-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7360744689-2">(</span><span class="p" data-group-id="7360744689-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7360744689-3">]</span><span class="p" data-group-id="7360744689-2">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="7360744689-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="7360744689-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7360744689-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="7360744689-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="7360744689-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="7360744689-6">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7360744689-7">(</span><span class="p" data-group-id="7360744689-8">[</span><span class="p" data-group-id="7360744689-9">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7360744689-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="p" data-group-id="7360744689-10">}</span><span class="p" data-group-id="7360744689-9">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7360744689-8">]</span><span class="p" data-group-id="7360744689-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7360744689-11">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7360744689-12">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7360744689-13">(</span><span class="n">F</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="7360744689-13">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="7360744689-12">}</span><span class="p" data-group-id="7360744689-11">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7360744689-14">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7360744689-15">(</span><span class="n">Rest</span><span class="p" data-group-id="7360744689-15">)</span><span class="p" data-group-id="7360744689-14">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7360744689-16">(</span><span class="p" data-group-id="7360744689-17">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7360744689-17">]</span><span class="p" data-group-id="7360744689-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7360744689-18">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7360744689-19">(</span><span class="n">Rest</span><span class="p" data-group-id="7360744689-19">)</span><span class="p" data-group-id="7360744689-18">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7360744689-20">(</span><span class="p" data-group-id="7360744689-21">[</span><span class="p" data-group-id="7360744689-21">]</span><span class="p" data-group-id="7360744689-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7360744689-22">[</span><span class="p" data-group-id="7360744689-22">]</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="7360744689-23">(</span><span class="p" data-group-id="7360744689-24">[</span><span class="p" data-group-id="7360744689-25">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7360744689-26">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7360744689-26">}</span><span class="p" data-group-id="7360744689-25">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7360744689-24">]</span><span class="p" data-group-id="7360744689-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7360744689-27">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7360744689-28">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7360744689-28">]</span><span class="p" data-group-id="7360744689-27">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="7360744689-29">(</span><span class="n">Rest</span><span class="p" data-group-id="7360744689-29">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="7360744689-30">(</span><span class="p" data-group-id="7360744689-31">[</span><span class="p" data-group-id="7360744689-31">]</span><span class="p" data-group-id="7360744689-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ok</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">56&gt; </span><span class="nf">c</span><span class="p" data-group-id="6123815381-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="6123815381-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6123815381-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut7</span><span class="p" data-group-id="6123815381-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">57&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="6123815381-3">(</span><span class="p" data-group-id="6123815381-4">[</span><span class="p" data-group-id="6123815381-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6123815381-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6123815381-6">}</span><span class="p" data-group-id="6123815381-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6123815381-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6123815381-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6123815381-8">}</span><span class="p" data-group-id="6123815381-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6123815381-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6123815381-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6123815381-10">}</span><span class="p" data-group-id="6123815381-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6123815381-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6123815381-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6123815381-12">}</span><span class="p" data-group-id="6123815381-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6123815381-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6123815381-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6123815381-14">}</span><span class="p" data-group-id="6123815381-13">}</span><span class="p" data-group-id="6123815381-4">]</span><span class="p" data-group-id="6123815381-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>Now a function has to be added to find the cities with the maximum and minimum
│ │ │  temperatures. The following program is not the most efficient way of doing this
│ │ │  as you walk through the list of cities four times. But it is better to first
│ │ │  strive for clarity and correctness and to make programs efficient only if
│ │ │ -needed.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4284836460-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="4284836460-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4284836460-2">(</span><span class="p" data-group-id="4284836460-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4284836460-3">]</span><span class="p" data-group-id="4284836460-2">)</span><span class="p">.</span><span class="w">
│ │ │ +needed.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7200614143-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="7200614143-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7200614143-2">(</span><span class="p" data-group-id="7200614143-3">[</span><span class="ss">format_temps</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7200614143-3">]</span><span class="p" data-group-id="7200614143-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">format_temps</span><span class="p" data-group-id="4284836460-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="4284836460-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4284836460-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="4284836460-5">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="4284836460-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="4284836460-6">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4284836460-7">{</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="4284836460-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="4284836460-8">(</span><span class="n">Converted_List</span><span class="p" data-group-id="4284836460-8">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_max_and_min</span><span class="p" data-group-id="4284836460-9">(</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="4284836460-9">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4284836460-10">(</span><span class="p" data-group-id="4284836460-11">[</span><span class="p" data-group-id="4284836460-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-13">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4284836460-13">}</span><span class="p" data-group-id="4284836460-12">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4284836460-11">]</span><span class="p" data-group-id="4284836460-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4284836460-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-16">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="4284836460-16">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="4284836460-15">}</span><span class="p" data-group-id="4284836460-14">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4284836460-17">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4284836460-18">(</span><span class="n">Rest</span><span class="p" data-group-id="4284836460-18">)</span><span class="p" data-group-id="4284836460-17">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4284836460-19">(</span><span class="p" data-group-id="4284836460-20">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4284836460-20">]</span><span class="p" data-group-id="4284836460-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4284836460-21">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4284836460-22">(</span><span class="n">Rest</span><span class="p" data-group-id="4284836460-22">)</span><span class="p" data-group-id="4284836460-21">]</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4284836460-23">(</span><span class="p" data-group-id="4284836460-24">[</span><span class="p" data-group-id="4284836460-24">]</span><span class="p" data-group-id="4284836460-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4284836460-25">[</span><span class="p" data-group-id="4284836460-25">]</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="4284836460-26">(</span><span class="p" data-group-id="4284836460-27">[</span><span class="p" data-group-id="4284836460-28">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-29">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4284836460-29">}</span><span class="p" data-group-id="4284836460-28">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4284836460-27">]</span><span class="p" data-group-id="4284836460-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4284836460-30">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-31">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4284836460-31">]</span><span class="p" data-group-id="4284836460-30">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">print_temp</span><span class="p" data-group-id="4284836460-32">(</span><span class="n">Rest</span><span class="p" data-group-id="4284836460-32">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">print_temp</span><span class="p" data-group-id="4284836460-33">(</span><span class="p" data-group-id="4284836460-34">[</span><span class="p" data-group-id="4284836460-34">]</span><span class="p" data-group-id="4284836460-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">format_temps</span><span class="p" data-group-id="7200614143-4">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="7200614143-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_List</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7200614143-5">(</span><span class="n">List_of_cities</span><span class="p" data-group-id="7200614143-5">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="7200614143-6">(</span><span class="n">Converted_List</span><span class="p" data-group-id="7200614143-6">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7200614143-7">{</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="7200614143-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="7200614143-8">(</span><span class="n">Converted_List</span><span class="p" data-group-id="7200614143-8">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_max_and_min</span><span class="p" data-group-id="7200614143-9">(</span><span class="n">Max_city</span><span class="p">,</span><span class="w"> </span><span class="n">Min_city</span><span class="p" data-group-id="7200614143-9">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7200614143-10">(</span><span class="p" data-group-id="7200614143-11">[</span><span class="p" data-group-id="7200614143-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-13">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7200614143-13">}</span><span class="p" data-group-id="7200614143-12">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7200614143-11">]</span><span class="p" data-group-id="7200614143-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Converted_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7200614143-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-16">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="mi">32</span><span class="p" data-group-id="7200614143-16">)</span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="7200614143-15">}</span><span class="p" data-group-id="7200614143-14">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7200614143-17">[</span><span class="n">Converted_City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7200614143-18">(</span><span class="n">Rest</span><span class="p" data-group-id="7200614143-18">)</span><span class="p" data-group-id="7200614143-17">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7200614143-19">(</span><span class="p" data-group-id="7200614143-20">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7200614143-20">]</span><span class="p" data-group-id="7200614143-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7200614143-21">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7200614143-22">(</span><span class="n">Rest</span><span class="p" data-group-id="7200614143-22">)</span><span class="p" data-group-id="7200614143-21">]</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="7200614143-23">(</span><span class="p" data-group-id="7200614143-24">[</span><span class="p" data-group-id="7200614143-24">]</span><span class="p" data-group-id="7200614143-23">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7200614143-25">[</span><span class="p" data-group-id="7200614143-25">]</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="7200614143-26">(</span><span class="p" data-group-id="7200614143-27">[</span><span class="p" data-group-id="7200614143-28">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-29">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7200614143-29">}</span><span class="p" data-group-id="7200614143-28">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7200614143-27">]</span><span class="p" data-group-id="7200614143-26">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7200614143-30">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> c</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-31">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7200614143-31">]</span><span class="p" data-group-id="7200614143-30">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">print_temp</span><span class="p" data-group-id="7200614143-32">(</span><span class="n">Rest</span><span class="p" data-group-id="7200614143-32">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">print_temp</span><span class="p" data-group-id="7200614143-33">(</span><span class="p" data-group-id="7200614143-34">[</span><span class="p" data-group-id="7200614143-34">]</span><span class="p" data-group-id="7200614143-33">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="4284836460-35">(</span><span class="p" data-group-id="4284836460-36">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4284836460-36">]</span><span class="p" data-group-id="4284836460-35">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="4284836460-37">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p" data-group-id="4284836460-37">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="7200614143-35">(</span><span class="p" data-group-id="7200614143-36">[</span><span class="n">City</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7200614143-36">]</span><span class="p" data-group-id="7200614143-35">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="7200614143-37">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">City</span><span class="p" data-group-id="7200614143-37">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="4284836460-38">(</span><span class="p" data-group-id="4284836460-39">[</span><span class="p" data-group-id="4284836460-40">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-41">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4284836460-41">}</span><span class="p" data-group-id="4284836460-40">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="4284836460-39">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="4284836460-42">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-43">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="4284836460-43">}</span><span class="p" data-group-id="4284836460-42">}</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="4284836460-44">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-45">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="4284836460-45">}</span><span class="p" data-group-id="4284836460-44">}</span><span class="p" data-group-id="4284836460-38">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="7200614143-38">(</span><span class="p" data-group-id="7200614143-39">[</span><span class="p" data-group-id="7200614143-40">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-41">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7200614143-41">}</span><span class="p" data-group-id="7200614143-40">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="7200614143-39">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="7200614143-42">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-43">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="7200614143-43">}</span><span class="p" data-group-id="7200614143-42">}</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="7200614143-44">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-45">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="7200614143-45">}</span><span class="p" data-group-id="7200614143-44">}</span><span class="p" data-group-id="7200614143-38">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">Temp</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="n">Max_Temp</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4284836460-46">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-47">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4284836460-47">}</span><span class="p" data-group-id="4284836460-46">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ +            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7200614143-46">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-47">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7200614143-47">}</span><span class="p" data-group-id="7200614143-46">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4284836460-48">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-49">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="4284836460-49">}</span><span class="p" data-group-id="4284836460-48">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ +            </span><span class="n">Max_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7200614143-48">{</span><span class="n">Max_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-49">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_Temp</span><span class="p" data-group-id="7200614143-49">}</span><span class="p" data-group-id="7200614143-48">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │           </span><span class="n">Temp</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Min_Temp</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4284836460-50">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-51">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4284836460-51">}</span><span class="p" data-group-id="4284836460-50">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │ +            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7200614143-50">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-51">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="7200614143-51">}</span><span class="p" data-group-id="7200614143-50">}</span><span class="p">;</span><span class="w">           </span><span class="c1">% Change</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4284836460-52">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-53">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="4284836460-53">}</span><span class="p" data-group-id="4284836460-52">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │ +            </span><span class="n">Min_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7200614143-52">{</span><span class="n">Min_Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-53">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_Temp</span><span class="p" data-group-id="7200614143-53">}</span><span class="p" data-group-id="7200614143-52">}</span><span class="w"> </span><span class="c1">% Unchanged</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="4284836460-54">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="4284836460-54">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">find_max_and_min</span><span class="p" data-group-id="7200614143-54">(</span><span class="n">Rest</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="7200614143-54">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="4284836460-55">(</span><span class="p" data-group-id="4284836460-56">[</span><span class="p" data-group-id="4284836460-56">]</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="4284836460-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4284836460-57">{</span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="4284836460-57">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">find_max_and_min</span><span class="p" data-group-id="7200614143-55">(</span><span class="p" data-group-id="7200614143-56">[</span><span class="p" data-group-id="7200614143-56">]</span><span class="p">,</span><span class="w"> </span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="7200614143-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7200614143-57">{</span><span class="n">Max_City</span><span class="p">,</span><span class="w"> </span><span class="n">Min_City</span><span class="p" data-group-id="7200614143-57">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">print_max_and_min</span><span class="p" data-group-id="4284836460-58">(</span><span class="p" data-group-id="4284836460-59">{</span><span class="n">Max_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-60">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_temp</span><span class="p" data-group-id="4284836460-60">}</span><span class="p" data-group-id="4284836460-59">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-61">{</span><span class="n">Min_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-62">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_temp</span><span class="p" data-group-id="4284836460-62">}</span><span class="p" data-group-id="4284836460-61">}</span><span class="p" data-group-id="4284836460-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4284836460-63">(</span><span class="s">&quot;Max temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-64">[</span><span class="n">Max_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Max_name</span><span class="p" data-group-id="4284836460-64">]</span><span class="p" data-group-id="4284836460-63">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4284836460-65">(</span><span class="s">&quot;Min temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4284836460-66">[</span><span class="n">Min_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Min_name</span><span class="p" data-group-id="4284836460-66">]</span><span class="p" data-group-id="4284836460-65">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">58&gt; </span><span class="nf">c</span><span class="p" data-group-id="4161303531-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="4161303531-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4161303531-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="4161303531-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">59&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="4161303531-3">(</span><span class="p" data-group-id="4161303531-4">[</span><span class="p" data-group-id="4161303531-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161303531-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4161303531-6">}</span><span class="p" data-group-id="4161303531-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161303531-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161303531-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4161303531-8">}</span><span class="p" data-group-id="4161303531-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4161303531-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161303531-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4161303531-10">}</span><span class="p" data-group-id="4161303531-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161303531-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161303531-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4161303531-12">}</span><span class="p" data-group-id="4161303531-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161303531-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4161303531-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4161303531-14">}</span><span class="p" data-group-id="4161303531-13">}</span><span class="p" data-group-id="4161303531-4">]</span><span class="p" data-group-id="4161303531-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">print_max_and_min</span><span class="p" data-group-id="7200614143-58">(</span><span class="p" data-group-id="7200614143-59">{</span><span class="n">Max_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-60">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Max_temp</span><span class="p" data-group-id="7200614143-60">}</span><span class="p" data-group-id="7200614143-59">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-61">{</span><span class="n">Min_name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-62">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Min_temp</span><span class="p" data-group-id="7200614143-62">}</span><span class="p" data-group-id="7200614143-61">}</span><span class="p" data-group-id="7200614143-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7200614143-63">(</span><span class="s">&quot;Max temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-64">[</span><span class="n">Max_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Max_name</span><span class="p" data-group-id="7200614143-64">]</span><span class="p" data-group-id="7200614143-63">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7200614143-65">(</span><span class="s">&quot;Min temperature was </span><span class="si">~w</span><span class="s"> c in </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7200614143-66">[</span><span class="n">Min_temp</span><span class="p">,</span><span class="w"> </span><span class="n">Min_name</span><span class="p" data-group-id="7200614143-66">]</span><span class="p" data-group-id="7200614143-65">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">58&gt; </span><span class="nf">c</span><span class="p" data-group-id="9403652171-1">(</span><span class="ss">tut7</span><span class="p" data-group-id="9403652171-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9403652171-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">tut7</span><span class="p" data-group-id="9403652171-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">59&gt; </span><span class="nc">tut7</span><span class="p">:</span><span class="nf">format_temps</span><span class="p" data-group-id="9403652171-3">(</span><span class="p" data-group-id="9403652171-4">[</span><span class="p" data-group-id="9403652171-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9403652171-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="9403652171-6">}</span><span class="p" data-group-id="9403652171-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9403652171-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9403652171-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="9403652171-8">}</span><span class="p" data-group-id="9403652171-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9403652171-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9403652171-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="9403652171-10">}</span><span class="p" data-group-id="9403652171-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9403652171-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9403652171-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="9403652171-12">}</span><span class="p" data-group-id="9403652171-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9403652171-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9403652171-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="9403652171-14">}</span><span class="p" data-group-id="9403652171-13">}</span><span class="p" data-group-id="9403652171-4">]</span><span class="p" data-group-id="9403652171-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="o">-</span><span class="mi">4</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="o">-</span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="mf">2.2222222222222223</span><span class="w"> </span><span class="ss">c</span><span class="w">
│ │ │  </span><span class="n">Max</span><span class="w"> </span><span class="ss">temperature</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="mf">21.11111111111111</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">cape_town</span><span class="w">
│ │ │  </span><span class="n">Min</span><span class="w"> </span><span class="ss">temperature</span><span class="w"> </span><span class="ss">was</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">moscow</span><span class="w">
│ │ │ @@ -773,88 +773,88 @@
│ │ │          </span><span class="no">Action</span><span class="w"> </span><span class="mi">4</span><span class="w">
│ │ │  </span><span class="n">end</span></code></pre><p>Notice that there is no <code class="inline">;</code> before <code class="inline">end</code>. Conditions do the same as guards, that
│ │ │  is, tests that succeed or fail. Erlang starts at the top and tests until it
│ │ │  finds a condition that succeeds. Then it evaluates (performs) the action
│ │ │  following the condition and ignores all other conditions and actions before the
│ │ │  <code class="inline">end</code>. If no condition matches, a run-time failure occurs. A condition that
│ │ │  always succeeds is the atom <code class="inline">true</code>. This is often used last in an <code class="inline">if</code>, meaning,
│ │ │ -do the action following the <code class="inline">true</code> if all other conditions have failed.</p><p>The following is a short program to show the workings of <code class="inline">if</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1841163755-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="1841163755-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1841163755-2">(</span><span class="p" data-group-id="1841163755-3">[</span><span class="ss">test_if</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1841163755-3">]</span><span class="p" data-group-id="1841163755-2">)</span><span class="p">.</span><span class="w">
│ │ │ +do the action following the <code class="inline">true</code> if all other conditions have failed.</p><p>The following is a short program to show the workings of <code class="inline">if</code>.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0948718569-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="0948718569-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0948718569-2">(</span><span class="p" data-group-id="0948718569-3">[</span><span class="ss">test_if</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0948718569-3">]</span><span class="p" data-group-id="0948718569-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">test_if</span><span class="p" data-group-id="1841163755-4">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="1841163755-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">test_if</span><span class="p" data-group-id="0948718569-4">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p" data-group-id="0948718569-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1841163755-5">(</span><span class="s">&quot;A == 5</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1841163755-6">[</span><span class="p" data-group-id="1841163755-6">]</span><span class="p" data-group-id="1841163755-5">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0948718569-5">(</span><span class="s">&quot;A == 5</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0948718569-6">[</span><span class="p" data-group-id="0948718569-6">]</span><span class="p" data-group-id="0948718569-5">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="ss">a_equals_5</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1841163755-7">(</span><span class="s">&quot;B == 6</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1841163755-8">[</span><span class="p" data-group-id="1841163755-8">]</span><span class="p" data-group-id="1841163755-7">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0948718569-7">(</span><span class="s">&quot;B == 6</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0948718569-8">[</span><span class="p" data-group-id="0948718569-8">]</span><span class="p" data-group-id="0948718569-7">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="ss">b_equals_6</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">                      </span><span class="c1">%That is A equals 2 and B equals 3</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1841163755-9">(</span><span class="s">&quot;A == 2, B == 3</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1841163755-10">[</span><span class="p" data-group-id="1841163755-10">]</span><span class="p" data-group-id="1841163755-9">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0948718569-9">(</span><span class="s">&quot;A == 2, B == 3</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0948718569-10">[</span><span class="p" data-group-id="0948718569-10">]</span><span class="p" data-group-id="0948718569-9">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="ss">a_equals_2_b_equals_3</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">                     </span><span class="c1">%That is A equals 1 or B equals 7</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1841163755-11">(</span><span class="s">&quot;A == 1 ; B == 7</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1841163755-12">[</span><span class="p" data-group-id="1841163755-12">]</span><span class="p" data-group-id="1841163755-11">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0948718569-11">(</span><span class="s">&quot;A == 1 ; B == 7</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0948718569-12">[</span><span class="p" data-group-id="0948718569-12">]</span><span class="p" data-group-id="0948718569-11">)</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Testing this program gives:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">60&gt; </span><span class="nf">c</span><span class="p" data-group-id="4238809209-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="4238809209-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4238809209-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut9</span><span class="p" data-group-id="4238809209-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">61&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4238809209-3">(</span><span class="mi">5</span><span class="p">,</span><span class="mi">33</span><span class="p" data-group-id="4238809209-3">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><p>Testing this program gives:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">60&gt; </span><span class="nf">c</span><span class="p" data-group-id="1557932355-1">(</span><span class="ss">tut9</span><span class="p" data-group-id="1557932355-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1557932355-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut9</span><span class="p" data-group-id="1557932355-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">61&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="1557932355-3">(</span><span class="mi">5</span><span class="p">,</span><span class="mi">33</span><span class="p" data-group-id="1557932355-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │  </span><span class="ss">a_equals_5</span><span class="w">
│ │ │ -</span><span class="gp unselectable">62&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4238809209-4">(</span><span class="mi">33</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="4238809209-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">62&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="1557932355-4">(</span><span class="mi">33</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="1557932355-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">6</span><span class="w">
│ │ │  </span><span class="ss">b_equals_6</span><span class="w">
│ │ │ -</span><span class="gp unselectable">63&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4238809209-5">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4238809209-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">63&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="1557932355-5">(</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1557932355-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">3</span><span class="w">
│ │ │  </span><span class="ss">a_equals_2_b_equals_3</span><span class="w">
│ │ │ -</span><span class="gp unselectable">64&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4238809209-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="4238809209-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">64&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="1557932355-6">(</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="1557932355-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w">
│ │ │  </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="w">
│ │ │ -</span><span class="gp unselectable">65&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4238809209-7">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="4238809209-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">65&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="1557932355-7">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="1557932355-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">A</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">7</span><span class="w">
│ │ │  </span><span class="ss">a_equals_1_or_b_equals_7</span><span class="w">
│ │ │ -</span><span class="gp unselectable">66&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="4238809209-8">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="4238809209-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">66&gt; </span><span class="nc">tut9</span><span class="p">:</span><span class="nf">test_if</span><span class="p" data-group-id="1557932355-8">(</span><span class="mi">33</span><span class="p">,</span><span class="w"> </span><span class="mi">33</span><span class="p" data-group-id="1557932355-8">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="gt">** exception error: no true branch found when evaluating an if expression
│ │ │       in function  tut9:test_if/2 (tut9.erl, line 5)</span></code></pre><p>Notice that <code class="inline">tut9:test_if(33,33)</code> does not cause any condition to succeed. This
│ │ │  leads to the run time error <code class="inline">if_clause</code>, here nicely formatted by the shell. See
│ │ │  <a href="../../doc/system/expressions.html">Guard Sequences</a> for details of the many guard tests
│ │ │  available.</p><p><code class="inline">case</code> is another construct in Erlang. Recall that the <code class="inline">convert_length</code> function
│ │ │ -was written as:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_length</span><span class="p" data-group-id="8906505694-1">(</span><span class="p" data-group-id="8906505694-2">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="8906505694-2">}</span><span class="p" data-group-id="8906505694-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8906505694-3">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="8906505694-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="8906505694-4">(</span><span class="p" data-group-id="8906505694-5">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="8906505694-5">}</span><span class="p" data-group-id="8906505694-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8906505694-6">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="8906505694-6">}</span><span class="p">.</span></code></pre><p>The same program can also be written as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4911104714-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="4911104714-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4911104714-2">(</span><span class="p" data-group-id="4911104714-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4911104714-3">]</span><span class="p" data-group-id="4911104714-2">)</span><span class="p">.</span><span class="w">
│ │ │ +was written as:</p><pre><code class="makeup erlang" translate="no"><span class="nf">convert_length</span><span class="p" data-group-id="5256827934-1">(</span><span class="p" data-group-id="5256827934-2">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="5256827934-2">}</span><span class="p" data-group-id="5256827934-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5256827934-3">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="5256827934-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="5256827934-4">(</span><span class="p" data-group-id="5256827934-5">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="5256827934-5">}</span><span class="p" data-group-id="5256827934-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5256827934-6">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="5256827934-6">}</span><span class="p">.</span></code></pre><p>The same program can also be written as:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2616895721-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="2616895721-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2616895721-2">(</span><span class="p" data-group-id="2616895721-3">[</span><span class="ss">convert_length</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2616895721-3">]</span><span class="p" data-group-id="2616895721-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_length</span><span class="p" data-group-id="4911104714-4">(</span><span class="n">Length</span><span class="p" data-group-id="4911104714-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">convert_length</span><span class="p" data-group-id="2616895721-4">(</span><span class="n">Length</span><span class="p" data-group-id="2616895721-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4911104714-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="4911104714-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4911104714-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="4911104714-6">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4911104714-7">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="4911104714-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4911104714-8">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="4911104714-8">}</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">67&gt; </span><span class="nf">c</span><span class="p" data-group-id="5640434908-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="5640434908-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5640434908-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut10</span><span class="p" data-group-id="5640434908-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">68&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="5640434908-3">(</span><span class="p" data-group-id="5640434908-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="5640434908-4">}</span><span class="p" data-group-id="5640434908-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5640434908-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">15.24</span><span class="p" data-group-id="5640434908-5">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">69&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="5640434908-6">(</span><span class="p" data-group-id="5640434908-7">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="mf">2.5</span><span class="p" data-group-id="5640434908-7">}</span><span class="p" data-group-id="5640434908-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5640434908-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">0.984251968503937</span><span class="p" data-group-id="5640434908-8">}</span></code></pre><p>Both <code class="inline">case</code> and <code class="inline">if</code> have <em>return values</em>, that is, in the above example <code class="inline">case</code>
│ │ │ +        </span><span class="p" data-group-id="2616895721-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p" data-group-id="2616895721-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2616895721-6">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="2616895721-6">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2616895721-7">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="p" data-group-id="2616895721-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2616895721-8">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mf">2.54</span><span class="p" data-group-id="2616895721-8">}</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">67&gt; </span><span class="nf">c</span><span class="p" data-group-id="2874610371-1">(</span><span class="ss">tut10</span><span class="p" data-group-id="2874610371-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2874610371-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut10</span><span class="p" data-group-id="2874610371-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">68&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2874610371-3">(</span><span class="p" data-group-id="2874610371-4">{</span><span class="ss">inch</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="2874610371-4">}</span><span class="p" data-group-id="2874610371-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2874610371-5">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="mf">15.24</span><span class="p" data-group-id="2874610371-5">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">69&gt; </span><span class="nc">tut10</span><span class="p">:</span><span class="nf">convert_length</span><span class="p" data-group-id="2874610371-6">(</span><span class="p" data-group-id="2874610371-7">{</span><span class="ss">centimeter</span><span class="p">,</span><span class="w"> </span><span class="mf">2.5</span><span class="p" data-group-id="2874610371-7">}</span><span class="p" data-group-id="2874610371-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2874610371-8">{</span><span class="ss">inch</span><span class="p">,</span><span class="mf">0.984251968503937</span><span class="p" data-group-id="2874610371-8">}</span></code></pre><p>Both <code class="inline">case</code> and <code class="inline">if</code> have <em>return values</em>, that is, in the above example <code class="inline">case</code>
│ │ │  returned either <code class="inline">{inch,X/2.54}</code> or <code class="inline">{centimeter,Y*2.54}</code>. The behaviour of
│ │ │  <code class="inline">case</code> can also be modified by using guards. The following example clarifies
│ │ │  this. It tells us the length of a month, given the year. The year must be known,
│ │ │ -since February has 29 days in a leap year.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1047670843-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="1047670843-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1047670843-2">(</span><span class="p" data-group-id="1047670843-3">[</span><span class="ss">month_length</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="1047670843-3">]</span><span class="p" data-group-id="1047670843-2">)</span><span class="p">.</span><span class="w">
│ │ │ +since February has 29 days in a leap year.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0320768500-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="0320768500-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0320768500-2">(</span><span class="p" data-group-id="0320768500-3">[</span><span class="ss">month_length</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="0320768500-3">]</span><span class="p" data-group-id="0320768500-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">month_length</span><span class="p" data-group-id="1047670843-4">(</span><span class="n">Year</span><span class="p">,</span><span class="w"> </span><span class="n">Month</span><span class="p" data-group-id="1047670843-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">month_length</span><span class="p" data-group-id="0320768500-4">(</span><span class="n">Year</span><span class="p">,</span><span class="w"> </span><span class="n">Month</span><span class="p" data-group-id="0320768500-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% All years divisible by 400 are leap</span><span class="w">
│ │ │      </span><span class="c1">%% Years divisible by 100 are not leap (except the 400 rule above)</span><span class="w">
│ │ │      </span><span class="c1">%% Years divisible by 4 are leap (except the 100 rule above)</span><span class="w">
│ │ │      </span><span class="n">Leap</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">if</span><span class="w">
│ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="1047670843-5">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="1047670843-5">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="0320768500-5">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="0320768500-5">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">leap</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="1047670843-6">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="1047670843-6">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">100</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="0320768500-6">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">100</span><span class="p" data-group-id="0320768500-6">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">100</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_leap</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">trunc</span><span class="p" data-group-id="1047670843-7">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1047670843-7">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nf">trunc</span><span class="p" data-group-id="0320768500-7">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="0320768500-7">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">leap</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">not_leap</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Month</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │          </span><span class="ss">sep</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">30</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">apr</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">30</span><span class="p">;</span><span class="w">
│ │ │ @@ -865,152 +865,152 @@
│ │ │          </span><span class="ss">jan</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">mar</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">may</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">jul</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">aug</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">oct</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">dec</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="mi">31</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">70&gt; </span><span class="nf">c</span><span class="p" data-group-id="5494339206-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="5494339206-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5494339206-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut11</span><span class="p" data-group-id="5494339206-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">71&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="5494339206-3">(</span><span class="mi">2004</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="5494339206-3">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">70&gt; </span><span class="nf">c</span><span class="p" data-group-id="6697353507-1">(</span><span class="ss">tut11</span><span class="p" data-group-id="6697353507-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6697353507-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut11</span><span class="p" data-group-id="6697353507-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">71&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="6697353507-3">(</span><span class="mi">2004</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="6697353507-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">29</span><span class="w">
│ │ │ -</span><span class="gp unselectable">72&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="5494339206-4">(</span><span class="mi">2003</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="5494339206-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">72&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="6697353507-4">(</span><span class="mi">2003</span><span class="p">,</span><span class="w"> </span><span class="ss">feb</span><span class="p" data-group-id="6697353507-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">28</span><span class="w">
│ │ │ -</span><span class="gp unselectable">73&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="5494339206-5">(</span><span class="mi">1947</span><span class="p">,</span><span class="w"> </span><span class="ss">aug</span><span class="p" data-group-id="5494339206-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">73&gt; </span><span class="nc">tut11</span><span class="p">:</span><span class="nf">month_length</span><span class="p" data-group-id="6697353507-5">(</span><span class="mi">1947</span><span class="p">,</span><span class="w"> </span><span class="ss">aug</span><span class="p" data-group-id="6697353507-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">31</span></code></pre><h2 id="built-in-functions-bifs" class="section-heading">
│ │ │    <a href="#built-in-functions-bifs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Built-In Functions (BIFs)</span>
│ │ │  </h2>
│ │ │  <p>BIFs are functions that for some reason are built-in to the Erlang virtual
│ │ │  machine. BIFs often implement functionality that is impossible or is too
│ │ │  inefficient to implement in Erlang. Some BIFs can be called using the function
│ │ │  name only but they are by default belonging to the <code class="inline">erlang</code> module. For example,
│ │ │  the call to the BIF <code class="inline">trunc</code> below is equivalent to a call to <code class="inline">erlang:trunc</code>.</p><p>As shown, first it is checked if a year is leap. If a year is divisible by 400,
│ │ │  it is a leap year. To determine this, first divide the year by 400 and use the
│ │ │  BIF <code class="inline">trunc</code> (more about this later) to cut off any decimals. Then multiply by
│ │ │  400 again and see if the same value is returned again. For example, year 2004:</p><pre><code class="makeup erlang" translate="no"><span class="mi">2004</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">5.01</span><span class="w">
│ │ │ -</span><span class="nf">trunc</span><span class="p" data-group-id="7425997661-1">(</span><span class="mf">5.01</span><span class="p" data-group-id="7425997661-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ +</span><span class="nf">trunc</span><span class="p" data-group-id="6029897284-1">(</span><span class="mf">5.01</span><span class="p" data-group-id="6029897284-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │  </span><span class="mi">5</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2000</span></code></pre><p>2000 is not the same as 2004, so 2004 is not divisible by 400. Year 2000:</p><pre><code class="makeup erlang" translate="no"><span class="mi">2000</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">5.0</span><span class="w">
│ │ │ -</span><span class="nf">trunc</span><span class="p" data-group-id="0243147208-1">(</span><span class="mf">5.0</span><span class="p" data-group-id="0243147208-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │ +</span><span class="nf">trunc</span><span class="p" data-group-id="0131225370-1">(</span><span class="mf">5.0</span><span class="p" data-group-id="0131225370-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │  </span><span class="mi">5</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2000</span></code></pre><p>That is, a leap year. The next two <code class="inline">trunc</code>-tests evaluate if the year is
│ │ │  divisible by 100 or 4 in the same way. The first <code class="inline">if</code> returns <code class="inline">leap</code> or
│ │ │  <code class="inline">not_leap</code>, which lands up in the variable <code class="inline">Leap</code>. This variable is used in the
│ │ │  guard for <code class="inline">feb</code> in the following <code class="inline">case</code> that tells us how long the month is.</p><p>This example showed the use of <code class="inline">trunc</code>. It is easier to use the Erlang operator
│ │ │  <code class="inline">rem</code> that gives the remainder after division, for example:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">74&gt; </span><span class="mi">2004</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">400</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="mi">4</span></code></pre><p>So instead of writing:</p><pre><code class="makeup erlang" translate="no"><span class="nf">trunc</span><span class="p" data-group-id="2252468022-1">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="2252468022-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="mi">4</span></code></pre><p>So instead of writing:</p><pre><code class="makeup erlang" translate="no"><span class="nf">trunc</span><span class="p" data-group-id="7731339786-1">(</span><span class="n">Year</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">400</span><span class="p" data-group-id="7731339786-1">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">Year</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">leap</span><span class="p">;</span></code></pre><p>it can be written:</p><pre><code class="makeup erlang" translate="no"><span class="n">Year</span><span class="w"> </span><span class="ow">rem</span><span class="w"> </span><span class="mi">400</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">leap</span><span class="p">;</span></code></pre><p>There are many other BIFs such as <code class="inline">trunc</code>. Only a few BIFs can be used in
│ │ │  guards, and you cannot use functions you have defined yourself in guards. (see
│ │ │  <a href="../../doc/system/expressions.html">Guard Sequences</a>) (For advanced readers: This is to
│ │ │  ensure that guards do not have side effects.) Let us play with a few of these
│ │ │ -functions in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">75&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="0070575127-1">(</span><span class="mf">5.6</span><span class="p" data-group-id="0070575127-1">)</span><span class="p">.</span><span class="w">
│ │ │ +functions in the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">75&gt; </span><span class="nf">trunc</span><span class="p" data-group-id="0553721267-1">(</span><span class="mf">5.6</span><span class="p" data-group-id="0553721267-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">5</span><span class="w">
│ │ │ -</span><span class="gp unselectable">76&gt; </span><span class="nf">round</span><span class="p" data-group-id="0070575127-2">(</span><span class="mf">5.6</span><span class="p" data-group-id="0070575127-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">76&gt; </span><span class="nf">round</span><span class="p" data-group-id="0553721267-2">(</span><span class="mf">5.6</span><span class="p" data-group-id="0553721267-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">6</span><span class="w">
│ │ │ -</span><span class="gp unselectable">77&gt; </span><span class="nf">length</span><span class="p" data-group-id="0070575127-3">(</span><span class="p" data-group-id="0070575127-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="0070575127-4">]</span><span class="p" data-group-id="0070575127-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">77&gt; </span><span class="nf">length</span><span class="p" data-group-id="0553721267-3">(</span><span class="p" data-group-id="0553721267-4">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p">,</span><span class="ss">d</span><span class="p" data-group-id="0553721267-4">]</span><span class="p" data-group-id="0553721267-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">4</span><span class="w">
│ │ │ -</span><span class="gp unselectable">78&gt; </span><span class="nf">float</span><span class="p" data-group-id="0070575127-5">(</span><span class="mi">5</span><span class="p" data-group-id="0070575127-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">78&gt; </span><span class="nf">float</span><span class="p" data-group-id="0553721267-5">(</span><span class="mi">5</span><span class="p" data-group-id="0553721267-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mf">5.0</span><span class="w">
│ │ │ -</span><span class="gp unselectable">79&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="0070575127-6">(</span><span class="ss">hello</span><span class="p" data-group-id="0070575127-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">79&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="0553721267-6">(</span><span class="ss">hello</span><span class="p" data-group-id="0553721267-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">80&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="0070575127-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0070575127-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">80&gt; </span><span class="nf">is_atom</span><span class="p" data-group-id="0553721267-7">(</span><span class="s">&quot;hello&quot;</span><span class="p" data-group-id="0553721267-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span><span class="w">
│ │ │ -</span><span class="gp unselectable">81&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="0070575127-8">(</span><span class="p" data-group-id="0070575127-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0070575127-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="0070575127-10">}</span><span class="p" data-group-id="0070575127-9">}</span><span class="p" data-group-id="0070575127-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">81&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="0553721267-8">(</span><span class="p" data-group-id="0553721267-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0553721267-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="0553721267-10">}</span><span class="p" data-group-id="0553721267-9">}</span><span class="p" data-group-id="0553721267-8">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">true</span><span class="w">
│ │ │ -</span><span class="gp unselectable">82&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="0070575127-11">(</span><span class="p" data-group-id="0070575127-12">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0070575127-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="0070575127-13">}</span><span class="p" data-group-id="0070575127-12">]</span><span class="p" data-group-id="0070575127-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">82&gt; </span><span class="nf">is_tuple</span><span class="p" data-group-id="0553721267-11">(</span><span class="p" data-group-id="0553721267-12">[</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0553721267-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="mi">30</span><span class="p" data-group-id="0553721267-13">}</span><span class="p" data-group-id="0553721267-12">]</span><span class="p" data-group-id="0553721267-11">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">false</span></code></pre><p>All of these can be used in guards. Now for some BIFs that cannot be used in
│ │ │ -guards:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">83&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="4963028597-1">(</span><span class="ss">hello</span><span class="p" data-group-id="4963028597-1">)</span><span class="p">.</span><span class="w">
│ │ │ +guards:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">83&gt; </span><span class="nf">atom_to_list</span><span class="p" data-group-id="3070940165-1">(</span><span class="ss">hello</span><span class="p" data-group-id="3070940165-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;hello&quot;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">84&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="4963028597-2">(</span><span class="s">&quot;goodbye&quot;</span><span class="p" data-group-id="4963028597-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">84&gt; </span><span class="nf">list_to_atom</span><span class="p" data-group-id="3070940165-2">(</span><span class="s">&quot;goodbye&quot;</span><span class="p" data-group-id="3070940165-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">goodbye</span><span class="w">
│ │ │ -</span><span class="gp unselectable">85&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="4963028597-3">(</span><span class="mi">22</span><span class="p" data-group-id="4963028597-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">85&gt; </span><span class="nf">integer_to_list</span><span class="p" data-group-id="3070940165-3">(</span><span class="mi">22</span><span class="p" data-group-id="3070940165-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="s">&quot;22&quot;</span></code></pre><p>These three BIFs do conversions that would be difficult (or impossible) to do in
│ │ │  Erlang.</p><h2 id="higher-order-functions-funs" class="section-heading">
│ │ │    <a href="#higher-order-functions-funs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Higher-Order Functions (Funs)</span>
│ │ │  </h2>
│ │ │  <p>Erlang, like most modern functional programming languages, has higher-order
│ │ │ -functions. Here is an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">86&gt; </span><span class="n">Xf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1990653354-1">(</span><span class="n">X</span><span class="p" data-group-id="1990653354-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +functions. Here is an example using the shell:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">86&gt; </span><span class="n">Xf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="9650333596-1">(</span><span class="n">X</span><span class="p" data-group-id="9650333596-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">87&gt; </span><span class="n">Xf</span><span class="p" data-group-id="1990653354-2">(</span><span class="mi">5</span><span class="p" data-group-id="1990653354-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">87&gt; </span><span class="n">Xf</span><span class="p" data-group-id="9650333596-2">(</span><span class="mi">5</span><span class="p" data-group-id="9650333596-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="mi">10</span></code></pre><p>Here is defined a function that doubles the value of a number and assigned this
│ │ │  function to a variable. Thus <code class="inline">Xf(5)</code> returns value 10. Two useful functions when
│ │ │ -working with lists are <code class="inline">foreach</code> and <code class="inline">map</code>, which are defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="0370515964-1">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0370515964-2">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0370515964-2">]</span><span class="p" data-group-id="0370515964-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">Fun</span><span class="p" data-group-id="0370515964-3">(</span><span class="n">First</span><span class="p" data-group-id="0370515964-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">foreach</span><span class="p" data-group-id="0370515964-4">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="0370515964-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">foreach</span><span class="p" data-group-id="0370515964-5">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0370515964-6">[</span><span class="p" data-group-id="0370515964-6">]</span><span class="p" data-group-id="0370515964-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +working with lists are <code class="inline">foreach</code> and <code class="inline">map</code>, which are defined as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">foreach</span><span class="p" data-group-id="3825784008-1">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3825784008-2">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="3825784008-2">]</span><span class="p" data-group-id="3825784008-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">Fun</span><span class="p" data-group-id="3825784008-3">(</span><span class="n">First</span><span class="p" data-group-id="3825784008-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">foreach</span><span class="p" data-group-id="3825784008-4">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="n">Rest</span><span class="p" data-group-id="3825784008-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">foreach</span><span class="p" data-group-id="3825784008-5">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3825784008-6">[</span><span class="p" data-group-id="3825784008-6">]</span><span class="p" data-group-id="3825784008-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="0370515964-7">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0370515964-8">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="0370515964-8">]</span><span class="p" data-group-id="0370515964-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0370515964-9">[</span><span class="n">Fun</span><span class="p" data-group-id="0370515964-10">(</span><span class="n">First</span><span class="p" data-group-id="0370515964-10">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="0370515964-11">(</span><span class="n">Fun</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="0370515964-11">)</span><span class="p" data-group-id="0370515964-9">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">map</span><span class="p" data-group-id="0370515964-12">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0370515964-13">[</span><span class="p" data-group-id="0370515964-13">]</span><span class="p" data-group-id="0370515964-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0370515964-14">[</span><span class="p" data-group-id="0370515964-14">]</span><span class="p">.</span></code></pre><p>These two functions are provided in the standard module <code class="inline">lists</code>. <code class="inline">foreach</code> takes
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="3825784008-7">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3825784008-8">[</span><span class="n">First</span><span class="p">|</span><span class="n">Rest</span><span class="p" data-group-id="3825784008-8">]</span><span class="p" data-group-id="3825784008-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3825784008-9">[</span><span class="n">Fun</span><span class="p" data-group-id="3825784008-10">(</span><span class="n">First</span><span class="p" data-group-id="3825784008-10">)</span><span class="p">|</span><span class="nf">map</span><span class="p" data-group-id="3825784008-11">(</span><span class="n">Fun</span><span class="p">,</span><span class="n">Rest</span><span class="p" data-group-id="3825784008-11">)</span><span class="p" data-group-id="3825784008-9">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">map</span><span class="p" data-group-id="3825784008-12">(</span><span class="n">Fun</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3825784008-13">[</span><span class="p" data-group-id="3825784008-13">]</span><span class="p" data-group-id="3825784008-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3825784008-14">[</span><span class="p" data-group-id="3825784008-14">]</span><span class="p">.</span></code></pre><p>These two functions are provided in the standard module <code class="inline">lists</code>. <code class="inline">foreach</code> takes
│ │ │  a list and applies a fun to every element in the list. <code class="inline">map</code> creates a new list
│ │ │  by applying a fun to every element in a list. Going back to the shell, <code class="inline">map</code> is
│ │ │ -used and a fun to add 3 to every element of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">88&gt; </span><span class="n">Add_3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3753240209-1">(</span><span class="n">X</span><span class="p" data-group-id="3753240209-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +used and a fun to add 3 to every element of a list:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">88&gt; </span><span class="n">Add_3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="8563768731-1">(</span><span class="n">X</span><span class="p" data-group-id="8563768731-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">89&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="3753240209-2">(</span><span class="n">Add_3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3753240209-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="3753240209-3">]</span><span class="p" data-group-id="3753240209-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3753240209-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="3753240209-4">]</span></code></pre><p>Let us (again) print the temperatures in a list of cities:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">90&gt; </span><span class="n">Print_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="6749606473-1">(</span><span class="p" data-group-id="6749606473-2">{</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6749606473-3">}</span><span class="p" data-group-id="6749606473-2">}</span><span class="p" data-group-id="6749606473-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6749606473-4">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6749606473-5">[</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="6749606473-5">]</span><span class="p" data-group-id="6749606473-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">89&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="8563768731-2">(</span><span class="n">Add_3</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8563768731-3">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8563768731-3">]</span><span class="p" data-group-id="8563768731-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8563768731-4">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p" data-group-id="8563768731-4">]</span></code></pre><p>Let us (again) print the temperatures in a list of cities:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">90&gt; </span><span class="n">Print_City</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="3379405043-1">(</span><span class="p" data-group-id="3379405043-2">{</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-3">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3379405043-3">}</span><span class="p" data-group-id="3379405043-2">}</span><span class="p" data-group-id="3379405043-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3379405043-4">(</span><span class="s">&quot;</span><span class="si">~-</span><span class="s">15w </span><span class="si">~w</span><span class="s"> </span><span class="si">~w</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3379405043-5">[</span><span class="n">City</span><span class="p">,</span><span class="w"> </span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3379405043-5">]</span><span class="p" data-group-id="3379405043-4">)</span><span class="w"> </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_eval</span><span class="p">.</span><span class="mf">5.123085357</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">91&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="6749606473-6">(</span><span class="n">Print_City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-7">[</span><span class="p" data-group-id="6749606473-8">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-9">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6749606473-9">}</span><span class="p" data-group-id="6749606473-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-10">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6749606473-11">}</span><span class="p" data-group-id="6749606473-10">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6749606473-12">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6749606473-13">}</span><span class="p" data-group-id="6749606473-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-14">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-15">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6749606473-15">}</span><span class="p" data-group-id="6749606473-14">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-16">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6749606473-17">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6749606473-17">}</span><span class="p" data-group-id="6749606473-16">}</span><span class="p" data-group-id="6749606473-7">]</span><span class="p" data-group-id="6749606473-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">91&gt; </span><span class="nc">lists</span><span class="p">:</span><span class="nf">foreach</span><span class="p" data-group-id="3379405043-6">(</span><span class="n">Print_City</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-7">[</span><span class="p" data-group-id="3379405043-8">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-9">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="3379405043-9">}</span><span class="p" data-group-id="3379405043-8">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-10">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-11">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="3379405043-11">}</span><span class="p" data-group-id="3379405043-10">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3379405043-12">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="3379405043-13">}</span><span class="p" data-group-id="3379405043-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-14">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-15">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="3379405043-15">}</span><span class="p" data-group-id="3379405043-14">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-16">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3379405043-17">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="3379405043-17">}</span><span class="p" data-group-id="3379405043-16">}</span><span class="p" data-group-id="3379405043-7">]</span><span class="p" data-group-id="3379405043-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">moscow</span><span class="w">          </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="w">
│ │ │  </span><span class="ss">cape_town</span><span class="w">       </span><span class="ss">f</span><span class="w"> </span><span class="mi">70</span><span class="w">
│ │ │  </span><span class="ss">stockholm</span><span class="w">       </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="w">
│ │ │  </span><span class="ss">paris</span><span class="w">           </span><span class="ss">f</span><span class="w"> </span><span class="mi">28</span><span class="w">
│ │ │  </span><span class="ss">london</span><span class="w">          </span><span class="ss">f</span><span class="w"> </span><span class="mi">36</span><span class="w">
│ │ │  </span><span class="ss">ok</span></code></pre><p>Let us now define a fun that can be used to go through a list of cities and
│ │ │ -temperatures and transform them all to Celsius.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3373971236-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="3373971236-1">)</span><span class="p">.</span><span class="w">
│ │ │ +temperatures and transform them all to Celsius.</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1558975309-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="1558975309-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3373971236-2">(</span><span class="p" data-group-id="3373971236-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="3373971236-3">]</span><span class="p" data-group-id="3373971236-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1558975309-2">(</span><span class="p" data-group-id="1558975309-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1558975309-3">]</span><span class="p" data-group-id="1558975309-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="3373971236-4">(</span><span class="p" data-group-id="3373971236-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3373971236-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3373971236-6">}</span><span class="p" data-group-id="3373971236-5">}</span><span class="p" data-group-id="3373971236-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3373971236-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3373971236-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="3373971236-9">(</span><span class="p" data-group-id="3373971236-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="3373971236-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="3373971236-9">)</span><span class="p" data-group-id="3373971236-8">}</span><span class="p" data-group-id="3373971236-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="3373971236-11">(</span><span class="p" data-group-id="3373971236-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3373971236-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3373971236-13">}</span><span class="p" data-group-id="3373971236-12">}</span><span class="p" data-group-id="3373971236-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3373971236-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3373971236-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="3373971236-15">}</span><span class="p" data-group-id="3373971236-14">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="3373971236-16">(</span><span class="n">List</span><span class="p" data-group-id="3373971236-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="3373971236-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="3373971236-17">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">92&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2000178661-1">(</span><span class="p" data-group-id="2000178661-2">[</span><span class="p" data-group-id="2000178661-3">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2000178661-4">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2000178661-4">}</span><span class="p" data-group-id="2000178661-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2000178661-5">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2000178661-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="2000178661-6">}</span><span class="p" data-group-id="2000178661-5">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2000178661-7">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2000178661-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2000178661-8">}</span><span class="p" data-group-id="2000178661-7">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2000178661-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2000178661-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="2000178661-10">}</span><span class="p" data-group-id="2000178661-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2000178661-11">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2000178661-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="2000178661-12">}</span><span class="p" data-group-id="2000178661-11">}</span><span class="p" data-group-id="2000178661-2">]</span><span class="p" data-group-id="2000178661-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2000178661-13">[</span><span class="p" data-group-id="2000178661-14">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="2000178661-15">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="2000178661-15">}</span><span class="p" data-group-id="2000178661-14">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2000178661-16">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="2000178661-17">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="2000178661-17">}</span><span class="p" data-group-id="2000178661-16">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2000178661-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="2000178661-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="2000178661-19">}</span><span class="p" data-group-id="2000178661-18">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2000178661-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="2000178661-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="2000178661-21">}</span><span class="p" data-group-id="2000178661-20">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="2000178661-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="2000178661-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="2000178661-23">}</span><span class="p" data-group-id="2000178661-22">}</span><span class="p" data-group-id="2000178661-13">]</span></code></pre><p>The <code class="inline">convert_to_c</code> function is the same as before, but here it is used as a fun:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1765727313-1">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1765727313-1">)</span></code></pre><p>When a function defined elsewhere is used as a fun, it can be referred to as
│ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="1558975309-4">(</span><span class="p" data-group-id="1558975309-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1558975309-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1558975309-6">}</span><span class="p" data-group-id="1558975309-5">}</span><span class="p" data-group-id="1558975309-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1558975309-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1558975309-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="1558975309-9">(</span><span class="p" data-group-id="1558975309-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="1558975309-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1558975309-9">)</span><span class="p" data-group-id="1558975309-8">}</span><span class="p" data-group-id="1558975309-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="1558975309-11">(</span><span class="p" data-group-id="1558975309-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1558975309-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1558975309-13">}</span><span class="p" data-group-id="1558975309-12">}</span><span class="p" data-group-id="1558975309-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1558975309-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1558975309-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="1558975309-15">}</span><span class="p" data-group-id="1558975309-14">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="1558975309-16">(</span><span class="n">List</span><span class="p" data-group-id="1558975309-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1558975309-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1558975309-17">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">92&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="5210909942-1">(</span><span class="p" data-group-id="5210909942-2">[</span><span class="p" data-group-id="5210909942-3">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5210909942-4">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="5210909942-4">}</span><span class="p" data-group-id="5210909942-3">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5210909942-5">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5210909942-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="5210909942-6">}</span><span class="p" data-group-id="5210909942-5">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5210909942-7">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5210909942-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="5210909942-8">}</span><span class="p" data-group-id="5210909942-7">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5210909942-9">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5210909942-10">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="5210909942-10">}</span><span class="p" data-group-id="5210909942-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5210909942-11">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5210909942-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="5210909942-12">}</span><span class="p" data-group-id="5210909942-11">}</span><span class="p" data-group-id="5210909942-2">]</span><span class="p" data-group-id="5210909942-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5210909942-13">[</span><span class="p" data-group-id="5210909942-14">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="5210909942-15">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="5210909942-15">}</span><span class="p" data-group-id="5210909942-14">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5210909942-16">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="5210909942-17">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="5210909942-17">}</span><span class="p" data-group-id="5210909942-16">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5210909942-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="5210909942-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="5210909942-19">}</span><span class="p" data-group-id="5210909942-18">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5210909942-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="5210909942-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="5210909942-21">}</span><span class="p" data-group-id="5210909942-20">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="5210909942-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="5210909942-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5210909942-23">}</span><span class="p" data-group-id="5210909942-22">}</span><span class="p" data-group-id="5210909942-13">]</span></code></pre><p>The <code class="inline">convert_to_c</code> function is the same as before, but here it is used as a fun:</p><pre><code class="makeup erlang" translate="no"><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="1096878603-1">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="1096878603-1">)</span></code></pre><p>When a function defined elsewhere is used as a fun, it can be referred to as
│ │ │  <code class="inline">Function/Arity</code> (remember that <code class="inline">Arity</code> = number of arguments). So in the
│ │ │  <code class="inline">map</code>-call <code class="inline">lists:map(fun convert_to_c/1, List)</code> is written. As shown,
│ │ │  <code class="inline">convert_list_to_c</code> becomes much shorter and easier to understand.</p><p>The standard module <code class="inline">lists</code> also contains a function <code class="inline">sort(Fun, List)</code> where
│ │ │  <code class="inline">Fun</code> is a fun with two arguments. This fun returns <code class="inline">true</code> if the first argument
│ │ │  is less than the second argument, or else <code class="inline">false</code>. Sorting is added to the
│ │ │ -<code class="inline">convert_list_to_c</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2422150683-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="2422150683-1">)</span><span class="p">.</span><span class="w">
│ │ │ +<code class="inline">convert_list_to_c</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4757037414-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="4757037414-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2422150683-2">(</span><span class="p" data-group-id="2422150683-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2422150683-3">]</span><span class="p" data-group-id="2422150683-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4757037414-2">(</span><span class="p" data-group-id="4757037414-3">[</span><span class="ss">convert_list_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4757037414-3">]</span><span class="p" data-group-id="4757037414-2">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="2422150683-4">(</span><span class="p" data-group-id="2422150683-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2422150683-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2422150683-6">}</span><span class="p" data-group-id="2422150683-5">}</span><span class="p" data-group-id="2422150683-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2422150683-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2422150683-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="2422150683-9">(</span><span class="p" data-group-id="2422150683-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="2422150683-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="2422150683-9">)</span><span class="p" data-group-id="2422150683-8">}</span><span class="p" data-group-id="2422150683-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">convert_to_c</span><span class="p" data-group-id="2422150683-11">(</span><span class="p" data-group-id="2422150683-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2422150683-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2422150683-13">}</span><span class="p" data-group-id="2422150683-12">}</span><span class="p" data-group-id="2422150683-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2422150683-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2422150683-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="2422150683-15">}</span><span class="p" data-group-id="2422150683-14">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="2422150683-16">(</span><span class="n">List</span><span class="p" data-group-id="2422150683-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">New_list</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="2422150683-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="2422150683-17">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="2422150683-18">(</span><span class="nf">fun</span><span class="p" data-group-id="2422150683-19">(</span><span class="p" data-group-id="2422150683-20">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2422150683-21">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="2422150683-21">}</span><span class="p" data-group-id="2422150683-20">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2422150683-22">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2422150683-23">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="2422150683-23">}</span><span class="p" data-group-id="2422150683-22">}</span><span class="p" data-group-id="2422150683-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                       </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">New_list</span><span class="p" data-group-id="2422150683-18">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">93&gt; </span><span class="nf">c</span><span class="p" data-group-id="6680040782-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="6680040782-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6680040782-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut13</span><span class="p" data-group-id="6680040782-2">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">94&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="6680040782-3">(</span><span class="p" data-group-id="6680040782-4">[</span><span class="p" data-group-id="6680040782-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6680040782-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6680040782-6">}</span><span class="p" data-group-id="6680040782-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6680040782-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6680040782-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="6680040782-8">}</span><span class="p" data-group-id="6680040782-7">}</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6680040782-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6680040782-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6680040782-10">}</span><span class="p" data-group-id="6680040782-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6680040782-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6680040782-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="6680040782-12">}</span><span class="p" data-group-id="6680040782-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6680040782-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6680040782-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="6680040782-14">}</span><span class="p" data-group-id="6680040782-13">}</span><span class="p" data-group-id="6680040782-4">]</span><span class="p" data-group-id="6680040782-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6680040782-15">[</span><span class="p" data-group-id="6680040782-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="6680040782-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="6680040782-17">}</span><span class="p" data-group-id="6680040782-16">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6680040782-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="6680040782-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="6680040782-19">}</span><span class="p" data-group-id="6680040782-18">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6680040782-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="6680040782-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="6680040782-21">}</span><span class="p" data-group-id="6680040782-20">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6680040782-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="6680040782-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="6680040782-23">}</span><span class="p" data-group-id="6680040782-22">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="6680040782-24">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="6680040782-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="6680040782-25">}</span><span class="p" data-group-id="6680040782-24">}</span><span class="p" data-group-id="6680040782-15">]</span></code></pre><p>In <code class="inline">sort</code> the fun is used:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="p" data-group-id="7106756321-1">(</span><span class="p" data-group-id="7106756321-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7106756321-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="7106756321-3">}</span><span class="p" data-group-id="7106756321-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7106756321-4">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7106756321-5">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="7106756321-5">}</span><span class="p" data-group-id="7106756321-4">}</span><span class="p" data-group-id="7106756321-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span></code></pre><p>Here the concept of an <em>anonymous variable</em> <code class="inline">_</code> is introduced. This is simply
│ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="4757037414-4">(</span><span class="p" data-group-id="4757037414-5">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4757037414-6">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4757037414-6">}</span><span class="p" data-group-id="4757037414-5">}</span><span class="p" data-group-id="4757037414-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4757037414-7">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4757037414-8">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="nf">trunc</span><span class="p" data-group-id="4757037414-9">(</span><span class="p" data-group-id="4757037414-10">(</span><span class="n">Temp</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">32</span><span class="p" data-group-id="4757037414-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="4757037414-9">)</span><span class="p" data-group-id="4757037414-8">}</span><span class="p" data-group-id="4757037414-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">convert_to_c</span><span class="p" data-group-id="4757037414-11">(</span><span class="p" data-group-id="4757037414-12">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4757037414-13">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4757037414-13">}</span><span class="p" data-group-id="4757037414-12">}</span><span class="p" data-group-id="4757037414-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4757037414-14">{</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4757037414-15">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp</span><span class="p" data-group-id="4757037414-15">}</span><span class="p" data-group-id="4757037414-14">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4757037414-16">(</span><span class="n">List</span><span class="p" data-group-id="4757037414-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">New_list</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="4757037414-17">(</span><span class="k">fun</span><span class="w"> </span><span class="ss">convert_to_c</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">List</span><span class="p" data-group-id="4757037414-17">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">lists</span><span class="p">:</span><span class="nf">sort</span><span class="p" data-group-id="4757037414-18">(</span><span class="nf">fun</span><span class="p" data-group-id="4757037414-19">(</span><span class="p" data-group-id="4757037414-20">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4757037414-21">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="4757037414-21">}</span><span class="p" data-group-id="4757037414-20">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4757037414-22">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4757037414-23">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="4757037414-23">}</span><span class="p" data-group-id="4757037414-22">}</span><span class="p" data-group-id="4757037414-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                       </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">New_list</span><span class="p" data-group-id="4757037414-18">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">93&gt; </span><span class="nf">c</span><span class="p" data-group-id="4940547628-1">(</span><span class="ss">tut13</span><span class="p" data-group-id="4940547628-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4940547628-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="ss">tut13</span><span class="p" data-group-id="4940547628-2">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">94&gt; </span><span class="nc">tut13</span><span class="p">:</span><span class="nf">convert_list_to_c</span><span class="p" data-group-id="4940547628-3">(</span><span class="p" data-group-id="4940547628-4">[</span><span class="p" data-group-id="4940547628-5">{</span><span class="ss">moscow</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4940547628-6">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4940547628-6">}</span><span class="p" data-group-id="4940547628-5">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4940547628-7">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4940547628-8">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">70</span><span class="p" data-group-id="4940547628-8">}</span><span class="p" data-group-id="4940547628-7">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4940547628-9">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4940547628-10">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4940547628-10">}</span><span class="p" data-group-id="4940547628-9">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4940547628-11">{</span><span class="ss">paris</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4940547628-12">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">28</span><span class="p" data-group-id="4940547628-12">}</span><span class="p" data-group-id="4940547628-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4940547628-13">{</span><span class="ss">london</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4940547628-14">{</span><span class="ss">f</span><span class="p">,</span><span class="w"> </span><span class="mi">36</span><span class="p" data-group-id="4940547628-14">}</span><span class="p" data-group-id="4940547628-13">}</span><span class="p" data-group-id="4940547628-4">]</span><span class="p" data-group-id="4940547628-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4940547628-15">[</span><span class="p" data-group-id="4940547628-16">{</span><span class="ss">moscow</span><span class="p">,</span><span class="p" data-group-id="4940547628-17">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">10</span><span class="p" data-group-id="4940547628-17">}</span><span class="p" data-group-id="4940547628-16">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4940547628-18">{</span><span class="ss">stockholm</span><span class="p">,</span><span class="p" data-group-id="4940547628-19">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">4</span><span class="p" data-group-id="4940547628-19">}</span><span class="p" data-group-id="4940547628-18">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4940547628-20">{</span><span class="ss">paris</span><span class="p">,</span><span class="p" data-group-id="4940547628-21">{</span><span class="ss">c</span><span class="p">,</span><span class="o">-</span><span class="mi">2</span><span class="p" data-group-id="4940547628-21">}</span><span class="p" data-group-id="4940547628-20">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4940547628-22">{</span><span class="ss">london</span><span class="p">,</span><span class="p" data-group-id="4940547628-23">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="4940547628-23">}</span><span class="p" data-group-id="4940547628-22">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="4940547628-24">{</span><span class="ss">cape_town</span><span class="p">,</span><span class="p" data-group-id="4940547628-25">{</span><span class="ss">c</span><span class="p">,</span><span class="mi">21</span><span class="p" data-group-id="4940547628-25">}</span><span class="p" data-group-id="4940547628-24">}</span><span class="p" data-group-id="4940547628-15">]</span></code></pre><p>In <code class="inline">sort</code> the fun is used:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="p" data-group-id="6129084488-1">(</span><span class="p" data-group-id="6129084488-2">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6129084488-3">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp1</span><span class="p" data-group-id="6129084488-3">}</span><span class="p" data-group-id="6129084488-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6129084488-4">{</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6129084488-5">{</span><span class="ss">c</span><span class="p">,</span><span class="w"> </span><span class="n">Temp2</span><span class="p" data-group-id="6129084488-5">}</span><span class="p" data-group-id="6129084488-4">}</span><span class="p" data-group-id="6129084488-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Temp1</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Temp2</span><span class="w"> </span><span class="k">end</span><span class="p">,</span></code></pre><p>Here the concept of an <em>anonymous variable</em> <code class="inline">_</code> is introduced. This is simply
│ │ │  shorthand for a variable that gets a value, but the value is ignored. This can
│ │ │  be used anywhere suitable, not just in funs. <code class="inline">Temp1 &lt; Temp2</code> returns <code class="inline">true</code> if
│ │ │  <code class="inline">Temp1</code> is less than <code class="inline">Temp2</code>.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/spec_proc.html
│ │ │ @@ -123,72 +123,72 @@
│ │ │    <a href="#simple-debugging" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simple Debugging</span>
│ │ │  </h2>
│ │ │  <p>The <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html"><code class="inline">sys</code></a> module has functions for simple debugging of processes implemented
│ │ │  using behaviours. The <code class="inline">code_lock</code> example from
│ │ │ -<a href="statem.html#example">gen_statem Behaviour</a> is used to illustrate this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="8283670869-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="8283670869-1">]</span><span class="w"> </span><span class="p" data-group-id="8283670869-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="8283670869-2">]</span><span class="w"> </span><span class="p" data-group-id="8283670869-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="8283670869-3">]</span><span class="w"> </span><span class="p" data-group-id="8283670869-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="8283670869-4">]</span><span class="w"> </span><span class="p" data-group-id="8283670869-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8283670869-5">]</span><span class="w"> </span><span class="p" data-group-id="8283670869-6">[</span><span class="ss">jit</span><span class="p" data-group-id="8283670869-6">]</span><span class="w">
│ │ │ +<a href="statem.html#example">gen_statem Behaviour</a> is used to illustrate this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="8884053617-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="8884053617-1">]</span><span class="w"> </span><span class="p" data-group-id="8884053617-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="8884053617-2">]</span><span class="w"> </span><span class="p" data-group-id="8884053617-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="8884053617-3">]</span><span class="w"> </span><span class="p" data-group-id="8884053617-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="8884053617-4">]</span><span class="w"> </span><span class="p" data-group-id="8884053617-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="8884053617-5">]</span><span class="w"> </span><span class="p" data-group-id="8884053617-6">[</span><span class="ss">jit</span><span class="p" data-group-id="8884053617-6">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="8283670869-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="8283670869-8">(</span><span class="p" data-group-id="8283670869-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="8283670869-7">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8283670869-9">(</span><span class="p" data-group-id="8283670869-10">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8283670869-10">]</span><span class="p" data-group-id="8283670869-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="8884053617-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="8884053617-8">(</span><span class="p" data-group-id="8884053617-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="8884053617-7">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8884053617-9">(</span><span class="p" data-group-id="8884053617-10">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8884053617-10">]</span><span class="p" data-group-id="8884053617-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="n">Lock</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8283670869-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="8283670869-11">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="8283670869-12">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8283670869-12">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8884053617-11">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="8884053617-11">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="8884053617-12">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8884053617-12">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="8283670869-13">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8283670869-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="8884053617-13">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8884053617-13">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="8283670869-14">(</span><span class="mi">1</span><span class="p" data-group-id="8283670869-14">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8283670869-15">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8283670869-15">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="8884053617-14">(</span><span class="mi">1</span><span class="p" data-group-id="8884053617-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8884053617-15">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8884053617-15">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8283670869-16">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8283670869-16">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="8283670869-17">(</span><span class="mi">2</span><span class="p" data-group-id="8283670869-17">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8283670869-18">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8283670869-18">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8884053617-16">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8884053617-16">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="8884053617-17">(</span><span class="mi">2</span><span class="p" data-group-id="8884053617-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8884053617-18">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8884053617-18">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8283670869-19">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8283670869-19">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="8283670869-20">(</span><span class="mi">3</span><span class="p" data-group-id="8283670869-20">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8283670869-21">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8283670869-21">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8884053617-19">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="8884053617-19">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="8884053617-20">(</span><span class="mi">3</span><span class="p" data-group-id="8884053617-20">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8884053617-21">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8884053617-21">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8283670869-22">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8283670869-22">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="8283670869-23">(</span><span class="mi">4</span><span class="p" data-group-id="8283670869-23">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8283670869-24">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8283670869-24">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8884053617-22">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8884053617-22">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="8884053617-23">(</span><span class="mi">4</span><span class="p" data-group-id="8884053617-23">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8884053617-24">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8884053617-24">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="n">Unlock</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8283670869-25">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8283670869-25">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="nb">start_timer</span><span class="w"> </span><span class="p" data-group-id="8283670869-26">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10000</span><span class="p">,</span><span class="ss">lock</span><span class="p">,</span><span class="p" data-group-id="8283670869-27">[</span><span class="p" data-group-id="8283670869-27">]</span><span class="p" data-group-id="8283670869-26">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">cast</span><span class="w"> </span><span class="p" data-group-id="8884053617-25">{</span><span class="ss">button</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8884053617-25">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="nb">start_timer</span><span class="w"> </span><span class="p" data-group-id="8884053617-26">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10000</span><span class="p">,</span><span class="ss">lock</span><span class="p">,</span><span class="p" data-group-id="8884053617-27">[</span><span class="p" data-group-id="8884053617-27">]</span><span class="p" data-group-id="8884053617-26">}</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │  </span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="k">receive</span><span class="w"> </span><span class="ss">state_timeout</span><span class="w"> </span><span class="ss">lock</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w">
│ │ │  </span><span class="n">Lock</span><span class="w">
│ │ │  </span><span class="o">*</span><span class="n">DBG</span><span class="o">*</span><span class="w"> </span><span class="ss">code_lock</span><span class="w"> </span><span class="ss">consume</span><span class="w"> </span><span class="ss">state_timeout</span><span class="w"> </span><span class="ss">lock</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">open</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">locked</span><span class="w">
│ │ │ -</span><span class="gp unselectable">8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="8283670869-28">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="8283670869-28">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8283670869-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="8283670869-30">[</span><span class="p" data-group-id="8283670869-31">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="8283670869-32">{</span><span class="p" data-group-id="8283670869-33">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8283670869-33">}</span><span class="p">,</span><span class="p" data-group-id="8283670869-34">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8283670869-34">}</span><span class="p" data-group-id="8283670869-32">}</span><span class="p" data-group-id="8283670869-31">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="8283670869-35">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="8283670869-36">{</span><span class="p" data-group-id="8283670869-37">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8283670869-37">}</span><span class="p">,</span><span class="p" data-group-id="8283670869-38">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">48</span><span class="p" data-group-id="8283670869-38">}</span><span class="p" data-group-id="8283670869-36">}</span><span class="p" data-group-id="8283670869-35">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="8283670869-39">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">4098</span><span class="p" data-group-id="8283670869-39">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="8283670869-40">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8283670869-40">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="8283670869-41">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="8283670869-41">}</span><span class="p" data-group-id="8283670869-30">]</span><span class="p" data-group-id="8283670869-29">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="8283670869-42">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="8283670869-42">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">10&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="8283670869-43">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="8283670869-43">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">11&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="8283670869-44">(</span><span class="ss">code_lock</span><span class="p" data-group-id="8283670869-44">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8283670869-45">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8283670869-46">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">gen_statem</span><span class="p" data-group-id="8283670869-46">}</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8283670869-47">[</span><span class="p" data-group-id="8283670869-48">[</span><span class="p" data-group-id="8283670869-49">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="8283670869-50">{</span><span class="ss">code_lock</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8283670869-50">}</span><span class="p" data-group-id="8283670869-49">}</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="8283670869-51">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="8283670869-52">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="8283670869-52">]</span><span class="p" data-group-id="8283670869-51">}</span><span class="p" data-group-id="8283670869-48">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="8283670869-53">[</span><span class="p" data-group-id="8283670869-53">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="8283670869-54">[</span><span class="p" data-group-id="8283670869-55">{</span><span class="ss">header</span><span class="p">,</span><span class="s">&quot;Status for state machine code_lock&quot;</span><span class="p" data-group-id="8283670869-55">}</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="8283670869-56">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="8283670869-57">[</span><span class="p" data-group-id="8283670869-58">{</span><span class="s">&quot;Status&quot;</span><span class="p">,</span><span class="ss">running</span><span class="p" data-group-id="8283670869-58">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="8283670869-59">{</span><span class="s">&quot;Parent&quot;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="8283670869-59">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="8283670869-60">{</span><span class="s">&quot;Modules&quot;</span><span class="p">,</span><span class="p" data-group-id="8283670869-61">[</span><span class="ss">code_lock</span><span class="p" data-group-id="8283670869-61">]</span><span class="p" data-group-id="8283670869-60">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="8283670869-62">{</span><span class="s">&quot;Time-outs&quot;</span><span class="p">,</span><span class="p" data-group-id="8283670869-63">{</span><span class="mi">0</span><span class="p">,</span><span class="p" data-group-id="8283670869-64">[</span><span class="p" data-group-id="8283670869-64">]</span><span class="p" data-group-id="8283670869-63">}</span><span class="p" data-group-id="8283670869-62">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="8283670869-65">{</span><span class="s">&quot;Logged Events&quot;</span><span class="p">,</span><span class="p" data-group-id="8283670869-66">[</span><span class="p" data-group-id="8283670869-66">]</span><span class="p" data-group-id="8283670869-65">}</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="8283670869-67">{</span><span class="s">&quot;Postponed&quot;</span><span class="p">,</span><span class="p" data-group-id="8283670869-68">[</span><span class="p" data-group-id="8283670869-68">]</span><span class="p" data-group-id="8283670869-67">}</span><span class="p" data-group-id="8283670869-57">]</span><span class="p" data-group-id="8283670869-56">}</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="8283670869-69">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="8283670869-70">[</span><span class="p" data-group-id="8283670869-71">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="w">
│ │ │ -                  </span><span class="p" data-group-id="8283670869-72">{</span><span class="ss">locked</span><span class="p">,</span><span class="p" data-group-id="8283670869-73">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8283670869-74">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8283670869-74">]</span><span class="p">,</span><span class="w">
│ │ │ -                            </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8283670869-75">[</span><span class="p" data-group-id="8283670869-75">]</span><span class="p" data-group-id="8283670869-73">}</span><span class="p" data-group-id="8283670869-72">}</span><span class="p" data-group-id="8283670869-71">}</span><span class="p" data-group-id="8283670869-70">]</span><span class="p" data-group-id="8283670869-69">}</span><span class="p" data-group-id="8283670869-54">]</span><span class="p" data-group-id="8283670869-47">]</span><span class="p" data-group-id="8283670869-45">}</span></code></pre><h2 id="special-processes" class="section-heading">
│ │ │ +</span><span class="gp unselectable">8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="8884053617-28">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="8884053617-28">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8884053617-29">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="8884053617-30">[</span><span class="p" data-group-id="8884053617-31">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="8884053617-32">{</span><span class="p" data-group-id="8884053617-33">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8884053617-33">}</span><span class="p">,</span><span class="p" data-group-id="8884053617-34">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8884053617-34">}</span><span class="p" data-group-id="8884053617-32">}</span><span class="p" data-group-id="8884053617-31">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8884053617-35">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="8884053617-36">{</span><span class="p" data-group-id="8884053617-37">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8884053617-37">}</span><span class="p">,</span><span class="p" data-group-id="8884053617-38">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">48</span><span class="p" data-group-id="8884053617-38">}</span><span class="p" data-group-id="8884053617-36">}</span><span class="p" data-group-id="8884053617-35">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8884053617-39">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">4098</span><span class="p" data-group-id="8884053617-39">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8884053617-40">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="8884053617-40">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8884053617-41">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="8884053617-41">}</span><span class="p" data-group-id="8884053617-30">]</span><span class="p" data-group-id="8884053617-29">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="8884053617-42">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="8884053617-42">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ +</span><span class="gp unselectable">10&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="8884053617-43">(</span><span class="ss">code_lock</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="8884053617-43">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ +</span><span class="gp unselectable">11&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="8884053617-44">(</span><span class="ss">code_lock</span><span class="p" data-group-id="8884053617-44">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8884053617-45">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8884053617-46">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">gen_statem</span><span class="p" data-group-id="8884053617-46">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8884053617-47">[</span><span class="p" data-group-id="8884053617-48">[</span><span class="p" data-group-id="8884053617-49">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="8884053617-50">{</span><span class="ss">code_lock</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="8884053617-50">}</span><span class="p" data-group-id="8884053617-49">}</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="8884053617-51">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="8884053617-52">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="8884053617-52">]</span><span class="p" data-group-id="8884053617-51">}</span><span class="p" data-group-id="8884053617-48">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="8884053617-53">[</span><span class="p" data-group-id="8884053617-53">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="8884053617-54">[</span><span class="p" data-group-id="8884053617-55">{</span><span class="ss">header</span><span class="p">,</span><span class="s">&quot;Status for state machine code_lock&quot;</span><span class="p" data-group-id="8884053617-55">}</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="8884053617-56">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="8884053617-57">[</span><span class="p" data-group-id="8884053617-58">{</span><span class="s">&quot;Status&quot;</span><span class="p">,</span><span class="ss">running</span><span class="p" data-group-id="8884053617-58">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="8884053617-59">{</span><span class="s">&quot;Parent&quot;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="8884053617-59">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="8884053617-60">{</span><span class="s">&quot;Modules&quot;</span><span class="p">,</span><span class="p" data-group-id="8884053617-61">[</span><span class="ss">code_lock</span><span class="p" data-group-id="8884053617-61">]</span><span class="p" data-group-id="8884053617-60">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="8884053617-62">{</span><span class="s">&quot;Time-outs&quot;</span><span class="p">,</span><span class="p" data-group-id="8884053617-63">{</span><span class="mi">0</span><span class="p">,</span><span class="p" data-group-id="8884053617-64">[</span><span class="p" data-group-id="8884053617-64">]</span><span class="p" data-group-id="8884053617-63">}</span><span class="p" data-group-id="8884053617-62">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="8884053617-65">{</span><span class="s">&quot;Logged Events&quot;</span><span class="p">,</span><span class="p" data-group-id="8884053617-66">[</span><span class="p" data-group-id="8884053617-66">]</span><span class="p" data-group-id="8884053617-65">}</span><span class="p">,</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="8884053617-67">{</span><span class="s">&quot;Postponed&quot;</span><span class="p">,</span><span class="p" data-group-id="8884053617-68">[</span><span class="p" data-group-id="8884053617-68">]</span><span class="p" data-group-id="8884053617-67">}</span><span class="p" data-group-id="8884053617-57">]</span><span class="p" data-group-id="8884053617-56">}</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="8884053617-69">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="8884053617-70">[</span><span class="p" data-group-id="8884053617-71">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="w">
│ │ │ +                  </span><span class="p" data-group-id="8884053617-72">{</span><span class="ss">locked</span><span class="p">,</span><span class="p" data-group-id="8884053617-73">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8884053617-74">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="8884053617-74">]</span><span class="p">,</span><span class="w">
│ │ │ +                            </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8884053617-75">[</span><span class="p" data-group-id="8884053617-75">]</span><span class="p" data-group-id="8884053617-73">}</span><span class="p" data-group-id="8884053617-72">}</span><span class="p" data-group-id="8884053617-71">}</span><span class="p" data-group-id="8884053617-70">]</span><span class="p" data-group-id="8884053617-69">}</span><span class="p" data-group-id="8884053617-54">]</span><span class="p" data-group-id="8884053617-47">]</span><span class="p" data-group-id="8884053617-45">}</span></code></pre><h2 id="special-processes" class="section-heading">
│ │ │    <a href="#special-processes" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Special Processes</span>
│ │ │  </h2>
│ │ │  <p>This section describes how to write a process that complies to the OTP design
│ │ │  principles, without using a standard behaviour. Such a process is to:</p><ul><li>Be started in a way that makes the process fit into a supervision tree</li><li>Support the <code class="inline">sys</code> <a href="spec_proc.html#debug">debug facilities</a></li><li>Take care of <a href="spec_proc.html#msg">system messages</a>.</li></ul><p>System messages are messages with a special meaning, used in the supervision
│ │ │ @@ -198,238 +198,238 @@
│ │ │    <a href="#example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example</span>
│ │ │  </h3>
│ │ │  <p>Here follows the simple server from
│ │ │  <a href="design_principles.html#ch1">Overview</a>,
│ │ │ -implemented using <code class="inline">sys</code> and <code class="inline">proc_lib</code> to fit into a supervision tree:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4990773878-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="4990773878-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4990773878-2">(</span><span class="p" data-group-id="4990773878-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4990773878-3">]</span><span class="p" data-group-id="4990773878-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4990773878-4">(</span><span class="p" data-group-id="4990773878-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4990773878-5">]</span><span class="p" data-group-id="4990773878-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4990773878-6">(</span><span class="p" data-group-id="4990773878-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4990773878-7">]</span><span class="p" data-group-id="4990773878-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4990773878-8">(</span><span class="p" data-group-id="4990773878-9">[</span><span class="ss">system_continue</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">system_terminate</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w">
│ │ │ +implemented using <code class="inline">sys</code> and <code class="inline">proc_lib</code> to fit into a supervision tree:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="7087665056-1">(</span><span class="ss">ch4</span><span class="p" data-group-id="7087665056-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7087665056-2">(</span><span class="p" data-group-id="7087665056-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="7087665056-3">]</span><span class="p" data-group-id="7087665056-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7087665056-4">(</span><span class="p" data-group-id="7087665056-5">[</span><span class="ss">alloc</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">free</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7087665056-5">]</span><span class="p" data-group-id="7087665056-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7087665056-6">(</span><span class="p" data-group-id="7087665056-7">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7087665056-7">]</span><span class="p" data-group-id="7087665056-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7087665056-8">(</span><span class="p" data-group-id="7087665056-9">[</span><span class="ss">system_continue</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="ss">system_terminate</span><span class="p">/</span><span class="mi">4</span><span class="p">,</span><span class="w">
│ │ │           </span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="ss">system_get_state</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">system_replace_state</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="4990773878-9">]</span><span class="p" data-group-id="4990773878-8">)</span><span class="p">.</span><span class="w">
│ │ │ +         </span><span class="ss">system_get_state</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">system_replace_state</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7087665056-9">]</span><span class="p" data-group-id="7087665056-8">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="4990773878-10">(</span><span class="p" data-group-id="4990773878-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4990773878-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990773878-12">[</span><span class="nf">self</span><span class="p" data-group-id="4990773878-13">(</span><span class="p" data-group-id="4990773878-13">)</span><span class="p" data-group-id="4990773878-12">]</span><span class="p" data-group-id="4990773878-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="7087665056-10">(</span><span class="p" data-group-id="7087665056-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="7087665056-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7087665056-12">[</span><span class="nf">self</span><span class="p" data-group-id="7087665056-13">(</span><span class="p" data-group-id="7087665056-13">)</span><span class="p" data-group-id="7087665056-12">]</span><span class="p" data-group-id="7087665056-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">alloc</span><span class="p" data-group-id="4990773878-14">(</span><span class="p" data-group-id="4990773878-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4990773878-15">{</span><span class="nf">self</span><span class="p" data-group-id="4990773878-16">(</span><span class="p" data-group-id="4990773878-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="4990773878-15">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">alloc</span><span class="p" data-group-id="7087665056-14">(</span><span class="p" data-group-id="7087665056-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7087665056-15">{</span><span class="nf">self</span><span class="p" data-group-id="7087665056-16">(</span><span class="p" data-group-id="7087665056-16">)</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="7087665056-15">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4990773878-17">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="4990773878-17">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7087665056-17">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Res</span><span class="p" data-group-id="7087665056-17">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">Res</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">free</span><span class="p" data-group-id="4990773878-18">(</span><span class="n">Ch</span><span class="p" data-group-id="4990773878-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4990773878-19">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4990773878-19">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">free</span><span class="p" data-group-id="7087665056-18">(</span><span class="n">Ch</span><span class="p" data-group-id="7087665056-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">ch4</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7087665056-19">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7087665056-19">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="4990773878-20">(</span><span class="n">Parent</span><span class="p" data-group-id="4990773878-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="4990773878-21">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4990773878-22">(</span><span class="p" data-group-id="4990773878-22">)</span><span class="p" data-group-id="4990773878-21">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="4990773878-23">(</span><span class="p" data-group-id="4990773878-23">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="4990773878-24">(</span><span class="p" data-group-id="4990773878-25">[</span><span class="p" data-group-id="4990773878-25">]</span><span class="p" data-group-id="4990773878-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="4990773878-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990773878-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="4990773878-28">(</span><span class="p" data-group-id="4990773878-28">)</span><span class="p" data-group-id="4990773878-27">}</span><span class="p" data-group-id="4990773878-26">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="4990773878-29">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="4990773878-29">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="7087665056-20">(</span><span class="n">Parent</span><span class="p" data-group-id="7087665056-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="7087665056-21">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7087665056-22">(</span><span class="p" data-group-id="7087665056-22">)</span><span class="p" data-group-id="7087665056-21">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Chs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">channels</span><span class="p" data-group-id="7087665056-23">(</span><span class="p" data-group-id="7087665056-23">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="7087665056-24">(</span><span class="p" data-group-id="7087665056-25">[</span><span class="p" data-group-id="7087665056-25">]</span><span class="p" data-group-id="7087665056-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="7087665056-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7087665056-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="7087665056-28">(</span><span class="p" data-group-id="7087665056-28">)</span><span class="p" data-group-id="7087665056-27">}</span><span class="p" data-group-id="7087665056-26">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="7087665056-29">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="7087665056-29">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="4990773878-30">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="4990773878-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="7087665056-30">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="7087665056-30">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4990773878-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="4990773878-31">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="4990773878-32">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990773878-33">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="4990773878-33">}</span><span class="p" data-group-id="4990773878-32">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4990773878-34">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="4990773878-34">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="4990773878-35">(</span><span class="n">Chs</span><span class="p" data-group-id="4990773878-35">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4990773878-36">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4990773878-36">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="4990773878-37">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990773878-38">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990773878-39">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4990773878-39">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="4990773878-38">}</span><span class="p" data-group-id="4990773878-37">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="4990773878-40">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="4990773878-40">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4990773878-41">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4990773878-41">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="4990773878-42">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990773878-43">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990773878-44">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="4990773878-44">}</span><span class="p" data-group-id="4990773878-43">}</span><span class="p" data-group-id="4990773878-42">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="4990773878-45">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4990773878-45">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="4990773878-46">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="4990773878-46">)</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -        </span><span class="p" data-group-id="4990773878-47">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="4990773878-47">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="4990773878-48">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ -                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4990773878-48">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7087665056-31">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="7087665056-31">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="7087665056-32">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7087665056-33">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="7087665056-33">}</span><span class="p" data-group-id="7087665056-32">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="7087665056-34">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="7087665056-34">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="7087665056-35">(</span><span class="n">Chs</span><span class="p" data-group-id="7087665056-35">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="7087665056-36">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7087665056-36">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="7087665056-37">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7087665056-38">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7087665056-39">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7087665056-39">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="7087665056-38">}</span><span class="p" data-group-id="7087665056-37">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="7087665056-40">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="7087665056-40">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7087665056-41">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7087665056-41">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="7087665056-42">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7087665056-43">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7087665056-44">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="7087665056-44">}</span><span class="p" data-group-id="7087665056-43">}</span><span class="p" data-group-id="7087665056-42">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="7087665056-45">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7087665056-45">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="7087665056-46">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="7087665056-46">)</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +        </span><span class="p" data-group-id="7087665056-47">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="7087665056-47">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="7087665056-48">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ +                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7087665056-48">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_continue</span><span class="p" data-group-id="4990773878-49">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4990773878-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="4990773878-50">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="4990773878-50">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_continue</span><span class="p" data-group-id="7087665056-49">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7087665056-49">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="7087665056-50">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="7087665056-50">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_terminate</span><span class="p" data-group-id="4990773878-51">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Chs</span><span class="p" data-group-id="4990773878-51">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="4990773878-52">(</span><span class="n">Reason</span><span class="p" data-group-id="4990773878-52">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_terminate</span><span class="p" data-group-id="7087665056-51">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Chs</span><span class="p" data-group-id="7087665056-51">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="7087665056-52">(</span><span class="n">Reason</span><span class="p" data-group-id="7087665056-52">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_get_state</span><span class="p" data-group-id="4990773878-53">(</span><span class="n">Chs</span><span class="p" data-group-id="4990773878-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4990773878-54">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4990773878-54">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_get_state</span><span class="p" data-group-id="7087665056-53">(</span><span class="n">Chs</span><span class="p" data-group-id="7087665056-53">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7087665056-54">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7087665056-54">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_replace_state</span><span class="p" data-group-id="4990773878-55">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="4990773878-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="4990773878-56">(</span><span class="n">Chs</span><span class="p" data-group-id="4990773878-56">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4990773878-57">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="4990773878-57">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_replace_state</span><span class="p" data-group-id="7087665056-55">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="7087665056-55">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="7087665056-56">(</span><span class="n">Chs</span><span class="p" data-group-id="7087665056-56">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7087665056-57">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="7087665056-57">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">write_debug</span><span class="p" data-group-id="4990773878-58">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="4990773878-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="4990773878-59">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990773878-60">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="4990773878-60">]</span><span class="p" data-group-id="4990773878-59">)</span><span class="p">.</span></code></pre><p id="ex">As it is not relevant to the example, the channel handling functions have been
│ │ │ +</span><span class="nf">write_debug</span><span class="p" data-group-id="7087665056-58">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="7087665056-58">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7087665056-59">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7087665056-60">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="7087665056-60">]</span><span class="p" data-group-id="7087665056-59">)</span><span class="p">.</span></code></pre><p id="ex">As it is not relevant to the example, the channel handling functions have been
│ │ │  omitted. To compile this example, the
│ │ │  <a href="design_principles.html#channels-implementation">implementation of channel handling</a>
│ │ │  needs to be added to the module.</p><p>Here is an example showing how the debugging functions in the <code class="inline">sys</code>
│ │ │  module can be used for <code class="inline">ch4</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">% erl</span><span class="w">
│ │ │ -</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="5698753933-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="5698753933-1">]</span><span class="w"> </span><span class="p" data-group-id="5698753933-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="5698753933-2">]</span><span class="w"> </span><span class="p" data-group-id="5698753933-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="5698753933-3">]</span><span class="w"> </span><span class="p" data-group-id="5698753933-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="5698753933-4">]</span><span class="w"> </span><span class="p" data-group-id="5698753933-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="5698753933-5">]</span><span class="w"> </span><span class="p" data-group-id="5698753933-6">[</span><span class="ss">jit</span><span class="p" data-group-id="5698753933-6">]</span><span class="w">
│ │ │ +</span><span class="n">Erlang</span><span class="o">/</span><span class="n">OTP</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="p" data-group-id="0420353448-1">[</span><span class="ss">erts</span><span class="o">-</span><span class="mf">15.0</span><span class="p" data-group-id="0420353448-1">]</span><span class="w"> </span><span class="p" data-group-id="0420353448-2">[</span><span class="mi">64</span><span class="o">-</span><span class="ss">bit</span><span class="p" data-group-id="0420353448-2">]</span><span class="w"> </span><span class="p" data-group-id="0420353448-3">[</span><span class="nc">smp</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p" data-group-id="0420353448-3">]</span><span class="w"> </span><span class="p" data-group-id="0420353448-4">[</span><span class="nc">ds</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">8</span><span class="p">:</span><span class="mi">10</span><span class="p" data-group-id="0420353448-4">]</span><span class="w"> </span><span class="p" data-group-id="0420353448-5">[</span><span class="ss">async</span><span class="o">-</span><span class="nc">threads</span><span class="p">:</span><span class="mi">1</span><span class="p" data-group-id="0420353448-5">]</span><span class="w"> </span><span class="p" data-group-id="0420353448-6">[</span><span class="ss">jit</span><span class="p" data-group-id="0420353448-6">]</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="5698753933-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="5698753933-8">(</span><span class="p" data-group-id="5698753933-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="5698753933-7">)</span><span class="w">
│ │ │ -</span><span class="gp unselectable">1&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5698753933-9">(</span><span class="p" data-group-id="5698753933-9">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5698753933-10">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5698753933-10">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5698753933-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5698753933-11">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="5698753933-12">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="5698753933-12">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">alloc</span><span class="p" data-group-id="5698753933-13">(</span><span class="p" data-group-id="5698753933-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5698753933-14">{</span><span class="ss">in</span><span class="p">,</span><span class="ss">alloc</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5698753933-14">}</span><span class="w">
│ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5698753933-15">{</span><span class="ss">out</span><span class="p">,</span><span class="p" data-group-id="5698753933-16">{</span><span class="ss">ch4</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5698753933-16">}</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5698753933-15">}</span><span class="w">
│ │ │ +</span><span class="n">Eshell</span><span class="w"> </span><span class="n">V15</span><span class="p">.</span><span class="mi">0</span><span class="w"> </span><span class="p" data-group-id="0420353448-7">(</span><span class="ss">press</span><span class="w"> </span><span class="n">Ctrl</span><span class="o">+</span><span class="n">G</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">abort</span><span class="p">,</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="nf">help</span><span class="p" data-group-id="0420353448-8">(</span><span class="p" data-group-id="0420353448-8">)</span><span class="p">.</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">help</span><span class="p" data-group-id="0420353448-7">)</span><span class="w">
│ │ │ +</span><span class="gp unselectable">1&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0420353448-9">(</span><span class="p" data-group-id="0420353448-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0420353448-10">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0420353448-10">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0420353448-11">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0420353448-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="0420353448-12">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="0420353448-12">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">alloc</span><span class="p" data-group-id="0420353448-13">(</span><span class="p" data-group-id="0420353448-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0420353448-14">{</span><span class="ss">in</span><span class="p">,</span><span class="ss">alloc</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0420353448-14">}</span><span class="w">
│ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0420353448-15">{</span><span class="ss">out</span><span class="p">,</span><span class="p" data-group-id="0420353448-16">{</span><span class="ss">ch4</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0420353448-16">}</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0420353448-15">}</span><span class="w">
│ │ │  </span><span class="mi">1</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">free</span><span class="p" data-group-id="5698753933-17">(</span><span class="ss">ch1</span><span class="p" data-group-id="5698753933-17">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5698753933-18">{</span><span class="ss">in</span><span class="p">,</span><span class="p" data-group-id="5698753933-19">{</span><span class="ss">free</span><span class="p">,</span><span class="ss">ch1</span><span class="p" data-group-id="5698753933-19">}</span><span class="p" data-group-id="5698753933-18">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">ch4</span><span class="p">:</span><span class="nf">free</span><span class="p" data-group-id="0420353448-17">(</span><span class="ss">ch1</span><span class="p" data-group-id="0420353448-17">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ch4</span><span class="w"> </span><span class="ss">event</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0420353448-18">{</span><span class="ss">in</span><span class="p">,</span><span class="p" data-group-id="0420353448-19">{</span><span class="ss">free</span><span class="p">,</span><span class="ss">ch1</span><span class="p" data-group-id="0420353448-19">}</span><span class="p" data-group-id="0420353448-18">}</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5698753933-20">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="5698753933-20">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5698753933-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="5698753933-22">[</span><span class="p" data-group-id="5698753933-23">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="5698753933-24">{</span><span class="p" data-group-id="5698753933-25">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5698753933-25">}</span><span class="p">,</span><span class="p" data-group-id="5698753933-26">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="5698753933-26">}</span><span class="p" data-group-id="5698753933-24">}</span><span class="p" data-group-id="5698753933-23">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="5698753933-27">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="5698753933-28">{</span><span class="p" data-group-id="5698753933-29">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5698753933-29">}</span><span class="p">,</span><span class="p" data-group-id="5698753933-30">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">49</span><span class="p" data-group-id="5698753933-30">}</span><span class="p" data-group-id="5698753933-28">}</span><span class="p" data-group-id="5698753933-27">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="5698753933-31">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">202</span><span class="p" data-group-id="5698753933-31">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="5698753933-32">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="5698753933-32">}</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="5698753933-33">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5698753933-33">}</span><span class="p" data-group-id="5698753933-22">]</span><span class="p" data-group-id="5698753933-21">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">7&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="5698753933-34">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="5698753933-34">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="5698753933-35">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="5698753933-35">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="5698753933-36">(</span><span class="ss">ch4</span><span class="p" data-group-id="5698753933-36">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5698753933-37">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5698753933-38">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">ch4</span><span class="p" data-group-id="5698753933-38">}</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="5698753933-39">[</span><span class="p" data-group-id="5698753933-40">[</span><span class="p" data-group-id="5698753933-41">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="5698753933-42">{</span><span class="ss">ch4</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5698753933-42">}</span><span class="p" data-group-id="5698753933-41">}</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="5698753933-43">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="5698753933-44">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="5698753933-44">]</span><span class="p" data-group-id="5698753933-43">}</span><span class="p" data-group-id="5698753933-40">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="5698753933-45">[</span><span class="p" data-group-id="5698753933-45">]</span><span class="p">,</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="5698753933-46">{</span><span class="p" data-group-id="5698753933-47">[</span><span class="mi">1</span><span class="p" data-group-id="5698753933-47">]</span><span class="p">,</span><span class="p" data-group-id="5698753933-48">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">18</span><span class="p">,</span><span class="mi">19</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5698753933-48">]</span><span class="p" data-group-id="5698753933-46">}</span><span class="p" data-group-id="5698753933-39">]</span><span class="p" data-group-id="5698753933-37">}</span></code></pre><h3 id="starting-the-process" class="section-heading">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0420353448-20">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="nb">get</span><span class="p" data-group-id="0420353448-20">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0420353448-21">{</span><span class="ss">ok</span><span class="p">,</span><span class="p" data-group-id="0420353448-22">[</span><span class="p" data-group-id="0420353448-23">{</span><span class="ss">start_time</span><span class="p">,</span><span class="p" data-group-id="0420353448-24">{</span><span class="p" data-group-id="0420353448-25">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0420353448-25">}</span><span class="p">,</span><span class="p" data-group-id="0420353448-26">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">13</span><span class="p" data-group-id="0420353448-26">}</span><span class="p" data-group-id="0420353448-24">}</span><span class="p" data-group-id="0420353448-23">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0420353448-27">{</span><span class="ss">current_time</span><span class="p">,</span><span class="p" data-group-id="0420353448-28">{</span><span class="p" data-group-id="0420353448-29">{</span><span class="mi">2024</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0420353448-29">}</span><span class="p">,</span><span class="p" data-group-id="0420353448-30">{</span><span class="mi">8</span><span class="p">,</span><span class="mi">26</span><span class="p">,</span><span class="mi">49</span><span class="p" data-group-id="0420353448-30">}</span><span class="p" data-group-id="0420353448-28">}</span><span class="p" data-group-id="0420353448-27">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0420353448-31">{</span><span class="ss">reductions</span><span class="p">,</span><span class="mi">202</span><span class="p" data-group-id="0420353448-31">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0420353448-32">{</span><span class="ss">messages_in</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="0420353448-32">}</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="0420353448-33">{</span><span class="ss">messages_out</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0420353448-33">}</span><span class="p" data-group-id="0420353448-22">]</span><span class="p" data-group-id="0420353448-21">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">7&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">statistics</span><span class="p" data-group-id="0420353448-34">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0420353448-34">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ +</span><span class="gp unselectable">8&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">trace</span><span class="p" data-group-id="0420353448-35">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">false</span><span class="p" data-group-id="0420353448-35">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="ss">ok</span><span class="w">
│ │ │ +</span><span class="gp unselectable">9&gt; </span><span class="nc">sys</span><span class="p">:</span><span class="nf">get_status</span><span class="p" data-group-id="0420353448-36">(</span><span class="ss">ch4</span><span class="p" data-group-id="0420353448-36">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0420353448-37">{</span><span class="ss">status</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.90</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0420353448-38">{</span><span class="ss">module</span><span class="p">,</span><span class="ss">ch4</span><span class="p" data-group-id="0420353448-38">}</span><span class="p">,</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0420353448-39">[</span><span class="p" data-group-id="0420353448-40">[</span><span class="p" data-group-id="0420353448-41">{</span><span class="ss">&#39;$initial_call&#39;</span><span class="p">,</span><span class="p" data-group-id="0420353448-42">{</span><span class="ss">ch4</span><span class="p">,</span><span class="ss">init</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0420353448-42">}</span><span class="p" data-group-id="0420353448-41">}</span><span class="p">,</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="0420353448-43">{</span><span class="ss">&#39;$ancestors&#39;</span><span class="p">,</span><span class="p" data-group-id="0420353448-44">[</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.87</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.70</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.65</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.69</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +                         </span><span class="o">&lt;</span><span class="mf">0.64</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">kernel_sup</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.47</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="0420353448-44">]</span><span class="p" data-group-id="0420353448-43">}</span><span class="p" data-group-id="0420353448-40">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="ss">running</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.88</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p">,</span><span class="p" data-group-id="0420353448-45">[</span><span class="p" data-group-id="0420353448-45">]</span><span class="p">,</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="0420353448-46">{</span><span class="p" data-group-id="0420353448-47">[</span><span class="mi">1</span><span class="p" data-group-id="0420353448-47">]</span><span class="p">,</span><span class="p" data-group-id="0420353448-48">[</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">,</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">,</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">,</span><span class="mi">10</span><span class="p">,</span><span class="mi">11</span><span class="p">,</span><span class="mi">12</span><span class="p">,</span><span class="mi">13</span><span class="p">,</span><span class="mi">14</span><span class="p">,</span><span class="mi">15</span><span class="p">,</span><span class="mi">16</span><span class="p">,</span><span class="mi">17</span><span class="p">,</span><span class="mi">18</span><span class="p">,</span><span class="mi">19</span><span class="p">|</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="0420353448-48">]</span><span class="p" data-group-id="0420353448-46">}</span><span class="p" data-group-id="0420353448-39">]</span><span class="p" data-group-id="0420353448-37">}</span></code></pre><h3 id="starting-the-process" class="section-heading">
│ │ │    <a href="#starting-the-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting the Process</span>
│ │ │  </h3>
│ │ │  <p>A function in the <a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html"><code class="inline">proc_lib</code></a> module is to be used to start the process. Several
│ │ │  functions are available, for example,
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#spawn_link/4"><code class="inline">proc_lib:spawn_link/3,4</code></a>
│ │ │  for asynchronous start and
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#start_link/5"><code class="inline">proc_lib:start_link/3,4,5</code></a> for synchronous start.</p><p>Information necessary for a process within a supervision tree, such as
│ │ │  details on ancestors and the initial call, is stored when a process
│ │ │  is started through one of these functions.</p><p>If the process terminates with a reason other than <code class="inline">normal</code> or <code class="inline">shutdown</code>, a
│ │ │  crash report is generated. For more information about the crash report, see
│ │ │  <a href="../../lib/kernel-10.2.7.4/doc/html/logger_chapter.html">Logging</a> in Kernel User's Guide.</p><p>In the example, synchronous start is used. The process starts by calling
│ │ │ -<code class="inline">ch4:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="1752326348-1">(</span><span class="p" data-group-id="1752326348-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1752326348-2">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1752326348-3">[</span><span class="nf">self</span><span class="p" data-group-id="1752326348-4">(</span><span class="p" data-group-id="1752326348-4">)</span><span class="p" data-group-id="1752326348-3">]</span><span class="p" data-group-id="1752326348-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch4:start_link/0</code> calls <a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>, which takes a module
│ │ │ +<code class="inline">ch4:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="4257530993-1">(</span><span class="p" data-group-id="4257530993-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4257530993-2">(</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4257530993-3">[</span><span class="nf">self</span><span class="p" data-group-id="4257530993-4">(</span><span class="p" data-group-id="4257530993-4">)</span><span class="p" data-group-id="4257530993-3">]</span><span class="p" data-group-id="4257530993-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch4:start_link/0</code> calls <a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>, which takes a module
│ │ │  name, a function name, and an argument list as arguments. It then
│ │ │  spawns a new process and establishes a link. The new process starts
│ │ │  by executing the given function, here <code class="inline">ch4:init(Pid)</code>, where <code class="inline">Pid</code> is
│ │ │  the pid of the parent process (obtained by the call to
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#self/0"><code class="inline">self()</code></a> in the call to <a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a>).</p><p>All initialization, including name registration, is done in <code class="inline">init/1</code>. The new
│ │ │ -process has to acknowledge that it has been started to the parent:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="5750975458-1">(</span><span class="n">Parent</span><span class="p" data-group-id="5750975458-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +process has to acknowledge that it has been started to the parent:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8458051508-1">(</span><span class="n">Parent</span><span class="p" data-group-id="8458051508-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="5750975458-2">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5750975458-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5750975458-4">(</span><span class="p" data-group-id="5750975458-4">)</span><span class="p" data-group-id="5750975458-3">}</span><span class="p" data-group-id="5750975458-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="5750975458-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5750975458-5">)</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a> is synchronous and does not return until
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="8458051508-2">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8458051508-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8458051508-4">(</span><span class="p" data-group-id="8458051508-4">)</span><span class="p" data-group-id="8458051508-3">}</span><span class="p" data-group-id="8458051508-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="8458051508-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8458051508-5">)</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#start_link/3"><code class="inline">proc_lib:start_link/3</code></a> is synchronous and does not return until
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#init_ack/2"><code class="inline">proc_lib:init_ack/1,2</code></a> or
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#init_fail/3"><code class="inline">proc_lib:init_fail/2,3</code></a> has been called,
│ │ │  or the process has exited.</p><p><a href="" id="debug"></a></p><h3 id="debugging" class="section-heading">
│ │ │    <a href="#debugging" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Debugging</span>
│ │ │  </h3>
│ │ │  <p>To support the debug facilities in <code class="inline">sys</code>, a <em>debug structure</em> is needed. The
│ │ │ -<code class="inline">Deb</code> term is initialized using <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9264391556-1">(</span><span class="n">Parent</span><span class="p" data-group-id="9264391556-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<code class="inline">Deb</code> term is initialized using <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="4741306016-1">(</span><span class="n">Parent</span><span class="p" data-group-id="4741306016-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="9264391556-2">(</span><span class="p" data-group-id="9264391556-3">[</span><span class="p" data-group-id="9264391556-3">]</span><span class="p" data-group-id="9264391556-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Deb</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="4741306016-2">(</span><span class="p" data-group-id="4741306016-3">[</span><span class="p" data-group-id="4741306016-3">]</span><span class="p" data-group-id="4741306016-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="9264391556-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="9264391556-4">)</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a> takes a list of options. Given an empty list as in this
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="4741306016-4">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="4741306016-4">)</span><span class="p">.</span></code></pre><p><a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a> takes a list of options. Given an empty list as in this
│ │ │  example means that debugging is initially disabled. For information about the
│ │ │  possible options, see <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html"><code class="inline">sys</code></a> in STDLIB.</p><p>For each <em>system event</em> to be logged or traced, the following function
│ │ │ -is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="1335244127-1">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Func</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="1335244127-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Deb1</span></code></pre><p>The arguments have the follow meaning:</p><ul><li><code class="inline">Deb</code> is the debug structure as returned from <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>.</li><li><code class="inline">Func</code> is a fun specifying a (user-defined) function used to format trace
│ │ │ +is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="8416839151-1">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Func</span><span class="p">,</span><span class="w"> </span><span class="n">Info</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="8416839151-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Deb1</span></code></pre><p>The arguments have the follow meaning:</p><ul><li><code class="inline">Deb</code> is the debug structure as returned from <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#debug_options/1"><code class="inline">sys:debug_options/1</code></a>.</li><li><code class="inline">Func</code> is a fun specifying a (user-defined) function used to format trace
│ │ │  output. For each system event, the format function is called as
│ │ │  <code class="inline">Func(Dev, Event, Info)</code>, where:<ul><li><code class="inline">Dev</code> is the I/O device to which the output is to be printed. See <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html"><code class="inline">io</code></a>
│ │ │  in STDLIB.</li><li><code class="inline">Event</code> and <code class="inline">Info</code> are passed as-is from the call to <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a>.</li></ul></li><li><code class="inline">Info</code> is used to pass more information to <code class="inline">Func</code>. It can be any term, and it
│ │ │  is passed as-is.</li><li><code class="inline">Event</code> is the system event. It is up to the user to define what a system
│ │ │  event is and how it is to be represented. Typically, at least incoming and
│ │ │  outgoing messages are considered system events and represented by the tuples
│ │ │  <code class="inline">{in,Msg[,From]}</code> and <code class="inline">{out,Msg,To[,State]}</code>, respectively.</li></ul><p><a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a> returns an updated debug structure <code class="inline">Deb1</code>.</p><p>In the example, <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#handle_debug/4"><code class="inline">sys:handle_debug/4</code></a> is called for each incoming and
│ │ │  outgoing message. The format function <code class="inline">Func</code> is the function
│ │ │ -<code class="inline">ch4:write_debug/3</code>, which prints the message using <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/3"><code class="inline">io:format/3</code></a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="8877311070-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="8877311070-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +<code class="inline">ch4:write_debug/3</code>, which prints the message using <a href="../../lib/stdlib-6.2.2.3/doc/html/io.html#format/3"><code class="inline">io:format/3</code></a>.</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="0353927838-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="0353927838-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8877311070-2">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="8877311070-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="8877311070-3">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8877311070-4">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="8877311070-4">}</span><span class="p" data-group-id="8877311070-3">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="8877311070-5">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="8877311070-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="8877311070-6">(</span><span class="n">Chs</span><span class="p" data-group-id="8877311070-6">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8877311070-7">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8877311070-7">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="8877311070-8">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8877311070-9">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8877311070-10">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8877311070-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="8877311070-9">}</span><span class="p" data-group-id="8877311070-8">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="8877311070-11">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="8877311070-11">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8877311070-12">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8877311070-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="8877311070-13">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8877311070-14">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8877311070-15">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="8877311070-15">}</span><span class="p" data-group-id="8877311070-14">}</span><span class="p" data-group-id="8877311070-13">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="8877311070-16">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="8877311070-16">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">loop</span><span class="p" data-group-id="8877311070-17">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="8877311070-17">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0353927838-2">{</span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p" data-group-id="0353927838-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0353927838-3">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0353927838-4">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="ss">alloc</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0353927838-4">}</span><span class="p" data-group-id="0353927838-3">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="0353927838-5">{</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs2</span><span class="p" data-group-id="0353927838-5">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">alloc</span><span class="p" data-group-id="0353927838-6">(</span><span class="n">Chs</span><span class="p" data-group-id="0353927838-6">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">From</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0353927838-7">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0353927838-7">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">Deb3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0353927838-8">(</span><span class="n">Deb2</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0353927838-9">{</span><span class="ss">out</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0353927838-10">{</span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0353927838-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p" data-group-id="0353927838-9">}</span><span class="p" data-group-id="0353927838-8">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0353927838-11">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb3</span><span class="p" data-group-id="0353927838-11">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="0353927838-12">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0353927838-12">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="n">Deb2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_debug</span><span class="p" data-group-id="0353927838-13">(</span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="nc">ch4</span><span class="p">:</span><span class="ss">write_debug</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0353927838-14">{</span><span class="ss">in</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0353927838-15">{</span><span class="ss">free</span><span class="p">,</span><span class="w"> </span><span class="n">Ch</span><span class="p" data-group-id="0353927838-15">}</span><span class="p" data-group-id="0353927838-14">}</span><span class="p" data-group-id="0353927838-13">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="n">Chs2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">free</span><span class="p" data-group-id="0353927838-16">(</span><span class="n">Ch</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="0353927838-16">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">loop</span><span class="p" data-group-id="0353927838-17">(</span><span class="n">Chs2</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb2</span><span class="p" data-group-id="0353927838-17">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">write_debug</span><span class="p" data-group-id="8877311070-18">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="8877311070-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8877311070-19">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8877311070-20">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="8877311070-20">]</span><span class="p" data-group-id="8877311070-19">)</span><span class="p">.</span></code></pre><p><a href="" id="msg"></a></p><h3 id="handling-system-messages" class="section-heading">
│ │ │ +</span><span class="nf">write_debug</span><span class="p" data-group-id="0353927838-18">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p" data-group-id="0353927838-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0353927838-19">(</span><span class="n">Dev</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="si">~p</span><span class="s"> event = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0353927838-20">[</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="0353927838-20">]</span><span class="p" data-group-id="0353927838-19">)</span><span class="p">.</span></code></pre><p><a href="" id="msg"></a></p><h3 id="handling-system-messages" class="section-heading">
│ │ │    <a href="#handling-system-messages" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Handling System Messages</span>
│ │ │  </h3>
│ │ │  <p><em>System messages</em> are received as:</p><pre><code class="text">{system, From, Request}</code></pre><p>The content and meaning of these messages are not to be interpreted by the
│ │ │ -process. Instead the following function is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="7378027422-1">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="7378027422-1">)</span></code></pre><p>The arguments have the following meaning:</p><ul><li><code class="inline">Request</code> and <code class="inline">From</code> from the received system message are to be
│ │ │ +process. Instead the following function is to be called:</p><pre><code class="makeup erlang" translate="no"><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="0380344225-1">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="0380344225-1">)</span></code></pre><p>The arguments have the following meaning:</p><ul><li><code class="inline">Request</code> and <code class="inline">From</code> from the received system message are to be
│ │ │  passed as-is to the call to <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a>.</li><li><code class="inline">Parent</code> is the pid of the parent process.</li><li><code class="inline">Module</code> is the name of the module implementing the speciall process.</li><li><code class="inline">Deb</code> is the debug structure.</li><li><code class="inline">State</code> is a term describing the internal state and is passed on to
│ │ │  <code class="inline">Module:system_continue/3</code>, <code class="inline">Module:system_terminate/4</code>/
│ │ │  <code class="inline">Module:system_get_state/1</code>, and <code class="inline">Module:system_replace_state/2</code>.</li></ul><p><a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a> does not return. It handles the system
│ │ │  message and <em>eventually</em> calls either of the following functions:</p><ul><li><p><code class="inline">Module:system_continue(Parent, Deb, State)</code> - if process execution is to
│ │ │  continue.</p></li><li><p><code class="inline">Module:system_terminate(Reason, Parent, Deb, State)</code> - if the
│ │ │  process is to terminate.</p></li></ul><p>While handling the system message, <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#handle_system_msg/6"><code class="inline">sys:handle_system_msg/6</code></a> can call
│ │ │  one of the following functions:</p><ul><li><p><code class="inline">Module:system_get_state(State)</code> - if the process is to return its state.</p></li><li><p><code class="inline">Module:system_replace_state(StateFun, State)</code> - if the process is
│ │ │  to replace its state using the fun <code class="inline">StateFun</code> fun. See <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#replace_state/3"><code class="inline">sys:replace_state/3</code></a>
│ │ │  for more information.</p></li><li><p><code class="inline">system_code_change(Misc, Module, OldVsn, Extra)</code> - if the process is to
│ │ │  perform a code change.</p></li></ul><p>A process in a supervision tree is expected to terminate with the same reason as
│ │ │ -its parent.</p><p>In the example, system messages are handed by the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="5918801273-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="5918801273-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +its parent.</p><p>In the example, system messages are handed by the following code:</p><pre><code class="makeup erlang" translate="no"><span class="nf">loop</span><span class="p" data-group-id="6907222380-1">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="6907222380-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -        </span><span class="p" data-group-id="5918801273-2">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="5918801273-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="5918801273-3">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ -                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5918801273-3">)</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="6907222380-2">{</span><span class="ss">system</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Request</span><span class="p" data-group-id="6907222380-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">sys</span><span class="p">:</span><span class="nf">handle_system_msg</span><span class="p" data-group-id="6907222380-3">(</span><span class="n">Request</span><span class="p">,</span><span class="w"> </span><span class="n">From</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w">
│ │ │ +                                  </span><span class="ss">ch4</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6907222380-3">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_continue</span><span class="p" data-group-id="5918801273-4">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5918801273-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="5918801273-5">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="5918801273-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_continue</span><span class="p" data-group-id="6907222380-4">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6907222380-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="6907222380-5">(</span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p" data-group-id="6907222380-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_terminate</span><span class="p" data-group-id="5918801273-6">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5918801273-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">exit</span><span class="p" data-group-id="5918801273-7">(</span><span class="n">Reason</span><span class="p" data-group-id="5918801273-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_terminate</span><span class="p" data-group-id="6907222380-6">(</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6907222380-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">exit</span><span class="p" data-group-id="6907222380-7">(</span><span class="n">Reason</span><span class="p" data-group-id="6907222380-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_get_state</span><span class="p" data-group-id="5918801273-8">(</span><span class="n">Chs</span><span class="p" data-group-id="5918801273-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5918801273-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5918801273-9">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">system_get_state</span><span class="p" data-group-id="6907222380-8">(</span><span class="n">Chs</span><span class="p" data-group-id="6907222380-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6907222380-9">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6907222380-9">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">system_replace_state</span><span class="p" data-group-id="5918801273-10">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="5918801273-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="5918801273-11">(</span><span class="n">Chs</span><span class="p" data-group-id="5918801273-11">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5918801273-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="5918801273-12">}</span><span class="p">.</span></code></pre><p>If a special process is configured to trap exits, it must take notice
│ │ │ +</span><span class="nf">system_replace_state</span><span class="p" data-group-id="6907222380-10">(</span><span class="n">StateFun</span><span class="p">,</span><span class="w"> </span><span class="n">Chs</span><span class="p" data-group-id="6907222380-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">NChs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">StateFun</span><span class="p" data-group-id="6907222380-11">(</span><span class="n">Chs</span><span class="p" data-group-id="6907222380-11">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6907222380-12">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p">,</span><span class="w"> </span><span class="n">NChs</span><span class="p" data-group-id="6907222380-12">}</span><span class="p">.</span></code></pre><p>If a special process is configured to trap exits, it must take notice
│ │ │  of 'EXIT' messages from its parent process and terminate using the
│ │ │ -same exit reason once the parent process has terminated.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1674187437-1">(</span><span class="n">Parent</span><span class="p" data-group-id="1674187437-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +same exit reason once the parent process has terminated.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9047268072-1">(</span><span class="n">Parent</span><span class="p" data-group-id="9047268072-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="1674187437-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1674187437-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="9047268072-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9047268072-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="1674187437-3">(</span><span class="n">Parent</span><span class="p" data-group-id="1674187437-3">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="9047268072-3">(</span><span class="n">Parent</span><span class="p" data-group-id="9047268072-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">loop</span><span class="p" data-group-id="1674187437-4">(</span><span class="n">Parent</span><span class="p" data-group-id="1674187437-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">loop</span><span class="p" data-group-id="9047268072-4">(</span><span class="n">Parent</span><span class="p" data-group-id="9047268072-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="1674187437-5">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="1674187437-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="9047268072-5">{</span><span class="ss">&#39;EXIT&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="9047268072-5">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="c1">%% Clean up here, if needed.</span><span class="w">
│ │ │ -            </span><span class="nf">exit</span><span class="p" data-group-id="1674187437-6">(</span><span class="n">Reason</span><span class="p" data-group-id="1674187437-6">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="nf">exit</span><span class="p" data-group-id="9047268072-6">(</span><span class="n">Reason</span><span class="p" data-group-id="9047268072-6">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><h2 id="user-defined-behaviours" class="section-heading">
│ │ │    <a href="#user-defined-behaviours" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">User-Defined Behaviours</span>
│ │ │  </h2>
│ │ │ @@ -448,71 +448,71 @@
│ │ │  function. Note that the <code class="inline">-optional_callbacks</code> attribute is to be used together
│ │ │  with the <code class="inline">-callback</code> attribute; it cannot be combined with the
│ │ │  <code class="inline">behaviour_info()</code> function described below.</p><p>Tools that need to know about optional callback functions can call
│ │ │  <code class="inline">Behaviour:behaviour_info(optional_callbacks)</code> to get a list of all optional
│ │ │  callback functions.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>We recommend using the <code class="inline">-callback</code> attribute rather than the
│ │ │  <code class="inline">behaviour_info()</code> function. The reason is that the extra type information can
│ │ │  be used by tools to produce documentation or find discrepancies.</p></section><p>As an alternative to the <code class="inline">-callback</code> and <code class="inline">-optional_callbacks</code> attributes you
│ │ │ -may directly implement and export <code class="inline">behaviour_info()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="2575027326-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="2575027326-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2575027326-2">[</span><span class="p" data-group-id="2575027326-3">{</span><span class="n">Name1</span><span class="p">,</span><span class="w"> </span><span class="n">Arity1</span><span class="p" data-group-id="2575027326-3">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="p" data-group-id="2575027326-4">{</span><span class="n">NameN</span><span class="p">,</span><span class="w"> </span><span class="n">ArityN</span><span class="p" data-group-id="2575027326-4">}</span><span class="p" data-group-id="2575027326-2">]</span><span class="p">.</span></code></pre><p>where each <code class="inline">{Name, Arity}</code> specifies the name and arity of a callback function.
│ │ │ +may directly implement and export <code class="inline">behaviour_info()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">behaviour_info</span><span class="p" data-group-id="6253015268-1">(</span><span class="ss">callbacks</span><span class="p" data-group-id="6253015268-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6253015268-2">[</span><span class="p" data-group-id="6253015268-3">{</span><span class="n">Name1</span><span class="p">,</span><span class="w"> </span><span class="n">Arity1</span><span class="p" data-group-id="6253015268-3">}</span><span class="p">,</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="p" data-group-id="6253015268-4">{</span><span class="n">NameN</span><span class="p">,</span><span class="w"> </span><span class="n">ArityN</span><span class="p" data-group-id="6253015268-4">}</span><span class="p" data-group-id="6253015268-2">]</span><span class="p">.</span></code></pre><p>where each <code class="inline">{Name, Arity}</code> specifies the name and arity of a callback function.
│ │ │  This function is otherwise automatically generated by the compiler using the
│ │ │  <code class="inline">-callback</code> attributes.</p><p>When the compiler encounters the module attribute <code class="inline">-behaviour(Behaviour).</code> in a
│ │ │  module <code class="inline">Mod</code>, it calls <code class="inline">Behaviour:behaviour_info(callbacks)</code> and compares the
│ │ │  result with the set of functions actually exported from <code class="inline">Mod</code>, and issues a
│ │ │  warning if any callback function is missing.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="c1">%% User-defined behaviour module</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5914560993-1">(</span><span class="ss">simple_server</span><span class="p" data-group-id="5914560993-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5914560993-2">(</span><span class="p" data-group-id="5914560993-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5914560993-3">]</span><span class="p" data-group-id="5914560993-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8533791906-1">(</span><span class="ss">simple_server</span><span class="p" data-group-id="8533791906-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8533791906-2">(</span><span class="p" data-group-id="8533791906-3">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8533791906-3">]</span><span class="p" data-group-id="8533791906-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">init</span><span class="p" data-group-id="5914560993-4">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="5914560993-5">(</span><span class="p" data-group-id="5914560993-5">)</span><span class="p" data-group-id="5914560993-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="5914560993-6">(</span><span class="n">Req</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="5914560993-7">(</span><span class="p" data-group-id="5914560993-7">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="5914560993-8">(</span><span class="p" data-group-id="5914560993-8">)</span><span class="p" data-group-id="5914560993-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5914560993-9">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="5914560993-10">(</span><span class="p" data-group-id="5914560993-10">)</span><span class="p" data-group-id="5914560993-9">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">terminate</span><span class="p" data-group-id="5914560993-11">(</span><span class="p" data-group-id="5914560993-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">format_state</span><span class="p" data-group-id="5914560993-12">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="5914560993-13">(</span><span class="p" data-group-id="5914560993-13">)</span><span class="p" data-group-id="5914560993-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="5914560993-14">(</span><span class="p" data-group-id="5914560993-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">init</span><span class="p" data-group-id="8533791906-4">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="8533791906-5">(</span><span class="p" data-group-id="8533791906-5">)</span><span class="p" data-group-id="8533791906-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="8533791906-6">(</span><span class="n">Req</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="8533791906-7">(</span><span class="p" data-group-id="8533791906-7">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="8533791906-8">(</span><span class="p" data-group-id="8533791906-8">)</span><span class="p" data-group-id="8533791906-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="8533791906-9">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="n">Reply</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="8533791906-10">(</span><span class="p" data-group-id="8533791906-10">)</span><span class="p" data-group-id="8533791906-9">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">terminate</span><span class="p" data-group-id="8533791906-11">(</span><span class="p" data-group-id="8533791906-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">&#39;ok&#39;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">callback</span><span class="w"> </span><span class="nf">format_state</span><span class="p" data-group-id="8533791906-12">(</span><span class="n">State</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="8533791906-13">(</span><span class="p" data-group-id="8533791906-13">)</span><span class="p" data-group-id="8533791906-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="8533791906-14">(</span><span class="p" data-group-id="8533791906-14">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">optional_callbacks</span><span class="p" data-group-id="5914560993-15">(</span><span class="p" data-group-id="5914560993-16">[</span><span class="ss">format_state</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5914560993-16">]</span><span class="p" data-group-id="5914560993-15">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">optional_callbacks</span><span class="p" data-group-id="8533791906-15">(</span><span class="p" data-group-id="8533791906-16">[</span><span class="ss">format_state</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8533791906-16">]</span><span class="p" data-group-id="8533791906-15">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Alternatively you may define:</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% -export([behaviour_info/1]).</span><span class="w">
│ │ │  </span><span class="c1">%% behaviour_info(callbacks) -&gt;</span><span class="w">
│ │ │  </span><span class="c1">%%     [{init,1},</span><span class="w">
│ │ │  </span><span class="c1">%%      {handle_req,2},</span><span class="w">
│ │ │  </span><span class="c1">%%      {terminate,0}].</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="5914560993-17">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="5914560993-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5914560993-18">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5914560993-19">[</span><span class="nf">self</span><span class="p" data-group-id="5914560993-20">(</span><span class="p" data-group-id="5914560993-20">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="5914560993-19">]</span><span class="p" data-group-id="5914560993-18">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="8533791906-17">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="8533791906-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8533791906-18">(</span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="ss">init</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8533791906-19">[</span><span class="nf">self</span><span class="p" data-group-id="8533791906-20">(</span><span class="p" data-group-id="8533791906-20">)</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="8533791906-19">]</span><span class="p" data-group-id="8533791906-18">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="5914560993-21">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="5914560993-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">register</span><span class="p" data-group-id="5914560993-22">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5914560993-23">(</span><span class="p" data-group-id="5914560993-23">)</span><span class="p" data-group-id="5914560993-22">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="8533791906-21">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p" data-group-id="8533791906-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">register</span><span class="p" data-group-id="8533791906-22">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8533791906-23">(</span><span class="p" data-group-id="8533791906-23">)</span><span class="p" data-group-id="8533791906-22">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Dbg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="5914560993-24">(</span><span class="p" data-group-id="5914560993-25">[</span><span class="p" data-group-id="5914560993-25">]</span><span class="p" data-group-id="5914560993-24">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="5914560993-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5914560993-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="5914560993-28">(</span><span class="p" data-group-id="5914560993-28">)</span><span class="p" data-group-id="5914560993-27">}</span><span class="p" data-group-id="5914560993-26">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">loop</span><span class="p" data-group-id="5914560993-29">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5914560993-29">)</span><span class="p">.</span><span class="w">
│ │ │ +    </span><span class="n">Dbg</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">sys</span><span class="p">:</span><span class="nf">debug_options</span><span class="p" data-group-id="8533791906-24">(</span><span class="p" data-group-id="8533791906-25">[</span><span class="p" data-group-id="8533791906-25">]</span><span class="p" data-group-id="8533791906-24">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">proc_lib</span><span class="p">:</span><span class="nf">init_ack</span><span class="p" data-group-id="8533791906-26">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8533791906-27">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="8533791906-28">(</span><span class="p" data-group-id="8533791906-28">)</span><span class="p" data-group-id="8533791906-27">}</span><span class="p" data-group-id="8533791906-26">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">loop</span><span class="p" data-group-id="8533791906-29">(</span><span class="n">Parent</span><span class="p">,</span><span class="w"> </span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Deb</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8533791906-29">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>In a callback module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4835698543-1">(</span><span class="ss">db</span><span class="p" data-group-id="4835698543-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4835698543-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="4835698543-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>In a callback module:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0610041975-1">(</span><span class="ss">db</span><span class="p" data-group-id="0610041975-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0610041975-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="0610041975-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4835698543-3">(</span><span class="p" data-group-id="4835698543-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4835698543-4">]</span><span class="p" data-group-id="4835698543-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0610041975-3">(</span><span class="p" data-group-id="0610041975-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0610041975-4">]</span><span class="p" data-group-id="0610041975-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The contracts specified with <code class="inline">-callback</code> attributes in behaviour modules can be
│ │ │  further refined by adding <code class="inline">-spec</code> attributes in callback modules. This can be
│ │ │  useful as <code class="inline">-callback</code> contracts are usually generic. The same callback module
│ │ │ -with contracts for the callbacks:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0910742246-1">(</span><span class="ss">db</span><span class="p" data-group-id="0910742246-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0910742246-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="0910742246-2">)</span><span class="p">.</span><span class="w">
│ │ │ +with contracts for the callbacks:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3199148404-1">(</span><span class="ss">db</span><span class="p" data-group-id="3199148404-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3199148404-2">(</span><span class="ss">simple_server</span><span class="p" data-group-id="3199148404-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0910742246-3">(</span><span class="p" data-group-id="0910742246-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0910742246-4">]</span><span class="p" data-group-id="0910742246-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3199148404-3">(</span><span class="p" data-group-id="3199148404-4">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">handle_req</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="ss">terminate</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3199148404-4">]</span><span class="p" data-group-id="3199148404-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0910742246-5">(</span><span class="ss">state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0910742246-6">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0910742246-7">[</span><span class="nf">atom</span><span class="p" data-group-id="0910742246-8">(</span><span class="p" data-group-id="0910742246-8">)</span><span class="p" data-group-id="0910742246-7">]</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0910742246-9">(</span><span class="p" data-group-id="0910742246-9">)</span><span class="p" data-group-id="0910742246-6">}</span><span class="p" data-group-id="0910742246-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="3199148404-5">(</span><span class="ss">state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3199148404-6">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3199148404-7">[</span><span class="nf">atom</span><span class="p" data-group-id="3199148404-8">(</span><span class="p" data-group-id="3199148404-8">)</span><span class="p" data-group-id="3199148404-7">]</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="3199148404-9">(</span><span class="p" data-group-id="3199148404-9">)</span><span class="p" data-group-id="3199148404-6">}</span><span class="p" data-group-id="3199148404-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="0910742246-10">(</span><span class="p" data-group-id="0910742246-10">)</span><span class="w">   </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="0910742246-11">{</span><span class="p" data-group-id="0910742246-11">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">request</span><span class="p" data-group-id="0910742246-12">(</span><span class="p" data-group-id="0910742246-12">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0910742246-13">{</span><span class="ss">&#39;store&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0910742246-14">(</span><span class="p" data-group-id="0910742246-14">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0910742246-15">(</span><span class="p" data-group-id="0910742246-15">)</span><span class="p" data-group-id="0910742246-13">}</span><span class="p">;</span><span class="w">
│ │ │ -                   </span><span class="p" data-group-id="0910742246-16">{</span><span class="ss">&#39;lookup&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0910742246-17">(</span><span class="p" data-group-id="0910742246-17">)</span><span class="p" data-group-id="0910742246-16">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="3199148404-10">(</span><span class="p" data-group-id="3199148404-10">)</span><span class="w">   </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">state</span><span class="p" data-group-id="3199148404-11">{</span><span class="p" data-group-id="3199148404-11">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">request</span><span class="p" data-group-id="3199148404-12">(</span><span class="p" data-group-id="3199148404-12">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="3199148404-13">{</span><span class="ss">&#39;store&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3199148404-14">(</span><span class="p" data-group-id="3199148404-14">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3199148404-15">(</span><span class="p" data-group-id="3199148404-15">)</span><span class="p" data-group-id="3199148404-13">}</span><span class="p">;</span><span class="w">
│ │ │ +                   </span><span class="p" data-group-id="3199148404-16">{</span><span class="ss">&#39;lookup&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3199148404-17">(</span><span class="p" data-group-id="3199148404-17">)</span><span class="p" data-group-id="3199148404-16">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="0910742246-18">(</span><span class="nf">request</span><span class="p" data-group-id="0910742246-19">(</span><span class="p" data-group-id="0910742246-19">)</span><span class="p">,</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="0910742246-20">(</span><span class="p" data-group-id="0910742246-20">)</span><span class="p" data-group-id="0910742246-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="0910742246-21">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0910742246-22">(</span><span class="p" data-group-id="0910742246-22">)</span><span class="p" data-group-id="0910742246-21">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">handle_req</span><span class="p" data-group-id="3199148404-18">(</span><span class="nf">request</span><span class="p" data-group-id="3199148404-19">(</span><span class="p" data-group-id="3199148404-19">)</span><span class="p">,</span><span class="w"> </span><span class="nf">state</span><span class="p" data-group-id="3199148404-20">(</span><span class="p" data-group-id="3199148404-20">)</span><span class="p" data-group-id="3199148404-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="3199148404-21">{</span><span class="ss">&#39;ok&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="3199148404-22">(</span><span class="p" data-group-id="3199148404-22">)</span><span class="p" data-group-id="3199148404-21">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Each <code class="inline">-spec</code> contract is to be a subtype of the respective <code class="inline">-callback</code> contract.</p>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/statem.html
│ │ │ @@ -124,15 +124,15 @@
│ │ │  </h2>
│ │ │  <p>Established Automata Theory does not deal much with how a <em>state transition</em>
│ │ │  is triggered, but assumes that the output is a function of the input
│ │ │  (and the state) and that they are some kind of values.</p><p>For an Event-Driven State Machine, the input is an <em>event</em> that triggers
│ │ │  a <em>state transition</em> and the output is actions executed during
│ │ │  the <em>state transition</em>.  Analogously to the mathematical model
│ │ │  of a Finite State Machine, it can be described as a set of relations
│ │ │ -of the following form:</p><pre><code class="makeup erlang" translate="no"><span class="n">State</span><span class="p" data-group-id="1838828114-1">(</span><span class="n">S</span><span class="p" data-group-id="1838828114-1">)</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="1838828114-2">(</span><span class="n">E</span><span class="p" data-group-id="1838828114-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Actions</span><span class="p" data-group-id="1838828114-3">(</span><span class="n">A</span><span class="p" data-group-id="1838828114-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="1838828114-4">(</span><span class="n">S</span><span class="err">&#39;</span><span class="p" data-group-id="1838828114-4">)</span></code></pre><p>These relations are interpreted as follows: if we are in state <code class="inline">S</code>,
│ │ │ +of the following form:</p><pre><code class="makeup erlang" translate="no"><span class="n">State</span><span class="p" data-group-id="4920181357-1">(</span><span class="n">S</span><span class="p" data-group-id="4920181357-1">)</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">Event</span><span class="p" data-group-id="4920181357-2">(</span><span class="n">E</span><span class="p" data-group-id="4920181357-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Actions</span><span class="p" data-group-id="4920181357-3">(</span><span class="n">A</span><span class="p" data-group-id="4920181357-3">)</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p" data-group-id="4920181357-4">(</span><span class="n">S</span><span class="err">&#39;</span><span class="p" data-group-id="4920181357-4">)</span></code></pre><p>These relations are interpreted as follows: if we are in state <code class="inline">S</code>,
│ │ │  and event <code class="inline">E</code> occurs, we are to perform actions <code class="inline">A</code>, and make a transition
│ │ │  to state <code class="inline">S'</code>.  Notice that <code class="inline">S'</code> can be equal to <code class="inline">S</code>,
│ │ │  and that <code class="inline">A</code> can be empty.</p><p>In <code class="inline">gen_statem</code> we define a <em>state change</em> as a <em>state transition</em> in which the
│ │ │  new state <code class="inline">S'</code> is different from the current state <code class="inline">S</code>, where &quot;different&quot; means
│ │ │  Erlang's strict inequality: <code class="inline">=/=</code> also known as &quot;does not match&quot;. <code class="inline">gen_statem</code>
│ │ │  does more things during <em>state changes</em> than during other <em>state transitions</em>.</p><p>As <code class="inline">A</code> and <code class="inline">S'</code> depend only on <code class="inline">S</code> and <code class="inline">E</code>, the kind of state machine described
│ │ │  here is a Mealy machine (see, for example, the Wikipedia article
│ │ │ @@ -405,20 +405,20 @@
│ │ │    </a>
│ │ │    <span class="text">State Enter Calls</span>
│ │ │  </h2>
│ │ │  <p>The <code class="inline">gen_statem</code> behaviour can, if this is enabled, regardless of <em>callback
│ │ │  mode</em>, automatically call the <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#t:state_enter/0"><em>state callback</em></a>
│ │ │  with special arguments whenever the state changes, so you can write
│ │ │  state enter actions near the rest of the <em>state transition</em> rules.
│ │ │ -It typically looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">StateName</span><span class="p" data-group-id="3044793976-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3044793976-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +It typically looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">StateName</span><span class="p" data-group-id="3250689357-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3250689357-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">state</span><span class="w"> </span><span class="ss">enter</span><span class="w"> </span><span class="ss">actions</span><span class="w"> </span><span class="ss">here</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3044793976-2">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="3044793976-2">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">StateName</span><span class="p" data-group-id="3044793976-3">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3044793976-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3250689357-2">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="3250689357-2">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="n">StateName</span><span class="p" data-group-id="3250689357-3">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3250689357-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">actions</span><span class="w"> </span><span class="ss">here</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3044793976-4">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewStateName</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="3044793976-4">}</span><span class="p">.</span></code></pre><p>Since the <em>state enter call</em> is not an event there are restrictions on the
│ │ │ +    </span><span class="p" data-group-id="3250689357-4">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="n">NewStateName</span><span class="p">,</span><span class="w"> </span><span class="n">NewData</span><span class="p" data-group-id="3250689357-4">}</span><span class="p">.</span></code></pre><p>Since the <em>state enter call</em> is not an event there are restrictions on the
│ │ │  allowed return value and state <a href="#transition-actions"><em>transition actions</em></a>.
│ │ │  You must not change the state, <a href="#postponing-events">postpone</a> this non-event,
│ │ │  <a href="#inserted-events">insert any events</a>, or change the
│ │ │  <a href="#callback-module"><em>callback module</em></a>.</p><p>The first state that is entered after <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#c:init/1"><code class="inline">gen_statem:init/1</code></a> will get
│ │ │  a <em>state enter call</em> with <code class="inline">OldState</code> equal to the current state.</p><p>You may repeat the <em>state enter call</em> using the <code class="inline">{repeat_state,...}</code> return
│ │ │  value from the <a href="#state-callback"><em>state callback</em></a>. In this case
│ │ │  <code class="inline">OldState</code> will also be equal to the current state.</p><p>Depending on how your state machine is specified, this can be a very useful
│ │ │ @@ -499,72 +499,72 @@
│ │ │  
│ │ │      locked      --&gt; check_code : {button, Button}\n* Collect Buttons
│ │ │      check_code  --&gt; locked     : Incorrect code
│ │ │      check_code  --&gt; open       : Correct code\n* do_unlock()\n* Clear Buttons\n* Set state_timeout 10 s
│ │ │  
│ │ │      open        --&gt; open   : {button, Digit}
│ │ │      open        --&gt; locked : state_timeout\n* do_lock()</code></pre><p>This code lock state machine can be implemented using <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html"><code class="inline">gen_statem</code></a> with
│ │ │ -the following <em>callback module</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="8692360486-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="8692360486-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="8692360486-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="8692360486-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8692360486-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock</span><span class="p" data-group-id="8692360486-3">)</span><span class="p">.</span><span class="w">
│ │ │ +the following <em>callback module</em>:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2308535727-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="2308535727-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2308535727-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="2308535727-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2308535727-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock</span><span class="p" data-group-id="2308535727-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8692360486-4">(</span><span class="p" data-group-id="8692360486-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8692360486-5">]</span><span class="p" data-group-id="8692360486-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8692360486-6">(</span><span class="p" data-group-id="8692360486-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="8692360486-7">]</span><span class="p" data-group-id="8692360486-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8692360486-8">(</span><span class="p" data-group-id="8692360486-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="8692360486-9">]</span><span class="p" data-group-id="8692360486-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8692360486-10">(</span><span class="p" data-group-id="8692360486-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="8692360486-11">]</span><span class="p" data-group-id="8692360486-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="8692360486-12">(</span><span class="n">Code</span><span class="p" data-group-id="8692360486-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8692360486-13">(</span><span class="p" data-group-id="8692360486-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="8692360486-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8692360486-15">[</span><span class="p" data-group-id="8692360486-15">]</span><span class="p" data-group-id="8692360486-13">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="8692360486-16">(</span><span class="n">Button</span><span class="p" data-group-id="8692360486-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="8692360486-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8692360486-18">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8692360486-18">}</span><span class="p" data-group-id="8692360486-17">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="8692360486-19">(</span><span class="n">Code</span><span class="p" data-group-id="8692360486-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="8692360486-20">(</span><span class="p" data-group-id="8692360486-20">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8692360486-21">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8692360486-22">(</span><span class="n">Code</span><span class="p" data-group-id="8692360486-22">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8692360486-23">[</span><span class="p" data-group-id="8692360486-23">]</span><span class="p" data-group-id="8692360486-21">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8692360486-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8692360486-24">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="8692360486-25">(</span><span class="p" data-group-id="8692360486-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="1299835820-1">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1299835820-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1299835820-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1299835820-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1299835820-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1299835820-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2308535727-4">(</span><span class="p" data-group-id="2308535727-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2308535727-5">]</span><span class="p" data-group-id="2308535727-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2308535727-6">(</span><span class="p" data-group-id="2308535727-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2308535727-7">]</span><span class="p" data-group-id="2308535727-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2308535727-8">(</span><span class="p" data-group-id="2308535727-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="2308535727-9">]</span><span class="p" data-group-id="2308535727-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2308535727-10">(</span><span class="p" data-group-id="2308535727-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="2308535727-11">]</span><span class="p" data-group-id="2308535727-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="2308535727-12">(</span><span class="n">Code</span><span class="p" data-group-id="2308535727-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2308535727-13">(</span><span class="p" data-group-id="2308535727-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="2308535727-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2308535727-15">[</span><span class="p" data-group-id="2308535727-15">]</span><span class="p" data-group-id="2308535727-13">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="2308535727-16">(</span><span class="n">Button</span><span class="p" data-group-id="2308535727-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="2308535727-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2308535727-18">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2308535727-18">}</span><span class="p" data-group-id="2308535727-17">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="2308535727-19">(</span><span class="n">Code</span><span class="p" data-group-id="2308535727-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="2308535727-20">(</span><span class="p" data-group-id="2308535727-20">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2308535727-21">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="2308535727-22">(</span><span class="n">Code</span><span class="p" data-group-id="2308535727-22">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="2308535727-23">[</span><span class="p" data-group-id="2308535727-23">]</span><span class="p" data-group-id="2308535727-21">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2308535727-24">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2308535727-24">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="2308535727-25">(</span><span class="p" data-group-id="2308535727-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="4997438632-1">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4997438632-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4997438632-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4997438632-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4997438632-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4997438632-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="1299835820-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="1299835820-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="4997438632-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="4997438632-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="1299835820-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="1299835820-5">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1299835820-6">[</span><span class="n">Button</span><span class="p" data-group-id="1299835820-6">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="4997438632-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="4997438632-5">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4997438632-6">[</span><span class="n">Button</span><span class="p" data-group-id="4997438632-6">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="1299835820-7">(</span><span class="p" data-group-id="1299835820-7">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="1299835820-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1299835820-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1299835820-10">[</span><span class="p" data-group-id="1299835820-10">]</span><span class="p" data-group-id="1299835820-9">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="1299835820-11">[</span><span class="p" data-group-id="1299835820-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1299835820-12">}</span><span class="p" data-group-id="1299835820-11">]</span><span class="p" data-group-id="1299835820-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="4997438632-7">(</span><span class="p" data-group-id="4997438632-7">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="4997438632-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4997438632-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4997438632-10">[</span><span class="p" data-group-id="4997438632-10">]</span><span class="p" data-group-id="4997438632-9">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="4997438632-11">[</span><span class="p" data-group-id="4997438632-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="4997438632-12">}</span><span class="p" data-group-id="4997438632-11">]</span><span class="p" data-group-id="4997438632-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="1299835820-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1299835820-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="1299835820-14">}</span><span class="p" data-group-id="1299835820-13">}</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="0804835906-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="0804835906-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="0804835906-2">(</span><span class="p" data-group-id="0804835906-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0804835906-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0804835906-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="0804835906-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0804835906-5">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0804835906-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0804835906-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0804835906-6">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0804835906-6">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="3340778249-1">(</span><span class="p" data-group-id="3340778249-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3340778249-2">(</span><span class="s">&quot;Lock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3340778249-3">[</span><span class="p" data-group-id="3340778249-3">]</span><span class="p" data-group-id="3340778249-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="3340778249-4">(</span><span class="p" data-group-id="3340778249-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3340778249-5">(</span><span class="s">&quot;Unlock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3340778249-6">[</span><span class="p" data-group-id="3340778249-6">]</span><span class="p" data-group-id="3340778249-5">)</span><span class="p">.</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="4997438632-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4997438632-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="4997438632-14">}</span><span class="p" data-group-id="4997438632-13">}</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="2074509949-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="2074509949-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="2074509949-2">(</span><span class="p" data-group-id="2074509949-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2074509949-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2074509949-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="2074509949-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2074509949-5">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2074509949-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2074509949-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2074509949-6">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2074509949-6">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="8004528503-1">(</span><span class="p" data-group-id="8004528503-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8004528503-2">(</span><span class="s">&quot;Lock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8004528503-3">[</span><span class="p" data-group-id="8004528503-3">]</span><span class="p" data-group-id="8004528503-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="8004528503-4">(</span><span class="p" data-group-id="8004528503-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8004528503-5">(</span><span class="s">&quot;Unlock</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8004528503-6">[</span><span class="p" data-group-id="8004528503-6">]</span><span class="p" data-group-id="8004528503-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="3340778249-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3340778249-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="3340778249-8">(</span><span class="p" data-group-id="3340778249-8">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="8004528503-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="8004528503-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="8004528503-8">(</span><span class="p" data-group-id="8004528503-8">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><p>The code is explained in the next sections.</p><h2 id="starting-gen_statem" class="section-heading">
│ │ │    <a href="#starting-gen_statem" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting gen_statem</span>
│ │ │  </h2>
│ │ │  <p>In the example in the previous section, <code class="inline">gen_statem</code> is started by calling
│ │ │ -<code class="inline">code_lock:start_link(Code)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="1015876464-1">(</span><span class="n">Code</span><span class="p" data-group-id="1015876464-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="1015876464-2">(</span><span class="p" data-group-id="1015876464-3">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="1015876464-3">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1015876464-4">[</span><span class="p" data-group-id="1015876464-4">]</span><span class="p" data-group-id="1015876464-2">)</span><span class="p">.</span></code></pre><p><code class="inline">start_link/1</code> calls function <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/4</code></a>,
│ │ │ +<code class="inline">code_lock:start_link(Code)</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="0916693200-1">(</span><span class="n">Code</span><span class="p" data-group-id="0916693200-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0916693200-2">(</span><span class="p" data-group-id="0916693200-3">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="0916693200-3">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0916693200-4">[</span><span class="p" data-group-id="0916693200-4">]</span><span class="p" data-group-id="0916693200-2">)</span><span class="p">.</span></code></pre><p><code class="inline">start_link/1</code> calls function <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/4</code></a>,
│ │ │  which spawns and links to a new process, a <code class="inline">gen_statem</code>.</p><ul><li><p>The first argument, <code class="inline">{local,?NAME}</code>, specifies the name. In this case, the
│ │ │  <code class="inline">gen_statem</code> is locally registered as <code class="inline">code_lock</code> through the macro <code class="inline">?NAME</code>.</p><p>If the name is omitted, the <code class="inline">gen_statem</code> is not registered. Instead its pid
│ │ │  must be used. The name can also be specified as <code class="inline">{global, Name}</code>, then the
│ │ │  <code class="inline">gen_statem</code> is registered using <a href="../../lib/kernel-10.2.7.4/doc/html/global.html#register_name/2"><code class="inline">global:register_name/2</code></a> in Kernel.</p></li><li><p>The second argument, <code class="inline">?MODULE</code>, is the name of the <em>callback module</em>,
│ │ │  that is, the module where the callback functions are located,
│ │ │  which is this module.</p><p>The interface functions (<code class="inline">start_link/1</code> and <code class="inline">button/1</code>) are located in the
│ │ │  same module as the callback functions (<code class="inline">init/1</code>, <code class="inline">locked/3</code>, and <code class="inline">open/3</code>).
│ │ │ @@ -574,184 +574,184 @@
│ │ │  see <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3</code></a>.</p></li></ul><p>If name registration succeeds, the new <code class="inline">gen_statem</code> process calls callback
│ │ │  function <code class="inline">code_lock:init(Code)</code>. This function is expected to return
│ │ │  <code class="inline">{ok, State, Data}</code>, where <code class="inline">State</code> is the initial state of the <code class="inline">gen_statem</code>,
│ │ │  in this case <code class="inline">locked</code>; assuming that the door is locked to begin with.
│ │ │  <code class="inline">Data</code> is the internal server data of the <code class="inline">gen_statem</code>. Here the server data
│ │ │  is a <a href="../../lib/stdlib-6.2.2.3/doc/html/maps.html"><code class="inline">map()</code></a> with key <code class="inline">code</code> that stores the correct
│ │ │  button sequence, key <code class="inline">length</code> store its length, and key <code class="inline">buttons</code>
│ │ │ -that stores the collected buttons up to the same length.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1355392917-1">(</span><span class="n">Code</span><span class="p" data-group-id="1355392917-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="1355392917-2">(</span><span class="p" data-group-id="1355392917-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1355392917-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1355392917-4">(</span><span class="n">Code</span><span class="p" data-group-id="1355392917-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1355392917-5">[</span><span class="p" data-group-id="1355392917-5">]</span><span class="p" data-group-id="1355392917-3">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1355392917-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1355392917-6">}</span><span class="p">.</span></code></pre><p>Function <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │ +that stores the collected buttons up to the same length.</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7701986693-1">(</span><span class="n">Code</span><span class="p" data-group-id="7701986693-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="7701986693-2">(</span><span class="p" data-group-id="7701986693-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7701986693-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="7701986693-4">(</span><span class="n">Code</span><span class="p" data-group-id="7701986693-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7701986693-5">[</span><span class="p" data-group-id="7701986693-5">]</span><span class="p" data-group-id="7701986693-3">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7701986693-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7701986693-6">}</span><span class="p">.</span></code></pre><p>Function <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │  is synchronous. It does not return until the <code class="inline">gen_statem</code> is initialized
│ │ │  and is ready to receive events.</p><p>Function <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#start_link/3"><code class="inline">gen_statem:start_link/3,4</code></a>
│ │ │  must be used if the <code class="inline">gen_statem</code> is part of a supervision tree, that is,
│ │ │  started by a supervisor.  Function,
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#start/3"><code class="inline">gen_statem:start/3,4</code></a> can be used to start
│ │ │  a standalone <code class="inline">gen_statem</code>, meaning it is not part of a supervision tree.</p><p>Function <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#c:callback_mode/0"><code class="inline">Module:callback_mode/0</code></a> selects
│ │ │  the <a href="#callback-modes"><code class="inline">CallbackMode</code></a> for the <em>callback module</em>,
│ │ │  in this case <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#t:callback_mode/0"><code class="inline">state_functions</code></a>.
│ │ │ -That is, each state has its own handler function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="0417142351-1">(</span><span class="p" data-group-id="0417142351-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +That is, each state has its own handler function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="1223317722-1">(</span><span class="p" data-group-id="1223317722-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">state_functions</span><span class="p">.</span></code></pre><h2 id="handling-events" class="section-heading">
│ │ │    <a href="#handling-events" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Handling Events</span>
│ │ │  </h2>
│ │ │  <p>The function notifying the code lock about a button event is implemented using
│ │ │ -<a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#cast/2"><code class="inline">gen_statem:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">button</span><span class="p" data-group-id="5813436620-1">(</span><span class="n">Button</span><span class="p" data-group-id="5813436620-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="5813436620-2">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5813436620-3">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5813436620-3">}</span><span class="p" data-group-id="5813436620-2">)</span><span class="p">.</span></code></pre><p>The first argument is the name of the <code class="inline">gen_statem</code> and must agree with
│ │ │ +<a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#cast/2"><code class="inline">gen_statem:cast/2</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">button</span><span class="p" data-group-id="2149670196-1">(</span><span class="n">Button</span><span class="p" data-group-id="2149670196-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="2149670196-2">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2149670196-3">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2149670196-3">}</span><span class="p" data-group-id="2149670196-2">)</span><span class="p">.</span></code></pre><p>The first argument is the name of the <code class="inline">gen_statem</code> and must agree with
│ │ │  the name used to start it. So, we use the same macro <code class="inline">?NAME</code> as when starting.
│ │ │  <code class="inline">{button, Button}</code> is the event content.</p><p>The event is sent to the <code class="inline">gen_statem</code>. When the event is received, the
│ │ │  <code class="inline">gen_statem</code> calls <code class="inline">StateName(cast, Event, Data)</code>, which is expected
│ │ │  to return a tuple <code class="inline">{next_state, NewStateName, NewData}</code>, or
│ │ │  <code class="inline">{next_state, NewStateName, NewData, Actions}</code>. <code class="inline">StateName</code> is the name
│ │ │  of the current state and <code class="inline">NewStateName</code> is the name of the next state.
│ │ │  <code class="inline">NewData</code> is a new value for the server data of the <code class="inline">gen_statem</code>,
│ │ │ -and <code class="inline">Actions</code> is a list of actions to be performed by the <code class="inline">gen_statem</code> engine.</p><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="1451238925-1">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1451238925-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1451238925-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1451238925-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1451238925-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1451238925-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +and <code class="inline">Actions</code> is a list of actions to be performed by the <code class="inline">gen_statem</code> engine.</p><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="4990485532-1">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4990485532-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4990485532-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4990485532-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4990485532-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4990485532-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="1451238925-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="1451238925-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="4990485532-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="4990485532-4">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="1451238925-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="1451238925-5">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="1451238925-6">[</span><span class="n">Button</span><span class="p" data-group-id="1451238925-6">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="4990485532-5">(</span><span class="n">Buttons</span><span class="p" data-group-id="4990485532-5">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="4990485532-6">[</span><span class="n">Button</span><span class="p" data-group-id="4990485532-6">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="1451238925-7">(</span><span class="p" data-group-id="1451238925-7">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="1451238925-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1451238925-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1451238925-10">[</span><span class="p" data-group-id="1451238925-10">]</span><span class="p" data-group-id="1451238925-9">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="1451238925-11">[</span><span class="p" data-group-id="1451238925-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1451238925-12">}</span><span class="p" data-group-id="1451238925-11">]</span><span class="p" data-group-id="1451238925-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="4990485532-7">(</span><span class="p" data-group-id="4990485532-7">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="4990485532-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4990485532-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4990485532-10">[</span><span class="p" data-group-id="4990485532-10">]</span><span class="p" data-group-id="4990485532-9">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="4990485532-11">[</span><span class="p" data-group-id="4990485532-12">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="4990485532-12">}</span><span class="p" data-group-id="4990485532-11">]</span><span class="p" data-group-id="4990485532-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="1451238925-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1451238925-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="1451238925-14">}</span><span class="p" data-group-id="1451238925-13">}</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="4990485532-13">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4990485532-14">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="4990485532-14">}</span><span class="p" data-group-id="4990485532-13">}</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>In state <code class="inline">locked</code>, when a button is pressed, it is collected with the
│ │ │  previously pressed buttons up to the length of the correct code, then
│ │ │  compared with the correct code. Depending on the result, the door is
│ │ │  either unlocked and the <code class="inline">gen_statem</code> goes to state <code class="inline">open</code>, or the door
│ │ │  remains in state <code class="inline">locked</code>.</p><p>When changing to state <code class="inline">open</code>, the collected buttons are reset, the lock
│ │ │ -unlocked, and a <em>state time-out</em> for 10 seconds is started.</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="2254900392-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2254900392-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2254900392-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2254900392-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2254900392-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2254900392-3">}</span><span class="p">.</span></code></pre><p>In state <code class="inline">open</code>, a button event is ignored by staying in the same state.
│ │ │ +unlocked, and a <em>state time-out</em> for 10 seconds is started.</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="4509723571-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4509723571-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="4509723571-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4509723571-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4509723571-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4509723571-3">}</span><span class="p">.</span></code></pre><p>In state <code class="inline">open</code>, a button event is ignored by staying in the same state.
│ │ │  This can also be done by returning <code class="inline">{keep_state, Data}</code>, or in this case
│ │ │  since <code class="inline">Data</code> is unchanged, by returning <code class="inline">keep_state_and_data</code>.</p><h2 id="state-time-outs" class="section-heading">
│ │ │    <a href="#state-time-outs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">State Time-Outs</span>
│ │ │  </h2>
│ │ │  <p>When a correct code has been given, the door is unlocked and the following
│ │ │ -tuple is returned from <code class="inline">locked/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9154394671-1">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9154394671-2">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9154394671-3">[</span><span class="p" data-group-id="9154394671-3">]</span><span class="p" data-group-id="9154394671-2">}</span><span class="p">,</span><span class="w">
│ │ │ - </span><span class="p" data-group-id="9154394671-4">[</span><span class="p" data-group-id="9154394671-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="9154394671-5">}</span><span class="p" data-group-id="9154394671-4">]</span><span class="p" data-group-id="9154394671-1">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span></code></pre><p>10,000 is a time-out value in milliseconds. After this time (10 seconds),
│ │ │ +tuple is returned from <code class="inline">locked/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1467237301-1">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1467237301-2">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="1467237301-3">[</span><span class="p" data-group-id="1467237301-3">]</span><span class="p" data-group-id="1467237301-2">}</span><span class="p">,</span><span class="w">
│ │ │ + </span><span class="p" data-group-id="1467237301-4">[</span><span class="p" data-group-id="1467237301-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1467237301-5">}</span><span class="p" data-group-id="1467237301-4">]</span><span class="p" data-group-id="1467237301-1">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span></code></pre><p>10,000 is a time-out value in milliseconds. After this time (10 seconds),
│ │ │  a time-out occurs. Then, <code class="inline">StateName(state_timeout, lock, Data)</code> is called.
│ │ │  The time-out occurs when the door has been in state <code class="inline">open</code> for 10 seconds.
│ │ │ -After that the door is locked again:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="7343432680-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="7343432680-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="7343432680-2">(</span><span class="p" data-group-id="7343432680-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7343432680-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7343432680-3">}</span><span class="p">;</span></code></pre><p>The timer for a <em>state time-out</em> is automatically canceled when
│ │ │ +After that the door is locked again:</p><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="8965981233-1">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w">  </span><span class="n">Data</span><span class="p" data-group-id="8965981233-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="8965981233-2">(</span><span class="p" data-group-id="8965981233-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8965981233-3">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8965981233-3">}</span><span class="p">;</span></code></pre><p>The timer for a <em>state time-out</em> is automatically canceled when
│ │ │  the state machine does a <em>state change</em>.</p><p>You can restart, cancel, or update a <em>state time-out</em>. See section
│ │ │  <a href="#time-outs"><em>Time-Outs</em></a> for details.</p><h2 id="all-state-events" class="section-heading">
│ │ │    <a href="#all-state-events" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">All State Events</span>
│ │ │  </h2>
│ │ │  <p>Sometimes events can arrive in any state of the <code class="inline">gen_statem</code>. It is convenient
│ │ │  to handle these in a common state handler function that all state functions
│ │ │  call for events not specific to the state.</p><p>Consider a <code class="inline">code_length/0</code> function that returns the length
│ │ │  of the correct code.  We dispatch all events that are not state-specific
│ │ │  to the common function <code class="inline">handle_common/3</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5293514028-1">(</span><span class="p" data-group-id="5293514028-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5293514028-2">]</span><span class="p" data-group-id="5293514028-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5833263697-1">(</span><span class="p" data-group-id="5833263697-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5833263697-2">]</span><span class="p" data-group-id="5833263697-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="5293514028-3">(</span><span class="p" data-group-id="5293514028-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="5293514028-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="5293514028-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="5833263697-3">(</span><span class="p" data-group-id="5833263697-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="5833263697-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="5833263697-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="5293514028-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5293514028-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="5293514028-6">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5293514028-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">handle_common</span><span class="p" data-group-id="5293514028-7">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5293514028-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="5833263697-5">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5833263697-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="5833263697-6">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5833263697-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">handle_common</span><span class="p" data-group-id="5833263697-7">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5833263697-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5293514028-8">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5293514028-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="5293514028-9">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5293514028-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">handle_common</span><span class="p" data-group-id="5293514028-10">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5293514028-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="5293514028-11">(</span><span class="p" data-group-id="5293514028-12">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="5293514028-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5293514028-13">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="5293514028-13">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5293514028-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5293514028-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="5293514028-15">[</span><span class="p" data-group-id="5293514028-16">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="5293514028-17">(</span><span class="n">Code</span><span class="p" data-group-id="5293514028-17">)</span><span class="p" data-group-id="5293514028-16">}</span><span class="p" data-group-id="5293514028-15">]</span><span class="p" data-group-id="5293514028-14">}</span><span class="p">.</span></code></pre><p>Another way to do it is through a convenience macro <code class="inline">?HANDLE_COMMON/0</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="8399938575-1">(</span><span class="p" data-group-id="8399938575-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="8399938575-2">]</span><span class="p" data-group-id="8399938575-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="5833263697-8">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="5833263697-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="5833263697-9">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5833263697-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">handle_common</span><span class="p" data-group-id="5833263697-10">(</span><span class="n">EventType</span><span class="p">,</span><span class="w"> </span><span class="n">EventContent</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5833263697-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="5833263697-11">(</span><span class="p" data-group-id="5833263697-12">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="5833263697-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5833263697-13">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="5833263697-13">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5833263697-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5833263697-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="5833263697-15">[</span><span class="p" data-group-id="5833263697-16">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="5833263697-17">(</span><span class="n">Code</span><span class="p" data-group-id="5833263697-17">)</span><span class="p" data-group-id="5833263697-16">}</span><span class="p" data-group-id="5833263697-15">]</span><span class="p" data-group-id="5833263697-14">}</span><span class="p">.</span></code></pre><p>Another way to do it is through a convenience macro <code class="inline">?HANDLE_COMMON/0</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3242419643-1">(</span><span class="p" data-group-id="3242419643-2">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3242419643-2">]</span><span class="p" data-group-id="3242419643-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="8399938575-3">(</span><span class="p" data-group-id="8399938575-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="8399938575-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="8399938575-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="3242419643-3">(</span><span class="p" data-group-id="3242419643-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3242419643-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="3242419643-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8399938575-5">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="8399938575-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="8399938575-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="8399938575-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="8399938575-7">)</span><span class="p" data-group-id="8399938575-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3242419643-5">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="3242419643-6">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="3242419643-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="3242419643-7">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="3242419643-7">)</span><span class="p" data-group-id="3242419643-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="8399938575-8">(</span><span class="p" data-group-id="8399938575-9">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="8399938575-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8399938575-10">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="8399938575-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8399938575-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="8399938575-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="8399938575-12">[</span><span class="p" data-group-id="8399938575-13">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="8399938575-14">(</span><span class="n">Code</span><span class="p" data-group-id="8399938575-14">)</span><span class="p" data-group-id="8399938575-13">}</span><span class="p" data-group-id="8399938575-12">]</span><span class="p" data-group-id="8399938575-11">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="3242419643-8">(</span><span class="p" data-group-id="3242419643-9">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="3242419643-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3242419643-10">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="3242419643-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3242419643-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3242419643-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="3242419643-12">[</span><span class="p" data-group-id="3242419643-13">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="3242419643-14">(</span><span class="n">Code</span><span class="p" data-group-id="3242419643-14">)</span><span class="p" data-group-id="3242419643-13">}</span><span class="p" data-group-id="3242419643-12">]</span><span class="p" data-group-id="3242419643-11">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="8399938575-15">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8399938575-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="3242419643-15">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3242419643-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="8399938575-16">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="8399938575-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="3242419643-16">(</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p" data-group-id="3242419643-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="p">;</span><span class="w">
│ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><p>This example uses <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#call/2"><code class="inline">gen_statem:call/2</code></a>, which waits for a reply from the server.
│ │ │  The reply is sent with a <code class="inline">{reply, From, Reply}</code> tuple in an action list in the
│ │ │  <code class="inline">{keep_state, ...}</code> tuple that retains the current state. This return form is
│ │ │  convenient when you want to stay in the current state but do not know or care
│ │ │  about what it is.</p><p>If the common <em>state callback</em> needs to know the current state a function
│ │ │ -<code class="inline">handle_common/4</code> can be used instead:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1264563998-1">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="1264563998-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="1264563998-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="1264563998-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="1264563998-3">)</span><span class="p" data-group-id="1264563998-1">)</span><span class="p">.</span></code></pre><h2 id="one-state-callback" class="section-heading">
│ │ │ +<code class="inline">handle_common/4</code> can be used instead:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="9213997996-1">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="9213997996-2">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9213997996-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="9213997996-3">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="9213997996-3">)</span><span class="p" data-group-id="9213997996-1">)</span><span class="p">.</span></code></pre><h2 id="one-state-callback" class="section-heading">
│ │ │    <a href="#one-state-callback" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">One State Callback</span>
│ │ │  </h2>
│ │ │  <p>If <a href="#callback-modes"><em>callback mode</em></a> <code class="inline">handle_event_function</code> is used,
│ │ │  all events are handled in
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#c:handle_event/4"><code class="inline">Module:handle_event/4</code></a> and we can
│ │ │  (but do not have to) use an event-centered approach where we first branch
│ │ │  depending on event and then depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5427686432-1">(</span><span class="p" data-group-id="5427686432-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="5427686432-2">]</span><span class="p" data-group-id="5427686432-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7356045831-1">(</span><span class="p" data-group-id="7356045831-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="7356045831-2">]</span><span class="p" data-group-id="7356045831-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="5427686432-3">(</span><span class="p" data-group-id="5427686432-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="7356045831-3">(</span><span class="p" data-group-id="7356045831-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="ss">handle_event_function</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5427686432-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5427686432-5">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5427686432-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5427686432-6">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="5427686432-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5427686432-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7356045831-4">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7356045831-5">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7356045831-5">}</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7356045831-6">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="7356045831-6">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7356045831-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">State</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │  	</span><span class="ss">locked</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="5427686432-7">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="5427686432-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="7356045831-7">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7356045831-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │                  </span><span class="k">if</span><span class="w">
│ │ │ -                    </span><span class="nf">length</span><span class="p" data-group-id="5427686432-8">(</span><span class="n">Buttons</span><span class="p" data-group-id="5427686432-8">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                    </span><span class="nf">length</span><span class="p" data-group-id="7356045831-8">(</span><span class="n">Buttons</span><span class="p" data-group-id="7356045831-8">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                          </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │                      </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                        </span><span class="nf">tl</span><span class="p" data-group-id="5427686432-9">(</span><span class="n">Buttons</span><span class="p" data-group-id="5427686432-9">)</span><span class="w">
│ │ │ -                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="5427686432-10">[</span><span class="n">Button</span><span class="p" data-group-id="5427686432-10">]</span><span class="p">,</span><span class="w">
│ │ │ +                        </span><span class="nf">tl</span><span class="p" data-group-id="7356045831-9">(</span><span class="n">Buttons</span><span class="p" data-group-id="7356045831-9">)</span><span class="w">
│ │ │ +                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="7356045831-10">[</span><span class="n">Button</span><span class="p" data-group-id="7356045831-10">]</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="k">if</span><span class="w">
│ │ │                  </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="5427686432-11">(</span><span class="p" data-group-id="5427686432-11">)</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="5427686432-12">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5427686432-13">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5427686432-14">[</span><span class="p" data-group-id="5427686432-14">]</span><span class="p" data-group-id="5427686432-13">}</span><span class="p">,</span><span class="w">
│ │ │ -                     </span><span class="p" data-group-id="5427686432-15">[</span><span class="p" data-group-id="5427686432-16">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="5427686432-16">}</span><span class="p" data-group-id="5427686432-15">]</span><span class="p" data-group-id="5427686432-12">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="7356045831-11">(</span><span class="p" data-group-id="7356045831-11">)</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="7356045831-12">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7356045831-13">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7356045831-14">[</span><span class="p" data-group-id="7356045831-14">]</span><span class="p" data-group-id="7356045831-13">}</span><span class="p">,</span><span class="w">
│ │ │ +                     </span><span class="p" data-group-id="7356045831-15">[</span><span class="p" data-group-id="7356045831-16">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="7356045831-16">}</span><span class="p" data-group-id="7356045831-15">]</span><span class="p" data-group-id="7356045831-12">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │                  </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -                    </span><span class="p" data-group-id="5427686432-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5427686432-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="5427686432-18">}</span><span class="p" data-group-id="5427686432-17">}</span><span class="w">
│ │ │ +                    </span><span class="p" data-group-id="7356045831-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7356045831-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="7356045831-18">}</span><span class="p" data-group-id="7356045831-17">}</span><span class="w">
│ │ │              </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">open</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5427686432-19">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5427686432-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="5427686432-20">(</span><span class="p" data-group-id="5427686432-20">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5427686432-21">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5427686432-21">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="5427686432-22">(</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="5427686432-23">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="5427686432-23">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5427686432-24">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="5427686432-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5427686432-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="5427686432-25">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="5427686432-26">[</span><span class="p" data-group-id="5427686432-27">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="5427686432-28">(</span><span class="n">Code</span><span class="p" data-group-id="5427686432-28">)</span><span class="p" data-group-id="5427686432-27">}</span><span class="p" data-group-id="5427686432-26">]</span><span class="p" data-group-id="5427686432-25">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7356045831-19">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7356045831-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="7356045831-20">(</span><span class="p" data-group-id="7356045831-20">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7356045831-21">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7356045831-21">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="7356045831-22">(</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7356045831-23">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="7356045831-23">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7356045831-24">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="7356045831-24">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7356045831-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7356045831-25">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="7356045831-26">[</span><span class="p" data-group-id="7356045831-27">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="7356045831-28">(</span><span class="n">Code</span><span class="p" data-group-id="7356045831-28">)</span><span class="p" data-group-id="7356045831-27">}</span><span class="p" data-group-id="7356045831-26">]</span><span class="p" data-group-id="7356045831-25">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><h2 id="stopping" class="section-heading">
│ │ │    <a href="#stopping" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Stopping</span>
│ │ │  </h2>
│ │ │ @@ -763,59 +763,59 @@
│ │ │  </h3>
│ │ │  <p>If the <code class="inline">gen_statem</code> is part of a supervision tree, no stop function is needed.
│ │ │  The <code class="inline">gen_statem</code> is automatically terminated by its supervisor. Exactly how
│ │ │  this is done is defined by a <a href="sup_princ.html#shutdown">shutdown strategy</a>
│ │ │  set in the supervisor.</p><p>If it is necessary to clean up before termination, the shutdown strategy
│ │ │  must be a time-out value and the <code class="inline">gen_statem</code> must in function <code class="inline">init/1</code>
│ │ │  set itself to trap exit signals by calling
│ │ │ -<a href="../../erts-15.2.7.8/doc/html/erlang.html#process_flag/2"><code class="inline">process_flag(trap_exit, true)</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7226164857-1">(</span><span class="n">Args</span><span class="p" data-group-id="7226164857-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="7226164857-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="7226164857-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="7226164857-3">(</span><span class="p" data-group-id="7226164857-3">)</span><span class="p">,</span><span class="w">
│ │ │ +<a href="../../erts-15.2.7.8/doc/html/erlang.html#process_flag/2"><code class="inline">process_flag(trap_exit, true)</code></a>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="1880969022-1">(</span><span class="n">Args</span><span class="p" data-group-id="1880969022-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="1880969022-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1880969022-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="1880969022-3">(</span><span class="p" data-group-id="1880969022-3">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>When ordered to shut down, the <code class="inline">gen_statem</code> then calls callback function
│ │ │  <code class="inline">terminate(shutdown, State, Data)</code>.</p><p>In this example, function <code class="inline">terminate/3</code> locks the door if it is open,
│ │ │  so we do not accidentally leave the door open
│ │ │ -when the supervision tree terminates:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="0117389388-1">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="0117389388-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="0117389388-2">(</span><span class="p" data-group-id="0117389388-2">)</span><span class="p">,</span><span class="w">
│ │ │ +when the supervision tree terminates:</p><pre><code class="makeup erlang" translate="no"><span class="nf">terminate</span><span class="p" data-group-id="2594497422-1">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2594497422-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="2594497422-2">(</span><span class="p" data-group-id="2594497422-2">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="standalone-gen_statem" class="section-heading">
│ │ │    <a href="#standalone-gen_statem" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Standalone gen_statem</span>
│ │ │  </h3>
│ │ │  <p>If the <code class="inline">gen_statem</code> is not part of a supervision tree, it can be stopped
│ │ │  using <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#stop/1"><code class="inline">gen_statem:stop/1</code></a>, preferably through
│ │ │  an API function:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6495464946-1">(</span><span class="p" data-group-id="6495464946-2">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6495464946-2">]</span><span class="p" data-group-id="6495464946-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4473276113-1">(</span><span class="p" data-group-id="4473276113-2">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4473276113-2">]</span><span class="p" data-group-id="4473276113-1">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="6495464946-3">(</span><span class="p" data-group-id="6495464946-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="6495464946-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="6495464946-4">)</span><span class="p">.</span></code></pre><p>This makes the <code class="inline">gen_statem</code> call callback function <code class="inline">terminate/3</code> just like
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="4473276113-3">(</span><span class="p" data-group-id="4473276113-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="4473276113-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4473276113-4">)</span><span class="p">.</span></code></pre><p>This makes the <code class="inline">gen_statem</code> call callback function <code class="inline">terminate/3</code> just like
│ │ │  for a supervised server and waits for the process to terminate.</p><h2 id="event-time-outs" class="section-heading">
│ │ │    <a href="#event-time-outs" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Event Time-Outs</span>
│ │ │  </h2>
│ │ │  <p>A time-out feature inherited from <code class="inline">gen_statem</code>'s predecessor <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_fsm.html"><code class="inline">gen_fsm</code></a>,
│ │ │  is an <em>event time-out</em>, that is, if an event arrives the timer is canceled.
│ │ │  You get either an event or a time-out, but not both.</p><p>It is ordered by the
│ │ │  <a href="#transition-actions"><em>transition action</em></a> <code class="inline">{timeout, Time, EventContent}</code>,
│ │ │  or just an integer <code class="inline">Time</code>, even without the enclosing actions list (the latter
│ │ │  is a form inherited from <code class="inline">gen_fsm</code>).</p><p>This type of time-out is useful, for example, to act on inactivity.
│ │ │  Let's restart the code sequence if no button is pressed for say 30 seconds:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="4693316639-1">(</span><span class="ss">timeout</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693316639-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4693316639-2">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693316639-3">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="4693316639-4">[</span><span class="p" data-group-id="4693316639-4">]</span><span class="p" data-group-id="4693316639-3">}</span><span class="p" data-group-id="4693316639-2">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="4693316639-5">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4693316639-6">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4693316639-6">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4693316639-7">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4693316639-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693316639-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="5581747062-1">(</span><span class="ss">timeout</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5581747062-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5581747062-2">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5581747062-3">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5581747062-4">[</span><span class="p" data-group-id="5581747062-4">]</span><span class="p" data-group-id="5581747062-3">}</span><span class="p" data-group-id="5581747062-2">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="5581747062-5">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5581747062-6">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5581747062-6">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5581747062-7">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="5581747062-7">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5581747062-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4693316639-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4693316639-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="4693316639-9">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p" data-group-id="4693316639-8">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="5581747062-8">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5581747062-9">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="5581747062-9">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p" data-group-id="5581747062-8">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Whenever we receive a button event we start an <em>event time-out</em> of 30 seconds,
│ │ │  and if we get an <em>event type</em> of <code class="inline">timeout</code> we reset the remaining
│ │ │  code sequence.</p><p>An <em>event time-out</em> is canceled by any other event so you either get
│ │ │  some other event or the time-out event. Therefore, canceling,
│ │ │  restarting, or updating an <em>event time-out</em> is neither possible nor
│ │ │  necessary. Whatever event you act on has already canceled
│ │ │  the <em>event time-out</em>, so there is never a running <em>event time-out</em>
│ │ │ @@ -834,30 +834,30 @@
│ │ │  another, maybe cancel the time-out without changing states, or perhaps run
│ │ │  multiple time-outs in parallel. All this can be accomplished with
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#t:generic_timeout/0"><em>generic time-outs</em></a>. They may look a little
│ │ │  bit like <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#t:event_timeout/0"><em>event time-outs</em></a> but contain
│ │ │  a name to allow for any number of them simultaneously and they are
│ │ │  not automatically canceled.</p><p>Here is how to accomplish the <em>state time-out</em> in the previous example
│ │ │  by instead using a <em>generic time-out</em> named for example <code class="inline">open</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="7993334860-1">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7993334860-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7993334860-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="7993334860-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7993334860-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7993334860-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="5145923078-1">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5145923078-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5145923078-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5145923078-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="5145923078-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5145923078-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="7993334860-4">(</span><span class="p" data-group-id="7993334860-4">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="7993334860-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7993334860-6">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="7993334860-7">[</span><span class="p" data-group-id="7993334860-7">]</span><span class="p" data-group-id="7993334860-6">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="7993334860-8">[</span><span class="p" data-group-id="7993334860-9">{</span><span class="p" data-group-id="7993334860-10">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="7993334860-10">}</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="7993334860-9">}</span><span class="p" data-group-id="7993334860-8">]</span><span class="p" data-group-id="7993334860-5">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="5145923078-4">(</span><span class="p" data-group-id="5145923078-4">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="5145923078-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5145923078-6">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="5145923078-7">[</span><span class="p" data-group-id="5145923078-7">]</span><span class="p" data-group-id="5145923078-6">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="5145923078-8">[</span><span class="p" data-group-id="5145923078-9">{</span><span class="p" data-group-id="5145923078-10">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="5145923078-10">}</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="5145923078-9">}</span><span class="p" data-group-id="5145923078-8">]</span><span class="p" data-group-id="5145923078-5">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="7993334860-11">(</span><span class="p" data-group-id="7993334860-12">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="7993334860-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7993334860-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="7993334860-13">(</span><span class="p" data-group-id="7993334860-13">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7993334860-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="7993334860-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="7993334860-15">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7993334860-16">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="7993334860-16">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7993334860-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7993334860-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="7993334860-17">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="5145923078-11">(</span><span class="p" data-group-id="5145923078-12">{</span><span class="ss">timeout</span><span class="p">,</span><span class="ss">open</span><span class="p" data-group-id="5145923078-12">}</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5145923078-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="5145923078-13">(</span><span class="p" data-group-id="5145923078-13">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5145923078-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="5145923078-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="5145923078-15">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5145923078-16">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="5145923078-16">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="5145923078-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5145923078-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="5145923078-17">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Specific <em>generic time-outs</em> can just as <a href="#state-time-outs"><em>state time-outs</em></a>
│ │ │  be restarted or canceled by setting it to a new time or <code class="inline">infinity</code>.</p><p>In this particular case we do not need to cancel the time-out since
│ │ │  the time-out event is the only possible reason to do a <em>state change</em>
│ │ │  from <code class="inline">open</code> to <code class="inline">locked</code>.</p><p>Instead of bothering with when to cancel a time-out, a late time-out event
│ │ │  can be handled by ignoring it if it arrives in a state
│ │ │  where it is known to be late.</p><p>You can restart, cancel, or update a <em>generic time-out</em>.
│ │ │  See section <a href="#time-outs"><em>Time-Outs</em></a> for details.</p><h2 id="erlang-timers" class="section-heading">
│ │ │ @@ -869,32 +869,32 @@
│ │ │  <p>The most versatile way to handle time-outs is to use Erlang Timers; see
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#start_timer/4"><code class="inline">erlang:start_timer/3,4</code></a>. Most time-out tasks
│ │ │  can be performed with the time-out features in <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html"><code class="inline">gen_statem</code></a>,
│ │ │  but an example of one that cannot is if you should need the return value
│ │ │  from <a href="../../erts-15.2.7.8/doc/html/erlang.html#cancel_timer/2"><code class="inline">erlang:cancel_timer(Tref)</code></a>, that is,
│ │ │  the remaining time of the timer.</p><p>Here is how to accomplish the <em>state time-out</em> in the previous example
│ │ │  by instead using an Erlang Timer:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="0024736181-1">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0024736181-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0024736181-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0024736181-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="0024736181-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0024736181-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="6810417098-1">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6810417098-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6810417098-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="6810417098-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="6810417098-3">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6810417098-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="0024736181-4">(</span><span class="p" data-group-id="0024736181-4">)</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="nf">do_unlock</span><span class="p" data-group-id="6810417098-4">(</span><span class="p" data-group-id="6810417098-4">)</span><span class="p">,</span><span class="w">
│ │ │  	    </span><span class="n">Tref</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -                 </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">start_timer</span><span class="p" data-group-id="0024736181-5">(</span><span class="w">
│ │ │ -                     </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0024736181-6">(</span><span class="p" data-group-id="0024736181-6">)</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p" data-group-id="0024736181-5">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="0024736181-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0024736181-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="0024736181-9">[</span><span class="p" data-group-id="0024736181-9">]</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="0024736181-8">}</span><span class="p" data-group-id="0024736181-7">}</span><span class="p">;</span><span class="w">
│ │ │ +                 </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">start_timer</span><span class="p" data-group-id="6810417098-5">(</span><span class="w">
│ │ │ +                     </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="6810417098-6">(</span><span class="p" data-group-id="6810417098-6">)</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p" data-group-id="6810417098-5">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="6810417098-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6810417098-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="6810417098-9">[</span><span class="p" data-group-id="6810417098-9">]</span><span class="p">,</span><span class="w"> </span><span class="ss">timer</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="6810417098-8">}</span><span class="p" data-group-id="6810417098-7">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="0024736181-10">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0024736181-11">{</span><span class="ss">timeout</span><span class="p">,</span><span class="n">Tref</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="0024736181-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0024736181-12">#{</span><span class="ss">timer</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="0024736181-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0024736181-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="0024736181-13">(</span><span class="p" data-group-id="0024736181-13">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0024736181-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="0024736181-15">(</span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0024736181-15">)</span><span class="p" data-group-id="0024736181-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="0024736181-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0024736181-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="0024736181-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0024736181-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0024736181-18">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="0024736181-18">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="6810417098-10">(</span><span class="ss">info</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6810417098-11">{</span><span class="ss">timeout</span><span class="p">,</span><span class="n">Tref</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="6810417098-11">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6810417098-12">#{</span><span class="ss">timer</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Tref</span><span class="p" data-group-id="6810417098-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6810417098-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="6810417098-13">(</span><span class="p" data-group-id="6810417098-13">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6810417098-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="ss">locked</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="6810417098-15">(</span><span class="ss">timer</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6810417098-15">)</span><span class="p" data-group-id="6810417098-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="6810417098-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6810417098-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6810417098-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6810417098-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="6810417098-18">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="6810417098-18">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Removing the <code class="inline">timer</code> key from the map when we do a <em>state change</em> to <code class="inline">locked</code>
│ │ │  is not strictly necessary since we can only get into state <code class="inline">open</code>
│ │ │  with an updated <code class="inline">timer</code> map value. But it can be nice to not have
│ │ │  outdated values in the state <code class="inline">Data</code>.</p><p>If you need to cancel a timer because of some other event, you can use
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#cancel_timer/2"><code class="inline">erlang:cancel_timer(Tref)</code></a>. Note that no time-out
│ │ │  message will arrive after this (because the timer has been
│ │ │  explicitly canceled), unless you have already postponed one earlier
│ │ │ @@ -910,16 +910,16 @@
│ │ │    <span class="text">Postponing Events</span>
│ │ │  </h2>
│ │ │  <p>If you want to ignore a particular event in the current state and handle it
│ │ │  in a future state, you can postpone the event. A postponed event
│ │ │  is retried after a <em>state change</em>, that is, <code class="inline">OldState =/= NewState</code>.</p><p>Postponing is ordered by the
│ │ │  <a href="#transition-actions"><em>transition action</em></a> <code class="inline">postpone</code>.</p><p>In this example, instead of ignoring button events while in the <code class="inline">open</code> state,
│ │ │  we can postpone them handle them later in the <code class="inline">locked</code> state:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="3971244476-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3971244476-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3971244476-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3971244476-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3971244476-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="3971244476-4">[</span><span class="ss">postpone</span><span class="p" data-group-id="3971244476-4">]</span><span class="p" data-group-id="3971244476-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="8945292254-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8945292254-2">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8945292254-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8945292254-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8945292254-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="8945292254-4">[</span><span class="ss">postpone</span><span class="p" data-group-id="8945292254-4">]</span><span class="p" data-group-id="8945292254-3">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>Since a postponed event is only retried after a <em>state change</em>, you have to
│ │ │  think about where to keep a state data item. You can keep it in the server
│ │ │  <code class="inline">Data</code> or in the <code class="inline">State</code> itself, for example by having two more or less
│ │ │  identical states to keep a boolean value, or by using a complex state (see
│ │ │  section <a href="#complex-state"><em>Complex State</em></a>) with
│ │ │  <a href="#callback-modes"><em>callback mode</em></a>
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#t:callback_mode/0"><code class="inline">handle_event_function</code></a>. If a change
│ │ │ @@ -940,55 +940,55 @@
│ │ │    <a href="#selective-receive" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Selective Receive</span>
│ │ │  </h3>
│ │ │  <p>Erlang's selective <code class="inline">receive</code> statement is often used to describe simple state
│ │ │  machine examples in straightforward Erlang code. The following is a possible
│ │ │ -implementation of the first example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="1021470594-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="1021470594-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="1021470594-2">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_1</span><span class="p" data-group-id="1021470594-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1021470594-3">(</span><span class="p" data-group-id="1021470594-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1021470594-4">]</span><span class="p" data-group-id="1021470594-3">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="1021470594-5">(</span><span class="n">Code</span><span class="p" data-group-id="1021470594-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">spawn</span><span class="p" data-group-id="1021470594-6">(</span><span class="w">
│ │ │ -      </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1021470594-7">(</span><span class="p" data-group-id="1021470594-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">register</span><span class="p" data-group-id="1021470594-8">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="1021470594-9">(</span><span class="p" data-group-id="1021470594-9">)</span><span class="p" data-group-id="1021470594-8">)</span><span class="p">,</span><span class="w">
│ │ │ -	      </span><span class="nf">do_lock</span><span class="p" data-group-id="1021470594-10">(</span><span class="p" data-group-id="1021470594-10">)</span><span class="p">,</span><span class="w">
│ │ │ -	      </span><span class="nf">locked</span><span class="p" data-group-id="1021470594-11">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1021470594-12">(</span><span class="n">Code</span><span class="p" data-group-id="1021470594-12">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1021470594-13">[</span><span class="p" data-group-id="1021470594-13">]</span><span class="p" data-group-id="1021470594-11">)</span><span class="w">
│ │ │ -      </span><span class="k">end</span><span class="p" data-group-id="1021470594-6">)</span><span class="p">.</span><span class="w">
│ │ │ +implementation of the first example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0918307238-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="0918307238-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="0918307238-2">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_1</span><span class="p" data-group-id="0918307238-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0918307238-3">(</span><span class="p" data-group-id="0918307238-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0918307238-4">]</span><span class="p" data-group-id="0918307238-3">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="0918307238-5">(</span><span class="n">Code</span><span class="p" data-group-id="0918307238-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">spawn</span><span class="p" data-group-id="0918307238-6">(</span><span class="w">
│ │ │ +      </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0918307238-7">(</span><span class="p" data-group-id="0918307238-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +	      </span><span class="ss">true</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">register</span><span class="p" data-group-id="0918307238-8">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="nf">self</span><span class="p" data-group-id="0918307238-9">(</span><span class="p" data-group-id="0918307238-9">)</span><span class="p" data-group-id="0918307238-8">)</span><span class="p">,</span><span class="w">
│ │ │ +	      </span><span class="nf">do_lock</span><span class="p" data-group-id="0918307238-10">(</span><span class="p" data-group-id="0918307238-10">)</span><span class="p">,</span><span class="w">
│ │ │ +	      </span><span class="nf">locked</span><span class="p" data-group-id="0918307238-11">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="0918307238-12">(</span><span class="n">Code</span><span class="p" data-group-id="0918307238-12">)</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0918307238-13">[</span><span class="p" data-group-id="0918307238-13">]</span><span class="p" data-group-id="0918307238-11">)</span><span class="w">
│ │ │ +      </span><span class="k">end</span><span class="p" data-group-id="0918307238-6">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="1021470594-14">(</span><span class="n">Button</span><span class="p" data-group-id="1021470594-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">NAME</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="1021470594-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1021470594-15">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="9402832655-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9402832655-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="0918307238-14">(</span><span class="n">Button</span><span class="p" data-group-id="0918307238-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">NAME</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="0918307238-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0918307238-15">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="2881347390-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="2881347390-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="9402832655-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9402832655-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2881347390-2">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2881347390-2">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │                  </span><span class="k">if</span><span class="w">
│ │ │ -                    </span><span class="nf">length</span><span class="p" data-group-id="9402832655-3">(</span><span class="n">Buttons</span><span class="p" data-group-id="9402832655-3">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                    </span><span class="nf">length</span><span class="p" data-group-id="2881347390-3">(</span><span class="n">Buttons</span><span class="p" data-group-id="2881347390-3">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                          </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │                      </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                        </span><span class="nf">tl</span><span class="p" data-group-id="9402832655-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="9402832655-4">)</span><span class="w">
│ │ │ -                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9402832655-5">[</span><span class="n">Button</span><span class="p" data-group-id="9402832655-5">]</span><span class="p">,</span><span class="w">
│ │ │ +                        </span><span class="nf">tl</span><span class="p" data-group-id="2881347390-4">(</span><span class="n">Buttons</span><span class="p" data-group-id="2881347390-4">)</span><span class="w">
│ │ │ +                </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2881347390-5">[</span><span class="n">Button</span><span class="p" data-group-id="2881347390-5">]</span><span class="p">,</span><span class="w">
│ │ │              </span><span class="k">if</span><span class="w">
│ │ │                  </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="9402832655-6">(</span><span class="p" data-group-id="9402832655-6">)</span><span class="p">,</span><span class="w">
│ │ │ -		    </span><span class="nf">open</span><span class="p" data-group-id="9402832655-7">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="9402832655-7">)</span><span class="p">;</span><span class="w">
│ │ │ +                    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2881347390-6">(</span><span class="p" data-group-id="2881347390-6">)</span><span class="p">,</span><span class="w">
│ │ │ +		    </span><span class="nf">open</span><span class="p" data-group-id="2881347390-7">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="2881347390-7">)</span><span class="p">;</span><span class="w">
│ │ │                  </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -                    </span><span class="nf">locked</span><span class="p" data-group-id="9402832655-8">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="9402832655-8">)</span><span class="w">
│ │ │ +                    </span><span class="nf">locked</span><span class="p" data-group-id="2881347390-8">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="2881347390-8">)</span><span class="w">
│ │ │              </span><span class="k">end</span><span class="w">
│ │ │ -    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="0586215997-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="0586215997-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="k">end</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="1828597310-1">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="1828597310-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">receive</span><span class="w">
│ │ │      </span><span class="k">after</span><span class="w"> </span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -	    </span><span class="nf">do_lock</span><span class="p" data-group-id="0586215997-2">(</span><span class="p" data-group-id="0586215997-2">)</span><span class="p">,</span><span class="w">
│ │ │ -	    </span><span class="nf">locked</span><span class="p" data-group-id="0586215997-3">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0586215997-4">[</span><span class="p" data-group-id="0586215997-4">]</span><span class="p" data-group-id="0586215997-3">)</span><span class="w">
│ │ │ +	    </span><span class="nf">do_lock</span><span class="p" data-group-id="1828597310-2">(</span><span class="p" data-group-id="1828597310-2">)</span><span class="p">,</span><span class="w">
│ │ │ +	    </span><span class="nf">locked</span><span class="p" data-group-id="1828597310-3">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1828597310-4">[</span><span class="p" data-group-id="1828597310-4">]</span><span class="p" data-group-id="1828597310-3">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">do_lock</span><span class="p" data-group-id="0586215997-5">(</span><span class="p" data-group-id="0586215997-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0586215997-6">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0586215997-7">[</span><span class="p" data-group-id="0586215997-7">]</span><span class="p" data-group-id="0586215997-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="0586215997-8">(</span><span class="p" data-group-id="0586215997-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="0586215997-9">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0586215997-10">[</span><span class="p" data-group-id="0586215997-10">]</span><span class="p" data-group-id="0586215997-9">)</span><span class="p">.</span></code></pre><p>The selective receive in this case causes <code class="inline">open</code> to implicitly postpone any
│ │ │ +</span><span class="nf">do_lock</span><span class="p" data-group-id="1828597310-5">(</span><span class="p" data-group-id="1828597310-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1828597310-6">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1828597310-7">[</span><span class="p" data-group-id="1828597310-7">]</span><span class="p" data-group-id="1828597310-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="1828597310-8">(</span><span class="p" data-group-id="1828597310-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1828597310-9">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1828597310-10">[</span><span class="p" data-group-id="1828597310-10">]</span><span class="p" data-group-id="1828597310-9">)</span><span class="p">.</span></code></pre><p>The selective receive in this case causes <code class="inline">open</code> to implicitly postpone any
│ │ │  events to the <code class="inline">locked</code> state.</p><p>A catch-all receive should never be used from a <code class="inline">gen_statem</code> behaviour
│ │ │  (or from any <code class="inline">gen_*</code> behaviour), as the receive statement is within
│ │ │  the <code class="inline">gen_*</code> engine itself. <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html"><code class="inline">sys</code></a>-compatible behaviours must respond to
│ │ │  system messages and therefore do that in their engine receive loop,
│ │ │  passing non-system messages to the <em>callback module</em>. Using a catch-all
│ │ │  receive can result in system messages being discarded, which in turn
│ │ │  can lead to unexpected behaviour. If a selective receive must be used,
│ │ │ @@ -1011,40 +1011,40 @@
│ │ │  section), especially if only one or a few states have state enter actions,
│ │ │  this is a perfect use case for the built in
│ │ │  <a href="#state-enter-calls"><em>state enter calls</em></a>.</p><p>You return a list containing <code class="inline">state_enter</code> from your
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#c:callback_mode/0"><code class="inline">callback_mode/0</code></a> function and the
│ │ │  <code class="inline">gen_statem</code> engine will call your <em>state callback</em> once with an event
│ │ │  <code class="inline">(enter, OldState, ...)</code> whenever it does a <em>state change</em>. Then you
│ │ │  just need to handle these event-like calls in all states.</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="4126430401-1">(</span><span class="n">Code</span><span class="p" data-group-id="4126430401-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="4126430401-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="4126430401-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4126430401-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="4126430401-4">(</span><span class="n">Code</span><span class="p" data-group-id="4126430401-4">)</span><span class="p" data-group-id="4126430401-3">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4126430401-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4126430401-5">}</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="4126430401-6">(</span><span class="p" data-group-id="4126430401-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4126430401-7">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="4126430401-7">]</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="4126430401-8">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4126430401-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="4126430401-9">(</span><span class="p" data-group-id="4126430401-9">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4126430401-10">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="4126430401-11">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4126430401-12">[</span><span class="p" data-group-id="4126430401-12">]</span><span class="p" data-group-id="4126430401-11">}</span><span class="p" data-group-id="4126430401-10">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="4126430401-13">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4126430401-14">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4126430401-14">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4126430401-15">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="4126430401-15">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4126430401-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="1959515964-1">(</span><span class="n">Code</span><span class="p" data-group-id="1959515964-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="1959515964-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="1959515964-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1959515964-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="1959515964-4">(</span><span class="n">Code</span><span class="p" data-group-id="1959515964-4">)</span><span class="p" data-group-id="1959515964-3">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1959515964-5">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1959515964-5">}</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="1959515964-6">(</span><span class="p" data-group-id="1959515964-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1959515964-7">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="1959515964-7">]</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="1959515964-8">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1959515964-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="1959515964-9">(</span><span class="p" data-group-id="1959515964-9">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1959515964-10">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="1959515964-11">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1959515964-12">[</span><span class="p" data-group-id="1959515964-12">]</span><span class="p" data-group-id="1959515964-11">}</span><span class="p" data-group-id="1959515964-10">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="1959515964-13">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1959515964-14">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1959515964-14">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="1959515964-15">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1959515964-15">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1959515964-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4126430401-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4126430401-16">}</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="1959515964-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1959515964-16">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="4126430401-17">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="4126430401-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="4126430401-18">(</span><span class="p" data-group-id="4126430401-18">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4126430401-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="4126430401-20">[</span><span class="p" data-group-id="4126430401-21">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="4126430401-21">}</span><span class="p" data-group-id="4126430401-20">]</span><span class="p" data-group-id="4126430401-19">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="4126430401-22">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4126430401-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4126430401-23">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4126430401-23">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="1959515964-17">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1959515964-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="1959515964-18">(</span><span class="p" data-group-id="1959515964-18">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1959515964-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="1959515964-20">[</span><span class="p" data-group-id="1959515964-21">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1959515964-21">}</span><span class="p" data-group-id="1959515964-20">]</span><span class="p" data-group-id="1959515964-19">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="1959515964-22">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1959515964-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1959515964-23">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1959515964-23">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>You can repeat the state enter code by returning one of
│ │ │  <code class="inline">{repeat_state, ...}</code>,<code class="inline">{repeat_state_and_data, _}</code>,
│ │ │  or <code class="inline">repeat_state_and_data</code> that otherwise behaves exactly like their
│ │ │  <code class="inline">keep_state</code> siblings.  See the type
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#t:state_callback_result/2"><code class="inline">state_callback_result()</code></a>
│ │ │  in the Reference Manual.</p><h2 id="inserted-events" class="section-heading">
│ │ │    <a href="#inserted-events" class="hover-link">
│ │ │ @@ -1066,44 +1066,44 @@
│ │ │  to dispatch pre-processed events as internal events to the main state
│ │ │  machine.</p><p>Using internal events also can make it easier to synchronize the state
│ │ │  machines.</p><p>A variant of this is to use a <a href="#complex-state">complex state</a> with
│ │ │  <a href="#one-state-callback">one state callback</a>, modeling the state
│ │ │  with, for example, a tuple <code class="inline">{MainFSMState, SubFSMState}</code>.</p><p>To illustrate this we make up an example where the buttons instead generate
│ │ │  down and up (press and release) events, and the lock responds
│ │ │  to an up event only after the corresponding down event.</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="1691735193-1">(</span><span class="p" data-group-id="1691735193-2">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="1691735193-2">]</span><span class="p" data-group-id="1691735193-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="7669955241-1">(</span><span class="p" data-group-id="7669955241-2">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="7669955241-2">]</span><span class="p" data-group-id="7669955241-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">down</span><span class="p" data-group-id="1691735193-3">(</span><span class="n">Button</span><span class="p" data-group-id="1691735193-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1691735193-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1691735193-5">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1691735193-5">}</span><span class="p" data-group-id="1691735193-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">down</span><span class="p" data-group-id="7669955241-3">(</span><span class="n">Button</span><span class="p" data-group-id="7669955241-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="7669955241-4">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7669955241-5">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7669955241-5">}</span><span class="p" data-group-id="7669955241-4">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">up</span><span class="p" data-group-id="1691735193-6">(</span><span class="n">Button</span><span class="p" data-group-id="1691735193-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="1691735193-7">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1691735193-8">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1691735193-8">}</span><span class="p" data-group-id="1691735193-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">up</span><span class="p" data-group-id="7669955241-6">(</span><span class="n">Button</span><span class="p" data-group-id="7669955241-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="7669955241-7">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7669955241-8">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7669955241-8">}</span><span class="p" data-group-id="7669955241-7">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="1691735193-9">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1691735193-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="1691735193-10">(</span><span class="p" data-group-id="1691735193-10">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1691735193-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="1691735193-12">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="1691735193-13">[</span><span class="p" data-group-id="1691735193-13">]</span><span class="p" data-group-id="1691735193-12">}</span><span class="p" data-group-id="1691735193-11">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="1691735193-14">(</span><span class="w">
│ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1691735193-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="1691735193-15">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1691735193-16">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="1691735193-16">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1691735193-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">handle_common</span><span class="p" data-group-id="6263501158-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6263501158-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6263501158-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6263501158-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6263501158-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6263501158-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="6263501158-4">}</span><span class="p" data-group-id="6263501158-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="6263501158-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6263501158-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6263501158-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6263501158-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="7669955241-9">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7669955241-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="7669955241-10">(</span><span class="p" data-group-id="7669955241-10">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7669955241-11">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="7669955241-12">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7669955241-13">[</span><span class="p" data-group-id="7669955241-13">]</span><span class="p" data-group-id="7669955241-12">}</span><span class="p" data-group-id="7669955241-11">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="7669955241-14">(</span><span class="w">
│ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7669955241-15">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="7669955241-15">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="7669955241-16">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="7669955241-16">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="7669955241-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">handle_common</span><span class="p" data-group-id="2017722425-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2017722425-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2017722425-2">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2017722425-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2017722425-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2017722425-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2017722425-4">}</span><span class="p" data-group-id="2017722425-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="2017722425-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2017722425-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2017722425-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2017722425-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6263501158-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="6263501158-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="6263501158-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="6263501158-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6263501158-9">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="6263501158-10">[</span><span class="p" data-group-id="6263501158-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="6263501158-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6263501158-12">}</span><span class="p" data-group-id="6263501158-11">}</span><span class="p" data-group-id="6263501158-10">]</span><span class="p" data-group-id="6263501158-8">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6263501158-13">#{</span><span class="p" data-group-id="6263501158-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2017722425-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2017722425-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2017722425-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="2017722425-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2017722425-9">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="2017722425-10">[</span><span class="p" data-group-id="2017722425-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="2017722425-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2017722425-12">}</span><span class="p" data-group-id="2017722425-11">}</span><span class="p" data-group-id="2017722425-10">]</span><span class="p" data-group-id="2017722425-8">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2017722425-13">#{</span><span class="p" data-group-id="2017722425-13">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="6263501158-14">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6263501158-15">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6263501158-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6263501158-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6263501158-16">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="6263501158-17">[</span><span class="ss">postpone</span><span class="p" data-group-id="6263501158-17">]</span><span class="p" data-group-id="6263501158-16">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="2017722425-14">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2017722425-15">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2017722425-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2017722425-14">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2017722425-16">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="n">Data</span><span class="p">,</span><span class="p" data-group-id="2017722425-17">[</span><span class="ss">postpone</span><span class="p" data-group-id="2017722425-17">]</span><span class="p" data-group-id="2017722425-16">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>If you start this program with <code class="inline">code_lock:start([17])</code> you can unlock with
│ │ │  <code class="inline">code_lock:down(17), code_lock:up(17).</code></p><h2 id="example-revisited" class="section-heading">
│ │ │    <a href="#example-revisited" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example Revisited</span>
│ │ │  </h2>
│ │ │ @@ -1131,152 +1131,152 @@
│ │ │  Also, the state diagram does not show that the <code class="inline">code_length/0</code> call
│ │ │  must be handled in every state.</p><h3 id="callback-mode-state_functions" class="section-heading">
│ │ │    <a href="#callback-mode-state_functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Callback Mode: state_functions</span>
│ │ │  </h3>
│ │ │ -<p>Using state functions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4246086280-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="4246086280-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4246086280-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="4246086280-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="4246086280-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_2</span><span class="p" data-group-id="4246086280-3">)</span><span class="p">.</span><span class="w">
│ │ │ +<p>Using state functions:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="3831191358-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="3831191358-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="3831191358-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="3831191358-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="3831191358-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_2</span><span class="p" data-group-id="3831191358-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4246086280-4">(</span><span class="p" data-group-id="4246086280-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4246086280-5">]</span><span class="p" data-group-id="4246086280-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4246086280-6">(</span><span class="p" data-group-id="4246086280-7">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4246086280-7">]</span><span class="p" data-group-id="4246086280-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4246086280-8">(</span><span class="p" data-group-id="4246086280-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4246086280-9">]</span><span class="p" data-group-id="4246086280-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4246086280-10">(</span><span class="p" data-group-id="4246086280-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="4246086280-11">]</span><span class="p" data-group-id="4246086280-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="4246086280-12">(</span><span class="n">Code</span><span class="p" data-group-id="4246086280-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4246086280-13">(</span><span class="p" data-group-id="4246086280-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4246086280-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4246086280-15">[</span><span class="p" data-group-id="4246086280-15">]</span><span class="p" data-group-id="4246086280-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="4246086280-16">(</span><span class="p" data-group-id="4246086280-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="4246086280-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="4246086280-17">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">down</span><span class="p" data-group-id="4246086280-18">(</span><span class="n">Button</span><span class="p" data-group-id="4246086280-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4246086280-19">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4246086280-20">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4246086280-20">}</span><span class="p" data-group-id="4246086280-19">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">up</span><span class="p" data-group-id="4246086280-21">(</span><span class="n">Button</span><span class="p" data-group-id="4246086280-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="4246086280-22">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4246086280-23">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4246086280-23">}</span><span class="p" data-group-id="4246086280-22">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">code_length</span><span class="p" data-group-id="4246086280-24">(</span><span class="p" data-group-id="4246086280-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="4246086280-25">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="4246086280-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="6523961296-1">(</span><span class="n">Code</span><span class="p" data-group-id="6523961296-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="6523961296-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="6523961296-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6523961296-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="6523961296-4">(</span><span class="n">Code</span><span class="p" data-group-id="6523961296-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6523961296-5">[</span><span class="p" data-group-id="6523961296-5">]</span><span class="p" data-group-id="6523961296-3">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6523961296-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6523961296-6">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3831191358-4">(</span><span class="p" data-group-id="3831191358-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3831191358-5">]</span><span class="p" data-group-id="3831191358-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3831191358-6">(</span><span class="p" data-group-id="3831191358-7">[</span><span class="ss">down</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">up</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">code_length</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="3831191358-7">]</span><span class="p" data-group-id="3831191358-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3831191358-8">(</span><span class="p" data-group-id="3831191358-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="3831191358-9">]</span><span class="p" data-group-id="3831191358-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3831191358-10">(</span><span class="p" data-group-id="3831191358-11">[</span><span class="ss">locked</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">open</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="3831191358-11">]</span><span class="p" data-group-id="3831191358-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="3831191358-12">(</span><span class="n">Code</span><span class="p" data-group-id="3831191358-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="3831191358-13">(</span><span class="p" data-group-id="3831191358-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="3831191358-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3831191358-15">[</span><span class="p" data-group-id="3831191358-15">]</span><span class="p" data-group-id="3831191358-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="3831191358-16">(</span><span class="p" data-group-id="3831191358-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="3831191358-17">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="3831191358-17">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">down</span><span class="p" data-group-id="3831191358-18">(</span><span class="n">Button</span><span class="p" data-group-id="3831191358-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="3831191358-19">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3831191358-20">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3831191358-20">}</span><span class="p" data-group-id="3831191358-19">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">up</span><span class="p" data-group-id="3831191358-21">(</span><span class="n">Button</span><span class="p" data-group-id="3831191358-21">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="3831191358-22">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3831191358-23">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3831191358-23">}</span><span class="p" data-group-id="3831191358-22">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">code_length</span><span class="p" data-group-id="3831191358-24">(</span><span class="p" data-group-id="3831191358-24">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="3831191358-25">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p" data-group-id="3831191358-25">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8805362384-1">(</span><span class="n">Code</span><span class="p" data-group-id="8805362384-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="8805362384-2">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8805362384-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8805362384-3">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8805362384-4">(</span><span class="n">Code</span><span class="p" data-group-id="8805362384-4">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8805362384-5">[</span><span class="p" data-group-id="8805362384-5">]</span><span class="p" data-group-id="8805362384-3">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8805362384-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8805362384-6">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="6523961296-7">(</span><span class="p" data-group-id="6523961296-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6523961296-8">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="6523961296-8">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="8805362384-7">(</span><span class="p" data-group-id="8805362384-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8805362384-8">[</span><span class="ss">state_functions</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="8805362384-8">]</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="6523961296-9">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="6523961296-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="6523961296-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="6523961296-11">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="6523961296-11">)</span><span class="p" data-group-id="6523961296-9">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="8805362384-9">(</span><span class="n">HANDLE_COMMON</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">?</span><span class="n">FUNCTION_NAME</span><span class="p" data-group-id="8805362384-10">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="8805362384-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">handle_common</span><span class="p" data-group-id="8805362384-11">(</span><span class="n">T</span><span class="p">,</span><span class="w"> </span><span class="n">C</span><span class="p">,</span><span class="w"> </span><span class="n">D</span><span class="p" data-group-id="8805362384-11">)</span><span class="p" data-group-id="8805362384-9">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="6523961296-12">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6523961296-13">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6523961296-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6523961296-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6523961296-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6523961296-15">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="6523961296-15">}</span><span class="p" data-group-id="6523961296-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="6523961296-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6523961296-17">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6523961296-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6523961296-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="8805362384-12">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8805362384-13">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8805362384-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8805362384-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8805362384-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8805362384-15">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="8805362384-15">}</span><span class="p" data-group-id="8805362384-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="8805362384-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8805362384-17">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8805362384-17">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8805362384-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6523961296-18">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="6523961296-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="6523961296-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="6523961296-20">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6523961296-20">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="6523961296-21">[</span><span class="p" data-group-id="6523961296-22">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="6523961296-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="6523961296-23">}</span><span class="p" data-group-id="6523961296-22">}</span><span class="p" data-group-id="6523961296-21">]</span><span class="p" data-group-id="6523961296-19">}</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6523961296-24">#{</span><span class="p" data-group-id="6523961296-24">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8805362384-18">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="8805362384-18">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8805362384-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="8805362384-20">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8805362384-20">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="8805362384-21">[</span><span class="p" data-group-id="8805362384-22">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="8805362384-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8805362384-23">}</span><span class="p" data-group-id="8805362384-22">}</span><span class="p" data-group-id="8805362384-21">]</span><span class="p" data-group-id="8805362384-19">}</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="8805362384-24">#{</span><span class="p" data-group-id="8805362384-24">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_common</span><span class="p" data-group-id="6523961296-25">(</span><span class="p" data-group-id="6523961296-26">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="6523961296-26">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6523961296-27">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="6523961296-27">}</span><span class="p" data-group-id="6523961296-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6523961296-28">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="6523961296-29">[</span><span class="p" data-group-id="6523961296-30">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="6523961296-31">(</span><span class="n">Code</span><span class="p" data-group-id="6523961296-31">)</span><span class="p" data-group-id="6523961296-30">}</span><span class="p" data-group-id="6523961296-29">]</span><span class="p" data-group-id="6523961296-28">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="3376869039-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3376869039-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="3376869039-2">(</span><span class="p" data-group-id="3376869039-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3376869039-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3376869039-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3376869039-5">[</span><span class="p" data-group-id="3376869039-5">]</span><span class="p" data-group-id="3376869039-4">}</span><span class="p" data-group-id="3376869039-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="3376869039-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3376869039-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3376869039-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3376869039-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="3376869039-9">[</span><span class="p" data-group-id="3376869039-9">]</span><span class="p" data-group-id="3376869039-8">}</span><span class="p" data-group-id="3376869039-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">locked</span><span class="p" data-group-id="3376869039-10">(</span><span class="w">
│ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3376869039-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="3376869039-11">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="3376869039-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="3376869039-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3376869039-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_common</span><span class="p" data-group-id="8805362384-25">(</span><span class="p" data-group-id="8805362384-26">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="8805362384-26">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8805362384-27">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="8805362384-27">}</span><span class="p" data-group-id="8805362384-25">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8805362384-28">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="8805362384-29">[</span><span class="p" data-group-id="8805362384-30">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="nf">length</span><span class="p" data-group-id="8805362384-31">(</span><span class="n">Code</span><span class="p" data-group-id="8805362384-31">)</span><span class="p" data-group-id="8805362384-30">}</span><span class="p" data-group-id="8805362384-29">]</span><span class="p" data-group-id="8805362384-28">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">locked</span><span class="p" data-group-id="8719917985-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8719917985-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="8719917985-2">(</span><span class="p" data-group-id="8719917985-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8719917985-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8719917985-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8719917985-5">[</span><span class="p" data-group-id="8719917985-5">]</span><span class="p" data-group-id="8719917985-4">}</span><span class="p" data-group-id="8719917985-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="8719917985-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8719917985-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8719917985-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8719917985-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8719917985-9">[</span><span class="p" data-group-id="8719917985-9">]</span><span class="p" data-group-id="8719917985-8">}</span><span class="p" data-group-id="8719917985-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">locked</span><span class="p" data-group-id="8719917985-10">(</span><span class="w">
│ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8719917985-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8719917985-11">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8719917985-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8719917985-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8719917985-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="3376869039-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="3376869039-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="8719917985-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="8719917985-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="3376869039-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="3376869039-14">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="3376869039-15">[</span><span class="n">Button</span><span class="p" data-group-id="3376869039-15">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="8719917985-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="8719917985-14">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="8719917985-15">[</span><span class="n">Button</span><span class="p" data-group-id="8719917985-15">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3376869039-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3376869039-16">}</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8719917985-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8719917985-16">}</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="3376869039-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3376869039-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="3376869039-18">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="3376869039-19">[</span><span class="p" data-group-id="3376869039-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="3376869039-20">}</span><span class="p" data-group-id="3376869039-19">]</span><span class="p" data-group-id="3376869039-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8719917985-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8719917985-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="8719917985-18">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="8719917985-19">[</span><span class="p" data-group-id="8719917985-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="8719917985-20">}</span><span class="p" data-group-id="8719917985-19">]</span><span class="p" data-group-id="8719917985-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="2367990389-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2367990389-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2367990389-2">(</span><span class="p" data-group-id="2367990389-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2367990389-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="2367990389-4">[</span><span class="p" data-group-id="2367990389-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="2367990389-5">}</span><span class="p" data-group-id="2367990389-4">]</span><span class="p" data-group-id="2367990389-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="2367990389-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2367990389-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2367990389-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2367990389-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">open</span><span class="p" data-group-id="2367990389-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2367990389-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2367990389-9">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="2367990389-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2367990389-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2367990389-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="2367990389-11">]</span><span class="p" data-group-id="2367990389-10">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">open</span><span class="p" data-group-id="3423182046-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3423182046-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3423182046-2">(</span><span class="p" data-group-id="3423182046-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3423182046-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="3423182046-4">[</span><span class="p" data-group-id="3423182046-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3423182046-5">}</span><span class="p" data-group-id="3423182046-4">]</span><span class="p" data-group-id="3423182046-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="3423182046-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3423182046-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3423182046-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3423182046-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">open</span><span class="p" data-group-id="3423182046-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3423182046-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3423182046-9">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3423182046-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3423182046-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3423182046-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="3423182046-11">]</span><span class="p" data-group-id="3423182046-10">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="o">?</span><span class="n">HANDLE_COMMON</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">do_lock</span><span class="p" data-group-id="2367990389-12">(</span><span class="p" data-group-id="2367990389-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2367990389-13">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2367990389-14">[</span><span class="p" data-group-id="2367990389-14">]</span><span class="p" data-group-id="2367990389-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="2367990389-15">(</span><span class="p" data-group-id="2367990389-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2367990389-16">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2367990389-17">[</span><span class="p" data-group-id="2367990389-17">]</span><span class="p" data-group-id="2367990389-16">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_lock</span><span class="p" data-group-id="3423182046-12">(</span><span class="p" data-group-id="3423182046-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3423182046-13">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3423182046-14">[</span><span class="p" data-group-id="3423182046-14">]</span><span class="p" data-group-id="3423182046-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="3423182046-15">(</span><span class="p" data-group-id="3423182046-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="3423182046-16">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3423182046-17">[</span><span class="p" data-group-id="3423182046-17">]</span><span class="p" data-group-id="3423182046-16">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="2367990389-18">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2367990389-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="2367990389-19">(</span><span class="p" data-group-id="2367990389-19">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="3423182046-18">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3423182046-18">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="3423182046-19">(</span><span class="p" data-group-id="3423182046-19">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h3 id="callback-mode-handle_event_function" class="section-heading">
│ │ │    <a href="#callback-mode-handle_event_function" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Callback Mode: handle_event_function</span>
│ │ │  </h3>
│ │ │  <p>This section describes what to change in the example to use one
│ │ │  <code class="inline">handle_event/4</code> function.  The previously used approach to first branch
│ │ │  depending on event does not work that well here because of
│ │ │ -the <em>state enter calls</em>, so this example first branches depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6420316112-1">(</span><span class="p" data-group-id="6420316112-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="6420316112-2">]</span><span class="p" data-group-id="6420316112-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="6784050806-1">(</span><span class="p" data-group-id="6784050806-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6784050806-2">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="6784050806-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ +the <em>state enter calls</em>, so this example first branches depending on state:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5547490646-1">(</span><span class="p" data-group-id="5547490646-2">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="5547490646-2">]</span><span class="p" data-group-id="5547490646-1">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">callback_mode</span><span class="p" data-group-id="2184918093-1">(</span><span class="p" data-group-id="2184918093-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2184918093-2">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="2184918093-2">]</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% State: locked</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0065238711-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0065238711-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="0065238711-2">(</span><span class="p" data-group-id="0065238711-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0065238711-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0065238711-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="0065238711-5">[</span><span class="p" data-group-id="0065238711-5">]</span><span class="p" data-group-id="0065238711-4">}</span><span class="p" data-group-id="0065238711-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0065238711-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0065238711-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0065238711-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0065238711-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="0065238711-9">[</span><span class="p" data-group-id="0065238711-9">]</span><span class="p" data-group-id="0065238711-8">}</span><span class="p" data-group-id="0065238711-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="0065238711-10">(</span><span class="w">
│ │ │ -  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0065238711-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="0065238711-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="0065238711-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="0065238711-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0065238711-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2715804022-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2715804022-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="2715804022-2">(</span><span class="p" data-group-id="2715804022-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2715804022-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2715804022-4">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2715804022-5">[</span><span class="p" data-group-id="2715804022-5">]</span><span class="p" data-group-id="2715804022-4">}</span><span class="p" data-group-id="2715804022-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2715804022-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2715804022-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2715804022-7">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2715804022-8">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="2715804022-9">[</span><span class="p" data-group-id="2715804022-9">]</span><span class="p" data-group-id="2715804022-8">}</span><span class="p" data-group-id="2715804022-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2715804022-10">(</span><span class="w">
│ │ │ +  </span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2715804022-11">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2715804022-11">}</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="2715804022-12">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="2715804022-12">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2715804022-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="0065238711-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="0065238711-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="2715804022-13">(</span><span class="n">Buttons</span><span class="p" data-group-id="2715804022-13">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="0065238711-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="0065238711-14">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="0065238711-15">[</span><span class="n">Button</span><span class="p" data-group-id="0065238711-15">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="2715804022-14">(</span><span class="n">Buttons</span><span class="p" data-group-id="2715804022-14">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="2715804022-15">[</span><span class="n">Button</span><span class="p" data-group-id="2715804022-15">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="0065238711-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0065238711-16">}</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2715804022-16">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2715804022-16">}</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="0065238711-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="0065238711-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="0065238711-18">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="0065238711-19">[</span><span class="p" data-group-id="0065238711-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="0065238711-20">}</span><span class="p" data-group-id="0065238711-19">]</span><span class="p" data-group-id="0065238711-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2715804022-17">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2715804022-18">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="2715804022-18">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="2715804022-19">[</span><span class="p" data-group-id="2715804022-20">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="2715804022-20">}</span><span class="p" data-group-id="2715804022-19">]</span><span class="p" data-group-id="2715804022-17">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1579138825-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1579138825-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="1579138825-2">(</span><span class="p" data-group-id="1579138825-2">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1579138825-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="1579138825-4">[</span><span class="p" data-group-id="1579138825-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1579138825-5">}</span><span class="p" data-group-id="1579138825-4">]</span><span class="p" data-group-id="1579138825-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1579138825-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1579138825-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1579138825-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="1579138825-7">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="1579138825-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1579138825-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1579138825-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1579138825-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1579138825-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="1579138825-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="1579138825-11">]</span><span class="p" data-group-id="1579138825-10">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%% Common events</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4839415291-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4839415291-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4839415291-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4839415291-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4839415291-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4839415291-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="4839415291-4">}</span><span class="p" data-group-id="4839415291-3">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4839415291-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4839415291-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4839415291-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4839415291-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3228274847-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3228274847-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3228274847-2">(</span><span class="p" data-group-id="3228274847-2">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3228274847-3">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="3228274847-4">[</span><span class="p" data-group-id="3228274847-5">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3228274847-5">}</span><span class="p" data-group-id="3228274847-4">]</span><span class="p" data-group-id="3228274847-3">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3228274847-6">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3228274847-6">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3228274847-7">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="ss">locked</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3228274847-7">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="3228274847-8">(</span><span class="ss">internal</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3228274847-9">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3228274847-9">}</span><span class="p">,</span><span class="w"> </span><span class="ss">open</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3228274847-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3228274847-10">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="3228274847-11">[</span><span class="ss">postpone</span><span class="p" data-group-id="3228274847-11">]</span><span class="p" data-group-id="3228274847-10">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%% Common events</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2512938501-1">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2512938501-2">{</span><span class="ss">down</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2512938501-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2512938501-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2512938501-3">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2512938501-4">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2512938501-4">}</span><span class="p" data-group-id="2512938501-3">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2512938501-5">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2512938501-6">{</span><span class="ss">up</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2512938501-6">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2512938501-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Data</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4839415291-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="4839415291-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4839415291-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="4839415291-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4839415291-9">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="4839415291-10">[</span><span class="p" data-group-id="4839415291-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="4839415291-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="4839415291-12">}</span><span class="p" data-group-id="4839415291-11">}</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="p" data-group-id="4839415291-13">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="4839415291-13">}</span><span class="p" data-group-id="4839415291-10">]</span><span class="p" data-group-id="4839415291-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="4839415291-14">#{</span><span class="p" data-group-id="4839415291-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2512938501-7">#{</span><span class="ss">button</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Button</span><span class="p" data-group-id="2512938501-7">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="2512938501-8">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="nc">maps</span><span class="p">:</span><span class="nf">remove</span><span class="p" data-group-id="2512938501-9">(</span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2512938501-9">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="2512938501-10">[</span><span class="p" data-group-id="2512938501-11">{</span><span class="ss">next_event</span><span class="p">,</span><span class="ss">internal</span><span class="p">,</span><span class="p" data-group-id="2512938501-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2512938501-12">}</span><span class="p" data-group-id="2512938501-11">}</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="p" data-group-id="2512938501-13">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="2512938501-13">}</span><span class="p" data-group-id="2512938501-10">]</span><span class="p" data-group-id="2512938501-8">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2512938501-14">#{</span><span class="p" data-group-id="2512938501-14">}</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │              </span><span class="ss">keep_state_and_data</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="4839415291-15">(</span><span class="p" data-group-id="4839415291-16">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="4839415291-16">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4839415291-17">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="4839415291-17">}</span><span class="p" data-group-id="4839415291-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4839415291-18">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="4839415291-19">[</span><span class="p" data-group-id="4839415291-20">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">Length</span><span class="p" data-group-id="4839415291-20">}</span><span class="p" data-group-id="4839415291-19">]</span><span class="p" data-group-id="4839415291-18">}</span><span class="p">.</span></code></pre><p>Notice that postponing buttons from the <code class="inline">open</code> state to the <code class="inline">locked</code> state
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2512938501-15">(</span><span class="p" data-group-id="2512938501-16">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="2512938501-16">}</span><span class="p">,</span><span class="w"> </span><span class="ss">code_length</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2512938501-17">#{</span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="2512938501-17">}</span><span class="p" data-group-id="2512938501-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2512938501-18">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="2512938501-19">[</span><span class="p" data-group-id="2512938501-20">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">Length</span><span class="p" data-group-id="2512938501-20">}</span><span class="p" data-group-id="2512938501-19">]</span><span class="p" data-group-id="2512938501-18">}</span><span class="p">.</span></code></pre><p>Notice that postponing buttons from the <code class="inline">open</code> state to the <code class="inline">locked</code> state
│ │ │  seems like a strange thing to do for a code lock, but it at least
│ │ │  illustrates event postponing.</p><h2 id="filter-the-state" class="section-heading">
│ │ │    <a href="#filter-the-state" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Filter the State</span>
│ │ │  </h2>
│ │ │ @@ -1286,30 +1286,30 @@
│ │ │  and which digits that remain to unlock.</p><p>This state data can be regarded as sensitive, and maybe not what you want
│ │ │  in the error log because of some unpredictable event.</p><p>Another reason to filter the state can be that the state is too large to print,
│ │ │  as it fills the error log with uninteresting details.</p><p>To avoid this, you can format the internal state that gets in the error log
│ │ │  and gets returned from <a href="../../lib/stdlib-6.2.2.3/doc/html/sys.html#get_status/1"><code class="inline">sys:get_status/1,2</code></a>
│ │ │  by implementing function
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#c:format_status/2"><code class="inline">Module:format_status/2</code></a>,
│ │ │  for example like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3966316784-1">(</span><span class="p" data-group-id="3966316784-2">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">format_status</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3966316784-2">]</span><span class="p" data-group-id="3966316784-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="3994434976-1">(</span><span class="p" data-group-id="3994434976-2">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p">,</span><span class="ss">format_status</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="3994434976-2">]</span><span class="p" data-group-id="3994434976-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">format_status</span><span class="p" data-group-id="3966316784-3">(</span><span class="n">Opt</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3966316784-4">[</span><span class="p">_</span><span class="n">PDict</span><span class="p">,</span><span class="n">State</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="3966316784-4">]</span><span class="p" data-group-id="3966316784-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">format_status</span><span class="p" data-group-id="3994434976-3">(</span><span class="n">Opt</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3994434976-4">[</span><span class="p">_</span><span class="n">PDict</span><span class="p">,</span><span class="n">State</span><span class="p">,</span><span class="n">Data</span><span class="p" data-group-id="3994434976-4">]</span><span class="p" data-group-id="3994434976-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">StateData</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -	</span><span class="p" data-group-id="3966316784-5">{</span><span class="n">State</span><span class="p">,</span><span class="w">
│ │ │ -	 </span><span class="nc">maps</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="3966316784-6">(</span><span class="w">
│ │ │ -	   </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3966316784-7">(</span><span class="ss">code</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3966316784-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="p">;</span><span class="w">
│ │ │ -	       </span><span class="p" data-group-id="3966316784-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3966316784-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="w">
│ │ │ +	</span><span class="p" data-group-id="3994434976-5">{</span><span class="n">State</span><span class="p">,</span><span class="w">
│ │ │ +	 </span><span class="nc">maps</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="3994434976-6">(</span><span class="w">
│ │ │ +	   </span><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3994434976-7">(</span><span class="ss">code</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3994434976-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">false</span><span class="p">;</span><span class="w">
│ │ │ +	       </span><span class="p" data-group-id="3994434976-8">(</span><span class="p">_</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="3994434976-8">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">true</span><span class="w">
│ │ │  	   </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -	   </span><span class="n">Data</span><span class="p" data-group-id="3966316784-6">)</span><span class="p" data-group-id="3966316784-5">}</span><span class="p">,</span><span class="w">
│ │ │ +	   </span><span class="n">Data</span><span class="p" data-group-id="3994434976-6">)</span><span class="p" data-group-id="3994434976-5">}</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">Opt</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │  	</span><span class="ss">terminate</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  	    </span><span class="n">StateData</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">normal</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -	    </span><span class="p" data-group-id="3966316784-9">[</span><span class="p" data-group-id="3966316784-10">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="3966316784-11">[</span><span class="p" data-group-id="3966316784-12">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="n">StateData</span><span class="p" data-group-id="3966316784-12">}</span><span class="p" data-group-id="3966316784-11">]</span><span class="p" data-group-id="3966316784-10">}</span><span class="p" data-group-id="3966316784-9">]</span><span class="w">
│ │ │ +	    </span><span class="p" data-group-id="3994434976-9">[</span><span class="p" data-group-id="3994434976-10">{</span><span class="ss">data</span><span class="p">,</span><span class="p" data-group-id="3994434976-11">[</span><span class="p" data-group-id="3994434976-12">{</span><span class="s">&quot;State&quot;</span><span class="p">,</span><span class="n">StateData</span><span class="p" data-group-id="3994434976-12">}</span><span class="p" data-group-id="3994434976-11">]</span><span class="p" data-group-id="3994434976-10">}</span><span class="p" data-group-id="3994434976-9">]</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span></code></pre><p>It is not mandatory to implement a
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#c:format_status/2"><code class="inline">Module:format_status/2</code></a> function.
│ │ │  If you do not, a default implementation is used that does the same
│ │ │  as this example function without filtering the <code class="inline">Data</code> term, that is,
│ │ │  <code class="inline">StateData = {State, Data}</code>, in this example containing sensitive information.</p><h2 id="complex-state" class="section-heading">
│ │ │    <a href="#complex-state" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -1322,104 +1322,104 @@
│ │ │  like a tuple.</p><p>One reason to use this is when you have a state item that when changed
│ │ │  should cancel the <a href="#state-time-outs"><em>state time-out</em></a>, or one that affects
│ │ │  the event handling in combination with postponing events. We will go for
│ │ │  the latter and complicate the previous example by introducing
│ │ │  a configurable lock button (this is the state item in question),
│ │ │  which in the <code class="inline">open</code> state immediately locks the door, and an API function
│ │ │  <code class="inline">set_lock_button/1</code> to set the lock button.</p><p>Suppose now that we call <code class="inline">set_lock_button</code> while the door is open,
│ │ │ -and we have already postponed a button event that was the new lock button:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="9602576446-1">(</span><span class="p" data-group-id="9602576446-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="9602576446-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">x</span><span class="p" data-group-id="9602576446-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9602576446-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.666</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="9602576446-3">}</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="9602576446-4">(</span><span class="ss">a</span><span class="p" data-group-id="9602576446-4">)</span><span class="p">.</span><span class="w">
│ │ │ +and we have already postponed a button event that was the new lock button:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6639854419-1">(</span><span class="p" data-group-id="6639854419-2">[</span><span class="ss">a</span><span class="p">,</span><span class="ss">b</span><span class="p">,</span><span class="ss">c</span><span class="p" data-group-id="6639854419-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">x</span><span class="p" data-group-id="6639854419-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6639854419-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="o">&lt;</span><span class="mf">0.666</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="p" data-group-id="6639854419-3">}</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="6639854419-4">(</span><span class="ss">a</span><span class="p" data-group-id="6639854419-4">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">3&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="9602576446-5">(</span><span class="ss">b</span><span class="p" data-group-id="9602576446-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">3&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="6639854419-5">(</span><span class="ss">b</span><span class="p" data-group-id="6639854419-5">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="9602576446-6">(</span><span class="ss">c</span><span class="p" data-group-id="9602576446-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">4&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="6639854419-6">(</span><span class="ss">c</span><span class="p" data-group-id="6639854419-6">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │  </span><span class="n">Open</span><span class="w">
│ │ │ -</span><span class="gp unselectable">5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="9602576446-7">(</span><span class="ss">y</span><span class="p" data-group-id="9602576446-7">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">5&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">button</span><span class="p" data-group-id="6639854419-7">(</span><span class="ss">y</span><span class="p" data-group-id="6639854419-7">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">ok</span><span class="w">
│ │ │ -</span><span class="gp unselectable">6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">set_lock_button</span><span class="p" data-group-id="9602576446-8">(</span><span class="ss">y</span><span class="p" data-group-id="9602576446-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="gp unselectable">6&gt; </span><span class="nc">code_lock</span><span class="p">:</span><span class="nf">set_lock_button</span><span class="p" data-group-id="6639854419-8">(</span><span class="ss">y</span><span class="p" data-group-id="6639854419-8">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="c1">% What should happen here?  Immediate lock or nothing?</span></code></pre><p>We could say that the button was pressed too early so it should not be
│ │ │  recognized as the lock button. Or we can make the lock button part of
│ │ │  the state so when we then change the lock button in the locked state,
│ │ │  the change becomes a <em>state change</em> and all postponed events are retried,
│ │ │  therefore the lock is immediately locked!</p><p>We define the state as <code class="inline">{StateName, LockButton}</code>, where <code class="inline">StateName</code>
│ │ │ -is as before and <code class="inline">LockButton</code> is the current lock button:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="2728363590-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="2728363590-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="2728363590-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="2728363590-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="2728363590-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_3</span><span class="p" data-group-id="2728363590-3">)</span><span class="p">.</span><span class="w">
│ │ │ +is as before and <code class="inline">LockButton</code> is the current lock button:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5885704473-1">(</span><span class="ss">code_lock</span><span class="p" data-group-id="5885704473-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5885704473-2">(</span><span class="ss">gen_statem</span><span class="p" data-group-id="5885704473-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">define</span><span class="p" data-group-id="5885704473-3">(</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="ss">code_lock_3</span><span class="p" data-group-id="5885704473-3">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2728363590-4">(</span><span class="p" data-group-id="2728363590-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="2728363590-5">]</span><span class="p" data-group-id="2728363590-4">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2728363590-6">(</span><span class="p" data-group-id="2728363590-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">set_lock_button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="2728363590-7">]</span><span class="p" data-group-id="2728363590-6">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2728363590-8">(</span><span class="p" data-group-id="2728363590-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="2728363590-9">]</span><span class="p" data-group-id="2728363590-8">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="2728363590-10">(</span><span class="p" data-group-id="2728363590-11">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="2728363590-11">]</span><span class="p" data-group-id="2728363590-10">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="2728363590-12">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">LockButton</span><span class="p" data-group-id="2728363590-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="2728363590-13">(</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2728363590-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="2728363590-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2728363590-15">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2728363590-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2728363590-16">[</span><span class="p" data-group-id="2728363590-16">]</span><span class="p" data-group-id="2728363590-13">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">stop</span><span class="p" data-group-id="2728363590-17">(</span><span class="p" data-group-id="2728363590-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="2728363590-18">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="2728363590-18">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">button</span><span class="p" data-group-id="2728363590-19">(</span><span class="n">Button</span><span class="p" data-group-id="2728363590-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="2728363590-20">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2728363590-21">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="2728363590-21">}</span><span class="p" data-group-id="2728363590-20">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">set_lock_button</span><span class="p" data-group-id="2728363590-22">(</span><span class="n">LockButton</span><span class="p" data-group-id="2728363590-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="2728363590-23">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2728363590-24">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2728363590-24">}</span><span class="p" data-group-id="2728363590-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="9964745642-1">(</span><span class="p" data-group-id="9964745642-2">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="9964745642-2">}</span><span class="p" data-group-id="9964745642-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">process_flag</span><span class="p" data-group-id="9964745642-3">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="9964745642-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9964745642-4">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="9964745642-5">(</span><span class="n">Code</span><span class="p" data-group-id="9964745642-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9964745642-6">[</span><span class="p" data-group-id="9964745642-6">]</span><span class="p" data-group-id="9964745642-4">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9964745642-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9964745642-8">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="9964745642-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9964745642-7">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5885704473-4">(</span><span class="p" data-group-id="5885704473-5">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">2</span><span class="p">,</span><span class="ss">stop</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5885704473-5">]</span><span class="p" data-group-id="5885704473-4">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5885704473-6">(</span><span class="p" data-group-id="5885704473-7">[</span><span class="ss">button</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">set_lock_button</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5885704473-7">]</span><span class="p" data-group-id="5885704473-6">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5885704473-8">(</span><span class="p" data-group-id="5885704473-9">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p">,</span><span class="ss">callback_mode</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="ss">terminate</span><span class="p">/</span><span class="mi">3</span><span class="p" data-group-id="5885704473-9">]</span><span class="p" data-group-id="5885704473-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5885704473-10">(</span><span class="p" data-group-id="5885704473-11">[</span><span class="ss">handle_event</span><span class="p">/</span><span class="mi">4</span><span class="p" data-group-id="5885704473-11">]</span><span class="p" data-group-id="5885704473-10">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="5885704473-12">(</span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="n">LockButton</span><span class="p" data-group-id="5885704473-12">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5885704473-13">(</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="5885704473-14">{</span><span class="ss">local</span><span class="p">,</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="5885704473-14">}</span><span class="p">,</span><span class="w"> </span><span class="o">?</span><span class="n">MODULE</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5885704473-15">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="5885704473-15">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5885704473-16">[</span><span class="p" data-group-id="5885704473-16">]</span><span class="p" data-group-id="5885704473-13">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">stop</span><span class="p" data-group-id="5885704473-17">(</span><span class="p" data-group-id="5885704473-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">stop</span><span class="p" data-group-id="5885704473-18">(</span><span class="o">?</span><span class="n">NAME</span><span class="p" data-group-id="5885704473-18">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">button</span><span class="p" data-group-id="5885704473-19">(</span><span class="n">Button</span><span class="p" data-group-id="5885704473-19">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">cast</span><span class="p" data-group-id="5885704473-20">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5885704473-21">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="5885704473-21">}</span><span class="p" data-group-id="5885704473-20">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">set_lock_button</span><span class="p" data-group-id="5885704473-22">(</span><span class="n">LockButton</span><span class="p" data-group-id="5885704473-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">gen_statem</span><span class="p">:</span><span class="nf">call</span><span class="p" data-group-id="5885704473-23">(</span><span class="o">?</span><span class="n">NAME</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5885704473-24">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="5885704473-24">}</span><span class="p" data-group-id="5885704473-23">)</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="8683066704-1">(</span><span class="p" data-group-id="8683066704-2">{</span><span class="n">Code</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="8683066704-2">}</span><span class="p" data-group-id="8683066704-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">process_flag</span><span class="p" data-group-id="8683066704-3">(</span><span class="ss">trap_exit</span><span class="p">,</span><span class="w"> </span><span class="ss">true</span><span class="p" data-group-id="8683066704-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">Data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8683066704-4">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">length</span><span class="p" data-group-id="8683066704-5">(</span><span class="n">Code</span><span class="p" data-group-id="8683066704-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="8683066704-6">[</span><span class="p" data-group-id="8683066704-6">]</span><span class="p" data-group-id="8683066704-4">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8683066704-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8683066704-8">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="8683066704-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8683066704-7">}</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">callback_mode</span><span class="p" data-group-id="9964745642-9">(</span><span class="p" data-group-id="9964745642-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9964745642-10">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="9964745642-10">]</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">callback_mode</span><span class="p" data-group-id="8683066704-9">(</span><span class="p" data-group-id="8683066704-9">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8683066704-10">[</span><span class="ss">handle_event_function</span><span class="p">,</span><span class="ss">state_enter</span><span class="p" data-group-id="8683066704-10">]</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% State: locked</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9964745642-11">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9964745642-12">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9964745642-12">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9964745642-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_lock</span><span class="p" data-group-id="9964745642-13">(</span><span class="p" data-group-id="9964745642-13">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9964745642-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9964745642-15">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9964745642-16">[</span><span class="p" data-group-id="9964745642-16">]</span><span class="p" data-group-id="9964745642-15">}</span><span class="p" data-group-id="9964745642-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9964745642-17">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9964745642-18">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="9964745642-18">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9964745642-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9964745642-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9964745642-20">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="9964745642-21">[</span><span class="p" data-group-id="9964745642-21">]</span><span class="p" data-group-id="9964745642-20">}</span><span class="p" data-group-id="9964745642-19">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9964745642-22">(</span><span class="w">
│ │ │ -  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9964745642-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="9964745642-23">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9964745642-24">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="9964745642-24">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9964745642-25">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="9964745642-25">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9964745642-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="8683066704-11">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8683066704-12">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8683066704-12">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8683066704-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_lock</span><span class="p" data-group-id="8683066704-13">(</span><span class="p" data-group-id="8683066704-13">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8683066704-14">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8683066704-15">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8683066704-16">[</span><span class="p" data-group-id="8683066704-16">]</span><span class="p" data-group-id="8683066704-15">}</span><span class="p" data-group-id="8683066704-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="8683066704-17">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">button</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8683066704-18">{</span><span class="ss">locked</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="8683066704-18">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8683066704-17">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8683066704-19">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8683066704-20">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="p" data-group-id="8683066704-21">[</span><span class="p" data-group-id="8683066704-21">]</span><span class="p" data-group-id="8683066704-20">}</span><span class="p" data-group-id="8683066704-19">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="8683066704-22">(</span><span class="w">
│ │ │ +  </span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8683066704-23">{</span><span class="ss">button</span><span class="p">,</span><span class="n">Button</span><span class="p" data-group-id="8683066704-23">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8683066704-24">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="8683066704-24">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="8683066704-25">#{</span><span class="ss">code</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Code</span><span class="p">,</span><span class="w"> </span><span class="nb">length</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Length</span><span class="p">,</span><span class="w"> </span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">Buttons</span><span class="p" data-group-id="8683066704-25">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8683066704-22">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │          </span><span class="k">if</span><span class="w">
│ │ │ -            </span><span class="nf">length</span><span class="p" data-group-id="9964745642-26">(</span><span class="n">Buttons</span><span class="p" data-group-id="9964745642-26">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">length</span><span class="p" data-group-id="8683066704-26">(</span><span class="n">Buttons</span><span class="p" data-group-id="8683066704-26">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">Length</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                  </span><span class="n">Buttons</span><span class="p">;</span><span class="w">
│ │ │              </span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                </span><span class="nf">tl</span><span class="p" data-group-id="9964745642-27">(</span><span class="n">Buttons</span><span class="p" data-group-id="9964745642-27">)</span><span class="w">
│ │ │ -        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="9964745642-28">[</span><span class="n">Button</span><span class="p" data-group-id="9964745642-28">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="nf">tl</span><span class="p" data-group-id="8683066704-27">(</span><span class="n">Buttons</span><span class="p" data-group-id="8683066704-27">)</span><span class="w">
│ │ │ +        </span><span class="k">end</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="p" data-group-id="8683066704-28">[</span><span class="n">Button</span><span class="p" data-group-id="8683066704-28">]</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="k">if</span><span class="w">
│ │ │          </span><span class="n">NewButtons</span><span class="w"> </span><span class="o">=:=</span><span class="w"> </span><span class="n">Code</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Correct</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9964745642-29">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9964745642-30">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="9964745642-30">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9964745642-29">}</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8683066704-29">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8683066704-30">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="8683066704-30">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8683066704-29">}</span><span class="p">;</span><span class="w">
│ │ │  	</span><span class="ss">true</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="c1">% Incomplete | Incorrect</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="9964745642-31">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9964745642-32">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="9964745642-32">}</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="p" data-group-id="9964745642-33">[</span><span class="p" data-group-id="9964745642-34">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="9964745642-34">}</span><span class="p" data-group-id="9964745642-33">]</span><span class="p" data-group-id="9964745642-31">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="8683066704-31">{</span><span class="ss">keep_state</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="8683066704-32">#{</span><span class="ss">buttons</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="n">NewButtons</span><span class="p" data-group-id="8683066704-32">}</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="p" data-group-id="8683066704-33">[</span><span class="p" data-group-id="8683066704-34">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">30</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">button</span><span class="p" data-group-id="8683066704-34">}</span><span class="p" data-group-id="8683066704-33">]</span><span class="p" data-group-id="8683066704-31">}</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6674665620-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6674665620-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6674665620-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="6674665620-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="6674665620-3">(</span><span class="p" data-group-id="6674665620-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6674665620-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="6674665620-5">[</span><span class="p" data-group-id="6674665620-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="6674665620-6">}</span><span class="p" data-group-id="6674665620-5">]</span><span class="p" data-group-id="6674665620-4">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6674665620-7">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6674665620-8">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6674665620-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6674665620-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6674665620-9">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6674665620-10">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6674665620-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6674665620-9">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6674665620-11">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6674665620-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6674665620-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6674665620-13">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6674665620-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6674665620-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6674665620-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6674665620-15">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="6674665620-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6674665620-14">}</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="6674665620-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6674665620-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6674665620-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6674665620-18">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="6674665620-18">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="6674665620-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6674665620-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="6674665620-20">[</span><span class="ss">postpone</span><span class="p" data-group-id="6674665620-20">]</span><span class="p" data-group-id="6674665620-19">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2417827191-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2417827191-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2417827191-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2417827191-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="2417827191-3">(</span><span class="p" data-group-id="2417827191-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2417827191-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="2417827191-5">[</span><span class="p" data-group-id="2417827191-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="2417827191-6">}</span><span class="p" data-group-id="2417827191-5">]</span><span class="p" data-group-id="2417827191-4">}</span><span class="p">;</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2417827191-7">(</span><span class="ss">state_timeout</span><span class="p">,</span><span class="w"> </span><span class="ss">lock</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2417827191-8">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2417827191-8">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2417827191-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2417827191-9">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2417827191-10">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2417827191-10">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2417827191-9">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2417827191-11">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2417827191-12">{</span><span class="ss">button</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2417827191-12">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2417827191-13">{</span><span class="ss">open</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2417827191-13">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2417827191-11">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2417827191-14">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2417827191-15">{</span><span class="ss">locked</span><span class="p">,</span><span class="n">LockButton</span><span class="p" data-group-id="2417827191-15">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="2417827191-14">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="2417827191-16">(</span><span class="ss">cast</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2417827191-17">{</span><span class="ss">button</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2417827191-17">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2417827191-18">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="2417827191-18">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="2417827191-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2417827191-19">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="p" data-group-id="2417827191-20">[</span><span class="ss">postpone</span><span class="p" data-group-id="2417827191-20">]</span><span class="p" data-group-id="2417827191-19">}</span><span class="p">;</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% Common events</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="9489302789-1">(</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9489302789-2">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="9489302789-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9489302789-3">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="9489302789-3">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="9489302789-4">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="9489302789-4">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="9489302789-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9489302789-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9489302789-6">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="9489302789-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="9489302789-7">[</span><span class="p" data-group-id="9489302789-8">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="9489302789-8">}</span><span class="p" data-group-id="9489302789-7">]</span><span class="p" data-group-id="9489302789-5">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="9221740229-1">(</span><span class="p" data-group-id="9221740229-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9221740229-2">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9221740229-3">[</span><span class="p" data-group-id="9221740229-3">]</span><span class="p" data-group-id="9221740229-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">do_unlock</span><span class="p" data-group-id="9221740229-4">(</span><span class="p" data-group-id="9221740229-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="9221740229-5">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9221740229-6">[</span><span class="p" data-group-id="9221740229-6">]</span><span class="p" data-group-id="9221740229-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="4124461358-1">(</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4124461358-2">{</span><span class="ss">call</span><span class="p">,</span><span class="n">From</span><span class="p" data-group-id="4124461358-2">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4124461358-3">{</span><span class="ss">set_lock_button</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="4124461358-3">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4124461358-4">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="4124461358-4">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="4124461358-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="4124461358-5">{</span><span class="ss">next_state</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4124461358-6">{</span><span class="n">StateName</span><span class="p">,</span><span class="n">NewLockButton</span><span class="p" data-group-id="4124461358-6">}</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="4124461358-7">[</span><span class="p" data-group-id="4124461358-8">{</span><span class="ss">reply</span><span class="p">,</span><span class="n">From</span><span class="p">,</span><span class="n">OldLockButton</span><span class="p" data-group-id="4124461358-8">}</span><span class="p" data-group-id="4124461358-7">]</span><span class="p" data-group-id="4124461358-5">}</span><span class="p">.</span></code></pre><pre><code class="makeup erlang" translate="no"><span class="nf">do_lock</span><span class="p" data-group-id="1296189193-1">(</span><span class="p" data-group-id="1296189193-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1296189193-2">(</span><span class="s">&quot;Locked</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1296189193-3">[</span><span class="p" data-group-id="1296189193-3">]</span><span class="p" data-group-id="1296189193-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">do_unlock</span><span class="p" data-group-id="1296189193-4">(</span><span class="p" data-group-id="1296189193-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="1296189193-5">(</span><span class="s">&quot;Open</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1296189193-6">[</span><span class="p" data-group-id="1296189193-6">]</span><span class="p" data-group-id="1296189193-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">terminate</span><span class="p" data-group-id="9221740229-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="9221740229-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="9221740229-8">(</span><span class="p" data-group-id="9221740229-8">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">terminate</span><span class="p" data-group-id="1296189193-7">(</span><span class="p">_</span><span class="n">Reason</span><span class="p">,</span><span class="w"> </span><span class="n">State</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1296189193-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">State</span><span class="w"> </span><span class="o">=/=</span><span class="w"> </span><span class="ss">locked</span><span class="w"> </span><span class="ow">andalso</span><span class="w"> </span><span class="nf">do_lock</span><span class="p" data-group-id="1296189193-8">(</span><span class="p" data-group-id="1296189193-8">)</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="ss">ok</span><span class="p">.</span></code></pre><h2 id="hibernation" class="section-heading">
│ │ │    <a href="#hibernation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Hibernation</span>
│ │ │  </h2>
│ │ │  <p>If you have many servers in one node and they have some state(s) in their
│ │ │ @@ -1428,19 +1428,19 @@
│ │ │  footprint of a server can be minimized by hibernating it through
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/proc_lib.html#hibernate/3"><code class="inline">proc_lib:hibernate/3</code></a>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>It is rather costly to hibernate a process; see <a href="../../erts-15.2.7.8/doc/html/erlang.html#hibernate/3"><code class="inline">erlang:hibernate/3</code></a>. It is
│ │ │  not something you want to do after every event.</p></section><p>We can in this example hibernate in the <code class="inline">{open, _}</code> state,
│ │ │  because what normally occurs in that state is that the <em>state time-out</em>
│ │ │  after a while triggers a transition to <code class="inline">{locked, _}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% State: open</span><span class="w">
│ │ │ -</span><span class="nf">handle_event</span><span class="p" data-group-id="3881882005-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3881882005-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="3881882005-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="3881882005-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">do_unlock</span><span class="p" data-group-id="3881882005-3">(</span><span class="p" data-group-id="3881882005-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3881882005-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ -     </span><span class="p" data-group-id="3881882005-5">[</span><span class="p" data-group-id="3881882005-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="3881882005-6">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ -      </span><span class="ss">hibernate</span><span class="p" data-group-id="3881882005-5">]</span><span class="p" data-group-id="3881882005-4">}</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">handle_event</span><span class="p" data-group-id="1552496331-1">(</span><span class="ss">enter</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">OldState</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1552496331-2">{</span><span class="ss">open</span><span class="p">,</span><span class="p">_</span><span class="p" data-group-id="1552496331-2">}</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="n">Data</span><span class="p" data-group-id="1552496331-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nf">do_unlock</span><span class="p" data-group-id="1552496331-3">(</span><span class="p" data-group-id="1552496331-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="1552496331-4">{</span><span class="ss">keep_state_and_data</span><span class="p">,</span><span class="w">
│ │ │ +     </span><span class="p" data-group-id="1552496331-5">[</span><span class="p" data-group-id="1552496331-6">{</span><span class="ss">state_timeout</span><span class="p">,</span><span class="mi">10</span><span class="p">_</span><span class="mi">000</span><span class="p">,</span><span class="ss">lock</span><span class="p" data-group-id="1552496331-6">}</span><span class="p">,</span><span class="w"> </span><span class="c1">% Time in milliseconds</span><span class="w">
│ │ │ +      </span><span class="ss">hibernate</span><span class="p" data-group-id="1552496331-5">]</span><span class="p" data-group-id="1552496331-4">}</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span></code></pre><p>The atom <a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#t:hibernate/0"><code class="inline">hibernate</code></a> in the action list on the
│ │ │  last line when entering the <code class="inline">{open, _}</code> state is the only change. If any event
│ │ │  arrives in the <code class="inline">{open, _},</code> state, we do not bother to rehibernate,
│ │ │  so the server stays awake after any event.</p><p>To change that we would need to insert action <code class="inline">hibernate</code> in more places.
│ │ │  For example, the state-independent <code class="inline">set_lock_button</code> operation
│ │ │  would have to use <code class="inline">hibernate</code> but only in the <code class="inline">{open, _}</code> state,
│ │ │  which would clutter the code.</p><p>Another not uncommon scenario is to use the
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/sup_princ.html
│ │ │ @@ -128,48 +128,48 @@
│ │ │  the order specified by this list, and are terminated in the reverse order.</p><h2 id="example" class="section-heading">
│ │ │    <a href="#example" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Example</span>
│ │ │  </h2>
│ │ │  <p>The callback module for a supervisor starting the server from
│ │ │ -<a href="gen_server_concepts.html#ex">gen_server Behaviour</a> can look as follows:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="6735985428-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="6735985428-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="6735985428-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="6735985428-2">)</span><span class="p">.</span><span class="w">
│ │ │ +<a href="gen_server_concepts.html#ex">gen_server Behaviour</a> can look as follows:</p><p><a href="" id="ex"></a></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="5469036860-1">(</span><span class="ss">ch_sup</span><span class="p" data-group-id="5469036860-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="5469036860-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="5469036860-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6735985428-3">(</span><span class="p" data-group-id="6735985428-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="6735985428-4">]</span><span class="p" data-group-id="6735985428-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="6735985428-5">(</span><span class="p" data-group-id="6735985428-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="6735985428-6">]</span><span class="p" data-group-id="6735985428-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5469036860-3">(</span><span class="p" data-group-id="5469036860-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="5469036860-4">]</span><span class="p" data-group-id="5469036860-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="5469036860-5">(</span><span class="p" data-group-id="5469036860-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="5469036860-6">]</span><span class="p" data-group-id="5469036860-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="6735985428-7">(</span><span class="p" data-group-id="6735985428-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6735985428-8">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6735985428-9">[</span><span class="p" data-group-id="6735985428-9">]</span><span class="p" data-group-id="6735985428-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="5469036860-7">(</span><span class="p" data-group-id="5469036860-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="5469036860-8">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5469036860-9">[</span><span class="p" data-group-id="5469036860-9">]</span><span class="p" data-group-id="5469036860-8">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="6735985428-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="6735985428-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6735985428-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_one</span><span class="p">,</span><span class="w"> </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="6735985428-11">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6735985428-12">[</span><span class="p" data-group-id="6735985428-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6735985428-14">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6735985428-15">[</span><span class="p" data-group-id="6735985428-15">]</span><span class="p" data-group-id="6735985428-14">}</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="5469036860-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="5469036860-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5469036860-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">one_for_one</span><span class="p">,</span><span class="w"> </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="5469036860-11">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5469036860-12">[</span><span class="p" data-group-id="5469036860-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5469036860-14">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5469036860-15">[</span><span class="p" data-group-id="5469036860-15">]</span><span class="p" data-group-id="5469036860-14">}</span><span class="p">,</span><span class="w">
│ │ │                      </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">permanent</span><span class="p">,</span><span class="w">
│ │ │                      </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w">
│ │ │                      </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="6735985428-16">[</span><span class="ss">ch3</span><span class="p" data-group-id="6735985428-16">]</span><span class="p" data-group-id="6735985428-13">}</span><span class="p" data-group-id="6735985428-12">]</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="6735985428-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6735985428-18">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="6735985428-18">}</span><span class="p" data-group-id="6735985428-17">}</span><span class="p">.</span></code></pre><p>The <code class="inline">SupFlags</code> variable in the return value from <code class="inline">init/1</code> represents the
│ │ │ +                    </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5469036860-16">[</span><span class="ss">ch3</span><span class="p" data-group-id="5469036860-16">]</span><span class="p" data-group-id="5469036860-13">}</span><span class="p" data-group-id="5469036860-12">]</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5469036860-17">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5469036860-18">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="5469036860-18">}</span><span class="p" data-group-id="5469036860-17">}</span><span class="p">.</span></code></pre><p>The <code class="inline">SupFlags</code> variable in the return value from <code class="inline">init/1</code> represents the
│ │ │  <a href="sup_princ.html#flags">supervisor flags</a>.</p><p>The <code class="inline">ChildSpecs</code> variable in the return value from <code class="inline">init/1</code> is a list of
│ │ │  <a href="sup_princ.html#spec">child specifications</a>.</p><p><a href="" id="flags"></a></p><h2 id="supervisor-flags" class="section-heading">
│ │ │    <a href="#supervisor-flags" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Supervisor Flags</span>
│ │ │  </h2>
│ │ │ -<p>This is the type definition for the supervisor flags:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sup_flags</span><span class="p" data-group-id="7769395726-1">(</span><span class="p" data-group-id="7769395726-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7769395726-2">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">strategy</span><span class="p" data-group-id="7769395726-3">(</span><span class="p" data-group-id="7769395726-3">)</span><span class="p">,</span><span class="w">           </span><span class="c1">% optional</span><span class="w">
│ │ │ -                </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="7769395726-4">(</span><span class="p" data-group-id="7769395726-4">)</span><span class="p">,</span><span class="w">   </span><span class="c1">% optional</span><span class="w">
│ │ │ -                </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="7769395726-5">(</span><span class="p" data-group-id="7769395726-5">)</span><span class="p">,</span><span class="w">          </span><span class="c1">% optional</span><span class="w">
│ │ │ -                </span><span class="ss">auto_shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="7769395726-6">(</span><span class="p" data-group-id="7769395726-6">)</span><span class="p" data-group-id="7769395726-2">}</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ -    </span><span class="nf">strategy</span><span class="p" data-group-id="7769395726-7">(</span><span class="p" data-group-id="7769395726-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">one_for_all</span><span class="w">
│ │ │ +<p>This is the type definition for the supervisor flags:</p><pre><code class="makeup erlang" translate="no"><span class="nf">sup_flags</span><span class="p" data-group-id="2478306182-1">(</span><span class="p" data-group-id="2478306182-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2478306182-2">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">strategy</span><span class="p" data-group-id="2478306182-3">(</span><span class="p" data-group-id="2478306182-3">)</span><span class="p">,</span><span class="w">           </span><span class="c1">% optional</span><span class="w">
│ │ │ +                </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">non_neg_integer</span><span class="p" data-group-id="2478306182-4">(</span><span class="p" data-group-id="2478306182-4">)</span><span class="p">,</span><span class="w">   </span><span class="c1">% optional</span><span class="w">
│ │ │ +                </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="2478306182-5">(</span><span class="p" data-group-id="2478306182-5">)</span><span class="p">,</span><span class="w">          </span><span class="c1">% optional</span><span class="w">
│ │ │ +                </span><span class="ss">auto_shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="2478306182-6">(</span><span class="p" data-group-id="2478306182-6">)</span><span class="p" data-group-id="2478306182-2">}</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ +    </span><span class="nf">strategy</span><span class="p" data-group-id="2478306182-7">(</span><span class="p" data-group-id="2478306182-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">one_for_all</span><span class="w">
│ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">one_for_one</span><span class="w">
│ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">rest_for_one</span><span class="w">
│ │ │                 </span><span class="p">|</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="w">
│ │ │ -    </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="7769395726-8">(</span><span class="p" data-group-id="7769395726-8">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">never</span><span class="w">
│ │ │ +    </span><span class="nf">auto_shutdown</span><span class="p" data-group-id="2478306182-8">(</span><span class="p" data-group-id="2478306182-8">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">never</span><span class="w">
│ │ │                      </span><span class="p">|</span><span class="w"> </span><span class="ss">any_significant</span><span class="w">
│ │ │                      </span><span class="p">|</span><span class="w"> </span><span class="ss">all_significant</span></code></pre><ul><li><code class="inline">strategy</code> specifies the <a href="sup_princ.html#strategy">restart strategy</a>.</li><li><code class="inline">intensity</code> and <code class="inline">period</code> specify the
│ │ │  <a href="sup_princ.html#max_intensity">maximum restart intensity</a>.</li><li><code class="inline">auto_shutdown</code> specifies whether and when a supervisor should
│ │ │  <a href="sup_princ.html#automatic-shutdown">automatically shut itself down</a>.</li></ul><p><a href="" id="strategy"></a></p><h2 id="restart-strategy" class="section-heading">
│ │ │    <a href="#restart-strategy" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -408,28 +408,28 @@
│ │ │  exhaust the <a href="sup_princ.html#max_intensity">Maximum Restart Intensity</a> of the
│ │ │  parent supervisor.</p></section><p><a href="" id="spec"></a></p><h2 id="child-specification" class="section-heading">
│ │ │    <a href="#child-specification" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Child Specification</span>
│ │ │  </h2>
│ │ │ -<p>The type definition for a child specification is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">child_spec</span><span class="p" data-group-id="1919528834-1">(</span><span class="p" data-group-id="1919528834-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1919528834-2">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">child_id</span><span class="p" data-group-id="1919528834-3">(</span><span class="p" data-group-id="1919528834-3">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% mandatory</span><span class="w">
│ │ │ -                 </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">mfargs</span><span class="p" data-group-id="1919528834-4">(</span><span class="p" data-group-id="1919528834-4">)</span><span class="p">,</span><span class="w">            </span><span class="c1">% mandatory</span><span class="w">
│ │ │ -                 </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">restart</span><span class="p" data-group-id="1919528834-5">(</span><span class="p" data-group-id="1919528834-5">)</span><span class="p">,</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ -                 </span><span class="ss">significant</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">significant</span><span class="p" data-group-id="1919528834-6">(</span><span class="p" data-group-id="1919528834-6">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ -                 </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">shutdown</span><span class="p" data-group-id="1919528834-7">(</span><span class="p" data-group-id="1919528834-7">)</span><span class="p">,</span><span class="w">       </span><span class="c1">% optional</span><span class="w">
│ │ │ -                 </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">worker</span><span class="p" data-group-id="1919528834-8">(</span><span class="p" data-group-id="1919528834-8">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% optional</span><span class="w">
│ │ │ -                 </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">modules</span><span class="p" data-group-id="1919528834-9">(</span><span class="p" data-group-id="1919528834-9">)</span><span class="p" data-group-id="1919528834-2">}</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ -    </span><span class="nf">child_id</span><span class="p" data-group-id="1919528834-10">(</span><span class="p" data-group-id="1919528834-10">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="1919528834-11">(</span><span class="p" data-group-id="1919528834-11">)</span><span class="w">
│ │ │ -    </span><span class="nf">mfargs</span><span class="p" data-group-id="1919528834-12">(</span><span class="p" data-group-id="1919528834-12">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1919528834-13">{</span><span class="n">M</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="1919528834-14">(</span><span class="p" data-group-id="1919528834-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="1919528834-15">(</span><span class="p" data-group-id="1919528834-15">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1919528834-16">[</span><span class="nf">term</span><span class="p" data-group-id="1919528834-17">(</span><span class="p" data-group-id="1919528834-17">)</span><span class="p" data-group-id="1919528834-16">]</span><span class="p" data-group-id="1919528834-13">}</span><span class="w">
│ │ │ -    </span><span class="nf">modules</span><span class="p" data-group-id="1919528834-18">(</span><span class="p" data-group-id="1919528834-18">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1919528834-19">[</span><span class="nf">module</span><span class="p" data-group-id="1919528834-20">(</span><span class="p" data-group-id="1919528834-20">)</span><span class="p" data-group-id="1919528834-19">]</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">dynamic</span><span class="w">
│ │ │ -    </span><span class="nf">restart</span><span class="p" data-group-id="1919528834-21">(</span><span class="p" data-group-id="1919528834-21">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">permanent</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">transient</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">temporary</span><span class="w">
│ │ │ -    </span><span class="nf">significant</span><span class="p" data-group-id="1919528834-22">(</span><span class="p" data-group-id="1919528834-22">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="1919528834-23">(</span><span class="p" data-group-id="1919528834-23">)</span><span class="w">
│ │ │ -    </span><span class="nf">shutdown</span><span class="p" data-group-id="1919528834-24">(</span><span class="p" data-group-id="1919528834-24">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">timeout</span><span class="p" data-group-id="1919528834-25">(</span><span class="p" data-group-id="1919528834-25">)</span><span class="w">
│ │ │ -    </span><span class="nf">worker</span><span class="p" data-group-id="1919528834-26">(</span><span class="p" data-group-id="1919528834-26">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">worker</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">supervisor</span></code></pre><ul><li><p><code class="inline">id</code> is used to identify the child specification internally by the supervisor.</p><p>The <code class="inline">id</code> key is mandatory.</p><p>Note that this identifier occasionally has been called &quot;name&quot;. As far as
│ │ │ +<p>The type definition for a child specification is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="nf">child_spec</span><span class="p" data-group-id="2631216093-1">(</span><span class="p" data-group-id="2631216093-1">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2631216093-2">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">child_id</span><span class="p" data-group-id="2631216093-3">(</span><span class="p" data-group-id="2631216093-3">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% mandatory</span><span class="w">
│ │ │ +                 </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">mfargs</span><span class="p" data-group-id="2631216093-4">(</span><span class="p" data-group-id="2631216093-4">)</span><span class="p">,</span><span class="w">            </span><span class="c1">% mandatory</span><span class="w">
│ │ │ +                 </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">restart</span><span class="p" data-group-id="2631216093-5">(</span><span class="p" data-group-id="2631216093-5">)</span><span class="p">,</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ +                 </span><span class="ss">significant</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">significant</span><span class="p" data-group-id="2631216093-6">(</span><span class="p" data-group-id="2631216093-6">)</span><span class="p">,</span><span class="w"> </span><span class="c1">% optional</span><span class="w">
│ │ │ +                 </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">shutdown</span><span class="p" data-group-id="2631216093-7">(</span><span class="p" data-group-id="2631216093-7">)</span><span class="p">,</span><span class="w">       </span><span class="c1">% optional</span><span class="w">
│ │ │ +                 </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">worker</span><span class="p" data-group-id="2631216093-8">(</span><span class="p" data-group-id="2631216093-8">)</span><span class="p">,</span><span class="w">             </span><span class="c1">% optional</span><span class="w">
│ │ │ +                 </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="nf">modules</span><span class="p" data-group-id="2631216093-9">(</span><span class="p" data-group-id="2631216093-9">)</span><span class="p" data-group-id="2631216093-2">}</span><span class="w">         </span><span class="c1">% optional</span><span class="w">
│ │ │ +    </span><span class="nf">child_id</span><span class="p" data-group-id="2631216093-10">(</span><span class="p" data-group-id="2631216093-10">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="2631216093-11">(</span><span class="p" data-group-id="2631216093-11">)</span><span class="w">
│ │ │ +    </span><span class="nf">mfargs</span><span class="p" data-group-id="2631216093-12">(</span><span class="p" data-group-id="2631216093-12">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2631216093-13">{</span><span class="n">M</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">module</span><span class="p" data-group-id="2631216093-14">(</span><span class="p" data-group-id="2631216093-14">)</span><span class="p">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="2631216093-15">(</span><span class="p" data-group-id="2631216093-15">)</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="2631216093-16">[</span><span class="nf">term</span><span class="p" data-group-id="2631216093-17">(</span><span class="p" data-group-id="2631216093-17">)</span><span class="p" data-group-id="2631216093-16">]</span><span class="p" data-group-id="2631216093-13">}</span><span class="w">
│ │ │ +    </span><span class="nf">modules</span><span class="p" data-group-id="2631216093-18">(</span><span class="p" data-group-id="2631216093-18">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2631216093-19">[</span><span class="nf">module</span><span class="p" data-group-id="2631216093-20">(</span><span class="p" data-group-id="2631216093-20">)</span><span class="p" data-group-id="2631216093-19">]</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">dynamic</span><span class="w">
│ │ │ +    </span><span class="nf">restart</span><span class="p" data-group-id="2631216093-21">(</span><span class="p" data-group-id="2631216093-21">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">permanent</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">transient</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">temporary</span><span class="w">
│ │ │ +    </span><span class="nf">significant</span><span class="p" data-group-id="2631216093-22">(</span><span class="p" data-group-id="2631216093-22">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">boolean</span><span class="p" data-group-id="2631216093-23">(</span><span class="p" data-group-id="2631216093-23">)</span><span class="w">
│ │ │ +    </span><span class="nf">shutdown</span><span class="p" data-group-id="2631216093-24">(</span><span class="p" data-group-id="2631216093-24">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">timeout</span><span class="p" data-group-id="2631216093-25">(</span><span class="p" data-group-id="2631216093-25">)</span><span class="w">
│ │ │ +    </span><span class="nf">worker</span><span class="p" data-group-id="2631216093-26">(</span><span class="p" data-group-id="2631216093-26">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">worker</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">supervisor</span></code></pre><ul><li><p><code class="inline">id</code> is used to identify the child specification internally by the supervisor.</p><p>The <code class="inline">id</code> key is mandatory.</p><p>Note that this identifier occasionally has been called &quot;name&quot;. As far as
│ │ │  possible, the terms &quot;identifier&quot; or &quot;id&quot; are now used but in order to keep
│ │ │  backwards compatibility, some occurrences of &quot;name&quot; can still be found, for
│ │ │  example in error messages.</p></li><li><p><code class="inline">start</code> defines the function call used to start the child process. It is a
│ │ │  module-function-arguments tuple used as <a href="../../erts-15.2.7.8/doc/html/erlang.html#apply/3"><code class="inline">apply(M, F, A)</code></a>.</p><p>It is to be (or result in) a call to any of the following:</p><ul><li><a href="../../lib/stdlib-6.2.2.3/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link/2,3</code></a></li><li><a href="../../lib/stdlib-6.2.2.3/doc/html/gen_server.html#start_link/4"><code class="inline">gen_server:start_link/3,4</code></a></li><li><a href="../../lib/stdlib-6.2.2.3/doc/html/gen_statem.html#start_link/4"><code class="inline">gen_statem:start_link/3,4</code></a></li><li><a href="../../lib/stdlib-6.2.2.3/doc/html/gen_event.html#start_link/2"><code class="inline">gen_event:start_link/0,1,2</code></a></li><li>A function compliant with these functions. For details, see
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/supervisor.html"><code class="inline">supervisor</code></a>.</li></ul><p>The <code class="inline">start</code> key is mandatory.</p></li><li><p><a href="" id="restart"></a> <code class="inline">restart</code> defines when a terminated child process is to be
│ │ │  restarted.</p><ul><li>A <code class="inline">permanent</code> child process is always restarted.</li><li>A <code class="inline">temporary</code> child process is never restarted (not even when the supervisor
│ │ │  restart strategy is <code class="inline">rest_for_one</code> or <code class="inline">one_for_all</code> and a sibling death
│ │ │ @@ -457,53 +457,53 @@
│ │ │  <code class="inline">supervisor</code>, the default value <code class="inline">infinity</code> will be used.</p></li><li><p><code class="inline">type</code> specifies whether the child process is a supervisor or a worker.</p><p>The <code class="inline">type</code> key is optional. If it is not given, the default value <code class="inline">worker</code>
│ │ │  will be used.</p></li><li><p><code class="inline">modules</code> has to be a list consisting of a single element. The value
│ │ │  of that element depends on the behaviour of the process:</p><ul><li>If the child process is a <code class="inline">gen_event</code>, the element has to be the atom
│ │ │  <code class="inline">dynamic</code>.</li><li>Otherwise, the element should be <code class="inline">Module</code>, where <code class="inline">Module</code> is the
│ │ │  name of the callback module.</li></ul><p>This information is used by the release handler during upgrades and
│ │ │  downgrades; see <a href="release_handling.html">Release Handling</a>.</p><p>The <code class="inline">modules</code> key is optional. If it is not given, it defaults to <code class="inline">[M]</code>, where
│ │ │  <code class="inline">M</code> comes from the child's start <code class="inline">{M,F,A}</code>.</p></li></ul><p><em>Example:</em> The child specification to start the server <code class="inline">ch3</code> in the previous
│ │ │ -example look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9971128375-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9971128375-2">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9971128375-3">[</span><span class="p" data-group-id="9971128375-3">]</span><span class="p" data-group-id="9971128375-2">}</span><span class="p">,</span><span class="w">
│ │ │ +example look as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9816505167-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9816505167-2">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9816505167-3">[</span><span class="p" data-group-id="9816505167-3">]</span><span class="p" data-group-id="9816505167-2">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">permanent</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">worker</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9971128375-4">[</span><span class="ss">ch3</span><span class="p" data-group-id="9971128375-4">]</span><span class="p" data-group-id="9971128375-1">}</span></code></pre><p>or simplified, relying on the default values:</p><pre><code class="text">#{id =&gt; ch3,
│ │ │ +  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9816505167-4">[</span><span class="ss">ch3</span><span class="p" data-group-id="9816505167-4">]</span><span class="p" data-group-id="9816505167-1">}</span></code></pre><p>or simplified, relying on the default values:</p><pre><code class="text">#{id =&gt; ch3,
│ │ │    start =&gt; {ch3, start_link, []},
│ │ │    shutdown =&gt; brutal_kill}</code></pre><p>Example: A child specification to start the event manager from the chapter about
│ │ │ -<a href="events.html#mgr">gen_event</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0721813614-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">error_man</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0721813614-2">{</span><span class="ss">gen_event</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0721813614-3">[</span><span class="p" data-group-id="0721813614-4">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="0721813614-4">}</span><span class="p" data-group-id="0721813614-3">]</span><span class="p" data-group-id="0721813614-2">}</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">dynamic</span><span class="p" data-group-id="0721813614-1">}</span></code></pre><p>Both server and event manager are registered processes which can be expected to
│ │ │ +<a href="events.html#mgr">gen_event</a>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="9476774028-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">error_man</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="9476774028-2">{</span><span class="ss">gen_event</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9476774028-3">[</span><span class="p" data-group-id="9476774028-4">{</span><span class="ss">local</span><span class="p">,</span><span class="w"> </span><span class="ss">error_man</span><span class="p" data-group-id="9476774028-4">}</span><span class="p" data-group-id="9476774028-3">]</span><span class="p" data-group-id="9476774028-2">}</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">modules</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">dynamic</span><span class="p" data-group-id="9476774028-1">}</span></code></pre><p>Both server and event manager are registered processes which can be expected to
│ │ │  be always accessible. Thus they are specified to be <code class="inline">permanent</code>.</p><p><code class="inline">ch3</code> does not need to do any cleaning up before termination. Thus, no shutdown
│ │ │  time is needed, but <code class="inline">brutal_kill</code> is sufficient. <code class="inline">error_man</code> can need some time
│ │ │  for the event handlers to clean up, thus the shutdown time is set to 5000 ms
│ │ │ -(which is the default value).</p><p>Example: A child specification to start another supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4742712040-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">sup</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4742712040-2">{</span><span class="ss">sup</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4742712040-3">[</span><span class="p" data-group-id="4742712040-3">]</span><span class="p" data-group-id="4742712040-2">}</span><span class="p">,</span><span class="w">
│ │ │ +(which is the default value).</p><p>Example: A child specification to start another supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5994086006-1">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">sup</span><span class="p">,</span><span class="w">
│ │ │ +  </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="5994086006-2">{</span><span class="ss">sup</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5994086006-3">[</span><span class="p" data-group-id="5994086006-3">]</span><span class="p" data-group-id="5994086006-2">}</span><span class="p">,</span><span class="w">
│ │ │    </span><span class="ss">restart</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">transient</span><span class="p">,</span><span class="w">
│ │ │ -  </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="4742712040-1">}</span><span class="w"> </span><span class="c1">% will cause default shutdown=&gt;infinity</span></code></pre><p><a href="" id="super_tree"></a></p><h2 id="starting-a-supervisor" class="section-heading">
│ │ │ +  </span><span class="ss">type</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">supervisor</span><span class="p" data-group-id="5994086006-1">}</span><span class="w"> </span><span class="c1">% will cause default shutdown=&gt;infinity</span></code></pre><p><a href="" id="super_tree"></a></p><h2 id="starting-a-supervisor" class="section-heading">
│ │ │    <a href="#starting-a-supervisor" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Starting a Supervisor</span>
│ │ │  </h2>
│ │ │  <p>In the previous example, the supervisor is started by calling
│ │ │ -<code class="inline">ch_sup:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="6321657285-1">(</span><span class="p" data-group-id="6321657285-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="6321657285-2">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6321657285-3">[</span><span class="p" data-group-id="6321657285-3">]</span><span class="p" data-group-id="6321657285-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch_sup:start_link</code> calls function <a href="../../lib/stdlib-6.2.2.3/doc/html/supervisor.html#start_link/2"><code class="inline">supervisor:start_link/2</code></a>, which spawns and
│ │ │ +<code class="inline">ch_sup:start_link()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">start_link</span><span class="p" data-group-id="8805284178-1">(</span><span class="p" data-group-id="8805284178-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="8805284178-2">(</span><span class="ss">ch_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8805284178-3">[</span><span class="p" data-group-id="8805284178-3">]</span><span class="p" data-group-id="8805284178-2">)</span><span class="p">.</span></code></pre><p><code class="inline">ch_sup:start_link</code> calls function <a href="../../lib/stdlib-6.2.2.3/doc/html/supervisor.html#start_link/2"><code class="inline">supervisor:start_link/2</code></a>, which spawns and
│ │ │  links to a new process, a supervisor.</p><ul><li>The first argument, <code class="inline">ch_sup</code>, is the name of the callback module, that is, the
│ │ │  module where the <code class="inline">init</code> callback function is located.</li><li>The second argument, <code class="inline">[]</code>, is a term that is passed as is to the callback
│ │ │  function <code class="inline">init</code>. Here, <code class="inline">init</code> does not need any data and ignores the argument.</li></ul><p>In this case, the supervisor is not registered. Instead its pid must be used. A
│ │ │  name can be specified by calling
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link({local, Name}, Module, Args)</code></a>
│ │ │  or
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link({global, Name}, Module, Args)</code></a>.</p><p>The new supervisor process calls the callback function <code class="inline">ch_sup:init([])</code>. <code class="inline">init</code>
│ │ │ -has to return <code class="inline">{ok, {SupFlags, ChildSpecs}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="0760008789-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="0760008789-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0760008789-2">#{</span><span class="p" data-group-id="0760008789-2">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0760008789-3">[</span><span class="p" data-group-id="0760008789-4">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0760008789-5">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0760008789-6">[</span><span class="p" data-group-id="0760008789-6">]</span><span class="p" data-group-id="0760008789-5">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="0760008789-4">}</span><span class="p" data-group-id="0760008789-3">]</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0760008789-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0760008789-8">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="0760008789-8">}</span><span class="p" data-group-id="0760008789-7">}</span><span class="p">.</span></code></pre><p>Subsequently, the supervisor starts its child processes according to the child
│ │ │ +has to return <code class="inline">{ok, {SupFlags, ChildSpecs}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">init</span><span class="p" data-group-id="7608850219-1">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="7608850219-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7608850219-2">#{</span><span class="p" data-group-id="7608850219-2">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7608850219-3">[</span><span class="p" data-group-id="7608850219-4">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">ch3</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="7608850219-5">{</span><span class="ss">ch3</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7608850219-6">[</span><span class="p" data-group-id="7608850219-6">]</span><span class="p" data-group-id="7608850219-5">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="7608850219-4">}</span><span class="p" data-group-id="7608850219-3">]</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7608850219-7">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7608850219-8">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="7608850219-8">}</span><span class="p" data-group-id="7608850219-7">}</span><span class="p">.</span></code></pre><p>Subsequently, the supervisor starts its child processes according to the child
│ │ │  specifications in the start specification. In this case there is a single child
│ │ │  process, called <code class="inline">ch3</code>.</p><p><a href="../../lib/stdlib-6.2.2.3/doc/html/supervisor.html#start_link/3"><code class="inline">supervisor:start_link/3</code></a> is synchronous. It does not return until all child
│ │ │  processes have been started.</p><h2 id="adding-a-child-process" class="section-heading">
│ │ │    <a href="#adding-a-child-process" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Adding a Child Process</span>
│ │ │ @@ -532,31 +532,31 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Simplified one_for_one Supervisors</span>
│ │ │  </h2>
│ │ │  <p>A supervisor with restart strategy <code class="inline">simple_one_for_one</code> is a simplified
│ │ │  <code class="inline">one_for_one</code> supervisor, where all child processes are dynamically added
│ │ │  instances of the same process.</p><p>The following is an example of a callback module for a <code class="inline">simple_one_for_one</code>
│ │ │ -supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="4769871148-1">(</span><span class="ss">simple_sup</span><span class="p" data-group-id="4769871148-1">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="4769871148-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="4769871148-2">)</span><span class="p">.</span><span class="w">
│ │ │ +supervisor:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">module</span><span class="p" data-group-id="0902744378-1">(</span><span class="ss">simple_sup</span><span class="p" data-group-id="0902744378-1">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">behaviour</span><span class="p" data-group-id="0902744378-2">(</span><span class="ss">supervisor</span><span class="p" data-group-id="0902744378-2">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4769871148-3">(</span><span class="p" data-group-id="4769871148-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="4769871148-4">]</span><span class="p" data-group-id="4769871148-3">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="4769871148-5">(</span><span class="p" data-group-id="4769871148-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="4769871148-6">]</span><span class="p" data-group-id="4769871148-5">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0902744378-3">(</span><span class="p" data-group-id="0902744378-4">[</span><span class="ss">start_link</span><span class="p">/</span><span class="mi">0</span><span class="p" data-group-id="0902744378-4">]</span><span class="p" data-group-id="0902744378-3">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">export</span><span class="p" data-group-id="0902744378-5">(</span><span class="p" data-group-id="0902744378-6">[</span><span class="ss">init</span><span class="p">/</span><span class="mi">1</span><span class="p" data-group-id="0902744378-6">]</span><span class="p" data-group-id="0902744378-5">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">start_link</span><span class="p" data-group-id="4769871148-7">(</span><span class="p" data-group-id="4769871148-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="4769871148-8">(</span><span class="ss">simple_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4769871148-9">[</span><span class="p" data-group-id="4769871148-9">]</span><span class="p" data-group-id="4769871148-8">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">start_link</span><span class="p" data-group-id="0902744378-7">(</span><span class="p" data-group-id="0902744378-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">supervisor</span><span class="p">:</span><span class="nf">start_link</span><span class="p" data-group-id="0902744378-8">(</span><span class="ss">simple_sup</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0902744378-9">[</span><span class="p" data-group-id="0902744378-9">]</span><span class="p" data-group-id="0902744378-8">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">init</span><span class="p" data-group-id="4769871148-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="4769871148-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4769871148-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nf">init</span><span class="p" data-group-id="0902744378-10">(</span><span class="p">_</span><span class="n">Args</span><span class="p" data-group-id="0902744378-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="n">SupFlags</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0902744378-11">#{</span><span class="ss">strategy</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">simple_one_for_one</span><span class="p">,</span><span class="w">
│ │ │                   </span><span class="ss">intensity</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ -                 </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4769871148-11">}</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4769871148-12">[</span><span class="p" data-group-id="4769871148-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">call</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="4769871148-14">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4769871148-15">[</span><span class="p" data-group-id="4769871148-15">]</span><span class="p" data-group-id="4769871148-14">}</span><span class="p">,</span><span class="w">
│ │ │ -                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="4769871148-13">}</span><span class="p" data-group-id="4769871148-12">]</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4769871148-16">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4769871148-17">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="4769871148-17">}</span><span class="p" data-group-id="4769871148-16">}</span><span class="p">.</span></code></pre><p>When started, the supervisor does not start any child
│ │ │ +                 </span><span class="ss">period</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0902744378-11">}</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="n">ChildSpecs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0902744378-12">[</span><span class="p" data-group-id="0902744378-13">#{</span><span class="ss">id</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">call</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">start</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p" data-group-id="0902744378-14">{</span><span class="ss">call</span><span class="p">,</span><span class="w"> </span><span class="ss">start_link</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0902744378-15">[</span><span class="p" data-group-id="0902744378-15">]</span><span class="p" data-group-id="0902744378-14">}</span><span class="p">,</span><span class="w">
│ │ │ +                    </span><span class="ss">shutdown</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">brutal_kill</span><span class="p" data-group-id="0902744378-13">}</span><span class="p" data-group-id="0902744378-12">]</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="0902744378-16">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0902744378-17">{</span><span class="n">SupFlags</span><span class="p">,</span><span class="w"> </span><span class="n">ChildSpecs</span><span class="p" data-group-id="0902744378-17">}</span><span class="p" data-group-id="0902744378-16">}</span><span class="p">.</span></code></pre><p>When started, the supervisor does not start any child
│ │ │  processes. Instead, all child processes need to be added dynamically by
│ │ │  calling <a href="../../lib/stdlib-6.2.2.3/doc/html/supervisor.html#start_child/2"><code class="inline">supervisor:start_child(Sup, List)</code></a>.</p><p><code class="inline">Sup</code> is the pid, or name, of the supervisor. <code class="inline">List</code> is an arbitrary list of
│ │ │  terms, which are added to the list of arguments specified in the child
│ │ │  specification. If the start function is specified as <code class="inline">{M, F, A}</code>, the child
│ │ │  process is started by calling <a href="../../erts-15.2.7.8/doc/html/erlang.html#apply/3"><code class="inline">apply(M, F, A++List)</code></a>.</p><p>For example, adding a child to <code class="inline">simple_sup</code> above:</p><pre><code class="text">supervisor:start_child(Pid, [id1])</code></pre><p>The result is that the child process is started by calling
│ │ │  <a href="../../erts-15.2.7.8/doc/html/erlang.html#apply/3"><code class="inline">apply(call, start_link, []++[id1])</code></a>, or actually:</p><pre><code class="text">call:start_link(id1)</code></pre><p>A child under a <code class="inline">simple_one_for_one</code> supervisor can be terminated with the
│ │ │  following:</p><pre><code class="text">supervisor:terminate_child(Sup, Pid)</code></pre><p><code class="inline">Sup</code> is the pid, or name, of the supervisor and <code class="inline">Pid</code> is the pid of the child.</p><p>Because a <code class="inline">simple_one_for_one</code> supervisor can have many children, it shuts them
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/tablesdatabases.html
│ │ │ @@ -146,73 +146,73 @@
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Deleting an Element</span>
│ │ │  </h3>
│ │ │  <p>The <code class="inline">delete</code> operation is considered successful if the element was not present
│ │ │  in the table. Hence all attempts to check that the element is present in the
│ │ │  Ets/Mnesia table before deletion are unnecessary. Here follows an example for
│ │ │ -Ets tables:</p><p><strong>DO</strong></p><pre><code class="text">ets:delete(Tab, Key),</code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7132011605-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="7132011605-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7132011605-2">[</span><span class="p" data-group-id="7132011605-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +Ets tables:</p><p><strong>DO</strong></p><pre><code class="text">ets:delete(Tab, Key),</code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="5848363768-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5848363768-1">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5848363768-2">[</span><span class="p" data-group-id="5848363768-2">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │          </span><span class="ss">ok</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7132011605-3">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="7132011605-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -        </span><span class="nc">ets</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="7132011605-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="7132011605-4">)</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5848363768-3">[</span><span class="p">_</span><span class="p">|</span><span class="p">_</span><span class="p" data-group-id="5848363768-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +        </span><span class="nc">ets</span><span class="p">:</span><span class="nf">delete</span><span class="p" data-group-id="5848363768-4">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="5848363768-4">)</span><span class="w">
│ │ │  </span><span class="k">end</span><span class="p">,</span></code></pre><h3 id="fetching-data" class="section-heading">
│ │ │    <a href="#fetching-data" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Fetching Data</span>
│ │ │  </h3>
│ │ │  <p>Do not fetch data that you already have.</p><p>Consider that you have a module that handles the abstract data type <code class="inline">Person</code>.
│ │ │  You export the interface function <code class="inline">print_person/1</code>, which uses the internal
│ │ │  functions <code class="inline">print_name/1</code>, <code class="inline">print_age/1</code>, and <code class="inline">print_occupation/1</code>.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>If the function <code class="inline">print_name/1</code>, and so on, had been interface functions, the
│ │ │  situation would have been different, as you do not want the user of the
│ │ │  interface to know about the internal data representation.</p></section><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ -</span><span class="nf">print_person</span><span class="p" data-group-id="8427380667-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="8427380667-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">print_person</span><span class="p" data-group-id="6220736649-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="6220736649-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Look up the person in the named table person,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="8427380667-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="8427380667-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8427380667-3">[</span><span class="n">Person</span><span class="p" data-group-id="8427380667-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">print_name</span><span class="p" data-group-id="8427380667-4">(</span><span class="n">Person</span><span class="p" data-group-id="8427380667-4">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">print_age</span><span class="p" data-group-id="8427380667-5">(</span><span class="n">Person</span><span class="p" data-group-id="8427380667-5">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">print_occupation</span><span class="p" data-group-id="8427380667-6">(</span><span class="n">Person</span><span class="p" data-group-id="8427380667-6">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="8427380667-7">[</span><span class="p" data-group-id="8427380667-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8427380667-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8427380667-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="8427380667-9">]</span><span class="p" data-group-id="8427380667-8">)</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="6220736649-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="6220736649-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="6220736649-3">[</span><span class="n">Person</span><span class="p" data-group-id="6220736649-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">print_name</span><span class="p" data-group-id="6220736649-4">(</span><span class="n">Person</span><span class="p" data-group-id="6220736649-4">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">print_age</span><span class="p" data-group-id="6220736649-5">(</span><span class="n">Person</span><span class="p" data-group-id="6220736649-5">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">print_occupation</span><span class="p" data-group-id="6220736649-6">(</span><span class="n">Person</span><span class="p" data-group-id="6220736649-6">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="6220736649-7">[</span><span class="p" data-group-id="6220736649-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6220736649-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6220736649-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="6220736649-9">]</span><span class="p" data-group-id="6220736649-8">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Internal functions</span><span class="w">
│ │ │ -</span><span class="nf">print_name</span><span class="p" data-group-id="8427380667-10">(</span><span class="n">Person</span><span class="p" data-group-id="8427380667-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8427380667-11">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8427380667-12">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="8427380667-12">]</span><span class="p" data-group-id="8427380667-11">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">print_name</span><span class="p" data-group-id="6220736649-10">(</span><span class="n">Person</span><span class="p" data-group-id="6220736649-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6220736649-11">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6220736649-12">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="6220736649-12">]</span><span class="p" data-group-id="6220736649-11">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">print_age</span><span class="p" data-group-id="8427380667-13">(</span><span class="n">Person</span><span class="p" data-group-id="8427380667-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8427380667-14">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8427380667-15">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="8427380667-15">]</span><span class="p" data-group-id="8427380667-14">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">print_age</span><span class="p" data-group-id="6220736649-13">(</span><span class="n">Person</span><span class="p" data-group-id="6220736649-13">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6220736649-14">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6220736649-15">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="6220736649-15">]</span><span class="p" data-group-id="6220736649-14">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">print_occupation</span><span class="p" data-group-id="8427380667-16">(</span><span class="n">Person</span><span class="p" data-group-id="8427380667-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="8427380667-17">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8427380667-18">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="8427380667-18">]</span><span class="p" data-group-id="8427380667-17">)</span><span class="p">.</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ -</span><span class="nf">print_person</span><span class="p" data-group-id="2435730419-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="2435730419-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="nf">print_occupation</span><span class="p" data-group-id="6220736649-16">(</span><span class="n">Person</span><span class="p" data-group-id="6220736649-16">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="6220736649-17">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6220736649-18">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="6220736649-18">]</span><span class="p" data-group-id="6220736649-17">)</span><span class="p">.</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="c1">%%% Interface function</span><span class="w">
│ │ │ +</span><span class="nf">print_person</span><span class="p" data-group-id="7490733758-1">(</span><span class="n">PersonId</span><span class="p" data-group-id="7490733758-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │      </span><span class="c1">%% Look up the person in the named table person,</span><span class="w">
│ │ │ -    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="2435730419-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="2435730419-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2435730419-3">[</span><span class="n">Person</span><span class="p" data-group-id="2435730419-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nf">print_name</span><span class="p" data-group-id="2435730419-4">(</span><span class="n">PersonID</span><span class="p" data-group-id="2435730419-4">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">print_age</span><span class="p" data-group-id="2435730419-5">(</span><span class="n">PersonID</span><span class="p" data-group-id="2435730419-5">)</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="nf">print_occupation</span><span class="p" data-group-id="2435730419-6">(</span><span class="n">PersonID</span><span class="p" data-group-id="2435730419-6">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="2435730419-7">[</span><span class="p" data-group-id="2435730419-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2435730419-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2435730419-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="2435730419-9">]</span><span class="p" data-group-id="2435730419-8">)</span><span class="w">
│ │ │ +    </span><span class="k">case</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7490733758-2">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="7490733758-2">)</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7490733758-3">[</span><span class="n">Person</span><span class="p" data-group-id="7490733758-3">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nf">print_name</span><span class="p" data-group-id="7490733758-4">(</span><span class="n">PersonID</span><span class="p" data-group-id="7490733758-4">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">print_age</span><span class="p" data-group-id="7490733758-5">(</span><span class="n">PersonID</span><span class="p" data-group-id="7490733758-5">)</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="nf">print_occupation</span><span class="p" data-group-id="7490733758-6">(</span><span class="n">PersonID</span><span class="p" data-group-id="7490733758-6">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7490733758-7">[</span><span class="p" data-group-id="7490733758-7">]</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +            </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7490733758-8">(</span><span class="s">&quot;No person with ID = </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7490733758-9">[</span><span class="n">PersonID</span><span class="p" data-group-id="7490733758-9">]</span><span class="p" data-group-id="7490733758-8">)</span><span class="w">
│ │ │      </span><span class="k">end</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%%% Internal functions</span><span class="w">
│ │ │ -</span><span class="nf">print_name</span><span class="p" data-group-id="2435730419-10">(</span><span class="n">PersonID</span><span class="p" data-group-id="2435730419-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2435730419-11">[</span><span class="n">Person</span><span class="p" data-group-id="2435730419-11">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="2435730419-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="2435730419-12">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2435730419-13">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2435730419-14">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="2435730419-14">]</span><span class="p" data-group-id="2435730419-13">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_age</span><span class="p" data-group-id="2435730419-15">(</span><span class="n">PersonID</span><span class="p" data-group-id="2435730419-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2435730419-16">[</span><span class="n">Person</span><span class="p" data-group-id="2435730419-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="2435730419-17">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="2435730419-17">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2435730419-18">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2435730419-19">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="2435730419-19">]</span><span class="p" data-group-id="2435730419-18">)</span><span class="p">.</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="nf">print_occupation</span><span class="p" data-group-id="2435730419-20">(</span><span class="n">PersonID</span><span class="p" data-group-id="2435730419-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="2435730419-21">[</span><span class="n">Person</span><span class="p" data-group-id="2435730419-21">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="2435730419-22">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="2435730419-22">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="2435730419-23">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2435730419-24">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="2435730419-24">]</span><span class="p" data-group-id="2435730419-23">)</span><span class="p">.</span></code></pre><h3 id="non-persistent-database-storage" class="section-heading">
│ │ │ +</span><span class="nf">print_name</span><span class="p" data-group-id="7490733758-10">(</span><span class="n">PersonID</span><span class="p" data-group-id="7490733758-10">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7490733758-11">[</span><span class="n">Person</span><span class="p" data-group-id="7490733758-11">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7490733758-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="7490733758-12">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7490733758-13">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7490733758-14">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="p" data-group-id="7490733758-14">]</span><span class="p" data-group-id="7490733758-13">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_age</span><span class="p" data-group-id="7490733758-15">(</span><span class="n">PersonID</span><span class="p" data-group-id="7490733758-15">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7490733758-16">[</span><span class="n">Person</span><span class="p" data-group-id="7490733758-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7490733758-17">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="7490733758-17">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7490733758-18">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7490733758-19">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="7490733758-19">]</span><span class="p" data-group-id="7490733758-18">)</span><span class="p">.</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="nf">print_occupation</span><span class="p" data-group-id="7490733758-20">(</span><span class="n">PersonID</span><span class="p" data-group-id="7490733758-20">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7490733758-21">[</span><span class="n">Person</span><span class="p" data-group-id="7490733758-21">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="7490733758-22">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="n">PersonId</span><span class="p" data-group-id="7490733758-22">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="nc">io</span><span class="p">:</span><span class="nf">format</span><span class="p" data-group-id="7490733758-23">(</span><span class="s">&quot;No person </span><span class="si">~p</span><span class="si">~n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7490733758-24">[</span><span class="n">Person</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">occupation</span><span class="p" data-group-id="7490733758-24">]</span><span class="p" data-group-id="7490733758-23">)</span><span class="p">.</span></code></pre><h3 id="non-persistent-database-storage" class="section-heading">
│ │ │    <a href="#non-persistent-database-storage" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Non-Persistent Database Storage</span>
│ │ │  </h3>
│ │ │  <p>For non-persistent database storage, prefer Ets tables over Mnesia
│ │ │  <code class="inline">local_content</code> tables. Even the Mnesia <code class="inline">dirty_write</code> operations carry a fixed
│ │ │ @@ -226,38 +226,38 @@
│ │ │  </h3>
│ │ │  <p>Assuming an Ets table that uses <code class="inline">idno</code> as key and contains the following:</p><pre><code class="text">[#person{idno = 1, name = &quot;Adam&quot;,  age = 31, occupation = &quot;mailman&quot;},
│ │ │   #person{idno = 2, name = &quot;Bryan&quot;, age = 31, occupation = &quot;cashier&quot;},
│ │ │   #person{idno = 3, name = &quot;Bryan&quot;, age = 35, occupation = &quot;banker&quot;},
│ │ │   #person{idno = 4, name = &quot;Carl&quot;,  age = 25, occupation = &quot;mailman&quot;}]</code></pre><p>If you <em>must</em> return all data stored in the Ets table, you can use
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/ets.html#tab2list/1"><code class="inline">ets:tab2list/1</code></a>. However, usually you are only interested in a subset of the
│ │ │  information in which case <a href="../../lib/stdlib-6.2.2.3/doc/html/ets.html#tab2list/1"><code class="inline">ets:tab2list/1</code></a> is expensive. If you only want to
│ │ │ -extract one field from each record, for example, the age of every person, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="8720170366-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8720170366-2">[</span><span class="p" data-group-id="8720170366-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8720170366-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ +extract one field from each record, for example, the age of every person, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="8248385577-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8248385577-2">[</span><span class="p" data-group-id="8248385577-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8248385577-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;$1&#39;</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="8720170366-4">}</span><span class="p">,</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="8720170366-5">[</span><span class="p" data-group-id="8720170366-5">]</span><span class="p">,</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="8720170366-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="8720170366-6">]</span><span class="p" data-group-id="8720170366-3">}</span><span class="p" data-group-id="8720170366-2">]</span><span class="p" data-group-id="8720170366-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="8367797187-1">(</span><span class="n">Tab</span><span class="p" data-group-id="8367797187-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="8367797187-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8367797187-3">(</span><span class="n">X</span><span class="p" data-group-id="8367797187-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="8367797187-2">)</span><span class="p">,</span></code></pre><p>If you are only interested in the age of all persons named &quot;Bryan&quot;, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="9040554940-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9040554940-2">[</span><span class="p" data-group-id="9040554940-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9040554940-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="8248385577-4">}</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="8248385577-5">[</span><span class="p" data-group-id="8248385577-5">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="8248385577-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="8248385577-6">]</span><span class="p" data-group-id="8248385577-3">}</span><span class="p" data-group-id="8248385577-2">]</span><span class="p" data-group-id="8248385577-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="8435523685-1">(</span><span class="n">Tab</span><span class="p" data-group-id="8435523685-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="8435523685-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8435523685-3">(</span><span class="n">X</span><span class="p" data-group-id="8435523685-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="8435523685-2">)</span><span class="p">,</span></code></pre><p>If you are only interested in the age of all persons named &quot;Bryan&quot;, then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="6088663855-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6088663855-2">[</span><span class="p" data-group-id="6088663855-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="6088663855-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Bryan&quot;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;$1&#39;</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="9040554940-4">}</span><span class="p">,</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="9040554940-5">[</span><span class="p" data-group-id="9040554940-5">]</span><span class="p">,</span><span class="w">
│ │ │ -                </span><span class="p" data-group-id="9040554940-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="9040554940-6">]</span><span class="p" data-group-id="9040554940-3">}</span><span class="p" data-group-id="9040554940-2">]</span><span class="p" data-group-id="9040554940-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="2554198710-1">(</span><span class="n">Tab</span><span class="p" data-group-id="2554198710-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="2554198710-2">(</span><span class="nf">fun</span><span class="p" data-group-id="2554198710-3">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="2554198710-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="6088663855-4">}</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="6088663855-5">[</span><span class="p" data-group-id="6088663855-5">]</span><span class="p">,</span><span class="w">
│ │ │ +                </span><span class="p" data-group-id="6088663855-6">[</span><span class="ss">&#39;$1&#39;</span><span class="p" data-group-id="6088663855-6">]</span><span class="p" data-group-id="6088663855-3">}</span><span class="p" data-group-id="6088663855-2">]</span><span class="p" data-group-id="6088663855-1">)</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="5269196939-1">(</span><span class="n">Tab</span><span class="p" data-group-id="5269196939-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">foldl</span><span class="p" data-group-id="5269196939-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5269196939-3">(</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="n">Acc</span><span class="p" data-group-id="5269196939-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │                                  </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                                    </span><span class="p" data-group-id="2554198710-4">[</span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="2554198710-4">]</span><span class="p">;</span><span class="w">
│ │ │ +                                    </span><span class="p" data-group-id="5269196939-4">[</span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p">|</span><span class="n">Acc</span><span class="p" data-group-id="5269196939-4">]</span><span class="p">;</span><span class="w">
│ │ │                                   </span><span class="p">_</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │                                       </span><span class="n">Acc</span><span class="w">
│ │ │                             </span><span class="k">end</span><span class="w">
│ │ │ -             </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2554198710-5">[</span><span class="p" data-group-id="2554198710-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="2554198710-2">)</span></code></pre><p>If you need all information stored in the Ets table about persons named &quot;Bryan&quot;,
│ │ │ -then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="5092223400-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5092223400-2">[</span><span class="p" data-group-id="5092223400-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5092223400-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5269196939-5">[</span><span class="p" data-group-id="5269196939-5">]</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="5269196939-2">)</span></code></pre><p>If you need all information stored in the Ets table about persons named &quot;Bryan&quot;,
│ │ │ +then:</p><p><strong>DO</strong></p><pre><code class="makeup erlang" translate="no"><span class="nc">ets</span><span class="p">:</span><span class="nf">select</span><span class="p" data-group-id="2366907080-1">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2366907080-2">[</span><span class="p" data-group-id="2366907080-3">{</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="2366907080-4">{</span><span class="ss">idno</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">name</span><span class="o">=</span><span class="s">&quot;Bryan&quot;</span><span class="p">,</span><span class="w">
│ │ │                            </span><span class="ss">age</span><span class="o">=</span><span class="ss">&#39;_&#39;</span><span class="p">,</span><span class="w">
│ │ │ -                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="5092223400-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5092223400-5">[</span><span class="p" data-group-id="5092223400-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5092223400-6">[</span><span class="ss">&#39;$_&#39;</span><span class="p" data-group-id="5092223400-6">]</span><span class="p" data-group-id="5092223400-3">}</span><span class="p" data-group-id="5092223400-2">]</span><span class="p" data-group-id="5092223400-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="8546112096-1">(</span><span class="n">Tab</span><span class="p" data-group-id="8546112096-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="8546112096-2">(</span><span class="nf">fun</span><span class="p" data-group-id="8546112096-3">(</span><span class="n">X</span><span class="p" data-group-id="8546112096-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="8546112096-2">)</span><span class="p">,</span></code></pre><h3 id="ordered_set-tables" class="section-heading">
│ │ │ +                          </span><span class="ss">occupation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="2366907080-4">}</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2366907080-5">[</span><span class="p" data-group-id="2366907080-5">]</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2366907080-6">[</span><span class="ss">&#39;$_&#39;</span><span class="p" data-group-id="2366907080-6">]</span><span class="p" data-group-id="2366907080-3">}</span><span class="p" data-group-id="2366907080-2">]</span><span class="p" data-group-id="2366907080-1">)</span><span class="p">,</span></code></pre><p><strong>DO NOT</strong></p><pre><code class="makeup erlang" translate="no"><span class="n">TabList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">tab2list</span><span class="p" data-group-id="9347097409-1">(</span><span class="n">Tab</span><span class="p" data-group-id="9347097409-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">filter</span><span class="p" data-group-id="9347097409-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9347097409-3">(</span><span class="n">X</span><span class="p" data-group-id="9347097409-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">&quot;Bryan&quot;</span><span class="w"> </span><span class="k">end</span><span class="p">,</span><span class="w"> </span><span class="n">TabList</span><span class="p" data-group-id="9347097409-2">)</span><span class="p">,</span></code></pre><h3 id="ordered_set-tables" class="section-heading">
│ │ │    <a href="#ordered_set-tables" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text"><code class="inline">ordered_set</code> Tables</span>
│ │ │  </h3>
│ │ │  <p>If the data in the table is to be accessed so that the order of the keys in the
│ │ │  table is significant, the table type <code class="inline">ordered_set</code> can be used instead of the
│ │ │ @@ -293,20 +293,20 @@
│ │ │  Clearly, the second table would have to be kept consistent with the master
│ │ │  table. Mnesia can do this for you, but a home-brew index table can be very
│ │ │  efficient compared to the overhead involved in using Mnesia.</p><p>An index table for the table in the previous examples would have to be a bag (as
│ │ │  keys would appear more than once) and can have the following contents:</p><pre><code class="text">[#index_entry{name=&quot;Adam&quot;, idno=1},
│ │ │   #index_entry{name=&quot;Bryan&quot;, idno=2},
│ │ │   #index_entry{name=&quot;Bryan&quot;, idno=3},
│ │ │   #index_entry{name=&quot;Carl&quot;, idno=4}]</code></pre><p>Given this index table, a lookup of the <code class="inline">age</code> fields for all persons named
│ │ │ -&quot;Bryan&quot; can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">MatchingIDs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="5949062236-1">(</span><span class="n">IndexTable</span><span class="p">,</span><span class="s">&quot;Bryan&quot;</span><span class="p" data-group-id="5949062236-1">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="5949062236-2">(</span><span class="nf">fun</span><span class="p" data-group-id="5949062236-3">(</span><span class="o">#</span><span class="ss">index_entry</span><span class="p" data-group-id="5949062236-4">{</span><span class="ss">idno</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="5949062236-4">}</span><span class="p" data-group-id="5949062236-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -                 </span><span class="p" data-group-id="5949062236-5">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5949062236-6">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="5949062236-6">}</span><span class="p" data-group-id="5949062236-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="5949062236-7">(</span><span class="n">PersonTable</span><span class="p">,</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="5949062236-7">)</span><span class="p">,</span><span class="w">
│ │ │ +&quot;Bryan&quot; can be done as follows:</p><pre><code class="makeup erlang" translate="no"><span class="n">MatchingIDs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="9732866701-1">(</span><span class="n">IndexTable</span><span class="p">,</span><span class="s">&quot;Bryan&quot;</span><span class="p" data-group-id="9732866701-1">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="nc">lists</span><span class="p">:</span><span class="nf">map</span><span class="p" data-group-id="9732866701-2">(</span><span class="nf">fun</span><span class="p" data-group-id="9732866701-3">(</span><span class="o">#</span><span class="ss">index_entry</span><span class="p" data-group-id="9732866701-4">{</span><span class="ss">idno</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="9732866701-4">}</span><span class="p" data-group-id="9732866701-3">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +                 </span><span class="p" data-group-id="9732866701-5">[</span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="9732866701-6">{</span><span class="ss">age</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Age</span><span class="p" data-group-id="9732866701-6">}</span><span class="p" data-group-id="9732866701-5">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">ets</span><span class="p">:</span><span class="nf">lookup</span><span class="p" data-group-id="9732866701-7">(</span><span class="n">PersonTable</span><span class="p">,</span><span class="w"> </span><span class="n">ID</span><span class="p" data-group-id="9732866701-7">)</span><span class="p">,</span><span class="w">
│ │ │                   </span><span class="n">Age</span><span class="w">
│ │ │            </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │ -          </span><span class="n">MatchingIDs</span><span class="p" data-group-id="5949062236-2">)</span><span class="p">,</span></code></pre><p>Notice that this code does not use <a href="../../lib/stdlib-6.2.2.3/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>, but instead uses the
│ │ │ +          </span><span class="n">MatchingIDs</span><span class="p" data-group-id="9732866701-2">)</span><span class="p">,</span></code></pre><p>Notice that this code does not use <a href="../../lib/stdlib-6.2.2.3/doc/html/ets.html#match/2"><code class="inline">ets:match/2</code></a>, but instead uses the
│ │ │  <a href="../../lib/stdlib-6.2.2.3/doc/html/ets.html#lookup/2"><code class="inline">ets:lookup/2</code></a> call. The <a href="../../lib/stdlib-6.2.2.3/doc/html/lists.html#map/2"><code class="inline">lists:map/2</code></a> call is only used to traverse the <code class="inline">idno</code>s
│ │ │  matching the name &quot;Bryan&quot; in the table; thus the number of lookups in the master
│ │ │  table is minimized.</p><p>Keeping an index table introduces some overhead when inserting records in the
│ │ │  table. The number of operations gained from the table must therefore be compared
│ │ │  against the number of operations inserting objects in the table. However, notice
│ │ │  that the gain is significant when the key can be used to lookup elements.</p><h2 id="mnesia" class="section-heading">
│ │ │    <a href="#mnesia" class="hover-link">
│ │ │ @@ -321,51 +321,51 @@
│ │ │    <span class="text">Secondary Index</span>
│ │ │  </h3>
│ │ │  <p>If you frequently do lookups on a field that is not the key of the table, you
│ │ │  lose performance using <a href="../../lib/mnesia-4.23.5.2/doc/html/mnesia.html#select/3">mnesia:select()</a> or
│ │ │  <a href="../../lib/mnesia-4.23.5.2/doc/html/mnesia.html#match_object/1"><code class="inline">mnesia:match_object()</code></a> as these function traverse
│ │ │  the whole table. Instead, you can create a secondary index and use
│ │ │  <a href="../../lib/mnesia-4.23.5.2/doc/html/mnesia.html#index_read/3"><code class="inline">mnesia:index_read/3</code></a> to get faster access at the expense of using more
│ │ │ -memory.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9613202655-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9613202655-2">{</span><span class="ss">idno</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">occupation</span><span class="p" data-group-id="9613202655-2">}</span><span class="p" data-group-id="9613202655-1">)</span><span class="p">.</span><span class="w">
│ │ │ +memory.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="9651253539-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9651253539-2">{</span><span class="ss">idno</span><span class="p">,</span><span class="w"> </span><span class="ss">name</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p">,</span><span class="w"> </span><span class="ss">occupation</span><span class="p" data-group-id="9651253539-2">}</span><span class="p" data-group-id="9651253539-1">)</span><span class="p">.</span><span class="w">
│ │ │          </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9613202655-3">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="9613202655-3">}</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">create_table</span><span class="p" data-group-id="9613202655-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9613202655-5">[</span><span class="p" data-group-id="9613202655-6">{</span><span class="ss">index</span><span class="p">,</span><span class="p" data-group-id="9613202655-7">[</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="9613202655-7">]</span><span class="p" data-group-id="9613202655-6">}</span><span class="p">,</span><span class="w">
│ │ │ -                              </span><span class="p" data-group-id="9613202655-8">{</span><span class="ss">attributes</span><span class="p">,</span><span class="w">
│ │ │ -                                    </span><span class="nf">record_info</span><span class="p" data-group-id="9613202655-9">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="9613202655-9">)</span><span class="p" data-group-id="9613202655-8">}</span><span class="p" data-group-id="9613202655-5">]</span><span class="p" data-group-id="9613202655-4">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9613202655-10">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="9613202655-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">add_table_index</span><span class="p" data-group-id="9613202655-11">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="9613202655-11">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9651253539-3">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="9651253539-3">}</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ +</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">create_table</span><span class="p" data-group-id="9651253539-4">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="9651253539-5">[</span><span class="p" data-group-id="9651253539-6">{</span><span class="ss">index</span><span class="p">,</span><span class="p" data-group-id="9651253539-7">[</span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="9651253539-7">]</span><span class="p" data-group-id="9651253539-6">}</span><span class="p">,</span><span class="w">
│ │ │ +                              </span><span class="p" data-group-id="9651253539-8">{</span><span class="ss">attributes</span><span class="p">,</span><span class="w">
│ │ │ +                                    </span><span class="nf">record_info</span><span class="p" data-group-id="9651253539-9">(</span><span class="ss">fields</span><span class="p">,</span><span class="w"> </span><span class="ss">person</span><span class="p" data-group-id="9651253539-9">)</span><span class="p" data-group-id="9651253539-8">}</span><span class="p" data-group-id="9651253539-5">]</span><span class="p" data-group-id="9651253539-4">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9651253539-10">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="ss">ok</span><span class="p" data-group-id="9651253539-10">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">add_table_index</span><span class="p" data-group-id="9651253539-11">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="ss">age</span><span class="p" data-group-id="9651253539-11">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="n">PersonsAge42</span><span class="w"> </span><span class="o">=</span><span class="w">
│ │ │ -     </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_index_read</span><span class="p" data-group-id="9613202655-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="9613202655-12">)</span><span class="p">,</span></code></pre><h3 id="transactions" class="section-heading">
│ │ │ +     </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_index_read</span><span class="p" data-group-id="9651253539-12">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="mi">42</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p">.</span><span class="ss">age</span><span class="p" data-group-id="9651253539-12">)</span><span class="p">,</span></code></pre><h3 id="transactions" class="section-heading">
│ │ │    <a href="#transactions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Transactions</span>
│ │ │  </h3>
│ │ │  <p>Using transactions is a way to guarantee that the distributed Mnesia database
│ │ │  remains consistent, even when many different processes update it in parallel.
│ │ │  However, if you have real-time requirements it is recommended to use dirtry
│ │ │  operations instead of transactions. When using dirty operations, you lose the
│ │ │  consistency guarantee; this is usually solved by only letting one process update
│ │ │  the table. Other processes must send update requests to that process.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="c1">%% Using transaction</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="1931057166-1">(</span><span class="p" data-group-id="1931057166-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -          </span><span class="p" data-group-id="1931057166-2">[</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="1931057166-3">(</span><span class="p" data-group-id="1931057166-4">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="1931057166-4">}</span><span class="p" data-group-id="1931057166-3">)</span><span class="p">,</span><span class="w">
│ │ │ -           </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="1931057166-5">(</span><span class="p" data-group-id="1931057166-6">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="1931057166-6">}</span><span class="p" data-group-id="1931057166-5">)</span><span class="p" data-group-id="1931057166-2">]</span><span class="w">
│ │ │ +</span><span class="n">Fun</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">fun</span><span class="p" data-group-id="7756392807-1">(</span><span class="p" data-group-id="7756392807-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +          </span><span class="p" data-group-id="7756392807-2">[</span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="7756392807-3">(</span><span class="p" data-group-id="7756392807-4">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="7756392807-4">}</span><span class="p" data-group-id="7756392807-3">)</span><span class="p">,</span><span class="w">
│ │ │ +           </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">read</span><span class="p" data-group-id="7756392807-5">(</span><span class="p" data-group-id="7756392807-6">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="7756392807-6">}</span><span class="p" data-group-id="7756392807-5">)</span><span class="p" data-group-id="7756392807-2">]</span><span class="w">
│ │ │        </span><span class="k">end</span><span class="p">,</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="1931057166-7">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1931057166-8">[</span><span class="n">Result1</span><span class="p">,</span><span class="w"> </span><span class="n">Result2</span><span class="p" data-group-id="1931057166-8">]</span><span class="p" data-group-id="1931057166-7">}</span><span class="w">  </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">transaction</span><span class="p" data-group-id="1931057166-9">(</span><span class="n">Fun</span><span class="p" data-group-id="1931057166-9">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7756392807-7">{</span><span class="ss">atomic</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7756392807-8">[</span><span class="n">Result1</span><span class="p">,</span><span class="w"> </span><span class="n">Result2</span><span class="p" data-group-id="7756392807-8">]</span><span class="p" data-group-id="7756392807-7">}</span><span class="w">  </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">transaction</span><span class="p" data-group-id="7756392807-9">(</span><span class="n">Fun</span><span class="p" data-group-id="7756392807-9">)</span><span class="p">,</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │  </span><span class="c1">%% Same thing using dirty operations</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">Result1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="1931057166-10">(</span><span class="p" data-group-id="1931057166-11">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="1931057166-11">}</span><span class="p" data-group-id="1931057166-10">)</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="n">Result2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="1931057166-12">(</span><span class="p" data-group-id="1931057166-13">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="1931057166-13">}</span><span class="p" data-group-id="1931057166-12">)</span><span class="p">,</span></code></pre>
│ │ │ +</span><span class="n">Result1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="7756392807-10">(</span><span class="p" data-group-id="7756392807-11">{</span><span class="n">Table</span><span class="p">,</span><span class="w"> </span><span class="n">Key</span><span class="p" data-group-id="7756392807-11">}</span><span class="p" data-group-id="7756392807-10">)</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="n">Result2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">mnesia</span><span class="p">:</span><span class="nf">dirty_read</span><span class="p" data-group-id="7756392807-12">(</span><span class="p" data-group-id="7756392807-13">{</span><span class="n">Table2</span><span class="p">,</span><span class="w"> </span><span class="n">Key2</span><span class="p" data-group-id="7756392807-13">}</span><span class="p" data-group-id="7756392807-12">)</span><span class="p">,</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="eff_guide_functions.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/system/typespec.html
│ │ │ @@ -238,124 +238,124 @@
│ │ │  and optional <code class="inline">(=&gt;)</code> association types. If an association type is mandatory, an
│ │ │  association with that type needs to be present. In the case of an optional
│ │ │  association type it is not required for the key type to be present.</p><p>The notation <code class="inline">#{}</code> specifies the singleton type for the empty map. Note that
│ │ │  this notation is not a shorthand for the <a href="../../erts-15.2.7.8/doc/html/erlang.html#t:map/0"><code class="inline">map/0</code></a> type.</p><p>For convenience, the following types are also built-in. They can be thought as
│ │ │  predefined aliases for the type unions also shown in the table.</p><p><a href="" id="builtin_types"></a></p><table><thead><tr><th style="text-align: left;"><em>Built-in type</em></th><th style="text-align: left;"><em>Defined as</em></th></tr></thead><tbody><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:term/0"><code class="inline">term/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:any/0"><code class="inline">any/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:binary/0"><code class="inline">binary/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:_*8&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:nonempty_binary/0"><code class="inline">nonempty_binary/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:8, _:_*8&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:bitstring/0"><code class="inline">bitstring/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:_*1&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:nonempty_bitstring/0"><code class="inline">nonempty_bitstring/0</code></a></td><td style="text-align: left;"><code class="inline">&lt;&lt;_:1, _:_*1&gt;&gt;</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a></td><td style="text-align: left;"><code class="inline">'false'</code> | <code class="inline">'true'</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:byte/0"><code class="inline">byte/0</code></a></td><td style="text-align: left;"><code class="inline">0..255</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:char/0"><code class="inline">char/0</code></a></td><td style="text-align: left;"><code class="inline">0..16#10ffff</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:nil/0"><code class="inline">nil/0</code></a></td><td style="text-align: left;"><code class="inline">[]</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:number/0"><code class="inline">number/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:integer/0"><code class="inline">integer/0</code></a> | <a href="../../erts-15.2.7.8/doc/html/erlang.html#t:float/0"><code class="inline">float/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:list/0"><code class="inline">list/0</code></a></td><td style="text-align: left;"><code class="inline">[any()]</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:maybe_improper_list/0"><code class="inline">maybe_improper_list/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:maybe_improper_list/2"><code class="inline">maybe_improper_list(any(), any())</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:nonempty_list/0"><code class="inline">nonempty_list/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:nonempty_list/1"><code class="inline">nonempty_list(any())</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:string/0"><code class="inline">string/0</code></a></td><td style="text-align: left;"><code class="inline">[char()]</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:nonempty_string/0"><code class="inline">nonempty_string/0</code></a></td><td style="text-align: left;"><code class="inline">[char(),...]</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:iodata/0"><code class="inline">iodata/0</code></a></td><td style="text-align: left;"><code class="inline">iolist()</code> | <code class="inline">binary()</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:iolist/0"><code class="inline">iolist/0</code></a></td><td style="text-align: left;"><code class="inline">maybe_improper_list(byte()</code> | <code class="inline">binary()</code> | <code class="inline">iolist(), binary()</code> | <code class="inline">[])</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:map/0"><code class="inline">map/0</code></a></td><td style="text-align: left;"><code class="inline">#{any() =&gt; any()}</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:function/0"><code class="inline">function/0</code></a></td><td style="text-align: left;"><code class="inline">fun()</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:module/0"><code class="inline">module/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:atom/0"><code class="inline">atom/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:mfa/0"><code class="inline">mfa/0</code></a></td><td style="text-align: left;"><code class="inline">{module(),atom(),arity()}</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:arity/0"><code class="inline">arity/0</code></a></td><td style="text-align: left;"><code class="inline">0..255</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:identifier/0"><code class="inline">identifier/0</code></a></td><td style="text-align: left;"><code class="inline">pid()</code> | <code class="inline">port()</code> | <code class="inline">reference()</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#node/0"><code class="inline">node/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:atom/0"><code class="inline">atom/0</code></a></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:timeout/0"><code class="inline">timeout/0</code></a></td><td style="text-align: left;"><code class="inline">'infinity'</code> | <code class="inline">non_neg_integer()</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a></td><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:none/0"><code class="inline">none/0</code></a></td></tr></tbody></table><p><em>Table: Built-in types, predefined aliases</em></p><p>In addition, the following three built-in types exist and can be thought as
│ │ │  defined below, though strictly their &quot;type definition&quot; is not valid syntax
│ │ │  according to the type language defined above.</p><table><thead><tr><th style="text-align: left;"><em>Built-in type</em></th><th style="text-align: left;"><em>Can be thought defined by the syntax</em></th></tr></thead><tbody><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:non_neg_integer/0"><code class="inline">non_neg_integer/0</code></a></td><td style="text-align: left;"><code class="inline">0..</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:pos_integer/0"><code class="inline">pos_integer/0</code></a></td><td style="text-align: left;"><code class="inline">1..</code></td></tr><tr><td style="text-align: left;"><a href="../../erts-15.2.7.8/doc/html/erlang.html#t:neg_integer/0"><code class="inline">neg_integer/0</code></a></td><td style="text-align: left;"><code class="inline">..-1</code></td></tr></tbody></table><p><em>Table: Additional built-in types</em></p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The following built-in list types also exist, but they are expected to be
│ │ │ -rarely used. Hence, they have long names:</p></section><pre><code class="makeup erlang" translate="no"><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="7238542762-1">(</span><span class="p" data-group-id="7238542762-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="7238542762-2">(</span><span class="nf">any</span><span class="p" data-group-id="7238542762-3">(</span><span class="p" data-group-id="7238542762-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="7238542762-4">(</span><span class="p" data-group-id="7238542762-4">)</span><span class="p" data-group-id="7238542762-2">)</span><span class="w">
│ │ │ -</span><span class="nf">nonempty_improper_list</span><span class="p" data-group-id="7238542762-5">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="7238542762-5">)</span><span class="w">
│ │ │ -</span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="7238542762-6">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="7238542762-6">)</span></code></pre><p>where the last two types define the set of Erlang terms one would expect.</p><p>Also for convenience, record notation is allowed to be used. Records are
│ │ │ -shorthands for the corresponding tuples:</p><pre><code class="makeup erlang" translate="no"><span class="n">Record</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="3627236968-1">{</span><span class="p" data-group-id="3627236968-1">}</span><span class="w">
│ │ │ -        </span><span class="p">|</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="3627236968-2">{</span><span class="n">Fields</span><span class="p" data-group-id="3627236968-2">}</span></code></pre><p>Records are extended to possibly contain type information. This is described in
│ │ │ +rarely used. Hence, they have long names:</p></section><pre><code class="makeup erlang" translate="no"><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="4477378456-1">(</span><span class="p" data-group-id="4477378456-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="4477378456-2">(</span><span class="nf">any</span><span class="p" data-group-id="4477378456-3">(</span><span class="p" data-group-id="4477378456-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="4477378456-4">(</span><span class="p" data-group-id="4477378456-4">)</span><span class="p" data-group-id="4477378456-2">)</span><span class="w">
│ │ │ +</span><span class="nf">nonempty_improper_list</span><span class="p" data-group-id="4477378456-5">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="4477378456-5">)</span><span class="w">
│ │ │ +</span><span class="nf">nonempty_maybe_improper_list</span><span class="p" data-group-id="4477378456-6">(</span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="n">Type2</span><span class="p" data-group-id="4477378456-6">)</span></code></pre><p>where the last two types define the set of Erlang terms one would expect.</p><p>Also for convenience, record notation is allowed to be used. Records are
│ │ │ +shorthands for the corresponding tuples:</p><pre><code class="makeup erlang" translate="no"><span class="n">Record</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="6258001524-1">{</span><span class="p" data-group-id="6258001524-1">}</span><span class="w">
│ │ │ +        </span><span class="p">|</span><span class="w"> </span><span class="p">#</span><span class="n">Erlang_Atom</span><span class="p" data-group-id="6258001524-2">{</span><span class="n">Fields</span><span class="p" data-group-id="6258001524-2">}</span></code></pre><p>Records are extended to possibly contain type information. This is described in
│ │ │  <a href="typespec.html#typeinrecords">Type Information in Record Declarations</a>.</p><h3 id="redefining-built-in-types" class="section-heading">
│ │ │    <a href="#redefining-built-in-types" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Redefining built-in types</span>
│ │ │  </h3>
│ │ │  <section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Starting from Erlang/OTP 26, it is permitted to define a type having the same
│ │ │  name as a built-in type.</p></section><p>It is recommended to avoid deliberately reusing built-in names because it can be
│ │ │  confusing. However, when an Erlang/OTP release introduces a new type, code that
│ │ │  happened to define its own type having the same name will continue to work.</p><p>As an example, imagine that the Erlang/OTP 42 release introduces a new type
│ │ │ -<code class="inline">gadget()</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="5328123109-1">(</span><span class="p" data-group-id="5328123109-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="5328123109-2">{</span><span class="ss">&#39;gadget&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">reference</span><span class="p" data-group-id="5328123109-3">(</span><span class="p" data-group-id="5328123109-3">)</span><span class="p" data-group-id="5328123109-2">}</span><span class="p">.</span></code></pre><p>Further imagine that some code has its own (different) definition of <code class="inline">gadget()</code>,
│ │ │ -for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="0950788627-1">(</span><span class="p" data-group-id="0950788627-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0950788627-2">#{</span><span class="p" data-group-id="0950788627-2">}</span><span class="p">.</span></code></pre><p>Since redefinitions are allowed, the code will still compile (but with a
│ │ │ +<code class="inline">gadget()</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="1864875568-1">(</span><span class="p" data-group-id="1864875568-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1864875568-2">{</span><span class="ss">&#39;gadget&#39;</span><span class="p">,</span><span class="w"> </span><span class="nf">reference</span><span class="p" data-group-id="1864875568-3">(</span><span class="p" data-group-id="1864875568-3">)</span><span class="p" data-group-id="1864875568-2">}</span><span class="p">.</span></code></pre><p>Further imagine that some code has its own (different) definition of <code class="inline">gadget()</code>,
│ │ │ +for example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">gadget</span><span class="p" data-group-id="1750748017-1">(</span><span class="p" data-group-id="1750748017-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="1750748017-2">#{</span><span class="p" data-group-id="1750748017-2">}</span><span class="p">.</span></code></pre><p>Since redefinitions are allowed, the code will still compile (but with a
│ │ │  warning), and Dialyzer will not emit any additional warnings.</p><h2 id="type-declarations-of-user-defined-types" class="section-heading">
│ │ │    <a href="#type-declarations-of-user-defined-types" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Type Declarations of User-Defined Types</span>
│ │ │  </h2>
│ │ │  <p>As seen, the basic syntax of a type is an atom followed by closed parentheses.
│ │ │  New types are declared using <code class="inline">-type</code> and <code class="inline">-opaque</code> attributes as in the
│ │ │ -following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_struct_type</span><span class="p" data-group-id="1811737327-1">(</span><span class="p" data-group-id="1811737327-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">my_opaq_type</span><span class="p" data-group-id="1811737327-2">(</span><span class="p" data-group-id="1811737327-2">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span></code></pre><p>The type name is the atom <code class="inline">my_struct_type</code>, followed by parentheses. <code class="inline">Type</code> is a
│ │ │ +following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">my_struct_type</span><span class="p" data-group-id="1478618977-1">(</span><span class="p" data-group-id="1478618977-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">opaque</span><span class="w"> </span><span class="nf">my_opaq_type</span><span class="p" data-group-id="1478618977-2">(</span><span class="p" data-group-id="1478618977-2">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span></code></pre><p>The type name is the atom <code class="inline">my_struct_type</code>, followed by parentheses. <code class="inline">Type</code> is a
│ │ │  type as defined in the previous section. A current restriction is that <code class="inline">Type</code>
│ │ │  can contain only predefined types, or user-defined types which are either of the
│ │ │  following:</p><ul><li>Module-local type, that is, with a definition that is present in the code of
│ │ │  the module</li><li>Remote type, that is, type defined in, and exported by, other modules; more
│ │ │  about this soon.</li></ul><p>For module-local types, the restriction that their definition exists in the
│ │ │  module is enforced by the compiler and results in a compilation error. (A
│ │ │  similar restriction currently exists for records.)</p><p>Type declarations can also be parameterized by including type variables between
│ │ │  the parentheses. The syntax of type variables is the same as Erlang variables,
│ │ │  that is, starts with an upper-case letter. These variables is to
│ │ │ -appear on the RHS of the definition. A concrete example follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">orddict</span><span class="p" data-group-id="4852722113-1">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="4852722113-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="4852722113-2">[</span><span class="p" data-group-id="4852722113-3">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="4852722113-3">}</span><span class="p" data-group-id="4852722113-2">]</span><span class="p">.</span></code></pre><p>A module can export some types to declare that other modules are allowed to
│ │ │ -refer to them as <em>remote types</em>. This declaration has the following form:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="3439612611-1">(</span><span class="p" data-group-id="3439612611-2">[</span><span class="n">T1</span><span class="o">/</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Tk</span><span class="o">/</span><span class="n">Ak</span><span class="p" data-group-id="3439612611-2">]</span><span class="p" data-group-id="3439612611-1">)</span><span class="p">.</span></code></pre><p>Here the <code class="inline">Ti</code>s are atoms (the name of the type) and the <code class="inline">Ai</code>s are their arguments.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="8126346992-1">(</span><span class="p" data-group-id="8126346992-2">[</span><span class="ss">my_struct_type</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">orddict</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="8126346992-2">]</span><span class="p" data-group-id="8126346992-1">)</span><span class="p">.</span></code></pre><p>Assuming that these types are exported from module <code class="inline">'mod'</code>, you can refer to
│ │ │ -them from other modules using remote type expressions like the following:</p><pre><code class="makeup erlang" translate="no"><span class="nc">mod</span><span class="p">:</span><span class="nf">my_struct_type</span><span class="p" data-group-id="7967486240-1">(</span><span class="p" data-group-id="7967486240-1">)</span><span class="w">
│ │ │ -</span><span class="nc">mod</span><span class="p">:</span><span class="nf">orddict</span><span class="p" data-group-id="7967486240-2">(</span><span class="nf">atom</span><span class="p" data-group-id="7967486240-3">(</span><span class="p" data-group-id="7967486240-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7967486240-4">(</span><span class="p" data-group-id="7967486240-4">)</span><span class="p" data-group-id="7967486240-2">)</span></code></pre><p>It is not allowed to refer to types that are not declared as exported.</p><p>Types declared as <code class="inline">opaque</code> represent sets of terms whose structure is not
│ │ │ +appear on the RHS of the definition. A concrete example follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">orddict</span><span class="p" data-group-id="7575800703-1">(</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="7575800703-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="7575800703-2">[</span><span class="p" data-group-id="7575800703-3">{</span><span class="n">Key</span><span class="p">,</span><span class="w"> </span><span class="n">Val</span><span class="p" data-group-id="7575800703-3">}</span><span class="p" data-group-id="7575800703-2">]</span><span class="p">.</span></code></pre><p>A module can export some types to declare that other modules are allowed to
│ │ │ +refer to them as <em>remote types</em>. This declaration has the following form:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="3551383147-1">(</span><span class="p" data-group-id="3551383147-2">[</span><span class="n">T1</span><span class="o">/</span><span class="n">A1</span><span class="p">,</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="p">,</span><span class="w"> </span><span class="n">Tk</span><span class="o">/</span><span class="n">Ak</span><span class="p" data-group-id="3551383147-2">]</span><span class="p" data-group-id="3551383147-1">)</span><span class="p">.</span></code></pre><p>Here the <code class="inline">Ti</code>s are atoms (the name of the type) and the <code class="inline">Ai</code>s are their arguments.</p><p><em>Example:</em></p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">export_type</span><span class="p" data-group-id="7657439965-1">(</span><span class="p" data-group-id="7657439965-2">[</span><span class="ss">my_struct_type</span><span class="p">/</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">orddict</span><span class="p">/</span><span class="mi">2</span><span class="p" data-group-id="7657439965-2">]</span><span class="p" data-group-id="7657439965-1">)</span><span class="p">.</span></code></pre><p>Assuming that these types are exported from module <code class="inline">'mod'</code>, you can refer to
│ │ │ +them from other modules using remote type expressions like the following:</p><pre><code class="makeup erlang" translate="no"><span class="nc">mod</span><span class="p">:</span><span class="nf">my_struct_type</span><span class="p" data-group-id="5098064267-1">(</span><span class="p" data-group-id="5098064267-1">)</span><span class="w">
│ │ │ +</span><span class="nc">mod</span><span class="p">:</span><span class="nf">orddict</span><span class="p" data-group-id="5098064267-2">(</span><span class="nf">atom</span><span class="p" data-group-id="5098064267-3">(</span><span class="p" data-group-id="5098064267-3">)</span><span class="p">,</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="5098064267-4">(</span><span class="p" data-group-id="5098064267-4">)</span><span class="p" data-group-id="5098064267-2">)</span></code></pre><p>It is not allowed to refer to types that are not declared as exported.</p><p>Types declared as <code class="inline">opaque</code> represent sets of terms whose structure is not
│ │ │  supposed to be visible from outside of their defining module. That is, only the
│ │ │  module defining them is allowed to depend on their term structure. Consequently,
│ │ │  such types do not make much sense as module local - module local types are not
│ │ │  accessible by other modules anyway - and is always to be exported.</p><p>Read more on <a href="opaques.html">Opaques</a></p><p><a href="" id="typeinrecords"></a></p><h2 id="type-information-in-record-declarations" class="section-heading">
│ │ │    <a href="#type-information-in-record-declarations" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Type Information in Record Declarations</span>
│ │ │  </h2>
│ │ │  <p>The types of record fields can be specified in the declaration of the record.
│ │ │ -The syntax for this is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5288180541-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5288180541-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="5288180541-2">}</span><span class="p" data-group-id="5288180541-1">)</span><span class="p">.</span></code></pre><p>For fields without type annotations, their type defaults to <code class="inline">any()</code>. That is, the
│ │ │ -previous example is a shorthand for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="2593873908-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="2593873908-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="2593873908-3">(</span><span class="p" data-group-id="2593873908-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="2593873908-2">}</span><span class="p" data-group-id="2593873908-1">)</span><span class="p">.</span></code></pre><p>In the presence of initial values for fields, the type must be declared after
│ │ │ -the initialization, as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4703286289-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4703286289-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="4703286289-3">[</span><span class="p" data-group-id="4703286289-3">]</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="4703286289-2">}</span><span class="p" data-group-id="4703286289-1">)</span><span class="p">.</span></code></pre><p>The initial values for fields are to be compatible with (that is, a member of)
│ │ │ +The syntax for this is as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="4707709640-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4707709640-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="4707709640-2">}</span><span class="p" data-group-id="4707709640-1">)</span><span class="p">.</span></code></pre><p>For fields without type annotations, their type defaults to <code class="inline">any()</code>. That is, the
│ │ │ +previous example is a shorthand for the following:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7121832485-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7121832485-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">any</span><span class="p" data-group-id="7121832485-3">(</span><span class="p" data-group-id="7121832485-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="7121832485-2">}</span><span class="p" data-group-id="7121832485-1">)</span><span class="p">.</span></code></pre><p>In the presence of initial values for fields, the type must be declared after
│ │ │ +the initialization, as follows:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="0160187521-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0160187521-2">{</span><span class="ss">field1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0160187521-3">[</span><span class="p" data-group-id="0160187521-3">]</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type1</span><span class="p">,</span><span class="w"> </span><span class="ss">field2</span><span class="p">,</span><span class="w"> </span><span class="ss">field3</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="n">Type3</span><span class="p" data-group-id="0160187521-2">}</span><span class="p" data-group-id="0160187521-1">)</span><span class="p">.</span></code></pre><p>The initial values for fields are to be compatible with (that is, a member of)
│ │ │  the corresponding types. This is checked by the compiler and results in a
│ │ │  compilation error if a violation is detected.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Change</h4><p>Before Erlang/OTP 19, for fields without initial values, the singleton type
│ │ │  <code class="inline">'undefined'</code> was added to all declared types. In other words, the following
│ │ │ -two record declarations had identical effects:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6328574490-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6328574490-2">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="6328574490-3">(</span><span class="p" data-group-id="6328574490-3">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="6328574490-4">(</span><span class="p" data-group-id="6328574490-4">)</span><span class="p">,</span><span class="w">
│ │ │ -             </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="6328574490-2">}</span><span class="p" data-group-id="6328574490-1">)</span><span class="p">.</span><span class="w">
│ │ │ +two record declarations had identical effects:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6778487207-1">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778487207-2">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="6778487207-3">(</span><span class="p" data-group-id="6778487207-3">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="6778487207-4">(</span><span class="p" data-group-id="6778487207-4">)</span><span class="p">,</span><span class="w">
│ │ │ +             </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="6778487207-2">}</span><span class="p" data-group-id="6778487207-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6328574490-5">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6328574490-6">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="6328574490-7">(</span><span class="p" data-group-id="6328574490-7">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="6328574490-8">(</span><span class="p" data-group-id="6328574490-8">)</span><span class="p">,</span><span class="w">
│ │ │ -              </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="6328574490-6">}</span><span class="p" data-group-id="6328574490-5">)</span><span class="p">.</span></code></pre><p>This is no longer the case. If you require <code class="inline">'undefined'</code> in your record field
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="6778487207-5">(</span><span class="ss">rec</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="6778487207-6">{</span><span class="ss">f1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="6778487207-7">(</span><span class="p" data-group-id="6778487207-7">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="ss">f2</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">float</span><span class="p" data-group-id="6778487207-8">(</span><span class="p" data-group-id="6778487207-8">)</span><span class="p">,</span><span class="w">
│ │ │ +              </span><span class="ss">f3</span><span class="w">      </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="ss">&#39;undefined&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;a&#39;</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;b&#39;</span><span class="p" data-group-id="6778487207-6">}</span><span class="p" data-group-id="6778487207-5">)</span><span class="p">.</span></code></pre><p>This is no longer the case. If you require <code class="inline">'undefined'</code> in your record field
│ │ │  type, you must explicitly add it to the typespec, as in the 2nd example.</p></section><p>Any record, containing type information or not, once defined, can be used as a
│ │ │  type using the following syntax:</p><pre><code class="text">#rec{}</code></pre><p>In addition, the record fields can be further specified when using a record type
│ │ │  by adding type information about the field as follows:</p><pre><code class="text">#rec{some_field :: Type}</code></pre><p>Any unspecified fields are assumed to have the type in the original record
│ │ │  declaration.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>When records are used to create patterns for ETS and Mnesia match functions,
│ │ │ -Dialyzer may need some help not to emit bad warnings. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="5209755876-1">(</span><span class="p" data-group-id="5209755876-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="5209755876-2">(</span><span class="p" data-group-id="5209755876-2">)</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="5209755876-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5209755876-4">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="5209755876-5">(</span><span class="p" data-group-id="5209755876-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="5209755876-6">(</span><span class="p" data-group-id="5209755876-6">)</span><span class="p" data-group-id="5209755876-4">}</span><span class="p" data-group-id="5209755876-3">)</span><span class="p">.</span><span class="w">
│ │ │ +Dialyzer may need some help not to emit bad warnings. For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7671827050-1">(</span><span class="p" data-group-id="7671827050-1">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="7671827050-2">(</span><span class="p" data-group-id="7671827050-2">)</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7671827050-3">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7671827050-4">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="7671827050-5">(</span><span class="p" data-group-id="7671827050-5">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7671827050-6">(</span><span class="p" data-group-id="7671827050-6">)</span><span class="p" data-group-id="7671827050-4">}</span><span class="p" data-group-id="7671827050-3">)</span><span class="p">.</span><span class="w">
│ │ │  
│ │ │ -</span><span class="nf">lookup</span><span class="p" data-group-id="5209755876-7">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="5209755876-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="5209755876-8">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="5209755876-9">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="5209755876-9">}</span><span class="p" data-group-id="5209755876-8">)</span><span class="p">.</span></code></pre><p>Dialyzer will emit a warning since <code class="inline">'_'</code> is not in the type of record field
│ │ │ +</span><span class="nf">lookup</span><span class="p" data-group-id="7671827050-7">(</span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="n">Tab</span><span class="p" data-group-id="7671827050-7">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="nc">ets</span><span class="p">:</span><span class="nf">match_object</span><span class="p" data-group-id="7671827050-8">(</span><span class="n">Tab</span><span class="p">,</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7671827050-9">{</span><span class="ss">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Name</span><span class="p">,</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="7671827050-9">}</span><span class="p" data-group-id="7671827050-8">)</span><span class="p">.</span></code></pre><p>Dialyzer will emit a warning since <code class="inline">'_'</code> is not in the type of record field
│ │ │  <code class="inline">height</code>.</p><p>The recommended way of dealing with this is to declare the smallest record
│ │ │  field types to accommodate all your needs, and then create refinements as
│ │ │ -needed. The modified example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="8364556085-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8364556085-2">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="8364556085-3">(</span><span class="p" data-group-id="8364556085-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="8364556085-4">(</span><span class="p" data-group-id="8364556085-4">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="8364556085-2">}</span><span class="p" data-group-id="8364556085-1">)</span><span class="p">.</span><span class="w">
│ │ │ +needed. The modified example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">record</span><span class="p" data-group-id="7449767583-1">(</span><span class="ss">person</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="7449767583-2">{</span><span class="ss">name</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">string</span><span class="p" data-group-id="7449767583-3">(</span><span class="p" data-group-id="7449767583-3">)</span><span class="p">,</span><span class="w"> </span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7449767583-4">(</span><span class="p" data-group-id="7449767583-4">)</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">&#39;_&#39;</span><span class="p" data-group-id="7449767583-2">}</span><span class="p" data-group-id="7449767583-1">)</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="w">
│ │ │ -</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">person</span><span class="p" data-group-id="8364556085-5">(</span><span class="p" data-group-id="8364556085-5">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="8364556085-6">{</span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="8364556085-7">(</span><span class="p" data-group-id="8364556085-7">)</span><span class="p" data-group-id="8364556085-6">}</span><span class="p">.</span></code></pre><p>In specifications and type declarations the type <code class="inline">person()</code> is to be preferred
│ │ │ +</span><span class="p">-</span><span class="na">type</span><span class="w"> </span><span class="nf">person</span><span class="p" data-group-id="7449767583-5">(</span><span class="p" data-group-id="7449767583-5">)</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="o">#</span><span class="ss">person</span><span class="p" data-group-id="7449767583-6">{</span><span class="ss">height</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">height</span><span class="p" data-group-id="7449767583-7">(</span><span class="p" data-group-id="7449767583-7">)</span><span class="p" data-group-id="7449767583-6">}</span><span class="p">.</span></code></pre><p>In specifications and type declarations the type <code class="inline">person()</code> is to be preferred
│ │ │  before <code class="inline">#person{}</code>.</p></section><h2 id="specifications-for-functions" class="section-heading">
│ │ │    <a href="#specifications-for-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Specifications for Functions</span>
│ │ │  </h2>
│ │ │  <p>A specification (or contract) for a function is given using the <code class="inline">-spec</code>
│ │ │  attribute. The general format is as follows:</p><pre><code class="text">-spec Function(ArgType1, ..., ArgTypeN) -&gt; ReturnType.</code></pre><p>An implementation of the function with the same name <code class="inline">Function</code> must exist in
│ │ │  the current module, and the arity of the function must match the number of
│ │ │  arguments, otherwise the compilation fails.</p><p>The following longer format with module name is also valid as long as <code class="inline">Module</code>
│ │ │  is the name of the current module. This can be useful for documentation
│ │ │  purposes.</p><pre><code class="text">-spec Module:Function(ArgType1, ..., ArgTypeN) -&gt; ReturnType.</code></pre><p>Also, for documentation purposes, argument names can be given:</p><pre><code class="text">-spec Function(ArgName1 :: Type1, ..., ArgNameN :: TypeN) -&gt; RT.</code></pre><p>A function specification can be overloaded. That is, it can have several types,
│ │ │ -separated by a semicolon (<code class="inline">;</code>). For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="3883092162-1">(</span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="3883092162-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T3</span><span class="p">;</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="3883092162-2">(</span><span class="n">T4</span><span class="p">,</span><span class="w"> </span><span class="n">T5</span><span class="p" data-group-id="3883092162-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T6</span><span class="p">.</span></code></pre><p>A current restriction, which currently results in a warning by Dialyzer, is that
│ │ │ +separated by a semicolon (<code class="inline">;</code>). For example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="2217068539-1">(</span><span class="n">T1</span><span class="p">,</span><span class="w"> </span><span class="n">T2</span><span class="p" data-group-id="2217068539-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T3</span><span class="p">;</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="2217068539-2">(</span><span class="n">T4</span><span class="p">,</span><span class="w"> </span><span class="n">T5</span><span class="p" data-group-id="2217068539-2">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">T6</span><span class="p">.</span></code></pre><p>A current restriction, which currently results in a warning by Dialyzer, is that
│ │ │  the domains of the argument types cannot overlap. For example, the following
│ │ │ -specification results in a warning:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="5030640918-1">(</span><span class="nf">pos_integer</span><span class="p" data-group-id="5030640918-2">(</span><span class="p" data-group-id="5030640918-2">)</span><span class="p" data-group-id="5030640918-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="5030640918-3">(</span><span class="p" data-group-id="5030640918-3">)</span><span class="p">;</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="5030640918-4">(</span><span class="nf">integer</span><span class="p" data-group-id="5030640918-5">(</span><span class="p" data-group-id="5030640918-5">)</span><span class="p" data-group-id="5030640918-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="5030640918-6">(</span><span class="p" data-group-id="5030640918-6">)</span><span class="p">.</span></code></pre><p>Type variables can be used in specifications to specify relations for the input
│ │ │ +specification results in a warning:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="8210009092-1">(</span><span class="nf">pos_integer</span><span class="p" data-group-id="8210009092-2">(</span><span class="p" data-group-id="8210009092-2">)</span><span class="p" data-group-id="8210009092-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">pos_integer</span><span class="p" data-group-id="8210009092-3">(</span><span class="p" data-group-id="8210009092-3">)</span><span class="p">;</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="8210009092-4">(</span><span class="nf">integer</span><span class="p" data-group-id="8210009092-5">(</span><span class="p" data-group-id="8210009092-5">)</span><span class="p" data-group-id="8210009092-4">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="8210009092-6">(</span><span class="p" data-group-id="8210009092-6">)</span><span class="p">.</span></code></pre><p>Type variables can be used in specifications to specify relations for the input
│ │ │  and output arguments of a function. For example, the following specification
│ │ │  defines the type of a polymorphic identity function:</p><pre><code class="text">-spec id(X) -&gt; X.</code></pre><p>Notice that the above specification does not restrict the input and output type
│ │ │  in any way. These types can be constrained by guard-like subtype constraints and
│ │ │ -provide bounded quantification:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="9750845912-1">(</span><span class="n">X</span><span class="p" data-group-id="9750845912-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="9750845912-2">(</span><span class="p" data-group-id="9750845912-2">)</span><span class="p">.</span></code></pre><p>Currently, the <code class="inline">::</code> constraint (read as &quot;is a subtype of&quot;) is the only guard
│ │ │ +provide bounded quantification:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="3858202867-1">(</span><span class="n">X</span><span class="p" data-group-id="3858202867-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="3858202867-2">(</span><span class="p" data-group-id="3858202867-2">)</span><span class="p">.</span></code></pre><p>Currently, the <code class="inline">::</code> constraint (read as &quot;is a subtype of&quot;) is the only guard
│ │ │  constraint that can be used in the <code class="inline">when</code> part of a <code class="inline">-spec</code> attribute.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>The above function specification uses multiple occurrences of the same type
│ │ │  variable. That provides more type information than the following function
│ │ │ -specification, where the type variables are missing:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="5037560775-1">(</span><span class="nf">tuple</span><span class="p" data-group-id="5037560775-2">(</span><span class="p" data-group-id="5037560775-2">)</span><span class="p" data-group-id="5037560775-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="5037560775-3">(</span><span class="p" data-group-id="5037560775-3">)</span><span class="p">.</span></code></pre><p>The latter specification says that the function takes some tuple and returns
│ │ │ +specification, where the type variables are missing:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">id</span><span class="p" data-group-id="9296511403-1">(</span><span class="nf">tuple</span><span class="p" data-group-id="9296511403-2">(</span><span class="p" data-group-id="9296511403-2">)</span><span class="p" data-group-id="9296511403-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">tuple</span><span class="p" data-group-id="9296511403-3">(</span><span class="p" data-group-id="9296511403-3">)</span><span class="p">.</span></code></pre><p>The latter specification says that the function takes some tuple and returns
│ │ │  some tuple. The specification with the <code class="inline">X</code> type variable specifies that the
│ │ │  function takes a tuple and returns <em>the same</em> tuple.</p><p>However, it is up to the tools that process the specifications to choose
│ │ │  whether to take this extra information into account or not.</p></section><p>The scope of a <code class="inline">::</code> constraint is the <code class="inline">(...) -&gt; RetType</code> specification after
│ │ │  which it appears. To avoid confusion, it is suggested that different variables
│ │ │  are used in different constituents of an overloaded contract, as shown in the
│ │ │ -following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0334912112-1">(</span><span class="p" data-group-id="0334912112-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="0334912112-3">(</span><span class="p" data-group-id="0334912112-3">)</span><span class="p" data-group-id="0334912112-2">}</span><span class="p" data-group-id="0334912112-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="0334912112-4">(</span><span class="p" data-group-id="0334912112-4">)</span><span class="p">;</span><span class="w">
│ │ │ -         </span><span class="p" data-group-id="0334912112-5">(</span><span class="p" data-group-id="0334912112-6">[</span><span class="n">Y</span><span class="p" data-group-id="0334912112-6">]</span><span class="p" data-group-id="0334912112-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="0334912112-7">(</span><span class="p" data-group-id="0334912112-7">)</span><span class="p">.</span></code></pre><p>Some functions in Erlang are not meant to return; either because they define
│ │ │ +following example:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="9681722154-1">(</span><span class="p" data-group-id="9681722154-2">{</span><span class="n">X</span><span class="p">,</span><span class="w"> </span><span class="nf">integer</span><span class="p" data-group-id="9681722154-3">(</span><span class="p" data-group-id="9681722154-3">)</span><span class="p" data-group-id="9681722154-2">}</span><span class="p" data-group-id="9681722154-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">atom</span><span class="p" data-group-id="9681722154-4">(</span><span class="p" data-group-id="9681722154-4">)</span><span class="p">;</span><span class="w">
│ │ │ +         </span><span class="p" data-group-id="9681722154-5">(</span><span class="p" data-group-id="9681722154-6">[</span><span class="n">Y</span><span class="p" data-group-id="9681722154-6">]</span><span class="p" data-group-id="9681722154-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="nf">number</span><span class="p" data-group-id="9681722154-7">(</span><span class="p" data-group-id="9681722154-7">)</span><span class="p">.</span></code></pre><p>Some functions in Erlang are not meant to return; either because they define
│ │ │  servers or because they are used to throw exceptions, as in the following
│ │ │ -function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_error</span><span class="p" data-group-id="9391604286-1">(</span><span class="n">Err</span><span class="p" data-group-id="9391604286-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="9391604286-2">(</span><span class="p" data-group-id="9391604286-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Err</span><span class="p" data-group-id="9391604286-3">}</span><span class="p" data-group-id="9391604286-2">)</span><span class="p">.</span></code></pre><p>For such functions, it is recommended to use the special <a href="../../erts-15.2.7.8/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a> type
│ │ │ +function:</p><pre><code class="makeup erlang" translate="no"><span class="nf">my_error</span><span class="p" data-group-id="4627646622-1">(</span><span class="n">Err</span><span class="p" data-group-id="4627646622-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">throw</span><span class="p" data-group-id="4627646622-2">(</span><span class="p" data-group-id="4627646622-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Err</span><span class="p" data-group-id="4627646622-3">}</span><span class="p" data-group-id="4627646622-2">)</span><span class="p">.</span></code></pre><p>For such functions, it is recommended to use the special <a href="../../erts-15.2.7.8/doc/html/erlang.html#t:no_return/0"><code class="inline">no_return/0</code></a> type
│ │ │  for their &quot;return&quot;, through a contract of the following form:</p><pre><code class="text">-spec my_error(term()) -&gt; no_return().</code></pre><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>Erlang uses the shorthand version <code class="inline">_</code> as an anonymous type variable equivalent
│ │ │  to <a href="../../erts-15.2.7.8/doc/html/erlang.html#t:term/0"><code class="inline">term/0</code></a> or <a href="../../erts-15.2.7.8/doc/html/erlang.html#t:any/0"><code class="inline">any/0</code></a>. For example, the following function</p><pre><code class="text">-spec Function(string(), _) -&gt; string().</code></pre><p>is equivalent to:</p><pre><code class="text">-spec Function(string(), any()) -&gt; string().</code></pre></section>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ ├── ./usr/share/doc/erlang-doc/html/doc/upcoming_incompatibilities.html
│ │ │ @@ -149,45 +149,45 @@
│ │ │  occurrences of <code class="inline">maybe</code> without quotes.</p><p><a href="" id="float_matching"></a></p><h3 id="0-0-and-0-0-will-no-longer-be-exactly-equal" class="section-heading">
│ │ │    <a href="#0-0-and-0-0-will-no-longer-be-exactly-equal" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">0.0 and -0.0 will no longer be exactly equal</span>
│ │ │  </h3>
│ │ │  <p>Currently, the floating point numbers <code class="inline">0.0</code> and <code class="inline">-0.0</code> have distinct internal
│ │ │ -representations. That can be seen if they are converted to binaries:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="9996301716-1">&lt;&lt;</span><span class="mf">0.0</span><span class="o">/</span><span class="nb">float</span><span class="p" data-group-id="9996301716-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9996301716-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="9996301716-2">&gt;&gt;</span><span class="w">
│ │ │ -</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="9996301716-3">&lt;&lt;</span><span class="o">-</span><span class="mf">0.0</span><span class="o">/</span><span class="nb">float</span><span class="p" data-group-id="9996301716-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9996301716-4">&lt;&lt;</span><span class="mi">128</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="9996301716-4">&gt;&gt;</span></code></pre><p>However, when they are matched against each other or compared using the <code class="inline">=:=</code>
│ │ │ +representations. That can be seen if they are converted to binaries:</p><pre><code class="makeup erlang" translate="no"><span class="gp unselectable">1&gt; </span><span class="p" data-group-id="4145364871-1">&lt;&lt;</span><span class="mf">0.0</span><span class="o">/</span><span class="nb">float</span><span class="p" data-group-id="4145364871-1">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4145364871-2">&lt;&lt;</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4145364871-2">&gt;&gt;</span><span class="w">
│ │ │ +</span><span class="gp unselectable">2&gt; </span><span class="p" data-group-id="4145364871-3">&lt;&lt;</span><span class="o">-</span><span class="mf">0.0</span><span class="o">/</span><span class="nb">float</span><span class="p" data-group-id="4145364871-3">&gt;&gt;</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4145364871-4">&lt;&lt;</span><span class="mi">128</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4145364871-4">&gt;&gt;</span></code></pre><p>However, when they are matched against each other or compared using the <code class="inline">=:=</code>
│ │ │  operator, they are considered to be equal. Thus, <code class="inline">0.0 =:= -0.0</code> currently
│ │ │  returns <code class="inline">true</code>.</p><p>In Erlang/OTP 27, <code class="inline">0.0 =:= -0.0</code> will return <code class="inline">false</code>, and matching <code class="inline">0.0</code> against
│ │ │  <code class="inline">-0.0</code> will fail. When used as map keys, <code class="inline">0.0</code> and <code class="inline">-0.0</code> will be considered to
│ │ │  be distinct.</p><p>The <code class="inline">==</code> operator will continue to return <code class="inline">true</code> for <code class="inline">0.0 == -0.0</code>.</p><p>To help to find code that might need to be revised, in OTP 27 there will be a
│ │ │  new compiler warning when matching against <code class="inline">0.0</code> or comparing to that value
│ │ │  using the <code class="inline">=:=</code> operator. The warning can be suppressed by matching against
│ │ │  <code class="inline">+0.0</code> instead of <code class="inline">0.0</code>.</p><p>We plan to introduce the same warning in OTP 26.1, but by default it will be
│ │ │  disabled.</p><p><a href="" id="singleton_typevars"></a></p><h3 id="singleton-type-variables-will-become-a-compile-time-error" class="section-heading">
│ │ │    <a href="#singleton-type-variables-will-become-a-compile-time-error" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Singleton type variables will become a compile-time error</span>
│ │ │  </h3>
│ │ │ -<p>Before Erlang/OTP 26, the compiler would silenty accept the following spec:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="0095588791-1">(</span><span class="n">Opts</span><span class="p" data-group-id="0095588791-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="0095588791-2">(</span><span class="p" data-group-id="0095588791-2">)</span><span class="w"> </span><span class="k">when</span><span class="w">
│ │ │ -    </span><span class="n">Opts</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="0095588791-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Unknown</span><span class="p" data-group-id="0095588791-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="0095588791-4">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Unknown</span><span class="p" data-group-id="0095588791-4">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="nf">f</span><span class="p" data-group-id="0095588791-5">(</span><span class="p">_</span><span class="p" data-group-id="0095588791-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="p">.</span></code></pre><p>In OTP 26, the compiler emits a warning pointing out that the type variable
│ │ │ -<code class="inline">Unknown</code> is unbound:</p><pre><code class="makeup erlang" translate="no"><span class="ss">t</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">6</span><span class="p">:</span><span class="mi">18</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="ss">variable</span><span class="w"> </span><span class="ss">&#39;Unknown&#39;</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">only</span><span class="w"> </span><span class="ss">used</span><span class="w"> </span><span class="nf">once</span><span class="w"> </span><span class="p" data-group-id="3955324022-1">(</span><span class="ss">is</span><span class="w"> </span><span class="ss">unbound</span><span class="p" data-group-id="3955324022-1">)</span><span class="w">
│ │ │ +<p>Before Erlang/OTP 26, the compiler would silenty accept the following spec:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">spec</span><span class="w"> </span><span class="nf">f</span><span class="p" data-group-id="7731406602-1">(</span><span class="n">Opts</span><span class="p" data-group-id="7731406602-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">term</span><span class="p" data-group-id="7731406602-2">(</span><span class="p" data-group-id="7731406602-2">)</span><span class="w"> </span><span class="k">when</span><span class="w">
│ │ │ +    </span><span class="n">Opts</span><span class="w"> </span><span class="p">:</span><span class="p">:</span><span class="w"> </span><span class="p" data-group-id="7731406602-3">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Unknown</span><span class="p" data-group-id="7731406602-3">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="7731406602-4">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Unknown</span><span class="p" data-group-id="7731406602-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="nf">f</span><span class="p" data-group-id="7731406602-5">(</span><span class="p">_</span><span class="p" data-group-id="7731406602-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">error</span><span class="p">.</span></code></pre><p>In OTP 26, the compiler emits a warning pointing out that the type variable
│ │ │ +<code class="inline">Unknown</code> is unbound:</p><pre><code class="makeup erlang" translate="no"><span class="ss">t</span><span class="p">.</span><span class="nc">erl</span><span class="p">:</span><span class="mi">6</span><span class="p">:</span><span class="mi">18</span><span class="p">:</span><span class="w"> </span><span class="n">Warning</span><span class="p">:</span><span class="w"> </span><span class="ss">type</span><span class="w"> </span><span class="ss">variable</span><span class="w"> </span><span class="ss">&#39;Unknown&#39;</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">only</span><span class="w"> </span><span class="ss">used</span><span class="w"> </span><span class="nf">once</span><span class="w"> </span><span class="p" data-group-id="5524918107-1">(</span><span class="ss">is</span><span class="w"> </span><span class="ss">unbound</span><span class="p" data-group-id="5524918107-1">)</span><span class="w">
│ │ │  </span><span class="c1">%    6|     Opts :: {ok, Unknown} | {error, Unknown}.</span><span class="w">
│ │ │  </span><span class="c1">%     |                  ^</span></code></pre><p>In OTP 27, that warning will become an error.</p><p><a href="" id="escripts_will_be_compiled"></a></p><h3 id="escripts-will-be-compiled-by-default" class="section-heading">
│ │ │    <a href="#escripts-will-be-compiled-by-default" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Escripts will be compiled by default</span>
│ │ │  </h3>
│ │ │  <p>Escripts will be compiled by default instead of interpreted. That means that the
│ │ │  <code class="inline">compiler</code> application must be available.</p><p>The old behavior of interpreting escripts can be restored by adding the
│ │ │ -following line to the script file:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">mode</span><span class="p" data-group-id="7611097974-1">(</span><span class="ss">interpret</span><span class="p" data-group-id="7611097974-1">)</span><span class="p">.</span></code></pre><p>In OTP 28, support for interpreting an escript will be removed.</p><h3 id="code_path_choice-will-default-to-strict" class="section-heading">
│ │ │ +following line to the script file:</p><pre><code class="makeup erlang" translate="no"><span class="p">-</span><span class="na">mode</span><span class="p" data-group-id="8105434606-1">(</span><span class="ss">interpret</span><span class="p" data-group-id="8105434606-1">)</span><span class="p">.</span></code></pre><p>In OTP 28, support for interpreting an escript will be removed.</p><h3 id="code_path_choice-will-default-to-strict" class="section-heading">
│ │ │    <a href="#code_path_choice-will-default-to-strict" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">-code_path_choice will default to strict</span>
│ │ │  </h3>
│ │ │  <p>This command line option controls if paths given in the command line, boot
│ │ │  scripts, and the code server should be interpreted as is strict or relaxed.</p><p>OTP 26 and earlier defaults to <code class="inline">relaxed</code>, which means <code class="inline">-pa myapp/ebin</code> would
│ │ │ @@ -231,18 +231,18 @@
│ │ │  &quot;
│ │ │  String Content
│ │ │  &quot;
│ │ │  %%
│ │ │  %% In OTP 27 it is instead interpreted as a
│ │ │  %% Triple-Quoted String equivalent to
│ │ │  &quot;String Content&quot;</code></pre><pre><code class="makeup erlang" translate="no"><span class="s">&quot;&quot;</span><span class="s">&quot;&quot;</span><span class="w">
│ │ │ -</span><span class="o">++</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="7832482285-1">(</span><span class="p" data-group-id="7832482285-1">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │ +</span><span class="o">++</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0020356770-1">(</span><span class="p" data-group-id="0020356770-1">)</span><span class="w"> </span><span class="o">++</span><span class="w">
│ │ │  </span><span class="s">&quot;&quot;</span><span class="s">&quot;&quot;</span><span class="w">
│ │ │  </span><span class="c1">%% Became</span><span class="w">
│ │ │ -</span><span class="s">&quot;&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="7832482285-2">(</span><span class="p" data-group-id="7832482285-2">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="w">
│ │ │ +</span><span class="s">&quot;&quot;</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="nf">foo</span><span class="p" data-group-id="0020356770-2">(</span><span class="p" data-group-id="0020356770-2">)</span><span class="w"> </span><span class="o">++</span><span class="w"> </span><span class="s">&quot;&quot;</span><span class="w">
│ │ │  </span><span class="c1">%%</span><span class="w">
│ │ │  </span><span class="c1">%% In OTP 27 it is instead interpreted as a</span><span class="w">
│ │ │  </span><span class="c1">%% Triple-Quoted String (triple-or-more) equivalent to</span><span class="w">
│ │ │  </span><span class="s">&quot;++ foo() ++&quot;</span></code></pre><p>From Erlang/OTP 26.1 up to 27.0 the compiler issues a warning for a sequence of
│ │ │  3 or more double-quote characters since that is almost certainly a mistake or
│ │ │  something like a result of bad automatic code generation. If a users gets that
│ │ │  warning, the code should be corrected for example by inserting appropriate
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/.build
│ │ │ @@ -42,15 +42,15 @@
│ │ │  dist/lato-latin-300-normal-YUMVEFOL.woff2
│ │ │  dist/lato-latin-400-normal-W7754I4D.woff2
│ │ │  dist/lato-latin-700-normal-2XVSBPG4.woff2
│ │ │  dist/lato-latin-ext-300-normal-DG5RYZUK.woff2
│ │ │  dist/lato-latin-ext-400-normal-ZXDJ7C2U.woff2
│ │ │  dist/lato-latin-ext-700-normal-3JFX6WED.woff2
│ │ │  dist/remixicon-NKANDIL5.woff2
│ │ │ -dist/search_data-8B3C849F.js
│ │ │ +dist/search_data-FC9EDC58.js
│ │ │  dist/sidebar_items-E25F4A7E.js
│ │ │  driver.html
│ │ │  driver_entry.html
│ │ │  epmd_cmd.html
│ │ │  erl_cmd.html
│ │ │  erl_dist_protocol.html
│ │ │  erl_driver.html
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/alt_dist.html
│ │ │ @@ -237,50 +237,50 @@
│ │ │  <code class="inline">uds_dist</code> example using a port driver written in C, <code class="inline">erl_uds_dist</code> is written
│ │ │  entirely in Erlang.</p><h3 id="exported-callback-functions" class="section-heading">
│ │ │    <a href="#exported-callback-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Exported Callback Functions</span>
│ │ │  </h3>
│ │ │ -<p>The following functions are mandatory:</p><ul><li><pre id="listen"><code class="makeup erlang" translate="no"><span class="nf">listen</span><span class="p" data-group-id="8724583436-1">(</span><span class="n">Name</span><span class="p" data-group-id="8724583436-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="8724583436-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8724583436-3">{</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p">,</span><span class="w"> </span><span class="n">Creation</span><span class="p" data-group-id="8724583436-3">}</span><span class="p" data-group-id="8724583436-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8724583436-4">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8724583436-4">}</span><span class="w">
│ │ │ -</span><span class="nf">listen</span><span class="p" data-group-id="8724583436-5">(</span><span class="n">Name</span><span class="p">,</span><span class="n">Host</span><span class="p" data-group-id="8724583436-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="8724583436-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8724583436-7">{</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p">,</span><span class="w"> </span><span class="n">Creation</span><span class="p" data-group-id="8724583436-7">}</span><span class="p" data-group-id="8724583436-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8724583436-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8724583436-8">}</span></code></pre><p><code class="inline">listen/2</code> is called once in order to listen for incoming connection requests.
│ │ │ +<p>The following functions are mandatory:</p><ul><li><pre id="listen"><code class="makeup erlang" translate="no"><span class="nf">listen</span><span class="p" data-group-id="8362680964-1">(</span><span class="n">Name</span><span class="p" data-group-id="8362680964-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="8362680964-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8362680964-3">{</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p">,</span><span class="w"> </span><span class="n">Creation</span><span class="p" data-group-id="8362680964-3">}</span><span class="p" data-group-id="8362680964-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8362680964-4">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8362680964-4">}</span><span class="w">
│ │ │ +</span><span class="nf">listen</span><span class="p" data-group-id="8362680964-5">(</span><span class="n">Name</span><span class="p">,</span><span class="n">Host</span><span class="p" data-group-id="8362680964-5">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="8362680964-6">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8362680964-7">{</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Address</span><span class="p">,</span><span class="w"> </span><span class="n">Creation</span><span class="p" data-group-id="8362680964-7">}</span><span class="p" data-group-id="8362680964-6">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8362680964-8">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8362680964-8">}</span></code></pre><p><code class="inline">listen/2</code> is called once in order to listen for incoming connection requests.
│ │ │  The call is made when the distribution is brought up. The argument <code class="inline">Name</code> is
│ │ │  the part of the node name before the <code class="inline">@</code> sign in the full node name. It can be
│ │ │  either an atom or a string. The argument <code class="inline">Host</code> is the part of the node name
│ │ │  after the <code class="inline">@</code> sign in the full node name. It is always a string.</p><p>The return value consists of a <code class="inline">Listen</code> handle (which is later passed to the
│ │ │  <a href="alt_dist.html#accept"><code class="inline">accept/1</code></a> callback), <code class="inline">Address</code> which is a
│ │ │  <code class="inline">#net_address{}</code> record with information about the address for the node (the
│ │ │  <code class="inline">#net_address{}</code> record is defined in <code class="inline">kernel/include/net_address.hrl</code>), and
│ │ │  <code class="inline">Creation</code> which (currently) is an integer <code class="inline">1</code>, <code class="inline">2</code>, or <code class="inline">3</code>.</p><p>If <a href="epmd_cmd.html"><code class="inline">epmd</code></a> is to be used for node discovery, you typically want
│ │ │  to use the <code class="inline">erl_epmd</code> module (part of the <code class="inline">kernel</code> application) in order to
│ │ │ -register the listen port with <code class="inline">epmd</code> and retrieve <code class="inline">Creation</code> to use.</p></li><li><pre id="address"><code class="makeup erlang" translate="no"><span class="nf">address</span><span class="p" data-group-id="4767748412-1">(</span><span class="p" data-group-id="4767748412-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +register the listen port with <code class="inline">epmd</code> and retrieve <code class="inline">Creation</code> to use.</p></li><li><pre id="address"><code class="makeup erlang" translate="no"><span class="nf">address</span><span class="p" data-group-id="6898405766-1">(</span><span class="p" data-group-id="6898405766-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="err"> </span><span class="err"> </span><span class="n">Address</span></code></pre><p><code class="inline">address/0</code> is called in order to get the <code class="inline">Address</code> part of the
│ │ │  <a href="alt_dist.html#listen"><code class="inline">listen/2</code></a> function without creating a listen socket.
│ │ │ -All fields except <code class="inline">address</code> have to be set in the returned record</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">address</span><span class="p" data-group-id="7198136584-1">(</span><span class="p" data-group-id="7198136584-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7198136584-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Host</span><span class="p" data-group-id="7198136584-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">inet</span><span class="p">:</span><span class="nf">gethostname</span><span class="p" data-group-id="7198136584-3">(</span><span class="p" data-group-id="7198136584-3">)</span><span class="p">,</span><span class="w">
│ │ │ -    </span><span class="o">#</span><span class="ss">net_address</span><span class="p" data-group-id="7198136584-4">{</span><span class="w"> </span><span class="ss">host</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Host</span><span class="p">,</span><span class="w"> </span><span class="ss">protocol</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">tcp</span><span class="p">,</span><span class="w"> </span><span class="ss">family</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">inet6</span><span class="w"> </span><span class="p" data-group-id="7198136584-4">}</span><span class="p">.</span></code></pre></li><li><pre id="accept"><code class="makeup erlang" translate="no"><span class="nf">accept</span><span class="p" data-group-id="5473993207-1">(</span><span class="n">Listen</span><span class="p" data-group-id="5473993207-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +All fields except <code class="inline">address</code> have to be set in the returned record</p><p>Example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">address</span><span class="p" data-group-id="5195290495-1">(</span><span class="p" data-group-id="5195290495-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="5195290495-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Host</span><span class="p" data-group-id="5195290495-2">}</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nc">inet</span><span class="p">:</span><span class="nf">gethostname</span><span class="p" data-group-id="5195290495-3">(</span><span class="p" data-group-id="5195290495-3">)</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="o">#</span><span class="ss">net_address</span><span class="p" data-group-id="5195290495-4">{</span><span class="w"> </span><span class="ss">host</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Host</span><span class="p">,</span><span class="w"> </span><span class="ss">protocol</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">tcp</span><span class="p">,</span><span class="w"> </span><span class="ss">family</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">inet6</span><span class="w"> </span><span class="p" data-group-id="5195290495-4">}</span><span class="p">.</span></code></pre></li><li><pre id="accept"><code class="makeup erlang" translate="no"><span class="nf">accept</span><span class="p" data-group-id="6321900310-1">(</span><span class="n">Listen</span><span class="p" data-group-id="6321900310-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="err"> </span><span class="err"> </span><span class="n">AcceptorPid</span></code></pre><p><code class="inline">accept/1</code> should spawn a process that accepts connections. This process
│ │ │  should preferably execute on <code class="inline">max</code> priority. The process identifier of this
│ │ │  process should be returned.</p><p>The <code class="inline">Listen</code> argument will be the same as the <code class="inline">Listen</code> handle part of the
│ │ │  return value of the <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback above.
│ │ │  <code class="inline">accept/1</code> is called only once when the distribution protocol is started.</p><p>The caller of this function is a representative for <code class="inline">net_kernel</code> (this may or
│ │ │  may not be the process registered as <code class="inline">net_kernel</code>) and is in this document
│ │ │  identified as <code class="inline">Kernel</code>. When a connection has been accepted by the acceptor
│ │ │  process, it needs to inform <code class="inline">Kernel</code> about the accepted connection. This is
│ │ │ -done by passing a message on the form:</p><pre><code class="makeup erlang" translate="no"><span class="n">Kernel</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="4524513030-1">{</span><span class="ss">accept</span><span class="p">,</span><span class="w"> </span><span class="n">AcceptorPid</span><span class="p">,</span><span class="w"> </span><span class="n">DistController</span><span class="p">,</span><span class="w"> </span><span class="n">Family</span><span class="p">,</span><span class="w"> </span><span class="n">Proto</span><span class="p" data-group-id="4524513030-1">}</span></code></pre><p><code class="inline">DistController</code> is either the process or port identifier of the distribution
│ │ │ +done by passing a message on the form:</p><pre><code class="makeup erlang" translate="no"><span class="n">Kernel</span><span class="w"> </span><span class="o">!</span><span class="w"> </span><span class="p" data-group-id="8219179836-1">{</span><span class="ss">accept</span><span class="p">,</span><span class="w"> </span><span class="n">AcceptorPid</span><span class="p">,</span><span class="w"> </span><span class="n">DistController</span><span class="p">,</span><span class="w"> </span><span class="n">Family</span><span class="p">,</span><span class="w"> </span><span class="n">Proto</span><span class="p" data-group-id="8219179836-1">}</span></code></pre><p><code class="inline">DistController</code> is either the process or port identifier of the distribution
│ │ │  controller for the connection. The distribution controller should be created
│ │ │  by the acceptor processes when a new connection is accepted. Its job is to
│ │ │  dispatch traffic on the connection.</p><p><code class="inline">Kernel</code> responds with one of the following messages:</p><ul><li><p><strong><code class="inline">{Kernel, controller, SupervisorPid}</code></strong> - The request was accepted and
│ │ │  <code class="inline">SupervisorPid</code> is the process identifier of the connection supervisor
│ │ │  process (which is created in the
│ │ │  <a href="alt_dist.html#accept_connection"><code class="inline">accept_connection/5</code></a> callback).</p></li><li><p><strong><code class="inline">{Kernel, unsupported_protocol}</code></strong> - The request was rejected. This is a
│ │ │  fatal error. The acceptor process should terminate.</p></li></ul><p>When an accept sequence has been completed the acceptor process is expected to
│ │ │ -continue accepting further requests.</p></li><li><pre id="accept_connection"><code class="makeup erlang" translate="no"><span class="nf">accept_connection</span><span class="p" data-group-id="1322306340-1">(</span><span class="n">AcceptorPid</span><span class="p">,</span><span class="w"> </span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">MyNode</span><span class="p">,</span><span class="w"> </span><span class="n">Allowed</span><span class="p">,</span><span class="w"> </span><span class="n">SetupTime</span><span class="p" data-group-id="1322306340-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +continue accepting further requests.</p></li><li><pre id="accept_connection"><code class="makeup erlang" translate="no"><span class="nf">accept_connection</span><span class="p" data-group-id="2752144473-1">(</span><span class="n">AcceptorPid</span><span class="p">,</span><span class="w"> </span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">MyNode</span><span class="p">,</span><span class="w"> </span><span class="n">Allowed</span><span class="p">,</span><span class="w"> </span><span class="n">SetupTime</span><span class="p" data-group-id="2752144473-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="err"> </span><span class="err"> </span><span class="n">ConnectionSupervisorPid</span></code></pre><p><code class="inline">accept_connection/5</code> should spawn a process that will perform the Erlang
│ │ │  distribution handshake for the connection. If the handshake successfully
│ │ │  completes it should continue to function as a connection supervisor. This
│ │ │  process should preferably execute on <code class="inline">max</code> priority and should be linked to
│ │ │  the caller. The <code class="inline">dist_util:net_ticker_spawn_options()</code> function can be called
│ │ │  to get spawn options suitable for this process which can be passed directly to
│ │ │  <a href="erlang.html#spawn_opt/4"><code class="inline">erlang:spawn_opt/4</code></a>. <code class="inline">dist_util:net_ticker_spawn_options()</code> will by default
│ │ │ @@ -294,15 +294,15 @@
│ │ │  <code class="inline">dist_util:handshake_other_started(HsData)</code>.</p></li><li><p><strong><code class="inline">Allowed</code></strong> - To be passed along to
│ │ │  <code class="inline">dist_util:handshake_other_started(HsData)</code>.</p></li><li><p><strong><code class="inline">SetupTime</code></strong> - Time used for creating a setup timer by a call to
│ │ │  <code class="inline">dist_util:start_timer(SetupTime)</code>. The timer should be passed along to
│ │ │  <code class="inline">dist_util:handshake_other_started(HsData)</code>.</p></li></ul><p>The created process should provide callbacks and other information needed for
│ │ │  the handshake in a <a href="alt_dist.html#hs_data_record"><code class="inline">#hs_data{}</code></a> record and call
│ │ │  <code class="inline">dist_util:handshake_other_started(HsData)</code> with this record.</p><p><code class="inline">dist_util:handshake_other_started(HsData)</code> will perform the handshake and if
│ │ │  the handshake successfully completes this process will then continue in a
│ │ │ -connection supervisor loop as long as the connection is up.</p></li><li><pre id="setup"><code class="makeup erlang" translate="no"><span class="nf">setup</span><span class="p" data-group-id="2290593433-1">(</span><span class="n">Node</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">MyNode</span><span class="p">,</span><span class="w"> </span><span class="n">LongOrShortNames</span><span class="p">,</span><span class="w"> </span><span class="n">SetupTime</span><span class="p" data-group-id="2290593433-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +connection supervisor loop as long as the connection is up.</p></li><li><pre id="setup"><code class="makeup erlang" translate="no"><span class="nf">setup</span><span class="p" data-group-id="2757343057-1">(</span><span class="n">Node</span><span class="p">,</span><span class="w"> </span><span class="n">Type</span><span class="p">,</span><span class="w"> </span><span class="n">MyNode</span><span class="p">,</span><span class="w"> </span><span class="n">LongOrShortNames</span><span class="p">,</span><span class="w"> </span><span class="n">SetupTime</span><span class="p" data-group-id="2757343057-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │  </span><span class="err"> </span><span class="err"> </span><span class="n">ConnectionSupervisorPid</span></code></pre><p><code class="inline">setup/5</code> should spawn a process that connects to <code class="inline">Node</code>. When connection has
│ │ │  been established it should perform the Erlang distribution handshake for the
│ │ │  connection. If the handshake successfully completes it should continue to
│ │ │  function as a connection supervisor. This process should preferably execute on
│ │ │  <code class="inline">max</code> priority and should be linked to the caller. The
│ │ │  <code class="inline">dist_util:net_ticker_spawn_options()</code> function can be called to get spawn
│ │ │  options suitable for this process which can be passed directly to
│ │ │ @@ -320,23 +320,23 @@
│ │ │  may not be the process registered as <code class="inline">net_kernel</code>) and is in this document
│ │ │  identified as <code class="inline">Kernel</code>.</p><p>This function should, besides spawning the connection supervisor, also create
│ │ │  a distribution controller. The distribution controller is either a process or
│ │ │  a port which is responsible for dispatching traffic.</p><p>The created process should provide callbacks and other information needed for
│ │ │  the handshake in a <a href="alt_dist.html#hs_data_record"><code class="inline">#hs_data{}</code></a> record and call
│ │ │  <code class="inline">dist_util:handshake_we_started(HsData)</code> with this record.</p><p><code class="inline">dist_util:handshake_we_started(HsData)</code> will perform the handshake and the
│ │ │  handshake successfully completes this process will then continue in a
│ │ │ -connection supervisor loop as long as the connection is up.</p></li><li><pre id="close"><code class="makeup erlang" translate="no"><span class="nf">close</span><span class="p" data-group-id="1990694205-1">(</span><span class="n">Listen</span><span class="p" data-group-id="1990694205-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="nf">void</span><span class="p" data-group-id="1990694205-2">(</span><span class="p" data-group-id="1990694205-2">)</span></code></pre><p>Called in order to close the <code class="inline">Listen</code> handle that originally was passed from
│ │ │ -the <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback.</p></li><li><pre id="select"><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="5865581563-1">(</span><span class="n">NodeName</span><span class="p" data-group-id="5865581563-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="nf">boolean</span><span class="p" data-group-id="5865581563-2">(</span><span class="p" data-group-id="5865581563-2">)</span></code></pre><p>Return <code class="inline">true</code> if the host name part of the <code class="inline">NodeName</code> is valid for use with
│ │ │ -this protocol; otherwise, <code class="inline">false</code>.</p></li></ul><p>There are also two optional functions that may be exported:</p><ul><li><pre id="setopts"><code class="makeup erlang" translate="no"><span class="nf">setopts</span><span class="p" data-group-id="5658125625-1">(</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="5658125625-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="5658125625-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="5658125625-2">}</span></code></pre><p>The argument <code class="inline">Listen</code> is the handle originally passed from the
│ │ │ +connection supervisor loop as long as the connection is up.</p></li><li><pre id="close"><code class="makeup erlang" translate="no"><span class="nf">close</span><span class="p" data-group-id="1776667879-1">(</span><span class="n">Listen</span><span class="p" data-group-id="1776667879-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="nf">void</span><span class="p" data-group-id="1776667879-2">(</span><span class="p" data-group-id="1776667879-2">)</span></code></pre><p>Called in order to close the <code class="inline">Listen</code> handle that originally was passed from
│ │ │ +the <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback.</p></li><li><pre id="select"><code class="makeup erlang" translate="no"><span class="nf">select</span><span class="p" data-group-id="8018345539-1">(</span><span class="n">NodeName</span><span class="p" data-group-id="8018345539-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="nf">boolean</span><span class="p" data-group-id="8018345539-2">(</span><span class="p" data-group-id="8018345539-2">)</span></code></pre><p>Return <code class="inline">true</code> if the host name part of the <code class="inline">NodeName</code> is valid for use with
│ │ │ +this protocol; otherwise, <code class="inline">false</code>.</p></li></ul><p>There are also two optional functions that may be exported:</p><ul><li><pre id="setopts"><code class="makeup erlang" translate="no"><span class="nf">setopts</span><span class="p" data-group-id="7456033867-1">(</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7456033867-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="7456033867-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="7456033867-2">}</span></code></pre><p>The argument <code class="inline">Listen</code> is the handle originally passed from the
│ │ │  <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback. The argument <code class="inline">Opts</code> is a list of
│ │ │ -options to set on future connections.</p></li><li><pre id="getopts"><code class="makeup erlang" translate="no"><span class="nf">getopts</span><span class="p" data-group-id="1562213526-1">(</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1562213526-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ -</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="1562213526-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">OptionValues</span><span class="p" data-group-id="1562213526-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="1562213526-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="1562213526-3">}</span></code></pre><p>The argument <code class="inline">Listen</code> is the handle originally passed from the
│ │ │ +options to set on future connections.</p></li><li><pre id="getopts"><code class="makeup erlang" translate="no"><span class="nf">getopts</span><span class="p" data-group-id="9173586190-1">(</span><span class="n">Listen</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="9173586190-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w">
│ │ │ +</span><span class="err"> </span><span class="err"> </span><span class="p" data-group-id="9173586190-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">OptionValues</span><span class="p" data-group-id="9173586190-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="9173586190-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="9173586190-3">}</span></code></pre><p>The argument <code class="inline">Listen</code> is the handle originally passed from the
│ │ │  <a href="alt_dist.html#listen"><code class="inline">listen/1</code></a> callback. The argument <code class="inline">Opts</code> is a list of
│ │ │  options to read for future connections.</p></li></ul><p><a href="" id="hs_data_record"></a></p><h3 id="the-hs_data-record" class="section-heading">
│ │ │    <a href="#the-hs_data-record" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">The #hs_data{} Record</span>
│ │ │  </h3>
│ │ │ @@ -350,44 +350,44 @@
│ │ │  <a href="alt_dist.html#accept_connection"><code class="inline">accept_connection/5</code></a>.</p></li><li><p><strong><code class="inline" id="hs_data_other_node">other_node</code></strong> - Name of the other node. This field
│ │ │  is only mandatory when this node initiates the connection. That is, when
│ │ │  connection is set up via <a href="alt_dist.html#setup"><code class="inline">setup/5</code></a>.</p></li><li><p><strong><code class="inline" id="hs_data_this_node">this_node</code></strong> - The node name of this node.</p></li><li><p><strong><code class="inline" id="hs_data_socket">socket</code></strong> - The identifier of the distribution
│ │ │  controller.</p></li><li><p><strong><code class="inline" id="hs_data_timer">timer</code></strong> - The timer created using
│ │ │  <code class="inline">dist_util:start_timer/1</code>.</p></li><li><p><strong><code class="inline" id="hs_data_allowed">allowed</code></strong> - Information passed as <code class="inline">Allowed</code> to
│ │ │  <code class="inline">accept_connection/5</code>. This field is only mandatory when the remote node
│ │ │  initiated the connection. That is, when the connection is set up via
│ │ │ -<a href="alt_dist.html#accept_connection"><code class="inline">accept_connection/5</code></a>.</p></li><li><p><strong><code class="inline" id="hs_data_f_send">f_send</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="6503725104-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="6503725104-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="6503725104-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="6503725104-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Data</code>
│ │ │ -is io data to pass to the other side.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_recv">f_recv</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2922131639-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="2922131639-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2922131639-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Packet</span><span class="p" data-group-id="2922131639-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="2922131639-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="2922131639-3">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. If
│ │ │ +<a href="alt_dist.html#accept_connection"><code class="inline">accept_connection/5</code></a>.</p></li><li><p><strong><code class="inline" id="hs_data_f_send">f_send</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3692105520-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Data</span><span class="p" data-group-id="3692105520-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="3692105520-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="3692105520-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Data</code>
│ │ │ +is io data to pass to the other side.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_recv">f_recv</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5056837993-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Length</span><span class="p" data-group-id="5056837993-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="5056837993-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Packet</span><span class="p" data-group-id="5056837993-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="5056837993-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Reason</span><span class="p" data-group-id="5056837993-3">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. If
│ │ │  <code class="inline">Length</code> is <code class="inline">0</code>, all available bytes should be returned. If <code class="inline">Length &gt; 0</code>,
│ │ │  exactly <code class="inline">Length</code> bytes should be returned, or an error; possibly discarding
│ │ │  less than <code class="inline">Length</code> bytes of data when the connection is closed from the other
│ │ │  side. It is used for passive receive of data from the other end.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_setopts_pre_nodeup">f_setopts_pre_nodeup</code></strong> - A fun with the
│ │ │ -following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0840484229-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="0840484229-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="0840484229-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="0840484229-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. Called
│ │ │ +following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4552460827-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="4552460827-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="4552460827-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="4552460827-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. Called
│ │ │  just before the distribution channel is taken up for normal traffic.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_setopts_post_nodeup">f_setopts_post_nodeup</code></strong> - A fun with
│ │ │ -the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="6064438616-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="6064438616-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="6064438616-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="6064438616-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. Called
│ │ │ -just after distribution channel has been taken up for normal traffic.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_getll">f_getll</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="0118499446-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="0118499446-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">ID</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">ID</code> is
│ │ │ +the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="8842355030-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="8842355030-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="8842355030-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="8842355030-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. Called
│ │ │ +just after distribution channel has been taken up for normal traffic.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_getll">f_getll</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2632257303-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="2632257303-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">ID</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">ID</code> is
│ │ │  the identifier of the low level entity that handles the connection (often
│ │ │ -<code class="inline">DistCtrlr</code> itself).</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_address">f_address</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="6407366913-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="6407366913-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">NetAddress</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Node</code> is
│ │ │ +<code class="inline">DistCtrlr</code> itself).</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_f_address">f_address</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4882345101-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p" data-group-id="4882345101-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">NetAddress</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Node</code> is
│ │ │  the node name of the node on the other end, and <code class="inline">NetAddress</code> is a
│ │ │  <code class="inline">#net_address{}</code> record with information about the address for the <code class="inline">Node</code> on
│ │ │  the other end of the connection. The <code class="inline">#net_address{}</code> record is defined in
│ │ │ -<code class="inline">kernel/include/net_address.hrl</code>.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_mf_tick">mf_tick</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4233200092-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="4233200092-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">void</span><span class="p" data-group-id="4233200092-2">(</span><span class="p" data-group-id="4233200092-2">)</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. This
│ │ │ +<code class="inline">kernel/include/net_address.hrl</code>.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_mf_tick">mf_tick</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4224241783-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="4224241783-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">void</span><span class="p" data-group-id="4224241783-2">(</span><span class="p" data-group-id="4224241783-2">)</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller. This
│ │ │  function should send information over the connection that is not interpreted
│ │ │  by the other end while increasing the statistics of received packets on the
│ │ │  other end. This is usually implemented by sending an empty packet.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>It is of vital importance that this operation does not block the caller for
│ │ │ -a long time. This since it is called from the connection supervisor.</p></section><p>Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_mf_getstat">mf_getstat</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="2474996469-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="2474996469-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="2474996469-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Received</span><span class="p">,</span><span class="w"> </span><span class="n">Sent</span><span class="p">,</span><span class="w"> </span><span class="n">PendSend</span><span class="p" data-group-id="2474996469-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Received</code>
│ │ │ +a long time. This since it is called from the connection supervisor.</p></section><p>Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_mf_getstat">mf_getstat</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="9275006643-1">(</span><span class="n">DistCtrlr</span><span class="p" data-group-id="9275006643-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="9275006643-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">Received</span><span class="p">,</span><span class="w"> </span><span class="n">Sent</span><span class="p">,</span><span class="w"> </span><span class="n">PendSend</span><span class="p" data-group-id="9275006643-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Received</code>
│ │ │  is received packets, <code class="inline">Sent</code> is sent packets, and <code class="inline">PendSend</code> is amount of data
│ │ │  in queue to be sent (typically in bytes, but <code class="inline">dist_util</code> only checks whether
│ │ │  the value is non-zero to know there is data in queue) or a <a href="erlang.html#t:boolean/0"><code class="inline">boolean/0</code></a>
│ │ │  indicating whether there are packets in queue to be sent.</p><section role="note" class="admonition info"><h4 class="admonition-title info">Note</h4><p>It is of vital importance that this operation does not block the caller for
│ │ │  a long time. This since it is called from the connection supervisor.</p></section><p>Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_request_type">request_type</code></strong> - The request <code class="inline">Type</code> as passed to
│ │ │  <a href="alt_dist.html#setup"><code class="inline">setup/5</code></a>. This is only mandatory when the connection has
│ │ │ -been initiated by this node. That is, the connection is set up via <code class="inline">setup/5</code>.</p></li><li><p><strong><code class="inline" id="hs_data_mf_setopts">mf_setopts</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="7712997261-1">(</span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="7712997261-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="7712997261-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="7712997261-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Opts</code>
│ │ │ -is a list of options to set on the connection.</p><p>This function is optional. Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_mf_getopts">mf_getopts</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1695715550-1">(</span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="1695715550-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="1695715550-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">OptionValues</span><span class="p" data-group-id="1695715550-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="1695715550-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="1695715550-3">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Opts</code>
│ │ │ +been initiated by this node. That is, the connection is set up via <code class="inline">setup/5</code>.</p></li><li><p><strong><code class="inline" id="hs_data_mf_setopts">mf_setopts</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="5302342721-1">(</span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="5302342721-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="ss">ok</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="5302342721-2">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="5302342721-2">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Opts</code>
│ │ │ +is a list of options to set on the connection.</p><p>This function is optional. Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_mf_getopts">mf_getopts</code></strong> - A fun with the following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="4720759175-1">(</span><span class="n">DistCtrl</span><span class="p">,</span><span class="w"> </span><span class="n">Opts</span><span class="p" data-group-id="4720759175-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p" data-group-id="4720759175-2">{</span><span class="ss">ok</span><span class="p">,</span><span class="w"> </span><span class="n">OptionValues</span><span class="p" data-group-id="4720759175-2">}</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="p" data-group-id="4720759175-3">{</span><span class="ss">error</span><span class="p">,</span><span class="w"> </span><span class="n">Error</span><span class="p" data-group-id="4720759175-3">}</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller and <code class="inline">Opts</code>
│ │ │  is a list of options to read for the connection.</p><p>This function is optional. Used when connection is up.</p></li><li><p><strong><code class="inline" id="hs_data_f_handshake_complete">f_handshake_complete</code></strong> - A fun with the
│ │ │ -following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="3136827834-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p">,</span><span class="w"> </span><span class="n">DHandle</span><span class="p" data-group-id="3136827834-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">void</span><span class="p" data-group-id="3136827834-2">(</span><span class="p" data-group-id="3136827834-2">)</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Node</code> is
│ │ │ +following signature:</p><pre><code class="makeup erlang" translate="no"><span class="nf">fun</span><span class="w"> </span><span class="p" data-group-id="1535968815-1">(</span><span class="n">DistCtrlr</span><span class="p">,</span><span class="w"> </span><span class="n">Node</span><span class="p">,</span><span class="w"> </span><span class="n">DHandle</span><span class="p" data-group-id="1535968815-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="nf">void</span><span class="p" data-group-id="1535968815-2">(</span><span class="p" data-group-id="1535968815-2">)</span></code></pre><p>where <code class="inline">DistCtrlr</code> is the identifier of the distribution controller, <code class="inline">Node</code> is
│ │ │  the node name of the node connected at the other end, and <code class="inline">DHandle</code> is a
│ │ │  distribution handle needed by a distribution controller process when calling
│ │ │  the following BIFs:</p><ul><li><a href="erlang.html#dist_ctrl_get_data/1"><code class="inline">erlang:dist_ctrl_get_data/1</code></a></li><li><a href="erlang.html#dist_ctrl_get_data_notification/1"><code class="inline">erlang:dist_ctrl_get_data_notification/1</code></a></li><li><a href="erlang.html#dist_ctrl_input_handler/2"><code class="inline">erlang:dist_ctrl_input_handler/2</code></a></li><li><a href="erlang.html#dist_ctrl_put_data/2"><code class="inline">erlang:dist_ctrl_put_data/2</code></a></li></ul><p>This function is called when the handshake has completed and the distribution
│ │ │  channel is up. The distribution controller can begin dispatching traffic over
│ │ │  the channel. This function is optional.</p><p>Only used during handshake phase.</p></li><li><p><strong><code class="inline" id="hs_data_add_flags">add_flags</code></strong> -
│ │ │  <a href="erl_dist_protocol.html#dflags">Distribution flags</a> to add to the connection.
│ │ │  Currently all (non obsolete) flags will automatically be enabled.</p><p>This flag field is optional.</p></li><li><p><strong><code class="inline" id="hs_data_reject_flags">reject_flags</code></strong> -
│ │ │ @@ -515,70 +515,70 @@
│ │ │  is needed. We will use the simple method of having a header of four bytes
│ │ │  containing the length of the package in a big-endian 32-bit integer. As Unix
│ │ │  domain sockets only can be used between processes on the same machine, we do not
│ │ │  need to code the integer in some special endianness, but we will do it anyway
│ │ │  because in most situation you need to do it. Unix domain sockets are reliable
│ │ │  and order maintaining, so we do not need to implement resends and such in the
│ │ │  driver.</p><p>We start writing the example Unix domain sockets driver by declaring prototypes
│ │ │ -and filling in a static <code class="inline">ErlDrvEntry</code> structure:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="6897435087-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6897435087-1">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdio</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-2">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6897435087-2">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdlib</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-3">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6897435087-3">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">string</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-4">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="6897435087-4">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">unistd</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-5">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="6897435087-5">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">errno</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-6">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="6897435087-6">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">sys</span><span class="o">/</span><span class="n">types</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-7">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="6897435087-7">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">sys</span><span class="o">/</span><span class="n">stat</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-8">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="6897435087-8">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">sys</span><span class="o">/</span><span class="n">socket</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-9">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="6897435087-9">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">sys</span><span class="o">/</span><span class="n">un</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-10">(</span><span class="mi">10</span><span class="p" data-group-id="6897435087-10">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">fcntl</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +and filling in a static <code class="inline">ErlDrvEntry</code> structure:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="6259494535-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="6259494535-1">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdio</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-2">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6259494535-2">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">stdlib</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-3">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="6259494535-3">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">string</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-4">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="6259494535-4">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">unistd</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-5">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="6259494535-5">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">errno</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-6">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="6259494535-6">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">sys</span><span class="o">/</span><span class="n">types</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-7">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="6259494535-7">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">sys</span><span class="o">/</span><span class="n">stat</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-8">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="6259494535-8">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">sys</span><span class="o">/</span><span class="n">socket</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-9">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="6259494535-9">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">sys</span><span class="o">/</span><span class="n">un</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-10">(</span><span class="mi">10</span><span class="p" data-group-id="6259494535-10">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="o">&lt;</span><span class="n">fcntl</span><span class="p">.</span><span class="n">h</span><span class="o">&gt;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="6897435087-11">(</span><span class="mi">11</span><span class="p" data-group-id="6897435087-11">)</span><span class="w"> </span><span class="kp">#define</span><span class="w"> </span><span class="no">HAVE_UIO_H</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-12">(</span><span class="mi">12</span><span class="p" data-group-id="6897435087-12">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="s">&quot;erl_driver.h&quot;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-11">(</span><span class="mi">11</span><span class="p" data-group-id="6259494535-11">)</span><span class="w"> </span><span class="kp">#define</span><span class="w"> </span><span class="no">HAVE_UIO_H</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-12">(</span><span class="mi">12</span><span class="p" data-group-id="6259494535-12">)</span><span class="w"> </span><span class="kp">#include</span><span class="w"> </span><span class="s">&quot;erl_driver.h&quot;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="6897435087-13">(</span><span class="mi">13</span><span class="p" data-group-id="6897435087-13">)</span><span class="w"> </span><span class="cm">/*
│ │ │ +</span><span class="p" data-group-id="6259494535-13">(</span><span class="mi">13</span><span class="p" data-group-id="6259494535-13">)</span><span class="w"> </span><span class="cm">/*
│ │ │  (14) ** Interface routines
│ │ │  (15) */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-14">(</span><span class="mi">16</span><span class="p" data-group-id="6897435087-14">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">uds_start</span><span class="p" data-group-id="6897435087-15">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="6897435087-15">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-16">(</span><span class="mi">17</span><span class="p" data-group-id="6897435087-16">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_stop</span><span class="p" data-group-id="6897435087-17">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p" data-group-id="6897435087-17">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-18">(</span><span class="mi">18</span><span class="p" data-group-id="6897435087-18">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_command</span><span class="p" data-group-id="6897435087-19">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="6897435087-19">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-20">(</span><span class="mi">19</span><span class="p" data-group-id="6897435087-20">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_input</span><span class="p" data-group-id="6897435087-21">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="no">ErlDrvEvent</span><span class="w"> </span><span class="n">event</span><span class="p" data-group-id="6897435087-21">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-22">(</span><span class="mi">20</span><span class="p" data-group-id="6897435087-22">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_output</span><span class="p" data-group-id="6897435087-23">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="no">ErlDrvEvent</span><span class="w"> </span><span class="n">event</span><span class="p" data-group-id="6897435087-23">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-24">(</span><span class="mi">21</span><span class="p" data-group-id="6897435087-24">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_finish</span><span class="p" data-group-id="6897435087-25">(</span><span class="kc">void</span><span class="p" data-group-id="6897435087-25">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-26">(</span><span class="mi">22</span><span class="p" data-group-id="6897435087-26">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">uds_control</span><span class="p" data-group-id="6897435087-27">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">command</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-28">(</span><span class="mi">23</span><span class="p" data-group-id="6897435087-28">)</span><span class="w">                        </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">count</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="o">*</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">res_size</span><span class="p" data-group-id="6897435087-27">)</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="p" data-group-id="6897435087-29">(</span><span class="mi">24</span><span class="p" data-group-id="6897435087-29">)</span><span class="w"> </span><span class="cm">/* The driver entry */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-30">(</span><span class="mi">25</span><span class="p" data-group-id="6897435087-30">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvEntry</span><span class="w"> </span><span class="n">uds_driver_entry</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6897435087-31">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-32">(</span><span class="mi">26</span><span class="p" data-group-id="6897435087-32">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* init, N/A */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-33">(</span><span class="mi">27</span><span class="p" data-group-id="6897435087-33">)</span><span class="w">     </span><span class="n">uds_start</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* start, called when port is opened */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-34">(</span><span class="mi">28</span><span class="p" data-group-id="6897435087-34">)</span><span class="w">     </span><span class="n">uds_stop</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* stop, called when port is closed */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-35">(</span><span class="mi">29</span><span class="p" data-group-id="6897435087-35">)</span><span class="w">     </span><span class="n">uds_command</span><span class="p">,</span><span class="w">                     </span><span class="cm">/* output, called when erlang has sent */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-36">(</span><span class="mi">30</span><span class="p" data-group-id="6897435087-36">)</span><span class="w">     </span><span class="n">uds_input</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* ready_input, called when input
│ │ │ +</span><span class="p" data-group-id="6259494535-14">(</span><span class="mi">16</span><span class="p" data-group-id="6259494535-14">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">uds_start</span><span class="p" data-group-id="6259494535-15">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="6259494535-15">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-16">(</span><span class="mi">17</span><span class="p" data-group-id="6259494535-16">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_stop</span><span class="p" data-group-id="6259494535-17">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p" data-group-id="6259494535-17">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-18">(</span><span class="mi">18</span><span class="p" data-group-id="6259494535-18">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_command</span><span class="p" data-group-id="6259494535-19">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="6259494535-19">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-20">(</span><span class="mi">19</span><span class="p" data-group-id="6259494535-20">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_input</span><span class="p" data-group-id="6259494535-21">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="no">ErlDrvEvent</span><span class="w"> </span><span class="n">event</span><span class="p" data-group-id="6259494535-21">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-22">(</span><span class="mi">20</span><span class="p" data-group-id="6259494535-22">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_output</span><span class="p" data-group-id="6259494535-23">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="no">ErlDrvEvent</span><span class="w"> </span><span class="n">event</span><span class="p" data-group-id="6259494535-23">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-24">(</span><span class="mi">21</span><span class="p" data-group-id="6259494535-24">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_finish</span><span class="p" data-group-id="6259494535-25">(</span><span class="kc">void</span><span class="p" data-group-id="6259494535-25">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-26">(</span><span class="mi">22</span><span class="p" data-group-id="6259494535-26">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">uds_control</span><span class="p" data-group-id="6259494535-27">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">command</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-28">(</span><span class="mi">23</span><span class="p" data-group-id="6259494535-28">)</span><span class="w">                        </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">count</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="o">*</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">res_size</span><span class="p" data-group-id="6259494535-27">)</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="p" data-group-id="6259494535-29">(</span><span class="mi">24</span><span class="p" data-group-id="6259494535-29">)</span><span class="w"> </span><span class="cm">/* The driver entry */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-30">(</span><span class="mi">25</span><span class="p" data-group-id="6259494535-30">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvEntry</span><span class="w"> </span><span class="n">uds_driver_entry</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6259494535-31">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-32">(</span><span class="mi">26</span><span class="p" data-group-id="6259494535-32">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* init, N/A */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-33">(</span><span class="mi">27</span><span class="p" data-group-id="6259494535-33">)</span><span class="w">     </span><span class="n">uds_start</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* start, called when port is opened */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-34">(</span><span class="mi">28</span><span class="p" data-group-id="6259494535-34">)</span><span class="w">     </span><span class="n">uds_stop</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* stop, called when port is closed */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-35">(</span><span class="mi">29</span><span class="p" data-group-id="6259494535-35">)</span><span class="w">     </span><span class="n">uds_command</span><span class="p">,</span><span class="w">                     </span><span class="cm">/* output, called when erlang has sent */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-36">(</span><span class="mi">30</span><span class="p" data-group-id="6259494535-36">)</span><span class="w">     </span><span class="n">uds_input</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* ready_input, called when input
│ │ │  (31)                                         descriptor ready */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-37">(</span><span class="mi">32</span><span class="p" data-group-id="6897435087-37">)</span><span class="w">     </span><span class="n">uds_output</span><span class="p">,</span><span class="w">                      </span><span class="cm">/* ready_output, called when output
│ │ │ +</span><span class="p" data-group-id="6259494535-37">(</span><span class="mi">32</span><span class="p" data-group-id="6259494535-37">)</span><span class="w">     </span><span class="n">uds_output</span><span class="p">,</span><span class="w">                      </span><span class="cm">/* ready_output, called when output
│ │ │  (33)                                         descriptor ready */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-38">(</span><span class="mi">34</span><span class="p" data-group-id="6897435087-38">)</span><span class="w">     </span><span class="s">&quot;uds_drv&quot;</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* char *driver_name, the argument
│ │ │ +</span><span class="p" data-group-id="6259494535-38">(</span><span class="mi">34</span><span class="p" data-group-id="6259494535-38">)</span><span class="w">     </span><span class="s">&quot;uds_drv&quot;</span><span class="p">,</span><span class="w">                       </span><span class="cm">/* char *driver_name, the argument
│ │ │  (35)                                         to open_port */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-39">(</span><span class="mi">36</span><span class="p" data-group-id="6897435087-39">)</span><span class="w">     </span><span class="n">uds_finish</span><span class="p">,</span><span class="w">                      </span><span class="cm">/* finish, called when unloaded */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-40">(</span><span class="mi">37</span><span class="p" data-group-id="6897435087-40">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* void * that is not used (BC) */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-41">(</span><span class="mi">38</span><span class="p" data-group-id="6897435087-41">)</span><span class="w">     </span><span class="n">uds_control</span><span class="p">,</span><span class="w">                     </span><span class="cm">/* control, port_control callback */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-42">(</span><span class="mi">39</span><span class="p" data-group-id="6897435087-42">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* timeout, called on timeouts */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-43">(</span><span class="mi">40</span><span class="p" data-group-id="6897435087-43">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* outputv, vector output interface */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-44">(</span><span class="mi">41</span><span class="p" data-group-id="6897435087-44">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* ready_async callback */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-45">(</span><span class="mi">42</span><span class="p" data-group-id="6897435087-45">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* flush callback */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-46">(</span><span class="mi">43</span><span class="p" data-group-id="6897435087-46">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* call callback */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-47">(</span><span class="mi">44</span><span class="p" data-group-id="6897435087-47">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* event callback */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-48">(</span><span class="mi">45</span><span class="p" data-group-id="6897435087-48">)</span><span class="w">     </span><span class="no">ERL_DRV_EXTENDED_MARKER</span><span class="p">,</span><span class="w">         </span><span class="cm">/* Extended driver interface marker */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-49">(</span><span class="mi">46</span><span class="p" data-group-id="6897435087-49">)</span><span class="w">     </span><span class="no">ERL_DRV_EXTENDED_MAJOR_VERSION</span><span class="p">,</span><span class="w">  </span><span class="cm">/* Major version number */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-50">(</span><span class="mi">47</span><span class="p" data-group-id="6897435087-50">)</span><span class="w">     </span><span class="no">ERL_DRV_EXTENDED_MINOR_VERSION</span><span class="p">,</span><span class="w">  </span><span class="cm">/* Minor version number */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-51">(</span><span class="mi">48</span><span class="p" data-group-id="6897435087-51">)</span><span class="w">     </span><span class="no">ERL_DRV_FLAG_SOFT_BUSY</span><span class="p">,</span><span class="w">          </span><span class="cm">/* Driver flags. Soft busy flag is
│ │ │ +</span><span class="p" data-group-id="6259494535-39">(</span><span class="mi">36</span><span class="p" data-group-id="6259494535-39">)</span><span class="w">     </span><span class="n">uds_finish</span><span class="p">,</span><span class="w">                      </span><span class="cm">/* finish, called when unloaded */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-40">(</span><span class="mi">37</span><span class="p" data-group-id="6259494535-40">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* void * that is not used (BC) */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-41">(</span><span class="mi">38</span><span class="p" data-group-id="6259494535-41">)</span><span class="w">     </span><span class="n">uds_control</span><span class="p">,</span><span class="w">                     </span><span class="cm">/* control, port_control callback */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-42">(</span><span class="mi">39</span><span class="p" data-group-id="6259494535-42">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* timeout, called on timeouts */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-43">(</span><span class="mi">40</span><span class="p" data-group-id="6259494535-43">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* outputv, vector output interface */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-44">(</span><span class="mi">41</span><span class="p" data-group-id="6259494535-44">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* ready_async callback */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-45">(</span><span class="mi">42</span><span class="p" data-group-id="6259494535-45">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* flush callback */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-46">(</span><span class="mi">43</span><span class="p" data-group-id="6259494535-46">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* call callback */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-47">(</span><span class="mi">44</span><span class="p" data-group-id="6259494535-47">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* event callback */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-48">(</span><span class="mi">45</span><span class="p" data-group-id="6259494535-48">)</span><span class="w">     </span><span class="no">ERL_DRV_EXTENDED_MARKER</span><span class="p">,</span><span class="w">         </span><span class="cm">/* Extended driver interface marker */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-49">(</span><span class="mi">46</span><span class="p" data-group-id="6259494535-49">)</span><span class="w">     </span><span class="no">ERL_DRV_EXTENDED_MAJOR_VERSION</span><span class="p">,</span><span class="w">  </span><span class="cm">/* Major version number */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-50">(</span><span class="mi">47</span><span class="p" data-group-id="6259494535-50">)</span><span class="w">     </span><span class="no">ERL_DRV_EXTENDED_MINOR_VERSION</span><span class="p">,</span><span class="w">  </span><span class="cm">/* Minor version number */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-51">(</span><span class="mi">48</span><span class="p" data-group-id="6259494535-51">)</span><span class="w">     </span><span class="no">ERL_DRV_FLAG_SOFT_BUSY</span><span class="p">,</span><span class="w">          </span><span class="cm">/* Driver flags. Soft busy flag is
│ │ │  (49)                                         required for distribution drivers */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-52">(</span><span class="mi">50</span><span class="p" data-group-id="6897435087-52">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* Reserved for internal use */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-53">(</span><span class="mi">51</span><span class="p" data-group-id="6897435087-53">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* process_exit callback */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-54">(</span><span class="mi">52</span><span class="p" data-group-id="6897435087-54">)</span><span class="w">     </span><span class="no">NULL</span><span class="w">                             </span><span class="cm">/* stop_select callback */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6897435087-55">(</span><span class="mi">53</span><span class="p" data-group-id="6897435087-55">)</span><span class="w"> </span><span class="p" data-group-id="6897435087-31">}</span><span class="p">;</span></code></pre><p>On line 1-10 the OS headers needed for the driver are included. As this driver
│ │ │ +</span><span class="p" data-group-id="6259494535-52">(</span><span class="mi">50</span><span class="p" data-group-id="6259494535-52">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* Reserved for internal use */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-53">(</span><span class="mi">51</span><span class="p" data-group-id="6259494535-53">)</span><span class="w">     </span><span class="no">NULL</span><span class="p">,</span><span class="w">                            </span><span class="cm">/* process_exit callback */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-54">(</span><span class="mi">52</span><span class="p" data-group-id="6259494535-54">)</span><span class="w">     </span><span class="no">NULL</span><span class="w">                             </span><span class="cm">/* stop_select callback */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6259494535-55">(</span><span class="mi">53</span><span class="p" data-group-id="6259494535-55">)</span><span class="w"> </span><span class="p" data-group-id="6259494535-31">}</span><span class="p">;</span></code></pre><p>On line 1-10 the OS headers needed for the driver are included. As this driver
│ │ │  is written for Solaris, we know that the header <code class="inline">uio.h</code> exists. So the
│ │ │  preprocessor variable <code class="inline">HAVE_UIO_H</code> can be defined before <code class="inline">erl_driver.h</code> is
│ │ │  included on line 12. The definition of <code class="inline">HAVE_UIO_H</code> will make the I/O vectors
│ │ │  used in Erlang's driver queues to correspond to the operating systems ditto,
│ │ │  which is very convenient.</p><p>On line 16-23 the different callback functions are declared (&quot;forward
│ │ │  declarations&quot;).</p><p>The driver structure is similar for statically linked-in drivers and dynamically
│ │ │  loaded. However, some of the fields are to be left empty (that is, initialized
│ │ │ @@ -621,25 +621,25 @@
│ │ │  <code class="inline">data</code> mode and all data is immediately read and passed further to the Erlang
│ │ │  emulator. In <code class="inline">data</code> mode, no data arriving to <code class="inline">uds_command</code> is interpreted, only
│ │ │  packaged and sent out on the socket. The <code class="inline">uds_control</code> callback does the
│ │ │  switching between those two modes.</p><p>While <code class="inline">net_kernel</code> informs different subsystems that the connection is coming
│ │ │  up, the port is to accept data to send. However, the port should not receive any
│ │ │  data, to avoid that data arrives from another node before every kernel subsystem
│ │ │  is prepared to handle it. A third mode, named <code class="inline">intermediate</code>, is used for this
│ │ │ -intermediate stage.</p><p>An enum is defined for the different types of ports:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="8792662861-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8792662861-1">)</span><span class="w"> </span><span class="k">typedef</span><span class="w"> </span><span class="k">enum</span><span class="w"> </span><span class="p" data-group-id="8792662861-2">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8792662861-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8792662861-3">)</span><span class="w">     </span><span class="n">portTypeUnknown</span><span class="p">,</span><span class="w">      </span><span class="cm">/* An uninitialized port */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8792662861-4">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8792662861-4">)</span><span class="w">     </span><span class="n">portTypeListener</span><span class="p">,</span><span class="w">     </span><span class="cm">/* A listening port/socket */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8792662861-5">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="8792662861-5">)</span><span class="w">     </span><span class="n">portTypeAcceptor</span><span class="p">,</span><span class="w">     </span><span class="cm">/* An intermediate stage when accepting
│ │ │ +intermediate stage.</p><p>An enum is defined for the different types of ports:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="9545126230-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9545126230-1">)</span><span class="w"> </span><span class="k">typedef</span><span class="w"> </span><span class="k">enum</span><span class="w"> </span><span class="p" data-group-id="9545126230-2">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9545126230-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9545126230-3">)</span><span class="w">     </span><span class="n">portTypeUnknown</span><span class="p">,</span><span class="w">      </span><span class="cm">/* An uninitialized port */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9545126230-4">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9545126230-4">)</span><span class="w">     </span><span class="n">portTypeListener</span><span class="p">,</span><span class="w">     </span><span class="cm">/* A listening port/socket */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9545126230-5">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="9545126230-5">)</span><span class="w">     </span><span class="n">portTypeAcceptor</span><span class="p">,</span><span class="w">     </span><span class="cm">/* An intermediate stage when accepting
│ │ │  ( 5)                              on a listen port */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8792662861-6">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="8792662861-6">)</span><span class="w">     </span><span class="n">portTypeConnector</span><span class="p">,</span><span class="w">    </span><span class="cm">/* An intermediate stage when connecting */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8792662861-7">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="8792662861-7">)</span><span class="w">     </span><span class="n">portTypeCommand</span><span class="p">,</span><span class="w">      </span><span class="cm">/* A connected open port in command mode */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8792662861-8">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="8792662861-8">)</span><span class="w">     </span><span class="n">portTypeIntermediate</span><span class="p">,</span><span class="w"> </span><span class="cm">/* A connected open port in special
│ │ │ +</span><span class="p" data-group-id="9545126230-6">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="9545126230-6">)</span><span class="w">     </span><span class="n">portTypeConnector</span><span class="p">,</span><span class="w">    </span><span class="cm">/* An intermediate stage when connecting */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9545126230-7">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="9545126230-7">)</span><span class="w">     </span><span class="n">portTypeCommand</span><span class="p">,</span><span class="w">      </span><span class="cm">/* A connected open port in command mode */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9545126230-8">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="9545126230-8">)</span><span class="w">     </span><span class="n">portTypeIntermediate</span><span class="p">,</span><span class="w"> </span><span class="cm">/* A connected open port in special
│ │ │  ( 9)                              half active mode */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8792662861-9">(</span><span class="mi">10</span><span class="p" data-group-id="8792662861-9">)</span><span class="w">     </span><span class="n">portTypeData</span><span class="w">          </span><span class="cm">/* A connected open port in data mode */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8792662861-10">(</span><span class="mi">11</span><span class="p" data-group-id="8792662861-10">)</span><span class="w"> </span><span class="p" data-group-id="8792662861-2">}</span><span class="w"> </span><span class="no">PortType</span><span class="p">;</span></code></pre><p>The different types are as follows:</p><ul><li><p><strong><code class="inline">portTypeUnknown</code></strong> - The type a port has when it is opened, but not bound
│ │ │ +</span><span class="p" data-group-id="9545126230-9">(</span><span class="mi">10</span><span class="p" data-group-id="9545126230-9">)</span><span class="w">     </span><span class="n">portTypeData</span><span class="w">          </span><span class="cm">/* A connected open port in data mode */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9545126230-10">(</span><span class="mi">11</span><span class="p" data-group-id="9545126230-10">)</span><span class="w"> </span><span class="p" data-group-id="9545126230-2">}</span><span class="w"> </span><span class="no">PortType</span><span class="p">;</span></code></pre><p>The different types are as follows:</p><ul><li><p><strong><code class="inline">portTypeUnknown</code></strong> - The type a port has when it is opened, but not bound
│ │ │  to any file descriptor.</p></li><li><p><strong><code class="inline">portTypeListener</code></strong> - A port that is connected to a listen socket. This
│ │ │  port does not do much, no data pumping is done on this socket, but read data
│ │ │  is available when one is trying to do an accept on the port.</p></li><li><p><strong><code class="inline">portTypeAcceptor</code></strong> - This port is to represent the result of an accept
│ │ │  operation. It is created when one wants to accept from a listen socket, and it
│ │ │  is converted to a <code class="inline">portTypeCommand</code> when the accept succeeds.</p></li><li><p><strong><code class="inline">portTypeConnector</code></strong> - Very similar to <code class="inline">portTypeAcceptor</code>, an intermediate
│ │ │  stage between the request for a connect operation and that the socket is
│ │ │  connected to an accepting ditto in the other end. When the sockets are
│ │ │ @@ -647,37 +647,37 @@
│ │ │  mode mentioned earlier.</p></li><li><p><strong><code class="inline">portTypeIntermediate</code></strong> - The intermediate stage for a connected socket.
│ │ │  There is to be no processing of input for this socket.</p></li><li><p><strong><code class="inline">portTypeData</code></strong> - The mode where data is pumped through the port and the
│ │ │  <code class="inline">uds_command</code> routine regards every call as a call where sending is wanted. In
│ │ │  this mode, all input available is read and sent to Erlang when it arrives on
│ │ │  the socket, much like in the active mode of a <code class="inline">gen_tcp</code> socket.</p></li></ul><p>We study the state that is needed for the ports. Notice that not all fields are
│ │ │  used for all types of ports. Some space could be saved by using unions, but that
│ │ │  would clutter the code with multiple indirections, so here is used one struct
│ │ │ -for all types of ports, for readability:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="2216263553-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2216263553-1">)</span><span class="w"> </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="no">Byte</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-2">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2216263553-2">)</span><span class="w"> </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="no">Word</span><span class="p">;</span><span class="w">
│ │ │ +for all types of ports, for readability:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="5613764292-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5613764292-1">)</span><span class="w"> </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="no">Byte</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-2">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5613764292-2">)</span><span class="w"> </span><span class="k">typedef</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="no">Word</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="2216263553-3">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2216263553-3">)</span><span class="w"> </span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="n">uds_data</span><span class="w"> </span><span class="p" data-group-id="2216263553-4">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-5">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="2216263553-5">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">fd</span><span class="p">;</span><span class="w">                   </span><span class="cm">/* File descriptor */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-6">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="2216263553-6">)</span><span class="w">     </span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">;</span><span class="w">          </span><span class="cm">/* The port identifier */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-7">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="2216263553-7">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">lockfd</span><span class="p">;</span><span class="w">               </span><span class="cm">/* The file descriptor for a lock file in
│ │ │ +</span><span class="p" data-group-id="5613764292-3">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5613764292-3">)</span><span class="w"> </span><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="n">uds_data</span><span class="w"> </span><span class="p" data-group-id="5613764292-4">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-5">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="5613764292-5">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">fd</span><span class="p">;</span><span class="w">                   </span><span class="cm">/* File descriptor */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-6">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="5613764292-6">)</span><span class="w">     </span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">;</span><span class="w">          </span><span class="cm">/* The port identifier */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-7">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="5613764292-7">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">lockfd</span><span class="p">;</span><span class="w">               </span><span class="cm">/* The file descriptor for a lock file in
│ │ │  ( 7)                                  case of listen sockets */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-8">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="2216263553-8">)</span><span class="w">     </span><span class="no">Byte</span><span class="w"> </span><span class="n">creation</span><span class="p">;</span><span class="w">            </span><span class="cm">/* The creation serial derived from the
│ │ │ +</span><span class="p" data-group-id="5613764292-8">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="5613764292-8">)</span><span class="w">     </span><span class="no">Byte</span><span class="w"> </span><span class="n">creation</span><span class="p">;</span><span class="w">            </span><span class="cm">/* The creation serial derived from the
│ │ │  ( 9)                                  lock file */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-9">(</span><span class="mi">10</span><span class="p" data-group-id="2216263553-9">)</span><span class="w">     </span><span class="no">PortType</span><span class="w"> </span><span class="n">type</span><span class="p">;</span><span class="w">            </span><span class="cm">/* Type of port */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-10">(</span><span class="mi">11</span><span class="p" data-group-id="2216263553-10">)</span><span class="w">     </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">;</span><span class="w">               </span><span class="cm">/* Short name of socket for unlink */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-11">(</span><span class="mi">12</span><span class="p" data-group-id="2216263553-11">)</span><span class="w">     </span><span class="no">Word</span><span class="w"> </span><span class="n">sent</span><span class="p">;</span><span class="w">                </span><span class="cm">/* Bytes sent */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-12">(</span><span class="mi">13</span><span class="p" data-group-id="2216263553-12">)</span><span class="w">     </span><span class="no">Word</span><span class="w"> </span><span class="n">received</span><span class="p">;</span><span class="w">            </span><span class="cm">/* Bytes received */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-13">(</span><span class="mi">14</span><span class="p" data-group-id="2216263553-13">)</span><span class="w">     </span><span class="k">struct</span><span class="w"> </span><span class="n">uds_data</span><span class="w"> </span><span class="o">*</span><span class="n">partner</span><span class="p">;</span><span class="w"> </span><span class="cm">/* The partner in an accept/listen pair */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-14">(</span><span class="mi">15</span><span class="p" data-group-id="2216263553-14">)</span><span class="w">     </span><span class="k">struct</span><span class="w"> </span><span class="n">uds_data</span><span class="w"> </span><span class="o">*</span><span class="n">next</span><span class="p">;</span><span class="w">    </span><span class="cm">/* Next structure in list */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-15">(</span><span class="mi">16</span><span class="p" data-group-id="2216263553-15">)</span><span class="w">     </span><span class="cm">/* The input buffer and its data */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-16">(</span><span class="mi">17</span><span class="p" data-group-id="2216263553-16">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">buffer_size</span><span class="p">;</span><span class="w">          </span><span class="cm">/* The allocated size of the input buffer */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-17">(</span><span class="mi">18</span><span class="p" data-group-id="2216263553-17">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">buffer_pos</span><span class="p">;</span><span class="w">           </span><span class="cm">/* Current position in input buffer */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-18">(</span><span class="mi">19</span><span class="p" data-group-id="2216263553-18">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">header_pos</span><span class="p">;</span><span class="w">           </span><span class="cm">/* Where the current header is in the
│ │ │ +</span><span class="p" data-group-id="5613764292-9">(</span><span class="mi">10</span><span class="p" data-group-id="5613764292-9">)</span><span class="w">     </span><span class="no">PortType</span><span class="w"> </span><span class="n">type</span><span class="p">;</span><span class="w">            </span><span class="cm">/* Type of port */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-10">(</span><span class="mi">11</span><span class="p" data-group-id="5613764292-10">)</span><span class="w">     </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">name</span><span class="p">;</span><span class="w">               </span><span class="cm">/* Short name of socket for unlink */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-11">(</span><span class="mi">12</span><span class="p" data-group-id="5613764292-11">)</span><span class="w">     </span><span class="no">Word</span><span class="w"> </span><span class="n">sent</span><span class="p">;</span><span class="w">                </span><span class="cm">/* Bytes sent */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-12">(</span><span class="mi">13</span><span class="p" data-group-id="5613764292-12">)</span><span class="w">     </span><span class="no">Word</span><span class="w"> </span><span class="n">received</span><span class="p">;</span><span class="w">            </span><span class="cm">/* Bytes received */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-13">(</span><span class="mi">14</span><span class="p" data-group-id="5613764292-13">)</span><span class="w">     </span><span class="k">struct</span><span class="w"> </span><span class="n">uds_data</span><span class="w"> </span><span class="o">*</span><span class="n">partner</span><span class="p">;</span><span class="w"> </span><span class="cm">/* The partner in an accept/listen pair */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-14">(</span><span class="mi">15</span><span class="p" data-group-id="5613764292-14">)</span><span class="w">     </span><span class="k">struct</span><span class="w"> </span><span class="n">uds_data</span><span class="w"> </span><span class="o">*</span><span class="n">next</span><span class="p">;</span><span class="w">    </span><span class="cm">/* Next structure in list */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-15">(</span><span class="mi">16</span><span class="p" data-group-id="5613764292-15">)</span><span class="w">     </span><span class="cm">/* The input buffer and its data */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-16">(</span><span class="mi">17</span><span class="p" data-group-id="5613764292-16">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">buffer_size</span><span class="p">;</span><span class="w">          </span><span class="cm">/* The allocated size of the input buffer */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-17">(</span><span class="mi">18</span><span class="p" data-group-id="5613764292-17">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">buffer_pos</span><span class="p">;</span><span class="w">           </span><span class="cm">/* Current position in input buffer */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-18">(</span><span class="mi">19</span><span class="p" data-group-id="5613764292-18">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">header_pos</span><span class="p">;</span><span class="w">           </span><span class="cm">/* Where the current header is in the
│ │ │  (20)                                  input buffer */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-19">(</span><span class="mi">21</span><span class="p" data-group-id="2216263553-19">)</span><span class="w">     </span><span class="no">Byte</span><span class="w"> </span><span class="o">*</span><span class="n">buffer</span><span class="p">;</span><span class="w">             </span><span class="cm">/* The actual input buffer */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2216263553-20">(</span><span class="mi">22</span><span class="p" data-group-id="2216263553-20">)</span><span class="w"> </span><span class="p" data-group-id="2216263553-4">}</span><span class="w"> </span><span class="no">UdsData</span><span class="p">;</span></code></pre><p>This structure is used for all types of ports although some fields are useless
│ │ │ +</span><span class="p" data-group-id="5613764292-19">(</span><span class="mi">21</span><span class="p" data-group-id="5613764292-19">)</span><span class="w">     </span><span class="no">Byte</span><span class="w"> </span><span class="o">*</span><span class="n">buffer</span><span class="p">;</span><span class="w">             </span><span class="cm">/* The actual input buffer */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5613764292-20">(</span><span class="mi">22</span><span class="p" data-group-id="5613764292-20">)</span><span class="w"> </span><span class="p" data-group-id="5613764292-4">}</span><span class="w"> </span><span class="no">UdsData</span><span class="p">;</span></code></pre><p>This structure is used for all types of ports although some fields are useless
│ │ │  for some types. The least memory consuming solution would be to arrange this
│ │ │  structure as a union of structures. However, the multiple indirections in the
│ │ │  code to access a field in such a structure would clutter the code too much for
│ │ │  an example.</p><p>The fields in the structure are as follows:</p><ul><li><p><strong><code class="inline">fd</code></strong> - The file descriptor of the socket associated with the port.</p></li><li><p><strong><code class="inline">port</code></strong> - The port identifier for the port that this structure corresponds
│ │ │  to. It is needed for most <code class="inline">driver_XXX</code> calls from the driver back to the
│ │ │  emulator.</p></li><li><p><strong><code class="inline">lockfd</code></strong> - If the socket is a listen socket, we use a separate (regular)
│ │ │  file for two purposes:</p><ul><li><p>We want a locking mechanism that gives no race conditions, to be sure if
│ │ │ @@ -718,105 +718,105 @@
│ │ │  details about buffering and other things unrelated to driver writing are not
│ │ │  explained. Likewise are some peculiarities of the UDS protocol not explained in
│ │ │  detail. The chosen protocol is not important.</p><p>Prototypes for the driver callback routines can be found in the <code class="inline">erl_driver.h</code>
│ │ │  header file.</p><p>The driver initialization routine is (usually) declared with a macro to make the
│ │ │  driver easier to port between different operating systems (and flavors of
│ │ │  systems). This is the only routine that must have a well-defined name. All other
│ │ │  callbacks are reached through the driver structure. The macro to use is named
│ │ │ -<code class="inline">DRIVER_INIT</code> and takes the driver name as parameter:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="5195083000-1">(</span><span class="mi">1</span><span class="p" data-group-id="5195083000-1">)</span><span class="w"> </span><span class="cm">/* Beginning of linked list of ports */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5195083000-2">(</span><span class="mi">2</span><span class="p" data-group-id="5195083000-2">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">first_data</span><span class="p">;</span><span class="w">
│ │ │ +<code class="inline">DRIVER_INIT</code> and takes the driver name as parameter:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="5092027350-1">(</span><span class="mi">1</span><span class="p" data-group-id="5092027350-1">)</span><span class="w"> </span><span class="cm">/* Beginning of linked list of ports */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5092027350-2">(</span><span class="mi">2</span><span class="p" data-group-id="5092027350-2">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">first_data</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="p" data-group-id="5195083000-3">(</span><span class="mi">3</span><span class="p" data-group-id="5195083000-3">)</span><span class="w"> </span><span class="no">DRIVER_INIT</span><span class="p" data-group-id="5195083000-4">(</span><span class="n">uds_drv</span><span class="p" data-group-id="5195083000-4">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5195083000-5">(</span><span class="mi">4</span><span class="p" data-group-id="5195083000-5">)</span><span class="w"> </span><span class="p" data-group-id="5195083000-6">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5195083000-7">(</span><span class="mi">5</span><span class="p" data-group-id="5195083000-7">)</span><span class="w">     </span><span class="n">first_data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5195083000-8">(</span><span class="mi">6</span><span class="p" data-group-id="5195083000-8">)</span><span class="w">     </span><span class="k">return</span><span class="w"> </span><span class="o">&amp;</span><span class="n">uds_driver_entry</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5195083000-9">(</span><span class="mi">7</span><span class="p" data-group-id="5195083000-9">)</span><span class="w"> </span><span class="p" data-group-id="5195083000-6">}</span></code></pre><p>The routine initializes the single global data structure and returns a pointer
│ │ │ +</span><span class="p" data-group-id="5092027350-3">(</span><span class="mi">3</span><span class="p" data-group-id="5092027350-3">)</span><span class="w"> </span><span class="no">DRIVER_INIT</span><span class="p" data-group-id="5092027350-4">(</span><span class="n">uds_drv</span><span class="p" data-group-id="5092027350-4">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5092027350-5">(</span><span class="mi">4</span><span class="p" data-group-id="5092027350-5">)</span><span class="w"> </span><span class="p" data-group-id="5092027350-6">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5092027350-7">(</span><span class="mi">5</span><span class="p" data-group-id="5092027350-7">)</span><span class="w">     </span><span class="n">first_data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5092027350-8">(</span><span class="mi">6</span><span class="p" data-group-id="5092027350-8">)</span><span class="w">     </span><span class="k">return</span><span class="w"> </span><span class="o">&amp;</span><span class="n">uds_driver_entry</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5092027350-9">(</span><span class="mi">7</span><span class="p" data-group-id="5092027350-9">)</span><span class="w"> </span><span class="p" data-group-id="5092027350-6">}</span></code></pre><p>The routine initializes the single global data structure and returns a pointer
│ │ │  to the driver entry. The routine is called when <code class="inline">erl_ddll:load_driver</code> is called
│ │ │  from Erlang.</p><p>The <code class="inline">uds_start</code> routine is called when a port is opened from Erlang. In this
│ │ │  case, we only allocate a structure and initialize it. Creating the actual socket
│ │ │ -is left to the <code class="inline">uds_command</code> routine.</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="2082557970-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2082557970-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">uds_start</span><span class="p" data-group-id="2082557970-2">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="2082557970-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2082557970-3">)</span><span class="w"> </span><span class="p" data-group-id="2082557970-4">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2082557970-5">)</span><span class="w">     </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-6">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="2082557970-6">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-7">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="2082557970-7">)</span><span class="w">     </span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">ALLOC</span><span class="p" data-group-id="2082557970-8">(</span><span class="nf">sizeof</span><span class="p" data-group-id="2082557970-9">(</span><span class="no">UdsData</span><span class="p" data-group-id="2082557970-9">)</span><span class="p" data-group-id="2082557970-8">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-10">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="2082557970-10">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">-</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-11">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="2082557970-11">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">lockfd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">-</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-12">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="2082557970-12">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">creation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-13">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="2082557970-13">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">port</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-14">(</span><span class="mi">10</span><span class="p" data-group-id="2082557970-14">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeUnknown</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-15">(</span><span class="mi">11</span><span class="p" data-group-id="2082557970-15">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-16">(</span><span class="mi">12</span><span class="p" data-group-id="2082557970-16">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">buffer_size</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-17">(</span><span class="mi">13</span><span class="p" data-group-id="2082557970-17">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">buffer_pos</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-18">(</span><span class="mi">14</span><span class="p" data-group-id="2082557970-18">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">header_pos</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-19">(</span><span class="mi">15</span><span class="p" data-group-id="2082557970-19">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">buffer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-20">(</span><span class="mi">16</span><span class="p" data-group-id="2082557970-20">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-21">(</span><span class="mi">17</span><span class="p" data-group-id="2082557970-21">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">received</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-22">(</span><span class="mi">18</span><span class="p" data-group-id="2082557970-22">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">partner</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-23">(</span><span class="mi">19</span><span class="p" data-group-id="2082557970-23">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">next</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">first_data</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-24">(</span><span class="mi">20</span><span class="p" data-group-id="2082557970-24">)</span><span class="w">     </span><span class="n">first_data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ud</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-25">(</span><span class="mi">21</span><span class="p" data-group-id="2082557970-25">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-26">(</span><span class="mi">22</span><span class="p" data-group-id="2082557970-26">)</span><span class="w">     </span><span class="nf">return</span><span class="p" data-group-id="2082557970-27">(</span><span class="p" data-group-id="2082557970-28">(</span><span class="no">ErlDrvData</span><span class="p" data-group-id="2082557970-28">)</span><span class="w"> </span><span class="n">ud</span><span class="p" data-group-id="2082557970-27">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2082557970-29">(</span><span class="mi">23</span><span class="p" data-group-id="2082557970-29">)</span><span class="w"> </span><span class="p" data-group-id="2082557970-4">}</span></code></pre><p>Every data item is initialized, so that no problems arise when a newly created
│ │ │ +is left to the <code class="inline">uds_command</code> routine.</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="2905099354-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2905099354-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">uds_start</span><span class="p" data-group-id="2905099354-2">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="2905099354-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="2905099354-3">)</span><span class="w"> </span><span class="p" data-group-id="2905099354-4">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="2905099354-5">)</span><span class="w">     </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-6">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="2905099354-6">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-7">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="2905099354-7">)</span><span class="w">     </span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">ALLOC</span><span class="p" data-group-id="2905099354-8">(</span><span class="nf">sizeof</span><span class="p" data-group-id="2905099354-9">(</span><span class="no">UdsData</span><span class="p" data-group-id="2905099354-9">)</span><span class="p" data-group-id="2905099354-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-10">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="2905099354-10">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">-</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-11">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="2905099354-11">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">lockfd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">-</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-12">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="2905099354-12">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">creation</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-13">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="2905099354-13">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">port</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-14">(</span><span class="mi">10</span><span class="p" data-group-id="2905099354-14">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeUnknown</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-15">(</span><span class="mi">11</span><span class="p" data-group-id="2905099354-15">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-16">(</span><span class="mi">12</span><span class="p" data-group-id="2905099354-16">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">buffer_size</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-17">(</span><span class="mi">13</span><span class="p" data-group-id="2905099354-17">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">buffer_pos</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-18">(</span><span class="mi">14</span><span class="p" data-group-id="2905099354-18">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">header_pos</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-19">(</span><span class="mi">15</span><span class="p" data-group-id="2905099354-19">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">buffer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-20">(</span><span class="mi">16</span><span class="p" data-group-id="2905099354-20">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-21">(</span><span class="mi">17</span><span class="p" data-group-id="2905099354-21">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">received</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-22">(</span><span class="mi">18</span><span class="p" data-group-id="2905099354-22">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">partner</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-23">(</span><span class="mi">19</span><span class="p" data-group-id="2905099354-23">)</span><span class="w">     </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">next</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">first_data</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-24">(</span><span class="mi">20</span><span class="p" data-group-id="2905099354-24">)</span><span class="w">     </span><span class="n">first_data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ud</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-25">(</span><span class="mi">21</span><span class="p" data-group-id="2905099354-25">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-26">(</span><span class="mi">22</span><span class="p" data-group-id="2905099354-26">)</span><span class="w">     </span><span class="nf">return</span><span class="p" data-group-id="2905099354-27">(</span><span class="p" data-group-id="2905099354-28">(</span><span class="no">ErlDrvData</span><span class="p" data-group-id="2905099354-28">)</span><span class="w"> </span><span class="n">ud</span><span class="p" data-group-id="2905099354-27">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2905099354-29">(</span><span class="mi">23</span><span class="p" data-group-id="2905099354-29">)</span><span class="w"> </span><span class="p" data-group-id="2905099354-4">}</span></code></pre><p>Every data item is initialized, so that no problems arise when a newly created
│ │ │  port is closed (without there being any corresponding socket). This routine is
│ │ │  called when <a href="erlang.html#open_port/2"><code class="inline">open_port({spawn, &quot;uds_drv&quot;},[])</code></a> is called from
│ │ │  Erlang.</p><p>The <code class="inline">uds_command</code> routine is the routine called when an Erlang process sends
│ │ │  data to the port. This routine handles all asynchronous commands when the port
│ │ │  is in <code class="inline">command</code> mode and the sending of all data when the port is in <code class="inline">data</code>
│ │ │ -mode:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="9826031450-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9826031450-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_command</span><span class="p" data-group-id="9826031450-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="9826031450-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="9826031450-3">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-4">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="9826031450-5">)</span><span class="w">     </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9826031450-6">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="9826031450-6">)</span><span class="w"> </span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="p" data-group-id="9826031450-7">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="9826031450-7">)</span><span class="w">     </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9826031450-8">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeData</span><span class="w"> </span><span class="o">||</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeIntermediate</span><span class="p" data-group-id="9826031450-8">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-9">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-10">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="9826031450-10">)</span><span class="w">         </span><span class="no">DEBUGF</span><span class="p" data-group-id="9826031450-11">(</span><span class="p" data-group-id="9826031450-12">(</span><span class="s">&quot;Passive do_send %d&quot;</span><span class="p">,</span><span class="n">bufflen</span><span class="p" data-group-id="9826031450-12">)</span><span class="p" data-group-id="9826031450-11">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-13">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="9826031450-13">)</span><span class="w">         </span><span class="nf">do_send</span><span class="p" data-group-id="9826031450-14">(</span><span class="n">ud</span><span class="p">,</span><span class="w"> </span><span class="n">buff</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">bufflen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9826031450-14">)</span><span class="p">;</span><span class="w"> </span><span class="cm">/* XXX */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-15">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="9826031450-15">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-16">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="9826031450-16">)</span><span class="w">     </span><span class="p" data-group-id="9826031450-9">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-17">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="9826031450-17">)</span><span class="w">     </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9826031450-18">(</span><span class="n">bufflen</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="9826031450-18">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-19">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-20">(</span><span class="mi">10</span><span class="p" data-group-id="9826031450-20">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-21">(</span><span class="mi">11</span><span class="p" data-group-id="9826031450-21">)</span><span class="w">     </span><span class="p" data-group-id="9826031450-19">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-22">(</span><span class="mi">12</span><span class="p" data-group-id="9826031450-22">)</span><span class="w">     </span><span class="k">switch</span><span class="w"> </span><span class="p" data-group-id="9826031450-23">(</span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="9826031450-23">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-24">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-25">(</span><span class="mi">13</span><span class="p" data-group-id="9826031450-25">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;L&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-26">(</span><span class="mi">14</span><span class="p" data-group-id="9826031450-26">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9826031450-27">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeUnknown</span><span class="p" data-group-id="9826031450-27">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-28">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-29">(</span><span class="mi">15</span><span class="p" data-group-id="9826031450-29">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="9826031450-30">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="9826031450-30">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-31">(</span><span class="mi">16</span><span class="p" data-group-id="9826031450-31">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-32">(</span><span class="mi">17</span><span class="p" data-group-id="9826031450-32">)</span><span class="w">         </span><span class="p" data-group-id="9826031450-28">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-33">(</span><span class="mi">18</span><span class="p" data-group-id="9826031450-33">)</span><span class="w">         </span><span class="nf">uds_command_listen</span><span class="p" data-group-id="9826031450-34">(</span><span class="n">ud</span><span class="p">,</span><span class="n">buff</span><span class="p">,</span><span class="n">bufflen</span><span class="p" data-group-id="9826031450-34">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-35">(</span><span class="mi">19</span><span class="p" data-group-id="9826031450-35">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-36">(</span><span class="mi">20</span><span class="p" data-group-id="9826031450-36">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;A&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-37">(</span><span class="mi">21</span><span class="p" data-group-id="9826031450-37">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9826031450-38">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeUnknown</span><span class="p" data-group-id="9826031450-38">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-39">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-40">(</span><span class="mi">22</span><span class="p" data-group-id="9826031450-40">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="9826031450-41">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="9826031450-41">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-42">(</span><span class="mi">23</span><span class="p" data-group-id="9826031450-42">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-43">(</span><span class="mi">24</span><span class="p" data-group-id="9826031450-43">)</span><span class="w">         </span><span class="p" data-group-id="9826031450-39">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-44">(</span><span class="mi">25</span><span class="p" data-group-id="9826031450-44">)</span><span class="w">         </span><span class="nf">uds_command_accept</span><span class="p" data-group-id="9826031450-45">(</span><span class="n">ud</span><span class="p">,</span><span class="n">buff</span><span class="p">,</span><span class="n">bufflen</span><span class="p" data-group-id="9826031450-45">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-46">(</span><span class="mi">26</span><span class="p" data-group-id="9826031450-46">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-47">(</span><span class="mi">27</span><span class="p" data-group-id="9826031450-47">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;C&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-48">(</span><span class="mi">28</span><span class="p" data-group-id="9826031450-48">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9826031450-49">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeUnknown</span><span class="p" data-group-id="9826031450-49">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-50">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-51">(</span><span class="mi">29</span><span class="p" data-group-id="9826031450-51">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="9826031450-52">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="9826031450-52">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-53">(</span><span class="mi">30</span><span class="p" data-group-id="9826031450-53">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-54">(</span><span class="mi">31</span><span class="p" data-group-id="9826031450-54">)</span><span class="w">         </span><span class="p" data-group-id="9826031450-50">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-55">(</span><span class="mi">32</span><span class="p" data-group-id="9826031450-55">)</span><span class="w">         </span><span class="nf">uds_command_connect</span><span class="p" data-group-id="9826031450-56">(</span><span class="n">ud</span><span class="p">,</span><span class="n">buff</span><span class="p">,</span><span class="n">bufflen</span><span class="p" data-group-id="9826031450-56">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-57">(</span><span class="mi">33</span><span class="p" data-group-id="9826031450-57">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-58">(</span><span class="mi">34</span><span class="p" data-group-id="9826031450-58">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;S&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-59">(</span><span class="mi">35</span><span class="p" data-group-id="9826031450-59">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9826031450-60">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="9826031450-60">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-61">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-62">(</span><span class="mi">36</span><span class="p" data-group-id="9826031450-62">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="9826031450-63">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="9826031450-63">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-64">(</span><span class="mi">37</span><span class="p" data-group-id="9826031450-64">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-65">(</span><span class="mi">38</span><span class="p" data-group-id="9826031450-65">)</span><span class="w">         </span><span class="p" data-group-id="9826031450-61">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-66">(</span><span class="mi">39</span><span class="p" data-group-id="9826031450-66">)</span><span class="w">         </span><span class="nf">do_send</span><span class="p" data-group-id="9826031450-67">(</span><span class="n">ud</span><span class="p">,</span><span class="w"> </span><span class="n">buff</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">bufflen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="9826031450-67">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-68">(</span><span class="mi">40</span><span class="p" data-group-id="9826031450-68">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-69">(</span><span class="mi">41</span><span class="p" data-group-id="9826031450-69">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;R&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-70">(</span><span class="mi">42</span><span class="p" data-group-id="9826031450-70">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="9826031450-71">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="9826031450-71">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-72">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-73">(</span><span class="mi">43</span><span class="p" data-group-id="9826031450-73">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="9826031450-74">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="9826031450-74">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-75">(</span><span class="mi">44</span><span class="p" data-group-id="9826031450-75">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-76">(</span><span class="mi">45</span><span class="p" data-group-id="9826031450-76">)</span><span class="w">         </span><span class="p" data-group-id="9826031450-72">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-77">(</span><span class="mi">46</span><span class="p" data-group-id="9826031450-77">)</span><span class="w">         </span><span class="nf">do_recv</span><span class="p" data-group-id="9826031450-78">(</span><span class="n">ud</span><span class="p" data-group-id="9826031450-78">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-79">(</span><span class="mi">47</span><span class="p" data-group-id="9826031450-79">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-80">(</span><span class="mi">48</span><span class="p" data-group-id="9826031450-80">)</span><span class="w">     </span><span class="ss">default</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-81">(</span><span class="mi">49</span><span class="p" data-group-id="9826031450-81">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-82">(</span><span class="mi">50</span><span class="p" data-group-id="9826031450-82">)</span><span class="w">     </span><span class="p" data-group-id="9826031450-24">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9826031450-83">(</span><span class="mi">51</span><span class="p" data-group-id="9826031450-83">)</span><span class="w"> </span><span class="p" data-group-id="9826031450-4">}</span></code></pre><p>The command routine takes three parameters; the handle returned for the port by
│ │ │ +mode:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="8628707361-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8628707361-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_command</span><span class="p" data-group-id="8628707361-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="8628707361-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8628707361-3">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-4">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8628707361-5">)</span><span class="w">     </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8628707361-6">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="8628707361-6">)</span><span class="w"> </span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="p" data-group-id="8628707361-7">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="8628707361-7">)</span><span class="w">     </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8628707361-8">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeData</span><span class="w"> </span><span class="o">||</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeIntermediate</span><span class="p" data-group-id="8628707361-8">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-9">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-10">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="8628707361-10">)</span><span class="w">         </span><span class="no">DEBUGF</span><span class="p" data-group-id="8628707361-11">(</span><span class="p" data-group-id="8628707361-12">(</span><span class="s">&quot;Passive do_send %d&quot;</span><span class="p">,</span><span class="n">bufflen</span><span class="p" data-group-id="8628707361-12">)</span><span class="p" data-group-id="8628707361-11">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-13">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="8628707361-13">)</span><span class="w">         </span><span class="nf">do_send</span><span class="p" data-group-id="8628707361-14">(</span><span class="n">ud</span><span class="p">,</span><span class="w"> </span><span class="n">buff</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">bufflen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8628707361-14">)</span><span class="p">;</span><span class="w"> </span><span class="cm">/* XXX */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-15">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="8628707361-15">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-16">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="8628707361-16">)</span><span class="w">     </span><span class="p" data-group-id="8628707361-9">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-17">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="8628707361-17">)</span><span class="w">     </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8628707361-18">(</span><span class="n">bufflen</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8628707361-18">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-19">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-20">(</span><span class="mi">10</span><span class="p" data-group-id="8628707361-20">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-21">(</span><span class="mi">11</span><span class="p" data-group-id="8628707361-21">)</span><span class="w">     </span><span class="p" data-group-id="8628707361-19">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-22">(</span><span class="mi">12</span><span class="p" data-group-id="8628707361-22">)</span><span class="w">     </span><span class="k">switch</span><span class="w"> </span><span class="p" data-group-id="8628707361-23">(</span><span class="o">*</span><span class="n">buff</span><span class="p" data-group-id="8628707361-23">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-24">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-25">(</span><span class="mi">13</span><span class="p" data-group-id="8628707361-25">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;L&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-26">(</span><span class="mi">14</span><span class="p" data-group-id="8628707361-26">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8628707361-27">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeUnknown</span><span class="p" data-group-id="8628707361-27">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-28">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-29">(</span><span class="mi">15</span><span class="p" data-group-id="8628707361-29">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="8628707361-30">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="8628707361-30">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-31">(</span><span class="mi">16</span><span class="p" data-group-id="8628707361-31">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-32">(</span><span class="mi">17</span><span class="p" data-group-id="8628707361-32">)</span><span class="w">         </span><span class="p" data-group-id="8628707361-28">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-33">(</span><span class="mi">18</span><span class="p" data-group-id="8628707361-33">)</span><span class="w">         </span><span class="nf">uds_command_listen</span><span class="p" data-group-id="8628707361-34">(</span><span class="n">ud</span><span class="p">,</span><span class="n">buff</span><span class="p">,</span><span class="n">bufflen</span><span class="p" data-group-id="8628707361-34">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-35">(</span><span class="mi">19</span><span class="p" data-group-id="8628707361-35">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-36">(</span><span class="mi">20</span><span class="p" data-group-id="8628707361-36">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;A&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-37">(</span><span class="mi">21</span><span class="p" data-group-id="8628707361-37">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8628707361-38">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeUnknown</span><span class="p" data-group-id="8628707361-38">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-39">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-40">(</span><span class="mi">22</span><span class="p" data-group-id="8628707361-40">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="8628707361-41">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="8628707361-41">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-42">(</span><span class="mi">23</span><span class="p" data-group-id="8628707361-42">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-43">(</span><span class="mi">24</span><span class="p" data-group-id="8628707361-43">)</span><span class="w">         </span><span class="p" data-group-id="8628707361-39">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-44">(</span><span class="mi">25</span><span class="p" data-group-id="8628707361-44">)</span><span class="w">         </span><span class="nf">uds_command_accept</span><span class="p" data-group-id="8628707361-45">(</span><span class="n">ud</span><span class="p">,</span><span class="n">buff</span><span class="p">,</span><span class="n">bufflen</span><span class="p" data-group-id="8628707361-45">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-46">(</span><span class="mi">26</span><span class="p" data-group-id="8628707361-46">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-47">(</span><span class="mi">27</span><span class="p" data-group-id="8628707361-47">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;C&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-48">(</span><span class="mi">28</span><span class="p" data-group-id="8628707361-48">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8628707361-49">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeUnknown</span><span class="p" data-group-id="8628707361-49">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-50">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-51">(</span><span class="mi">29</span><span class="p" data-group-id="8628707361-51">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="8628707361-52">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="8628707361-52">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-53">(</span><span class="mi">30</span><span class="p" data-group-id="8628707361-53">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-54">(</span><span class="mi">31</span><span class="p" data-group-id="8628707361-54">)</span><span class="w">         </span><span class="p" data-group-id="8628707361-50">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-55">(</span><span class="mi">32</span><span class="p" data-group-id="8628707361-55">)</span><span class="w">         </span><span class="nf">uds_command_connect</span><span class="p" data-group-id="8628707361-56">(</span><span class="n">ud</span><span class="p">,</span><span class="n">buff</span><span class="p">,</span><span class="n">bufflen</span><span class="p" data-group-id="8628707361-56">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-57">(</span><span class="mi">33</span><span class="p" data-group-id="8628707361-57">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-58">(</span><span class="mi">34</span><span class="p" data-group-id="8628707361-58">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;S&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-59">(</span><span class="mi">35</span><span class="p" data-group-id="8628707361-59">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8628707361-60">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="8628707361-60">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-61">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-62">(</span><span class="mi">36</span><span class="p" data-group-id="8628707361-62">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="8628707361-63">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="8628707361-63">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-64">(</span><span class="mi">37</span><span class="p" data-group-id="8628707361-64">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-65">(</span><span class="mi">38</span><span class="p" data-group-id="8628707361-65">)</span><span class="w">         </span><span class="p" data-group-id="8628707361-61">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-66">(</span><span class="mi">39</span><span class="p" data-group-id="8628707361-66">)</span><span class="w">         </span><span class="nf">do_send</span><span class="p" data-group-id="8628707361-67">(</span><span class="n">ud</span><span class="p">,</span><span class="w"> </span><span class="n">buff</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">bufflen</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8628707361-67">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-68">(</span><span class="mi">40</span><span class="p" data-group-id="8628707361-68">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-69">(</span><span class="mi">41</span><span class="p" data-group-id="8628707361-69">)</span><span class="w">     </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;R&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-70">(</span><span class="mi">42</span><span class="p" data-group-id="8628707361-70">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8628707361-71">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="8628707361-71">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-72">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-73">(</span><span class="mi">43</span><span class="p" data-group-id="8628707361-73">)</span><span class="w">             </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="8628707361-74">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">ENOTSUP</span><span class="p" data-group-id="8628707361-74">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-75">(</span><span class="mi">44</span><span class="p" data-group-id="8628707361-75">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-76">(</span><span class="mi">45</span><span class="p" data-group-id="8628707361-76">)</span><span class="w">         </span><span class="p" data-group-id="8628707361-72">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-77">(</span><span class="mi">46</span><span class="p" data-group-id="8628707361-77">)</span><span class="w">         </span><span class="nf">do_recv</span><span class="p" data-group-id="8628707361-78">(</span><span class="n">ud</span><span class="p" data-group-id="8628707361-78">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-79">(</span><span class="mi">47</span><span class="p" data-group-id="8628707361-79">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-80">(</span><span class="mi">48</span><span class="p" data-group-id="8628707361-80">)</span><span class="w">     </span><span class="ss">default</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-81">(</span><span class="mi">49</span><span class="p" data-group-id="8628707361-81">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-82">(</span><span class="mi">50</span><span class="p" data-group-id="8628707361-82">)</span><span class="w">     </span><span class="p" data-group-id="8628707361-24">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8628707361-83">(</span><span class="mi">51</span><span class="p" data-group-id="8628707361-83">)</span><span class="w"> </span><span class="p" data-group-id="8628707361-4">}</span></code></pre><p>The command routine takes three parameters; the handle returned for the port by
│ │ │  <code class="inline">uds_start</code>, which is a pointer to the internal port structure, the data buffer,
│ │ │  and the length of the data buffer. The buffer is the data sent from Erlang (a
│ │ │  list of bytes) converted to an C array (of bytes).</p><p>If Erlang sends, for example, the list <code class="inline">[$a,$b,$c]</code> to the port, the <code class="inline">bufflen</code>
│ │ │  variable is <code class="inline">3</code> and the <code class="inline">buff</code> variable contains <code class="inline">{'a','b','c'}</code> (no <code class="inline">NULL</code>
│ │ │  termination). Usually the first byte is used as an opcode, which is the case in
│ │ │  this driver too (at least when the port is in <code class="inline">command</code> mode). The opcodes are
│ │ │  defined as follows:</p><ul><li><p><strong><code class="inline">'L'&lt;socket name&gt;</code></strong> - Creates and listens on socket with the specified
│ │ │ @@ -837,127 +837,127 @@
│ │ │  example, line 15). Notice that the failure routines make a call to the
│ │ │  <code class="inline">uds_stop</code> routine, which will remove the internal port data. The handle (and
│ │ │  the casted handle <code class="inline">ud</code>) is therefore <em>invalid pointers</em> after a <code class="inline">driver_failure</code>
│ │ │  call and we should <em>return immediately</em>. The runtime system will send exit
│ │ │  signals to all linked processes.</p><p>The <code class="inline">uds_input</code> routine is called when data is available on a file descriptor
│ │ │  previously passed to the <code class="inline">driver_select</code> routine. This occurs typically when a
│ │ │  read command is issued and no data is available. The <code class="inline">do_recv</code> routine is as
│ │ │ -follows:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="5047538976-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5047538976-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">do_recv</span><span class="p" data-group-id="5047538976-2">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="p" data-group-id="5047538976-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5047538976-3">)</span><span class="w"> </span><span class="p" data-group-id="5047538976-4">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5047538976-5">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-6">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="5047538976-6">)</span><span class="w">     </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">ibuf</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-7">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="5047538976-7">)</span><span class="w">     </span><span class="nf">for</span><span class="p" data-group-id="5047538976-8">(</span><span class="p">;</span><span class="p">;</span><span class="p" data-group-id="5047538976-8">)</span><span class="w"> </span><span class="p" data-group-id="5047538976-9">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-10">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="5047538976-10">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5047538976-11">(</span><span class="p" data-group-id="5047538976-12">(</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">buffered_read_package</span><span class="p" data-group-id="5047538976-13">(</span><span class="n">ud</span><span class="p">,</span><span class="o">&amp;</span><span class="n">ibuf</span><span class="p" data-group-id="5047538976-13">)</span><span class="p" data-group-id="5047538976-12">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5047538976-11">)</span><span class="w"> </span><span class="p" data-group-id="5047538976-14">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-15">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="5047538976-15">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5047538976-16">(</span><span class="n">res</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="no">NORMAL_READ_FAILURE</span><span class="p" data-group-id="5047538976-16">)</span><span class="w"> </span><span class="p" data-group-id="5047538976-17">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-18">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="5047538976-18">)</span><span class="w">                 </span><span class="nf">driver_select</span><span class="p" data-group-id="5047538976-19">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5047538976-20">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="5047538976-20">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5047538976-19">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-21">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="5047538976-21">)</span><span class="w">             </span><span class="p" data-group-id="5047538976-17">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="5047538976-22">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-23">(</span><span class="mi">10</span><span class="p" data-group-id="5047538976-23">)</span><span class="w">                 </span><span class="nf">driver_failure_eof</span><span class="p" data-group-id="5047538976-24">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="5047538976-24">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-25">(</span><span class="mi">11</span><span class="p" data-group-id="5047538976-25">)</span><span class="w">             </span><span class="p" data-group-id="5047538976-22">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-26">(</span><span class="mi">12</span><span class="p" data-group-id="5047538976-26">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-27">(</span><span class="mi">13</span><span class="p" data-group-id="5047538976-27">)</span><span class="w">         </span><span class="p" data-group-id="5047538976-14">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-28">(</span><span class="mi">14</span><span class="p" data-group-id="5047538976-28">)</span><span class="w">         </span><span class="cm">/* Got a package */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-29">(</span><span class="mi">15</span><span class="p" data-group-id="5047538976-29">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5047538976-30">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="5047538976-30">)</span><span class="w"> </span><span class="p" data-group-id="5047538976-31">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-32">(</span><span class="mi">16</span><span class="p" data-group-id="5047538976-32">)</span><span class="w">             </span><span class="n">ibuf</span><span class="p" data-group-id="5047538976-33">[</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5047538976-33">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="err">&#39;</span><span class="no">R</span><span class="err">&#39;</span><span class="p">;</span><span class="w"> </span><span class="cm">/* There is always room for a single byte
│ │ │ +follows:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="1528751735-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1528751735-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">do_recv</span><span class="p" data-group-id="1528751735-2">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="p" data-group-id="1528751735-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1528751735-3">)</span><span class="w"> </span><span class="p" data-group-id="1528751735-4">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1528751735-5">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">res</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-6">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1528751735-6">)</span><span class="w">     </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">ibuf</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-7">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="1528751735-7">)</span><span class="w">     </span><span class="nf">for</span><span class="p" data-group-id="1528751735-8">(</span><span class="p">;</span><span class="p">;</span><span class="p" data-group-id="1528751735-8">)</span><span class="w"> </span><span class="p" data-group-id="1528751735-9">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-10">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="1528751735-10">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1528751735-11">(</span><span class="p" data-group-id="1528751735-12">(</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">buffered_read_package</span><span class="p" data-group-id="1528751735-13">(</span><span class="n">ud</span><span class="p">,</span><span class="o">&amp;</span><span class="n">ibuf</span><span class="p" data-group-id="1528751735-13">)</span><span class="p" data-group-id="1528751735-12">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1528751735-11">)</span><span class="w"> </span><span class="p" data-group-id="1528751735-14">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-15">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="1528751735-15">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1528751735-16">(</span><span class="n">res</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="no">NORMAL_READ_FAILURE</span><span class="p" data-group-id="1528751735-16">)</span><span class="w"> </span><span class="p" data-group-id="1528751735-17">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-18">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="1528751735-18">)</span><span class="w">                 </span><span class="nf">driver_select</span><span class="p" data-group-id="1528751735-19">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1528751735-20">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="1528751735-20">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1528751735-19">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-21">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1528751735-21">)</span><span class="w">             </span><span class="p" data-group-id="1528751735-17">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="1528751735-22">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-23">(</span><span class="mi">10</span><span class="p" data-group-id="1528751735-23">)</span><span class="w">                 </span><span class="nf">driver_failure_eof</span><span class="p" data-group-id="1528751735-24">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="1528751735-24">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-25">(</span><span class="mi">11</span><span class="p" data-group-id="1528751735-25">)</span><span class="w">             </span><span class="p" data-group-id="1528751735-22">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-26">(</span><span class="mi">12</span><span class="p" data-group-id="1528751735-26">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-27">(</span><span class="mi">13</span><span class="p" data-group-id="1528751735-27">)</span><span class="w">         </span><span class="p" data-group-id="1528751735-14">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-28">(</span><span class="mi">14</span><span class="p" data-group-id="1528751735-28">)</span><span class="w">         </span><span class="cm">/* Got a package */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-29">(</span><span class="mi">15</span><span class="p" data-group-id="1528751735-29">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1528751735-30">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="1528751735-30">)</span><span class="w"> </span><span class="p" data-group-id="1528751735-31">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-32">(</span><span class="mi">16</span><span class="p" data-group-id="1528751735-32">)</span><span class="w">             </span><span class="n">ibuf</span><span class="p" data-group-id="1528751735-33">[</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="1528751735-33">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="err">&#39;</span><span class="no">R</span><span class="err">&#39;</span><span class="p">;</span><span class="w"> </span><span class="cm">/* There is always room for a single byte
│ │ │  (17)                                opcode before the actual buffer
│ │ │  (18)                                (where the packet header was) */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-34">(</span><span class="mi">19</span><span class="p" data-group-id="5047538976-34">)</span><span class="w">             </span><span class="nf">driver_output</span><span class="p" data-group-id="5047538976-35">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="n">ibuf</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5047538976-35">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-36">(</span><span class="mi">20</span><span class="p" data-group-id="5047538976-36">)</span><span class="w">             </span><span class="nf">driver_select</span><span class="p" data-group-id="5047538976-37">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5047538976-38">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="5047538976-38">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="5047538976-37">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-39">(</span><span class="mi">21</span><span class="p" data-group-id="5047538976-39">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-40">(</span><span class="mi">22</span><span class="p" data-group-id="5047538976-40">)</span><span class="w">         </span><span class="p" data-group-id="5047538976-31">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="5047538976-41">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-42">(</span><span class="mi">23</span><span class="p" data-group-id="5047538976-42">)</span><span class="w">             </span><span class="n">ibuf</span><span class="p" data-group-id="5047538976-43">[</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="5047538976-43">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">DIST_MAGIC_RECV_TAG</span><span class="p">;</span><span class="w"> </span><span class="cm">/* XXX */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-44">(</span><span class="mi">24</span><span class="p" data-group-id="5047538976-44">)</span><span class="w">             </span><span class="nf">driver_output</span><span class="p" data-group-id="5047538976-45">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="n">ibuf</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5047538976-45">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-46">(</span><span class="mi">25</span><span class="p" data-group-id="5047538976-46">)</span><span class="w">             </span><span class="nf">driver_select</span><span class="p" data-group-id="5047538976-47">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5047538976-48">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="5047538976-48">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="5047538976-47">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-49">(</span><span class="mi">26</span><span class="p" data-group-id="5047538976-49">)</span><span class="w">         </span><span class="p" data-group-id="5047538976-41">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-50">(</span><span class="mi">27</span><span class="p" data-group-id="5047538976-50">)</span><span class="w">     </span><span class="p" data-group-id="5047538976-9">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5047538976-51">(</span><span class="mi">28</span><span class="p" data-group-id="5047538976-51">)</span><span class="w"> </span><span class="p" data-group-id="5047538976-4">}</span></code></pre><p>The routine tries to read data until a packet is read or the
│ │ │ +</span><span class="p" data-group-id="1528751735-34">(</span><span class="mi">19</span><span class="p" data-group-id="1528751735-34">)</span><span class="w">             </span><span class="nf">driver_output</span><span class="p" data-group-id="1528751735-35">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="n">ibuf</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1528751735-35">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-36">(</span><span class="mi">20</span><span class="p" data-group-id="1528751735-36">)</span><span class="w">             </span><span class="nf">driver_select</span><span class="p" data-group-id="1528751735-37">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1528751735-38">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="1528751735-38">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="1528751735-37">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-39">(</span><span class="mi">21</span><span class="p" data-group-id="1528751735-39">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-40">(</span><span class="mi">22</span><span class="p" data-group-id="1528751735-40">)</span><span class="w">         </span><span class="p" data-group-id="1528751735-31">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="1528751735-41">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-42">(</span><span class="mi">23</span><span class="p" data-group-id="1528751735-42">)</span><span class="w">             </span><span class="n">ibuf</span><span class="p" data-group-id="1528751735-43">[</span><span class="o">-</span><span class="mi">1</span><span class="p" data-group-id="1528751735-43">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">DIST_MAGIC_RECV_TAG</span><span class="p">;</span><span class="w"> </span><span class="cm">/* XXX */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-44">(</span><span class="mi">24</span><span class="p" data-group-id="1528751735-44">)</span><span class="w">             </span><span class="nf">driver_output</span><span class="p" data-group-id="1528751735-45">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="n">ibuf</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1528751735-45">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-46">(</span><span class="mi">25</span><span class="p" data-group-id="1528751735-46">)</span><span class="w">             </span><span class="nf">driver_select</span><span class="p" data-group-id="1528751735-47">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1528751735-48">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="1528751735-48">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1528751735-47">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-49">(</span><span class="mi">26</span><span class="p" data-group-id="1528751735-49">)</span><span class="w">         </span><span class="p" data-group-id="1528751735-41">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-50">(</span><span class="mi">27</span><span class="p" data-group-id="1528751735-50">)</span><span class="w">     </span><span class="p" data-group-id="1528751735-9">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1528751735-51">(</span><span class="mi">28</span><span class="p" data-group-id="1528751735-51">)</span><span class="w"> </span><span class="p" data-group-id="1528751735-4">}</span></code></pre><p>The routine tries to read data until a packet is read or the
│ │ │  <code class="inline">buffered_read_package</code> routine returns a <code class="inline">NORMAL_READ_FAILURE</code> (an internally
│ │ │  defined constant for the module, which means that the read operation resulted in
│ │ │  an <code class="inline">EWOULDBLOCK</code>). If the port is in <code class="inline">command</code> mode, the reading stops when one
│ │ │  package is read. If the port is in <code class="inline">data</code> mode, the reading continues until the
│ │ │  socket buffer is empty (read failure). If no more data can be read and more is
│ │ │  wanted (which is always the case when the socket is in <code class="inline">data</code> mode),
│ │ │  <code class="inline">driver_select</code> is called to make the <code class="inline">uds_input</code> callback be called when more
│ │ │  data is available for reading.</p><p>When the port is in <code class="inline">data</code> mode, all data is sent to Erlang in a format that
│ │ │  suits the distribution. In fact, the raw data will never reach any Erlang
│ │ │  process, but will be translated/interpreted by the emulator itself and then
│ │ │  delivered in the correct format to the correct processes. In the current
│ │ │  emulator version, received data is to be tagged with a single byte of 100. That
│ │ │  is what the macro <code class="inline">DIST_MAGIC_RECV_TAG</code> is defined to. The tagging of data in
│ │ │  the distribution can be changed in the future.</p><p>The <code class="inline">uds_input</code> routine handles other input events (like non-blocking <code class="inline">accept</code>),
│ │ │ -but most importantly handle data arriving at the socket by calling <code class="inline">do_recv</code>:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="5932564108-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="5932564108-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_input</span><span class="p" data-group-id="5932564108-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="no">ErlDrvEvent</span><span class="w"> </span><span class="n">event</span><span class="p" data-group-id="5932564108-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="5932564108-3">)</span><span class="w"> </span><span class="p" data-group-id="5932564108-4">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="5932564108-5">)</span><span class="w">     </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5932564108-6">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="5932564108-6">)</span><span class="w"> </span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="p" data-group-id="5932564108-7">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="5932564108-7">)</span><span class="w">     </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5932564108-8">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeListener</span><span class="p" data-group-id="5932564108-8">)</span><span class="w"> </span><span class="p" data-group-id="5932564108-9">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-10">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="5932564108-10">)</span><span class="w">         </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ad</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">partner</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-11">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="5932564108-11">)</span><span class="w">         </span><span class="k">struct</span><span class="w"> </span><span class="n">sockaddr_un</span><span class="w"> </span><span class="n">peer</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-12">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="5932564108-12">)</span><span class="w">         </span><span class="kt">int</span><span class="w"> </span><span class="n">pl</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">sizeof</span><span class="p" data-group-id="5932564108-13">(</span><span class="k">struct</span><span class="w"> </span><span class="n">sockaddr_un</span><span class="p" data-group-id="5932564108-13">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-14">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="5932564108-14">)</span><span class="w">         </span><span class="kt">int</span><span class="w"> </span><span class="n">fd</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="p" data-group-id="5932564108-15">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="5932564108-15">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5932564108-16">(</span><span class="p" data-group-id="5932564108-17">(</span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">accept</span><span class="p" data-group-id="5932564108-18">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5932564108-19">(</span><span class="k">struct</span><span class="w"> </span><span class="n">sockaddr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="5932564108-19">)</span><span class="w"> </span><span class="o">&amp;</span><span class="n">peer</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">pl</span><span class="p" data-group-id="5932564108-18">)</span><span class="p" data-group-id="5932564108-17">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5932564108-16">)</span><span class="w"> </span><span class="p" data-group-id="5932564108-20">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-21">(</span><span class="mi">10</span><span class="p" data-group-id="5932564108-21">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="5932564108-22">(</span><span class="n">errno</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="no">EWOULDBLOCK</span><span class="p" data-group-id="5932564108-22">)</span><span class="w"> </span><span class="p" data-group-id="5932564108-23">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-24">(</span><span class="mi">11</span><span class="p" data-group-id="5932564108-24">)</span><span class="w">                 </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="5932564108-25">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="n">errno</span><span class="p" data-group-id="5932564108-25">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-26">(</span><span class="mi">12</span><span class="p" data-group-id="5932564108-26">)</span><span class="w">                 </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-27">(</span><span class="mi">13</span><span class="p" data-group-id="5932564108-27">)</span><span class="w">             </span><span class="p" data-group-id="5932564108-23">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-28">(</span><span class="mi">14</span><span class="p" data-group-id="5932564108-28">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-29">(</span><span class="mi">15</span><span class="p" data-group-id="5932564108-29">)</span><span class="w">         </span><span class="p" data-group-id="5932564108-20">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-30">(</span><span class="mi">16</span><span class="p" data-group-id="5932564108-30">)</span><span class="w">         </span><span class="no">SET_NONBLOCKING</span><span class="p" data-group-id="5932564108-31">(</span><span class="n">fd</span><span class="p" data-group-id="5932564108-31">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-32">(</span><span class="mi">17</span><span class="p" data-group-id="5932564108-32">)</span><span class="w">         </span><span class="n">ad</span><span class="o">-&gt;</span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">fd</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-33">(</span><span class="mi">18</span><span class="p" data-group-id="5932564108-33">)</span><span class="w">         </span><span class="n">ad</span><span class="o">-&gt;</span><span class="n">partner</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-34">(</span><span class="mi">19</span><span class="p" data-group-id="5932564108-34">)</span><span class="w">         </span><span class="n">ad</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-35">(</span><span class="mi">20</span><span class="p" data-group-id="5932564108-35">)</span><span class="w">         </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">partner</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-36">(</span><span class="mi">21</span><span class="p" data-group-id="5932564108-36">)</span><span class="w">         </span><span class="nf">driver_select</span><span class="p" data-group-id="5932564108-37">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="5932564108-38">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="5932564108-38">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="5932564108-37">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-39">(</span><span class="mi">22</span><span class="p" data-group-id="5932564108-39">)</span><span class="w">         </span><span class="nf">driver_output</span><span class="p" data-group-id="5932564108-40">(</span><span class="n">ad</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Aok&quot;</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="5932564108-40">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-41">(</span><span class="mi">23</span><span class="p" data-group-id="5932564108-41">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-42">(</span><span class="mi">24</span><span class="p" data-group-id="5932564108-42">)</span><span class="w">     </span><span class="p" data-group-id="5932564108-9">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-43">(</span><span class="mi">25</span><span class="p" data-group-id="5932564108-43">)</span><span class="w">     </span><span class="nf">do_recv</span><span class="p" data-group-id="5932564108-44">(</span><span class="n">ud</span><span class="p" data-group-id="5932564108-44">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5932564108-45">(</span><span class="mi">26</span><span class="p" data-group-id="5932564108-45">)</span><span class="w"> </span><span class="p" data-group-id="5932564108-4">}</span></code></pre><p>The important line is the last line in the function: the <code class="inline">do_read</code> routine is
│ │ │ +but most importantly handle data arriving at the socket by calling <code class="inline">do_recv</code>:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="0079923860-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0079923860-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_input</span><span class="p" data-group-id="0079923860-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="no">ErlDrvEvent</span><span class="w"> </span><span class="n">event</span><span class="p" data-group-id="0079923860-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0079923860-3">)</span><span class="w"> </span><span class="p" data-group-id="0079923860-4">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="0079923860-5">)</span><span class="w">     </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0079923860-6">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="0079923860-6">)</span><span class="w"> </span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="p" data-group-id="0079923860-7">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="0079923860-7">)</span><span class="w">     </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0079923860-8">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeListener</span><span class="p" data-group-id="0079923860-8">)</span><span class="w"> </span><span class="p" data-group-id="0079923860-9">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-10">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="0079923860-10">)</span><span class="w">         </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ad</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">partner</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-11">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="0079923860-11">)</span><span class="w">         </span><span class="k">struct</span><span class="w"> </span><span class="n">sockaddr_un</span><span class="w"> </span><span class="n">peer</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-12">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="0079923860-12">)</span><span class="w">         </span><span class="kt">int</span><span class="w"> </span><span class="n">pl</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">sizeof</span><span class="p" data-group-id="0079923860-13">(</span><span class="k">struct</span><span class="w"> </span><span class="n">sockaddr_un</span><span class="p" data-group-id="0079923860-13">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-14">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="0079923860-14">)</span><span class="w">         </span><span class="kt">int</span><span class="w"> </span><span class="n">fd</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="p" data-group-id="0079923860-15">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="0079923860-15">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0079923860-16">(</span><span class="p" data-group-id="0079923860-17">(</span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">accept</span><span class="p" data-group-id="0079923860-18">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0079923860-19">(</span><span class="k">struct</span><span class="w"> </span><span class="n">sockaddr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="0079923860-19">)</span><span class="w"> </span><span class="o">&amp;</span><span class="n">peer</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">pl</span><span class="p" data-group-id="0079923860-18">)</span><span class="p" data-group-id="0079923860-17">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0079923860-16">)</span><span class="w"> </span><span class="p" data-group-id="0079923860-20">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-21">(</span><span class="mi">10</span><span class="p" data-group-id="0079923860-21">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0079923860-22">(</span><span class="n">errno</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="no">EWOULDBLOCK</span><span class="p" data-group-id="0079923860-22">)</span><span class="w"> </span><span class="p" data-group-id="0079923860-23">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-24">(</span><span class="mi">11</span><span class="p" data-group-id="0079923860-24">)</span><span class="w">                 </span><span class="nf">driver_failure_posix</span><span class="p" data-group-id="0079923860-25">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="n">errno</span><span class="p" data-group-id="0079923860-25">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-26">(</span><span class="mi">12</span><span class="p" data-group-id="0079923860-26">)</span><span class="w">                 </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-27">(</span><span class="mi">13</span><span class="p" data-group-id="0079923860-27">)</span><span class="w">             </span><span class="p" data-group-id="0079923860-23">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-28">(</span><span class="mi">14</span><span class="p" data-group-id="0079923860-28">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-29">(</span><span class="mi">15</span><span class="p" data-group-id="0079923860-29">)</span><span class="w">         </span><span class="p" data-group-id="0079923860-20">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-30">(</span><span class="mi">16</span><span class="p" data-group-id="0079923860-30">)</span><span class="w">         </span><span class="no">SET_NONBLOCKING</span><span class="p" data-group-id="0079923860-31">(</span><span class="n">fd</span><span class="p" data-group-id="0079923860-31">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-32">(</span><span class="mi">17</span><span class="p" data-group-id="0079923860-32">)</span><span class="w">         </span><span class="n">ad</span><span class="o">-&gt;</span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">fd</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-33">(</span><span class="mi">18</span><span class="p" data-group-id="0079923860-33">)</span><span class="w">         </span><span class="n">ad</span><span class="o">-&gt;</span><span class="n">partner</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-34">(</span><span class="mi">19</span><span class="p" data-group-id="0079923860-34">)</span><span class="w">         </span><span class="n">ad</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-35">(</span><span class="mi">20</span><span class="p" data-group-id="0079923860-35">)</span><span class="w">         </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">partner</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-36">(</span><span class="mi">21</span><span class="p" data-group-id="0079923860-36">)</span><span class="w">         </span><span class="nf">driver_select</span><span class="p" data-group-id="0079923860-37">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="0079923860-38">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="0079923860-38">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0079923860-37">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-39">(</span><span class="mi">22</span><span class="p" data-group-id="0079923860-39">)</span><span class="w">         </span><span class="nf">driver_output</span><span class="p" data-group-id="0079923860-40">(</span><span class="n">ad</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Aok&quot;</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="0079923860-40">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-41">(</span><span class="mi">23</span><span class="p" data-group-id="0079923860-41">)</span><span class="w">         </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-42">(</span><span class="mi">24</span><span class="p" data-group-id="0079923860-42">)</span><span class="w">     </span><span class="p" data-group-id="0079923860-9">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-43">(</span><span class="mi">25</span><span class="p" data-group-id="0079923860-43">)</span><span class="w">     </span><span class="nf">do_recv</span><span class="p" data-group-id="0079923860-44">(</span><span class="n">ud</span><span class="p" data-group-id="0079923860-44">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0079923860-45">(</span><span class="mi">26</span><span class="p" data-group-id="0079923860-45">)</span><span class="w"> </span><span class="p" data-group-id="0079923860-4">}</span></code></pre><p>The important line is the last line in the function: the <code class="inline">do_read</code> routine is
│ │ │  called to handle new input. The remaining function handles input on a listen
│ │ │  socket, which means that it is to be possible to do an accept on the socket,
│ │ │  which is also recognized as a read event.</p><p>The output mechanisms are similar to the input. The <code class="inline">do_send</code> routine is as
│ │ │ -follows:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="3964498519-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3964498519-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">do_send</span><span class="p" data-group-id="3964498519-2">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="3964498519-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3964498519-3">)</span><span class="w"> </span><span class="p" data-group-id="3964498519-4">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3964498519-5">)</span><span class="w">     </span><span class="kt">char</span><span class="w"> </span><span class="n">header</span><span class="p" data-group-id="3964498519-6">[</span><span class="mi">4</span><span class="p" data-group-id="3964498519-6">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-7">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="3964498519-7">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">written</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-8">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="3964498519-8">)</span><span class="w">     </span><span class="no">SysIOVec</span><span class="w"> </span><span class="n">iov</span><span class="p" data-group-id="3964498519-9">[</span><span class="mi">2</span><span class="p" data-group-id="3964498519-9">]</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-10">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="3964498519-10">)</span><span class="w">     </span><span class="no">ErlIOVec</span><span class="w"> </span><span class="n">eio</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-11">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="3964498519-11">)</span><span class="w">     </span><span class="no">ErlDrvBinary</span><span class="w"> </span><span class="o">*</span><span class="n">binv</span><span class="p" data-group-id="3964498519-12">[</span><span class="p" data-group-id="3964498519-12">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3964498519-13">{</span><span class="no">NULL</span><span class="p">,</span><span class="no">NULL</span><span class="p" data-group-id="3964498519-13">}</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="p" data-group-id="3964498519-14">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="3964498519-14">)</span><span class="w">     </span><span class="nf">put_packet_length</span><span class="p" data-group-id="3964498519-15">(</span><span class="n">header</span><span class="p">,</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="3964498519-15">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-16">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="3964498519-16">)</span><span class="w">     </span><span class="n">iov</span><span class="p" data-group-id="3964498519-17">[</span><span class="mi">0</span><span class="p" data-group-id="3964498519-17">]</span><span class="p">.</span><span class="n">iov_base</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3964498519-18">(</span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="3964498519-18">)</span><span class="w"> </span><span class="n">header</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-19">(</span><span class="mi">10</span><span class="p" data-group-id="3964498519-19">)</span><span class="w">     </span><span class="n">iov</span><span class="p" data-group-id="3964498519-20">[</span><span class="mi">0</span><span class="p" data-group-id="3964498519-20">]</span><span class="p">.</span><span class="n">iov_len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-21">(</span><span class="mi">11</span><span class="p" data-group-id="3964498519-21">)</span><span class="w">     </span><span class="n">iov</span><span class="p" data-group-id="3964498519-22">[</span><span class="mi">1</span><span class="p" data-group-id="3964498519-22">]</span><span class="p">.</span><span class="n">iov_base</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-23">(</span><span class="mi">12</span><span class="p" data-group-id="3964498519-23">)</span><span class="w">     </span><span class="n">iov</span><span class="p" data-group-id="3964498519-24">[</span><span class="mi">1</span><span class="p" data-group-id="3964498519-24">]</span><span class="p">.</span><span class="n">iov_len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">bufflen</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-25">(</span><span class="mi">13</span><span class="p" data-group-id="3964498519-25">)</span><span class="w">     </span><span class="n">eio</span><span class="p">.</span><span class="n">iov</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">iov</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-26">(</span><span class="mi">14</span><span class="p" data-group-id="3964498519-26">)</span><span class="w">     </span><span class="n">eio</span><span class="p">.</span><span class="n">binv</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">binv</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-27">(</span><span class="mi">15</span><span class="p" data-group-id="3964498519-27">)</span><span class="w">     </span><span class="n">eio</span><span class="p">.</span><span class="n">vsize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-28">(</span><span class="mi">16</span><span class="p" data-group-id="3964498519-28">)</span><span class="w">     </span><span class="n">eio</span><span class="p">.</span><span class="n">size</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">bufflen</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-29">(</span><span class="mi">17</span><span class="p" data-group-id="3964498519-29">)</span><span class="w">     </span><span class="n">written</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-30">(</span><span class="mi">18</span><span class="p" data-group-id="3964498519-30">)</span><span class="w">     </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3964498519-31">(</span><span class="nf">driver_sizeq</span><span class="p" data-group-id="3964498519-32">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="3964498519-32">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3964498519-31">)</span><span class="w"> </span><span class="p" data-group-id="3964498519-33">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-34">(</span><span class="mi">19</span><span class="p" data-group-id="3964498519-34">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3964498519-35">(</span><span class="p" data-group-id="3964498519-36">(</span><span class="n">written</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">writev</span><span class="p" data-group-id="3964498519-37">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="n">iov</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3964498519-37">)</span><span class="p" data-group-id="3964498519-36">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">eio</span><span class="p">.</span><span class="n">size</span><span class="p" data-group-id="3964498519-35">)</span><span class="w"> </span><span class="p" data-group-id="3964498519-38">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-39">(</span><span class="mi">20</span><span class="p" data-group-id="3964498519-39">)</span><span class="w">             </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">written</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-40">(</span><span class="mi">21</span><span class="p" data-group-id="3964498519-40">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3964498519-41">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="3964498519-41">)</span><span class="w"> </span><span class="p" data-group-id="3964498519-42">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-43">(</span><span class="mi">22</span><span class="p" data-group-id="3964498519-43">)</span><span class="w">                 </span><span class="nf">driver_output</span><span class="p" data-group-id="3964498519-44">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Sok&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3964498519-44">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-45">(</span><span class="mi">23</span><span class="p" data-group-id="3964498519-45">)</span><span class="w">             </span><span class="p" data-group-id="3964498519-42">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-46">(</span><span class="mi">24</span><span class="p" data-group-id="3964498519-46">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-47">(</span><span class="mi">25</span><span class="p" data-group-id="3964498519-47">)</span><span class="w">         </span><span class="p" data-group-id="3964498519-38">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3964498519-48">(</span><span class="n">written</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3964498519-48">)</span><span class="w"> </span><span class="p" data-group-id="3964498519-49">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-50">(</span><span class="mi">26</span><span class="p" data-group-id="3964498519-50">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3964498519-51">(</span><span class="n">errno</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="no">EWOULDBLOCK</span><span class="p" data-group-id="3964498519-51">)</span><span class="w"> </span><span class="p" data-group-id="3964498519-52">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-53">(</span><span class="mi">27</span><span class="p" data-group-id="3964498519-53">)</span><span class="w">                 </span><span class="nf">driver_failure_eof</span><span class="p" data-group-id="3964498519-54">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="3964498519-54">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-55">(</span><span class="mi">28</span><span class="p" data-group-id="3964498519-55">)</span><span class="w">                 </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-56">(</span><span class="mi">29</span><span class="p" data-group-id="3964498519-56">)</span><span class="w">             </span><span class="p" data-group-id="3964498519-52">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="3964498519-57">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-58">(</span><span class="mi">30</span><span class="p" data-group-id="3964498519-58">)</span><span class="w">                 </span><span class="n">written</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-59">(</span><span class="mi">31</span><span class="p" data-group-id="3964498519-59">)</span><span class="w">             </span><span class="p" data-group-id="3964498519-57">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-60">(</span><span class="mi">32</span><span class="p" data-group-id="3964498519-60">)</span><span class="w">         </span><span class="p" data-group-id="3964498519-49">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="3964498519-61">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-62">(</span><span class="mi">33</span><span class="p" data-group-id="3964498519-62">)</span><span class="w">             </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">written</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-63">(</span><span class="mi">34</span><span class="p" data-group-id="3964498519-63">)</span><span class="w">         </span><span class="p" data-group-id="3964498519-61">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-64">(</span><span class="mi">35</span><span class="p" data-group-id="3964498519-64">)</span><span class="w">         </span><span class="cm">/* Enqueue remaining */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-65">(</span><span class="mi">36</span><span class="p" data-group-id="3964498519-65">)</span><span class="w">     </span><span class="p" data-group-id="3964498519-33">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-66">(</span><span class="mi">37</span><span class="p" data-group-id="3964498519-66">)</span><span class="w">     </span><span class="nf">driver_enqv</span><span class="p" data-group-id="3964498519-67">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">eio</span><span class="p">,</span><span class="w"> </span><span class="n">written</span><span class="p" data-group-id="3964498519-67">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-68">(</span><span class="mi">38</span><span class="p" data-group-id="3964498519-68">)</span><span class="w">     </span><span class="nf">send_out_queue</span><span class="p" data-group-id="3964498519-69">(</span><span class="n">ud</span><span class="p" data-group-id="3964498519-69">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3964498519-70">(</span><span class="mi">39</span><span class="p" data-group-id="3964498519-70">)</span><span class="w"> </span><span class="p" data-group-id="3964498519-4">}</span></code></pre><p>This driver uses the <code class="inline">writev</code> system call to send data onto the socket. A
│ │ │ +follows:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="0342837389-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="0342837389-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">do_send</span><span class="p" data-group-id="0342837389-2">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buff</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="0342837389-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0342837389-3">)</span><span class="w"> </span><span class="p" data-group-id="0342837389-4">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="0342837389-5">)</span><span class="w">     </span><span class="kt">char</span><span class="w"> </span><span class="n">header</span><span class="p" data-group-id="0342837389-6">[</span><span class="mi">4</span><span class="p" data-group-id="0342837389-6">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-7">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="0342837389-7">)</span><span class="w">     </span><span class="kt">int</span><span class="w"> </span><span class="n">written</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-8">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="0342837389-8">)</span><span class="w">     </span><span class="no">SysIOVec</span><span class="w"> </span><span class="n">iov</span><span class="p" data-group-id="0342837389-9">[</span><span class="mi">2</span><span class="p" data-group-id="0342837389-9">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-10">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="0342837389-10">)</span><span class="w">     </span><span class="no">ErlIOVec</span><span class="w"> </span><span class="n">eio</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-11">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="0342837389-11">)</span><span class="w">     </span><span class="no">ErlDrvBinary</span><span class="w"> </span><span class="o">*</span><span class="n">binv</span><span class="p" data-group-id="0342837389-12">[</span><span class="p" data-group-id="0342837389-12">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0342837389-13">{</span><span class="no">NULL</span><span class="p">,</span><span class="no">NULL</span><span class="p" data-group-id="0342837389-13">}</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="p" data-group-id="0342837389-14">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="0342837389-14">)</span><span class="w">     </span><span class="nf">put_packet_length</span><span class="p" data-group-id="0342837389-15">(</span><span class="n">header</span><span class="p">,</span><span class="w"> </span><span class="n">bufflen</span><span class="p" data-group-id="0342837389-15">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-16">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="0342837389-16">)</span><span class="w">     </span><span class="n">iov</span><span class="p" data-group-id="0342837389-17">[</span><span class="mi">0</span><span class="p" data-group-id="0342837389-17">]</span><span class="p">.</span><span class="n">iov_base</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0342837389-18">(</span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="0342837389-18">)</span><span class="w"> </span><span class="n">header</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-19">(</span><span class="mi">10</span><span class="p" data-group-id="0342837389-19">)</span><span class="w">     </span><span class="n">iov</span><span class="p" data-group-id="0342837389-20">[</span><span class="mi">0</span><span class="p" data-group-id="0342837389-20">]</span><span class="p">.</span><span class="n">iov_len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-21">(</span><span class="mi">11</span><span class="p" data-group-id="0342837389-21">)</span><span class="w">     </span><span class="n">iov</span><span class="p" data-group-id="0342837389-22">[</span><span class="mi">1</span><span class="p" data-group-id="0342837389-22">]</span><span class="p">.</span><span class="n">iov_base</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">buff</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-23">(</span><span class="mi">12</span><span class="p" data-group-id="0342837389-23">)</span><span class="w">     </span><span class="n">iov</span><span class="p" data-group-id="0342837389-24">[</span><span class="mi">1</span><span class="p" data-group-id="0342837389-24">]</span><span class="p">.</span><span class="n">iov_len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">bufflen</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-25">(</span><span class="mi">13</span><span class="p" data-group-id="0342837389-25">)</span><span class="w">     </span><span class="n">eio</span><span class="p">.</span><span class="n">iov</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">iov</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-26">(</span><span class="mi">14</span><span class="p" data-group-id="0342837389-26">)</span><span class="w">     </span><span class="n">eio</span><span class="p">.</span><span class="n">binv</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">binv</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-27">(</span><span class="mi">15</span><span class="p" data-group-id="0342837389-27">)</span><span class="w">     </span><span class="n">eio</span><span class="p">.</span><span class="n">vsize</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-28">(</span><span class="mi">16</span><span class="p" data-group-id="0342837389-28">)</span><span class="w">     </span><span class="n">eio</span><span class="p">.</span><span class="n">size</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">bufflen</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">4</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-29">(</span><span class="mi">17</span><span class="p" data-group-id="0342837389-29">)</span><span class="w">     </span><span class="n">written</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-30">(</span><span class="mi">18</span><span class="p" data-group-id="0342837389-30">)</span><span class="w">     </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0342837389-31">(</span><span class="nf">driver_sizeq</span><span class="p" data-group-id="0342837389-32">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="0342837389-32">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0342837389-31">)</span><span class="w"> </span><span class="p" data-group-id="0342837389-33">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-34">(</span><span class="mi">19</span><span class="p" data-group-id="0342837389-34">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0342837389-35">(</span><span class="p" data-group-id="0342837389-36">(</span><span class="n">written</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">writev</span><span class="p" data-group-id="0342837389-37">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="n">iov</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="0342837389-37">)</span><span class="p" data-group-id="0342837389-36">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">eio</span><span class="p">.</span><span class="n">size</span><span class="p" data-group-id="0342837389-35">)</span><span class="w"> </span><span class="p" data-group-id="0342837389-38">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-39">(</span><span class="mi">20</span><span class="p" data-group-id="0342837389-39">)</span><span class="w">             </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">written</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-40">(</span><span class="mi">21</span><span class="p" data-group-id="0342837389-40">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0342837389-41">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="0342837389-41">)</span><span class="w"> </span><span class="p" data-group-id="0342837389-42">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-43">(</span><span class="mi">22</span><span class="p" data-group-id="0342837389-43">)</span><span class="w">                 </span><span class="nf">driver_output</span><span class="p" data-group-id="0342837389-44">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Sok&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="0342837389-44">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-45">(</span><span class="mi">23</span><span class="p" data-group-id="0342837389-45">)</span><span class="w">             </span><span class="p" data-group-id="0342837389-42">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-46">(</span><span class="mi">24</span><span class="p" data-group-id="0342837389-46">)</span><span class="w">             </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-47">(</span><span class="mi">25</span><span class="p" data-group-id="0342837389-47">)</span><span class="w">         </span><span class="p" data-group-id="0342837389-38">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0342837389-48">(</span><span class="n">written</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="0342837389-48">)</span><span class="w"> </span><span class="p" data-group-id="0342837389-49">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-50">(</span><span class="mi">26</span><span class="p" data-group-id="0342837389-50">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="0342837389-51">(</span><span class="n">errno</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="no">EWOULDBLOCK</span><span class="p" data-group-id="0342837389-51">)</span><span class="w"> </span><span class="p" data-group-id="0342837389-52">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-53">(</span><span class="mi">27</span><span class="p" data-group-id="0342837389-53">)</span><span class="w">                 </span><span class="nf">driver_failure_eof</span><span class="p" data-group-id="0342837389-54">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="0342837389-54">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-55">(</span><span class="mi">28</span><span class="p" data-group-id="0342837389-55">)</span><span class="w">                 </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-56">(</span><span class="mi">29</span><span class="p" data-group-id="0342837389-56">)</span><span class="w">             </span><span class="p" data-group-id="0342837389-52">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="0342837389-57">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-58">(</span><span class="mi">30</span><span class="p" data-group-id="0342837389-58">)</span><span class="w">                 </span><span class="n">written</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-59">(</span><span class="mi">31</span><span class="p" data-group-id="0342837389-59">)</span><span class="w">             </span><span class="p" data-group-id="0342837389-57">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-60">(</span><span class="mi">32</span><span class="p" data-group-id="0342837389-60">)</span><span class="w">         </span><span class="p" data-group-id="0342837389-49">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="0342837389-61">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-62">(</span><span class="mi">33</span><span class="p" data-group-id="0342837389-62">)</span><span class="w">             </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">written</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-63">(</span><span class="mi">34</span><span class="p" data-group-id="0342837389-63">)</span><span class="w">         </span><span class="p" data-group-id="0342837389-61">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-64">(</span><span class="mi">35</span><span class="p" data-group-id="0342837389-64">)</span><span class="w">         </span><span class="cm">/* Enqueue remaining */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-65">(</span><span class="mi">36</span><span class="p" data-group-id="0342837389-65">)</span><span class="w">     </span><span class="p" data-group-id="0342837389-33">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-66">(</span><span class="mi">37</span><span class="p" data-group-id="0342837389-66">)</span><span class="w">     </span><span class="nf">driver_enqv</span><span class="p" data-group-id="0342837389-67">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">eio</span><span class="p">,</span><span class="w"> </span><span class="n">written</span><span class="p" data-group-id="0342837389-67">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-68">(</span><span class="mi">38</span><span class="p" data-group-id="0342837389-68">)</span><span class="w">     </span><span class="nf">send_out_queue</span><span class="p" data-group-id="0342837389-69">(</span><span class="n">ud</span><span class="p" data-group-id="0342837389-69">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0342837389-70">(</span><span class="mi">39</span><span class="p" data-group-id="0342837389-70">)</span><span class="w"> </span><span class="p" data-group-id="0342837389-4">}</span></code></pre><p>This driver uses the <code class="inline">writev</code> system call to send data onto the socket. A
│ │ │  combination of <code class="inline">writev</code> and the driver output queues is very convenient. An
│ │ │  <code class="inline">ErlIOVec</code> structure contains a <code class="inline">SysIOVec</code> (which is equivalent to the
│ │ │  <code class="inline">struct iovec</code> structure defined in <code class="inline">uio.h</code>. The <code class="inline">ErlIOVec</code> also contains an
│ │ │  array of <code class="inline">ErlDrvBinary</code> pointers, of the same length as the number of buffers in
│ │ │  the I/O vector itself. One can use this to allocate the binaries for the queue
│ │ │  &quot;manually&quot; in the driver, but here the binary array is filled with <code class="inline">NULL</code> values
│ │ │  (line 7). The runtime system then allocates its own buffers when <code class="inline">driver_enqv</code>
│ │ │ @@ -965,60 +965,60 @@
│ │ │  opcode has been removed and the buffer length decreased by the output routine).
│ │ │  If the queue is empty, we write the data directly to the socket (or at least try
│ │ │  to). If any data is left, it is stored in the queue and then we try to send the
│ │ │  queue (line 38). An acknowledgement is sent when the message is delivered
│ │ │  completely (line 22). The <code class="inline">send_out_queue</code> sends acknowledgements if the sending
│ │ │  is completed there. If the port is in <code class="inline">command</code> mode, the Erlang code serializes
│ │ │  the send operations so that only one packet can be waiting for delivery at a
│ │ │ -time. Therefore the acknowledgement can be sent whenever the queue is empty.</p><p>The <code class="inline">send_out_queue</code> routine is as follows:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="1545996033-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1545996033-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">send_out_queue</span><span class="p" data-group-id="1545996033-2">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="p" data-group-id="1545996033-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1545996033-3">)</span><span class="w"> </span><span class="p" data-group-id="1545996033-4">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1545996033-5">)</span><span class="w">     </span><span class="nf">for</span><span class="p" data-group-id="1545996033-6">(</span><span class="p">;</span><span class="p">;</span><span class="p" data-group-id="1545996033-6">)</span><span class="w"> </span><span class="p" data-group-id="1545996033-7">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-8">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1545996033-8">)</span><span class="w">         </span><span class="kt">int</span><span class="w"> </span><span class="n">vlen</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-9">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="1545996033-9">)</span><span class="w">         </span><span class="no">SysIOVec</span><span class="w"> </span><span class="o">*</span><span class="n">tmp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">driver_peekq</span><span class="p" data-group-id="1545996033-10">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">vlen</span><span class="p" data-group-id="1545996033-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-11">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="1545996033-11">)</span><span class="w">         </span><span class="kt">int</span><span class="w"> </span><span class="n">wrote</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-12">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="1545996033-12">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1545996033-13">(</span><span class="n">tmp</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="1545996033-13">)</span><span class="w"> </span><span class="p" data-group-id="1545996033-14">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-15">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="1545996033-15">)</span><span class="w">             </span><span class="nf">driver_select</span><span class="p" data-group-id="1545996033-16">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1545996033-17">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="1545996033-17">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_WRITE</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1545996033-16">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-18">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1545996033-18">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1545996033-19">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="1545996033-19">)</span><span class="w"> </span><span class="p" data-group-id="1545996033-20">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-21">(</span><span class="mi">10</span><span class="p" data-group-id="1545996033-21">)</span><span class="w">                 </span><span class="nf">driver_output</span><span class="p" data-group-id="1545996033-22">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Sok&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1545996033-22">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-23">(</span><span class="mi">11</span><span class="p" data-group-id="1545996033-23">)</span><span class="w">             </span><span class="p" data-group-id="1545996033-20">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-24">(</span><span class="mi">12</span><span class="p" data-group-id="1545996033-24">)</span><span class="w">             </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-25">(</span><span class="mi">13</span><span class="p" data-group-id="1545996033-25">)</span><span class="w">         </span><span class="p" data-group-id="1545996033-14">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-26">(</span><span class="mi">14</span><span class="p" data-group-id="1545996033-26">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1545996033-27">(</span><span class="n">vlen</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="no">IO_VECTOR_MAX</span><span class="p" data-group-id="1545996033-27">)</span><span class="w"> </span><span class="p" data-group-id="1545996033-28">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-29">(</span><span class="mi">15</span><span class="p" data-group-id="1545996033-29">)</span><span class="w">             </span><span class="n">vlen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">IO_VECTOR_MAX</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-30">(</span><span class="mi">16</span><span class="p" data-group-id="1545996033-30">)</span><span class="w">         </span><span class="p" data-group-id="1545996033-28">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-31">(</span><span class="mi">17</span><span class="p" data-group-id="1545996033-31">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1545996033-32">(</span><span class="p" data-group-id="1545996033-33">(</span><span class="n">wrote</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">writev</span><span class="p" data-group-id="1545996033-34">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="n">tmp</span><span class="p">,</span><span class="w"> </span><span class="n">vlen</span><span class="p" data-group-id="1545996033-34">)</span><span class="p" data-group-id="1545996033-33">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1545996033-32">)</span><span class="w"> </span><span class="p" data-group-id="1545996033-35">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-36">(</span><span class="mi">18</span><span class="p" data-group-id="1545996033-36">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1545996033-37">(</span><span class="n">errno</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="no">EWOULDBLOCK</span><span class="p" data-group-id="1545996033-37">)</span><span class="w"> </span><span class="p" data-group-id="1545996033-38">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-39">(</span><span class="mi">19</span><span class="p" data-group-id="1545996033-39">)</span><span class="w">                 </span><span class="nf">driver_select</span><span class="p" data-group-id="1545996033-40">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1545996033-41">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="1545996033-41">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-42">(</span><span class="mi">20</span><span class="p" data-group-id="1545996033-42">)</span><span class="w">                               </span><span class="no">DO_WRITE</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1545996033-40">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-43">(</span><span class="mi">21</span><span class="p" data-group-id="1545996033-43">)</span><span class="w">                 </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-44">(</span><span class="mi">22</span><span class="p" data-group-id="1545996033-44">)</span><span class="w">             </span><span class="p" data-group-id="1545996033-38">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="1545996033-45">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-46">(</span><span class="mi">23</span><span class="p" data-group-id="1545996033-46">)</span><span class="w">                 </span><span class="nf">driver_failure_eof</span><span class="p" data-group-id="1545996033-47">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="1545996033-47">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-48">(</span><span class="mi">24</span><span class="p" data-group-id="1545996033-48">)</span><span class="w">                 </span><span class="k">return</span><span class="w"> </span><span class="o">-</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-49">(</span><span class="mi">25</span><span class="p" data-group-id="1545996033-49">)</span><span class="w">             </span><span class="p" data-group-id="1545996033-45">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-50">(</span><span class="mi">26</span><span class="p" data-group-id="1545996033-50">)</span><span class="w">         </span><span class="p" data-group-id="1545996033-35">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-51">(</span><span class="mi">27</span><span class="p" data-group-id="1545996033-51">)</span><span class="w">         </span><span class="nf">driver_deq</span><span class="p" data-group-id="1545996033-52">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="n">wrote</span><span class="p" data-group-id="1545996033-52">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-53">(</span><span class="mi">28</span><span class="p" data-group-id="1545996033-53">)</span><span class="w">         </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">wrote</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-54">(</span><span class="mi">29</span><span class="p" data-group-id="1545996033-54">)</span><span class="w">     </span><span class="p" data-group-id="1545996033-7">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1545996033-55">(</span><span class="mi">30</span><span class="p" data-group-id="1545996033-55">)</span><span class="w"> </span><span class="p" data-group-id="1545996033-4">}</span></code></pre><p>We simply pick out an I/O vector from the queue (which is the whole queue as a
│ │ │ +time. Therefore the acknowledgement can be sent whenever the queue is empty.</p><p>The <code class="inline">send_out_queue</code> routine is as follows:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="4147063634-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4147063634-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">send_out_queue</span><span class="p" data-group-id="4147063634-2">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="p" data-group-id="4147063634-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="4147063634-3">)</span><span class="w"> </span><span class="p" data-group-id="4147063634-4">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4147063634-5">)</span><span class="w">     </span><span class="nf">for</span><span class="p" data-group-id="4147063634-6">(</span><span class="p">;</span><span class="p">;</span><span class="p" data-group-id="4147063634-6">)</span><span class="w"> </span><span class="p" data-group-id="4147063634-7">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-8">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="4147063634-8">)</span><span class="w">         </span><span class="kt">int</span><span class="w"> </span><span class="n">vlen</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-9">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="4147063634-9">)</span><span class="w">         </span><span class="no">SysIOVec</span><span class="w"> </span><span class="o">*</span><span class="n">tmp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">driver_peekq</span><span class="p" data-group-id="4147063634-10">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">vlen</span><span class="p" data-group-id="4147063634-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-11">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="4147063634-11">)</span><span class="w">         </span><span class="kt">int</span><span class="w"> </span><span class="n">wrote</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-12">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="4147063634-12">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4147063634-13">(</span><span class="n">tmp</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="4147063634-13">)</span><span class="w"> </span><span class="p" data-group-id="4147063634-14">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-15">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="4147063634-15">)</span><span class="w">             </span><span class="nf">driver_select</span><span class="p" data-group-id="4147063634-16">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4147063634-17">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="4147063634-17">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_WRITE</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4147063634-16">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-18">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="4147063634-18">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4147063634-19">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="4147063634-19">)</span><span class="w"> </span><span class="p" data-group-id="4147063634-20">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-21">(</span><span class="mi">10</span><span class="p" data-group-id="4147063634-21">)</span><span class="w">                 </span><span class="nf">driver_output</span><span class="p" data-group-id="4147063634-22">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Sok&quot;</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="4147063634-22">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-23">(</span><span class="mi">11</span><span class="p" data-group-id="4147063634-23">)</span><span class="w">             </span><span class="p" data-group-id="4147063634-20">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-24">(</span><span class="mi">12</span><span class="p" data-group-id="4147063634-24">)</span><span class="w">             </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-25">(</span><span class="mi">13</span><span class="p" data-group-id="4147063634-25">)</span><span class="w">         </span><span class="p" data-group-id="4147063634-14">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-26">(</span><span class="mi">14</span><span class="p" data-group-id="4147063634-26">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4147063634-27">(</span><span class="n">vlen</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="no">IO_VECTOR_MAX</span><span class="p" data-group-id="4147063634-27">)</span><span class="w"> </span><span class="p" data-group-id="4147063634-28">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-29">(</span><span class="mi">15</span><span class="p" data-group-id="4147063634-29">)</span><span class="w">             </span><span class="n">vlen</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">IO_VECTOR_MAX</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-30">(</span><span class="mi">16</span><span class="p" data-group-id="4147063634-30">)</span><span class="w">         </span><span class="p" data-group-id="4147063634-28">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-31">(</span><span class="mi">17</span><span class="p" data-group-id="4147063634-31">)</span><span class="w">         </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4147063634-32">(</span><span class="p" data-group-id="4147063634-33">(</span><span class="n">wrote</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">writev</span><span class="p" data-group-id="4147063634-34">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="n">tmp</span><span class="p">,</span><span class="w"> </span><span class="n">vlen</span><span class="p" data-group-id="4147063634-34">)</span><span class="p" data-group-id="4147063634-33">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4147063634-32">)</span><span class="w"> </span><span class="p" data-group-id="4147063634-35">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-36">(</span><span class="mi">18</span><span class="p" data-group-id="4147063634-36">)</span><span class="w">             </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="4147063634-37">(</span><span class="n">errno</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="no">EWOULDBLOCK</span><span class="p" data-group-id="4147063634-37">)</span><span class="w"> </span><span class="p" data-group-id="4147063634-38">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-39">(</span><span class="mi">19</span><span class="p" data-group-id="4147063634-39">)</span><span class="w">                 </span><span class="nf">driver_select</span><span class="p" data-group-id="4147063634-40">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="4147063634-41">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="4147063634-41">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-42">(</span><span class="mi">20</span><span class="p" data-group-id="4147063634-42">)</span><span class="w">                               </span><span class="no">DO_WRITE</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="4147063634-40">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-43">(</span><span class="mi">21</span><span class="p" data-group-id="4147063634-43">)</span><span class="w">                 </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-44">(</span><span class="mi">22</span><span class="p" data-group-id="4147063634-44">)</span><span class="w">             </span><span class="p" data-group-id="4147063634-38">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="4147063634-45">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-46">(</span><span class="mi">23</span><span class="p" data-group-id="4147063634-46">)</span><span class="w">                 </span><span class="nf">driver_failure_eof</span><span class="p" data-group-id="4147063634-47">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="4147063634-47">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-48">(</span><span class="mi">24</span><span class="p" data-group-id="4147063634-48">)</span><span class="w">                 </span><span class="k">return</span><span class="w"> </span><span class="o">-</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-49">(</span><span class="mi">25</span><span class="p" data-group-id="4147063634-49">)</span><span class="w">             </span><span class="p" data-group-id="4147063634-45">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-50">(</span><span class="mi">26</span><span class="p" data-group-id="4147063634-50">)</span><span class="w">         </span><span class="p" data-group-id="4147063634-35">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-51">(</span><span class="mi">27</span><span class="p" data-group-id="4147063634-51">)</span><span class="w">         </span><span class="nf">driver_deq</span><span class="p" data-group-id="4147063634-52">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="n">wrote</span><span class="p" data-group-id="4147063634-52">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-53">(</span><span class="mi">28</span><span class="p" data-group-id="4147063634-53">)</span><span class="w">         </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">wrote</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-54">(</span><span class="mi">29</span><span class="p" data-group-id="4147063634-54">)</span><span class="w">     </span><span class="p" data-group-id="4147063634-7">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4147063634-55">(</span><span class="mi">30</span><span class="p" data-group-id="4147063634-55">)</span><span class="w"> </span><span class="p" data-group-id="4147063634-4">}</span></code></pre><p>We simply pick out an I/O vector from the queue (which is the whole queue as a
│ │ │  <code class="inline">SysIOVec</code>). If the I/O vector is too long (<code class="inline">IO_VECTOR_MAX</code> is defined to 16),
│ │ │  the vector length is decreased (line 15), otherwise the <code class="inline">writev</code> call (line 17)
│ │ │  fails. Writing is tried and anything written is dequeued (line 27). If the write
│ │ │  fails with <code class="inline">EWOULDBLOCK</code> (notice that all sockets are in non-blocking mode),
│ │ │  <code class="inline">driver_select</code> is called to make the <code class="inline">uds_output</code> routine be called when there
│ │ │ -is space to write again.</p><p>We continue trying to write until the queue is empty or the writing blocks.</p><p>The routine above is called from the <code class="inline">uds_output</code> routine:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="1450303352-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1450303352-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_output</span><span class="p" data-group-id="1450303352-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="no">ErlDrvEvent</span><span class="w"> </span><span class="n">event</span><span class="p" data-group-id="1450303352-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1450303352-3">)</span><span class="w"> </span><span class="p" data-group-id="1450303352-4">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1450303352-5">)</span><span class="w">    </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1450303352-6">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="1450303352-6">)</span><span class="w"> </span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-7">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1450303352-7">)</span><span class="w">    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1450303352-8">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeConnector</span><span class="p" data-group-id="1450303352-8">)</span><span class="w"> </span><span class="p" data-group-id="1450303352-9">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-10">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="1450303352-10">)</span><span class="w">        </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-11">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="1450303352-11">)</span><span class="w">        </span><span class="nf">driver_select</span><span class="p" data-group-id="1450303352-12">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1450303352-13">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="1450303352-13">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_WRITE</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1450303352-12">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-14">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="1450303352-14">)</span><span class="w">        </span><span class="nf">driver_output</span><span class="p" data-group-id="1450303352-15">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Cok&quot;</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1450303352-15">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-16">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="1450303352-16">)</span><span class="w">        </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-17">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1450303352-17">)</span><span class="w">    </span><span class="p" data-group-id="1450303352-9">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-18">(</span><span class="mi">10</span><span class="p" data-group-id="1450303352-18">)</span><span class="w">    </span><span class="nf">send_out_queue</span><span class="p" data-group-id="1450303352-19">(</span><span class="n">ud</span><span class="p" data-group-id="1450303352-19">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1450303352-20">(</span><span class="mi">11</span><span class="p" data-group-id="1450303352-20">)</span><span class="w"> </span><span class="p" data-group-id="1450303352-4">}</span></code></pre><p>The routine is simple: it first handles the fact that the output select will
│ │ │ +is space to write again.</p><p>We continue trying to write until the queue is empty or the writing blocks.</p><p>The routine above is called from the <code class="inline">uds_output</code> routine:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="8300082078-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="8300082078-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">uds_output</span><span class="p" data-group-id="8300082078-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="no">ErlDrvEvent</span><span class="w"> </span><span class="n">event</span><span class="p" data-group-id="8300082078-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="8300082078-3">)</span><span class="w"> </span><span class="p" data-group-id="8300082078-4">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-5">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="8300082078-5">)</span><span class="w">    </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="8300082078-6">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="8300082078-6">)</span><span class="w"> </span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-7">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="8300082078-7">)</span><span class="w">    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8300082078-8">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">portTypeConnector</span><span class="p" data-group-id="8300082078-8">)</span><span class="w"> </span><span class="p" data-group-id="8300082078-9">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-10">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="8300082078-10">)</span><span class="w">        </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-11">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="8300082078-11">)</span><span class="w">        </span><span class="nf">driver_select</span><span class="p" data-group-id="8300082078-12">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="8300082078-13">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="8300082078-13">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_WRITE</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="8300082078-12">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-14">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="8300082078-14">)</span><span class="w">        </span><span class="nf">driver_output</span><span class="p" data-group-id="8300082078-15">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Cok&quot;</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="8300082078-15">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-16">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="8300082078-16">)</span><span class="w">        </span><span class="k">return</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-17">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="8300082078-17">)</span><span class="w">    </span><span class="p" data-group-id="8300082078-9">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-18">(</span><span class="mi">10</span><span class="p" data-group-id="8300082078-18">)</span><span class="w">    </span><span class="nf">send_out_queue</span><span class="p" data-group-id="8300082078-19">(</span><span class="n">ud</span><span class="p" data-group-id="8300082078-19">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8300082078-20">(</span><span class="mi">11</span><span class="p" data-group-id="8300082078-20">)</span><span class="w"> </span><span class="p" data-group-id="8300082078-4">}</span></code></pre><p>The routine is simple: it first handles the fact that the output select will
│ │ │  concern a socket in the business of connecting (and the connecting blocked). If
│ │ │  the socket is in a connected state, it simply sends the output queue. This
│ │ │  routine is called when it is possible to write to a socket where we have an
│ │ │  output queue, so there is no question what to do.</p><p>The driver implements a control interface, which is a synchronous interface
│ │ │  called when Erlang calls <a href="erlang.html#port_control/3"><code class="inline">erlang:port_control/3</code></a>. Only this interface can
│ │ │  control the driver when it is in <code class="inline">data</code> mode. It can be called with the
│ │ │  following opcodes:</p><ul><li><p><strong><code class="inline">'C'</code></strong> - Sets port in <code class="inline">command</code> mode.</p></li><li><p><strong><code class="inline">'I'</code></strong> - Sets port in <code class="inline">intermediate</code> mode.</p></li><li><p><strong><code class="inline">'D'</code></strong> - Sets port in <code class="inline">data</code> mode.</p></li><li><p><strong><code class="inline">'N'</code></strong> - Gets identification number for listen port. This identification
│ │ │ @@ -1034,93 +1034,93 @@
│ │ │  caller. If <code class="inline">erlang:port_command</code> is used, use <a href="erlang.html#port_command/3"><code class="inline">erlang:port_command/3</code></a> and pass
│ │ │  <code class="inline">[force]</code> as option list; otherwise the caller can be blocked indefinitely on
│ │ │  a busy port and prevent the system from taking down a connection that is not
│ │ │  functioning.</p></li><li><p><strong><code class="inline">'R'</code></strong> - Gets creation number of a listen socket, which is used to dig out
│ │ │  the number stored in the lock file to differentiate between invocations of
│ │ │  Erlang nodes with the same name.</p></li></ul><p>The control interface gets a buffer to return its value in, but is free to
│ │ │  allocate its own buffer if the provided one is too small. The <code class="inline">uds_control</code> code
│ │ │ -is as follows:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="1572975763-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="1572975763-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">uds_control</span><span class="p" data-group-id="1572975763-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">command</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="1572975763-3">)</span><span class="w">                        </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">count</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="o">*</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">res_size</span><span class="p" data-group-id="1572975763-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-4">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="1572975763-4">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-5">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-6">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1572975763-6">)</span><span class="w"> </span><span class="cm">/* Local macro to ensure large enough buffer. */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-7">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="1572975763-7">)</span><span class="w"> </span><span class="kp">#define</span><span class="w"> </span><span class="no">ENSURE</span><span class="p" data-group-id="1572975763-8">(</span><span class="no">N</span><span class="p" data-group-id="1572975763-8">)</span><span class="w">                               </span><span class="err">\</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-9">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="1572975763-9">)</span><span class="w">    </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="1572975763-10">{</span><span class="w">                                         </span><span class="err">\</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-11">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="1572975763-11">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1572975763-12">(</span><span class="n">res_size</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="no">N</span><span class="p" data-group-id="1572975763-12">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-13">{</span><span class="w">                      </span><span class="err">\</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-14">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="1572975763-14">)</span><span class="w">            </span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">ALLOC</span><span class="p" data-group-id="1572975763-15">(</span><span class="no">N</span><span class="p" data-group-id="1572975763-15">)</span><span class="p">;</span><span class="w">                     </span><span class="err">\</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-16">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="1572975763-16">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-13">}</span><span class="w">                                        </span><span class="err">\</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-17">(</span><span class="mi">10</span><span class="p" data-group-id="1572975763-17">)</span><span class="w">    </span><span class="p" data-group-id="1572975763-10">}</span><span class="w"> </span><span class="nf">while</span><span class="p" data-group-id="1572975763-18">(</span><span class="mi">0</span><span class="p" data-group-id="1572975763-18">)</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="p" data-group-id="1572975763-19">(</span><span class="mi">11</span><span class="p" data-group-id="1572975763-19">)</span><span class="w">    </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1572975763-20">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="1572975763-20">)</span><span class="w"> </span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="p" data-group-id="1572975763-21">(</span><span class="mi">12</span><span class="p" data-group-id="1572975763-21">)</span><span class="w">    </span><span class="k">switch</span><span class="w"> </span><span class="p" data-group-id="1572975763-22">(</span><span class="n">command</span><span class="p" data-group-id="1572975763-22">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-23">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-24">(</span><span class="mi">13</span><span class="p" data-group-id="1572975763-24">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;S&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-25">(</span><span class="mi">14</span><span class="p" data-group-id="1572975763-25">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-26">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-27">(</span><span class="mi">15</span><span class="p" data-group-id="1572975763-27">)</span><span class="w">            </span><span class="no">ENSURE</span><span class="p" data-group-id="1572975763-28">(</span><span class="mi">13</span><span class="p" data-group-id="1572975763-28">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-29">(</span><span class="mi">16</span><span class="p" data-group-id="1572975763-29">)</span><span class="w">            </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-30">(</span><span class="mi">17</span><span class="p" data-group-id="1572975763-30">)</span><span class="w">            </span><span class="nf">put_packet_length</span><span class="p" data-group-id="1572975763-31">(</span><span class="p" data-group-id="1572975763-32">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="1572975763-32">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">received</span><span class="p" data-group-id="1572975763-31">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-33">(</span><span class="mi">18</span><span class="p" data-group-id="1572975763-33">)</span><span class="w">            </span><span class="nf">put_packet_length</span><span class="p" data-group-id="1572975763-34">(</span><span class="p" data-group-id="1572975763-35">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="1572975763-35">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="p" data-group-id="1572975763-34">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-36">(</span><span class="mi">19</span><span class="p" data-group-id="1572975763-36">)</span><span class="w">            </span><span class="nf">put_packet_length</span><span class="p" data-group-id="1572975763-37">(</span><span class="p" data-group-id="1572975763-38">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="1572975763-38">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="nf">driver_sizeq</span><span class="p" data-group-id="1572975763-39">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="1572975763-39">)</span><span class="p" data-group-id="1572975763-37">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-40">(</span><span class="mi">20</span><span class="p" data-group-id="1572975763-40">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="mi">13</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-41">(</span><span class="mi">21</span><span class="p" data-group-id="1572975763-41">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-26">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-42">(</span><span class="mi">22</span><span class="p" data-group-id="1572975763-42">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;C&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-43">(</span><span class="mi">23</span><span class="p" data-group-id="1572975763-43">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1572975763-44">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="1572975763-44">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-45">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-46">(</span><span class="mi">24</span><span class="p" data-group-id="1572975763-46">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="1572975763-47">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="1572975763-47">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-48">(</span><span class="mi">25</span><span class="p" data-group-id="1572975763-48">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-45">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-49">(</span><span class="mi">26</span><span class="p" data-group-id="1572975763-49">)</span><span class="w">        </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-50">(</span><span class="mi">27</span><span class="p" data-group-id="1572975763-50">)</span><span class="w">        </span><span class="nf">driver_select</span><span class="p" data-group-id="1572975763-51">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1572975763-52">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="1572975763-52">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1572975763-51">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-53">(</span><span class="mi">28</span><span class="p" data-group-id="1572975763-53">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="1572975763-54">(</span><span class="mi">1</span><span class="p" data-group-id="1572975763-54">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-55">(</span><span class="mi">29</span><span class="p" data-group-id="1572975763-55">)</span><span class="w">        </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-56">(</span><span class="mi">30</span><span class="p" data-group-id="1572975763-56">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-57">(</span><span class="mi">31</span><span class="p" data-group-id="1572975763-57">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;I&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-58">(</span><span class="mi">32</span><span class="p" data-group-id="1572975763-58">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1572975763-59">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="1572975763-59">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-60">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-61">(</span><span class="mi">33</span><span class="p" data-group-id="1572975763-61">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="1572975763-62">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="1572975763-62">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-63">(</span><span class="mi">34</span><span class="p" data-group-id="1572975763-63">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-60">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-64">(</span><span class="mi">35</span><span class="p" data-group-id="1572975763-64">)</span><span class="w">        </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeIntermediate</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-65">(</span><span class="mi">36</span><span class="p" data-group-id="1572975763-65">)</span><span class="w">        </span><span class="nf">driver_select</span><span class="p" data-group-id="1572975763-66">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="1572975763-67">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="1572975763-67">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1572975763-66">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-68">(</span><span class="mi">37</span><span class="p" data-group-id="1572975763-68">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="1572975763-69">(</span><span class="mi">1</span><span class="p" data-group-id="1572975763-69">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-70">(</span><span class="mi">38</span><span class="p" data-group-id="1572975763-70">)</span><span class="w">        </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-71">(</span><span class="mi">39</span><span class="p" data-group-id="1572975763-71">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-72">(</span><span class="mi">40</span><span class="p" data-group-id="1572975763-72">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;D&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-73">(</span><span class="mi">41</span><span class="p" data-group-id="1572975763-73">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1572975763-74">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="1572975763-74">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-75">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-76">(</span><span class="mi">42</span><span class="p" data-group-id="1572975763-76">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="1572975763-77">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="1572975763-77">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-78">(</span><span class="mi">43</span><span class="p" data-group-id="1572975763-78">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-75">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-79">(</span><span class="mi">44</span><span class="p" data-group-id="1572975763-79">)</span><span class="w">        </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeData</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-80">(</span><span class="mi">45</span><span class="p" data-group-id="1572975763-80">)</span><span class="w">        </span><span class="nf">do_recv</span><span class="p" data-group-id="1572975763-81">(</span><span class="n">ud</span><span class="p" data-group-id="1572975763-81">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-82">(</span><span class="mi">46</span><span class="p" data-group-id="1572975763-82">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="1572975763-83">(</span><span class="mi">1</span><span class="p" data-group-id="1572975763-83">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-84">(</span><span class="mi">47</span><span class="p" data-group-id="1572975763-84">)</span><span class="w">        </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-85">(</span><span class="mi">48</span><span class="p" data-group-id="1572975763-85">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-86">(</span><span class="mi">49</span><span class="p" data-group-id="1572975763-86">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;N&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-87">(</span><span class="mi">50</span><span class="p" data-group-id="1572975763-87">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1572975763-88">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeListener</span><span class="p" data-group-id="1572975763-88">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-89">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-90">(</span><span class="mi">51</span><span class="p" data-group-id="1572975763-90">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="1572975763-91">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="1572975763-91">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-92">(</span><span class="mi">52</span><span class="p" data-group-id="1572975763-92">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-89">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-93">(</span><span class="mi">53</span><span class="p" data-group-id="1572975763-93">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="1572975763-94">(</span><span class="mi">5</span><span class="p" data-group-id="1572975763-94">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-95">(</span><span class="mi">54</span><span class="p" data-group-id="1572975763-95">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-96">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="1572975763-96">)</span><span class="p" data-group-id="1572975763-97">[</span><span class="mi">0</span><span class="p" data-group-id="1572975763-97">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-98">(</span><span class="mi">55</span><span class="p" data-group-id="1572975763-98">)</span><span class="w">        </span><span class="nf">put_packet_length</span><span class="p" data-group-id="1572975763-99">(</span><span class="p" data-group-id="1572975763-100">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="1572975763-100">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p" data-group-id="1572975763-99">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-101">(</span><span class="mi">56</span><span class="p" data-group-id="1572975763-101">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-102">(</span><span class="mi">57</span><span class="p" data-group-id="1572975763-102">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;T&#39;</span><span class="p">:</span><span class="w"> </span><span class="cm">/* tick */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-103">(</span><span class="mi">58</span><span class="p" data-group-id="1572975763-103">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1572975763-104">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeData</span><span class="p" data-group-id="1572975763-104">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-105">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-106">(</span><span class="mi">59</span><span class="p" data-group-id="1572975763-106">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="1572975763-107">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="1572975763-107">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-108">(</span><span class="mi">60</span><span class="p" data-group-id="1572975763-108">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-105">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-109">(</span><span class="mi">61</span><span class="p" data-group-id="1572975763-109">)</span><span class="w">        </span><span class="nf">do_send</span><span class="p" data-group-id="1572975763-110">(</span><span class="n">ud</span><span class="p">,</span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="1572975763-110">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-111">(</span><span class="mi">62</span><span class="p" data-group-id="1572975763-111">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="1572975763-112">(</span><span class="mi">1</span><span class="p" data-group-id="1572975763-112">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-113">(</span><span class="mi">63</span><span class="p" data-group-id="1572975763-113">)</span><span class="w">        </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-114">(</span><span class="mi">64</span><span class="p" data-group-id="1572975763-114">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-115">(</span><span class="mi">65</span><span class="p" data-group-id="1572975763-115">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;R&#39;</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-116">(</span><span class="mi">66</span><span class="p" data-group-id="1572975763-116">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="1572975763-117">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeListener</span><span class="p" data-group-id="1572975763-117">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-118">{</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-119">(</span><span class="mi">67</span><span class="p" data-group-id="1572975763-119">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="1572975763-120">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="1572975763-120">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-121">(</span><span class="mi">68</span><span class="p" data-group-id="1572975763-121">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-118">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-122">(</span><span class="mi">69</span><span class="p" data-group-id="1572975763-122">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="1572975763-123">(</span><span class="mi">2</span><span class="p" data-group-id="1572975763-123">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-124">(</span><span class="mi">70</span><span class="p" data-group-id="1572975763-124">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-125">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="1572975763-125">)</span><span class="p" data-group-id="1572975763-126">[</span><span class="mi">0</span><span class="p" data-group-id="1572975763-126">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-127">(</span><span class="mi">71</span><span class="p" data-group-id="1572975763-127">)</span><span class="w">        </span><span class="p" data-group-id="1572975763-128">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="1572975763-128">)</span><span class="p" data-group-id="1572975763-129">[</span><span class="mi">1</span><span class="p" data-group-id="1572975763-129">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">creation</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-130">(</span><span class="mi">72</span><span class="p" data-group-id="1572975763-130">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-131">(</span><span class="mi">73</span><span class="p" data-group-id="1572975763-131">)</span><span class="w">    </span><span class="ss">default</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-132">(</span><span class="mi">74</span><span class="p" data-group-id="1572975763-132">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="1572975763-133">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="1572975763-133">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-134">(</span><span class="mi">75</span><span class="p" data-group-id="1572975763-134">)</span><span class="w">    </span><span class="p" data-group-id="1572975763-23">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-135">(</span><span class="mi">76</span><span class="p" data-group-id="1572975763-135">)</span><span class="w"> </span><span class="kp">#undef</span><span class="w"> </span><span class="no">ENSURE</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1572975763-136">(</span><span class="mi">77</span><span class="p" data-group-id="1572975763-136">)</span><span class="w"> </span><span class="p" data-group-id="1572975763-5">}</span></code></pre><p>The macro <code class="inline">ENSURE</code> (line 5-10) is used to ensure that the buffer is large enough
│ │ │ +is as follows:</p><pre><code class="makeup c" translate="no"><span class="p" data-group-id="3089586158-1">(</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="3089586158-1">)</span><span class="w"> </span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">uds_control</span><span class="p" data-group-id="3089586158-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">handle</span><span class="p">,</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">command</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-3">(</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="3089586158-3">)</span><span class="w">                        </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">count</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="o">*</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">res_size</span><span class="p" data-group-id="3089586158-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-4">(</span><span class="w"> </span><span class="mi">3</span><span class="p" data-group-id="3089586158-4">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-5">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-6">(</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="3089586158-6">)</span><span class="w"> </span><span class="cm">/* Local macro to ensure large enough buffer. */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-7">(</span><span class="w"> </span><span class="mi">5</span><span class="p" data-group-id="3089586158-7">)</span><span class="w"> </span><span class="kp">#define</span><span class="w"> </span><span class="no">ENSURE</span><span class="p" data-group-id="3089586158-8">(</span><span class="no">N</span><span class="p" data-group-id="3089586158-8">)</span><span class="w">                               </span><span class="err">\</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-9">(</span><span class="w"> </span><span class="mi">6</span><span class="p" data-group-id="3089586158-9">)</span><span class="w">    </span><span class="k">do</span><span class="w"> </span><span class="p" data-group-id="3089586158-10">{</span><span class="w">                                         </span><span class="err">\</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-11">(</span><span class="w"> </span><span class="mi">7</span><span class="p" data-group-id="3089586158-11">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3089586158-12">(</span><span class="n">res_size</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="no">N</span><span class="p" data-group-id="3089586158-12">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-13">{</span><span class="w">                      </span><span class="err">\</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-14">(</span><span class="w"> </span><span class="mi">8</span><span class="p" data-group-id="3089586158-14">)</span><span class="w">            </span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">ALLOC</span><span class="p" data-group-id="3089586158-15">(</span><span class="no">N</span><span class="p" data-group-id="3089586158-15">)</span><span class="p">;</span><span class="w">                     </span><span class="err">\</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-16">(</span><span class="w"> </span><span class="mi">9</span><span class="p" data-group-id="3089586158-16">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-13">}</span><span class="w">                                        </span><span class="err">\</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-17">(</span><span class="mi">10</span><span class="p" data-group-id="3089586158-17">)</span><span class="w">    </span><span class="p" data-group-id="3089586158-10">}</span><span class="w"> </span><span class="nf">while</span><span class="p" data-group-id="3089586158-18">(</span><span class="mi">0</span><span class="p" data-group-id="3089586158-18">)</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="p" data-group-id="3089586158-19">(</span><span class="mi">11</span><span class="p" data-group-id="3089586158-19">)</span><span class="w">    </span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="n">ud</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3089586158-20">(</span><span class="no">UdsData</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="3089586158-20">)</span><span class="w"> </span><span class="n">handle</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="p" data-group-id="3089586158-21">(</span><span class="mi">12</span><span class="p" data-group-id="3089586158-21">)</span><span class="w">    </span><span class="k">switch</span><span class="w"> </span><span class="p" data-group-id="3089586158-22">(</span><span class="n">command</span><span class="p" data-group-id="3089586158-22">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-23">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-24">(</span><span class="mi">13</span><span class="p" data-group-id="3089586158-24">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;S&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-25">(</span><span class="mi">14</span><span class="p" data-group-id="3089586158-25">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-26">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-27">(</span><span class="mi">15</span><span class="p" data-group-id="3089586158-27">)</span><span class="w">            </span><span class="no">ENSURE</span><span class="p" data-group-id="3089586158-28">(</span><span class="mi">13</span><span class="p" data-group-id="3089586158-28">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-29">(</span><span class="mi">16</span><span class="p" data-group-id="3089586158-29">)</span><span class="w">            </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-30">(</span><span class="mi">17</span><span class="p" data-group-id="3089586158-30">)</span><span class="w">            </span><span class="nf">put_packet_length</span><span class="p" data-group-id="3089586158-31">(</span><span class="p" data-group-id="3089586158-32">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="3089586158-32">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">received</span><span class="p" data-group-id="3089586158-31">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-33">(</span><span class="mi">18</span><span class="p" data-group-id="3089586158-33">)</span><span class="w">            </span><span class="nf">put_packet_length</span><span class="p" data-group-id="3089586158-34">(</span><span class="p" data-group-id="3089586158-35">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="3089586158-35">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">sent</span><span class="p" data-group-id="3089586158-34">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-36">(</span><span class="mi">19</span><span class="p" data-group-id="3089586158-36">)</span><span class="w">            </span><span class="nf">put_packet_length</span><span class="p" data-group-id="3089586158-37">(</span><span class="p" data-group-id="3089586158-38">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="3089586158-38">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="nf">driver_sizeq</span><span class="p" data-group-id="3089586158-39">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p" data-group-id="3089586158-39">)</span><span class="p" data-group-id="3089586158-37">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-40">(</span><span class="mi">20</span><span class="p" data-group-id="3089586158-40">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="mi">13</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-41">(</span><span class="mi">21</span><span class="p" data-group-id="3089586158-41">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-26">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-42">(</span><span class="mi">22</span><span class="p" data-group-id="3089586158-42">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;C&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-43">(</span><span class="mi">23</span><span class="p" data-group-id="3089586158-43">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3089586158-44">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="3089586158-44">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-45">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-46">(</span><span class="mi">24</span><span class="p" data-group-id="3089586158-46">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="3089586158-47">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="3089586158-47">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-48">(</span><span class="mi">25</span><span class="p" data-group-id="3089586158-48">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-45">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-49">(</span><span class="mi">26</span><span class="p" data-group-id="3089586158-49">)</span><span class="w">        </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-50">(</span><span class="mi">27</span><span class="p" data-group-id="3089586158-50">)</span><span class="w">        </span><span class="nf">driver_select</span><span class="p" data-group-id="3089586158-51">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3089586158-52">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="3089586158-52">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3089586158-51">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-53">(</span><span class="mi">28</span><span class="p" data-group-id="3089586158-53">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="3089586158-54">(</span><span class="mi">1</span><span class="p" data-group-id="3089586158-54">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-55">(</span><span class="mi">29</span><span class="p" data-group-id="3089586158-55">)</span><span class="w">        </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-56">(</span><span class="mi">30</span><span class="p" data-group-id="3089586158-56">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-57">(</span><span class="mi">31</span><span class="p" data-group-id="3089586158-57">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;I&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-58">(</span><span class="mi">32</span><span class="p" data-group-id="3089586158-58">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3089586158-59">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="3089586158-59">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-60">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-61">(</span><span class="mi">33</span><span class="p" data-group-id="3089586158-61">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="3089586158-62">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="3089586158-62">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-63">(</span><span class="mi">34</span><span class="p" data-group-id="3089586158-63">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-60">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-64">(</span><span class="mi">35</span><span class="p" data-group-id="3089586158-64">)</span><span class="w">        </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeIntermediate</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-65">(</span><span class="mi">36</span><span class="p" data-group-id="3089586158-65">)</span><span class="w">        </span><span class="nf">driver_select</span><span class="p" data-group-id="3089586158-66">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="p" data-group-id="3089586158-67">(</span><span class="no">ErlDrvEvent</span><span class="p" data-group-id="3089586158-67">)</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="no">DO_READ</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3089586158-66">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-68">(</span><span class="mi">37</span><span class="p" data-group-id="3089586158-68">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="3089586158-69">(</span><span class="mi">1</span><span class="p" data-group-id="3089586158-69">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-70">(</span><span class="mi">38</span><span class="p" data-group-id="3089586158-70">)</span><span class="w">        </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-71">(</span><span class="mi">39</span><span class="p" data-group-id="3089586158-71">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-72">(</span><span class="mi">40</span><span class="p" data-group-id="3089586158-72">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;D&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-73">(</span><span class="mi">41</span><span class="p" data-group-id="3089586158-73">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3089586158-74">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">portTypeCommand</span><span class="p" data-group-id="3089586158-74">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-75">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-76">(</span><span class="mi">42</span><span class="p" data-group-id="3089586158-76">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="3089586158-77">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="3089586158-77">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-78">(</span><span class="mi">43</span><span class="p" data-group-id="3089586158-78">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-75">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-79">(</span><span class="mi">44</span><span class="p" data-group-id="3089586158-79">)</span><span class="w">        </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">portTypeData</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-80">(</span><span class="mi">45</span><span class="p" data-group-id="3089586158-80">)</span><span class="w">        </span><span class="nf">do_recv</span><span class="p" data-group-id="3089586158-81">(</span><span class="n">ud</span><span class="p" data-group-id="3089586158-81">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-82">(</span><span class="mi">46</span><span class="p" data-group-id="3089586158-82">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="3089586158-83">(</span><span class="mi">1</span><span class="p" data-group-id="3089586158-83">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-84">(</span><span class="mi">47</span><span class="p" data-group-id="3089586158-84">)</span><span class="w">        </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-85">(</span><span class="mi">48</span><span class="p" data-group-id="3089586158-85">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-86">(</span><span class="mi">49</span><span class="p" data-group-id="3089586158-86">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;N&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-87">(</span><span class="mi">50</span><span class="p" data-group-id="3089586158-87">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3089586158-88">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeListener</span><span class="p" data-group-id="3089586158-88">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-89">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-90">(</span><span class="mi">51</span><span class="p" data-group-id="3089586158-90">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="3089586158-91">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="3089586158-91">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-92">(</span><span class="mi">52</span><span class="p" data-group-id="3089586158-92">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-89">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-93">(</span><span class="mi">53</span><span class="p" data-group-id="3089586158-93">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="3089586158-94">(</span><span class="mi">5</span><span class="p" data-group-id="3089586158-94">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-95">(</span><span class="mi">54</span><span class="p" data-group-id="3089586158-95">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-96">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="3089586158-96">)</span><span class="p" data-group-id="3089586158-97">[</span><span class="mi">0</span><span class="p" data-group-id="3089586158-97">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-98">(</span><span class="mi">55</span><span class="p" data-group-id="3089586158-98">)</span><span class="w">        </span><span class="nf">put_packet_length</span><span class="p" data-group-id="3089586158-99">(</span><span class="p" data-group-id="3089586158-100">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="3089586158-100">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">fd</span><span class="p" data-group-id="3089586158-99">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-101">(</span><span class="mi">56</span><span class="p" data-group-id="3089586158-101">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">5</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-102">(</span><span class="mi">57</span><span class="p" data-group-id="3089586158-102">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;T&#39;</span><span class="p">:</span><span class="w"> </span><span class="cm">/* tick */</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-103">(</span><span class="mi">58</span><span class="p" data-group-id="3089586158-103">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3089586158-104">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeData</span><span class="p" data-group-id="3089586158-104">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-105">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-106">(</span><span class="mi">59</span><span class="p" data-group-id="3089586158-106">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="3089586158-107">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="3089586158-107">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-108">(</span><span class="mi">60</span><span class="p" data-group-id="3089586158-108">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-105">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-109">(</span><span class="mi">61</span><span class="p" data-group-id="3089586158-109">)</span><span class="w">        </span><span class="nf">do_send</span><span class="p" data-group-id="3089586158-110">(</span><span class="n">ud</span><span class="p">,</span><span class="s">&quot;&quot;</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="3089586158-110">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-111">(</span><span class="mi">62</span><span class="p" data-group-id="3089586158-111">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="3089586158-112">(</span><span class="mi">1</span><span class="p" data-group-id="3089586158-112">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-113">(</span><span class="mi">63</span><span class="p" data-group-id="3089586158-113">)</span><span class="w">        </span><span class="o">*</span><span class="o">*</span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-114">(</span><span class="mi">64</span><span class="p" data-group-id="3089586158-114">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-115">(</span><span class="mi">65</span><span class="p" data-group-id="3089586158-115">)</span><span class="w">    </span><span class="k">case</span><span class="w"> </span><span class="ss">&#39;R&#39;</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-116">(</span><span class="mi">66</span><span class="p" data-group-id="3089586158-116">)</span><span class="w">        </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="3089586158-117">(</span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">type</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">portTypeListener</span><span class="p" data-group-id="3089586158-117">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-118">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-119">(</span><span class="mi">67</span><span class="p" data-group-id="3089586158-119">)</span><span class="w">            </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="3089586158-120">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="3089586158-120">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-121">(</span><span class="mi">68</span><span class="p" data-group-id="3089586158-121">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-118">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-122">(</span><span class="mi">69</span><span class="p" data-group-id="3089586158-122">)</span><span class="w">        </span><span class="no">ENSURE</span><span class="p" data-group-id="3089586158-123">(</span><span class="mi">2</span><span class="p" data-group-id="3089586158-123">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-124">(</span><span class="mi">70</span><span class="p" data-group-id="3089586158-124">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-125">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="3089586158-125">)</span><span class="p" data-group-id="3089586158-126">[</span><span class="mi">0</span><span class="p" data-group-id="3089586158-126">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-127">(</span><span class="mi">71</span><span class="p" data-group-id="3089586158-127">)</span><span class="w">        </span><span class="p" data-group-id="3089586158-128">(</span><span class="o">*</span><span class="n">res</span><span class="p" data-group-id="3089586158-128">)</span><span class="p" data-group-id="3089586158-129">[</span><span class="mi">1</span><span class="p" data-group-id="3089586158-129">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ud</span><span class="o">-&gt;</span><span class="n">creation</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-130">(</span><span class="mi">72</span><span class="p" data-group-id="3089586158-130">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-131">(</span><span class="mi">73</span><span class="p" data-group-id="3089586158-131">)</span><span class="w">    </span><span class="ss">default</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-132">(</span><span class="mi">74</span><span class="p" data-group-id="3089586158-132">)</span><span class="w">        </span><span class="k">return</span><span class="w"> </span><span class="nf">report_control_error</span><span class="p" data-group-id="3089586158-133">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">res_size</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;einval&quot;</span><span class="p" data-group-id="3089586158-133">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-134">(</span><span class="mi">75</span><span class="p" data-group-id="3089586158-134">)</span><span class="w">    </span><span class="p" data-group-id="3089586158-23">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-135">(</span><span class="mi">76</span><span class="p" data-group-id="3089586158-135">)</span><span class="w"> </span><span class="kp">#undef</span><span class="w"> </span><span class="no">ENSURE</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3089586158-136">(</span><span class="mi">77</span><span class="p" data-group-id="3089586158-136">)</span><span class="w"> </span><span class="p" data-group-id="3089586158-5">}</span></code></pre><p>The macro <code class="inline">ENSURE</code> (line 5-10) is used to ensure that the buffer is large enough
│ │ │  for the answer. We switch on the command and take actions. We always have read
│ │ │  select active on a port in <code class="inline">data</code> mode (achieved by calling <code class="inline">do_recv</code> on line
│ │ │  45), but we turn off read selection in <code class="inline">intermediate</code> and <code class="inline">command</code> modes (line
│ │ │  27 and 36).</p><p>The rest of the driver is more or less UDS-specific and not of general interest.</p><h2 id="putting-it-all-together" class="section-heading">
│ │ │    <a href="#putting-it-all-together" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/automaticyieldingofccode.html
│ │ │ @@ -209,17 +209,17 @@
│ │ │  they have to follow certain restrictions. The convention for making
│ │ │  this clear is to have a comment above the function that explains that
│ │ │  the function is transformed by YCF (see <code class="inline">maps_values_1_helper</code> in
│ │ │  <code class="inline">erl_map.c</code> for an example). If only the transformed version of the
│ │ │  function is used, the convention is to &quot;comment out&quot; the source for the
│ │ │  function by surrounding it with the following <code class="inline">#ifdef</code> (this way, one
│ │ │  will not get warnings about unused functions):</p><pre><code class="makeup erlang" translate="no"><span class="p">#</span><span class="ss">ifdef</span><span class="w"> </span><span class="n">INCLUDE_YCF_TRANSFORMED_ONLY_FUNCTIONS</span><span class="w">
│ │ │ -</span><span class="ss">void</span><span class="w"> </span><span class="nf">my_fun</span><span class="p" data-group-id="8109663607-1">(</span><span class="p" data-group-id="8109663607-1">)</span><span class="w"> </span><span class="p" data-group-id="8109663607-2">{</span><span class="w">
│ │ │ +</span><span class="ss">void</span><span class="w"> </span><span class="nf">my_fun</span><span class="p" data-group-id="1387794175-1">(</span><span class="p" data-group-id="1387794175-1">)</span><span class="w"> </span><span class="p" data-group-id="1387794175-2">{</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8109663607-2">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1387794175-2">}</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="ss">endif</span><span class="w"> </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">INCLUDE_YCF_TRANSFORMED_ONLY_FUNCTIONS</span><span class="w"> </span><span class="o">*</span><span class="o">/</span></code></pre><p>While editing the function one can define
│ │ │  <code class="inline">INCLUDE_YCF_TRANSFORMED_ONLY_FUNCTIONS</code> so that one can see errors
│ │ │  and warnings in the non-transformed source.</p><h3 id="where-to-place-ycf-transformed-functions" class="section-heading">
│ │ │    <a href="#where-to-place-ycf-transformed-functions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Where to Place YCF Transformed Functions</span>
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/beam_makeops.html
│ │ │ @@ -151,17 +151,17 @@
│ │ │  The loader translates generic instructions to specific instructions.
│ │ │  In general, for each generic instruction, there exists a family of
│ │ │  specific instructions.  The OTP 20 release has 389 specific
│ │ │  instructions.</p></li><li><p>The implementation of specific instructions for the traditional
│ │ │  BEAM interpreter. For the <a href="beamasm.html">BeamAsm JIT</a> introduced
│ │ │  in OTP 24, the implementation of instructions are defined in emitter
│ │ │  functions written in C++.</p></li></ul><p>Generic instructions have typed operands. Here are a few examples of
│ │ │ -operands for <code class="inline">move/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1452876753-1">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="1452876753-2">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">id</span><span class="p" data-group-id="1452876753-2">}</span><span class="p">,</span><span class="p" data-group-id="1452876753-3">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1452876753-3">}</span><span class="p" data-group-id="1452876753-1">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1452876753-4">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="1452876753-5">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="1452876753-5">}</span><span class="p">,</span><span class="p" data-group-id="1452876753-6">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="1452876753-6">}</span><span class="p" data-group-id="1452876753-4">}</span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1452876753-7">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="1452876753-8">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="1452876753-8">}</span><span class="p">,</span><span class="p" data-group-id="1452876753-9">{</span><span class="ss">y</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1452876753-9">}</span><span class="p" data-group-id="1452876753-7">}</span><span class="p">.</span></code></pre><p>When those instructions are loaded, the loader rewrites them
│ │ │ +operands for <code class="inline">move/2</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="7193469766-1">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="7193469766-2">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">id</span><span class="p" data-group-id="7193469766-2">}</span><span class="p">,</span><span class="p" data-group-id="7193469766-3">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="7193469766-3">}</span><span class="p" data-group-id="7193469766-1">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7193469766-4">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="7193469766-5">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">3</span><span class="p" data-group-id="7193469766-5">}</span><span class="p">,</span><span class="p" data-group-id="7193469766-6">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="7193469766-6">}</span><span class="p" data-group-id="7193469766-4">}</span><span class="p">.</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7193469766-7">{</span><span class="ss">move</span><span class="p">,</span><span class="p" data-group-id="7193469766-8">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">2</span><span class="p" data-group-id="7193469766-8">}</span><span class="p">,</span><span class="p" data-group-id="7193469766-9">{</span><span class="ss">y</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="7193469766-9">}</span><span class="p" data-group-id="7193469766-7">}</span><span class="p">.</span></code></pre><p>When those instructions are loaded, the loader rewrites them
│ │ │  to specific instructions:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move_cx</span><span class="w"> </span><span class="ss">id</span><span class="w"> </span><span class="mi">5</span><span class="w">
│ │ │  </span><span class="ss">move_xx</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="mi">0</span><span class="w">
│ │ │  </span><span class="ss">move_xy</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="mi">1</span></code></pre><p>Corresponding to each generic instruction, there is a family of
│ │ │  specific instructions.  The types that an instance of a specific
│ │ │  instruction can handle are encoded in the instruction names.  For
│ │ │  example, <code class="inline">move_xy</code> takes an X register number as the first operand and
│ │ │  a Y register number as the second operand.  <code class="inline">move_cx</code> takes a tagged
│ │ │ @@ -185,17 +185,17 @@
│ │ │  </span><span class="ss">move</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="ss">x</span></code></pre><p>Each specific instructions is defined by following the name of the
│ │ │  instruction with the types for each operand.  An operand type is a
│ │ │  single letter.  For example, <code class="inline">x</code> means an X register, <code class="inline">y</code>
│ │ │  means a Y register, and <code class="inline">c</code> is a &quot;constant&quot; (a tagged term such as
│ │ │  an integer, an atom, or a literal).</p><p>Now let's look at the implementation of the <code class="inline">move</code> instruction.  There
│ │ │  are multiple files containing implementations of instructions in the
│ │ │  <code class="inline">erts/emulator/beam/emu</code> directory.  The <code class="inline">move</code> instruction is defined
│ │ │ -in <code class="inline">instrs.tab</code>.  It looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="2528679694-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="2528679694-1">)</span><span class="w"> </span><span class="p" data-group-id="2528679694-2">{</span><span class="w">
│ │ │ +in <code class="inline">instrs.tab</code>.  It looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="3071679452-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="3071679452-1">)</span><span class="w"> </span><span class="p" data-group-id="3071679452-2">{</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2528679694-2">}</span></code></pre><p>The implementation for an instruction largely follows the C syntax,
│ │ │ +</span><span class="p" data-group-id="3071679452-2">}</span></code></pre><p>The implementation for an instruction largely follows the C syntax,
│ │ │  except that the variables in the function head don't have any types.
│ │ │  The <code class="inline">$</code> before an identifier denotes a macro expansion.  Thus,
│ │ │  <code class="inline">$Src</code> will expand to the code to pick up the source operand for
│ │ │  the instruction and <code class="inline">$Dst</code> to the code for the destination register.</p><p>We will look at the code for each specific instruction in turn.  To
│ │ │  make the code easier to understand, let's first look at the memory
│ │ │  layout for the instruction <code class="inline">{move,{atom,id},{x,5}}</code>:</p><pre><code class="makeup erlang" translate="no"><span class="w">     </span><span class="o">+</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">+</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">+</span><span class="w">
│ │ │  </span><span class="n">I</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">|</span><span class="w">                 </span><span class="mi">40</span><span class="w"> </span><span class="p">|</span><span class="w">       </span><span class="p">&amp;&amp;</span><span class="ss">lb_move_cx</span><span class="w"> </span><span class="p">|</span><span class="w">
│ │ │ @@ -204,61 +204,61 @@
│ │ │       </span><span class="o">+</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">+</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">--</span><span class="o">+</span></code></pre><p>This example and all other examples in the document assumes a 64-bit
│ │ │  architecture, and furthermore that pointers to C code fit in 32 bits.</p><p><code class="inline">I</code> in the BEAM virtual machine is the instruction pointer.  When BEAM
│ │ │  executes an instruction, <code class="inline">I</code> points to the first word of the
│ │ │  instruction.</p><p><code class="inline">&amp;&amp;lb_move_cx</code> is the address to C code that implements <code class="inline">move_cx</code>.  It
│ │ │  is stored in the lower 32 bits of the word.  In the upper 32 bits is
│ │ │  the byte offset to the X register; the register number 5 has been
│ │ │  multiplied by the word size size 8.</p><p>In the next word the tagged atom <code class="inline">id</code> is stored.</p><p>With that background, we can look at the generated code for <code class="inline">move_cx</code>
│ │ │ -in <code class="inline">beam_hot.h</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="6379536389-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="6379536389-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6379536389-2">{</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="6379536389-3">(</span><span class="n">I</span><span class="p" data-group-id="6379536389-4">[</span><span class="mi">2</span><span class="p" data-group-id="6379536389-4">]</span><span class="p" data-group-id="6379536389-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">xb</span><span class="p" data-group-id="6379536389-5">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6379536389-6">(</span><span class="n">I</span><span class="p" data-group-id="6379536389-7">[</span><span class="mi">0</span><span class="p" data-group-id="6379536389-7">]</span><span class="p" data-group-id="6379536389-6">)</span><span class="p" data-group-id="6379536389-5">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="6379536389-8">[</span><span class="mi">1</span><span class="p" data-group-id="6379536389-8">]</span><span class="p">;</span><span class="w">
│ │ │ +in <code class="inline">beam_hot.h</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="6753659767-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="6753659767-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6753659767-2">{</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="6753659767-3">(</span><span class="n">I</span><span class="p" data-group-id="6753659767-4">[</span><span class="mi">2</span><span class="p" data-group-id="6753659767-4">]</span><span class="p" data-group-id="6753659767-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">xb</span><span class="p" data-group-id="6753659767-5">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6753659767-6">(</span><span class="n">I</span><span class="p" data-group-id="6753659767-7">[</span><span class="mi">0</span><span class="p" data-group-id="6753659767-7">]</span><span class="p" data-group-id="6753659767-6">)</span><span class="p" data-group-id="6753659767-5">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="6753659767-8">[</span><span class="mi">1</span><span class="p" data-group-id="6753659767-8">]</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="6379536389-9">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="6379536389-10">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6379536389-10">)</span><span class="p" data-group-id="6379536389-9">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="6379536389-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6379536389-11">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6379536389-2">}</span></code></pre><p>We will go through each line in turn.</p><ul><li><p><code class="inline">OpCase(move_cx):</code> defines a label for the instruction.  The
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="6753659767-9">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="6753659767-10">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6753659767-10">)</span><span class="p" data-group-id="6753659767-9">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="6753659767-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6753659767-11">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6753659767-2">}</span></code></pre><p>We will go through each line in turn.</p><ul><li><p><code class="inline">OpCase(move_cx):</code> defines a label for the instruction.  The
│ │ │  <code class="inline">OpCase()</code> macro is defined in <code class="inline">beam_emu.c</code>.  It will expand this line
│ │ │  to <code class="inline">lb_move_cx:</code>.</p></li><li><p><code class="inline">BeamInstr next_pf = BeamCodeAddr(I[2]);</code> fetches the pointer to
│ │ │  code for the next instruction to be executed.  The <code class="inline">BeamCodeAddr()</code>
│ │ │  macro extracts the pointer from the lower 32 bits of the instruction
│ │ │  word.</p></li><li><p><code class="inline">xb(BeamExtraData(I[0])) = I[1];</code> is the expansion of <code class="inline">$Dst = $Src</code>.
│ │ │  <code class="inline">BeamExtraData()</code> is a macro that will extract the upper 32 bits from
│ │ │  the instruction word.  In this example, it will return 40 which is the
│ │ │  byte offset for X register 5.  The <code class="inline">xb()</code> macro will cast a byte
│ │ │  pointer to an <code class="inline">Eterm</code> pointer and dereference it.  The <code class="inline">I[1]</code> on
│ │ │  the right-hand side of the <code class="inline">=</code> fetches an Erlang term (the atom <code class="inline">id</code> in
│ │ │  this case).</p></li><li><p><code class="inline">I += 2</code> advances the instruction pointer to the next
│ │ │  instruction.</p></li><li><p>In a debug-compiled emulator, <code class="inline">ASSERT(VALID_INSTR(next_pf));</code> makes
│ │ │  sure that <code class="inline">next_pf</code> is a valid instruction (that is, that it points
│ │ │ -within the <code class="inline">process_main()</code> function in <code class="inline">beam_emu.c</code>).</p></li><li><p><code class="inline">GotoPF(next_pf);</code> transfers control to the next instruction.</p></li></ul><p>Now let's look at the implementation of <code class="inline">move_xx</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="0569519222-1">(</span><span class="ss">move_xx</span><span class="p" data-group-id="0569519222-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0569519222-2">{</span><span class="w">
│ │ │ -  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">tmp_packed1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamExtraData</span><span class="p" data-group-id="0569519222-3">(</span><span class="n">I</span><span class="p" data-group-id="0569519222-4">[</span><span class="mi">0</span><span class="p" data-group-id="0569519222-4">]</span><span class="p" data-group-id="0569519222-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="0569519222-5">(</span><span class="n">I</span><span class="p" data-group-id="0569519222-6">[</span><span class="mi">1</span><span class="p" data-group-id="0569519222-6">]</span><span class="p" data-group-id="0569519222-5">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">xb</span><span class="p" data-group-id="0569519222-7">(</span><span class="p" data-group-id="0569519222-8">(</span><span class="ss">tmp_packed1</span><span class="p">&gt;&gt;</span><span class="n">BEAM_TIGHT_SHIFT</span><span class="p" data-group-id="0569519222-8">)</span><span class="p" data-group-id="0569519222-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="0569519222-9">(</span><span class="ss">tmp_packed1</span><span class="err">&amp;</span><span class="n">BEAM_TIGHT_MASK</span><span class="p" data-group-id="0569519222-9">)</span><span class="p">;</span><span class="w">
│ │ │ +within the <code class="inline">process_main()</code> function in <code class="inline">beam_emu.c</code>).</p></li><li><p><code class="inline">GotoPF(next_pf);</code> transfers control to the next instruction.</p></li></ul><p>Now let's look at the implementation of <code class="inline">move_xx</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="5028836879-1">(</span><span class="ss">move_xx</span><span class="p" data-group-id="5028836879-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5028836879-2">{</span><span class="w">
│ │ │ +  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">tmp_packed1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamExtraData</span><span class="p" data-group-id="5028836879-3">(</span><span class="n">I</span><span class="p" data-group-id="5028836879-4">[</span><span class="mi">0</span><span class="p" data-group-id="5028836879-4">]</span><span class="p" data-group-id="5028836879-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="5028836879-5">(</span><span class="n">I</span><span class="p" data-group-id="5028836879-6">[</span><span class="mi">1</span><span class="p" data-group-id="5028836879-6">]</span><span class="p" data-group-id="5028836879-5">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">xb</span><span class="p" data-group-id="5028836879-7">(</span><span class="p" data-group-id="5028836879-8">(</span><span class="ss">tmp_packed1</span><span class="p">&gt;&gt;</span><span class="n">BEAM_TIGHT_SHIFT</span><span class="p" data-group-id="5028836879-8">)</span><span class="p" data-group-id="5028836879-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="5028836879-9">(</span><span class="ss">tmp_packed1</span><span class="err">&amp;</span><span class="n">BEAM_TIGHT_MASK</span><span class="p" data-group-id="5028836879-9">)</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="0569519222-10">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="0569519222-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="0569519222-11">)</span><span class="p" data-group-id="0569519222-10">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="0569519222-12">(</span><span class="ss">next_pf</span><span class="p" data-group-id="0569519222-12">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0569519222-2">}</span></code></pre><p>We will go through the lines that are new or have changed compared to
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="5028836879-10">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="5028836879-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="5028836879-11">)</span><span class="p" data-group-id="5028836879-10">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="5028836879-12">(</span><span class="ss">next_pf</span><span class="p" data-group-id="5028836879-12">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5028836879-2">}</span></code></pre><p>We will go through the lines that are new or have changed compared to
│ │ │  <code class="inline">move_cx</code>.</p><ul><li><p><code class="inline">Eterm tmp_packed1 = BeamExtraData(I[0]);</code> picks up both X register
│ │ │  numbers packed into the upper 32 bits of the instruction word.</p></li><li><p><code class="inline">BeamInstr next_pf = BeamCodeAddr(I[1]);</code> pre-fetches the address of
│ │ │  the next instruction. Note that because both X registers operands fits
│ │ │  into the instruction word, the next instruction is in the very next
│ │ │  word.</p></li><li><p><code class="inline">xb((tmp_packed1&gt;&gt;BEAM_TIGHT_SHIFT)) = xb(tmp_packed1&amp;BEAM_TIGHT_MASK);</code>
│ │ │  copies the source to the destination.  (For a 64-bit architecture,
│ │ │  <code class="inline">BEAM_TIGHT_SHIFT</code> is 16 and <code class="inline">BEAM_TIGHT_MASK</code> is <code class="inline">0xFFFF</code>.)</p></li><li><p><code class="inline">I += 1;</code> advances the instruction pointer to the next instruction.</p></li></ul><p><code class="inline">move_xy</code> is almost identical to <code class="inline">move_xx</code>.  The only difference is
│ │ │  the use of the <code class="inline">yb()</code> macro instead of <code class="inline">xb()</code> to reference the
│ │ │ -destination register:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="6609390622-1">(</span><span class="ss">move_xy</span><span class="p" data-group-id="6609390622-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6609390622-2">{</span><span class="w">
│ │ │ -  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">tmp_packed1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamExtraData</span><span class="p" data-group-id="6609390622-3">(</span><span class="n">I</span><span class="p" data-group-id="6609390622-4">[</span><span class="mi">0</span><span class="p" data-group-id="6609390622-4">]</span><span class="p" data-group-id="6609390622-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="6609390622-5">(</span><span class="n">I</span><span class="p" data-group-id="6609390622-6">[</span><span class="mi">1</span><span class="p" data-group-id="6609390622-6">]</span><span class="p" data-group-id="6609390622-5">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">yb</span><span class="p" data-group-id="6609390622-7">(</span><span class="p" data-group-id="6609390622-8">(</span><span class="ss">tmp_packed1</span><span class="p">&gt;&gt;</span><span class="n">BEAM_TIGHT_SHIFT</span><span class="p" data-group-id="6609390622-8">)</span><span class="p" data-group-id="6609390622-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="6609390622-9">(</span><span class="ss">tmp_packed1</span><span class="err">&amp;</span><span class="n">BEAM_TIGHT_MASK</span><span class="p" data-group-id="6609390622-9">)</span><span class="p">;</span><span class="w">
│ │ │ +destination register:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="8165750932-1">(</span><span class="ss">move_xy</span><span class="p" data-group-id="8165750932-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8165750932-2">{</span><span class="w">
│ │ │ +  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">tmp_packed1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamExtraData</span><span class="p" data-group-id="8165750932-3">(</span><span class="n">I</span><span class="p" data-group-id="8165750932-4">[</span><span class="mi">0</span><span class="p" data-group-id="8165750932-4">]</span><span class="p" data-group-id="8165750932-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="8165750932-5">(</span><span class="n">I</span><span class="p" data-group-id="8165750932-6">[</span><span class="mi">1</span><span class="p" data-group-id="8165750932-6">]</span><span class="p" data-group-id="8165750932-5">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">yb</span><span class="p" data-group-id="8165750932-7">(</span><span class="p" data-group-id="8165750932-8">(</span><span class="ss">tmp_packed1</span><span class="p">&gt;&gt;</span><span class="n">BEAM_TIGHT_SHIFT</span><span class="p" data-group-id="8165750932-8">)</span><span class="p" data-group-id="8165750932-7">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="8165750932-9">(</span><span class="ss">tmp_packed1</span><span class="err">&amp;</span><span class="n">BEAM_TIGHT_MASK</span><span class="p" data-group-id="8165750932-9">)</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="6609390622-10">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="6609390622-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6609390622-11">)</span><span class="p" data-group-id="6609390622-10">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="6609390622-12">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6609390622-12">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6609390622-2">}</span></code></pre><h3 id="transformation-rules" class="section-heading">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="8165750932-10">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="8165750932-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="8165750932-11">)</span><span class="p" data-group-id="8165750932-10">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="8165750932-12">(</span><span class="ss">next_pf</span><span class="p" data-group-id="8165750932-12">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8165750932-2">}</span></code></pre><h3 id="transformation-rules" class="section-heading">
│ │ │    <a href="#transformation-rules" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Transformation rules</span>
│ │ │  </h3>
│ │ │  <p>Next let's look at how we can do some optimizations using transformation
│ │ │  rules.  For simple instructions such as <code class="inline">move/2</code>, the instruction dispatch
│ │ │ @@ -271,21 +271,21 @@
│ │ │  with an uppercase letter just as in Erlang.  A pattern variable may be
│ │ │  followed <code class="inline">=</code> and one or more type letters to constrain the match to
│ │ │  one of those types.  The variables that are bound on the left-hand side can
│ │ │  be used on the right-hand side.</p><p>We will also need to define a specific instruction and an implementation:</p><pre><code class="makeup erlang" translate="no"><span class="p">#</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="ss">ops</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │  </span><span class="ss">move2</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">y</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="ss">instrs</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │ -</span><span class="nf">move2</span><span class="p" data-group-id="2454714241-1">(</span><span class="n">S1</span><span class="p">,</span><span class="w"> </span><span class="n">D1</span><span class="p">,</span><span class="w"> </span><span class="n">S2</span><span class="p">,</span><span class="w"> </span><span class="n">D2</span><span class="p" data-group-id="2454714241-1">)</span><span class="w"> </span><span class="p" data-group-id="2454714241-2">{</span><span class="w">
│ │ │ +</span><span class="nf">move2</span><span class="p" data-group-id="9981461879-1">(</span><span class="n">S1</span><span class="p">,</span><span class="w"> </span><span class="n">D1</span><span class="p">,</span><span class="w"> </span><span class="n">S2</span><span class="p">,</span><span class="w"> </span><span class="n">D2</span><span class="p" data-group-id="9981461879-1">)</span><span class="w"> </span><span class="p" data-group-id="9981461879-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="n">V1</span><span class="p">,</span><span class="w"> </span><span class="n">V2</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">V1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">V2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="mi">1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">V1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="mi">2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">V2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2454714241-2">}</span></code></pre><p>When the loader has found a match and replaced the matched instructions,
│ │ │ +</span><span class="p" data-group-id="9981461879-2">}</span></code></pre><p>When the loader has found a match and replaced the matched instructions,
│ │ │  it will match the new instructions against the transformation rules.
│ │ │  Because of that, we can define the rule for a <code class="inline">move3/6</code> instruction
│ │ │  as follows:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move2</span><span class="w"> </span><span class="n">X1</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y1</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="n">X2</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y2</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">move</span><span class="w"> </span><span class="n">X3</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y3</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │        </span><span class="ss">move3</span><span class="w"> </span><span class="n">X1</span><span class="w"> </span><span class="n">Y1</span><span class="w"> </span><span class="n">X2</span><span class="w"> </span><span class="n">Y2</span><span class="w"> </span><span class="n">X3</span><span class="w"> </span><span class="n">Y3</span></code></pre><p>(For readability, a long transformation line can be broken after <code class="inline">|</code>
│ │ │  and <code class="inline">=&gt;</code> operators.)</p><p>It would also be possible to define it like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="n">X1</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y1</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">move</span><span class="w"> </span><span class="n">X2</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y2</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="ss">move</span><span class="w"> </span><span class="n">X3</span><span class="o">=</span><span class="ss">x</span><span class="w"> </span><span class="n">Y3</span><span class="o">=</span><span class="ss">y</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │       </span><span class="ss">move3</span><span class="w"> </span><span class="n">X1</span><span class="w"> </span><span class="n">Y1</span><span class="w"> </span><span class="n">X2</span><span class="w"> </span><span class="n">Y2</span><span class="w"> </span><span class="n">X3</span><span class="w"> </span><span class="n">Y3</span></code></pre><p>but in that case it must be defined before the rule for <code class="inline">move2/4</code>
│ │ │  because the first matching rule will be applied.</p><p>One must be careful not to create infinite loops.  For example, if we
│ │ │ @@ -433,29 +433,29 @@
│ │ │  </span><span class="ss">i_bs_get_integer_32</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">f</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="c1">%endif</span></code></pre><p>The specific instruction <code class="inline">i_bs_get_integer_32</code> will only be defined
│ │ │  on a 64-bit machine.</p><p>The condition can be inverted by using <code class="inline">%unless</code> instead of <code class="inline">%if</code>:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%unless NO_FPE_SIGNALS</span><span class="w">
│ │ │  </span><span class="ss">fcheckerror</span><span class="w"> </span><span class="ss">p</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">i_fcheckerror</span><span class="w">
│ │ │  </span><span class="ss">i_fcheckerror</span><span class="w">
│ │ │  </span><span class="ss">fclearerror</span><span class="w">
│ │ │  </span><span class="c1">%endif</span></code></pre><p>It is also possible to add an <code class="inline">%else</code> clause:</p><pre><code class="makeup erlang" translate="no"><span class="c1">%if ARCH_64</span><span class="w">
│ │ │ -</span><span class="n">BS_SAFE_MUL</span><span class="p" data-group-id="1737242231-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="1737242231-1">)</span><span class="w"> </span><span class="p" data-group-id="1737242231-2">{</span><span class="w">
│ │ │ -    </span><span class="n">Uint64</span><span class="w"> </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1737242231-3">(</span><span class="sc">$A</span><span class="p" data-group-id="1737242231-3">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="1737242231-4">(</span><span class="sc">$B</span><span class="p" data-group-id="1737242231-4">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="1737242231-5">(</span><span class="ss">res</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="sc">$B</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="p" data-group-id="1737242231-5">)</span><span class="w"> </span><span class="p" data-group-id="1737242231-6">{</span><span class="w">
│ │ │ +</span><span class="n">BS_SAFE_MUL</span><span class="p" data-group-id="2507289316-1">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="2507289316-1">)</span><span class="w"> </span><span class="p" data-group-id="2507289316-2">{</span><span class="w">
│ │ │ +    </span><span class="n">Uint64</span><span class="w"> </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2507289316-3">(</span><span class="sc">$A</span><span class="p" data-group-id="2507289316-3">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="2507289316-4">(</span><span class="sc">$B</span><span class="p" data-group-id="2507289316-4">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="2507289316-5">(</span><span class="ss">res</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="sc">$B</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="p" data-group-id="2507289316-5">)</span><span class="w"> </span><span class="p" data-group-id="2507289316-6">{</span><span class="w">
│ │ │          </span><span class="sc">$F</span><span class="ss">ail</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1737242231-6">}</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2507289316-6">}</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">res</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1737242231-2">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2507289316-2">}</span><span class="w">
│ │ │  </span><span class="c1">%else</span><span class="w">
│ │ │ -</span><span class="n">BS_SAFE_MUL</span><span class="p" data-group-id="1737242231-7">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="1737242231-7">)</span><span class="w"> </span><span class="p" data-group-id="1737242231-8">{</span><span class="w">
│ │ │ -    </span><span class="n">Uint64</span><span class="w"> </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1737242231-9">(</span><span class="n">Uint64</span><span class="p" data-group-id="1737242231-9">)</span><span class="p" data-group-id="1737242231-10">(</span><span class="sc">$A</span><span class="p" data-group-id="1737242231-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="1737242231-11">(</span><span class="n">Uint64</span><span class="p" data-group-id="1737242231-11">)</span><span class="p" data-group-id="1737242231-12">(</span><span class="sc">$B</span><span class="p" data-group-id="1737242231-12">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="1737242231-13">(</span><span class="p" data-group-id="1737242231-14">(</span><span class="ss">res</span><span class="w"> </span><span class="p">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="1737242231-15">(</span><span class="mi">8</span><span class="o">*</span><span class="nf">sizeof</span><span class="p" data-group-id="1737242231-16">(</span><span class="n">Uint</span><span class="p" data-group-id="1737242231-16">)</span><span class="p" data-group-id="1737242231-15">)</span><span class="p" data-group-id="1737242231-14">)</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1737242231-13">)</span><span class="w"> </span><span class="p" data-group-id="1737242231-17">{</span><span class="w">
│ │ │ +</span><span class="n">BS_SAFE_MUL</span><span class="p" data-group-id="2507289316-7">(</span><span class="n">A</span><span class="p">,</span><span class="w"> </span><span class="n">B</span><span class="p">,</span><span class="w"> </span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="2507289316-7">)</span><span class="w"> </span><span class="p" data-group-id="2507289316-8">{</span><span class="w">
│ │ │ +    </span><span class="n">Uint64</span><span class="w"> </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2507289316-9">(</span><span class="n">Uint64</span><span class="p" data-group-id="2507289316-9">)</span><span class="p" data-group-id="2507289316-10">(</span><span class="sc">$A</span><span class="p" data-group-id="2507289316-10">)</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="2507289316-11">(</span><span class="n">Uint64</span><span class="p" data-group-id="2507289316-11">)</span><span class="p" data-group-id="2507289316-12">(</span><span class="sc">$B</span><span class="p" data-group-id="2507289316-12">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="2507289316-13">(</span><span class="p" data-group-id="2507289316-14">(</span><span class="ss">res</span><span class="w"> </span><span class="p">&gt;&gt;</span><span class="w"> </span><span class="p" data-group-id="2507289316-15">(</span><span class="mi">8</span><span class="o">*</span><span class="nf">sizeof</span><span class="p" data-group-id="2507289316-16">(</span><span class="n">Uint</span><span class="p" data-group-id="2507289316-16">)</span><span class="p" data-group-id="2507289316-15">)</span><span class="p" data-group-id="2507289316-14">)</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="2507289316-13">)</span><span class="w"> </span><span class="p" data-group-id="2507289316-17">{</span><span class="w">
│ │ │          </span><span class="sc">$F</span><span class="ss">ail</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1737242231-17">}</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2507289316-17">}</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">res</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1737242231-8">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2507289316-8">}</span><span class="w">
│ │ │  </span><span class="c1">%endif</span></code></pre><h4>Symbols that are defined in directives</h4><p>The following symbols are always defined.</p><ul><li><code class="inline">ARCH_64</code> - is 1 for a 64-bit machine, and 0 otherwise.</li><li><code class="inline">ARCH_32</code> - is 1 for 32-bit machine, and 0 otherwise.</li></ul><p>The <code class="inline">Makefile</code> for building the emulator currently defines the
│ │ │  following symbols by using the <code class="inline">-D</code> option on the command line for
│ │ │  <strong>beam_makeops</strong>.</p><ul><li><code class="inline">USE_VM_PROBES</code> - 1 if the runtime system is compiled to use VM
│ │ │  probes (support for dtrace or systemtap), 0 otherwise.</li></ul><h3 id="defining-external-generic-instructions" class="section-heading">
│ │ │    <a href="#defining-external-generic-instructions" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -676,15 +676,15 @@
│ │ │  match both source and destination registers.  As an operand in a specific
│ │ │  instruction, it must only be used for a destination register.)</p></li><li><p><code class="inline">o</code> - Overflow.  An untagged integer that does not fit in a machine word.</p></li></ul><h4>Predicates</h4><p>If the constraints described so far is not enough, additional
│ │ │  constraints can be implemented in C and be called as a guard function
│ │ │  on the left-hand side of the transformation.  If the guard function returns
│ │ │  a non-zero value, the matching of the rule will continue, otherwise
│ │ │  the match will fail.  Such guard functions are hereafter called
│ │ │  <em>predicates</em>.</p><p>The most commonly used guard constraints is <code class="inline">equal()</code>. It can be used
│ │ │ -to remove a redundant <code class="inline">move</code> instructio like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="n">R1</span><span class="w"> </span><span class="n">R2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">equal</span><span class="p" data-group-id="5226116339-1">(</span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="5226116339-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">_</span></code></pre><p>or remove a redundant <code class="inline">is_eq_exact</code> instruction like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">is_eq_exact</span><span class="w"> </span><span class="n">Lbl</span><span class="w"> </span><span class="n">Src1</span><span class="w"> </span><span class="n">Src2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">equal</span><span class="p" data-group-id="9102922350-1">(</span><span class="n">Src1</span><span class="p">,</span><span class="w"> </span><span class="n">Src2</span><span class="p" data-group-id="9102922350-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">_</span></code></pre><p>At the time of writing, all predicates are defined in files named
│ │ │ +to remove a redundant <code class="inline">move</code> instructio like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="n">R1</span><span class="w"> </span><span class="n">R2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">equal</span><span class="p" data-group-id="6081079157-1">(</span><span class="n">R1</span><span class="p">,</span><span class="w"> </span><span class="n">R2</span><span class="p" data-group-id="6081079157-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">_</span></code></pre><p>or remove a redundant <code class="inline">is_eq_exact</code> instruction like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">is_eq_exact</span><span class="w"> </span><span class="n">Lbl</span><span class="w"> </span><span class="n">Src1</span><span class="w"> </span><span class="n">Src2</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="nf">equal</span><span class="p" data-group-id="5274266555-1">(</span><span class="n">Src1</span><span class="p">,</span><span class="w"> </span><span class="n">Src2</span><span class="p" data-group-id="5274266555-1">)</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">_</span></code></pre><p>At the time of writing, all predicates are defined in files named
│ │ │  <code class="inline">predicates.tab</code> in several directories.  In <code class="inline">predicates.tab</code> directly
│ │ │  in <code class="inline">$ERL_TOP/erts/emulator/beam</code>, predicates that are used by both the
│ │ │  traditinal emulator and the JIT implementations are contained.
│ │ │  Predicates only used by the emulator can be found in
│ │ │  <code class="inline">emu/predicates.tab</code>.</p><h3 id="a-very-brief-note-on-implementation-of-predicates" class="section-heading">
│ │ │    <a href="#a-very-brief-note-on-implementation-of-predicates" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -692,41 +692,41 @@
│ │ │    <span class="text">A very brief note on implementation of predicates</span>
│ │ │  </h3>
│ │ │  <p>It is outside the scope for this document to describe in detail how
│ │ │  predicates are implemented because it requires knowledge of the
│ │ │  internal loader data structures, but here is quick look at the
│ │ │  implementation of a simple predicate called <code class="inline">literal_is_map()</code>.</p><p>Here is first an example how it is used:</p><p>   is<em>map Fail Lit=q | literal_is_map(Lit) =&gt; </em></p><p>If the <code class="inline">Lit</code> operand is a literal, then the <code class="inline">literal_is_map()</code>
│ │ │  predicate is called to determine whether it is a map literal.
│ │ │ -If it is, the instruction is not needed and can be removed.</p><p><code class="inline">literal_is_map()</code> is implemented like this (in <code class="inline">emu/predicates.tab</code>):</p><pre><code class="makeup erlang" translate="no"><span class="ss">pred</span><span class="p">.</span><span class="nf">literal_is_map</span><span class="p" data-group-id="1262858408-1">(</span><span class="n">Lit</span><span class="p" data-group-id="1262858408-1">)</span><span class="w"> </span><span class="p" data-group-id="1262858408-2">{</span><span class="w">
│ │ │ +If it is, the instruction is not needed and can be removed.</p><p><code class="inline">literal_is_map()</code> is implemented like this (in <code class="inline">emu/predicates.tab</code>):</p><pre><code class="makeup erlang" translate="no"><span class="ss">pred</span><span class="p">.</span><span class="nf">literal_is_map</span><span class="p" data-group-id="0760235341-1">(</span><span class="n">Lit</span><span class="p" data-group-id="0760235341-1">)</span><span class="w"> </span><span class="p" data-group-id="0760235341-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="1262858408-3">(</span><span class="n">Lit</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_q</span><span class="p" data-group-id="1262858408-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">beamfile_get_literal</span><span class="p" data-group-id="1262858408-4">(</span><span class="err">&amp;</span><span class="n">S</span><span class="p">-&gt;</span><span class="ss">beam</span><span class="p">,</span><span class="w"> </span><span class="n">Lit</span><span class="p">.</span><span class="ss">val</span><span class="p" data-group-id="1262858408-4">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">return</span><span class="w"> </span><span class="nf">is_map</span><span class="p" data-group-id="1262858408-5">(</span><span class="ss">term</span><span class="p" data-group-id="1262858408-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1262858408-2">}</span></code></pre><p>The <code class="inline">pred.</code> prefix tells <strong>beam_makeops</strong> that this function is a
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="0760235341-3">(</span><span class="n">Lit</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_q</span><span class="p" data-group-id="0760235341-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">beamfile_get_literal</span><span class="p" data-group-id="0760235341-4">(</span><span class="err">&amp;</span><span class="n">S</span><span class="p">-&gt;</span><span class="ss">beam</span><span class="p">,</span><span class="w"> </span><span class="n">Lit</span><span class="p">.</span><span class="ss">val</span><span class="p" data-group-id="0760235341-4">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">return</span><span class="w"> </span><span class="nf">is_map</span><span class="p" data-group-id="0760235341-5">(</span><span class="ss">term</span><span class="p" data-group-id="0760235341-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0760235341-2">}</span></code></pre><p>The <code class="inline">pred.</code> prefix tells <strong>beam_makeops</strong> that this function is a
│ │ │  predicate.  Without the prefix, it would have been interpreted as the
│ │ │  implementation of an instruction (described in <strong>Defining the
│ │ │  implementation</strong>).</p><p>Predicate functions have a magic variabled called <code class="inline">S</code>, which is a
│ │ │  pointer to a state struct. In the example,
│ │ │  <code class="inline">beamfile_get_literal(&amp;S-&gt;beam, Lit.val);</code> is used to retrieve the actual term
│ │ │  for the literal.</p><p>At the time of writing, the expanded C code generated by
│ │ │ -<strong>beam_makeops</strong> looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">static</span><span class="w"> </span><span class="ss">int</span><span class="w"> </span><span class="nf">literal_is_map</span><span class="p" data-group-id="9859002598-1">(</span><span class="n">LoaderState</span><span class="o">*</span><span class="w"> </span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="n">BeamOpArg</span><span class="w"> </span><span class="n">Lit</span><span class="p" data-group-id="9859002598-1">)</span><span class="w"> </span><span class="p" data-group-id="9859002598-2">{</span><span class="w">
│ │ │ +<strong>beam_makeops</strong> looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">static</span><span class="w"> </span><span class="ss">int</span><span class="w"> </span><span class="nf">literal_is_map</span><span class="p" data-group-id="3852310801-1">(</span><span class="n">LoaderState</span><span class="o">*</span><span class="w"> </span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="n">BeamOpArg</span><span class="w"> </span><span class="n">Lit</span><span class="p" data-group-id="3852310801-1">)</span><span class="w"> </span><span class="p" data-group-id="3852310801-2">{</span><span class="w">
│ │ │    </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="9859002598-3">(</span><span class="n">Lit</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_q</span><span class="p" data-group-id="9859002598-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p">-&gt;</span><span class="ss">literals</span><span class="p" data-group-id="9859002598-4">[</span><span class="n">Lit</span><span class="p">.</span><span class="ss">val</span><span class="p" data-group-id="9859002598-4">]</span><span class="p">.</span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="ss">return</span><span class="w"> </span><span class="nf">is_map</span><span class="p" data-group-id="9859002598-5">(</span><span class="ss">term</span><span class="p" data-group-id="9859002598-5">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9859002598-2">}</span></code></pre><h4>Handling instructions with variable number of operands</h4><p>Some instructions, such as <code class="inline">select_val/3</code>, essentially has a variable
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="3852310801-3">(</span><span class="n">Lit</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_q</span><span class="p" data-group-id="3852310801-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">S</span><span class="p">-&gt;</span><span class="ss">literals</span><span class="p" data-group-id="3852310801-4">[</span><span class="n">Lit</span><span class="p">.</span><span class="ss">val</span><span class="p" data-group-id="3852310801-4">]</span><span class="p">.</span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="ss">return</span><span class="w"> </span><span class="nf">is_map</span><span class="p" data-group-id="3852310801-5">(</span><span class="ss">term</span><span class="p" data-group-id="3852310801-5">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3852310801-2">}</span></code></pre><h4>Handling instructions with variable number of operands</h4><p>Some instructions, such as <code class="inline">select_val/3</code>, essentially has a variable
│ │ │  number of operands.  Such instructions have a <code class="inline">{list,[...]}</code> operand
│ │ │ -as their last operand in the BEAM assembly code.  For example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4835118709-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="4835118709-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4835118709-2">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4835118709-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4835118709-3">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="4835118709-4">{</span><span class="ss">list</span><span class="p">,</span><span class="p" data-group-id="4835118709-5">[</span><span class="p" data-group-id="4835118709-6">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4835118709-6">}</span><span class="p">,</span><span class="p" data-group-id="4835118709-7">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4835118709-7">}</span><span class="p">,</span><span class="p" data-group-id="4835118709-8">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4835118709-8">}</span><span class="p">,</span><span class="p" data-group-id="4835118709-9">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4835118709-9">}</span><span class="p" data-group-id="4835118709-5">]</span><span class="p" data-group-id="4835118709-4">}</span><span class="p" data-group-id="4835118709-1">}</span><span class="p">.</span></code></pre><p>The loader will convert a <code class="inline">{list,[...]}</code> operand to an <code class="inline">u</code> operand whose
│ │ │ +as their last operand in the BEAM assembly code.  For example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="6225198194-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="6225198194-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="6225198194-2">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="6225198194-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="6225198194-3">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="6225198194-4">{</span><span class="ss">list</span><span class="p">,</span><span class="p" data-group-id="6225198194-5">[</span><span class="p" data-group-id="6225198194-6">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="6225198194-6">}</span><span class="p">,</span><span class="p" data-group-id="6225198194-7">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="6225198194-7">}</span><span class="p">,</span><span class="p" data-group-id="6225198194-8">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="6225198194-8">}</span><span class="p">,</span><span class="p" data-group-id="6225198194-9">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="6225198194-9">}</span><span class="p" data-group-id="6225198194-5">]</span><span class="p" data-group-id="6225198194-4">}</span><span class="p" data-group-id="6225198194-1">}</span><span class="p">.</span></code></pre><p>The loader will convert a <code class="inline">{list,[...]}</code> operand to an <code class="inline">u</code> operand whose
│ │ │  value is the number of elements in the list, followed by each element in
│ │ │  the list.  The instruction above would be translated to the following
│ │ │ -generic instruction:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4993534008-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="4993534008-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4993534008-2">}</span><span class="p">,</span><span class="p" data-group-id="4993534008-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4993534008-3">}</span><span class="p">,</span><span class="p" data-group-id="4993534008-4">{</span><span class="ss">u</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4993534008-4">}</span><span class="p">,</span><span class="p" data-group-id="4993534008-5">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4993534008-5">}</span><span class="p">,</span><span class="p" data-group-id="4993534008-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4993534008-6">}</span><span class="p">,</span><span class="p" data-group-id="4993534008-7">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4993534008-7">}</span><span class="p">,</span><span class="p" data-group-id="4993534008-8">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4993534008-8">}</span><span class="p" data-group-id="4993534008-1">}</span></code></pre><p>To match a variable number of arguments we need to use the special
│ │ │ +generic instruction:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1395860786-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="1395860786-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="1395860786-2">}</span><span class="p">,</span><span class="p" data-group-id="1395860786-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="1395860786-3">}</span><span class="p">,</span><span class="p" data-group-id="1395860786-4">{</span><span class="ss">u</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1395860786-4">}</span><span class="p">,</span><span class="p" data-group-id="1395860786-5">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="1395860786-5">}</span><span class="p">,</span><span class="p" data-group-id="1395860786-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="1395860786-6">}</span><span class="p">,</span><span class="p" data-group-id="1395860786-7">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="1395860786-7">}</span><span class="p">,</span><span class="p" data-group-id="1395860786-8">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="1395860786-8">}</span><span class="p" data-group-id="1395860786-1">}</span></code></pre><p>To match a variable number of arguments we need to use the special
│ │ │  operand type <code class="inline">*</code> like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">select_val</span><span class="w"> </span><span class="n">Src</span><span class="o">=</span><span class="ss">aiq</span><span class="w"> </span><span class="n">Fail</span><span class="o">=</span><span class="ss">f</span><span class="w"> </span><span class="n">Size</span><span class="o">=</span><span class="ss">u</span><span class="w"> </span><span class="n">List</span><span class="o">=</span><span class="o">*</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │      </span><span class="ss">i_const_select_val</span><span class="w"> </span><span class="n">Src</span><span class="w"> </span><span class="n">Fail</span><span class="w"> </span><span class="n">Size</span><span class="w"> </span><span class="n">List</span></code></pre><p>This transformation renames a <code class="inline">select_val/3</code> instruction
│ │ │  with a constant source operand to <code class="inline">i_const_select_val/3</code>.</p><h4>Constructing new instructions on the right-hand side</h4><p>The most common operand on the right-hand side is a variable that was
│ │ │  bound while matching the pattern on the left-hand side.  For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">trim</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">Remaining</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="ss">i_trim</span><span class="w"> </span><span class="n">N</span></code></pre><p>An operand can also be a type letter to construct an operand of that
│ │ │  type.  Each type has a default value.  For example, the type <code class="inline">x</code> has
│ │ │  the default value 1023, which is the highest X register.  That makes
│ │ │  <code class="inline">x</code> on the right-hand side a convenient shortcut for a temporary X
│ │ │ @@ -746,53 +746,53 @@
│ │ │  transformation rule.</p><ul><li><p><code class="inline">u</code> - Construct an untagged integer.  The default value is 0.</p></li><li><p><code class="inline">x</code> - X register.  The default value is 1023.  That makes <code class="inline">x</code> convenient to
│ │ │  use as a temporary X register.</p></li><li><p><code class="inline">y</code> - Y register.  The default value is 0.</p></li><li><p><code class="inline">l</code> - Floating point register number.  The default value is 0.</p></li><li><p><code class="inline">i</code> - Tagged literal integer.  The default value is 0.</p></li><li><p><code class="inline">a</code> - Tagged atom.  The default value is the empty atom (<code class="inline">am_Empty</code>).</p></li><li><p><code class="inline">p</code> - Zero failure label.</p></li><li><p><code class="inline">n</code> - NIL (<code class="inline">[]</code>, the empty list).</p></li></ul><h4>Function call on the right-hand side</h4><p>Transformations that are not possible to describe with the rule
│ │ │  language as described here can be implemented as a generator function
│ │ │  in C and called from the right-hand side of a transformation.  The left-hand
│ │ │  side of the transformation will perform the match and bind operands to
│ │ │  variables.  The variables can then be passed to a generator function
│ │ │  on the right-hand side.  For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">bif2</span><span class="w"> </span><span class="n">Fail</span><span class="o">=</span><span class="ss">j</span><span class="w"> </span><span class="ss">u</span><span class="sc">$b</span><span class="nc">if</span><span class="p">:</span><span class="nc">erlang</span><span class="p">:</span><span class="nb">element</span><span class="p">/</span><span class="mi">2</span><span class="w"> </span><span class="n">Index</span><span class="o">=</span><span class="ss">s</span><span class="w"> </span><span class="n">Tuple</span><span class="o">=</span><span class="ss">xy</span><span class="w"> </span><span class="n">Dst</span><span class="o">=</span><span class="ss">d</span><span class="w"> </span><span class="p">=&gt;</span><span class="w">
│ │ │ -    </span><span class="nf">element</span><span class="p" data-group-id="2673722266-1">(</span><span class="n">Jump</span><span class="p">,</span><span class="w"> </span><span class="n">Index</span><span class="p">,</span><span class="w"> </span><span class="n">Tuple</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="2673722266-1">)</span></code></pre><p>This transformation rule matches a call to the BIF <a href="erlang.html#element/2"><code class="inline">element/2</code></a>.
│ │ │ +    </span><span class="nf">element</span><span class="p" data-group-id="0266312072-1">(</span><span class="n">Jump</span><span class="p">,</span><span class="w"> </span><span class="n">Index</span><span class="p">,</span><span class="w"> </span><span class="n">Tuple</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="0266312072-1">)</span></code></pre><p>This transformation rule matches a call to the BIF <a href="erlang.html#element/2"><code class="inline">element/2</code></a>.
│ │ │  The operands will be captured and the generator function <code class="inline">element()</code> will
│ │ │  be called.</p><p>The <code class="inline">element()</code> generator will produce one of two instructions
│ │ │  depending on <code class="inline">Index</code>.  If <code class="inline">Index</code> is an integer in the range from 1 up
│ │ │  to the maximum tuple size, the instruction <code class="inline">i_fast_element/2</code> will be
│ │ │  produced, otherwise the instruction <code class="inline">i_element/4</code> will be produced.
│ │ │  The corresponding specific instructions are:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_fast_element</span><span class="w"> </span><span class="ss">xy</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_element</span><span class="w"> </span><span class="ss">xy</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The <code class="inline">i_fast_element/2</code> instruction is faster because the tuple is
│ │ │  already an untagged integer.  It also knows that the index is at least
│ │ │  1, so it does not have to test for that.  The <code class="inline">i_element/4</code>
│ │ │  instruction will have to fetch the index from a register, test that it
│ │ │  is an integer, and untag the integer.</p><p>At the time of writing, all generators functions were defined in files
│ │ │  named <code class="inline">generators.tab</code> in several directories (in the same directories
│ │ │  as the <code class="inline">predicates.tab</code> files).</p><p>It is outside the scope of this document to describe in detail how
│ │ │  generator functions are written, but here is the implementation of
│ │ │ -<code class="inline">element()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">gen</span><span class="p">.</span><span class="nf">element</span><span class="p" data-group-id="1060006117-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Index</span><span class="p">,</span><span class="w"> </span><span class="n">Tuple</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="1060006117-1">)</span><span class="w"> </span><span class="p" data-group-id="1060006117-2">{</span><span class="w">
│ │ │ +<code class="inline">element()</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">gen</span><span class="p">.</span><span class="nf">element</span><span class="p" data-group-id="2109630519-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Index</span><span class="p">,</span><span class="w"> </span><span class="n">Tuple</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="2109630519-1">)</span><span class="w"> </span><span class="p" data-group-id="2109630519-2">{</span><span class="w">
│ │ │      </span><span class="n">BeamOp</span><span class="o">*</span><span class="w"> </span><span class="ss">op</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="sc">$N</span><span class="nf">ewBeamOp</span><span class="p" data-group-id="1060006117-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="ss">op</span><span class="p" data-group-id="1060006117-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$N</span><span class="nf">ewBeamOp</span><span class="p" data-group-id="2109630519-3">(</span><span class="n">S</span><span class="p">,</span><span class="w"> </span><span class="ss">op</span><span class="p" data-group-id="2109630519-3">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="1060006117-4">(</span><span class="n">Index</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_i</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w"> </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="2109630519-4">(</span><span class="n">Index</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_i</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w"> </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w">
│ │ │          </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">&lt;=</span><span class="w"> </span><span class="n">ERTS_MAX_TUPLE_SIZE</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="1060006117-5">(</span><span class="n">Tuple</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Tuple</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_y</span><span class="p" data-group-id="1060006117-5">)</span><span class="p" data-group-id="1060006117-4">)</span><span class="w"> </span><span class="p" data-group-id="1060006117-6">{</span><span class="w">
│ │ │ -        </span><span class="sc">$B</span><span class="nf">eamOpNameArity</span><span class="p" data-group-id="1060006117-7">(</span><span class="ss">op</span><span class="p">,</span><span class="w"> </span><span class="ss">i_fast_element</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1060006117-7">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1060006117-8">[</span><span class="mi">0</span><span class="p" data-group-id="1060006117-8">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Tuple</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1060006117-9">[</span><span class="mi">1</span><span class="p" data-group-id="1060006117-9">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Fail</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1060006117-10">[</span><span class="mi">2</span><span class="p" data-group-id="1060006117-10">]</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">TAG_u</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1060006117-11">[</span><span class="mi">2</span><span class="p" data-group-id="1060006117-11">]</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1060006117-12">[</span><span class="mi">3</span><span class="p" data-group-id="1060006117-12">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dst</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1060006117-6">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="1060006117-13">{</span><span class="w">
│ │ │ -        </span><span class="sc">$B</span><span class="nf">eamOpNameArity</span><span class="p" data-group-id="1060006117-14">(</span><span class="ss">op</span><span class="p">,</span><span class="w"> </span><span class="ss">i_element</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="1060006117-14">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1060006117-15">[</span><span class="mi">0</span><span class="p" data-group-id="1060006117-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Tuple</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1060006117-16">[</span><span class="mi">1</span><span class="p" data-group-id="1060006117-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Fail</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1060006117-17">[</span><span class="mi">2</span><span class="p" data-group-id="1060006117-17">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Index</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="1060006117-18">[</span><span class="mi">3</span><span class="p" data-group-id="1060006117-18">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dst</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1060006117-13">}</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="2109630519-5">(</span><span class="n">Tuple</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_x</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="n">Tuple</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">TAG_y</span><span class="p" data-group-id="2109630519-5">)</span><span class="p" data-group-id="2109630519-4">)</span><span class="w"> </span><span class="p" data-group-id="2109630519-6">{</span><span class="w">
│ │ │ +        </span><span class="sc">$B</span><span class="nf">eamOpNameArity</span><span class="p" data-group-id="2109630519-7">(</span><span class="ss">op</span><span class="p">,</span><span class="w"> </span><span class="ss">i_fast_element</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="2109630519-7">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="2109630519-8">[</span><span class="mi">0</span><span class="p" data-group-id="2109630519-8">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Tuple</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="2109630519-9">[</span><span class="mi">1</span><span class="p" data-group-id="2109630519-9">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Fail</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="2109630519-10">[</span><span class="mi">2</span><span class="p" data-group-id="2109630519-10">]</span><span class="p">.</span><span class="ss">type</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">TAG_u</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="2109630519-11">[</span><span class="mi">2</span><span class="p" data-group-id="2109630519-11">]</span><span class="p">.</span><span class="ss">val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Index</span><span class="p">.</span><span class="ss">val</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="2109630519-12">[</span><span class="mi">3</span><span class="p" data-group-id="2109630519-12">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dst</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2109630519-6">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="2109630519-13">{</span><span class="w">
│ │ │ +        </span><span class="sc">$B</span><span class="nf">eamOpNameArity</span><span class="p" data-group-id="2109630519-14">(</span><span class="ss">op</span><span class="p">,</span><span class="w"> </span><span class="ss">i_element</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p" data-group-id="2109630519-14">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="2109630519-15">[</span><span class="mi">0</span><span class="p" data-group-id="2109630519-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Tuple</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="2109630519-16">[</span><span class="mi">1</span><span class="p" data-group-id="2109630519-16">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Fail</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="2109630519-17">[</span><span class="mi">2</span><span class="p" data-group-id="2109630519-17">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Index</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="ss">op</span><span class="p">-&gt;</span><span class="ss">a</span><span class="p" data-group-id="2109630519-18">[</span><span class="mi">3</span><span class="p" data-group-id="2109630519-18">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Dst</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="2109630519-13">}</span><span class="w">
│ │ │  
│ │ │      </span><span class="ss">return</span><span class="w"> </span><span class="ss">op</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1060006117-2">}</span></code></pre><p>The <code class="inline">gen.</code> prefix tells <strong>beam_makeops</strong> that this function is a
│ │ │ +</span><span class="p" data-group-id="2109630519-2">}</span></code></pre><p>The <code class="inline">gen.</code> prefix tells <strong>beam_makeops</strong> that this function is a
│ │ │  generator.  Without the prefix, it would have been interpreted as the
│ │ │  implementation of an instruction (described in <strong>Defining the
│ │ │  implementation</strong>).</p><p>Generator functions have a magic variabled called <code class="inline">S</code>, which is a
│ │ │  pointer to a state struct.  In the example, <code class="inline">S</code> is used in the invocation
│ │ │  of the <code class="inline">NewBeamOp</code> macro.</p><h3 id="defining-the-implementation" class="section-heading">
│ │ │    <a href="#defining-the-implementation" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │ @@ -814,473 +814,473 @@
│ │ │  </span><span class="ss">msg_instrs</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │  </span><span class="ss">select_instrs</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │  </span><span class="ss">trace_instrs</span><span class="p">.</span><span class="ss">tab</span></code></pre><p>There is also a file that only contains macro definitions:</p><pre><code class="makeup erlang" translate="no"><span class="ss">macros</span><span class="p">.</span><span class="ss">tab</span></code></pre><p>The syntax of each file is similar to C code.  In fact, most of
│ │ │  the contents <em>is</em> C code, interspersed with macro invocations.</p><p>To allow Emacs to auto-indent the code, each file starts with the
│ │ │  following line:</p><pre><code class="makeup erlang" translate="no"><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="o">-</span><span class="o">*</span><span class="o">-</span><span class="w"> </span><span class="ss">c</span><span class="w"> </span><span class="o">-</span><span class="o">*</span><span class="o">-</span></code></pre><p>To avoid messing up the indentation, all comments are written
│ │ │  as C++ style comments (<code class="inline">//</code>) instead of <code class="inline">#</code>.  Note that a comment
│ │ │  must start at the beginning of a line.</p><p>The meat of an instruction definition file are macro definitions.
│ │ │ -We have seen this macro definition before:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="8956642730-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="8956642730-1">)</span><span class="w"> </span><span class="p" data-group-id="8956642730-2">{</span><span class="w">
│ │ │ +We have seen this macro definition before:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="4131792684-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="4131792684-1">)</span><span class="w"> </span><span class="p" data-group-id="4131792684-2">{</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8956642730-2">}</span></code></pre><p>A macro definitions must start at the beginning of the line (no spaces
│ │ │ +</span><span class="p" data-group-id="4131792684-2">}</span></code></pre><p>A macro definitions must start at the beginning of the line (no spaces
│ │ │  allowed), the opening curly bracket must be on the same line, and the
│ │ │  finishing curly bracket must be at the beginning of a line.  It is
│ │ │  recommended that the macro body is properly indented.</p><p>As a convention, the macro arguments in the head all start with an
│ │ │  uppercase letter.  In the body, the macro arguments can be expanded
│ │ │  by preceding them with <code class="inline">$</code>.</p><p>A macro definition whose name and arity matches a family of
│ │ │  specific instructions is assumed to be the implementation of that
│ │ │  instruction.</p><p>A macro can also be invoked from within another macro.  For example,
│ │ │  <code class="inline">move_deallocate_return/2</code> avoids repeating code by invoking
│ │ │ -<code class="inline">$deallocate_return()</code> as a macro:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move_deallocate_return</span><span class="p" data-group-id="9056355933-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Deallocate</span><span class="p" data-group-id="9056355933-1">)</span><span class="w"> </span><span class="p" data-group-id="9056355933-2">{</span><span class="w">
│ │ │ -    </span><span class="nf">x</span><span class="p" data-group-id="9056355933-3">(</span><span class="mi">0</span><span class="p" data-group-id="9056355933-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="sc">$d</span><span class="nf">eallocate_return</span><span class="p" data-group-id="9056355933-4">(</span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p" data-group-id="9056355933-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9056355933-2">}</span></code></pre><p>Here is the definition of <code class="inline">deallocate_return/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">deallocate_return</span><span class="p" data-group-id="2756643351-1">(</span><span class="n">Deallocate</span><span class="p" data-group-id="2756643351-1">)</span><span class="w"> </span><span class="p" data-group-id="2756643351-2">{</span><span class="w">
│ │ │ +<code class="inline">$deallocate_return()</code> as a macro:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move_deallocate_return</span><span class="p" data-group-id="9308961438-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Deallocate</span><span class="p" data-group-id="9308961438-1">)</span><span class="w"> </span><span class="p" data-group-id="9308961438-2">{</span><span class="w">
│ │ │ +    </span><span class="nf">x</span><span class="p" data-group-id="9308961438-3">(</span><span class="mi">0</span><span class="p" data-group-id="9308961438-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$d</span><span class="nf">eallocate_return</span><span class="p" data-group-id="9308961438-4">(</span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p" data-group-id="9308961438-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9308961438-2">}</span></code></pre><p>Here is the definition of <code class="inline">deallocate_return/1</code>:</p><pre><code class="makeup erlang" translate="no"><span class="nf">deallocate_return</span><span class="p" data-group-id="0784151924-1">(</span><span class="n">Deallocate</span><span class="p" data-group-id="0784151924-1">)</span><span class="w"> </span><span class="p" data-group-id="0784151924-2">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_next</span><span class="w">
│ │ │      </span><span class="ss">int</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">SET_I</span><span class="p" data-group-id="2756643351-3">(</span><span class="p" data-group-id="2756643351-4">(</span><span class="n">BeamInstr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="2756643351-4">)</span><span class="w"> </span><span class="nf">cp_val</span><span class="p" data-group-id="2756643351-5">(</span><span class="o">*</span><span class="n">E</span><span class="p" data-group-id="2756643351-5">)</span><span class="p" data-group-id="2756643351-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ADD_BYTE_OFFSET</span><span class="p" data-group-id="2756643351-6">(</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="p" data-group-id="2756643351-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">CHECK_TERM</span><span class="p" data-group-id="2756643351-7">(</span><span class="nf">x</span><span class="p" data-group-id="2756643351-8">(</span><span class="mi">0</span><span class="p" data-group-id="2756643351-8">)</span><span class="p" data-group-id="2756643351-7">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">SET_I</span><span class="p" data-group-id="0784151924-3">(</span><span class="p" data-group-id="0784151924-4">(</span><span class="n">BeamInstr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="0784151924-4">)</span><span class="w"> </span><span class="nf">cp_val</span><span class="p" data-group-id="0784151924-5">(</span><span class="o">*</span><span class="n">E</span><span class="p" data-group-id="0784151924-5">)</span><span class="p" data-group-id="0784151924-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ADD_BYTE_OFFSET</span><span class="p" data-group-id="0784151924-6">(</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="p" data-group-id="0784151924-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">CHECK_TERM</span><span class="p" data-group-id="0784151924-7">(</span><span class="nf">x</span><span class="p" data-group-id="0784151924-8">(</span><span class="mi">0</span><span class="p" data-group-id="0784151924-8">)</span><span class="p" data-group-id="0784151924-7">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">DispatchReturn</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2756643351-2">}</span></code></pre><p>The expanded code for <code class="inline">move_deallocate_return</code> will look this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="3484082634-1">(</span><span class="ss">move_deallocate_return_cQ</span><span class="p" data-group-id="3484082634-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3484082634-2">{</span><span class="w">
│ │ │ -  </span><span class="nf">x</span><span class="p" data-group-id="3484082634-3">(</span><span class="mi">0</span><span class="p" data-group-id="3484082634-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="3484082634-4">[</span><span class="mi">1</span><span class="p" data-group-id="3484082634-4">]</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="ss">do</span><span class="w"> </span><span class="p" data-group-id="3484082634-5">{</span><span class="w">
│ │ │ -    </span><span class="ss">int</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Qb</span><span class="p" data-group-id="3484082634-6">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="3484082634-7">(</span><span class="n">I</span><span class="p" data-group-id="3484082634-8">[</span><span class="mi">0</span><span class="p" data-group-id="3484082634-8">]</span><span class="p" data-group-id="3484082634-7">)</span><span class="p" data-group-id="3484082634-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">SET_I</span><span class="p" data-group-id="3484082634-9">(</span><span class="p" data-group-id="3484082634-10">(</span><span class="n">BeamInstr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="3484082634-10">)</span><span class="w"> </span><span class="nf">cp_val</span><span class="p" data-group-id="3484082634-11">(</span><span class="o">*</span><span class="n">E</span><span class="p" data-group-id="3484082634-11">)</span><span class="p" data-group-id="3484082634-9">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ADD_BYTE_OFFSET</span><span class="p" data-group-id="3484082634-12">(</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="p" data-group-id="3484082634-12">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">CHECK_TERM</span><span class="p" data-group-id="3484082634-13">(</span><span class="nf">x</span><span class="p" data-group-id="3484082634-14">(</span><span class="mi">0</span><span class="p" data-group-id="3484082634-14">)</span><span class="p" data-group-id="3484082634-13">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0784151924-2">}</span></code></pre><p>The expanded code for <code class="inline">move_deallocate_return</code> will look this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="1032119191-1">(</span><span class="ss">move_deallocate_return_cQ</span><span class="p" data-group-id="1032119191-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1032119191-2">{</span><span class="w">
│ │ │ +  </span><span class="nf">x</span><span class="p" data-group-id="1032119191-3">(</span><span class="mi">0</span><span class="p" data-group-id="1032119191-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="1032119191-4">[</span><span class="mi">1</span><span class="p" data-group-id="1032119191-4">]</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="ss">do</span><span class="w"> </span><span class="p" data-group-id="1032119191-5">{</span><span class="w">
│ │ │ +    </span><span class="ss">int</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Qb</span><span class="p" data-group-id="1032119191-6">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="1032119191-7">(</span><span class="n">I</span><span class="p" data-group-id="1032119191-8">[</span><span class="mi">0</span><span class="p" data-group-id="1032119191-8">]</span><span class="p" data-group-id="1032119191-7">)</span><span class="p" data-group-id="1032119191-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">SET_I</span><span class="p" data-group-id="1032119191-9">(</span><span class="p" data-group-id="1032119191-10">(</span><span class="n">BeamInstr</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="1032119191-10">)</span><span class="w"> </span><span class="nf">cp_val</span><span class="p" data-group-id="1032119191-11">(</span><span class="o">*</span><span class="n">E</span><span class="p" data-group-id="1032119191-11">)</span><span class="p" data-group-id="1032119191-9">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ADD_BYTE_OFFSET</span><span class="p" data-group-id="1032119191-12">(</span><span class="n">E</span><span class="p">,</span><span class="w"> </span><span class="ss">words_to_pop</span><span class="p" data-group-id="1032119191-12">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">CHECK_TERM</span><span class="p" data-group-id="1032119191-13">(</span><span class="nf">x</span><span class="p" data-group-id="1032119191-14">(</span><span class="mi">0</span><span class="p" data-group-id="1032119191-14">)</span><span class="p" data-group-id="1032119191-13">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">DispatchReturn</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="3484082634-5">}</span><span class="w"> </span><span class="nf">while</span><span class="w"> </span><span class="p" data-group-id="3484082634-15">(</span><span class="mi">0</span><span class="p" data-group-id="3484082634-15">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3484082634-2">}</span></code></pre><p>When expanding macros, <strong>beam_makeops</strong> wraps the expansion in a
│ │ │ +  </span><span class="p" data-group-id="1032119191-5">}</span><span class="w"> </span><span class="nf">while</span><span class="w"> </span><span class="p" data-group-id="1032119191-15">(</span><span class="mi">0</span><span class="p" data-group-id="1032119191-15">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1032119191-2">}</span></code></pre><p>When expanding macros, <strong>beam_makeops</strong> wraps the expansion in a
│ │ │  <code class="inline">do</code>/<code class="inline">while</code> wrapper unless <strong>beam_makeops</strong> can clearly see that no
│ │ │  wrapper is needed.  In this case, the wrapper is needed.</p><p>Note that arguments for macros cannot be complex expressions, because
│ │ │  the arguments are split on <code class="inline">,</code>.  For example, the following would
│ │ │  not work because <strong>beam_makeops</strong> would split the expression into
│ │ │ -two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$d</span><span class="nf">eallocate_return</span><span class="p" data-group-id="7089084062-1">(</span><span class="nf">get_deallocation</span><span class="p" data-group-id="7089084062-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p" data-group-id="7089084062-2">)</span><span class="p" data-group-id="7089084062-1">)</span><span class="p">;</span></code></pre><h4>Code generation directives</h4><p>Within macro definitions, <code class="inline">//</code> comments are in general not treated
│ │ │ +two arguments:</p><pre><code class="makeup erlang" translate="no"><span class="sc">$d</span><span class="nf">eallocate_return</span><span class="p" data-group-id="5267692646-1">(</span><span class="nf">get_deallocation</span><span class="p" data-group-id="5267692646-2">(</span><span class="ss">y</span><span class="p">,</span><span class="w"> </span><span class="sc">$D</span><span class="ss">eallocate</span><span class="p" data-group-id="5267692646-2">)</span><span class="p" data-group-id="5267692646-1">)</span><span class="p">;</span></code></pre><h4>Code generation directives</h4><p>Within macro definitions, <code class="inline">//</code> comments are in general not treated
│ │ │  specially.  They will be copied to the file with the generated code
│ │ │  along with the rest of code in the body.</p><p>However, there is an exception. Within a macro definition, a line that
│ │ │  starts with whitespace followed by <code class="inline">//|</code> is treated specially.  The
│ │ │  rest of the line is assumed to contain directives to control code
│ │ │  generation.</p><p>Currently, two code generation directives are recognized:</p><ul><li><code class="inline">-no_prefetch</code></li><li><code class="inline">-no_next</code></li></ul><h5>The -no_prefetch directive</h5><p>To see what <code class="inline">-no_prefetch</code> does, let's first look at the default code
│ │ │ -generation.  Here is the code generated for <code class="inline">move_cx</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="9255131967-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="9255131967-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9255131967-2">{</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="9255131967-3">(</span><span class="n">I</span><span class="p" data-group-id="9255131967-4">[</span><span class="mi">2</span><span class="p" data-group-id="9255131967-4">]</span><span class="p" data-group-id="9255131967-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="nf">xb</span><span class="p" data-group-id="9255131967-5">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="9255131967-6">(</span><span class="n">I</span><span class="p" data-group-id="9255131967-7">[</span><span class="mi">0</span><span class="p" data-group-id="9255131967-7">]</span><span class="p" data-group-id="9255131967-6">)</span><span class="p" data-group-id="9255131967-5">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="9255131967-8">[</span><span class="mi">1</span><span class="p" data-group-id="9255131967-8">]</span><span class="p">;</span><span class="w">
│ │ │ +generation.  Here is the code generated for <code class="inline">move_cx</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="1060268727-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="1060268727-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1060268727-2">{</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="1060268727-3">(</span><span class="n">I</span><span class="p" data-group-id="1060268727-4">[</span><span class="mi">2</span><span class="p" data-group-id="1060268727-4">]</span><span class="p" data-group-id="1060268727-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="nf">xb</span><span class="p" data-group-id="1060268727-5">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="1060268727-6">(</span><span class="n">I</span><span class="p" data-group-id="1060268727-7">[</span><span class="mi">0</span><span class="p" data-group-id="1060268727-7">]</span><span class="p" data-group-id="1060268727-6">)</span><span class="p" data-group-id="1060268727-5">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="1060268727-8">[</span><span class="mi">1</span><span class="p" data-group-id="1060268727-8">]</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="9255131967-9">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="9255131967-10">(</span><span class="ss">next_pf</span><span class="p" data-group-id="9255131967-10">)</span><span class="p" data-group-id="9255131967-9">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="9255131967-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="9255131967-11">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9255131967-2">}</span></code></pre><p>Note that the very first thing done is to fetch the address to the
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="1060268727-9">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="1060268727-10">(</span><span class="ss">next_pf</span><span class="p" data-group-id="1060268727-10">)</span><span class="p" data-group-id="1060268727-9">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="1060268727-11">(</span><span class="ss">next_pf</span><span class="p" data-group-id="1060268727-11">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1060268727-2">}</span></code></pre><p>Note that the very first thing done is to fetch the address to the
│ │ │  next instruction.  The reason is that it usually improves performance.</p><p>Just as a demonstration, we can add a <code class="inline">-no_prefetch</code> directive to
│ │ │ -the <code class="inline">move/2</code> instruction:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="2349179440-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="2349179440-1">)</span><span class="w"> </span><span class="p" data-group-id="2349179440-2">{</span><span class="w">
│ │ │ +the <code class="inline">move/2</code> instruction:</p><pre><code class="makeup erlang" translate="no"><span class="nf">move</span><span class="p" data-group-id="0587400839-1">(</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="0587400839-1">)</span><span class="w"> </span><span class="p" data-group-id="0587400839-2">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_prefetch</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2349179440-2">}</span></code></pre><p>We can see that the prefetch is no longer done:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="6063852824-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="6063852824-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6063852824-2">{</span><span class="w">
│ │ │ -  </span><span class="nf">xb</span><span class="p" data-group-id="6063852824-3">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6063852824-4">(</span><span class="n">I</span><span class="p" data-group-id="6063852824-5">[</span><span class="mi">0</span><span class="p" data-group-id="6063852824-5">]</span><span class="p" data-group-id="6063852824-4">)</span><span class="p" data-group-id="6063852824-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="6063852824-6">[</span><span class="mi">1</span><span class="p" data-group-id="6063852824-6">]</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0587400839-2">}</span></code></pre><p>We can see that the prefetch is no longer done:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="0266261264-1">(</span><span class="ss">move_cx</span><span class="p" data-group-id="0266261264-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0266261264-2">{</span><span class="w">
│ │ │ +  </span><span class="nf">xb</span><span class="p" data-group-id="0266261264-3">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="0266261264-4">(</span><span class="n">I</span><span class="p" data-group-id="0266261264-5">[</span><span class="mi">0</span><span class="p" data-group-id="0266261264-5">]</span><span class="p" data-group-id="0266261264-4">)</span><span class="p" data-group-id="0266261264-3">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="0266261264-6">[</span><span class="mi">1</span><span class="p" data-group-id="0266261264-6">]</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="6063852824-7">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="6063852824-8">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="6063852824-8">)</span><span class="p" data-group-id="6063852824-7">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">Goto</span><span class="p" data-group-id="6063852824-9">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="6063852824-9">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6063852824-2">}</span></code></pre><p>When would we want to turn off the prefetch in practice?</p><p>In instructions that will not always execute the next instruction.
│ │ │ -For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">is_atom</span><span class="p" data-group-id="4726581332-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="4726581332-1">)</span><span class="w"> </span><span class="p" data-group-id="4726581332-2">{</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="4726581332-3">(</span><span class="nf">is_not_atom</span><span class="p" data-group-id="4726581332-4">(</span><span class="sc">$S</span><span class="ss">rc</span><span class="p" data-group-id="4726581332-4">)</span><span class="p" data-group-id="4726581332-3">)</span><span class="w"> </span><span class="p" data-group-id="4726581332-5">{</span><span class="w">
│ │ │ -        </span><span class="sc">$F</span><span class="n">AIL</span><span class="p" data-group-id="4726581332-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="4726581332-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="4726581332-5">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4726581332-2">}</span><span class="w">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="0266261264-7">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="0266261264-8">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="0266261264-8">)</span><span class="p" data-group-id="0266261264-7">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">Goto</span><span class="p" data-group-id="0266261264-9">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="0266261264-9">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="0266261264-2">}</span></code></pre><p>When would we want to turn off the prefetch in practice?</p><p>In instructions that will not always execute the next instruction.
│ │ │ +For example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">is_atom</span><span class="p" data-group-id="9058332334-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="9058332334-1">)</span><span class="w"> </span><span class="p" data-group-id="9058332334-2">{</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="9058332334-3">(</span><span class="nf">is_not_atom</span><span class="p" data-group-id="9058332334-4">(</span><span class="sc">$S</span><span class="ss">rc</span><span class="p" data-group-id="9058332334-4">)</span><span class="p" data-group-id="9058332334-3">)</span><span class="w"> </span><span class="p" data-group-id="9058332334-5">{</span><span class="w">
│ │ │ +        </span><span class="sc">$F</span><span class="n">AIL</span><span class="p" data-group-id="9058332334-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="9058332334-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="9058332334-5">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9058332334-2">}</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">From</span><span class="w"> </span><span class="ss">macros</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │ -</span><span class="n">FAIL</span><span class="p" data-group-id="4726581332-7">(</span><span class="n">Fail</span><span class="p" data-group-id="4726581332-7">)</span><span class="w"> </span><span class="p" data-group-id="4726581332-8">{</span><span class="w">
│ │ │ +</span><span class="n">FAIL</span><span class="p" data-group-id="9058332334-7">(</span><span class="n">Fail</span><span class="p" data-group-id="9058332334-7">)</span><span class="w"> </span><span class="p" data-group-id="9058332334-8">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_prefetch</span><span class="w">
│ │ │ -    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="4726581332-9">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="4726581332-9">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">Goto</span><span class="p" data-group-id="4726581332-10">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="4726581332-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4726581332-8">}</span></code></pre><p><code class="inline">is_atom/2</code> may either execute the next instruction (if the second
│ │ │ -operand is an atom) or branch to the failure label.</p><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="1151244533-1">(</span><span class="ss">is_atom_fx</span><span class="p" data-group-id="1151244533-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1151244533-2">{</span><span class="w">
│ │ │ -  </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="1151244533-3">(</span><span class="nf">is_not_atom</span><span class="p" data-group-id="1151244533-4">(</span><span class="nf">xb</span><span class="p" data-group-id="1151244533-5">(</span><span class="n">I</span><span class="p" data-group-id="1151244533-6">[</span><span class="mi">1</span><span class="p" data-group-id="1151244533-6">]</span><span class="p" data-group-id="1151244533-5">)</span><span class="p" data-group-id="1151244533-4">)</span><span class="p" data-group-id="1151244533-3">)</span><span class="w"> </span><span class="p" data-group-id="1151244533-7">{</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="1151244533-8">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="1151244533-9">(</span><span class="o">*</span><span class="p" data-group-id="1151244533-10">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="1151244533-11">(</span><span class="nf">fb</span><span class="p" data-group-id="1151244533-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="1151244533-13">(</span><span class="n">I</span><span class="p" data-group-id="1151244533-14">[</span><span class="mi">0</span><span class="p" data-group-id="1151244533-14">]</span><span class="p" data-group-id="1151244533-13">)</span><span class="p" data-group-id="1151244533-12">)</span><span class="p" data-group-id="1151244533-11">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1151244533-10">)</span><span class="p" data-group-id="1151244533-9">)</span><span class="p" data-group-id="1151244533-8">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="1151244533-15">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="1151244533-16">(</span><span class="n">I</span><span class="p" data-group-id="1151244533-17">[</span><span class="mi">0</span><span class="p" data-group-id="1151244533-17">]</span><span class="p" data-group-id="1151244533-16">)</span><span class="p" data-group-id="1151244533-15">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">Goto</span><span class="p" data-group-id="1151244533-18">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="1151244533-18">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="1151244533-7">}</span><span class="w">
│ │ │ +    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="9058332334-9">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="9058332334-9">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">Goto</span><span class="p" data-group-id="9058332334-10">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="9058332334-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9058332334-8">}</span></code></pre><p><code class="inline">is_atom/2</code> may either execute the next instruction (if the second
│ │ │ +operand is an atom) or branch to the failure label.</p><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="4987249115-1">(</span><span class="ss">is_atom_fx</span><span class="p" data-group-id="4987249115-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4987249115-2">{</span><span class="w">
│ │ │ +  </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="4987249115-3">(</span><span class="nf">is_not_atom</span><span class="p" data-group-id="4987249115-4">(</span><span class="nf">xb</span><span class="p" data-group-id="4987249115-5">(</span><span class="n">I</span><span class="p" data-group-id="4987249115-6">[</span><span class="mi">1</span><span class="p" data-group-id="4987249115-6">]</span><span class="p" data-group-id="4987249115-5">)</span><span class="p" data-group-id="4987249115-4">)</span><span class="p" data-group-id="4987249115-3">)</span><span class="w"> </span><span class="p" data-group-id="4987249115-7">{</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="4987249115-8">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="4987249115-9">(</span><span class="o">*</span><span class="p" data-group-id="4987249115-10">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="4987249115-11">(</span><span class="nf">fb</span><span class="p" data-group-id="4987249115-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="4987249115-13">(</span><span class="n">I</span><span class="p" data-group-id="4987249115-14">[</span><span class="mi">0</span><span class="p" data-group-id="4987249115-14">]</span><span class="p" data-group-id="4987249115-13">)</span><span class="p" data-group-id="4987249115-12">)</span><span class="p" data-group-id="4987249115-11">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="4987249115-10">)</span><span class="p" data-group-id="4987249115-9">)</span><span class="p" data-group-id="4987249115-8">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="4987249115-15">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="4987249115-16">(</span><span class="n">I</span><span class="p" data-group-id="4987249115-17">[</span><span class="mi">0</span><span class="p" data-group-id="4987249115-17">]</span><span class="p" data-group-id="4987249115-16">)</span><span class="p" data-group-id="4987249115-15">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">Goto</span><span class="p" data-group-id="4987249115-18">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="4987249115-18">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="4987249115-7">}</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="1151244533-19">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="1151244533-20">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="1151244533-20">)</span><span class="p" data-group-id="1151244533-19">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">Goto</span><span class="p" data-group-id="1151244533-21">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="1151244533-21">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1151244533-2">}</span></code></pre><h5>The -no_next directive</h5><p>Next we will look at when the <code class="inline">-no_next</code> directive can be used.  Here
│ │ │ -is the <code class="inline">jump/1</code> instruction:</p><pre><code class="makeup erlang" translate="no"><span class="nf">jump</span><span class="p" data-group-id="4905225399-1">(</span><span class="n">Fail</span><span class="p" data-group-id="4905225399-1">)</span><span class="w"> </span><span class="p" data-group-id="4905225399-2">{</span><span class="w">
│ │ │ -    </span><span class="sc">$J</span><span class="n">UMP</span><span class="p" data-group-id="4905225399-3">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="4905225399-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4905225399-2">}</span><span class="w">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="4987249115-19">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="4987249115-20">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="4987249115-20">)</span><span class="p" data-group-id="4987249115-19">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">Goto</span><span class="p" data-group-id="4987249115-21">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="4987249115-21">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4987249115-2">}</span></code></pre><h5>The -no_next directive</h5><p>Next we will look at when the <code class="inline">-no_next</code> directive can be used.  Here
│ │ │ +is the <code class="inline">jump/1</code> instruction:</p><pre><code class="makeup erlang" translate="no"><span class="nf">jump</span><span class="p" data-group-id="6628628815-1">(</span><span class="n">Fail</span><span class="p" data-group-id="6628628815-1">)</span><span class="w"> </span><span class="p" data-group-id="6628628815-2">{</span><span class="w">
│ │ │ +    </span><span class="sc">$J</span><span class="n">UMP</span><span class="p" data-group-id="6628628815-3">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="6628628815-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6628628815-2">}</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">From</span><span class="w"> </span><span class="ss">macros</span><span class="p">.</span><span class="ss">tab</span><span class="w">
│ │ │ -</span><span class="n">JUMP</span><span class="p" data-group-id="4905225399-4">(</span><span class="n">Fail</span><span class="p" data-group-id="4905225399-4">)</span><span class="w"> </span><span class="p" data-group-id="4905225399-5">{</span><span class="w">
│ │ │ +</span><span class="n">JUMP</span><span class="p" data-group-id="6628628815-4">(</span><span class="n">Fail</span><span class="p" data-group-id="6628628815-4">)</span><span class="w"> </span><span class="p" data-group-id="6628628815-5">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_next</span><span class="w">
│ │ │ -    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="4905225399-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="4905225399-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">Goto</span><span class="p" data-group-id="4905225399-7">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="4905225399-7">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4905225399-5">}</span></code></pre><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="6157233306-1">(</span><span class="ss">jump_f</span><span class="p" data-group-id="6157233306-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6157233306-2">{</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="6157233306-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="6157233306-4">(</span><span class="o">*</span><span class="p" data-group-id="6157233306-5">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="6157233306-6">(</span><span class="nf">fb</span><span class="p" data-group-id="6157233306-7">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6157233306-8">(</span><span class="n">I</span><span class="p" data-group-id="6157233306-9">[</span><span class="mi">0</span><span class="p" data-group-id="6157233306-9">]</span><span class="p" data-group-id="6157233306-8">)</span><span class="p" data-group-id="6157233306-7">)</span><span class="p" data-group-id="6157233306-6">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6157233306-5">)</span><span class="p" data-group-id="6157233306-4">)</span><span class="p" data-group-id="6157233306-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="6157233306-10">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6157233306-11">(</span><span class="n">I</span><span class="p" data-group-id="6157233306-12">[</span><span class="mi">0</span><span class="p" data-group-id="6157233306-12">]</span><span class="p" data-group-id="6157233306-11">)</span><span class="p" data-group-id="6157233306-10">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">Goto</span><span class="p" data-group-id="6157233306-13">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="6157233306-13">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6157233306-2">}</span></code></pre><p>If we remove the <code class="inline">-no_next</code> directive, the code would look like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="6372067123-1">(</span><span class="ss">jump_f</span><span class="p" data-group-id="6372067123-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6372067123-2">{</span><span class="w">
│ │ │ -  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="6372067123-3">(</span><span class="n">I</span><span class="p" data-group-id="6372067123-4">[</span><span class="mi">1</span><span class="p" data-group-id="6372067123-4">]</span><span class="p" data-group-id="6372067123-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="6372067123-5">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="6372067123-6">(</span><span class="o">*</span><span class="p" data-group-id="6372067123-7">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="6372067123-8">(</span><span class="nf">fb</span><span class="p" data-group-id="6372067123-9">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6372067123-10">(</span><span class="n">I</span><span class="p" data-group-id="6372067123-11">[</span><span class="mi">0</span><span class="p" data-group-id="6372067123-11">]</span><span class="p" data-group-id="6372067123-10">)</span><span class="p" data-group-id="6372067123-9">)</span><span class="p" data-group-id="6372067123-8">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="6372067123-7">)</span><span class="p" data-group-id="6372067123-6">)</span><span class="p" data-group-id="6372067123-5">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="6372067123-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="6372067123-13">(</span><span class="n">I</span><span class="p" data-group-id="6372067123-14">[</span><span class="mi">0</span><span class="p" data-group-id="6372067123-14">]</span><span class="p" data-group-id="6372067123-13">)</span><span class="p" data-group-id="6372067123-12">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">Goto</span><span class="p" data-group-id="6372067123-15">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="6372067123-15">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="6628628815-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="6628628815-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">Goto</span><span class="p" data-group-id="6628628815-7">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="6628628815-7">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6628628815-5">}</span></code></pre><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="1950604963-1">(</span><span class="ss">jump_f</span><span class="p" data-group-id="1950604963-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1950604963-2">{</span><span class="w">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="1950604963-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="1950604963-4">(</span><span class="o">*</span><span class="p" data-group-id="1950604963-5">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="1950604963-6">(</span><span class="nf">fb</span><span class="p" data-group-id="1950604963-7">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="1950604963-8">(</span><span class="n">I</span><span class="p" data-group-id="1950604963-9">[</span><span class="mi">0</span><span class="p" data-group-id="1950604963-9">]</span><span class="p" data-group-id="1950604963-8">)</span><span class="p" data-group-id="1950604963-7">)</span><span class="p" data-group-id="1950604963-6">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1950604963-5">)</span><span class="p" data-group-id="1950604963-4">)</span><span class="p" data-group-id="1950604963-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="1950604963-10">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="1950604963-11">(</span><span class="n">I</span><span class="p" data-group-id="1950604963-12">[</span><span class="mi">0</span><span class="p" data-group-id="1950604963-12">]</span><span class="p" data-group-id="1950604963-11">)</span><span class="p" data-group-id="1950604963-10">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">Goto</span><span class="p" data-group-id="1950604963-13">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="1950604963-13">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1950604963-2">}</span></code></pre><p>If we remove the <code class="inline">-no_next</code> directive, the code would look like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="1243481184-1">(</span><span class="ss">jump_f</span><span class="p" data-group-id="1243481184-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1243481184-2">{</span><span class="w">
│ │ │ +  </span><span class="n">BeamInstr</span><span class="w"> </span><span class="ss">next_pf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">BeamCodeAddr</span><span class="p" data-group-id="1243481184-3">(</span><span class="n">I</span><span class="p" data-group-id="1243481184-4">[</span><span class="mi">1</span><span class="p" data-group-id="1243481184-4">]</span><span class="p" data-group-id="1243481184-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="1243481184-5">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="1243481184-6">(</span><span class="o">*</span><span class="p" data-group-id="1243481184-7">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="1243481184-8">(</span><span class="nf">fb</span><span class="p" data-group-id="1243481184-9">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="1243481184-10">(</span><span class="n">I</span><span class="p" data-group-id="1243481184-11">[</span><span class="mi">0</span><span class="p" data-group-id="1243481184-11">]</span><span class="p" data-group-id="1243481184-10">)</span><span class="p" data-group-id="1243481184-9">)</span><span class="p" data-group-id="1243481184-8">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="1243481184-7">)</span><span class="p" data-group-id="1243481184-6">)</span><span class="p" data-group-id="1243481184-5">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="nf">fb</span><span class="p" data-group-id="1243481184-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="1243481184-13">(</span><span class="n">I</span><span class="p" data-group-id="1243481184-14">[</span><span class="mi">0</span><span class="p" data-group-id="1243481184-14">]</span><span class="p" data-group-id="1243481184-13">)</span><span class="p" data-group-id="1243481184-12">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">Goto</span><span class="p" data-group-id="1243481184-15">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="1243481184-15">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │    </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">ASSERT</span><span class="p" data-group-id="6372067123-16">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="6372067123-17">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6372067123-17">)</span><span class="p" data-group-id="6372067123-16">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">GotoPF</span><span class="p" data-group-id="6372067123-18">(</span><span class="ss">next_pf</span><span class="p" data-group-id="6372067123-18">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6372067123-2">}</span></code></pre><p>In the end, the C compiler will probably optimize this code to the
│ │ │ +  </span><span class="n">ASSERT</span><span class="p" data-group-id="1243481184-16">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="1243481184-17">(</span><span class="ss">next_pf</span><span class="p" data-group-id="1243481184-17">)</span><span class="p" data-group-id="1243481184-16">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="n">GotoPF</span><span class="p" data-group-id="1243481184-18">(</span><span class="ss">next_pf</span><span class="p" data-group-id="1243481184-18">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1243481184-2">}</span></code></pre><p>In the end, the C compiler will probably optimize this code to the
│ │ │  same native code as the first version, but the first version is certainly
│ │ │  much easier to read for human readers.</p><h4>Macros in the macros.tab file</h4><p>The file <code class="inline">macros.tab</code> contains many useful macros.  When implementing
│ │ │  new instructions it is good practice to look through <code class="inline">macros.tab</code> to
│ │ │  see if any of existing macros can be used rather than re-inventing
│ │ │  the wheel.</p><p>We will describe a few of the most useful macros here.</p><p><a href="" id="the-GC_REGEXP-definition"></a></p><h5>The GC_REGEXP definition</h5><p>The following line defines a regular expression that will recognize
│ │ │  a call to a function that does a garbage collection:</p><pre><code class="makeup erlang" translate="no"><span class="w"> </span><span class="n">GC_REGEXP</span><span class="o">=</span><span class="ss">erts_garbage_collect</span><span class="p">|</span><span class="ss">erts_gc</span><span class="p">|</span><span class="n">GcBifFunction</span><span class="p">;</span></code></pre><p>The purpose is that <strong>beam_makeops</strong> can verify that an instruction
│ │ │  that does a garbage collection and has an <code class="inline">d</code> operand uses the
│ │ │  <code class="inline">$REFRESH_GEN_DEST()</code> macro.</p><p>If you need to define a new function that does garbage collection,
│ │ │  you should give it the prefix <code class="inline">erts_gc_</code>.  If that is not possible
│ │ │  you should update the regular expression so that it will match your
│ │ │ -new function.</p><h5>FAIL(Fail)</h5><p>Branch to <code class="inline">$Fail</code>.  Will suppress prefetch (<code class="inline">-no_prefetch</code>).  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">is_nonempty_list</span><span class="p" data-group-id="9780132464-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="9780132464-1">)</span><span class="w"> </span><span class="p" data-group-id="9780132464-2">{</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="9780132464-3">(</span><span class="nf">is_not_list</span><span class="p" data-group-id="9780132464-4">(</span><span class="sc">$S</span><span class="ss">rc</span><span class="p" data-group-id="9780132464-4">)</span><span class="p" data-group-id="9780132464-3">)</span><span class="w"> </span><span class="p" data-group-id="9780132464-5">{</span><span class="w">
│ │ │ -        </span><span class="sc">$F</span><span class="n">AIL</span><span class="p" data-group-id="9780132464-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="9780132464-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="9780132464-5">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="9780132464-2">}</span></code></pre><h5>JUMP(Fail)</h5><p>Branch to <code class="inline">$Fail</code>.  Suppresses generation of dispatch of the next
│ │ │ -instruction (<code class="inline">-no_next</code>).  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">jump</span><span class="p" data-group-id="8459915140-1">(</span><span class="n">Fail</span><span class="p" data-group-id="8459915140-1">)</span><span class="w"> </span><span class="p" data-group-id="8459915140-2">{</span><span class="w">
│ │ │ -    </span><span class="sc">$J</span><span class="n">UMP</span><span class="p" data-group-id="8459915140-3">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="8459915140-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8459915140-2">}</span></code></pre><h5>GC_TEST(NeedStack, NeedHeap, Live)</h5><p><code class="inline">$GC_TEST(NeedStack, NeedHeap, Live)</code> tests that given amount of
│ │ │ +new function.</p><h5>FAIL(Fail)</h5><p>Branch to <code class="inline">$Fail</code>.  Will suppress prefetch (<code class="inline">-no_prefetch</code>).  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">is_nonempty_list</span><span class="p" data-group-id="8441816673-1">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="8441816673-1">)</span><span class="w"> </span><span class="p" data-group-id="8441816673-2">{</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="8441816673-3">(</span><span class="nf">is_not_list</span><span class="p" data-group-id="8441816673-4">(</span><span class="sc">$S</span><span class="ss">rc</span><span class="p" data-group-id="8441816673-4">)</span><span class="p" data-group-id="8441816673-3">)</span><span class="w"> </span><span class="p" data-group-id="8441816673-5">{</span><span class="w">
│ │ │ +        </span><span class="sc">$F</span><span class="n">AIL</span><span class="p" data-group-id="8441816673-6">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="8441816673-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="8441816673-5">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8441816673-2">}</span></code></pre><h5>JUMP(Fail)</h5><p>Branch to <code class="inline">$Fail</code>.  Suppresses generation of dispatch of the next
│ │ │ +instruction (<code class="inline">-no_next</code>).  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">jump</span><span class="p" data-group-id="8052490498-1">(</span><span class="n">Fail</span><span class="p" data-group-id="8052490498-1">)</span><span class="w"> </span><span class="p" data-group-id="8052490498-2">{</span><span class="w">
│ │ │ +    </span><span class="sc">$J</span><span class="n">UMP</span><span class="p" data-group-id="8052490498-3">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="8052490498-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="8052490498-2">}</span></code></pre><h5>GC_TEST(NeedStack, NeedHeap, Live)</h5><p><code class="inline">$GC_TEST(NeedStack, NeedHeap, Live)</code> tests that given amount of
│ │ │  stack space and heap space is available.  If not it will do a
│ │ │ -garbage collection.  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">test_heap</span><span class="p" data-group-id="8955425624-1">(</span><span class="n">Nh</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p" data-group-id="8955425624-1">)</span><span class="w"> </span><span class="p" data-group-id="8955425624-2">{</span><span class="w">
│ │ │ -    </span><span class="sc">$G</span><span class="n">C_TEST</span><span class="p" data-group-id="8955425624-3">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="ss">h</span><span class="p">,</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p" data-group-id="8955425624-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8955425624-2">}</span></code></pre><h5>AH(NeedStack, NeedHeap, Live)</h5><p><code class="inline">AH(NeedStack, NeedHeap, Live)</code> allocates a stack frame and
│ │ │ +garbage collection.  Typical use:</p><pre><code class="makeup erlang" translate="no"><span class="nf">test_heap</span><span class="p" data-group-id="2430339010-1">(</span><span class="n">Nh</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p" data-group-id="2430339010-1">)</span><span class="w"> </span><span class="p" data-group-id="2430339010-2">{</span><span class="w">
│ │ │ +    </span><span class="sc">$G</span><span class="n">C_TEST</span><span class="p" data-group-id="2430339010-3">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="ss">h</span><span class="p">,</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p" data-group-id="2430339010-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2430339010-2">}</span></code></pre><h5>AH(NeedStack, NeedHeap, Live)</h5><p><code class="inline">AH(NeedStack, NeedHeap, Live)</code> allocates a stack frame and
│ │ │  optionally additional heap space.</p><h4>Pre-defined macros and variables</h4><p><strong>beam_makeops</strong> defines several built-in macros and pre-bound variables.</p><h5>The NEXT_INSTRUCTION pre-bound variable</h5><p>The NEXT_INSTRUCTION is a pre-bound variable that is available in
│ │ │ -all instructions.  It expands to the address of the next instruction.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">i_call</span><span class="p" data-group-id="7522942898-1">(</span><span class="n">CallDest</span><span class="p" data-group-id="7522942898-1">)</span><span class="w"> </span><span class="p" data-group-id="7522942898-2">{</span><span class="w">
│ │ │ +all instructions.  It expands to the address of the next instruction.</p><p>Here is an example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">i_call</span><span class="p" data-group-id="4149931340-1">(</span><span class="n">CallDest</span><span class="p" data-group-id="4149931340-1">)</span><span class="w"> </span><span class="p" data-group-id="4149931340-2">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_next</span><span class="w">
│ │ │ -    </span><span class="sc">$S</span><span class="n">AVE_CONTINUATION_POINTER</span><span class="p" data-group-id="7522942898-3">(</span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p" data-group-id="7522942898-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="sc">$D</span><span class="n">ISPATCH_REL</span><span class="p" data-group-id="7522942898-4">(</span><span class="sc">$C</span><span class="ss">allDest</span><span class="p" data-group-id="7522942898-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7522942898-2">}</span></code></pre><p>When calling a function, the return address is first stored in <code class="inline">E[0]</code>
│ │ │ +    </span><span class="sc">$S</span><span class="n">AVE_CONTINUATION_POINTER</span><span class="p" data-group-id="4149931340-3">(</span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p" data-group-id="4149931340-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$D</span><span class="n">ISPATCH_REL</span><span class="p" data-group-id="4149931340-4">(</span><span class="sc">$C</span><span class="ss">allDest</span><span class="p" data-group-id="4149931340-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4149931340-2">}</span></code></pre><p>When calling a function, the return address is first stored in <code class="inline">E[0]</code>
│ │ │  (using the <code class="inline">$SAVE_CONTINUATION_POINTER()</code> macro), and then control is
│ │ │ -transferred to the callee.  Here is the generated code:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="5760601630-1">(</span><span class="ss">i_call_f</span><span class="p" data-group-id="5760601630-1">)</span><span class="p">:</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5760601630-2">{</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="5760601630-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="5760601630-4">(</span><span class="o">*</span><span class="p" data-group-id="5760601630-5">(</span><span class="n">I</span><span class="o">+</span><span class="mi">2</span><span class="p" data-group-id="5760601630-5">)</span><span class="p" data-group-id="5760601630-4">)</span><span class="p" data-group-id="5760601630-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="o">*</span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5760601630-6">(</span><span class="n">BeamInstr</span><span class="p" data-group-id="5760601630-6">)</span><span class="w"> </span><span class="p" data-group-id="5760601630-7">(</span><span class="n">I</span><span class="o">+</span><span class="mi">2</span><span class="p" data-group-id="5760601630-7">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │ +transferred to the callee.  Here is the generated code:</p><pre><code class="makeup erlang" translate="no"><span class="n">OpCase</span><span class="p" data-group-id="6348158777-1">(</span><span class="ss">i_call_f</span><span class="p" data-group-id="6348158777-1">)</span><span class="p">:</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="6348158777-2">{</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="6348158777-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="6348158777-4">(</span><span class="o">*</span><span class="p" data-group-id="6348158777-5">(</span><span class="n">I</span><span class="o">+</span><span class="mi">2</span><span class="p" data-group-id="6348158777-5">)</span><span class="p" data-group-id="6348158777-4">)</span><span class="p" data-group-id="6348158777-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="o">*</span><span class="n">E</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6348158777-6">(</span><span class="n">BeamInstr</span><span class="p" data-group-id="6348158777-6">)</span><span class="w"> </span><span class="p" data-group-id="6348158777-7">(</span><span class="n">I</span><span class="o">+</span><span class="mi">2</span><span class="p" data-group-id="6348158777-7">)</span><span class="p">;</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │      </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">dispatch</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">intentionally</span><span class="w"> </span><span class="ss">left</span><span class="w"> </span><span class="ss">out</span><span class="w"> </span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="5760601630-2">}</span></code></pre><p>We can see that that <code class="inline">$NEXT_INSTRUCTION</code> has been expanded to <code class="inline">I+2</code>.
│ │ │ +</span><span class="p" data-group-id="6348158777-2">}</span></code></pre><p>We can see that that <code class="inline">$NEXT_INSTRUCTION</code> has been expanded to <code class="inline">I+2</code>.
│ │ │  That makes sense since the size of the <code class="inline">i_call_f/1</code> instruction is
│ │ │  two words.</p><h5>The IP_ADJUSTMENT pre-bound variable</h5><p><code class="inline">$IP_ADJUSTMENT</code> is usually 0.  In a few combined instructions
│ │ │  (described below) it can be non-zero.  It is used like this
│ │ │ -in <code class="inline">macros.tab</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">SET_I_REL</span><span class="p" data-group-id="8465369104-1">(</span><span class="n">Offset</span><span class="p" data-group-id="8465369104-1">)</span><span class="w"> </span><span class="p" data-group-id="8465369104-2">{</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="8465369104-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="8465369104-4">(</span><span class="o">*</span><span class="p" data-group-id="8465369104-5">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="8465369104-6">(</span><span class="sc">$O</span><span class="ss">ffset</span><span class="p" data-group-id="8465369104-6">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="p" data-group-id="8465369104-5">)</span><span class="p" data-group-id="8465369104-4">)</span><span class="p" data-group-id="8465369104-3">)</span><span class="p">;</span><span class="w">
│ │ │ +in <code class="inline">macros.tab</code>:</p><pre><code class="makeup erlang" translate="no"><span class="n">SET_I_REL</span><span class="p" data-group-id="0530298526-1">(</span><span class="n">Offset</span><span class="p" data-group-id="0530298526-1">)</span><span class="w"> </span><span class="p" data-group-id="0530298526-2">{</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="0530298526-3">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="0530298526-4">(</span><span class="o">*</span><span class="p" data-group-id="0530298526-5">(</span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="p" data-group-id="0530298526-6">(</span><span class="sc">$O</span><span class="ss">ffset</span><span class="p" data-group-id="0530298526-6">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="p" data-group-id="0530298526-5">)</span><span class="p" data-group-id="0530298526-4">)</span><span class="p" data-group-id="0530298526-3">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="sc">$O</span><span class="ss">ffset</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8465369104-2">}</span></code></pre><p>Avoid using <code class="inline">IP_ADJUSTMENT</code> directly.  Use <code class="inline">SET_I_REL()</code> or
│ │ │ +</span><span class="p" data-group-id="0530298526-2">}</span></code></pre><p>Avoid using <code class="inline">IP_ADJUSTMENT</code> directly.  Use <code class="inline">SET_I_REL()</code> or
│ │ │  one of the macros that invoke such as <code class="inline">FAIL()</code> or <code class="inline">JUMP()</code>
│ │ │  defined in <code class="inline">macros.tab</code>.</p><h4>Pre-defined macro functions</h4><h5>The IF() macro</h5><p><code class="inline">$IF(Expr, IfTrue, IfFalse)</code> evaluates <code class="inline">Expr</code>, which must be a valid
│ │ │  Perl expression (which for simple numeric expressions have the same
│ │ │  syntax as C).  If <code class="inline">Expr</code> evaluates to 0, the entire <code class="inline">IF()</code> expression will be
│ │ │  replaced with <code class="inline">IfFalse</code>, otherwise it will be replaced with <code class="inline">IfTrue</code>.</p><p>See the description of <code class="inline">OPERAND_POSITION()</code> for an example.</p><h5>The OPERAND_POSITION() macro</h5><p><code class="inline">$OPERAND_POSITION(Expr)</code> returns the position for <code class="inline">Expr</code>, if
│ │ │  <code class="inline">Expr</code> is an operand that is not packed.  The first operand is
│ │ │ -at position 1.</p><p>Returns 0 otherwise.</p><p>This macro could be used like this in order to share code:</p><pre><code class="makeup erlang" translate="no"><span class="n">FAIL</span><span class="p" data-group-id="1174528712-1">(</span><span class="n">Fail</span><span class="p" data-group-id="1174528712-1">)</span><span class="w"> </span><span class="p" data-group-id="1174528712-2">{</span><span class="w">
│ │ │ +at position 1.</p><p>Returns 0 otherwise.</p><p>This macro could be used like this in order to share code:</p><pre><code class="makeup erlang" translate="no"><span class="n">FAIL</span><span class="p" data-group-id="1344310161-1">(</span><span class="n">Fail</span><span class="p" data-group-id="1344310161-1">)</span><span class="w"> </span><span class="p" data-group-id="1344310161-2">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_prefetch</span><span class="w">
│ │ │ -    </span><span class="sc">$I</span><span class="n">F</span><span class="p" data-group-id="1174528712-3">(</span><span class="sc">$O</span><span class="n">PERAND_POSITION</span><span class="p" data-group-id="1174528712-4">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="1174528712-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │ +    </span><span class="sc">$I</span><span class="n">F</span><span class="p" data-group-id="1344310161-3">(</span><span class="sc">$O</span><span class="n">PERAND_POSITION</span><span class="p" data-group-id="1344310161-4">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="1344310161-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="p">&amp;&amp;</span><span class="w"> </span><span class="sc">$I</span><span class="n">P_ADJUSTMENT</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w">
│ │ │          </span><span class="ss">goto</span><span class="w"> </span><span class="ss">common_jump</span><span class="p">,</span><span class="w">
│ │ │ -        </span><span class="sc">$D</span><span class="n">O_JUMP</span><span class="p" data-group-id="1174528712-5">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="1174528712-5">)</span><span class="p" data-group-id="1174528712-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1174528712-2">}</span><span class="w">
│ │ │ +        </span><span class="sc">$D</span><span class="n">O_JUMP</span><span class="p" data-group-id="1344310161-5">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="1344310161-5">)</span><span class="p" data-group-id="1344310161-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1344310161-2">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="n">DO_JUMP</span><span class="p" data-group-id="1174528712-6">(</span><span class="n">Fail</span><span class="p" data-group-id="1174528712-6">)</span><span class="w"> </span><span class="p" data-group-id="1174528712-7">{</span><span class="w">
│ │ │ -    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="1174528712-8">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="1174528712-8">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">Goto</span><span class="p" data-group-id="1174528712-9">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="1174528712-9">)</span><span class="p">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1174528712-7">}</span><span class="w">
│ │ │ +</span><span class="n">DO_JUMP</span><span class="p" data-group-id="1344310161-6">(</span><span class="n">Fail</span><span class="p" data-group-id="1344310161-6">)</span><span class="w"> </span><span class="p" data-group-id="1344310161-7">{</span><span class="w">
│ │ │ +    </span><span class="sc">$S</span><span class="n">ET_I_REL</span><span class="p" data-group-id="1344310161-8">(</span><span class="sc">$F</span><span class="ss">ail</span><span class="p" data-group-id="1344310161-8">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">Goto</span><span class="p" data-group-id="1344310161-9">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="1344310161-9">)</span><span class="p">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="1344310161-7">}</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="ss">beam_emu</span><span class="p">.</span><span class="nc">c</span><span class="p">:</span><span class="w">
│ │ │  </span><span class="nc">common_jump</span><span class="p">:</span><span class="w">
│ │ │ -   </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="1174528712-10">[</span><span class="mi">1</span><span class="p" data-group-id="1174528712-10">]</span><span class="p">;</span><span class="w">
│ │ │ -   </span><span class="n">Goto</span><span class="p" data-group-id="1174528712-11">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="1174528712-11">)</span><span class="p">)</span><span class="p">;</span></code></pre><h4>The $REFRESH_GEN_DEST() macro</h4><p>When a specific instruction has a <code class="inline">d</code> operand, early during execution
│ │ │ +   </span><span class="n">I</span><span class="w"> </span><span class="o">+</span><span class="o">=</span><span class="w"> </span><span class="n">I</span><span class="p" data-group-id="1344310161-10">[</span><span class="mi">1</span><span class="p" data-group-id="1344310161-10">]</span><span class="p">;</span><span class="w">
│ │ │ +   </span><span class="n">Goto</span><span class="p" data-group-id="1344310161-11">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="1344310161-11">)</span><span class="p">)</span><span class="p">;</span></code></pre><h4>The $REFRESH_GEN_DEST() macro</h4><p>When a specific instruction has a <code class="inline">d</code> operand, early during execution
│ │ │  of the instruction, a pointer will be initialized to point to the X or
│ │ │  Y register in question.</p><p>If there is a garbage collection before the result is stored,
│ │ │  the stack will move and if the <code class="inline">d</code> operand referred to a Y
│ │ │  register, the pointer will no longer be valid.  (Y registers are
│ │ │  stored on the stack.)</p><p>In those circumstances, <code class="inline">$REFRESH_GEN_DEST()</code> must be invoked
│ │ │  to set up the pointer again. <strong>beam_makeops</strong> will notice
│ │ │  if there is a call to a function that does a garbage collection and
│ │ │  <code class="inline">$REFRESH_GEN_DEST()</code> is not called.</p><p>Here is a complete example.  The <code class="inline">new_map</code> instruction is defined
│ │ │ -like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">new_map</span><span class="w"> </span><span class="ss">d</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="n">I</span></code></pre><p>It is implemented like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new_map</span><span class="p" data-group-id="3505985332-1">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="3505985332-1">)</span><span class="w"> </span><span class="p" data-group-id="3505985332-2">{</span><span class="w">
│ │ │ +like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">new_map</span><span class="w"> </span><span class="ss">d</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="n">I</span></code></pre><p>It is implemented like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">new_map</span><span class="p" data-group-id="2622709723-1">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">N</span><span class="p" data-group-id="2622709723-1">)</span><span class="w"> </span><span class="p" data-group-id="2622709723-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">res</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │      </span><span class="n">HEAVY_SWAPOUT</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_new_map</span><span class="p" data-group-id="3505985332-3">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p" data-group-id="3505985332-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_new_map</span><span class="p" data-group-id="2622709723-3">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="p">,</span><span class="w"> </span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p" data-group-id="2622709723-3">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPIN</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="3505985332-4">(</span><span class="p" data-group-id="3505985332-4">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="2622709723-4">(</span><span class="p" data-group-id="2622709723-4">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">res</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="sc">$N</span><span class="n">EXT</span><span class="p" data-group-id="3505985332-5">(</span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="o">+</span><span class="sc">$N</span><span class="p" data-group-id="3505985332-5">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3505985332-2">}</span></code></pre><p>If we have forgotten the <code class="inline">$REFRESH_GEN_DEST()</code> there would be a message
│ │ │ -similar to this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pointer</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">destination</span><span class="w"> </span><span class="nb">register</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">invalid</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="n">GC</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="ss">use</span><span class="w"> </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="5926625977-1">(</span><span class="p" data-group-id="5926625977-1">)</span><span class="w">
│ │ │ -</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">body</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="ss">new_map</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">beam</span><span class="o">/</span><span class="ss">map_instrs</span><span class="p">.</span><span class="nf">tab</span><span class="p" data-group-id="5926625977-2">(</span><span class="mi">30</span><span class="p" data-group-id="5926625977-2">)</span></code></pre><h4>Variable number of operands</h4><p>Here follows an example of how to handle an instruction with a variable number
│ │ │ +    </span><span class="sc">$N</span><span class="n">EXT</span><span class="p" data-group-id="2622709723-5">(</span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="o">+</span><span class="sc">$N</span><span class="p" data-group-id="2622709723-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2622709723-2">}</span></code></pre><p>If we have forgotten the <code class="inline">$REFRESH_GEN_DEST()</code> there would be a message
│ │ │ +similar to this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">pointer</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">destination</span><span class="w"> </span><span class="nb">register</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">invalid</span><span class="w"> </span><span class="k">after</span><span class="w"> </span><span class="n">GC</span><span class="w"> </span><span class="o">--</span><span class="w"> </span><span class="ss">use</span><span class="w"> </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="4645213729-1">(</span><span class="p" data-group-id="4645213729-1">)</span><span class="w">
│ │ │ +</span><span class="p">.</span><span class="p">.</span><span class="p">.</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">body</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="ss">new_map</span><span class="w"> </span><span class="ss">at</span><span class="w"> </span><span class="ss">beam</span><span class="o">/</span><span class="ss">map_instrs</span><span class="p">.</span><span class="nf">tab</span><span class="p" data-group-id="4645213729-2">(</span><span class="mi">30</span><span class="p" data-group-id="4645213729-2">)</span></code></pre><h4>Variable number of operands</h4><p>Here follows an example of how to handle an instruction with a variable number
│ │ │  of operands for the interpreter.  Here is the instruction definition in <code class="inline">emu/ops.tab</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">put_tuple2</span><span class="w"> </span><span class="ss">xy</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">*</span></code></pre><p>For the interpreter, the <code class="inline">*</code> is optional, because it does not effect code generation
│ │ │  in any way. However, it is recommended to include it to make it clear for human readers
│ │ │  that there is a variable number of operands.</p><p>Use the <code class="inline">$NEXT_INSTRUCTION</code> macro to obtain a pointer to the first of the variable
│ │ │ -operands.</p><p>Here is the implementation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">put_tuple2</span><span class="p" data-group-id="3136097767-1">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Arity</span><span class="p" data-group-id="3136097767-1">)</span><span class="w"> </span><span class="p" data-group-id="3136097767-2">{</span><span class="w">
│ │ │ +operands.</p><p>Here is the implementation:</p><pre><code class="makeup erlang" translate="no"><span class="nf">put_tuple2</span><span class="p" data-group-id="7228404563-1">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Arity</span><span class="p" data-group-id="7228404563-1">)</span><span class="w"> </span><span class="p" data-group-id="7228404563-2">{</span><span class="w">
│ │ │  </span><span class="n">Eterm</span><span class="o">*</span><span class="w"> </span><span class="ss">hp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">HTOP</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">arity</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="ss">rity</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">Eterm</span><span class="o">*</span><span class="w"> </span><span class="ss">dst_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="err">&amp;</span><span class="p" data-group-id="3136097767-3">(</span><span class="sc">$D</span><span class="ss">st</span><span class="p" data-group-id="3136097767-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="n">Eterm</span><span class="o">*</span><span class="w"> </span><span class="ss">dst_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="err">&amp;</span><span class="p" data-group-id="7228404563-3">(</span><span class="sc">$D</span><span class="ss">st</span><span class="p" data-group-id="7228404563-3">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">/</span><span class="p">|</span><span class="w"> </span><span class="o">-</span><span class="ss">no_next</span><span class="w">
│ │ │ -</span><span class="n">ASSERT</span><span class="p" data-group-id="3136097767-4">(</span><span class="ss">arity</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3136097767-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_arityval</span><span class="p" data-group-id="3136097767-5">(</span><span class="ss">arity</span><span class="p" data-group-id="3136097767-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="n">ASSERT</span><span class="p" data-group-id="7228404563-4">(</span><span class="ss">arity</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7228404563-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_arityval</span><span class="p" data-group-id="7228404563-5">(</span><span class="ss">arity</span><span class="p" data-group-id="7228404563-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="n">The</span><span class="w"> </span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="w"> </span><span class="ss">macro</span><span class="w"> </span><span class="ss">points</span><span class="w"> </span><span class="ss">just</span><span class="w"> </span><span class="ss">beyond</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">fixed</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="ss">operands</span><span class="p">.</span><span class="w"> </span><span class="n">In</span><span class="w"> </span><span class="ss">this</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="ss">it</span><span class="w"> </span><span class="ss">points</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">descriptor</span><span class="w"> </span><span class="k">of</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">first</span><span class="w"> </span><span class="nb">element</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">be</span><span class="w"> </span><span class="nb">put</span><span class="w"> </span><span class="ss">into</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">tuple</span><span class="p">.</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │  </span><span class="n">I</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="n">EXT_INSTRUCTION</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="ss">do</span><span class="w"> </span><span class="p" data-group-id="3136097767-6">{</span><span class="w">
│ │ │ +</span><span class="ss">do</span><span class="w"> </span><span class="p" data-group-id="7228404563-6">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">*</span><span class="n">I</span><span class="o">++</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">switch</span><span class="w"> </span><span class="p" data-group-id="3136097767-7">(</span><span class="nf">loader_tag</span><span class="p" data-group-id="3136097767-8">(</span><span class="ss">term</span><span class="p" data-group-id="3136097767-8">)</span><span class="p" data-group-id="3136097767-7">)</span><span class="w"> </span><span class="p" data-group-id="3136097767-9">{</span><span class="w">
│ │ │ +    </span><span class="nf">switch</span><span class="w"> </span><span class="p" data-group-id="7228404563-7">(</span><span class="nf">loader_tag</span><span class="p" data-group-id="7228404563-8">(</span><span class="ss">term</span><span class="p" data-group-id="7228404563-8">)</span><span class="p" data-group-id="7228404563-7">)</span><span class="w"> </span><span class="p" data-group-id="7228404563-9">{</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">LOADER_X_REG</span><span class="p">:</span><span class="w">
│ │ │ -    </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">x</span><span class="p" data-group-id="3136097767-10">(</span><span class="nf">loader_x_reg_index</span><span class="p" data-group-id="3136097767-11">(</span><span class="ss">term</span><span class="p" data-group-id="3136097767-11">)</span><span class="p" data-group-id="3136097767-10">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">x</span><span class="p" data-group-id="7228404563-10">(</span><span class="nf">loader_x_reg_index</span><span class="p" data-group-id="7228404563-11">(</span><span class="ss">term</span><span class="p" data-group-id="7228404563-11">)</span><span class="p" data-group-id="7228404563-10">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">break</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="n">LOADER_Y_REG</span><span class="p">:</span><span class="w">
│ │ │ -    </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">y</span><span class="p" data-group-id="3136097767-12">(</span><span class="nf">loader_y_reg_index</span><span class="p" data-group-id="3136097767-13">(</span><span class="ss">term</span><span class="p" data-group-id="3136097767-13">)</span><span class="p" data-group-id="3136097767-12">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">y</span><span class="p" data-group-id="7228404563-12">(</span><span class="nf">loader_y_reg_index</span><span class="p" data-group-id="7228404563-13">(</span><span class="ss">term</span><span class="p" data-group-id="7228404563-13">)</span><span class="p" data-group-id="7228404563-12">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">break</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="nc">default</span><span class="p">:</span><span class="w">
│ │ │      </span><span class="o">*</span><span class="ss">hp</span><span class="o">++</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">term</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">break</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="3136097767-9">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3136097767-6">}</span><span class="w"> </span><span class="nf">while</span><span class="w"> </span><span class="p" data-group-id="3136097767-14">(</span><span class="o">--</span><span class="ss">arity</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="3136097767-14">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="o">*</span><span class="ss">dst_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_tuple</span><span class="p" data-group-id="3136097767-15">(</span><span class="n">HTOP</span><span class="p" data-group-id="3136097767-15">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7228404563-9">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7228404563-6">}</span><span class="w"> </span><span class="nf">while</span><span class="w"> </span><span class="p" data-group-id="7228404563-14">(</span><span class="o">--</span><span class="ss">arity</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p" data-group-id="7228404563-14">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="o">*</span><span class="ss">dst_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_tuple</span><span class="p" data-group-id="7228404563-15">(</span><span class="n">HTOP</span><span class="p" data-group-id="7228404563-15">)</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="n">HTOP</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">hp</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">ASSERT</span><span class="p" data-group-id="3136097767-16">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="3136097767-17">(</span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="3136097767-18">(</span><span class="n">Eterm</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="3136097767-18">)</span><span class="n">I</span><span class="p" data-group-id="3136097767-17">)</span><span class="p" data-group-id="3136097767-16">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="n">Goto</span><span class="p" data-group-id="3136097767-19">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="3136097767-19">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="3136097767-2">}</span></code></pre><h4>Combined instructions</h4><p><strong>Problem</strong>: For frequently executed instructions we want to use
│ │ │ +</span><span class="n">ASSERT</span><span class="p" data-group-id="7228404563-16">(</span><span class="n">VALID_INSTR</span><span class="p" data-group-id="7228404563-17">(</span><span class="o">*</span><span class="w"> </span><span class="p" data-group-id="7228404563-18">(</span><span class="n">Eterm</span><span class="w"> </span><span class="o">*</span><span class="p" data-group-id="7228404563-18">)</span><span class="n">I</span><span class="p" data-group-id="7228404563-17">)</span><span class="p" data-group-id="7228404563-16">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="n">Goto</span><span class="p" data-group-id="7228404563-19">(</span><span class="o">*</span><span class="n">I</span><span class="p" data-group-id="7228404563-19">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7228404563-2">}</span></code></pre><h4>Combined instructions</h4><p><strong>Problem</strong>: For frequently executed instructions we want to use
│ │ │  &quot;fast&quot; operands types such as <code class="inline">x</code> and <code class="inline">y</code>, as opposed to <code class="inline">s</code> or <code class="inline">S</code>.
│ │ │  To avoid an explosion in code size, we want to share most of the
│ │ │  implementation between the instructions.  Here are the specific
│ │ │  instructions for <code class="inline">i_increment/5</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_increment</span><span class="w"> </span><span class="ss">r</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_increment</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │ -</span><span class="ss">i_increment</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The <code class="inline">i_increment</code> instruction is implemented like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">i_increment</span><span class="p" data-group-id="7903477294-1">(</span><span class="n">Source</span><span class="p">,</span><span class="w"> </span><span class="n">IncrementVal</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="7903477294-1">)</span><span class="w"> </span><span class="p" data-group-id="7903477294-2">{</span><span class="w">
│ │ │ +</span><span class="ss">i_increment</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The <code class="inline">i_increment</code> instruction is implemented like this:</p><pre><code class="makeup erlang" translate="no"><span class="nf">i_increment</span><span class="p" data-group-id="7510096016-1">(</span><span class="n">Source</span><span class="p">,</span><span class="w"> </span><span class="n">IncrementVal</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="7510096016-1">)</span><span class="w"> </span><span class="p" data-group-id="7510096016-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_reg_source</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">ource</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$I</span><span class="ss">ncrementVal</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Uint</span><span class="w"> </span><span class="ss">live</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">result</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7903477294-3">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="7903477294-4">(</span><span class="nf">is_small</span><span class="p" data-group-id="7903477294-5">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="7903477294-5">)</span><span class="p" data-group-id="7903477294-4">)</span><span class="p" data-group-id="7903477294-3">)</span><span class="w"> </span><span class="p" data-group-id="7903477294-6">{</span><span class="w">
│ │ │ -        </span><span class="n">Sint</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">signed_val</span><span class="p" data-group-id="7903477294-7">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="7903477294-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">increment_val</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7903477294-8">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="7903477294-9">(</span><span class="n">IS_SSMALL</span><span class="p" data-group-id="7903477294-10">(</span><span class="ss">i</span><span class="p" data-group-id="7903477294-10">)</span><span class="p" data-group-id="7903477294-9">)</span><span class="p" data-group-id="7903477294-8">)</span><span class="w"> </span><span class="p" data-group-id="7903477294-11">{</span><span class="w">
│ │ │ -            </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="7903477294-12">(</span><span class="ss">i</span><span class="p" data-group-id="7903477294-12">)</span><span class="p">;</span><span class="w">
│ │ │ -            </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="7903477294-13">(</span><span class="p" data-group-id="7903477294-13">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="7903477294-11">}</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7903477294-6">}</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7510096016-3">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="7510096016-4">(</span><span class="nf">is_small</span><span class="p" data-group-id="7510096016-5">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="7510096016-5">)</span><span class="p" data-group-id="7510096016-4">)</span><span class="p" data-group-id="7510096016-3">)</span><span class="w"> </span><span class="p" data-group-id="7510096016-6">{</span><span class="w">
│ │ │ +        </span><span class="n">Sint</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">signed_val</span><span class="p" data-group-id="7510096016-7">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="7510096016-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">increment_val</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7510096016-8">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="7510096016-9">(</span><span class="n">IS_SSMALL</span><span class="p" data-group-id="7510096016-10">(</span><span class="ss">i</span><span class="p" data-group-id="7510096016-10">)</span><span class="p" data-group-id="7510096016-9">)</span><span class="p" data-group-id="7510096016-8">)</span><span class="w"> </span><span class="p" data-group-id="7510096016-11">{</span><span class="w">
│ │ │ +            </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="7510096016-12">(</span><span class="ss">i</span><span class="p" data-group-id="7510096016-12">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="7510096016-13">(</span><span class="p" data-group-id="7510096016-13">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="7510096016-11">}</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7510096016-6">}</span><span class="w">
│ │ │      </span><span class="ss">live</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPOUT</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">reg</span><span class="p" data-group-id="7903477294-14">[</span><span class="ss">live</span><span class="p" data-group-id="7903477294-14">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">reg</span><span class="p" data-group-id="7903477294-15">[</span><span class="ss">live</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="7903477294-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="7903477294-16">(</span><span class="ss">increment_val</span><span class="p" data-group-id="7903477294-16">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_mixed_plus</span><span class="p" data-group-id="7903477294-17">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="ss">live</span><span class="p" data-group-id="7903477294-17">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">reg</span><span class="p" data-group-id="7510096016-14">[</span><span class="ss">live</span><span class="p" data-group-id="7510096016-14">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">reg</span><span class="p" data-group-id="7510096016-15">[</span><span class="ss">live</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="7510096016-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="7510096016-16">(</span><span class="ss">increment_val</span><span class="p" data-group-id="7510096016-16">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_mixed_plus</span><span class="p" data-group-id="7510096016-17">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="ss">live</span><span class="p" data-group-id="7510096016-17">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPIN</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ERTS_HOLE_CHECK</span><span class="p" data-group-id="7903477294-18">(</span><span class="ss">c_p</span><span class="p" data-group-id="7903477294-18">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7903477294-19">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="7903477294-20">(</span><span class="nf">is_value</span><span class="p" data-group-id="7903477294-21">(</span><span class="ss">result</span><span class="p" data-group-id="7903477294-21">)</span><span class="p" data-group-id="7903477294-20">)</span><span class="p" data-group-id="7903477294-19">)</span><span class="w"> </span><span class="p" data-group-id="7903477294-22">{</span><span class="w">
│ │ │ -        </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="7903477294-23">(</span><span class="p" data-group-id="7903477294-23">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">ERTS_HOLE_CHECK</span><span class="p" data-group-id="7510096016-18">(</span><span class="ss">c_p</span><span class="p" data-group-id="7510096016-18">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="7510096016-19">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="7510096016-20">(</span><span class="nf">is_value</span><span class="p" data-group-id="7510096016-21">(</span><span class="ss">result</span><span class="p" data-group-id="7510096016-21">)</span><span class="p" data-group-id="7510096016-20">)</span><span class="p" data-group-id="7510096016-19">)</span><span class="w"> </span><span class="p" data-group-id="7510096016-22">{</span><span class="w">
│ │ │ +        </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="7510096016-23">(</span><span class="p" data-group-id="7510096016-23">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">result</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="7903477294-24">(</span><span class="p" data-group-id="7903477294-24">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7903477294-22">}</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="7903477294-25">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">freason</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="n">BADMATCH</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_value</span><span class="p" data-group-id="7903477294-26">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">fvalue</span><span class="p" data-group-id="7903477294-26">)</span><span class="p" data-group-id="7903477294-25">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="7510096016-24">(</span><span class="p" data-group-id="7510096016-24">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7510096016-22">}</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="7510096016-25">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">freason</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="n">BADMATCH</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_value</span><span class="p" data-group-id="7510096016-26">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">fvalue</span><span class="p" data-group-id="7510096016-26">)</span><span class="p" data-group-id="7510096016-25">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">goto</span><span class="w"> </span><span class="ss">find_func_info</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7903477294-2">}</span></code></pre><p>There will be three almost identical copies of the code.  Given the
│ │ │ +</span><span class="p" data-group-id="7510096016-2">}</span></code></pre><p>There will be three almost identical copies of the code.  Given the
│ │ │  size of the code, that could be too high cost to pay.</p><p>To avoid the three copies of the code, we could use only one specific
│ │ │  instruction:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_increment</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span></code></pre><p>(The same implementation as above will work.)</p><p>That reduces the code size, but is slower because <code class="inline">S</code> means that
│ │ │  there will be extra code to test whether the operand refers to an X
│ │ │  register or a Y register.</p><p><strong>Solution</strong>: We can use &quot;combined instructions&quot;.  Combined
│ │ │  instructions are combined from instruction fragments.  The
│ │ │  bulk of the code can be shared.</p><p>Here we will show how <code class="inline">i_increment</code> can be implemented as a combined
│ │ │  instruction.  We will show each individual fragment first, and then
│ │ │  show how to connect them together.  First we will need a variable that
│ │ │ -we can store the value fetched from the register in:</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">head</span><span class="p" data-group-id="0087243423-1">(</span><span class="p" data-group-id="0087243423-1">)</span><span class="w"> </span><span class="p" data-group-id="0087243423-2">{</span><span class="w">
│ │ │ +we can store the value fetched from the register in:</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">head</span><span class="p" data-group-id="6131211377-1">(</span><span class="p" data-group-id="6131211377-1">)</span><span class="w"> </span><span class="p" data-group-id="6131211377-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0087243423-2">}</span></code></pre><p>The name <code class="inline">increment</code> is the name of the group that the fragment
│ │ │ +</span><span class="p" data-group-id="6131211377-2">}</span></code></pre><p>The name <code class="inline">increment</code> is the name of the group that the fragment
│ │ │  belongs to.  Note that it does not need to have the same
│ │ │  name as the instruction.  The group name is followed by <code class="inline">.</code> and
│ │ │  the name of the fragment.  The name <code class="inline">head</code> is pre-defined.
│ │ │  The code in it will be placed at the beginning of a block, so
│ │ │  that all fragments in the group can access it.</p><p>Next we define the fragment that will pick up the value from the
│ │ │ -register from the first operand:</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">fetch</span><span class="p" data-group-id="6238033017-1">(</span><span class="n">Src</span><span class="p" data-group-id="6238033017-1">)</span><span class="w"> </span><span class="p" data-group-id="6238033017-2">{</span><span class="w">
│ │ │ +register from the first operand:</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">fetch</span><span class="p" data-group-id="3210777966-1">(</span><span class="n">Src</span><span class="p" data-group-id="3210777966-1">)</span><span class="w"> </span><span class="p" data-group-id="3210777966-2">{</span><span class="w">
│ │ │      </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6238033017-2">}</span></code></pre><p>We call this fragment <code class="inline">fetch</code>.  This fragment will be duplicated three
│ │ │ -times, one for each value of the first operand (<code class="inline">r</code>, <code class="inline">x</code>, and <code class="inline">y</code>).</p><p>Next we define the main part of the code that do the actual incrementing.</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="0753385118-1">(</span><span class="n">IncrementVal</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="0753385118-1">)</span><span class="w"> </span><span class="p" data-group-id="0753385118-2">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3210777966-2">}</span></code></pre><p>We call this fragment <code class="inline">fetch</code>.  This fragment will be duplicated three
│ │ │ +times, one for each value of the first operand (<code class="inline">r</code>, <code class="inline">x</code>, and <code class="inline">y</code>).</p><p>Next we define the main part of the code that do the actual incrementing.</p><pre><code class="makeup erlang" translate="no"><span class="ss">increment</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="3082222638-1">(</span><span class="n">IncrementVal</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="3082222638-1">)</span><span class="w"> </span><span class="p" data-group-id="3082222638-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$I</span><span class="ss">ncrementVal</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Uint</span><span class="w"> </span><span class="ss">live</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">result</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="0753385118-3">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="0753385118-4">(</span><span class="nf">is_small</span><span class="p" data-group-id="0753385118-5">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="0753385118-5">)</span><span class="p" data-group-id="0753385118-4">)</span><span class="p" data-group-id="0753385118-3">)</span><span class="w"> </span><span class="p" data-group-id="0753385118-6">{</span><span class="w">
│ │ │ -        </span><span class="n">Sint</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">signed_val</span><span class="p" data-group-id="0753385118-7">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="0753385118-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">increment_val</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="0753385118-8">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="0753385118-9">(</span><span class="n">IS_SSMALL</span><span class="p" data-group-id="0753385118-10">(</span><span class="ss">i</span><span class="p" data-group-id="0753385118-10">)</span><span class="p" data-group-id="0753385118-9">)</span><span class="p" data-group-id="0753385118-8">)</span><span class="w"> </span><span class="p" data-group-id="0753385118-11">{</span><span class="w">
│ │ │ -            </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="0753385118-12">(</span><span class="ss">i</span><span class="p" data-group-id="0753385118-12">)</span><span class="p">;</span><span class="w">
│ │ │ -            </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="0753385118-13">(</span><span class="p" data-group-id="0753385118-13">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="0753385118-11">}</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0753385118-6">}</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="3082222638-3">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="3082222638-4">(</span><span class="nf">is_small</span><span class="p" data-group-id="3082222638-5">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="3082222638-5">)</span><span class="p" data-group-id="3082222638-4">)</span><span class="p" data-group-id="3082222638-3">)</span><span class="w"> </span><span class="p" data-group-id="3082222638-6">{</span><span class="w">
│ │ │ +        </span><span class="n">Sint</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">signed_val</span><span class="p" data-group-id="3082222638-7">(</span><span class="ss">increment_reg_val</span><span class="p" data-group-id="3082222638-7">)</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="ss">increment_val</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="3082222638-8">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="3082222638-9">(</span><span class="n">IS_SSMALL</span><span class="p" data-group-id="3082222638-10">(</span><span class="ss">i</span><span class="p" data-group-id="3082222638-10">)</span><span class="p" data-group-id="3082222638-9">)</span><span class="p" data-group-id="3082222638-8">)</span><span class="w"> </span><span class="p" data-group-id="3082222638-11">{</span><span class="w">
│ │ │ +            </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="3082222638-12">(</span><span class="ss">i</span><span class="p" data-group-id="3082222638-12">)</span><span class="p">;</span><span class="w">
│ │ │ +            </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="3082222638-13">(</span><span class="p" data-group-id="3082222638-13">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="p" data-group-id="3082222638-11">}</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3082222638-6">}</span><span class="w">
│ │ │      </span><span class="ss">live</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$L</span><span class="ss">ive</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPOUT</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">reg</span><span class="p" data-group-id="0753385118-14">[</span><span class="ss">live</span><span class="p" data-group-id="0753385118-14">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">reg</span><span class="p" data-group-id="0753385118-15">[</span><span class="ss">live</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="0753385118-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="0753385118-16">(</span><span class="ss">increment_val</span><span class="p" data-group-id="0753385118-16">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_mixed_plus</span><span class="p" data-group-id="0753385118-17">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="ss">live</span><span class="p" data-group-id="0753385118-17">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">reg</span><span class="p" data-group-id="3082222638-14">[</span><span class="ss">live</span><span class="p" data-group-id="3082222638-14">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">reg</span><span class="p" data-group-id="3082222638-15">[</span><span class="ss">live</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="3082222638-15">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">make_small</span><span class="p" data-group-id="3082222638-16">(</span><span class="ss">increment_val</span><span class="p" data-group-id="3082222638-16">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_gc_mixed_plus</span><span class="p" data-group-id="3082222638-17">(</span><span class="ss">c_p</span><span class="p">,</span><span class="w"> </span><span class="ss">reg</span><span class="p">,</span><span class="w"> </span><span class="ss">live</span><span class="p" data-group-id="3082222638-17">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">HEAVY_SWAPIN</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ERTS_HOLE_CHECK</span><span class="p" data-group-id="0753385118-18">(</span><span class="ss">c_p</span><span class="p" data-group-id="0753385118-18">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="0753385118-19">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="0753385118-20">(</span><span class="nf">is_value</span><span class="p" data-group-id="0753385118-21">(</span><span class="ss">result</span><span class="p" data-group-id="0753385118-21">)</span><span class="p" data-group-id="0753385118-20">)</span><span class="p" data-group-id="0753385118-19">)</span><span class="w"> </span><span class="p" data-group-id="0753385118-22">{</span><span class="w">
│ │ │ -        </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="0753385118-23">(</span><span class="p" data-group-id="0753385118-23">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">ERTS_HOLE_CHECK</span><span class="p" data-group-id="3082222638-18">(</span><span class="ss">c_p</span><span class="p" data-group-id="3082222638-18">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">if</span><span class="w"> </span><span class="p" data-group-id="3082222638-19">(</span><span class="n">ERTS_LIKELY</span><span class="p" data-group-id="3082222638-20">(</span><span class="nf">is_value</span><span class="p" data-group-id="3082222638-21">(</span><span class="ss">result</span><span class="p" data-group-id="3082222638-21">)</span><span class="p" data-group-id="3082222638-20">)</span><span class="p" data-group-id="3082222638-19">)</span><span class="w"> </span><span class="p" data-group-id="3082222638-22">{</span><span class="w">
│ │ │ +        </span><span class="sc">$R</span><span class="n">EFRESH_GEN_DEST</span><span class="p" data-group-id="3082222638-23">(</span><span class="p" data-group-id="3082222638-23">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="sc">$D</span><span class="ss">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">result</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="0753385118-24">(</span><span class="p" data-group-id="0753385118-24">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="0753385118-22">}</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="0753385118-25">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">freason</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="n">BADMATCH</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_value</span><span class="p" data-group-id="0753385118-26">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">fvalue</span><span class="p" data-group-id="0753385118-26">)</span><span class="p" data-group-id="0753385118-25">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="sc">$N</span><span class="n">EXT0</span><span class="p" data-group-id="3082222638-24">(</span><span class="p" data-group-id="3082222638-24">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3082222638-22">}</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="3082222638-25">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">freason</span><span class="w"> </span><span class="o">!</span><span class="o">=</span><span class="w"> </span><span class="n">BADMATCH</span><span class="w"> </span><span class="p">||</span><span class="w"> </span><span class="nf">is_value</span><span class="p" data-group-id="3082222638-26">(</span><span class="ss">c_p</span><span class="p">-&gt;</span><span class="ss">fvalue</span><span class="p" data-group-id="3082222638-26">)</span><span class="p" data-group-id="3082222638-25">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">goto</span><span class="w"> </span><span class="ss">find_func_info</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0753385118-2">}</span></code></pre><p>We call this fragment <code class="inline">execute</code>.  It will handle the three remaining
│ │ │ +</span><span class="p" data-group-id="3082222638-2">}</span></code></pre><p>We call this fragment <code class="inline">execute</code>.  It will handle the three remaining
│ │ │  operands (<code class="inline">W t d</code>).  There will only be one copy of this fragment.</p><p>Now that we have defined the fragments, we need to inform
│ │ │  <strong>beam_makeops</strong> how they should be connected:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_increment</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">increment</span><span class="p">.</span><span class="ss">fetch</span><span class="p">.</span><span class="ss">execute</span><span class="p">;</span></code></pre><p>To the left of the <code class="inline">:=</code> is the name of the specific instruction that
│ │ │  should be implemented by the fragments, in this case <code class="inline">i_increment</code>.
│ │ │  To the right of <code class="inline">:=</code> is the name of the group with the fragments,
│ │ │  followed by a <code class="inline">.</code>.  Then the name of the fragments in the group are
│ │ │  listed in the order they should be executed.  Note that the <code class="inline">head</code>
│ │ │  fragment is not listed.</p><p>The line ends in <code class="inline">;</code> (to avoid messing up the indentation in Emacs).</p><p>(Note that in practice the <code class="inline">:=</code> line is usually placed before the
│ │ │ -fragments.)</p><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4619510141-1">{</span><span class="w">
│ │ │ +fragments.)</p><p>The generated code looks like this:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="5025044230-1">{</span><span class="w">
│ │ │    </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">increment_reg_val</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="n">OpCase</span><span class="p" data-group-id="4619510141-2">(</span><span class="ss">i_increment_rWtd</span><span class="p" data-group-id="4619510141-2">)</span><span class="p">:</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4619510141-3">{</span><span class="w">
│ │ │ -    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">r</span><span class="p" data-group-id="4619510141-4">(</span><span class="mi">0</span><span class="p" data-group-id="4619510141-4">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4619510141-3">}</span><span class="w">
│ │ │ +  </span><span class="n">OpCase</span><span class="p" data-group-id="5025044230-2">(</span><span class="ss">i_increment_rWtd</span><span class="p" data-group-id="5025044230-2">)</span><span class="p">:</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5025044230-3">{</span><span class="w">
│ │ │ +    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">r</span><span class="p" data-group-id="5025044230-4">(</span><span class="mi">0</span><span class="p" data-group-id="5025044230-4">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5025044230-3">}</span><span class="w">
│ │ │    </span><span class="ss">goto</span><span class="w"> </span><span class="ss">increment__execute</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="n">OpCase</span><span class="p" data-group-id="4619510141-5">(</span><span class="ss">i_increment_xWtd</span><span class="p" data-group-id="4619510141-5">)</span><span class="p">:</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4619510141-6">{</span><span class="w">
│ │ │ -    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="4619510141-7">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="4619510141-8">(</span><span class="n">I</span><span class="p" data-group-id="4619510141-9">[</span><span class="mi">0</span><span class="p" data-group-id="4619510141-9">]</span><span class="p" data-group-id="4619510141-8">)</span><span class="p" data-group-id="4619510141-7">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4619510141-6">}</span><span class="w">
│ │ │ +  </span><span class="n">OpCase</span><span class="p" data-group-id="5025044230-5">(</span><span class="ss">i_increment_xWtd</span><span class="p" data-group-id="5025044230-5">)</span><span class="p">:</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5025044230-6">{</span><span class="w">
│ │ │ +    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">xb</span><span class="p" data-group-id="5025044230-7">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="5025044230-8">(</span><span class="n">I</span><span class="p" data-group-id="5025044230-9">[</span><span class="mi">0</span><span class="p" data-group-id="5025044230-9">]</span><span class="p" data-group-id="5025044230-8">)</span><span class="p" data-group-id="5025044230-7">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5025044230-6">}</span><span class="w">
│ │ │    </span><span class="ss">goto</span><span class="w"> </span><span class="ss">increment__execute</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -  </span><span class="n">OpCase</span><span class="p" data-group-id="4619510141-10">(</span><span class="ss">i_increment_yWtd</span><span class="p" data-group-id="4619510141-10">)</span><span class="p">:</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4619510141-11">{</span><span class="w">
│ │ │ -    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">yb</span><span class="p" data-group-id="4619510141-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="4619510141-13">(</span><span class="n">I</span><span class="p" data-group-id="4619510141-14">[</span><span class="mi">0</span><span class="p" data-group-id="4619510141-14">]</span><span class="p" data-group-id="4619510141-13">)</span><span class="p" data-group-id="4619510141-12">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4619510141-11">}</span><span class="w">
│ │ │ +  </span><span class="n">OpCase</span><span class="p" data-group-id="5025044230-10">(</span><span class="ss">i_increment_yWtd</span><span class="p" data-group-id="5025044230-10">)</span><span class="p">:</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5025044230-11">{</span><span class="w">
│ │ │ +    </span><span class="ss">increment_reg_val</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">yb</span><span class="p" data-group-id="5025044230-12">(</span><span class="n">BeamExtraData</span><span class="p" data-group-id="5025044230-13">(</span><span class="n">I</span><span class="p" data-group-id="5025044230-14">[</span><span class="mi">0</span><span class="p" data-group-id="5025044230-14">]</span><span class="p" data-group-id="5025044230-13">)</span><span class="p" data-group-id="5025044230-12">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5025044230-11">}</span><span class="w">
│ │ │    </span><span class="ss">goto</span><span class="w"> </span><span class="ss">increment__execute</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │    </span><span class="nc">increment__execute</span><span class="p">:</span><span class="w">
│ │ │ -  </span><span class="p" data-group-id="4619510141-15">{</span><span class="w">
│ │ │ -    </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Here</span><span class="w"> </span><span class="ss">follows</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">increment</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="4619510141-16">(</span><span class="p" data-group-id="4619510141-16">)</span><span class="w">
│ │ │ +  </span><span class="p" data-group-id="5025044230-15">{</span><span class="w">
│ │ │ +    </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Here</span><span class="w"> </span><span class="ss">follows</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">increment</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="5025044230-16">(</span><span class="p" data-group-id="5025044230-16">)</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="4619510141-15">}</span></code></pre><h5>Some notes about combined instructions</h5><p>The operands that are different must be at
│ │ │ +</span><span class="p" data-group-id="5025044230-15">}</span></code></pre><h5>Some notes about combined instructions</h5><p>The operands that are different must be at
│ │ │  the beginning of the instruction.  All operands in the last
│ │ │  fragment must have the same operands in all variants of
│ │ │  the specific instruction.</p><p>As an example, the following specific instructions cannot be
│ │ │  implemented as a combined instruction:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_times</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_times</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_times</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">d</span></code></pre><p>We would have to change the order of the operands so that the
│ │ │  two operands that are different are placed first:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_times</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_times</span><span class="w"> </span><span class="ss">x</span><span class="w"> </span><span class="ss">y</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span><span class="w">
│ │ │  </span><span class="ss">i_times</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="w"> </span><span class="ss">d</span></code></pre><p>We can then define:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_times</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">times</span><span class="p">.</span><span class="ss">fetch</span><span class="p">.</span><span class="ss">execute</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">times</span><span class="p">.</span><span class="ss">head</span><span class="w"> </span><span class="p" data-group-id="8016926921-1">{</span><span class="w">
│ │ │ +</span><span class="ss">times</span><span class="p">.</span><span class="ss">head</span><span class="w"> </span><span class="p" data-group-id="5104633792-1">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">op1</span><span class="p">,</span><span class="w"> </span><span class="ss">op2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8016926921-1">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5104633792-1">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">times</span><span class="p">.</span><span class="nf">fetch</span><span class="p" data-group-id="8016926921-2">(</span><span class="n">Src1</span><span class="p">,</span><span class="w"> </span><span class="n">Src2</span><span class="p" data-group-id="8016926921-2">)</span><span class="w"> </span><span class="p" data-group-id="8016926921-3">{</span><span class="w">
│ │ │ +</span><span class="ss">times</span><span class="p">.</span><span class="nf">fetch</span><span class="p" data-group-id="5104633792-2">(</span><span class="n">Src1</span><span class="p">,</span><span class="w"> </span><span class="n">Src2</span><span class="p" data-group-id="5104633792-2">)</span><span class="w"> </span><span class="p" data-group-id="5104633792-3">{</span><span class="w">
│ │ │      </span><span class="ss">op1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc1</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">op2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$S</span><span class="ss">rc2</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8016926921-3">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5104633792-3">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">times</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="8016926921-4">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="8016926921-4">)</span><span class="w"> </span><span class="p" data-group-id="8016926921-5">{</span><span class="w">
│ │ │ +</span><span class="ss">times</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="5104633792-4">(</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="5104633792-4">)</span><span class="w"> </span><span class="p" data-group-id="5104633792-5">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Multiply</span><span class="w"> </span><span class="ss">op1</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">op2</span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8016926921-5">}</span></code></pre><p>Several instructions can share a group.  As an example, the following
│ │ │ +</span><span class="p" data-group-id="5104633792-5">}</span></code></pre><p>Several instructions can share a group.  As an example, the following
│ │ │  instructions have different names, but in the end they all create a
│ │ │  binary.  The last two operands are common for all of them:</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_bs_init_fail</span><span class="w">       </span><span class="ss">xy</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init_fail_heap</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="ss">j</span><span class="o">?</span><span class="w"> </span><span class="ss">t</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init</span><span class="w">                </span><span class="n">W</span><span class="w"> </span><span class="ss">t</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init_heap</span><span class="w">         </span><span class="n">W</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="ss">t</span><span class="o">?</span><span class="w"> </span><span class="ss">x</span></code></pre><p>The instructions are defined like this (formatted with extra
│ │ │  spaces for clarity):</p><pre><code class="makeup erlang" translate="no"><span class="ss">i_bs_init_fail_heap</span><span class="w"> </span><span class="p">:=</span><span class="w"> </span><span class="ss">bs_init</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">fail_heap</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">verify</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">execute</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init_fail</span><span class="w">      </span><span class="p">:=</span><span class="w"> </span><span class="ss">bs_init</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">fail</span><span class="w">      </span><span class="p">.</span><span class="w"> </span><span class="ss">verify</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">execute</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init</span><span class="w">           </span><span class="p">:=</span><span class="w"> </span><span class="ss">bs_init</span><span class="w"> </span><span class="p">.</span><span class="w">           </span><span class="p">.</span><span class="w">  </span><span class="ss">plain</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">execute</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="ss">i_bs_init_heap</span><span class="w">      </span><span class="p">:=</span><span class="w"> </span><span class="ss">bs_init</span><span class="w"> </span><span class="p">.</span><span class="w">               </span><span class="ss">heap</span><span class="w"> </span><span class="p">.</span><span class="w"> </span><span class="ss">execute</span><span class="p">;</span></code></pre><p>Note that the first two instruction have three fragments, while the
│ │ │ -other two only have two fragments.  Here are the fragments:</p><pre><code class="makeup erlang" translate="no"><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">head</span><span class="p" data-group-id="0095966533-1">(</span><span class="p" data-group-id="0095966533-1">)</span><span class="w"> </span><span class="p" data-group-id="0095966533-2">{</span><span class="w">
│ │ │ +other two only have two fragments.  Here are the fragments:</p><pre><code class="makeup erlang" translate="no"><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">head</span><span class="p" data-group-id="7552034407-1">(</span><span class="p" data-group-id="7552034407-1">)</span><span class="w"> </span><span class="p" data-group-id="7552034407-2">{</span><span class="w">
│ │ │      </span><span class="n">Eterm</span><span class="w"> </span><span class="ss">num_bits_term</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Uint</span><span class="w"> </span><span class="ss">num_bits</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">Uint</span><span class="w"> </span><span class="ss">alloc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0095966533-2">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7552034407-2">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">plain</span><span class="p" data-group-id="0095966533-3">(</span><span class="n">NumBits</span><span class="p" data-group-id="0095966533-3">)</span><span class="w"> </span><span class="p" data-group-id="0095966533-4">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">plain</span><span class="p" data-group-id="7552034407-3">(</span><span class="n">NumBits</span><span class="p" data-group-id="7552034407-3">)</span><span class="w"> </span><span class="p" data-group-id="7552034407-4">{</span><span class="w">
│ │ │      </span><span class="ss">num_bits</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="ss">umBits</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">alloc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0095966533-4">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7552034407-4">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">heap</span><span class="p" data-group-id="0095966533-5">(</span><span class="n">NumBits</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="0095966533-5">)</span><span class="w"> </span><span class="p" data-group-id="0095966533-6">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">heap</span><span class="p" data-group-id="7552034407-5">(</span><span class="n">NumBits</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="7552034407-5">)</span><span class="w"> </span><span class="p" data-group-id="7552034407-6">{</span><span class="w">
│ │ │      </span><span class="ss">num_bits</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="ss">umBits</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">alloc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="ss">lloc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0095966533-6">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7552034407-6">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">fail</span><span class="p" data-group-id="0095966533-7">(</span><span class="n">NumBitsTerm</span><span class="p" data-group-id="0095966533-7">)</span><span class="w"> </span><span class="p" data-group-id="0095966533-8">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">fail</span><span class="p" data-group-id="7552034407-7">(</span><span class="n">NumBitsTerm</span><span class="p" data-group-id="7552034407-7">)</span><span class="w"> </span><span class="p" data-group-id="7552034407-8">{</span><span class="w">
│ │ │      </span><span class="ss">num_bits_term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="ss">umBitsTerm</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">alloc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0095966533-8">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7552034407-8">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">fail_heap</span><span class="p" data-group-id="0095966533-9">(</span><span class="n">NumBitsTerm</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="0095966533-9">)</span><span class="w"> </span><span class="p" data-group-id="0095966533-10">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">fail_heap</span><span class="p" data-group-id="7552034407-9">(</span><span class="n">NumBitsTerm</span><span class="p">,</span><span class="w"> </span><span class="n">Alloc</span><span class="p" data-group-id="7552034407-9">)</span><span class="w"> </span><span class="p" data-group-id="7552034407-10">{</span><span class="w">
│ │ │      </span><span class="ss">num_bits_term</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$N</span><span class="ss">umBitsTerm</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">alloc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">$A</span><span class="ss">lloc</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0095966533-10">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7552034407-10">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">verify</span><span class="p" data-group-id="0095966533-11">(</span><span class="n">Fail</span><span class="p" data-group-id="0095966533-11">)</span><span class="w"> </span><span class="p" data-group-id="0095966533-12">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">verify</span><span class="p" data-group-id="7552034407-11">(</span><span class="n">Fail</span><span class="p" data-group-id="7552034407-11">)</span><span class="w"> </span><span class="p" data-group-id="7552034407-12">{</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Verify</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">num_bits_term</span><span class="p">,</span><span class="w"> </span><span class="ss">fail</span><span class="w"> </span><span class="ss">using</span><span class="w"> </span><span class="sc">$F</span><span class="n">AIL</span><span class="w">
│ │ │      </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="ss">there</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">problem</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="w">
│ │ │  </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0095966533-12">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7552034407-12">}</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="0095966533-13">(</span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="0095966533-13">)</span><span class="w"> </span><span class="p" data-group-id="0095966533-14">{</span><span class="w">
│ │ │ +</span><span class="ss">bs_init_bits</span><span class="p">.</span><span class="nf">execute</span><span class="p" data-group-id="7552034407-13">(</span><span class="n">Live</span><span class="p">,</span><span class="w"> </span><span class="n">Dst</span><span class="p" data-group-id="7552034407-13">)</span><span class="w"> </span><span class="p" data-group-id="7552034407-14">{</span><span class="w">
│ │ │     </span><span class="o">/</span><span class="o">/</span><span class="w"> </span><span class="n">Long</span><span class="w"> </span><span class="ss">complicated</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">create</span><span class="w"> </span><span class="ss">a</span><span class="w"> </span><span class="ss">binary</span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │     </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0095966533-14">}</span></code></pre><p>The full definitions of those instructions can be found in <code class="inline">bs_instrs.tab</code>.
│ │ │ +</span><span class="p" data-group-id="7552034407-14">}</span></code></pre><p>The full definitions of those instructions can be found in <code class="inline">bs_instrs.tab</code>.
│ │ │  The generated code can be found in <code class="inline">beam_warm.h</code>.</p><h3 id="code-generation-for-beamasm" class="section-heading">
│ │ │    <a href="#code-generation-for-beamasm" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Code generation for BeamAsm</span>
│ │ │  </h3>
│ │ │  <p>For the BeamAsm runtime system, the implementation of each instruction is defined
│ │ │  by emitter functions written in C++ that emit the assembly code for each instruction.
│ │ │  There is one emitter function for each family of specific instructions.</p><p>Take for example the <code class="inline">move</code> instruction. In <code class="inline">beam/asm/ops.tab</code> there is a
│ │ │ -single specific instruction for <code class="inline">move</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The implementation is found in <code class="inline">beam/asm/instr_common.cpp</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_move</span><span class="p" data-group-id="8206048372-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Dst</span><span class="p" data-group-id="8206048372-1">)</span><span class="w"> </span><span class="p" data-group-id="8206048372-2">{</span><span class="w">
│ │ │ -    </span><span class="nf">mov_arg</span><span class="p" data-group-id="8206048372-3">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="8206048372-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8206048372-2">}</span></code></pre><p>The <code class="inline">mov_arg()</code> helper function will handle all combinations of source and destination
│ │ │ -operands.  For example, the instruction <code class="inline">{move,{x,1},{y,1}}</code> will be translated like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mov</span><span class="w"> </span><span class="ss">rdi</span><span class="p">,</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="7383074636-1">[</span><span class="ss">rbx</span><span class="o">+</span><span class="mi">8</span><span class="p" data-group-id="7383074636-1">]</span><span class="w">
│ │ │ -</span><span class="ss">mov</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="7383074636-2">[</span><span class="ss">rsp</span><span class="o">+</span><span class="mi">8</span><span class="p" data-group-id="7383074636-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">rdi</span></code></pre><p>while <code class="inline">{move,{integer,42},{x,0}}</code> will be translated like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mov</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="8758923208-1">[</span><span class="ss">rbx</span><span class="p" data-group-id="8758923208-1">]</span><span class="p">,</span><span class="w"> </span><span class="mi">687</span></code></pre><p>It is possible to define more than one specific instruction, but there will still be
│ │ │ +single specific instruction for <code class="inline">move</code> defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">move</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">d</span></code></pre><p>The implementation is found in <code class="inline">beam/asm/instr_common.cpp</code>:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_move</span><span class="p" data-group-id="7059223718-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Dst</span><span class="p" data-group-id="7059223718-1">)</span><span class="w"> </span><span class="p" data-group-id="7059223718-2">{</span><span class="w">
│ │ │ +    </span><span class="nf">mov_arg</span><span class="p" data-group-id="7059223718-3">(</span><span class="n">Dst</span><span class="p">,</span><span class="w"> </span><span class="n">Src</span><span class="p" data-group-id="7059223718-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7059223718-2">}</span></code></pre><p>The <code class="inline">mov_arg()</code> helper function will handle all combinations of source and destination
│ │ │ +operands.  For example, the instruction <code class="inline">{move,{x,1},{y,1}}</code> will be translated like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mov</span><span class="w"> </span><span class="ss">rdi</span><span class="p">,</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="3812008023-1">[</span><span class="ss">rbx</span><span class="o">+</span><span class="mi">8</span><span class="p" data-group-id="3812008023-1">]</span><span class="w">
│ │ │ +</span><span class="ss">mov</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="3812008023-2">[</span><span class="ss">rsp</span><span class="o">+</span><span class="mi">8</span><span class="p" data-group-id="3812008023-2">]</span><span class="p">,</span><span class="w"> </span><span class="ss">rdi</span></code></pre><p>while <code class="inline">{move,{integer,42},{x,0}}</code> will be translated like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">mov</span><span class="w"> </span><span class="ss">qword</span><span class="w"> </span><span class="p" data-group-id="5343260587-1">[</span><span class="ss">rbx</span><span class="p" data-group-id="5343260587-1">]</span><span class="p">,</span><span class="w"> </span><span class="mi">687</span></code></pre><p>It is possible to define more than one specific instruction, but there will still be
│ │ │  only one emitter function. For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">fload</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="ss">l</span><span class="w">
│ │ │  </span><span class="ss">fload</span><span class="w"> </span><span class="ss">q</span><span class="w"> </span><span class="ss">l</span></code></pre><p>By defining <code class="inline">fload</code> like this, the source operand must be a X register, Y register, or
│ │ │  a literal.  If not, the loading will be aborted.  If the instruction instead had been
│ │ │  defined like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">fload</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">l</span></code></pre><p>attempting to load an invalid instruction such as <code class="inline">{fload,{atom,clearly_bad},{fr,0}}</code>
│ │ │  would cause a crash (either at load time or when the instruction was executed).</p><p>Regardless on how many specific instructions there are in the family,
│ │ │ -only a single <code class="inline">emit_fload()</code> function is allowed:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_fload</span><span class="p" data-group-id="0701038697-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Dst</span><span class="p" data-group-id="0701038697-1">)</span><span class="w"> </span><span class="p" data-group-id="0701038697-2">{</span><span class="w">
│ │ │ +only a single <code class="inline">emit_fload()</code> function is allowed:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_fload</span><span class="p" data-group-id="0636357378-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Dst</span><span class="p" data-group-id="0636357378-1">)</span><span class="w"> </span><span class="p" data-group-id="0636357378-2">{</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │      </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0701038697-2">}</span></code></pre><p><a href="" id="handling-a-variable-number-of-operands"></a></p><h4>Handling a variable number of operands</h4><p>Here follows an example of how an instruction with a variable number
│ │ │ +</span><span class="p" data-group-id="0636357378-2">}</span></code></pre><p><a href="" id="handling-a-variable-number-of-operands"></a></p><h4>Handling a variable number of operands</h4><p>Here follows an example of how an instruction with a variable number
│ │ │  of operands could be handled.  One such instructions is
│ │ │ -<code class="inline">select_val/3</code>. Here is an example how it can look like in BEAM code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="0008284231-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="0008284231-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="0008284231-2">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="0008284231-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="0008284231-3">}</span><span class="p">,</span><span class="w">
│ │ │ -            </span><span class="p" data-group-id="0008284231-4">{</span><span class="ss">list</span><span class="p">,</span><span class="p" data-group-id="0008284231-5">[</span><span class="p" data-group-id="0008284231-6">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="0008284231-6">}</span><span class="p">,</span><span class="p" data-group-id="0008284231-7">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="0008284231-7">}</span><span class="p">,</span><span class="p" data-group-id="0008284231-8">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="0008284231-8">}</span><span class="p">,</span><span class="p" data-group-id="0008284231-9">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="0008284231-9">}</span><span class="p" data-group-id="0008284231-5">]</span><span class="p" data-group-id="0008284231-4">}</span><span class="p" data-group-id="0008284231-1">}</span><span class="p">.</span></code></pre><p>The loader will convert a <code class="inline">{list,[...]}</code> operand to an <code class="inline">u</code> operand whose
│ │ │ +<code class="inline">select_val/3</code>. Here is an example how it can look like in BEAM code:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4119051511-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="4119051511-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4119051511-2">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="4119051511-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4119051511-3">}</span><span class="p">,</span><span class="w">
│ │ │ +            </span><span class="p" data-group-id="4119051511-4">{</span><span class="ss">list</span><span class="p">,</span><span class="p" data-group-id="4119051511-5">[</span><span class="p" data-group-id="4119051511-6">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4119051511-6">}</span><span class="p">,</span><span class="p" data-group-id="4119051511-7">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4119051511-7">}</span><span class="p">,</span><span class="p" data-group-id="4119051511-8">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4119051511-8">}</span><span class="p">,</span><span class="p" data-group-id="4119051511-9">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4119051511-9">}</span><span class="p" data-group-id="4119051511-5">]</span><span class="p" data-group-id="4119051511-4">}</span><span class="p" data-group-id="4119051511-1">}</span><span class="p">.</span></code></pre><p>The loader will convert a <code class="inline">{list,[...]}</code> operand to an <code class="inline">u</code> operand whose
│ │ │  value is the number of elements in the list, followed by each element in
│ │ │  the list.  The instruction above would be translated to the following
│ │ │ -instruction:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4763949357-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="4763949357-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="4763949357-2">}</span><span class="p">,</span><span class="p" data-group-id="4763949357-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="4763949357-3">}</span><span class="p">,</span><span class="p" data-group-id="4763949357-4">{</span><span class="ss">u</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4763949357-4">}</span><span class="p">,</span><span class="p" data-group-id="4763949357-5">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="4763949357-5">}</span><span class="p">,</span><span class="p" data-group-id="4763949357-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="4763949357-6">}</span><span class="p">,</span><span class="p" data-group-id="4763949357-7">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="4763949357-7">}</span><span class="p">,</span><span class="p" data-group-id="4763949357-8">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="4763949357-8">}</span><span class="p" data-group-id="4763949357-1">}</span></code></pre><p>A definition of a specific instruction for that instruction would look
│ │ │ +instruction:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="3411816632-1">{</span><span class="ss">select_val</span><span class="p">,</span><span class="p" data-group-id="3411816632-2">{</span><span class="ss">x</span><span class="p">,</span><span class="mi">0</span><span class="p" data-group-id="3411816632-2">}</span><span class="p">,</span><span class="p" data-group-id="3411816632-3">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">1</span><span class="p" data-group-id="3411816632-3">}</span><span class="p">,</span><span class="p" data-group-id="3411816632-4">{</span><span class="ss">u</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3411816632-4">}</span><span class="p">,</span><span class="p" data-group-id="3411816632-5">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">b</span><span class="p" data-group-id="3411816632-5">}</span><span class="p">,</span><span class="p" data-group-id="3411816632-6">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">4</span><span class="p" data-group-id="3411816632-6">}</span><span class="p">,</span><span class="p" data-group-id="3411816632-7">{</span><span class="ss">atom</span><span class="p">,</span><span class="ss">a</span><span class="p" data-group-id="3411816632-7">}</span><span class="p">,</span><span class="p" data-group-id="3411816632-8">{</span><span class="ss">f</span><span class="p">,</span><span class="mi">5</span><span class="p" data-group-id="3411816632-8">}</span><span class="p" data-group-id="3411816632-1">}</span></code></pre><p>A definition of a specific instruction for that instruction would look
│ │ │  like this:</p><pre><code class="makeup erlang" translate="no"><span class="ss">select_val</span><span class="w"> </span><span class="ss">s</span><span class="w"> </span><span class="ss">f</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">*</span></code></pre><p>The <code class="inline">*</code> as the last operand will make sure that the variable operands
│ │ │  are passed in as a <code class="inline">Span</code> of <code class="inline">ArgVal</code> (will be <code class="inline">std::span</code> in C++20 onwards).
│ │ │ -Here is the emitter function:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_select_val</span><span class="p" data-group-id="6976121219-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w">
│ │ │ +Here is the emitter function:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_select_val</span><span class="p" data-group-id="9692592502-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p">,</span><span class="w">
│ │ │                                            </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Fail</span><span class="p">,</span><span class="w">
│ │ │                                            </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Size</span><span class="p">,</span><span class="w">
│ │ │ -                                          </span><span class="ss">const</span><span class="w"> </span><span class="n">Span</span><span class="o">&lt;</span><span class="n">ArgVal</span><span class="o">&gt;</span><span class="w"> </span><span class="err">&amp;</span><span class="ss">args</span><span class="p" data-group-id="6976121219-1">)</span><span class="w"> </span><span class="p" data-group-id="6976121219-2">{</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="6976121219-3">(</span><span class="n">Size</span><span class="p">.</span><span class="nf">getValue</span><span class="p" data-group-id="6976121219-4">(</span><span class="p" data-group-id="6976121219-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="ss">args</span><span class="p">.</span><span class="nf">size</span><span class="p" data-group-id="6976121219-5">(</span><span class="p" data-group-id="6976121219-5">)</span><span class="p" data-group-id="6976121219-3">)</span><span class="p">;</span><span class="w">
│ │ │ +                                          </span><span class="ss">const</span><span class="w"> </span><span class="n">Span</span><span class="o">&lt;</span><span class="n">ArgVal</span><span class="o">&gt;</span><span class="w"> </span><span class="err">&amp;</span><span class="ss">args</span><span class="p" data-group-id="9692592502-1">)</span><span class="w"> </span><span class="p" data-group-id="9692592502-2">{</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="9692592502-3">(</span><span class="n">Size</span><span class="p">.</span><span class="nf">getValue</span><span class="p" data-group-id="9692592502-4">(</span><span class="p" data-group-id="9692592502-4">)</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="ss">args</span><span class="p">.</span><span class="nf">size</span><span class="p" data-group-id="9692592502-5">(</span><span class="p" data-group-id="9692592502-5">)</span><span class="p" data-group-id="9692592502-3">)</span><span class="p">;</span><span class="w">
│ │ │         </span><span class="p">.</span><span class="w">
│ │ │         </span><span class="p">.</span><span class="w">
│ │ │         </span><span class="p">.</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6976121219-2">}</span></code></pre>
│ │ │ +</span><span class="p" data-group-id="9692592502-2">}</span></code></pre>
│ │ │  </div>
│ │ │  
│ │ │  <div class="bottom-actions" id="bottom-actions">
│ │ │    <div class="bottom-actions-item">
│ │ │  
│ │ │        <a href="tracing.html" class="bottom-actions-button" rel="prev">
│ │ │          <span class="subheader">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/beamasm.html
│ │ │ @@ -145,26 +145,26 @@
│ │ │  </h2>
│ │ │  <p>The code is loaded very similarly to how it is loaded for the interpreter. Each beam
│ │ │  file is parsed and then optimized through the transformations described in
│ │ │  <a href="beam_makeops.html#defining-transformation-rules">beam_makeops</a>. The transformations
│ │ │  used in BeamAsm are much simpler than the interpreter's, as most of the
│ │ │  transformations for the interpreter are done only to eliminate the instruction
│ │ │  dispatch overhead.</p><p>Then each instruction is encoded using the C++ functions in the
│ │ │ -<code class="inline">jit/$ARCH/instr_*.cpp</code> files. For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_is_nonempty_list</span><span class="p" data-group-id="2941654530-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p" data-group-id="2941654530-1">)</span><span class="w"> </span><span class="p" data-group-id="2941654530-2">{</span><span class="w">
│ │ │ -  </span><span class="ss">a</span><span class="p">.</span><span class="nf">test</span><span class="p" data-group-id="2941654530-3">(</span><span class="nf">getArgRef</span><span class="p" data-group-id="2941654530-4">(</span><span class="n">Src</span><span class="p" data-group-id="2941654530-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">imm</span><span class="p" data-group-id="2941654530-5">(</span><span class="p">_</span><span class="n">TAG_PRIMARY_MASK</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">TAG_PRIMARY_LIST</span><span class="p" data-group-id="2941654530-5">)</span><span class="p" data-group-id="2941654530-3">)</span><span class="p">;</span><span class="w">
│ │ │ -  </span><span class="ss">a</span><span class="p">.</span><span class="nf">jne</span><span class="p" data-group-id="2941654530-6">(</span><span class="ss">labels</span><span class="p" data-group-id="2941654530-7">[</span><span class="n">Fail</span><span class="p">.</span><span class="nf">getLabel</span><span class="p" data-group-id="2941654530-8">(</span><span class="p" data-group-id="2941654530-8">)</span><span class="p" data-group-id="2941654530-7">]</span><span class="p" data-group-id="2941654530-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2941654530-2">}</span></code></pre><p><a href="https://github.com/asmjit/asmjit">asmjit</a> provides a fairly straightforward
│ │ │ +<code class="inline">jit/$ARCH/instr_*.cpp</code> files. For example:</p><pre><code class="makeup erlang" translate="no"><span class="ss">void</span><span class="w"> </span><span class="n">BeamModuleAssembler</span><span class="p">:</span><span class="p">:</span><span class="nf">emit_is_nonempty_list</span><span class="p" data-group-id="4909775579-1">(</span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Fail</span><span class="p">,</span><span class="w"> </span><span class="ss">const</span><span class="w"> </span><span class="n">ArgVal</span><span class="w"> </span><span class="err">&amp;</span><span class="n">Src</span><span class="p" data-group-id="4909775579-1">)</span><span class="w"> </span><span class="p" data-group-id="4909775579-2">{</span><span class="w">
│ │ │ +  </span><span class="ss">a</span><span class="p">.</span><span class="nf">test</span><span class="p" data-group-id="4909775579-3">(</span><span class="nf">getArgRef</span><span class="p" data-group-id="4909775579-4">(</span><span class="n">Src</span><span class="p" data-group-id="4909775579-4">)</span><span class="p">,</span><span class="w"> </span><span class="nf">imm</span><span class="p" data-group-id="4909775579-5">(</span><span class="p">_</span><span class="n">TAG_PRIMARY_MASK</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">TAG_PRIMARY_LIST</span><span class="p" data-group-id="4909775579-5">)</span><span class="p" data-group-id="4909775579-3">)</span><span class="p">;</span><span class="w">
│ │ │ +  </span><span class="ss">a</span><span class="p">.</span><span class="nf">jne</span><span class="p" data-group-id="4909775579-6">(</span><span class="ss">labels</span><span class="p" data-group-id="4909775579-7">[</span><span class="n">Fail</span><span class="p">.</span><span class="nf">getLabel</span><span class="p" data-group-id="4909775579-8">(</span><span class="p" data-group-id="4909775579-8">)</span><span class="p" data-group-id="4909775579-7">]</span><span class="p" data-group-id="4909775579-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4909775579-2">}</span></code></pre><p><a href="https://github.com/asmjit/asmjit">asmjit</a> provides a fairly straightforward
│ │ │  mapping from a C++ function call to the x86 assembly instruction. The above
│ │ │  instruction tests if the value in the <code class="inline">Src</code> register is a non-empty list and if
│ │ │  it is not then it jumps to the fail label.</p><p>For comparison, the interpreter has 8 combinations and specializations of
│ │ │  this implementation to minimize the instruction dispatch overhead for
│ │ │  common patterns.</p><p>The original register allocation done by the Erlang compiler is used to manage the
│ │ │  liveness of values and the physical registers are statically allocated to keep
│ │ │  the necessary process state. At the moment this is the static register
│ │ │ -allocation on x86-64:</p><pre><code class="makeup erlang" translate="no"><span class="nc">rbx</span><span class="p">:</span><span class="w"> </span><span class="n">ErtsSchedulerRegisters</span><span class="w"> </span><span class="nf">struct</span><span class="w"> </span><span class="p" data-group-id="6953018695-1">(</span><span class="ss">contains</span><span class="w"> </span><span class="ss">x</span><span class="o">/</span><span class="nb">float</span><span class="w"> </span><span class="ss">registers</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">some</span><span class="w"> </span><span class="ss">metadata</span><span class="p" data-group-id="6953018695-1">)</span><span class="w">
│ │ │ +allocation on x86-64:</p><pre><code class="makeup erlang" translate="no"><span class="nc">rbx</span><span class="p">:</span><span class="w"> </span><span class="n">ErtsSchedulerRegisters</span><span class="w"> </span><span class="nf">struct</span><span class="w"> </span><span class="p" data-group-id="2455115218-1">(</span><span class="ss">contains</span><span class="w"> </span><span class="ss">x</span><span class="o">/</span><span class="nb">float</span><span class="w"> </span><span class="ss">registers</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">some</span><span class="w"> </span><span class="ss">metadata</span><span class="p" data-group-id="2455115218-1">)</span><span class="w">
│ │ │  </span><span class="nc">rbp</span><span class="p">:</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="ss">frame</span><span class="w"> </span><span class="ss">pointer</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="err">`</span><span class="ss">perf</span><span class="err">`</span><span class="w"> </span><span class="ss">support</span><span class="w"> </span><span class="ss">is</span><span class="w"> </span><span class="ss">enabled</span><span class="p">,</span><span class="w"> </span><span class="ss">otherwise</span><span class="w"> </span><span class="ss">this</span><span class="w">
│ │ │       </span><span class="ss">is</span><span class="w"> </span><span class="ss">an</span><span class="w"> </span><span class="ss">optional</span><span class="w"> </span><span class="ss">save</span><span class="w"> </span><span class="ss">slot</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="ss">stack</span><span class="w"> </span><span class="ss">pointer</span><span class="w"> </span><span class="k">when</span><span class="w"> </span><span class="ss">executing</span><span class="w"> </span><span class="n">C</span><span class="w">
│ │ │       </span><span class="ss">code</span><span class="p">.</span><span class="w">
│ │ │  </span><span class="nc">r12</span><span class="p">:</span><span class="w"> </span><span class="n">Active</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">index</span><span class="w">
│ │ │  </span><span class="nc">r13</span><span class="p">:</span><span class="w"> </span><span class="n">Current</span><span class="w"> </span><span class="ss">running</span><span class="w"> </span><span class="ss">process</span><span class="w">
│ │ │  </span><span class="nc">r14</span><span class="p">:</span><span class="w"> </span><span class="n">Remaining</span><span class="w"> </span><span class="ss">reductions</span><span class="w">
│ │ │  </span><span class="nc">r15</span><span class="p">:</span><span class="w"> </span><span class="n">Erlang</span><span class="w"> </span><span class="ss">heap</span><span class="w"> </span><span class="ss">pointer</span></code></pre><p>Note that all of these are callee save registers under the System V and Windows
│ │ │ @@ -183,21 +183,21 @@
│ │ │  shared and only the arguments to the instructions vary. Using as little memory as
│ │ │  possible has many advantages; less memory is used, loading time decreases,
│ │ │  higher cache hit-rate.</p><p>In BeamAsm we need to achieve something similar since the load-time of a module
│ │ │  scales almost linearly with the amount of memory it uses. Early BeamAsm prototypes
│ │ │  used about double the amount of memory for code as the interpreter, while current
│ │ │  versions use about 10% more. How was this achieved?</p><p>In BeamAsm we heavily use shared code fragments to try to emit as much code as
│ │ │  possible as global shared fragments instead of duplicating the code unnecessarily.
│ │ │ -For instance, the return instruction looks something like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Label</span><span class="w"> </span><span class="ss">yield</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">a</span><span class="p">.</span><span class="nf">newLabel</span><span class="p" data-group-id="9802154656-1">(</span><span class="p" data-group-id="9802154656-1">)</span><span class="p">;</span><span class="w">
│ │ │ +For instance, the return instruction looks something like this:</p><pre><code class="makeup erlang" translate="no"><span class="n">Label</span><span class="w"> </span><span class="ss">yield</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">a</span><span class="p">.</span><span class="nf">newLabel</span><span class="p" data-group-id="5210835857-1">(</span><span class="p" data-group-id="5210835857-1">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">Decrement</span><span class="w"> </span><span class="ss">reduction</span><span class="w"> </span><span class="ss">counter</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">dec</span><span class="p" data-group-id="9802154656-2">(</span><span class="n">FCALLS</span><span class="p" data-group-id="9802154656-2">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">dec</span><span class="p" data-group-id="5210835857-2">(</span><span class="n">FCALLS</span><span class="p" data-group-id="5210835857-2">)</span><span class="p">;</span><span class="w">
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">If</span><span class="w"> </span><span class="n">FCALLS</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="ss">jump</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">yield</span><span class="o">-</span><span class="ss">on</span><span class="o">-</span><span class="ss">return</span><span class="w"> </span><span class="ss">fragment</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">jl</span><span class="p" data-group-id="9802154656-3">(</span><span class="nf">resolve_fragment</span><span class="p" data-group-id="9802154656-4">(</span><span class="ss">ga</span><span class="p">-&gt;</span><span class="nf">get_dispatch_return</span><span class="p" data-group-id="9802154656-5">(</span><span class="p" data-group-id="9802154656-5">)</span><span class="p" data-group-id="9802154656-4">)</span><span class="p" data-group-id="9802154656-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">ret</span><span class="p" data-group-id="9802154656-6">(</span><span class="p" data-group-id="9802154656-6">)</span><span class="p">;</span></code></pre><p>The code above is not exactly what is emitted, but close enough. The thing to note
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">jl</span><span class="p" data-group-id="5210835857-3">(</span><span class="nf">resolve_fragment</span><span class="p" data-group-id="5210835857-4">(</span><span class="ss">ga</span><span class="p">-&gt;</span><span class="nf">get_dispatch_return</span><span class="p" data-group-id="5210835857-5">(</span><span class="p" data-group-id="5210835857-5">)</span><span class="p" data-group-id="5210835857-4">)</span><span class="p" data-group-id="5210835857-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">ret</span><span class="p" data-group-id="5210835857-6">(</span><span class="p" data-group-id="5210835857-6">)</span><span class="p">;</span></code></pre><p>The code above is not exactly what is emitted, but close enough. The thing to note
│ │ │  is that the code for doing the context switch is never emitted. Instead, we jump
│ │ │  to a global fragment that all return instructions share. This greatly reduces
│ │ │  the amount of code that has to be emitted for each module.</p><h2 id="running-erlang-code" class="section-heading">
│ │ │    <a href="#running-erlang-code" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running Erlang code</span>
│ │ │ @@ -239,43 +239,43 @@
│ │ │    <a href="#running-c-code" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Running C code</span>
│ │ │  </h2>
│ │ │  <p>As Erlang stacks can be very small, we have to switch over to a different stack
│ │ │  when we need to execute C code (which may expect a much larger stack). This is
│ │ │ -done through <code class="inline">emit_enter_runtime</code> and <code class="inline">emit_leave_runtime</code>, for example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mov_arg</span><span class="p" data-group-id="7465003554-1">(</span><span class="n">ARG4</span><span class="p">,</span><span class="w"> </span><span class="n">NumFree</span><span class="p" data-group-id="7465003554-1">)</span><span class="p">;</span><span class="w">
│ │ │ +done through <code class="inline">emit_enter_runtime</code> and <code class="inline">emit_leave_runtime</code>, for example:</p><pre><code class="makeup erlang" translate="no"><span class="nf">mov_arg</span><span class="p" data-group-id="6250457465-1">(</span><span class="n">ARG4</span><span class="p">,</span><span class="w"> </span><span class="n">NumFree</span><span class="p" data-group-id="6250457465-1">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">Move</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="ss">stack</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">swap</span><span class="w"> </span><span class="ss">out</span><span class="w"> </span><span class="ss">our</span><span class="w"> </span><span class="ss">current</span><span class="w"> </span><span class="ss">reductions</span><span class="p">,</span><span class="w"> </span><span class="ss">stack</span><span class="o">-</span><span class="p">,</span><span class="w"> </span><span class="ow">and</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="ss">heap</span><span class="w"> </span><span class="ss">pointer</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">process</span><span class="w"> </span><span class="ss">structure</span><span class="p">.</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">emit_enter_runtime</span><span class="o">&lt;</span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eReductions</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eStack</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eHeap</span><span class="o">&gt;</span><span class="p" data-group-id="7465003554-2">(</span><span class="p" data-group-id="7465003554-2">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">emit_enter_runtime</span><span class="o">&lt;</span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eReductions</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eStack</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eHeap</span><span class="o">&gt;</span><span class="p" data-group-id="6250457465-2">(</span><span class="p" data-group-id="6250457465-2">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">mov</span><span class="p" data-group-id="7465003554-3">(</span><span class="n">ARG1</span><span class="p">,</span><span class="w"> </span><span class="ss">c_p</span><span class="p" data-group-id="7465003554-3">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">load_x_reg_array</span><span class="p" data-group-id="7465003554-4">(</span><span class="n">ARG2</span><span class="p" data-group-id="7465003554-4">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="nf">make_move_patch</span><span class="p" data-group-id="7465003554-5">(</span><span class="n">ARG3</span><span class="p">,</span><span class="w"> </span><span class="ss">lambdas</span><span class="p" data-group-id="7465003554-6">[</span><span class="n">Fun</span><span class="p">.</span><span class="nf">getValue</span><span class="p" data-group-id="7465003554-7">(</span><span class="p" data-group-id="7465003554-7">)</span><span class="p" data-group-id="7465003554-6">]</span><span class="p">.</span><span class="ss">patches</span><span class="p" data-group-id="7465003554-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">mov</span><span class="p" data-group-id="6250457465-3">(</span><span class="n">ARG1</span><span class="p">,</span><span class="w"> </span><span class="ss">c_p</span><span class="p" data-group-id="6250457465-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">load_x_reg_array</span><span class="p" data-group-id="6250457465-4">(</span><span class="n">ARG2</span><span class="p" data-group-id="6250457465-4">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="nf">make_move_patch</span><span class="p" data-group-id="6250457465-5">(</span><span class="n">ARG3</span><span class="p">,</span><span class="w"> </span><span class="ss">lambdas</span><span class="p" data-group-id="6250457465-6">[</span><span class="n">Fun</span><span class="p">.</span><span class="nf">getValue</span><span class="p" data-group-id="6250457465-7">(</span><span class="p" data-group-id="6250457465-7">)</span><span class="p" data-group-id="6250457465-6">]</span><span class="p">.</span><span class="ss">patches</span><span class="p" data-group-id="6250457465-5">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">Call</span><span class="w"> </span><span class="err">`</span><span class="ss">new_fun</span><span class="err">`</span><span class="p">,</span><span class="w"> </span><span class="ss">asserting</span><span class="w"> </span><span class="ss">that</span><span class="w"> </span><span class="ss">we</span><span class="err">&#39;</span><span class="ss">re</span><span class="w"> </span><span class="ss">on</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="ss">stack</span><span class="p">.</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">runtime_call</span><span class="o">&lt;</span><span class="mi">4</span><span class="o">&gt;</span><span class="p" data-group-id="7465003554-8">(</span><span class="ss">new_fun</span><span class="p" data-group-id="7465003554-8">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">runtime_call</span><span class="o">&lt;</span><span class="mi">4</span><span class="o">&gt;</span><span class="p" data-group-id="6250457465-8">(</span><span class="ss">new_fun</span><span class="p" data-group-id="6250457465-8">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="o">/</span><span class="o">*</span><span class="w"> </span><span class="n">Move</span><span class="w"> </span><span class="ss">back</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="ss">stack</span><span class="p">,</span><span class="w"> </span><span class="ow">and</span><span class="w"> </span><span class="ss">read</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">updated</span><span class="w"> </span><span class="ss">values</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">process</span><span class="w">
│ │ │   </span><span class="o">*</span><span class="w"> </span><span class="ss">structure</span><span class="w"> </span><span class="o">*</span><span class="o">/</span><span class="w">
│ │ │ -</span><span class="ss">emit_leave_runtime</span><span class="o">&lt;</span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eReductions</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eStack</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eHeap</span><span class="o">&gt;</span><span class="p" data-group-id="7465003554-9">(</span><span class="p" data-group-id="7465003554-9">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="ss">emit_leave_runtime</span><span class="o">&lt;</span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eReductions</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eStack</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Update</span><span class="p">:</span><span class="p">:</span><span class="ss">eHeap</span><span class="o">&gt;</span><span class="p" data-group-id="6250457465-9">(</span><span class="p" data-group-id="6250457465-9">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="ss">a</span><span class="p">.</span><span class="nf">mov</span><span class="p" data-group-id="7465003554-10">(</span><span class="nf">getXRef</span><span class="p" data-group-id="7465003554-11">(</span><span class="mi">0</span><span class="p" data-group-id="7465003554-11">)</span><span class="p">,</span><span class="w"> </span><span class="n">RET</span><span class="p" data-group-id="7465003554-10">)</span><span class="p">;</span></code></pre><p>All combinations of the <code class="inline">Update</code> constants are legal, but the ones given to
│ │ │ +</span><span class="ss">a</span><span class="p">.</span><span class="nf">mov</span><span class="p" data-group-id="6250457465-10">(</span><span class="nf">getXRef</span><span class="p" data-group-id="6250457465-11">(</span><span class="mi">0</span><span class="p" data-group-id="6250457465-11">)</span><span class="p">,</span><span class="w"> </span><span class="n">RET</span><span class="p" data-group-id="6250457465-10">)</span><span class="p">;</span></code></pre><p>All combinations of the <code class="inline">Update</code> constants are legal, but the ones given to
│ │ │  <code class="inline">emit_leave_runtime</code> <em>must</em> be the same as those given to <code class="inline">emit_enter_runtime</code>.</p><h2 id="tracing-and-nif-loading" class="section-heading">
│ │ │    <a href="#tracing-and-nif-loading" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Tracing and NIF Loading</span>
│ │ │  </h2>
│ │ │  <p>To make tracing and NIF loading work there needs to be a way to intercept
│ │ │  any function call. In the interpreter, this is done by rewriting the loaded
│ │ │  BEAM code, but this is more complicated in BeamAsm as we want to have a fast
│ │ │  and compact way to do this. This is solved by emitting the code below at the
│ │ │ -start of each function (x86 variant below):</p><pre><code class="makeup erlang" translate="no"><span class="w">  </span><span class="mi">0</span><span class="nc">x0</span><span class="p">:</span><span class="w"> </span><span class="ss">short</span><span class="w"> </span><span class="ss">jmp</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="p" data-group-id="4017467190-1">(</span><span class="ss">address</span><span class="w"> </span><span class="mi">0</span><span class="ss">x8</span><span class="p" data-group-id="4017467190-1">)</span><span class="w">
│ │ │ +start of each function (x86 variant below):</p><pre><code class="makeup erlang" translate="no"><span class="w">  </span><span class="mi">0</span><span class="nc">x0</span><span class="p">:</span><span class="w"> </span><span class="ss">short</span><span class="w"> </span><span class="ss">jmp</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="p" data-group-id="0495793579-1">(</span><span class="ss">address</span><span class="w"> </span><span class="mi">0</span><span class="ss">x8</span><span class="p" data-group-id="0495793579-1">)</span><span class="w">
│ │ │    </span><span class="mi">0</span><span class="nc">x2</span><span class="p">:</span><span class="w"> </span><span class="ss">nop</span><span class="w">
│ │ │    </span><span class="mi">0</span><span class="nc">x3</span><span class="p">:</span><span class="w"> </span><span class="ss">relative</span><span class="w"> </span><span class="ss">near</span><span class="w"> </span><span class="ss">call</span><span class="w"> </span><span class="ss">to</span><span class="w"> </span><span class="ss">shared</span><span class="w"> </span><span class="ss">breakpoint</span><span class="w"> </span><span class="ss">fragment</span><span class="w">
│ │ │    </span><span class="mi">0</span><span class="nc">x8</span><span class="p">:</span><span class="w"> </span><span class="ss">actual</span><span class="w"> </span><span class="ss">code</span><span class="w"> </span><span class="ss">for</span><span class="w"> </span><span class="ss">function</span></code></pre><p>When code starts to execute it will simply see the <code class="inline">short jmp 6</code> instruction
│ │ │  which skips the prologue and starts to execute the code directly.</p><p>When we want to enable a certain breakpoint we set the jmp target to be 1,
│ │ │  which means it will land on the call to the shared breakpoint fragment. This
│ │ │  fragment checks the current <code class="inline">breakpoint_flag</code> stored in the ErtsCodeInfo of
│ │ │  this function, and then calls <code class="inline">erts_call_nif_early</code> and
│ │ │ @@ -289,31 +289,31 @@
│ │ │    <span class="text">Updating code</span>
│ │ │  </h3>
│ │ │  <p>Because many environments enforce <a href="https://en.wikipedia.org/wiki/W%5EX" title="">W^X</a> it's not always possible to write
│ │ │  directly to the code pages. Because of this we map code twice: once with an
│ │ │  executable page and once with a writable page. Since they're backed by the
│ │ │  same memory, writes to the writable page appear magically in the executable
│ │ │  one.</p><p>The <code class="inline">erts_writable_code_ptr</code> function can be used to get writable pointers
│ │ │ -given a module instance, provided that it has been unsealed first:</p><pre><code class="makeup erlang" translate="no"><span class="nf">for</span><span class="w"> </span><span class="p" data-group-id="2237283596-1">(</span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="ss">n</span><span class="p">;</span><span class="w"> </span><span class="ss">i</span><span class="o">++</span><span class="p" data-group-id="2237283596-1">)</span><span class="w"> </span><span class="p" data-group-id="2237283596-2">{</span><span class="w">
│ │ │ +given a module instance, provided that it has been unsealed first:</p><pre><code class="makeup erlang" translate="no"><span class="nf">for</span><span class="w"> </span><span class="p" data-group-id="2655219465-1">(</span><span class="ss">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="ss">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="ss">n</span><span class="p">;</span><span class="w"> </span><span class="ss">i</span><span class="o">++</span><span class="p" data-group-id="2655219465-1">)</span><span class="w"> </span><span class="p" data-group-id="2655219465-2">{</span><span class="w">
│ │ │      </span><span class="ss">const</span><span class="w"> </span><span class="n">ErtsCodeInfo</span><span class="o">*</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">ErtsCodeInfo</span><span class="o">*</span><span class="w"> </span><span class="ss">ci_rw</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="ss">void</span><span class="w"> </span><span class="o">*</span><span class="ss">w_ptr</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">erts_unseal_module</span><span class="p" data-group-id="2237283596-3">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p" data-group-id="2237283596-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">erts_unseal_module</span><span class="p" data-group-id="2655219465-3">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p" data-group-id="2655219465-3">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="ss">ci_exec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">code_hdr</span><span class="p">-&gt;</span><span class="ss">functions</span><span class="p" data-group-id="2237283596-4">[</span><span class="ss">i</span><span class="p" data-group-id="2237283596-4">]</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">w_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_writable_code_ptr</span><span class="p" data-group-id="2237283596-5">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p" data-group-id="2237283596-5">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="ss">ci_rw</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2237283596-6">(</span><span class="n">ErtsCodeInfo</span><span class="o">*</span><span class="p" data-group-id="2237283596-6">)</span><span class="ss">w_ptr</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">ci_exec</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="ss">code_hdr</span><span class="p">-&gt;</span><span class="ss">functions</span><span class="p" data-group-id="2655219465-4">[</span><span class="ss">i</span><span class="p" data-group-id="2655219465-4">]</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">w_ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">erts_writable_code_ptr</span><span class="p" data-group-id="2655219465-5">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p" data-group-id="2655219465-5">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="ss">ci_rw</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2655219465-6">(</span><span class="n">ErtsCodeInfo</span><span class="o">*</span><span class="p" data-group-id="2655219465-6">)</span><span class="ss">w_ptr</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">uninstall_breakpoint</span><span class="p" data-group-id="2237283596-7">(</span><span class="ss">ci_rw</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p" data-group-id="2237283596-7">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">consolidate_bp_data</span><span class="p" data-group-id="2237283596-8">(</span><span class="ss">modp</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_rw</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2237283596-8">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">ASSERT</span><span class="p" data-group-id="2237283596-9">(</span><span class="ss">ci_rw</span><span class="p">-&gt;</span><span class="ss">gen_bp</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">NULL</span><span class="p" data-group-id="2237283596-9">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">uninstall_breakpoint</span><span class="p" data-group-id="2655219465-7">(</span><span class="ss">ci_rw</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_exec</span><span class="p" data-group-id="2655219465-7">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">consolidate_bp_data</span><span class="p" data-group-id="2655219465-8">(</span><span class="ss">modp</span><span class="p">,</span><span class="w"> </span><span class="ss">ci_rw</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p" data-group-id="2655219465-8">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">ASSERT</span><span class="p" data-group-id="2655219465-9">(</span><span class="ss">ci_rw</span><span class="p">-&gt;</span><span class="ss">gen_bp</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">NULL</span><span class="p" data-group-id="2655219465-9">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="nf">erts_seal_module</span><span class="p" data-group-id="2237283596-10">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p" data-group-id="2237283596-10">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="2237283596-2">}</span></code></pre><p>Without the module instance there's no reliable way to figure out the writable
│ │ │ +    </span><span class="nf">erts_seal_module</span><span class="p" data-group-id="2655219465-10">(</span><span class="err">&amp;</span><span class="ss">modp</span><span class="p">-&gt;</span><span class="ss">curr</span><span class="p" data-group-id="2655219465-10">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2655219465-2">}</span></code></pre><p>Without the module instance there's no reliable way to figure out the writable
│ │ │  address of a code page, and we rely on <em>address space layout randomization</em>
│ │ │  (ASLR) to make it difficult to guess. On some platforms, security is further
│ │ │  enhanced by protecting the writable area from writes until the module has been
│ │ │  unsealed by <code class="inline">erts_unseal_module</code>.</p><h3 id="export-tracing" class="section-heading">
│ │ │    <a href="#export-tracing" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │ @@ -393,15 +393,15 @@
│ │ │  </span><span class="ss">perf</span><span class="w"> </span><span class="ss">script</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">perf</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="ss">run</span><span class="w"> </span><span class="ss">stackcollapse</span><span class="w">
│ │ │  </span><span class="ss">stackcollapse</span><span class="o">-</span><span class="ss">perf</span><span class="p">.</span><span class="ss">pl</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">perf</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="n">Create</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">svg</span><span class="w">
│ │ │  </span><span class="ss">flamegraph</span><span class="p">.</span><span class="ss">pl</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">svg</span></code></pre><p>We get a graph that would look something like this:</p><p><img src="assets/perf-beamasm.svg" alt="Linux Perf FlameGraph: dialyzer PLT build"/></p><p>You can view a larger version <a href="assets/perf-beamasm.svg">here</a>. It contains
│ │ │  the same information, but it is easier to share with others as it does
│ │ │  not need the symbols in the executable.</p><p>Using the same data we can also produce a graph where the scheduler profile data
│ │ │ -has been merged by using <code class="inline">sed</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="n">Strip</span><span class="w"> </span><span class="p" data-group-id="1098074461-1">[</span><span class="mi">0</span><span class="o">-</span><span class="mi">9</span><span class="p" data-group-id="1098074461-1">]</span><span class="o">+</span><span class="p">_</span><span class="w"> </span><span class="ow">and</span><span class="o">/</span><span class="ow">or</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="1098074461-2">[</span><span class="mi">0</span><span class="o">-</span><span class="mi">9</span><span class="p" data-group-id="1098074461-2">]</span><span class="o">+</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">scheduler</span><span class="w"> </span><span class="ss">names</span><span class="w">
│ │ │ +has been merged by using <code class="inline">sed</code>:</p><pre><code class="makeup erlang" translate="no"><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="n">Strip</span><span class="w"> </span><span class="p" data-group-id="9721911752-1">[</span><span class="mi">0</span><span class="o">-</span><span class="mi">9</span><span class="p" data-group-id="9721911752-1">]</span><span class="o">+</span><span class="p">_</span><span class="w"> </span><span class="ow">and</span><span class="o">/</span><span class="ow">or</span><span class="w"> </span><span class="p">_</span><span class="p" data-group-id="9721911752-2">[</span><span class="mi">0</span><span class="o">-</span><span class="mi">9</span><span class="p" data-group-id="9721911752-2">]</span><span class="o">+</span><span class="w"> </span><span class="ss">from</span><span class="w"> </span><span class="ss">all</span><span class="w"> </span><span class="ss">scheduler</span><span class="w"> </span><span class="ss">names</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="ss">scheduler</span><span class="w"> </span><span class="ss">names</span><span class="w"> </span><span class="ss">changed</span><span class="w"> </span><span class="ss">in</span><span class="w"> </span><span class="n">OTP26</span><span class="p">,</span><span class="w"> </span><span class="ss">hence</span><span class="w"> </span><span class="ss">two</span><span class="w"> </span><span class="ss">expressions</span><span class="w">
│ │ │  </span><span class="ss">sed</span><span class="w"> </span><span class="o">-</span><span class="ss">e</span><span class="w"> </span><span class="ss">&#39;s/^[0-9]\+_//&#39;</span><span class="w"> </span><span class="o">-</span><span class="ss">e</span><span class="w"> </span><span class="ss">&#39;s/^erts_\([^_]\+\)_[0-9]\+/erts_\1/&#39;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded_sched</span><span class="w">
│ │ │  </span><span class="p">#</span><span class="p">#</span><span class="w"> </span><span class="n">Create</span><span class="w"> </span><span class="ss">the</span><span class="w"> </span><span class="ss">svg</span><span class="w">
│ │ │  </span><span class="ss">flamegraph</span><span class="p">.</span><span class="ss">pl</span><span class="w"> </span><span class="ss">out</span><span class="p">.</span><span class="ss">folded_sched</span><span class="w"> </span><span class="o">&gt;</span><span class="w"> </span><span class="ss">out_sched</span><span class="p">.</span><span class="ss">svg</span></code></pre><p><img src="assets/perf-beamasm-merged.svg" alt="Linux Perf FlameGraph: dialyzer PLT build"/></p><p>You can view a larger version <a href="assets/perf-beamasm-merged.svg">here</a>.
│ │ │  There are many different transformations that you can do to make the graph show
│ │ │  you what you want.</p><h3 id="annotate-perf-functions" class="section-heading">
│ │ │    <a href="#annotate-perf-functions" class="hover-link">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/codeloading.html
│ │ │ @@ -163,16 +163,16 @@
│ │ │  only be done by one loader process at a time. A second loader process
│ │ │  trying to enter finishing phase will be suspended until the first
│ │ │  loader is done. This will only block the process, the scheduler is
│ │ │  free to schedule other work while the second loader is waiting. (See
│ │ │  <code class="inline">erts_try_seize_code_load_permission</code> and
│ │ │  <code class="inline">erts_release_code_load_permission</code>).</p><p>The ability to prepare several modules in parallel is not currently
│ │ │  used as almost all code loading is serialized by the code_server
│ │ │ -process. The BIF interface is however prepared for this.</p><pre><code class="makeup erlang" translate="no"><span class="w">  </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">prepare_loading</span><span class="p" data-group-id="8949788845-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="8949788845-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">LoaderState</span><span class="w">
│ │ │ -  </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">finish_loading</span><span class="p" data-group-id="8949788845-2">(</span><span class="p" data-group-id="8949788845-3">[</span><span class="n">LoaderState</span><span class="p" data-group-id="8949788845-3">]</span><span class="p" data-group-id="8949788845-2">)</span></code></pre><p>The idea is that <code class="inline">prepare_loading</code> could be called in parallel for
│ │ │ +process. The BIF interface is however prepared for this.</p><pre><code class="makeup erlang" translate="no"><span class="w">  </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">prepare_loading</span><span class="p" data-group-id="1913512715-1">(</span><span class="n">Module</span><span class="p">,</span><span class="w"> </span><span class="n">Code</span><span class="p" data-group-id="1913512715-1">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">LoaderState</span><span class="w">
│ │ │ +  </span><span class="nc">erlang</span><span class="p">:</span><span class="nf">finish_loading</span><span class="p" data-group-id="1913512715-2">(</span><span class="p" data-group-id="1913512715-3">[</span><span class="n">LoaderState</span><span class="p" data-group-id="1913512715-3">]</span><span class="p" data-group-id="1913512715-2">)</span></code></pre><p>The idea is that <code class="inline">prepare_loading</code> could be called in parallel for
│ │ │  different modules and returns a &quot;magic binary&quot; containing the internal
│ │ │  state of each prepared module. Function <code class="inline">finish_loading</code> could take a
│ │ │  list of such states and do the finishing of all of them in one go.</p><p>Currently we use the legacy BIF <code class="inline">erlang:load_module</code> which is now
│ │ │  implemented in Erlang by calling the above two functions in
│ │ │  sequence. Function <code class="inline">finish_loading</code> is limited to only accepts a list
│ │ │  with one module state as we do not yet use the multi module loading
│ │ │  feature.</p><h2 id="the-finishing-sequence" class="section-heading">
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/crash_dump.html
│ │ │ @@ -401,21 +401,21 @@
│ │ │  <a href="erlang.html#put/2"><code class="inline">put/2</code></a> and <a href="erlang.html#get/1"><code class="inline">get/1</code></a> thing) is non-empty.</p><p>The raw memory information can be decoded by the Crashdump Viewer tool. You can
│ │ │  then see the stack dump, the message queue (if any), and the dictionary (if
│ │ │  any).</p><p>The stack dump is a dump of the Erlang process stack. Most of the live data
│ │ │  (that is, variables currently in use) are placed on the stack; thus this can be
│ │ │  interesting. One has to &quot;guess&quot; what is what, but as the information is
│ │ │  symbolic, thorough reading of this information can be useful. As an example, we
│ │ │  can find the state variable of the Erlang primitive loader online <code class="inline">(5)</code> and
│ │ │ -<code class="inline">(6)</code> in the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="1913063564-1">(</span><span class="mi">1</span><span class="p" data-group-id="1913063564-1">)</span><span class="w">  </span><span class="mi">3</span><span class="ss">cac44</span><span class="w">   </span><span class="n">Return</span><span class="w"> </span><span class="ss">addr</span><span class="w"> </span><span class="mi">0</span><span class="nf">x13BF58</span><span class="w"> </span><span class="p" data-group-id="1913063564-2">(</span><span class="o">&lt;</span><span class="ss">terminate</span><span class="w"> </span><span class="ss">process</span><span class="w"> </span><span class="ss">normally</span><span class="o">&gt;</span><span class="p" data-group-id="1913063564-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1913063564-3">(</span><span class="mi">2</span><span class="p" data-group-id="1913063564-3">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="1913063564-4">(</span><span class="mi">0</span><span class="p" data-group-id="1913063564-4">)</span><span class="w">     </span><span class="p" data-group-id="1913063564-5">[</span><span class="s">&quot;/view/siri_r10_dev/clearcase/otp/erts/lib/kernel/ebin&quot;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1913063564-6">(</span><span class="mi">3</span><span class="p" data-group-id="1913063564-6">)</span><span class="w">            </span><span class="s">&quot;/view/siri_r10_dev/clearcase/otp/erts/lib/stdlib/ebin&quot;</span><span class="p" data-group-id="1913063564-5">]</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1913063564-7">(</span><span class="mi">4</span><span class="p" data-group-id="1913063564-7">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="1913063564-8">(</span><span class="mi">1</span><span class="p" data-group-id="1913063564-8">)</span><span class="w">     </span><span class="o">&lt;</span><span class="mf">0.1</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1913063564-9">(</span><span class="mi">5</span><span class="p" data-group-id="1913063564-9">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="1913063564-10">(</span><span class="mi">2</span><span class="p" data-group-id="1913063564-10">)</span><span class="w">     </span><span class="p" data-group-id="1913063564-11">{</span><span class="ss">state</span><span class="p">,</span><span class="p" data-group-id="1913063564-12">[</span><span class="p" data-group-id="1913063564-12">]</span><span class="p">,</span><span class="ss">none</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">6.7085890</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">undefined</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">7.9000327</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1913063564-13">(</span><span class="mi">6</span><span class="p" data-group-id="1913063564-13">)</span><span class="w">            </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">8.116480692</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.2</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">9.10708760</span><span class="o">&gt;</span><span class="p" data-group-id="1913063564-11">}</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1913063564-14">(</span><span class="mi">7</span><span class="p" data-group-id="1913063564-14">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="1913063564-15">(</span><span class="mi">3</span><span class="p" data-group-id="1913063564-15">)</span><span class="w">     </span><span class="ss">infinity</span></code></pre><p>When interpreting the data for a process, it is helpful to know that anonymous
│ │ │ +<code class="inline">(6)</code> in the following example:</p><pre><code class="makeup erlang" translate="no"><span class="p" data-group-id="4034679318-1">(</span><span class="mi">1</span><span class="p" data-group-id="4034679318-1">)</span><span class="w">  </span><span class="mi">3</span><span class="ss">cac44</span><span class="w">   </span><span class="n">Return</span><span class="w"> </span><span class="ss">addr</span><span class="w"> </span><span class="mi">0</span><span class="nf">x13BF58</span><span class="w"> </span><span class="p" data-group-id="4034679318-2">(</span><span class="o">&lt;</span><span class="ss">terminate</span><span class="w"> </span><span class="ss">process</span><span class="w"> </span><span class="ss">normally</span><span class="o">&gt;</span><span class="p" data-group-id="4034679318-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4034679318-3">(</span><span class="mi">2</span><span class="p" data-group-id="4034679318-3">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="4034679318-4">(</span><span class="mi">0</span><span class="p" data-group-id="4034679318-4">)</span><span class="w">     </span><span class="p" data-group-id="4034679318-5">[</span><span class="s">&quot;/view/siri_r10_dev/clearcase/otp/erts/lib/kernel/ebin&quot;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4034679318-6">(</span><span class="mi">3</span><span class="p" data-group-id="4034679318-6">)</span><span class="w">            </span><span class="s">&quot;/view/siri_r10_dev/clearcase/otp/erts/lib/stdlib/ebin&quot;</span><span class="p" data-group-id="4034679318-5">]</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4034679318-7">(</span><span class="mi">4</span><span class="p" data-group-id="4034679318-7">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="4034679318-8">(</span><span class="mi">1</span><span class="p" data-group-id="4034679318-8">)</span><span class="w">     </span><span class="o">&lt;</span><span class="mf">0.1</span><span class="p">.</span><span class="mi">0</span><span class="o">&gt;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4034679318-9">(</span><span class="mi">5</span><span class="p" data-group-id="4034679318-9">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="4034679318-10">(</span><span class="mi">2</span><span class="p" data-group-id="4034679318-10">)</span><span class="w">     </span><span class="p" data-group-id="4034679318-11">{</span><span class="ss">state</span><span class="p">,</span><span class="p" data-group-id="4034679318-12">[</span><span class="p" data-group-id="4034679318-12">]</span><span class="p">,</span><span class="ss">none</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">6.7085890</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">undefined</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">7.9000327</span><span class="o">&gt;</span><span class="p">,</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4034679318-13">(</span><span class="mi">6</span><span class="p" data-group-id="4034679318-13">)</span><span class="w">            </span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">8.116480692</span><span class="o">&gt;</span><span class="p">,</span><span class="p">#</span><span class="n">Port</span><span class="o">&lt;</span><span class="mf">0.2</span><span class="o">&gt;</span><span class="p">,</span><span class="ss">infinity</span><span class="p">,</span><span class="p">#</span><span class="n">Fun</span><span class="o">&lt;</span><span class="ss">erl_prim_loader</span><span class="p">.</span><span class="mf">9.10708760</span><span class="o">&gt;</span><span class="p" data-group-id="4034679318-11">}</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4034679318-14">(</span><span class="mi">7</span><span class="p" data-group-id="4034679318-14">)</span><span class="w">  </span><span class="nf">y</span><span class="p" data-group-id="4034679318-15">(</span><span class="mi">3</span><span class="p" data-group-id="4034679318-15">)</span><span class="w">     </span><span class="ss">infinity</span></code></pre><p>When interpreting the data for a process, it is helpful to know that anonymous
│ │ │  function objects (funs) are given the following:</p><ul><li>A name constructed from the name of the function in which they are created</li><li>A number (starting with 0) indicating the number of that fun within that
│ │ │  function</li></ul><h2 id="atoms" class="section-heading">
│ │ │    <a href="#atoms" class="hover-link">
│ │ │      <i class="ri-link-m" aria-hidden="true"></i>
│ │ │    </a>
│ │ │    <span class="text">Atoms</span>
│ │ │  </h2>
│ │ ├── ./usr/share/doc/erlang-doc/html/erts-15.2.7.8/doc/html/driver.html
│ │ │ @@ -176,20 +176,20 @@
│ │ │  simple set of commands: <code class="inline">connect</code> to log in to the database, <code class="inline">disconnect</code> to log
│ │ │  out, and <code class="inline">select</code> to send a SQL-query and get the result. All results are
│ │ │  returned through <code class="inline">rbuf</code>. The library <a href="../../../lib/erl_interface-5.5.2/doc/html/ei.html" title=""><code class="inline">ei</code></a> in <a href="../../../lib/erl_interface-5.5.2/doc/html/index.html"><code class="inline">erl_interface</code></a>
│ │ │  is used to encode data in binary term format. The result is returned to the emulator as binary
│ │ │  terms, so <code class="inline">binary_to_term</code> is called in Erlang to convert the result to term
│ │ │  form.</p><p>The code is available in <code class="inline">pg_sync.c</code> in the <code class="inline">sample</code> directory of <code class="inline">erts</code>.</p><p>The driver entry contains the functions that will be called by the emulator. In
│ │ │  this example, only <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#start" title=""><code class="inline">start</code></a>, <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#stop" title=""><code class="inline">stop</code></a>, and <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#control" title=""><code class="inline">control</code></a> are provided:</p><pre><code class="makeup c" translate="no"><span class="cm">/* Driver interface declarations */</span><span class="w">
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="7486610065-1">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">command</span><span class="p" data-group-id="7486610065-1">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">stop</span><span class="p" data-group-id="7486610065-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">drv_data</span><span class="p" data-group-id="7486610065-2">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">control</span><span class="p" data-group-id="7486610065-3">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">drv_data</span><span class="p">,</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">command</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w">
│ │ │ -                   </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="o">*</span><span class="n">rbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rlen</span><span class="p" data-group-id="7486610065-3">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="9459863743-1">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">command</span><span class="p" data-group-id="9459863743-1">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">stop</span><span class="p" data-group-id="9459863743-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">drv_data</span><span class="p" data-group-id="9459863743-2">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">control</span><span class="p" data-group-id="9459863743-3">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">drv_data</span><span class="p">,</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">command</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w">
│ │ │ +                   </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="o">*</span><span class="n">rbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rlen</span><span class="p" data-group-id="9459863743-3">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvEntry</span><span class="w"> </span><span class="n">pq_driver_entry</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="7486610065-4">{</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvEntry</span><span class="w"> </span><span class="n">pq_driver_entry</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="9459863743-4">{</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* init */</span><span class="w">
│ │ │      </span><span class="n">start</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="n">stop</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* output */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* ready_input */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* ready_output */</span><span class="w">
│ │ │      </span><span class="s">&quot;pg_sync&quot;</span><span class="p">,</span><span class="w">                   </span><span class="cm">/* the name of the driver */</span><span class="w">
│ │ │ @@ -198,18 +198,18 @@
│ │ │      </span><span class="n">control</span><span class="p">,</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* timeout */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* outputv */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* ready_async */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* flush */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="p">,</span><span class="w">                        </span><span class="cm">/* call */</span><span class="w">
│ │ │      </span><span class="no">NULL</span><span class="w">                         </span><span class="cm">/* event */</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7486610065-4">}</span><span class="p">;</span></code></pre><p>We have a structure to store state needed by the driver, in this case we only
│ │ │ -need to keep the database connection:</p><pre><code class="makeup c" translate="no"><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="n">our_data_s</span><span class="w"> </span><span class="p" data-group-id="6887309990-1">{</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="9459863743-4">}</span><span class="p">;</span></code></pre><p>We have a structure to store state needed by the driver, in this case we only
│ │ │ +need to keep the database connection:</p><pre><code class="makeup c" translate="no"><span class="k">typedef</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="n">our_data_s</span><span class="w"> </span><span class="p" data-group-id="7701478983-1">{</span><span class="w">
│ │ │      </span><span class="no">PGconn</span><span class="o">*</span><span class="w"> </span><span class="n">conn</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6887309990-1">}</span><span class="w"> </span><span class="n">our_data_t</span><span class="p">;</span></code></pre><p>The control codes that we have defined are as follows:</p><pre><code class="makeup c" translate="no"><span class="cm">/* Keep the following definitions in alignment with the
│ │ │ +</span><span class="p" data-group-id="7701478983-1">}</span><span class="w"> </span><span class="n">our_data_t</span><span class="p">;</span></code></pre><p>The control codes that we have defined are as follows:</p><pre><code class="makeup c" translate="no"><span class="cm">/* Keep the following definitions in alignment with the
│ │ │   * defines in erl_pq_sync.erl
│ │ │   */</span><span class="w">
│ │ │  
│ │ │  </span><span class="kp">#define</span><span class="w"> </span><span class="no">DRV_CONNECT</span><span class="w">             </span><span class="err">&#39;</span><span class="no">C</span><span class="err">&#39;</span><span class="w">
│ │ │  </span><span class="kp">#define</span><span class="w"> </span><span class="no">DRV_DISCONNECT</span><span class="w">          </span><span class="err">&#39;</span><span class="no">D</span><span class="err">&#39;</span><span class="w">
│ │ │  </span><span class="kp">#define</span><span class="w"> </span><span class="no">DRV_SELECT</span><span class="w">              </span><span class="err">&#39;</span><span class="no">S</span><span class="err">&#39;</span></code></pre><p>This returns the driver structure. The macro <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#DRIVER_INIT" title=""><code class="inline">DRIVER_INIT</code></a> defines the only
│ │ │  exported function. All the other functions are static, and will not be exported
│ │ │ @@ -217,138 +217,138 @@
│ │ │  
│ │ │  </span><span class="cm">/*
│ │ │   * This is the init function called after this driver has been loaded.
│ │ │   * It must *not* be declared static. Must return the address to
│ │ │   * the driver entry.
│ │ │   */</span><span class="w">
│ │ │  
│ │ │ -</span><span class="no">DRIVER_INIT</span><span class="p" data-group-id="0449197729-1">(</span><span class="n">pq_drv</span><span class="p" data-group-id="0449197729-1">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0449197729-2">{</span><span class="w">
│ │ │ +</span><span class="no">DRIVER_INIT</span><span class="p" data-group-id="4378257425-1">(</span><span class="n">pq_drv</span><span class="p" data-group-id="4378257425-1">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4378257425-2">{</span><span class="w">
│ │ │      </span><span class="k">return</span><span class="w"> </span><span class="o">&amp;</span><span class="n">pq_driver_entry</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0449197729-2">}</span></code></pre><p>Here some initialization is done, <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#start" title=""><code class="inline">start</code></a> is called from <a href="erlang.html#open_port/2"><code class="inline">open_port/2</code></a>. The data
│ │ │ +</span><span class="p" data-group-id="4378257425-2">}</span></code></pre><p>Here some initialization is done, <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#start" title=""><code class="inline">start</code></a> is called from <a href="erlang.html#open_port/2"><code class="inline">open_port/2</code></a>. The data
│ │ │  will be passed to <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#control" title=""><code class="inline">control</code></a> and <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#stop" title=""><code class="inline">stop</code></a>.</p><pre><code class="makeup c" translate="no"><span class="cm">/* DRIVER INTERFACE */</span><span class="w">
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="0876542386-1">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">command</span><span class="p" data-group-id="0876542386-1">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0876542386-2">{</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="no">ErlDrvData</span><span class="w"> </span><span class="nf">start</span><span class="p" data-group-id="5311680405-1">(</span><span class="no">ErlDrvPort</span><span class="w"> </span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">command</span><span class="p" data-group-id="5311680405-1">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5311680405-2">{</span><span class="w">
│ │ │      </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │ -    </span><span class="n">data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="0876542386-3">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="p" data-group-id="0876542386-3">)</span><span class="nf">driver_alloc</span><span class="p" data-group-id="0876542386-4">(</span><span class="nf">sizeof</span><span class="p" data-group-id="0876542386-5">(</span><span class="n">our_data_t</span><span class="p" data-group-id="0876542386-5">)</span><span class="p" data-group-id="0876542386-4">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="5311680405-3">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="p" data-group-id="5311680405-3">)</span><span class="nf">driver_alloc</span><span class="p" data-group-id="5311680405-4">(</span><span class="nf">sizeof</span><span class="p" data-group-id="5311680405-5">(</span><span class="n">our_data_t</span><span class="p" data-group-id="5311680405-5">)</span><span class="p" data-group-id="5311680405-4">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">set_port_control_flags</span><span class="p" data-group-id="0876542386-6">(</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">PORT_CONTROL_FLAG_BINARY</span><span class="p" data-group-id="0876542386-6">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="0876542386-7">(</span><span class="no">ErlDrvData</span><span class="p" data-group-id="0876542386-7">)</span><span class="n">data</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="0876542386-2">}</span></code></pre><p>We call disconnect to log out from the database. (This should have been done
│ │ │ -from Erlang, but just in case.)</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_disconnect</span><span class="p" data-group-id="6770320551-1">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="6770320551-1">)</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">stop</span><span class="p" data-group-id="6770320551-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">drv_data</span><span class="p" data-group-id="6770320551-2">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6770320551-3">{</span><span class="w">
│ │ │ -    </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="6770320551-4">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="p" data-group-id="6770320551-4">)</span><span class="n">drv_data</span><span class="p">;</span><span class="w">
│ │ │ -
│ │ │ -    </span><span class="nf">do_disconnect</span><span class="p" data-group-id="6770320551-5">(</span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="6770320551-5">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">driver_free</span><span class="p" data-group-id="6770320551-6">(</span><span class="n">data</span><span class="p" data-group-id="6770320551-6">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6770320551-3">}</span></code></pre><p>We use the binary format only to return data to the emulator; input data is a
│ │ │ +    </span><span class="nf">set_port_control_flags</span><span class="p" data-group-id="5311680405-6">(</span><span class="n">port</span><span class="p">,</span><span class="w"> </span><span class="no">PORT_CONTROL_FLAG_BINARY</span><span class="p" data-group-id="5311680405-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="k">return</span><span class="w"> </span><span class="p" data-group-id="5311680405-7">(</span><span class="no">ErlDrvData</span><span class="p" data-group-id="5311680405-7">)</span><span class="n">data</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5311680405-2">}</span></code></pre><p>We call disconnect to log out from the database. (This should have been done
│ │ │ +from Erlang, but just in case.)</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_disconnect</span><span class="p" data-group-id="2433648334-1">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="2433648334-1">)</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kc">void</span><span class="w"> </span><span class="nf">stop</span><span class="p" data-group-id="2433648334-2">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">drv_data</span><span class="p" data-group-id="2433648334-2">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2433648334-3">{</span><span class="w">
│ │ │ +    </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="2433648334-4">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="p" data-group-id="2433648334-4">)</span><span class="n">drv_data</span><span class="p">;</span><span class="w">
│ │ │ +
│ │ │ +    </span><span class="nf">do_disconnect</span><span class="p" data-group-id="2433648334-5">(</span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="2433648334-5">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">driver_free</span><span class="p" data-group-id="2433648334-6">(</span><span class="n">data</span><span class="p" data-group-id="2433648334-6">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2433648334-3">}</span></code></pre><p>We use the binary format only to return data to the emulator; input data is a
│ │ │  string parameter for <code class="inline">connect</code> and <code class="inline">select</code>. The returned data consists of
│ │ │  Erlang terms.</p><p>The functions <code class="inline">get_s</code> and <code class="inline">ei_x_to_new_binary</code> are utilities that are used to
│ │ │  make the code shorter. <code class="inline">get_s</code> duplicates the string and zero-terminates it, as
│ │ │  the postgres client library wants that. <code class="inline">ei_x_to_new_binary</code> takes an
│ │ │  <code class="inline">ei_x_buff</code> buffer, allocates a binary, and copies the data there. This binary
│ │ │  is returned in <code class="inline">*rbuf</code>. (Notice that this binary is freed by the emulator, not
│ │ │ -by us.)</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="nf">get_s</span><span class="p" data-group-id="1565439716-1">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="1565439716-1">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_connect</span><span class="p" data-group-id="1565439716-2">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="1565439716-2">)</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_select</span><span class="p" data-group-id="1565439716-3">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="1565439716-3">)</span><span class="p">;</span><span class="w">
│ │ │ +by us.)</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="nf">get_s</span><span class="p" data-group-id="3172224836-1">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="3172224836-1">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_connect</span><span class="p" data-group-id="3172224836-2">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="3172224836-2">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_select</span><span class="p" data-group-id="3172224836-3">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="3172224836-3">)</span><span class="p">;</span><span class="w">
│ │ │  
│ │ │  </span><span class="cm">/* As we are operating in binary mode, the return value from control
│ │ │   * is irrelevant, as long as it is not negative.
│ │ │   */</span><span class="w">
│ │ │ -</span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">control</span><span class="p" data-group-id="1565439716-4">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">drv_data</span><span class="p">,</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">command</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w">
│ │ │ -                   </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="o">*</span><span class="n">rbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rlen</span><span class="p" data-group-id="1565439716-4">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1565439716-5">{</span><span class="w">
│ │ │ +</span><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">control</span><span class="p" data-group-id="3172224836-4">(</span><span class="no">ErlDrvData</span><span class="w"> </span><span class="n">drv_data</span><span class="p">,</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">command</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">buf</span><span class="p">,</span><span class="w">
│ │ │ +                   </span><span class="kt">int</span><span class="w"> </span><span class="n">len</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="o">*</span><span class="n">rbuf</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">rlen</span><span class="p" data-group-id="3172224836-4">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="3172224836-5">{</span><span class="w">
│ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">r</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">ei_x_buff</span><span class="w"> </span><span class="n">x</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1565439716-6">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="p" data-group-id="1565439716-6">)</span><span class="n">drv_data</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">get_s</span><span class="p" data-group-id="1565439716-7">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="1565439716-7">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">ei_x_new_with_version</span><span class="p" data-group-id="1565439716-8">(</span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="1565439716-8">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">switch</span><span class="w"> </span><span class="p" data-group-id="1565439716-9">(</span><span class="n">command</span><span class="p" data-group-id="1565439716-9">)</span><span class="w"> </span><span class="p" data-group-id="1565439716-10">{</span><span class="w">
│ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="ss">DRV_CONNECT</span><span class="p">:</span><span class="w">    </span><span class="n">r</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">do_connect</span><span class="p" data-group-id="1565439716-11">(</span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="1565439716-11">)</span><span class="p">;</span><span class="w">  </span><span class="k">break</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="ss">DRV_DISCONNECT</span><span class="p">:</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">do_disconnect</span><span class="p" data-group-id="1565439716-12">(</span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="1565439716-12">)</span><span class="p">;</span><span class="w">  </span><span class="k">break</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">case</span><span class="w"> </span><span class="ss">DRV_SELECT</span><span class="p">:</span><span class="w">     </span><span class="n">r</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">do_select</span><span class="p" data-group-id="1565439716-13">(</span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="1565439716-13">)</span><span class="p">;</span><span class="w">   </span><span class="k">break</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3172224836-6">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="p" data-group-id="3172224836-6">)</span><span class="n">drv_data</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">get_s</span><span class="p" data-group-id="3172224836-7">(</span><span class="n">buf</span><span class="p">,</span><span class="w"> </span><span class="n">len</span><span class="p" data-group-id="3172224836-7">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">ei_x_new_with_version</span><span class="p" data-group-id="3172224836-8">(</span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="3172224836-8">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="k">switch</span><span class="w"> </span><span class="p" data-group-id="3172224836-9">(</span><span class="n">command</span><span class="p" data-group-id="3172224836-9">)</span><span class="w"> </span><span class="p" data-group-id="3172224836-10">{</span><span class="w">
│ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="ss">DRV_CONNECT</span><span class="p">:</span><span class="w">    </span><span class="n">r</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">do_connect</span><span class="p" data-group-id="3172224836-11">(</span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="3172224836-11">)</span><span class="p">;</span><span class="w">  </span><span class="k">break</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="ss">DRV_DISCONNECT</span><span class="p">:</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">do_disconnect</span><span class="p" data-group-id="3172224836-12">(</span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="3172224836-12">)</span><span class="p">;</span><span class="w">  </span><span class="k">break</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="k">case</span><span class="w"> </span><span class="ss">DRV_SELECT</span><span class="p">:</span><span class="w">     </span><span class="n">r</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nf">do_select</span><span class="p" data-group-id="3172224836-13">(</span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="3172224836-13">)</span><span class="p">;</span><span class="w">   </span><span class="k">break</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="ss">default</span><span class="p">:</span><span class="w">             </span><span class="n">r</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">-</span><span class="mi">1</span><span class="p">;</span><span class="w">        </span><span class="k">break</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="1565439716-10">}</span><span class="w">
│ │ │ -    </span><span class="o">*</span><span class="n">rbuf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="1565439716-14">(</span><span class="kt">char</span><span class="o">*</span><span class="p" data-group-id="1565439716-14">)</span><span class="nf">ei_x_to_new_binary</span><span class="p" data-group-id="1565439716-15">(</span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="1565439716-15">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">ei_x_free</span><span class="p" data-group-id="1565439716-16">(</span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="1565439716-16">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">driver_free</span><span class="p" data-group-id="1565439716-17">(</span><span class="n">s</span><span class="p" data-group-id="1565439716-17">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="3172224836-10">}</span><span class="w">
│ │ │ +    </span><span class="o">*</span><span class="n">rbuf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p" data-group-id="3172224836-14">(</span><span class="kt">char</span><span class="o">*</span><span class="p" data-group-id="3172224836-14">)</span><span class="nf">ei_x_to_new_binary</span><span class="p" data-group-id="3172224836-15">(</span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="3172224836-15">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">ei_x_free</span><span class="p" data-group-id="3172224836-16">(</span><span class="o">&amp;</span><span class="n">x</span><span class="p" data-group-id="3172224836-16">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">driver_free</span><span class="p" data-group-id="3172224836-17">(</span><span class="n">s</span><span class="p" data-group-id="3172224836-17">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="k">return</span><span class="w"> </span><span class="n">r</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="1565439716-5">}</span></code></pre><p><code class="inline">do_connect</code> is where we log in to the database. If the connection was
│ │ │ +</span><span class="p" data-group-id="3172224836-5">}</span></code></pre><p><code class="inline">do_connect</code> is where we log in to the database. If the connection was
│ │ │  successful, we store the connection handle in the driver data, and return
│ │ │  <code class="inline">'ok'</code>. Otherwise, we return the error message from postgres and store <code class="inline">NULL</code> in
│ │ │ -the driver data.</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_connect</span><span class="p" data-group-id="7427815801-1">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="7427815801-1">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7427815801-2">{</span><span class="w">
│ │ │ -    </span><span class="no">PGconn</span><span class="o">*</span><span class="w"> </span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">PQconnectdb</span><span class="p" data-group-id="7427815801-3">(</span><span class="n">s</span><span class="p" data-group-id="7427815801-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="7427815801-4">(</span><span class="no">PQstatus</span><span class="p" data-group-id="7427815801-5">(</span><span class="n">conn</span><span class="p" data-group-id="7427815801-5">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="no">CONNECTION_OK</span><span class="p" data-group-id="7427815801-4">)</span><span class="w"> </span><span class="p" data-group-id="7427815801-6">{</span><span class="w">
│ │ │ -        </span><span class="nf">encode_error</span><span class="p" data-group-id="7427815801-7">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">conn</span><span class="p" data-group-id="7427815801-7">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="no">PQfinish</span><span class="p" data-group-id="7427815801-8">(</span><span class="n">conn</span><span class="p" data-group-id="7427815801-8">)</span><span class="p">;</span><span class="w">
│ │ │ +the driver data.</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_connect</span><span class="p" data-group-id="7715668372-1">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="7715668372-1">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="7715668372-2">{</span><span class="w">
│ │ │ +    </span><span class="no">PGconn</span><span class="o">*</span><span class="w"> </span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">PQconnectdb</span><span class="p" data-group-id="7715668372-3">(</span><span class="n">s</span><span class="p" data-group-id="7715668372-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="7715668372-4">(</span><span class="no">PQstatus</span><span class="p" data-group-id="7715668372-5">(</span><span class="n">conn</span><span class="p" data-group-id="7715668372-5">)</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="no">CONNECTION_OK</span><span class="p" data-group-id="7715668372-4">)</span><span class="w"> </span><span class="p" data-group-id="7715668372-6">{</span><span class="w">
│ │ │ +        </span><span class="nf">encode_error</span><span class="p" data-group-id="7715668372-7">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">conn</span><span class="p" data-group-id="7715668372-7">)</span><span class="p">;</span><span class="w">
│ │ │ +        </span><span class="no">PQfinish</span><span class="p" data-group-id="7715668372-8">(</span><span class="n">conn</span><span class="p" data-group-id="7715668372-8">)</span><span class="p">;</span><span class="w">
│ │ │          </span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7427815801-6">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="7427815801-9">{</span><span class="w">
│ │ │ -        </span><span class="nf">encode_ok</span><span class="p" data-group-id="7427815801-10">(</span><span class="n">x</span><span class="p" data-group-id="7427815801-10">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="p" data-group-id="7427815801-9">}</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7715668372-6">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p" data-group-id="7715668372-9">{</span><span class="w">
│ │ │ +        </span><span class="nf">encode_ok</span><span class="p" data-group-id="7715668372-10">(</span><span class="n">x</span><span class="p" data-group-id="7715668372-10">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="p" data-group-id="7715668372-9">}</span><span class="w">
│ │ │      </span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">conn</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="7427815801-2">}</span></code></pre><p>If we are connected (and if the connection handle is not <code class="inline">NULL</code>), we log out
│ │ │ +</span><span class="p" data-group-id="7715668372-2">}</span></code></pre><p>If we are connected (and if the connection handle is not <code class="inline">NULL</code>), we log out
│ │ │  from the database. We need to check if we should encode an <code class="inline">'ok'</code>, as we can get
│ │ │ -here from function <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#stop" title=""><code class="inline">stop</code></a>, which does not return data to the emulator:</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_disconnect</span><span class="p" data-group-id="8985860065-1">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="8985860065-1">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8985860065-2">{</span><span class="w">
│ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8985860065-3">(</span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="8985860065-3">)</span><span class="w">
│ │ │ +here from function <a href="../../../erts-15.2.7.8/doc/html/driver_entry.html#stop" title=""><code class="inline">stop</code></a>, which does not return data to the emulator:</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_disconnect</span><span class="p" data-group-id="2771692034-1">(</span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="2771692034-1">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2771692034-2">{</span><span class="w">
│ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2771692034-3">(</span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="2771692034-3">)</span><span class="w">
│ │ │          </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="no">PQfinish</span><span class="p" data-group-id="8985860065-4">(</span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="p" data-group-id="8985860065-4">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="no">PQfinish</span><span class="p" data-group-id="2771692034-4">(</span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="p" data-group-id="2771692034-4">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">NULL</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="8985860065-5">(</span><span class="n">x</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="8985860065-5">)</span><span class="w">
│ │ │ -        </span><span class="nf">encode_ok</span><span class="p" data-group-id="8985860065-6">(</span><span class="n">x</span><span class="p" data-group-id="8985860065-6">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="k">if</span><span class="w"> </span><span class="p" data-group-id="2771692034-5">(</span><span class="n">x</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="no">NULL</span><span class="p" data-group-id="2771692034-5">)</span><span class="w">
│ │ │ +        </span><span class="nf">encode_ok</span><span class="p" data-group-id="2771692034-6">(</span><span class="n">x</span><span class="p" data-group-id="2771692034-6">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="8985860065-2">}</span></code></pre><p>We execute a query and encode the result. Encoding is done in another C module,
│ │ │ -<code class="inline">pg_encode.c</code>, which is also provided as sample code.</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_select</span><span class="p" data-group-id="6437923146-1">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="6437923146-1">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6437923146-2">{</span><span class="w">
│ │ │ -   </span><span class="no">PGresult</span><span class="o">*</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">PQexec</span><span class="p" data-group-id="6437923146-3">(</span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p" data-group-id="6437923146-3">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="nf">encode_result</span><span class="p" data-group-id="6437923146-4">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="p" data-group-id="6437923146-4">)</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="no">PQclear</span><span class="p" data-group-id="6437923146-5">(</span><span class="n">res</span><span class="p" data-group-id="6437923146-5">)</span><span class="p">;</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="2771692034-2">}</span></code></pre><p>We execute a query and encode the result. Encoding is done in another C module,
│ │ │ +<code class="inline">pg_encode.c</code>, which is also provided as sample code.</p><pre><code class="makeup c" translate="no"><span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="nf">do_select</span><span class="p" data-group-id="4456115512-1">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">s</span><span class="p">,</span><span class="w"> </span><span class="n">our_data_t</span><span class="o">*</span><span class="w"> </span><span class="n">data</span><span class="p">,</span><span class="w"> </span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p" data-group-id="4456115512-1">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="4456115512-2">{</span><span class="w">
│ │ │ +   </span><span class="no">PGresult</span><span class="o">*</span><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">PQexec</span><span class="p" data-group-id="4456115512-3">(</span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p" data-group-id="4456115512-3">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="nf">encode_result</span><span class="p" data-group-id="4456115512-4">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">data</span><span class="o">-&gt;</span><span class="n">conn</span><span class="p" data-group-id="4456115512-4">)</span><span class="p">;</span><span class="w">
│ │ │ +    </span><span class="no">PQclear</span><span class="p" data-group-id="4456115512-5">(</span><span class="n">res</span><span class="p" data-group-id="4456115512-5">)</span><span class="p">;</span><span class="w">
│ │ │      </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6437923146-2">}</span></code></pre><p>Here we check the result from postgres. If it is data, we encode it as lists of
│ │ │ +</span><span class="p" data-group-id="4456115512-2">}</span></code></pre><p>Here we check the result from postgres. If it is data, we encode it as lists of
│ │ │  lists with column data. Everything from postgres is C strings, so we use
│ │ │  <a href="../../../lib/erl_interface-5.5.2/doc/html/ei.html#ei_x_encode_string" title=""><code class="inline">ei_x_encode_string</code></a> to send the result as strings to Erlang. (The head of the
│ │ │ -list contains the column names.)</p><pre><code class="makeup c" translate="no"><span class="kc">void</span><span class="w"> </span><span class="nf">encode_result</span><span class="p" data-group-id="6715376801-1">(</span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="no">PGresult</span><span class="o">*</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="no">PGconn</span><span class="o">*</span><span class="w"> </span><span class="n">conn</span><span class="p" data-group-id="6715376801-1">)</span><span class="w">
│ │ │ -</span><span class="p" data-group-id="6715376801-2">{</span><span class="w">
│ │ │ +list contains the column names.)</p><pre><code class="makeup c" translate="no"><span class="kc">void</span><span class="w"> </span><span class="nf">encode_result</span><span class="p" data-group-id="5072955006-1">(</span><span class="n">ei_x_buff</span><span class="o">*</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="no">PGresult</span><span class="o">*</span><span class="w"> </span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="no">PGconn</span><span class="o">*</span><span class="w"> </span><span class="n">conn</span><span class="p" data-group-id="5072955006-1">)</span><span class="w">
│ │ │ +</span><span class="p" data-group-id="5072955006-2">{</span><span class="w">
│ │ │      </span><span class="kt">int</span><span class="w"> </span><span class="n">row</span><span class="p">,</span><span class="w"> </span><span class="n">n_rows</span><span class="p">,</span><span class="w"> </span><span class="n">col</span><span class="p">,</span><span class="w"> </span><span class="n">n_cols</span><span class="p">;</span><span class="w">
│ │ │ -    </span><span class="k">switch</span><span class="w"> </span><span class="p" data-group-id="6715376801-3">(</span><span class="no">PQresultStatus</span><span class="p" data-group-id="6715376801-4">(</span><span class="n">res</span><span class="p" data-group-id="6715376801-4">)</span><span class="p" data-group-id="6715376801-3">)</span><span class="w"> </span><span class="p" data-group-id="6715376801-5">{</span><span class="w">
│ │ │ +    </span><span class="k">switch</span><span class="w"> </span><span class="p" data-group-id="5072955006-3">(</span><span class="no">PQresultStatus</span><span class="p" data-group-id="5072955006-4">(</span><span class="n">res</span><span class="p" data-group-id="5072955006-4">)</span><span class="p" data-group-id="5072955006-3">)</span><span class="w"> </span><span class="p" data-group-id="5072955006-5">{</span><span class="w">
│ │ │      </span><span class="k">case</span><span class="w"> </span><span class="ss">PGRES_TUPLES_OK</span><span class="p">:</span><span class="w">
│ │ │ -        </span><span class="n">n_rows</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">PQntuples</span><span class="p" data-group-id="6715376801-6">(</span><span class="n">res</span><span class="p" data-group-id="6715376801-6">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="n">n_cols</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="no">PQnfields</span><span class="p" data-group-id="6715376801-7">(</span><span class="n">res</span><span class="p" data-group-id="6715376801-7">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">ei_x_encode_tuple_header</span><span class="p" data-group-id="6715376801-8">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p" data-group-id="6715376801-8">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">encode_ok</span><span class="p" data-group-id="6715376801-9">(</span><span class="n">x</span><span class="p" data-group-id="6715376801-9">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">ei_x_encode_list_header</span><span class="p" data-group-id="6715376801-10">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">n_rows</span><span class="o">+</span><span class="mi">1</span><span class="p" data-group-id="6715376801-10">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="nf">ei_x_encode_list_header</span><span class="p" data-group-id="6715376801-11">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">n_cols</span><span class="p" data-group-id="6715376801-11">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">for</span><span class="w"> </span><span class="p" data-group-id="6715376801-12">(</span><span class="n">col</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n_cols</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">col</span><span class="p" data-group-id="6715376801-12">)</span><span class="w"> </span><span class="p" data-group-id="6715376801-13">{</span><span class="w">
│ │ │ -            </span><span class="nf">ei_x_encode_string</span><span class="p" data-group-id="6715376801-14">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="no">PQfname</span><span class="p" data-group-id="6715376801-15">(</span><span class="n">res</span><span class="p">,</span><span class="w"> </span><span class="n">col</span><span class="p" data-group-id="6715376801-15">)</span><span class="p" data-group-id="6715376801-14">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="p" data-group-id="6715376801-13">}</span><span class="w">
│ │ │ -        </span><span class="nf">ei_x_encode_empty_list</span><span class="p" data-group-id="6715376801-16">(</span><span class="n">x</span><span class="p" data-group-id="6715376801-16">)</span><span class="p">;</span><span class="w">
│ │ │ -        </span><span class="k">for</span><span class="w"> </span><span class="p" data-group-id="6715376801-17">(</span><span class="n">row</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="n">n_rows</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">row</span><span class="p" data-group-id="6715376801-17">)</span><span class="w"> </span><span class="p" data-group-id="6715376801-18">{</span><span class="w">
│ │ │ -            </span><span class="nf">ei_x_encode_list_header</span><span class="p" data-group-id="6715376801-19">(</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">n_cols</span><span class="p" data-group-id="6715376801-19">)</span><span class="p">;</span><span class="w">
│ │ │ -            </span><span class="k">for</span><span class="w"> </span><span class="p" data-group-id="6715376801-20">(</span><span class="n">col</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><s

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